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Solar Pumping For Water Supply

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Solar Pumping for Water Supply

Copyright practicalactionpublishing.com
Praise for this book
‘This book is a truly fantastic “one stop shop” for all solar water pumping
needs; it covers examples from humanitarian and developments across the
entire globe and deals with both simple and easy-to-follow rules of thumb
and also extremely detailed design parameters. There is no other book on
solar water pumping with the breadth and depth that this one covers in such
a practical and down-to-earth way. It’s an essential reading and reference book
for anybody designing and installing solar water systems.’
Andy Bastable, Head of Water & Sanitation, Oxfam

‘Solar Pumping for Water Supply is an excellent book that brings together a
perfect merger of the theory and practice of the subject matter. It provides
a clear road map from the project conceptualisation, its design, imple-
mentation including the social impact of such projects. With engineering
formulae and photographic illustrations it goes to provide excellent examples
of how to and how not to do Solar pumping water supplies, with cases drawn
from across Africa and Asia. I highly recommend the book for practitioners
and learners of water supply and solar renewable energy as it provides the
fusion of the two disciplines to deliver the scare water resources in the most
economical manner.’
Dr MAS Waweru, Managing Director Davis & Shirtliff Ltd

‘This is a good reference book to be used by anybody – not just technicians –

keen on knowing more about all aspects of solar PV pumping in emergency
and developments projects, going from technology, design, installation,
maintenance and financing of solar pumping systems. The book also provides
interesting and useful case studies in the annexes.’
Jean-Paul Louineau, Director, Alliance Soleil

‘A great book that reflects the experience of the authors in the energy
and humanitarian sector and that will surely be very well received by
those who have to work in the implementation of photovoltaic systems
for water pumping.’
Dr. Salvador Seguí-Chilet, Univ. Politécnica de Valencia

‘This is a very timely and comprehensive guide to support the design, siting,
procurement, installation, commissioning, operation and maintenance and
monitoring of solar powered water systems. This guide will help to reduce
the technical issues arising from inadequately designed solar powered water
systems which have impeded the full utilisation of solar powered water systems
to ensure the quality, equity and sustainability of safe water services.’
Silvia Gaya, Senior Advisor Water and Environment,
WASH Programme Division, UNICEF HQ

Copyright practicalactionpublishing.com
Solar Pumping for Water Supply
Harnessing solar power in humanitarian
and development contexts

Asenath W. Kiprono and Alberto Ibáñez Llario

Copyright practicalactionpublishing.com
Practical Action Publishing Ltd
27a, Albert Street, Rugby,
Warwickshire, CV21 2SG, UK
www.practicalactionpublishing.com

© Asenath W. Kiprono and Alberto Ibáñez Llario, 2020

This open access article is distributed under a Creative Commons

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appropriate credit must be given, the material must not be used for
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Product or corporate names may be trademarks or registered trademarks, and

are used only for identification and explanation without intent to infringe.

A catalogue record for this book is available from the British Library.

A catalogue record for this book has been requested from the Library of Congress.

ISBN 978-1-78853-036-1 Paperback

ISBN 978-1-78853-035-4 Hardback
ISBN 978-1-78044-781-0 Library PDF
ISBN 978-1-78044-782-7 Epub

Citation: Kiprono, A W., Llario, A I., (2020) Solar Pumping for Water Supply:
Harnessing solar power in humanitarian and development, Rugby, UK: Practical
Action Publishing <http://dx.doi.org/10.3362/9781780447810>.

Since 1974, Practical Action Publishing has published and disseminated

books and information in support of international development work
throughout the world. Practical Action Publishing is a trading name of
Practical Action Publishing Ltd (Company Reg. No. 1159018), the wholly
owned publishing company of Practical Action. Practical Action Publishing
trades only in support of its parent charity objectives and any profits are
covenanted back to Practical Action (Charity Reg. No. 247257, Group VAT
Registration No. 880 9924 76).

The views and opinions in this publication are those of the author and do
not represent those of Practical Action Publishing Ltd or its parent charity
Practical Action. Reasonable efforts have been made to publish reliable data
and information, but the authors and publisher cannot assume responsibility
for the validity of all materials or for the consequences of their use.

Cover photos: Top photo shows IOM water scheme at Kutupalong Balukhali
Expansion Site refugee camp, courtesy of IOM Bangladesh. Bottom photo shows
villagers in Darfur, Sudan with a new solar water pump – part of an Integrated
Water Resources Management (IWRM) system that came out of a collaboration
between Practical Action, local governments, technical departments and the
communities affected by drought, courtesy of Practical Action.

Cover design by RCO.design

Typeset by vPrompt eServices, India
Printed in the United Kingdom

1. Solar photovoltaic solutions for water pumping 1

1.1 Solar PV water pumping in humanitarian and
development contexts 1
1.2 Factors influencing the renewed interest in solar PV
water pumping 3
1.3 Guidance note on the use of solar pumping 5

2 Definitions and principles of solar energy production 9

2.1 The solar resource 9
2.2 Sun and water: the perfect relationship 10
2.3 Solar radiation 11
2.4 Solar photovoltaic 12
2.5 Solar irradiance 14
2.6 Solar insolation 18
2.7 Standard test conditions 18
2.8 Solar resource maps for peak sun hours 21
2.9 Basic DC electric concepts 23
2.10 Solar module I-V curve and maximum power point 25

3 Solar-powered water system configurations and components 27

3.1 SPWS concept and revolution 27
3.2 SPWS configurations 28
3.3 SPWS components 32
3.4 SPWS balance-of-system components 42
3.5 SPWS equipment manufacturers 46
3.6 Importance of quality considerations in SPWSs 47

4 Energy losses in solar photovoltaic energy production 49

4.1 Calculating energy losses 49
4.2 Cell temperature energy losses 51
4.3 Wiring energy losses 54
4.4 Sun irradiance energy losses 56
4.5 PV module energy losses 61
4.6 Module mounting energy losses 63
4.7 Power converters and the balance-of-system energy losses 64
4.8 Estimation of the energy yield 66

5 Design of a solar-powered water scheme 67

5.1 Solar pump design 67
5.2 Important design concepts and considerations 68
5.3 Steps to design a solar-powered water scheme 69
Copyright practicalactionpublishing.com
vi SOLAR PUMPING FOR WATER SUPPLY

6 Electrical and mechanical installation of solar-powered

water systems 87
6.1 Pumping system installation 87
6.2 Installation sequence and process 89
6.3 Earthing, lightning protection, and surge protection 106
6.4 Electrical safety 108

7 Specific considerations and limitations for solar-powered

water pumping 109
7.1 Chlorination 109
7.2 Full-tank detection at long distances 111
7.3 Solar tracking 112
7.4 Emergency solar pumping kits 112
7.5 Power range for pump motors and inverters 113
7.6 Vandalism and theft 114
7.7 Overpumping of aquifers 117
7.8 Hot climate zones and hot water pumping 118
7.9 Frequently asked questions 120

8 Solar-powered water pumping for agriculture 123

8.1 Water for irrigated agriculture 123
8.2 The influence of pressure on energy requirements
in irrigation 123
8.3 Greenhouse gas emissions from agriculture and
climate-change adaptation 125
8.4 Financing solar-powered irrigation systems 126
8.5 Financing instruments to develop solar irrigation 127
8.6 The risks and challenges of solar irrigation 128
8.7 Recommendations for solar irrigation challenges 129

9 Economic analysis: life-cycle cost of different pumping

technologies 133
9.1 The importance of economic considerations 133
9.2 Life-cycle cost analysis 134
9.3 Life-cycle costing for water pumping 135
9.4 Comparing LCCA of solar and generator systems 138
9.5 Cost of ownership 144

10 Calls for proposal and bidding 147

10.1 Selection criteria for solar pumping products and services 147
10.2 Desired features of key components 147
10.3 Supplier selection 150
10.4 Bidding process 151
10.5 Bidding template: technical terms of reference 152
10.6 Quality of solar modules 156
10.7 Practical aspects of equipment and supplier selection 160

11 Testing and commissioning, operation and maintenance 163

11.1 Testing and commissioning 163
11.2 Operation and maintenance of equipment 167

12 Warranties, social models for management, and monitoring 179

12.1 Warranties 179
12.2 Social models for management 182
12.3 Monitoring 183

Annex A Pump and generator design basics 187

Annex B Manual calculation of solar system 195

Annex C Example of calculation of losses due to non-optimum

tilt angle of PV modules 211

Annex D Cable sizing 215

Annex E Product warranty card sample 219

Annex F Routine inspection and maintenance activity sheets 221

Annex G Preventive maintenance plan 225

Annex H General troubleshooting for SPWSs 229

Annex I Financing instruments for solar-powered irrigation systems 233

Annex J Physical control installation and maintenance checklists 237

Annex K Daily photovoltaic module and pump

operation/monitoring format 241

Glossary 243

References 249

Boxes

Box 2.1 Solar PV components 13

Box 4.1 Minimizing losses due to temperature 55

Box 4.2 Minimizing wiring losses 57

Box 4.3 Minimizing losses due to soiling 59

Box 4.4 Minimizing losses due to shading 59

Box 4.5 Minimizing losses due to incorrect azimuth and tilt angle 61

Box 4.6 Minimizing mismatching losses 62

Box 4.7 Minimizing ageing losses 63

Box 4.8 Minimizing losses due to availability 65

Box 10.1 Dimensions of product quality 148

Box 10.2 Criteria for supplier selection 150

Box 10.3 A reference guide for the SPWS procurement process 152

Box 10.4 Checking module quality 160

Box 11.1 When to call a technician 172

Box 11.2 Example of essential provisions in a maintenance

service agreement 175

Box 12.1 Commonalities between successful community-managed

water schemes in Kenya 183

Box 12.2 For local community projects, should solar water be free? 183

Figures

Figure 1.1 Global map of appropriate locations for solar applications 2

Figure 1.2 Evolution of price of PV cells, 1977–2015 4

Figure 2.1 Sun and water: a perfect relationship 10

Figure 2.2 Global Horizontal Irradiation 11

Figure 2.3 Conversion of sunlight to electricity 12

Figure 2.4 The ‘PV effect’ process 13

Figure 2.5 Illustration of PV cell, module, array, and generator 14

Figure 2.6 A typical solar-powered water system 15

Figure 2.7 Weekly irradiation in Valencia in the month of July 16

Figure 2.8 Time-based solar irradiance in Valencia during summer

for two consecutive days 17

Figure 2.9 Graph of daily insolation 18

Figure 2.10 Solar irradiance during two days of July and

corresponding insolation 19

Figure 2.11 Air mass for different sun positions 20

Figure 2.12 PSH map for Jordan 22

Figure 2.13 Typical I-V and power curves for a crystalline PV

module operating at STC 25

Figure 2.14 I-V curve under varying irradiance and temperature 26

Figure 3.1 Typical flow output profile of a solar-powered pump 29

Figure 3.2 Stand-alone solar installation 30

Figure 3.3 Hybrid installation 30

Figure 3.4 Stand-alone surface Installation 31

Figure 3.5 Illustration of a solar module construction 38

Figure 3.6 Different types of solar modules (clockwise from

top left: mono-Si, poly-Si, a-Si and TFPV) 40

Figure 3.7 Parts of a cable 44

Figure 3.8 The components of a solar water pumping system 46

Figure 3.9 Worn-out conduit due to high temperatures in Iraq 48

Figure 4.1 Temperature difference for a c-Si plant with a fixed-tilt

angle of 30° in Valencia, Spain 52

Figure 4.2 Effect of sun irradiance in efficiency of c-Si PV modules 53

Figure 4.3 Spacers between modules to increase cooling 55

Figure 4.4 Sand on PV modules limiting power output 58

Figure 4.5 Shading of PV modules limiting power output 58

Figure 4.6 Example of warranty given by Trina Solar for Tallmax

monocrystalline modules 63

Figure 4.7 Bypass diode activation in shadowed PV modules 64

Figure 5.1 Series connection 75

Figure 5.2 Parallel connection 75

Figure 5.3 Combination of series and parallel connections 76

Figure 5.4 Module array layout 77

Figure 5.5 Sun’s position in the sky with respect to the earth’s surface 79

Figure 5.6 Effect of tilt on solar energy capture 80

Figure 5.7 PV modules in Sheikhan, Iraq, facing south at 36° tilt 81

Figure 5.8 Inverter box located under modules in Somali

Region, Ethiopia 82

Figure 5.9 Hybrid solar-generator scheme at Adjumani refugee

settlement in Uganda 85

Figure 6.1 Sample nameplates for (left) PV module, and (right)

solar controller 88

Figure 6.2 Pump installation using a hydraulic winch 91

Figure 6.3 Horizontal surface pumps installed on a concrete plinth

in Itang Water Supply, Ethiopia 93

Figure 6.4 Installed controls (left to right): AC changeover switch,

inverter, surge protector, PV disconnection switch 94

Figure 6.5 Inverter installed in a lockable meshed enclosure under

the PV array at Turkana, Kenya 95

Figure 6.6 Examples of poor cable management in South Sudan 97

Figure 6.7 Examples of good cable management in South Sudan and

Tanzania respectively 97

Figure 6.8 Ground mount structure in Kawrgosk refugee camp, Iraq 98

Figure 6.9 Pole mounted PV modules in Bidibidi refugee settlement,

Uganda 98

Figure 6.10 Roof mount on a flat tank roof in Gaza 99

Figure 6.11 Combined roof and pole mount installation at

Rohingya Mega camp (Cover photo) 100

Figure 6.12 Example of ground screw structure 100

Figure 6.13 Tank-mounted structure in an IDP camp near

Maiduguri, Nigeria 102

Figure 6.14 Failed pole mount in Yida, South Sudan, modules

blown off in Fafen, Ethiopia (right) 103

Figure 6.15 A tight connection of solar module MC3 quick connectors 103

Figure 6.16 Leap-frog connection of modules 104

Figure 6.17 Example of untidy and tidy module cables 105

Figure 6.18 Walkway on a roof mount at Strathmore University, Kenya 105

Figure 6.19 Walkway on a ground mount in Koboko, Uganda 106

Figure 6.20 Lorentz surge protection device 107

Figure 7.1 Valve-regulated bypass chlorinator 111

Figure 7.2 Solar trackers: double-axis tracking (left) and single-axis

tracking (right) 112

Figure 7.3 Fenced SPWS with a solar light for security in Turkana, Kenya 115

Figure 7.4 Extreme module security measures in Burao, Somalia 116

Figure 7.5 Awareness raising of the value of the SPWS to avoid theft

and vandalism 117

Figure 8.1 Yield response of crops to water availability in China 124

Figure 8.2 Approximate shares of greenhouse gas emissions (in CO2

equivalent) emitted by the global agri-food sector in 2010 125

Figure 9.1 Steps for technical design and economic appraisal 137

Figure 9.2 Comparison over time of costs for solar vs generator 141

Figure 9.3 LCCA of stand-alone generator vs hybrid vs solar at

Nyarugusu, Tanzania 144

Figure 9.4 Business models for financing solar-powered water systems 144

Figure 10.1 Quality of solar panels matters 148

Figure 10.2 Example of a solar-powered water system layout

provided to bidders 153

Figure 10.3 Cheap will become expensive with time 161

Figure 11.1 Duration of different phases in the life of a solar

pumping scheme 168

Figure 11.2 Routine maintenance activities to ensure proper daily

functionality 171

Figure 12. 1 Lorentz communication system for monitoring from

phone via Bluetooth or from computer via Internet 184

Figure 12.2 Fluke clamp meter 186

Figure A1 Layout of total dynamic head calculation 188

Figure A2 Layout of worked example 191

Figure B1 Number of modules arranged in series and parallel 197

Figure B2 Grundfos sizing result 199

Figure B3 Lorentz sizing result 200

Figure B4 Grundfos SP 9 head-flow curve 201

Figure B5 Grundfos SP 9 pump data sheet 202

Figure B6 Grundfos SP 9 power-flow curves 203

Figure B7 Grundfos motor data sheet 204

Figure B8 Solar resource map for Kenya 205

Figure D1 Table of cable current capacity and voltage drop 216

Figure D2 Table of cable sizes 217

Tables

Table 1.1 Advantages and disadvantages of solar PV water

pumping schemes 3

Table 2.1 Analogy of electricity and water 24

Table 3.1 List of solar-powered water systems found in the field 28

Table 3.2 Example of module characteristics 40

Table 4.1 Table of estimated losses as a percentage of total

energy produced 50

Table 4.2 NOCT, g, and efficiency factors for different PV module

technologies 54

Table 4.3 Variation of resistivity and conductivity with temperature 56

Table 5.1 Data needed to design a solar-powered water scheme 68

Table 5.2 Expected lifetime of solar components 70

Table 5.3 Example of worst-month calculation where constant water

required: Yumbe, Uganda (3N, 31E) 72

Table 5.4 Example of worst-month calculation where variable water

required: Yumbe, Uganda (3N, 31E) 72

Table 5.5 Quick guidance for water tank capacity 83

Table 7.1 Summary of Global Solar and Water Initiative specifications

for small, medium-sized, and large solar pumping kits for
rapid deployment 113

Table 9.1 Data required for life-cycle analysis 136

Table 9.2 Estimated cost for maintenance of a good-quality

diesel generator 137

Table 9.3 Estimated generator fuel consumption at different loads 138

Table 9.4 LCCA for the given water scheme with a diesel generator 139

Table 9.5 Capital cost of the main components of the given solar PV

pumping system 140

Table 9.6 LCCA for the given water scheme with a solar PV

pumping system 140

Table 9.7 Cost comparison between existing generator stand-alone

systems in South Sudan and equivalent solar or
hybrid systems 143

Table 10.1 Minimum recommended characteristics of solar components 149

Table 11.1 Inspections and functionality tests for solar-powered

water systems 164

Table 11.2 System performance tests for a solar-powered water system 165

Table 11.3 SPWS testing report template 166

Table 11.4 Documentation set accompanying the solar water-pumping

scheme 169

Table 11.5 Records of service and maintenance activities at site level 170

Table 11.6 Routine maintenance activities for solar-powered

water systems 171

Copyright practicalactionpublishing.com
Acronyms
BEP best efficiency point
BoS balance of system
FAO Food and Agriculture Organization
FiT feed-in tariff
GLOWSI Global Solar and Water Initiative
GHG greenhouse gas
IDP internally displaced person
LCCA life-cycle cost analysis
LCB linear current booster
MPP maximum power point
MPPT maximum power point tracking
NOTC nominal operating temperature of a cell
O&M operation and maintenance
PPA power purchase agreement
PSH peak sun hours
PW present worth
SPIS solar-powered irrigation system
SPWS solar-powered water system
STC standard test conditions
SPD surge protection devices
TDH total dynamic head
TFPV thin-film photovoltaic cells

Copyright practicalactionpublishing.com
Copyright practicalactionpublishing.com
Preface
While solar water pumping has been in operation since the 1970s, it is
only in last few years that it has expanded globally, offering more robust,
larger and efficient solutions for water supply projects. Tens of thousands of
solar pumping schemes have been installed in the last decade, in both rural
communities and in large urban settings, as well as in camps for internally
displaced people and refugees; in emergency and post-emergency contexts
and also in more developmental situations.
This book is based on five years’ work developed within the framework of
the Global Solar and Water Initiative. This Initiative is designed to mainstream
quality solar pumping solutions in low- and medium-income countries,
working hand in hand with governments, the private sector, manufacturers,
academic institutions, NGOs and United Nations agencies.
In writing this book we have examined current technology, best practices,
product quality and availability; we analysed costs and compared them
with other available technologies; and we reviewed different operation and
maintenance models. In the process, over a hundred IDP and refugee camps
and communities were visited in 12 different countries, and hundreds
of engineers were trained either in onsite events or via dedicated online
training courses.
This book is the result of all this work. We have tried to explain in simple and
clear language not only the theoretical knowledge needed to understand the
technology, but also the practicalities and lessons learnt through all the visits,
meetings and interviews carried out since 2016 relating to solar water pumping
in humanitarian and development contexts. All the material developed
within the Global Solar and Water Initiative, together with news about trainings
helpline and other resources can be found at www.thesolarhub.org.
We extend our thanks to Albert Reichert and Jonathan Hamrell, from the
Bureau for Humanitarian Assistance in USAID, who provided the support
and the funds to write and publish this book.
We want to thank the hundreds of people we have met in the field in
recent years for their work, interest, time and curiosity about solar water
pumping solutions.
We are grateful to the publishers, Practical Action Publishing, who have
been a source of guidance during the whole process of writing and publishing
this book.
Special acknowledgement is due to Professor Salvador Seguí Chilet
(Polytechnic University of Valencia, Spain) who authored chapter 4, and
Florent Eveillé (FAO) who authored chapter 8. We thank the following

people who provided technical review and gave invaluable feedback: Brian
McSorley (Oxfam), Kai Rainecke (Lorentz), Andrew Armstrong and Jeff Zapor
(Water Mission), Antonio Torres (IOM) and Professor Ellen Milnes (University
of Neuchatel, Switzerland). Finally, we thank Jerome Burlot, who provided
great support in starting the Global Solar and Water Initiative back in 2016,
together with his colleagues Daniel Clauss and Denis Heidebroek (ECHO).
Our deepest gratitude goes to our families, Ezekiel, Kuan-Yun and Arnaud,
for their unwavering support and sacrifice in allowing us to work long
hours and to depart on long work trips, while they often shouldered greater
responsibilities. To Lisa, Joshua, Nina and Noa – thank you for allowing us
time away from you to work on this book.

Copyright practicalactionpublishing.com
CHAPTER 1
Solar photovoltaic solutions
for water pumping
Following a worldwide energy transition to renewable solutions, humanitarian and
development actors are increasingly using solar photovoltaic technology in their water
supply projects. A number of factors, including reduced costs, reliable technology,
a booming private sector, high solar radiation in vast areas of Africa and Asia,
and environmental concerns, among others, have been pivotal to bringing about
this renewed interest in solar PV solutions in the relief sector. Despite its numerous
advantages, solar PV pumping is not a panacea and careful contextual analysis
beyond technical considerations should be carried out before its adoption.

Keywords: energy transition, humanitarian energy, solar pumping guidance,

solar pumping advantages, solar cost reduction

1.1 Solar PV water pumping in humanitarian and development contexts

An energy transition is well on the way worldwide, with an exponential
expansion in the use of renewable energy solutions in both developed and
developing countries. This expansion is creating local value and jobs, mitigating
climate change, and creating stronger community resilience (REN21, 2019).
The supply of constant and reliable energy is of paramount importance
to ensure the provision of basic services, such as water. In a large number
of water supply projects, water is pumped from boreholes or surface water
bodies to elevated storage tanks and fed into distribution systems using the
force of gravity. Especially in developing countries, the energy required for
pumping water is dependent on generators and fuel and/or electrical grids
that are unreliable or faulty. Due to deep groundwater tables, distant water
points, and/or the requirement for large quantities of water, pumping of water
is linked to high energy consumption, resulting in high recurrent costs, partic-
ularly for fuel supply and maintenance of equipment.
In addition, water supply projects are often implemented in hard to reach
locations where insecurity, poor roads, and harsh weather constrain access,
making the supply of fuel and other consumables for repair and maintenance
expensive and cumbersome. Other inconveniences linked to the operation
and maintenance of fuel-powered generators used to pump water include
the risk of misuse of fuel, the logistics of ensuring regular fuel supply, and
recurrent breakdowns, leading to water shortages.
The sun, on the other hand, is a potential source of energy and is environ-
mentally friendly. Solar PV water pumping – or the direct conversion of solar

http://dx.doi.org/10.3362/9781780447810.001
Copyright practicalactionpublishing.com
2 SOLAR PUMPING FOR WATER SUPPLY

energy into electricity to power a water pump – is considered in a number

of contexts and regions the most appropriate and cost-effective solution to
enable sustainable and reliable water supply (see Figure 1.1). Its operation and
maintenance is much simpler and cost-effective, meaning that water shortages
due to equipment breakdown, such as those encountered with generators, can
be reduced or avoided (see Table 1.1). This makes solar PV pumping a particularly
relevant technology for off-grid and weak-grid locations, and contexts where the
procurement and logistics for fuel provision are too costly or erratic.
In particular, solar PV pumping is a
relevant and cost-effective solution in
Solar vs wind power
vast areas of Africa, America, Oceania,
Wind pumping solutions rely on wind and Asia, where fuel can be expensive
patterns which can be highly unpre-
dictable, require specialized parts,
to transport, electrical grids absent or
and must be regularly maintained, unreliable, and access to water points
making solar pumping technology limited, but where solar irradiation is
a more reliable choice for a wider fairly constant and high.
number of contexts.
While the costs for solarizing water
points are normally higher compared
to diesel pumping systems, it has been established that adoption of solar PV
pumping systems translates to higher savings in short to medium periods of
time (GLOSWI, 2018).
Why is it then that solar pumping is not mainstreamed, especially in the
relief sector? The severe shortage of solar energy expertise among NGOs in water,
sanitation, and hygiene (WASH), United Nations agencies, and government
water officers is probably the single most important barrier towards an effective
and wider use of solar pumping technology in water supply projects, in both
emergency and development contexts.

Appropriate for
solar power plants
Excellent
Very good
Good
Poor

Figure 1.1 Global map of appropriate locations for solar applications

Table 1.1 Advantages and disadvantages of solar PV water pumping schemes

Advantages Disadvantages
Low operation costs since fuel is not Capital costs typically higher than
needed and the system is run on sunlight equivalent diesel solutions. However,
system prices are increasingly dropping
No dependency on erratic or expensive Most applications need water storage
fuel chain supply (also avoiding the risk capacity typically larger than for equivalent
of fuel theft) diesel or grid systems
Low regular maintenance requirements Risk of theft of panels, which are seen as a
since solar panels and inverters have no valuable commodity in some locations
moving parts
No pollution or noise produced System depends on solar radiation levels
Extended lifetime (good-quality solar panels Spare parts and knowledgeable technicians
are warrantied for 25 years, inverters are typically available only in capital cities
typically for 6–8 years) and are lacking at field level
A modular solution that can be expanded Technical expertise of most humanitarian
easily by adding modules and other and developemnt water organizations
accessories remains low

Other constraints are that:

• Water stakeholders have not institutionalized their scattered solar

expertise.
• Clear policy detailing circumstances favourable to solar pumping is
lacking.
• Organizations have few incentives to adopt better energy solutions
in the field.
• Practitioners are not able to properly show the benefits to donors and
management.
• Some donor decisions are dominated by initial investments.

Despite these challenges, the interest in and number of solar pumping

projects in humanitarian operations have increased steadily, including
their inclusion in strategic documents of United Nations agencies and
non-government organizations.

1.2 Factors influencing the renewed interest in solar PV water pumping

Solar pumping is not a new technology, with projects traced as far back as
the late 1970s. While the possibilities of powering pumps with solar energy
attracted a lot of interest initially, this faded away quickly, and it is only
in recent years that a wide range of stakeholders have increasingly turned
their attention to solar pumping solutions. Several factors are behind this
renewed interest.

1.2.1 Environment
In the global context of climate change, the need to reduce greenhouse
emissions has become of paramount importance. Environmentally friendly
solutions, such as adoption of solar energy, are gaining more ground, including
in emergency and development programmes.

1.2.2 Cost reduction

The use of renewable energy sources is increasing dramatically world-
wide, with power installed doubling for five consecutive years to 2018
(IRENA, 2019).
Solar PV is one of the star performers, with an exponential increase
over the last 10 years. In 2017 alone, over 40,000 new solar panels were
installed every hour worldwide [2]. This large-scale use has resulted in
economies of scale with solar PV panels (over 200-fold cheaper today when
compared to the late 1970s and a cost reduction of about 80 per cent in the
last ten years), with predicted further cost reductions of about 40 per cent
over the next ten years.

80
$76.00

60
Price history of silicon PV cells
in US$ per watt
50
$/watt

10 $0.30

1977 1981 1985 1990 1995 2000 2005 2010 2015

Figure 1.2 Evolution of price of PV cells, 1977–2015

Source: IEA PVPS and Bloomberg

1.2.3 High solar radiation

Areas of the world with high and regular solar radiation (radiant energy
emitted by the sun), including most of the countries where emergency and
development programmes take place, are also often regions that lack reliable
electrical grids or where fuel is, for logistical or other reasons, expensive and/
or of erratic supply (see Figure 1.1).

1.2.4 National solar private sector

Solar PV markets are rapidly evolving in the developing world with a trend
that started in East Africa now spreading in West Africa and South Asia
(IRENA, 2019).
This has helped create the conditions for a knowledgeable solar focused
private sector to boom in many of these countries. The availability of the
know-how and good-quality solar products at national level that other
organizations can tap into is facilitating the expansion of the use of solar PV
solutions, including solar pumping (GLOSWI, 2018a).

1.2.5 Technological advances

Technological advances in solar pumping technology have resulted in
robust, versatile, and low-maintenance equipment. The extended range
of powers that solar equipment can now handle means a wide range
of electrical submersible and surface water pumps can be powered with
solar energy.

1.2.6 National energy policies

The development of favourable policies committed to renewable energy goals
from an increasing number of governments (REN21, 2019) is supporting the
uptake of solar pumping solutions.

1.3 Guidance note on the use of solar pumping

1.3.1 Rationale for the use of solar PV pumping solutions
The factors mentioned in section 1.2 make conditions ripe for solar pumping
to be considered as a default option for water provision in places with
medium to high levels of solar irradiation (4–8 kWh/m2), especially in off-grid
locations, long-term camp contexts, or where water supply is fuel dependent
but the fuel supply is too costly or erratic.
The presence of some trained private-sector contractors with good-quality
solar pumping equipment in many countries further supports solar uptake
and can be counted on by relief and development organizations to facilitate
adoption of solar solutions for water supply projects.

There is a high potential for cost reductions to be realized if analysis and

funding decisions are based on costs over the life cycle of schemes costs over
time), rather than only considering capital costs of installation.
In addition, environmental considerations make solar pumping technology
a climate-smart choice, especially when considered against any diesel-based
option.

1.3.2 Camp contexts: mainstreaming of solar pumping

In camp contexts with the prospect of being in place for more than two to three
years, solar pumping should be considered as a default solution. It should be
considered from as early a stage as possible, whenever solar pumping solutions
are able to meet a significant amount of
the water demand (GLOSWI, 2018b). Solar pumping solutions should be the
Stand-alone solar systems should default option in refugee camps with high
be favoured over hybrids (solar + solar radiation and their adoption should
diesel generator or other back-up be considered as early as possible.
power source) because of their higher
cost-saving opportunity and simplicity of operation and maintenance.
However, care should be taken whenever a rapid change in context could
translate into longer pumping hours going beyond the solar day, for example,
when population figures are not well known or are prone to sudden increases
at short notice (e.g. large refugee inflows), or when the behaviour of the
aquifer is largely unknown (e.g. unknown safe pumping yields or possibility
of large variations in drawdown over the seasons). In these cases, a back-up
power source should be considered so that pumping beyond the solar day is
possible if needed.
In older camps, solarization of water schemes should be prioritized to
ensure water provision, looking first at camps with high recurrent costs or
with high water shortages due to irregular or nonexistent electricity or fuel
supply to power water pumps.

1.3.3 Host community context: social aspects before technology choice

Solar pumping is, from the technical point of view, equally appropriate
for water supply projects at host community level (villages and towns) as
for refugee or internally displaced people camps. It should be considered
as a default option, in order to increase sustainability and resilience of
communities. In contrast to camps where there is normally a permanent
presence of relief organizations, aspects to do with ownership, operation,
and maintenance add an extra layer of complexity in the host community
context.
At host community level, adjustments related to the collection and use of
water fees will need to be introduced and discussed, as solar solutions may
not require a constant inflow of funds to operate and it may take years before

equipment breaks down. Therefore, the narrative of solar-powered water

systems for communities should shift from ‘tapping into a cost-free source of
energy to pump water’ to ‘accumulating funds for system replacement’.
A well-thought social approach, involving contribution from users and
external technical support for maintenance and repair should come before
technology choice. In this sense, prioritizing communities with strong social
cohesion and coordinating approaches with government water offices and/or
knowledgeable private-sector companies is a prerequisite.

1.3.4 When solar pumping should be discouraged

Solar pumping should not be seen as a blanket solution to every water supply
project and its use is discouraged in some cases, namely:

• where theft and/or vandalism of solar pumping schemes is widespread,

as reported from past interventions;
• when the expertise of the implementing organization is low and private-
sector support cannot be counted upon;
• where solar technology does not bring any significant technical,
economic, or enviromental advantage over existing solutions in terms
of amount of water supplied, greenhouse gas emission reduction,
cost savings over time, or simplicity of operation and maintenance
of equipment.

1.3.5 Issues related to operation and maintenance, and training and evaluation
Solar pumping schemes will suffer fewer breakdowns and have much less
intensive maintenance than generator or hand pump schemes. However, solar
pumping schemes can and will experience technical problems at some point
in time that cannot be solved at community level (or for which the organi-
zation in charge of the water scheme
will probably need external support),
Geographical clustering and maintenance
service agreements are a good way to regardless of the training provided in
ensure timely servicing and repairs in the past.
places where parts and technicians are It is important that service agree-
available only in capital cities. ments are established with a good-
quality private contractor, water utility,
water service provider, or relevant government technical office, before any
installation and they should be renewed as needed.
Since the single most important barrier towards a wider adoption of solar
pumping solutions is the weak technical expertise of most WASH organizations,
support from the private sector, government, and/or the donor community
should be provided or encouraged for capacity-building activities in areas
with high potential for adoption of solar pumping solutions (e.g. areas with
high solar radiation and high dependency on fuel-based solutions for the
supply of water).

In addition, ways of collaborating (with, for example, academic institutions,

knowledgeable private companies, or water utilities) should be encouraged
in order to make training activities as sustainable or over as long a duration
as possible.
Finally, since adoption of solar pumping solutions is often based on the
long life expectancy of solar products, it is important to support evaluations
of older (more than five years) solar systems in order to build up stronger
evidence on the adequacy of solar pumping technology for the given context,
as well as to inform future water strategies in the country of work.

Facts and figures

• The working life of solar modules is warrantied to 25 years.

• The cost of solar modules has decreased by 80 per cent in the last 10 years.
• Cost recovery of solar pumping investments vs diesel technology is on average 0 to
4 years.
• Cost reduction over life of the system is 40–90 per cent when compared to diesel
generators.
• Well-designed and maintained solar systems can function for more than 10 years
without any major failure.
• Solar pumping heads of +450 m; pumping rates of +240 m3/h.
• Average cost of service agreements with contractors to ensure functionality is about
US$1,500 a year.

Source: GLOSWI, 2018

Copyright practicalactionpublishing.com
CHAPTER 2
Definitions and principles of solar
energy production
The high and constant level of solar irradiance in most areas where relief
projects take place make solar photovoltaic pumping an ideal choice for water
supply projects. Sun and water work well together as the sunnier it is, the more
electricity is produced and the more water is pumped. A number of basic solar
and electricity concepts need to be understood by water engineers in order to
feel confident in the use of solar PV solutions for their water supply projects,
including the different electrical parameters of a solar module, the parameters
to measure the solar resource in a certain area, and basic DC electricity concepts
and formulas.

Keywords: solar resource, irradiation, insolation, I-V curve, maximum

power point tracking (MPPT), solar maps, solar DC, peak sun hours (PSH),
solar photovoltaic, standard test conditions (STC), solar module, PV array

2.1 The solar resource

Globally, energy consumption is expected to double by 2050 (IRENA, 2019).
Oil supplies are increasingly dwindling and solar provides a clean and viable
renewable energy alternative for meeting the growing energy demand while
mitigating against environmental damage caused by fossil fuel use. Solar
energy is renewable because it will be available as long as the sun continues
to shine. The sun is estimated to provide the same level of solar radiation for
another 4 to 5 billion years.
The enormous amount of energy provided by the sun can be tapped
directly using photovoltaic technology. More energy from sunlight
strikes the earth in 1 hour (4.3 × 1020 J) than all the energy consumed
on the planet in a year (4.1 × 1020 J). The energy from the sun is free,
sustainable (cannot be depleted), is found everywhere, and is non-polluting.
Yet solar energy comes with its own shortfalls as it is not constant during
the day and through the year. There are, however, ways to overcome
these shortfalls, as will be seen through the design process of a solar water
pumping scheme.
The abundant solar energy available in most regions of the developing
world can be exploited for water pumping for both drinking water and
irrigation, particularly in humanitarian and development contexts which are
often faced with severe water and energy supply challenges.

http://dx.doi.org/10.3362/9781780447810.002
Copyright practicalactionpublishing.com
10 SOLAR PUMPING FOR WATER SUPPLY

2.2 Sun and water: the perfect relationship

Water for drinking, irrigation, livestock watering, and other purposes is
obtained from a variety of surface sources (e.g. rivers, lakes, dams, water pans,
berkads, springs, rock catchments) and underground sources (e.g. shallow
wells, deep boreholes).
Energy is required to pump the water from the source to the point of
use. Visits by the Global Solar and Water Initiative (2016–2020) to more
than 100 camps and communities in 12 countries, which are reported in
GLOSWI country reports, have revealed that the majority of water supplies
are from underground sources, particularly deep boreholes. Pumping from
deep boreholes requires relatively high amounts of energy, which is often
lacking in many project locations, particularly, where grid electricity is
non-existent or unreliable and transport of fuel expensive and difficult.
The abundance of solar energy, the great need for water, and the lack
of other energy sources in these locations introduces a perfect relationship
between the sun and water. In other words, more sun means more water is
required. Surface waters decrease in the dry season, whilst arid lands have
greater water needs and agricultural water needs increase during the dry
season. More sun also means more solar power is available, and more power
means more water can be pumped. This is a natural correlation that bodes well
for PV water pumping.
With well-established, sophisticated technologies, solar energy is used
to power a water pump that transfers water from the source to the point
of delivery. As long as there is enough sunshine, water can be pumped

More sun

More power More water can be pumped

Figure 2.1 Sun and water: a perfect relationship

either to a tank or directly to the consumer’s tap, keeping the arrangement

simple, efficient, and free of energy storage devices, such as batteries.

2.3 Solar radiation

Solar radiation is a general term for the electromagnetic waves emitted by
the sun. In space, solar radiation is practically constant; on earth, it varies
with the day of the year, time of the day, the latitude, and the state of the
atmosphere (e.g. presence of humidity, smoke, smog, dust), but remains
predictable and constant year to year. A solar surface known as a solar collector
captures the solar radiation, with the position of the surface and the local
landscape also influencing the amount of radiation that can be collected.
Solar radiation can be converted into electricity using photovoltaic technol-
ogies, such as PV modules. The amount of electricity generated from a module
depends on the sunlight intensity. The more intense the sunlight, the more
electricity is produced.
As sunlight passes through the atmosphere, some of it is absorbed, scattered,
and reflected by air molecules, water vapour, clouds, dust, and pollutants.
The total radiation received on a horizontal surface on the earth is called the
Global Horizontal Radiation and is made up of direct, diffuse, and reflected
radiation. Diffuse solar radiation is the portion scattering downwards from
the atmosphere that arrives at the earth’s surface. The reflected portion is the
energy that bounces off from the surface of the earth. The solar radiation that
reaches the earth’s surface without being diffused in the atmosphere is called
direct solar radiation (Figure 2.2).
Measurements of solar energy are typically expressed as total solar radiation
on a horizontal or tilted surface and calculated from the relationship;

Global Horizontal Radiation = direct + diffuse + reflected

Solar constant
Reduction of
solar radiation

Diffuse
Direct

Reflected

Figure 2.2 Global Horizontal Irradiation

In designing and sizing solar energy systems, the quantification of the

amount of solar energy incoming to solar collectors can be represented as
irradiance and insolation (discussed in section 2.5 and section 2.6).

2.4 Solar photovoltaic

The term solar photovoltaic (PV) is used to refer to generation of
electricity from the sun’s energy. A solar PV cell transforms the energy of
the sun into electricity. The PV effect happens when photons of light hit
a collection of solar cells, exciting electrons into a higher state of energy,
making them act as charge carriers of an electric current. Explained
differently, solar radiation strikes solar cells, the atoms in the solar cells
absorb some of the photons of sunlight, get excited and release electrons.
The electrons flow through a conductor to produce electrical current.
The current is proportional to the intensity of the radiation striking the
collector (Figure 2.3).
The PV effect takes place in a semiconductor material, the most widely
used being crystalline silicon. The active semiconductor material (silicon)
has atoms that are held together by valence electrons. Since silicon has very
few electrons at room temperature, it is ‘doped’ to create a positive-negative
junction (p-n junction). This is done by introducing particular impurities,
such as boron (p-type) which has an excess of holes (absence of an electron is
a hole that leaves a net positive charge), or phosphorus (n-type) which has an
excess of electrons (Figure 2.4). This makes the semiconductor material more
conductive (carries current), provides an electric field (creates voltage),
and allows current to flow only in one direction. The valence electrons

Photons Electrons

Sunlight PV Module Electricity

+ +

– –

Figure 2.3 Conversion of sunlight to electricity

Sunlight

n-type material

p-n junction
p-type material
Solar Panel
Photons

Electron
flow

Hole
flow

Figure 2.4 The ‘PV effect’ process

Box 2.1 Solar PV components

Solar cell – The basic solar building block, an individual photovoltaic cell. They convert
light to electricity.
PV module – Also known as a solar panel, PV panel, or solar module, this is a collection of
interconnected solar cells usually encased in glass with an aluminium frame.
Solar array – Several modules electrically connected in series or parallel.
Solar generator – Several arrays electrically connected in series and parallel to increase the
total available power to the required voltage and current.
String – A set of solar modules electrically connected in series.

are released by energizing them using light and they become free to move,
creating electricity.
A single cell will only produce a small current or voltage, unsuitable for
most applications. Therefore, cells are added together in various series or
parallel configurations, and encapsulated in aluminium or glass to produce
solar modules with varying current, voltage, and power outputs.

Array
assembly of panels
Cell Module/panel connected in series

Photovoltaic generator
assembly of arrays connected
in parallel to obtain the required power
Figure 2.5 Illustration of PV cell, module, array, and generator

The solar PV generator is connected through a control unit (controller)

to power a pumping system (the load). The basic configuration of the
system consists of a PV array/generator, a controller, and an electric pump
(see Figure 2.6).

2.5. Solar irradiance

Solar irradiance is used to define the instantaneous power of solar radiation
received on a surface per unit area. It is expressed in W/m2 (or kW/m2).
The typical amount of irradiance received on a tilted surface at the equator
on a clear day at noon (when the sun is overhead) is equal to 1,000 W/m2.
This means 1,000 W is received on a 1 m2 surface at any given time. On clear
days, a surface receiving solar energy will capture mainly direct radiation,
while on cloudy days the surface will receive mostly diffuse radiation because
direct radiation has been obstructed by the clouds. Irradiance values greater
than 1,000 W/m2 can also be achieved due to a combination of direct and
diffuse radiation.
Non-tropic countries (e.g. countries in Europe) experience lower solar
radiation than equatorial countries because the incident angle of the sun’s rays
is not perpendicular to the earth, and much more of the resource is absorbed
in the atmosphere.

PV array

Controller

Storage tank

Well

Pump

Figure 2.6 A typical solar-powered water system

The solar irradiance will vary throughout the day with minimum values
at dawn and dusk and maximum values at midday. For example, on a
clear day in Valencia, Spain, the irradiance value at 9:00 a.m. will be less
than the irradiance value at noon. This is explained by the earth’s rotation
about its axis, which causes the distance travelled by sunlight through
the earth’s atmosphere to be at a minimum at solar noon. At this hour,
the sun’s rays are striking a surface perpendicularly and through the least
atmosphere.
Figure 2.7 shows the solar radiation arriving on a photovoltaic installation
in Valencia, oriented to the south and with a tilt of 30 degrees with respect to
the horizontal during a week in the middle of July (summer). The maximum
level of solar radiation is 900 W/m2 at noon.
Figure 2.8 shows the changes in the amount of solar energy received on
a surface during a clear day (left part of the plot). In the morning and late
afternoon, less power (irradiance) is received because the surface is not at an
optimum angle to the sun. At noon, the amount of power received is the
highest (around 900 W/m2). However, the actual amount of power received
instantaneously varies with passing clouds and atmospheric clarity due to
dust in the atmosphere (the right part of the plot shows the effect of some
passing clouds at noon).

200
400
600
800

0:00:00
3:10:00
6:20:00
9:30:00
12:40:00
15:50:00
19:00:00
22:10:00
1:20:00
4:30:00
7:40:00
10:50:00
14:00:00
17:10:00
20:20:00
Source: Polytechnic University of Valence, Spain

23:30:00
2:40:00
5:50:00
9:00:00
Figure 2.7 Weekly irradiation in Valencia in the month of July

12:10:00
15:20:00
18:30:00
21:40:00
0:50:00
4:00:00
7:10:00
Time
10:20:00
13:30:00
Irradiance (W/m2)

16:40:00
19:50:00
23:00:00
2:10:00
5:20:00
8:30:00
11:40:00
14:50:00
18:00:00
21:10:00
0:20:00
3:30:00
6:40:00
9:50:00
13:00:00
16:10:00
19:20:00
22:30:00
1:40:00
4:50:00
8:00:00
11:10:00
14:20:00
17:30:00
20:40:00
23:50:00
SOLAR PUMPING FOR WATER SUPPLY 16
Copyright practicalactionpublishing.com
1000
1200

200
400
600
800

0:00:00
0:55:00
1:50:00
2:45:00
3:40:00
4:35:00
5:30:00
6:25:00
7:20:00
8:15:00
9:10:00
10:05:00
11:00:00
11:55:00
12:50:00
Source: Polytechnic University of Valence, Spain

13:45:00
14:40:00
Clear day

15:35:00
16:30:00
17:25:00
18:20:00
19:15:00
20:10:00
21:05:00
22:00:00
22:55:00
23:50:00
0:45:00
1:40:00
2:35:00

Figure 2.8 Time-based solar irradiance in Valencia during summer for two consecutive days
3:30:00
Irradiance (W/m2)

4:25:00
5:20:00
6:15:00
7:10:00
8:05:00
9:00:00
9:55:00
10:50:00
11:45:00
12:40:00
13:35:00
14:30:00
15:25:00
Cloudy day

16:20:00
17:15:00
18:10:00
19:05:00
20:00:00
20:55:00
21:50:00
22:45:00
23:40:00
17 DEFINITIONS AND PRINCIPLES OF SOLAR ENERGY PRODUCTION
18 SOLAR PUMPING FOR WATER SUPPLY

Peak sun hours

Irradiance

Sun at noon
1000 W/m 2
Solar Irradiance (W/m2)

Solar insolation
Sun at morning 5 h x 1000 W/m2 Sun at evening
= 5000 Wh/m2
Sunshine
6 am 5 hours 6 pm hours

Time of Day (hrs)

Figure 2.9 Graph of daily insolation

2.6 Solar insolation

Solar insolation is a measure of the cumulative irradiance received on a specific
area over a period of time, measured in Wh/m2 or kWh/m2. It is typically the
area under the irradiance curve over hourly, daily, monthly, and yearly data.
For practical design purposes, the daily insolation is considered, that is, the
accumulation of irradiance over a day. Simply put, it is the energy received on
a 1 m2 surface over a period of one hour, hence the unit of kilowatt hours per
square metre (kWh/m2).
Insolation is also expressed in terms of peak sun hours or the number
of hours per day during which solar irradiance averages 1,000 W/m2 (see
Figure 2.9). For example, if the daily insolation is 5 kWh/m2, then dividing by
1 kW/m2 (1,000 W/m2) gives five peak sun hours.
As can be seen in Figure 2.10, the irradiance changes throughout the
day. The energy of the first day is equivalent to seven hours of irradiance
at 1,000 W/m2. Seven peak sun hours (PSH) means that the energy received
during total daylight hours equals the energy that would have been
received if the sun had shone for seven hours at a rate of 1,000 W/m2.
The second day has 6.6 PSH due to the smaller irradiance during the passing
of the clouds. Peak sun hours are useful because they simplify design calcu-
lations. The energy produced by a PV array is directly proportional to the
amount of insolation received.

2.7 Standard test conditions

The disadvantage of solar-powered systems is that energy supply is not
continuous and constant during the day and varies from day to day
throughout the year. The amount of energy received will vary depending

200
400
600
800

0:00:00
0:55:00
1:50:00
2:45:00
3:40:00
4:35:00
5:30:00
6:25:00
7:20:00
8:15:00
9:10:00
10:05:00
11:00:00
11:55:00
12:50:00
Source: Polytechnic University of Valence, Spain

13:45:00
14:40:00
15:35:00
16:30:00
17:25:00
18:20:00
19:15:00
20:10:00
21:05:00
22:00:00
22:55:00

Figure 2.10 Solar irradiance during two days of July and corresponding insolation
23:50:00
0:45:00
1:40:00
6.75 PSH
7.02 PSH

2:35:00
3:30:00
Irradiance (W/m2)

4:25:00
5:20:00
6:15:00
7:10:00
8:05:00
9:00:00
9:55:00
10:50:00
11:45:00
12:40:00
13:35:00
14:30:00
15:25:00
16:20:00
17:15:00
18:10:00
19:05:00
20:00:00
20:55:00
21:50:00
22:45:00
23:40:00
19 DEFINITIONS AND PRINCIPLES OF SOLAR ENERGY PRODUCTION
20 SOLAR PUMPING FOR WATER SUPPLY

on the location, the season, the time of day, and the weather (especially
cloud cover). This will in turn affect the amount of power produced by a
solar module and hence the water output in a solar-powered water system.
Therefore, a PV module will give different power outputs at different
locations, different seasons, different times of the day, and different weather
conditions.
For uniformity, PV modules are tested and rated in standard test conditions.
STC make it possible to conduct uniform comparisons of photovoltaic
modules from different manufacturers and to accurately compare and rate
them against each other.
Solar modules are tested and rated at STC of:

• solar radiation of 1,000 W/m2 – typical at noon on a clear day

• module temperature of 25 degrees Celsius – the temperature of the cell
itself and not ambient temperature
• air mass equal to 1.5 (AM1.5) – the thickness of atmosphere the sun
passes through. AM0 is the value of solar radiation outside the earth’s
atmosphere (1,350 W/m2). AM1 is the value on the earth’s surface when
the sun is overhead and the radiation travels through the thickness of
the atmosphere at a right angle (Figure 2.11).

AM 1.5
48.2°

AM 0

AM 1.0
Atmosphere

Figure 2.11 Air mass for different sun positions

A peak watt (Wp) is the amount of power output a PV module produces

at STC. When a module is working outside of STC conditions (which is
often the case in real-life conditions), output will vary according to the
prevailing conditions of irradiation and temperature (air mass has little
effect in practice). A module with a rating of 300 Wp will give only 300 W
at 1,000 W/m2 solar irradiation and 25°C cell temperature. When the
irradiation drops below 1,000 W/m2 and/or the cell temperature rises
above 25°C there is a corresponding decrease in the power output from
the module. It is possible for this module to give more than 300 W when
the irradiation is more than 1,000 W/m2 and/or the cell temperature
below 25°C within the tolerance value stated by the manufacturer. This is
discussed in more detail in Chapter 4.
In theory, a water pump of 3 kW connected to panels rated at 3 kW under
STC would run as if connected to a generator or grid power.

2.8 Solar resource maps for peak sun hours

Peak sun hours are used to size and design a suitable PV generator to
meet the energy demand of the pump to provide the required water output.
PSH is used to define the amount of energy available per day in a given
location.
The PSH is a useful value for comparing the energy differences at different
locations. In pumping, the PSH is used to give an indication of how many
hours in a day there will be maximum power for the pump to achieve
peak pumping.
Databases are available that use systematically processed historical weather
information of many years to provide long-term average weather data. Three
of these databases are:

• Solargis solar resource maps <https://solargis.com/maps-and-gis-data/

download/>
• POWER Data Access Viewer <https://power.larc.nasa.gov/data-access-
viewer/>
• European Commission’s Photovoltaic Geographical Information System
<https://re.jrc.ec.europa.eu/pvg_download/map_index.html>

These three databases are reputable sources of high-quality, reliable

solar resource data that is validated globally, and one can find data for
most locations in the world. The maps or data can be downloaded for free
by region or by country (terms of use can be checked on these websites).
The global solar irradiation map shown in Figure 1.1 gives information
about the annual and daily PSH (kWh/m2/year or day) in the different
regions of the world.
Looking at the map in Figure 1.1, Africa has approximate daily PSH values
of between 4.6 and 7.4 hours, while Europe has daily PSH values from as low

Example of PSH and pumping

After a pumping test, a new borehole in Madaba, Jordan, has a safe yield of 20 m3/hr.
The borehole will supply a village with a population of 2,000 people at 40 litres per day
for each person. Ignoring temperature effect and other factors, can this demand be met
using solar pumping?

2,000 people x 40 litres/day = 80,000 litres/day = 80 m3/day

From the solar resource map for Jordan (see Figure 2.12), Madaba has a yearly insolation of
about 2,100 kWh/m2. This translates to a daily insolation of 5.8 kWh/m2 (i.e. 2,100/365 =
5.8). This means that the peak sun hours for Madaba is 5.8 PSH (i.e. Madaba receives
1,000 W/m2 over a translated period of 5.8 hours daily).

Maximum possible borehole supply = safe yield x PSH = 20 m3/hr x 5.8 = 116 m3/day

The amount of water that can be pumped during the peak sun hours is more than the
demand. It is possible to supply the water needs of this village with a solar scheme.

Figure 2.12 PSH map for Jordan

Source: solargis.com

as 2.2 up to 4.6 hours. In theory this means that at STC, a pump connected
to a PV power source can produce peak flow for 7.4 hours in some parts of
Africa but will only produce peak flow for a maximum 4.6 hours in some
parts of Europe (assuming the same size of PV power and same installation in
both scenarios).
In practice, it will be seen in the
Application note
following chapters that by oversizing
the solar PV generator in a water When the PSH is less than 3.0 hours,
it would be important to critically
pumping scheme, longer hours of
examine the cost of installing solar
pumping can be achieved. PV pumping vis-a-vis the benefit
To get the global irradiation map to be realized. It may be necessary
of any region or country, visit https:// to discard the solar option for such
solargis.com/maps-and-gis-data/ low PSH values unless it is the only
option available.
download, from the drop-down menu
select region (e.g. Africa, Asia), then
select country (e.g. Kenya, Jordan), scroll down to Global Horizontal Irradiation
and click on download.

2.9 Basic DC electric concepts

Current, voltage, and resistance are three important concepts of electricity
it is important to become familiar with to understand power generation
using solar.
A small light bulb connected to the positive and negative side of a solar
module creates a closed circuit where electrons can flow between the terminals
(through the wires) to make the lamp light up. This flow of electrons is called
electrical current.
In this circuit, there will be an opposition to the flow of electrons and it is
called resistance.
Current will only flow if there is an electrical potential difference between
the positive and negative terminals. The potential difference between the
terminals is called electrical voltage and is caused by the resistance to flow of
electrons. It is the force exerted on the electrons to produce current.
Ohm’s law relates the three as follows:

Voltage (V) = Current (I) × Resistance (R)

The electrical power is the product of current and voltage and electrical
power is what is generated at any given instant. The relationship between
power, current, and voltage is expressed using the power law.

Power (P) = Current (I) × Voltage (V)

The electrical energy is the power generated during a period of time.

This concept can also be understood in this manner: the flow of water in
a pipe is the equivalent of the current in an electrical circuit. For the water to

flow through the pipe there must be a pressure difference (head) between the
two points, and this pressure difference is equivalent to voltage. If the pipe
is clogged at some point or due to friction, the flow of water is restricted and
the flow through the pipe is reduced. The friction (or clog) is equivalent to
resistance. This is summarised in Table 2.1.
Power losses in a cable are influenced by the length, size, and type
of wire conductor. Specifically, resistance is directly proportional to the
length of the wire and inversely proportional to the thickness of the wire.
In other words, the longer the wire, the greater the loss and the larger the
wire diameter, the less the loss. The energy loss is also influenced by
the wire material: a good conductor, such as copper, has a low resistance
and will result in less energy loss.

Table 2.1 Analogy of electricity and water

Electricity in a cable Water in a pipe
Definition Term Unit Definition Term Unit
Flow of electrons Current (I) Amperes (A) Flow of water Flow (Q) m /hr
3

Potential Voltage (V) Volts (V) Pressure Head (H) Metres (m)
difference difference
Resistance to Resistance Ohms (Ω) Resistance to Friction (Hf) Metres (m)
flow (R) flow
Instant power Electric Watts (W) Hydraulic Hydraulic Watts (W)
generated = I x V Power (P) load = Q x H power (P)
Power generated Electric Watt hours Power Hydraulic Watt hours
in a period = P x Energy (E) (Wh) generated in energy (E) (Wh)
time a given time
High voltage + small cable = High current + High pressure + small pipe = High
high resistance + cable losses = heat and fire velocity + high friction losses = pipe bursts

Another effective way to reduce electrical losses in a system is to decrease

the current flow (keeping the electric power of the application). Power losses
in an electrical circuit are proportional to the square of the current, as shown
in this equation.

Power loss = Current2 × Resistance

Consequently, from the power law (P = I × V), increasing the voltage while
reducing the current will result in the same power transmission, but with less
power loss. Therefore, higher voltage pumps tend to be more efficient than
lower voltage pumps, assuming all other properties are similar.
It is important to keep in mind that there are two forms of electricity,
alternating current (AC) and direct current (DC), and the two cannot be mixed
together directly. Solar PV modules always produce DC power, while fuel
generators and grid sources give AC power. Direct current has fixed polarity
(i.e. does not change direction) but for alternating current the polarity

changes. A DC load (such as a DC pump) is powered directly using DC power

through a simple on–off switch. An AC load (such as an AC pump) can also be
powered using DC power from the solar modules, but the DC power must first
be converted to AC to power the AC load. This conversion is achieved by use
of a DC–AC inverter. More on this is discussed in Chapter 3.

2.10 Solar module I-V curve and maximum power point

The electrical characteristics of a PV module can be defined using the
relationship between the current and voltage plotted on a curve (the same
way that the hydraulic characteristics of a water pump are defined by
plotting on a curve their hydraulic head versus the flow output). The values
of current and voltage vary from zero to a maximum and are obtained by
exposing the module to a constant irradiation and temperature, varying the
load resistance from zero to infinity and measuring the current and voltage.
The values are then plotted on an I-V curve on the horizontal and vertical axes
respectively, as shown in Figure 2.13.
Open-circuit voltage (Voc) is the maximum voltage measured and is achieved
when there is no load connected to the module (open circuit) meaning there
is a potential difference (voltage) but no flow of electrons (zero current).
In solar design, the Voc is used to calculate the maximum voltage input into
the controller.
Short-circuit current (Isc) is the maximum current and is achieved when
the circuit is shorted, meaning there is a flow of electrons but no potential
difference (zero voltage between the negative and positive terminal). In design,

4
I sc = 3.5 A p = 53 W 50
mp

3 I mp = 3.08 A 40
IV Curve
Power (W)
Current (A)

30
2

PV Curve 20

1
10
V mp = 17.2 V
0
0 4 8 12 16 20 24
Voltage (V)

Figure 2.13 Typical I-V and power curves for a crystalline PV module operating at STC

CS6-265M / I-V CURVES Maximum power point (MPP)

A Short circuit (Isc) A
10 10
9 9
8 8
7 7
6 6
5 5
4 4
3 3
2 2
1 Open circuit (Voc) 1
0 V0 V
5 10 15 20 25 30 35 40 5 10 15 20 25 30 35 40
1000 W/m2 5ºc
800 W/m2 Variable sun Variable temp 25ºc
600 W/m2 45ºc
400 W/m2 65ºc

Figure 2.14 I-V curve under varying irradiance and temperature

the Isc is used to size all the DC accessories, including DC switches and DC
cabling, since it is the maximum current generated by the module.
Since practically the two maximum values cannot be achieved on load
(i.e. no power is produced at short-circuit current with zero voltage and at
open-circuit voltage with zero current), the maximum power is obtained at
the point on the curve where the product of voltage and current is maximum.
This occurs at the knee of the curve. This point is known as the maximum
power point (MPP) and is the highest possible power output of a solar module.
This point represents the maximum efficiency of the module in converting
sunlight into electricity. The point at which power is maximum gives the
maximum peak current (Imp or IMPP) and the maximum peak voltage (Vmp or VMPP).
The MPP is the desired point of operation of the module and operation outside
this point reduces the amount of power generated.
In real conditions, irradiation and temperature are not constant and
therefore the module’s MPP will shift according to changes in irradiation and
temperature (see Figure 2.14). Lower irradiances reduce the current output but
its effect on voltage is negligible, and higher temperatures reduce the voltage
but its effect on current is minimal.
Since power is the product of current and voltage (Ohm’s law), then reduction
in irradiance and increase in temperature results in reduced power output.
By using MPP tracking (MPPT) technology in solar controllers, the resistance of the
load can be varied to ensure that the module is always operating at its maximum
power point at varying current and voltage conditions. Solar pump controllers
will therefore include an MPPT function that will take power out of the PV array
at its most efficient value by adjusting the load, thereby avoiding needless energy
losses. MPPT is an important feature to look out for in solar controllers.

Copyright practicalactionpublishing.com
CHAPTER 3
Solar-powered water system
configurations and components
While solar pumping is not a new concept, with projects dating back to the late
1970s, the technical revolution in terms of inverters (converters of solar DC electricity
into AC) has opened the door to the solarization of a much wider range of water
pumps, both surface and submersible. Depending on whether the water required
can be supplied during the solar day or pumping is needed beyond, configuration
of schemes will be stand-alone or hybrid (one or more energy sources). This chapter
presents the main components of a solar pumping scheme.

Keywords: balance of system components, inverters, solar stand-alone, solar

hybrid, solar pumps, solar controllers, variable frequency, disconnect switch

3.1 SPWS concept and revolution

The benefits of solar-powered water systems (SPWSs) cannot be overempha-
sized: simple, reliable, durable, modular, and low maintenance. In SPWSs, the
solar energy is coupled directly to power an electric pump motor through
a solar controller. The electric pump can be either a surface pump, submersible
pump, DC pump, or AC pump. The controller can be either a DC control
box or an inverter. Therefore a photovoltaic water pumping system is generally
like any other pumping system, with the exception that the power source is
solar energy.
Previously the capacity of SPWSs was limited. Fifteen years ago, the biggest
solar pump on the market was probably a 4 kW DC pump with a daily
hydraulic duty of between 1,500 and 2,000 m4 (approximately 10–200 m3/day
at an inverse head of 10–200 m). The drastic reduction in solar PV prices in the
last decade has triggered technological advancements of robust and reliable
solar pumping equipment.
The development of variable-frequency inverters has extended the solar
pump performance range tenfold since they work with standard electric
motors. Literally any electric pump can be solarized and can also be powered
using dual power sources (solar and AC power). These developments have
led to a revolution in the use of solar for off-grid water pumping and the
emergence of a vibrant private sector with good technical knowledge offering
quality solar pumping products in most countries (see GLOSWI country reports
from 2016 to 2020). SPWSs are technically non-restricting these days with
large solar pumping systems feasible (see more on SPWS sizes in section 7.5).

http://dx.doi.org/10.3362/9781780447810.003
Copyright practicalactionpublishing.com
28 SOLAR PUMPING FOR WATER SUPPLY

Table 3.1 List of solar-powered water systems found in the field

Country Location Motor PV generator Average Total Price
size (kW) size (W) output dynamic (USD)1
(m3/day) head [m]
Kenya Lodwar 0.9 1,400 18 70 $8,535
Nigeria Maiduguri 1.4 1,000 17 61 $7,955
Sudan Zamzam 1.7 1,560 26 55 $11,013
Ethiopia Fafen/Awbare 3.0 7,500 108 47 $24,309
South Bentiu 4.0 10,920 120 68 $23,998
Sudan
Uganda Rhino 4.0 4,000 30 90 $17,057
Ethiopia Fafen/Babile 4.0 6,750 59 80 $20,264
Kenya Songot 4.0 3,500 35 85 $15,893
South Bentiu 5.5 15,600 197 58 $32,747
Sudan
Uganda Bidibidi Zone 1 7.5 15,000 95 121 $34,554
Iraq Erbil 18.5 32,130 277 110 $50,567
Kenya Nablon 30.0 51,000 450 100 $79,820

Note: The price is for an installed SPWS up to the borehole surface, including pump,
1

motor, solar generator, solar controller, DC accessories, cabling, and drop pipes.
Source: GLOSWI Country reports, 2016–2020

Table 3.1 shows a representative list of some of the systems encountered in the
field together with their prices.
One of the distinguishing factors of an SPWS is the feature of variable-
frequency operation. Traditional water pumping using grid or diesel is
typically configured to operate on constant pump speed, that is, the pump is
designed to start and operate at a certain fixed minimum speed (usually 50 Hz
or 60 Hz).
As seen in Chapter 2, available solar energy fluctuates throughout the day
depending on the irradiation from the sun, thus limiting the operation of a
fixed-speed pump. Solar pumping technology has therefore been engineered
to overcome this hurdle. This means that solar pumping systems are designed
to be able to start even at low frequencies and to adjust the operating
frequency according to the available energy from the sun. Consequently, the
flow delivered by the pump also fluctuates relative to the speed of the pump,
allowing water to be delivered throughout the solar day, albeit at low quantities
in the morning and evening when the sun’s intensity is low (Figure 3.1).

3.2 SPWS configurations

Different solar pumping configurations are possible based on the power source
(solar stand-alone vs hybrid) and water source (submersible vs surface).

6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00

Output grid/Generator (m3/hr) Output solar (m3/hr)

Figure 3.1 Typical flow output profile of a solar-powered pump

Note: Light grey area shows the output of a constant/fixed speed pump running on generator
or grid power during the same period

3.2.1 Solar stand-alone vs hybrid configuration

A stand-alone SPWS has solar as the only source of power. It consists of
a PV array connected to a pump assembly via controller, as shown in
Figure 3.2.
A hybrid SPWS will have solar as the primary source of power with an
alternative source of power connected, such as AC power from either a
diesel generator or grid supply, for pumping when solar energy is insuf-
ficient to run the pump (Figure 3.3). It enables pumping where water
demand cannot be met using solar and pumping is required beyond the
solar day; or in cases where the water source is constrained and cannot
provide enough water over a 4–9 hour solar pumping day; or where water
demand is variable with the seasons and a supplementary power source
can be switched on as needed to meet the increased demand (intermittent
usage). More of this is discussed in section 5.3.8.
Whenever possible and where the solution can meet the demand duty, solar
stand-alone should be prioritized over hybrid as it is the most cost-effective
with the shortest payback period. Such a decision should always begin with
availability of full water-source data, such as a test pumping report, as well as
reliable water-requirements data.

5 1 PV modules
6 2 Controller
1 3 Pump
2 7 4 Water source
5 Storage
6 Tap stand
7 Irrigated crops

4
3

Figure 3.2 Stand-alone solar installation

1 PV modules
2 Changeover switch
8
3 Pump
1 5 4 Water source
5 Storage
6 6 Tapstand
7 Inverter
10
8 Grid or diesel generator
9 Irrigated crops
2 10 AC controller
7 9
4

Figure 3.3 Hybrid installation

3.2.2 Submersible vs surface configuration

Submersible configuration has a submersible pump installed completely submerged
in the water source (mainly in wells and boreholes). Submersible pumps can also
be installed horizontally inside water reservoirs at a minimum depth of 0.5 m, well
anchored and fitted with a cooling sleeve (plastic or metallic cylindrical shroud
put around the motor) to enable enough cooling to the motor.
Surface configuration has the pump mounted outside and near the water
source (e.g. tank, river, dam, lake). They are mounted at ground level with the
inlet connected to the water source through a suction pipe and the outlet to
the delivery pipe (Figure 3.4).
Both submersible and surface pumps can also be installed floating in
a surface water source such as a river, lake, or a dam. This is applicable in

1 5 1. PV modules
2. Controller
3. Pump
6 4. Water source
5. Storage
2 6. Tapstand
7. Irrigated crops

4
3 7

Figure 3.4 Stand-alone surface Installation

situations where it is not possible to install the surface pump close enough to
the water source, which would otherwise result in a very high suction head
that could cause cavitation problems (see section 3.3.1, ‘Surface pumps vs
submersible pumps’). Where water levels fluctuate, to mitigate against flooding
the surface pump in the rainy season and to manage the suction lift in the dry
season, the pump is installed floating on the water source.
The optimal configuration (solar stand-alone or hybrid) is determined
based on multiple criteria:

• Solar resource – locations where peak sun hours are insufficient to meet
demand will require a hybrid configuration for prolonged pumping
beyond the solar day.
• Prevailing weather – some locations have seasons when the weather is
overcast, necessitating a hybrid system which will allow intermittent
diesel pumping during prolonged periods of cloud cover.
• Water demand – where the water demand exceeds that which solar
stand-alone can provide, a hybrid system is necessary.
• Water source – a water source that has a limited flow will result in a small
pump that will require prolonged pumping beyond daylight hours to
meet demand. A surface water source will typically be equipped with a
surface pumping system.
• Economic reasons – solar systems have a low cost of ownership and a
short payback period, making it preferred over hybrid systems.
• Demographic factors – contexts where the population is unknown,
uncertain, or expected to fluctuate unpredictably should be installed
with a hybrid system to cushion against water supply fluctuations and
shortages when the population increases.
• Social aspects – some communities may have low acceptance and may
resist installation of solar, necessitating installation of a hybrid system
until there is wide acceptance of the technology.

In addition, some scenarios call for specific contextual considerations,

such as:

• Locations where fuel supplies are irregular or difficult to transport to site

due to inaccessibility and/or security will adopt solar stand-alone even if
there is no economic rationale for solar.
• Critical water supplies which would affect an entire population or bring
operations to a halt when the water system is down would require a
hybrid configuration to ensure supply continues when one power
supply is faulty.
• Where spare parts or technical services are not immediately available,
the use of hybrid systems ensures continued pumping while the solar
system is being repaired, which can take several days to weeks in
remote locations.

Application note

Specific equipment constraints may also influence the choice of configuration in favour
of solar, but with a diesel option to meet demand. For example, considering a demand of
600 m3/day and the largest solar pumping solution available in the country/local market
is a 30 kW pump giving 40 m3/hr. Instead of installing a 55 kW diesel system with a flow
of 60 m3/hr running for 10 hours to meet the demand, the 30 kW solar system can be
installed to run on solar for approximately 7 hours (40 m3/hr x 7 hr = 280 m3/day), with
night pumping for 8 hours on diesel to meet the shortfall of 320 m3/day. Comparing the
fuel consumption of the two options, the 55 kw pump would be connected to a 140 kVA
diesel generator consuming 25 litres x 10 hours = 250 litres of diesel per day. With the
second option, the 30 kW pump will be connected to a 75 kVA generator consuming
15 litres x 8 hours = 120 litres of diesel. The cost benefit of choosing the second option
is obvious. Note if a 55 kW solar pump solution was available there would be no need to
pump using diesel, it is the SPWS equipment constraints in this context which necessi-
tates the need for a hybrid system.

3.3 SPWS components

A solar-powered water scheme will have the DC side (entire part of the
system that generates and conveys DC power, including the PV generator, DC
terminals, DC isolators, DC switches, DC cables, controller, DC pump) and/
or the AC side (entire part of the PV system which begins after conversion of
DC power to AC power, including AC switches, changeover switch, AC cables,
AC pump). All electrical components are rated for the form of power they
will be used to convey, so equipment used to convey DC power is rated for
DC, and equipment used to convey AC power is rated for AC. They must be
designed and used in compliance with the relevant electrical codes.
A solar water pumping system has three major components which constitute
on average 60 per cent of the total cost of the scheme, with the balance of
system components (DC accessories, cabling, drop pipes, etc.) accounting for
the remaining 40 per cent.

• Pump – the pump can be either DC or AC type, centrifugal or helical

rotor type, surface or submersible type.
• Controller – DC pumps use DC power directly from the solar modules
through a simple control box. For an AC pump, an inverter is required
to invert DC power from solar modules to AC power required by the AC
pump.
• Solar module – the solar modules generate DC power and supply it to
the pump through the control box or inverter.

3.3.1 Water pumps

Pumps are rated in flow (m3/hr) and head (m) and are connected to an electrical
motor that is rated in kilowatts (kW). The motor draws power from the source
(solar PV generator in this case) and drives the pump to deliver water.
Solar pumps can be broadly sorted into three categories:

• the motor power type – solar DC vs AC pumps;

• the pump end design: positive displacement vs centrifugal pumps;
• the installation set-up: submersible vs surface pumps.

The pump set should be matched to the water source, the power source,
and the application.
Selection of the appropriate pump size is based on the duty point, which
is the required flow output and head. Manufacturers’ pump performance
curves or computer software are used to determine this. An explanation of the
selection process is provided in Annex A and Annex B.
A key factor in pump selection is ensuring that the pump duty point is at
the best efficiency point (BEP). A common practice is to select the duty point
to the right of the BEP on the pump performance curve, so that as the pump
wears out the duty point shifts towards the BEP, thereby achieving efficient
operation over the life of the system.

Solar DC pumps vs solar AC pumps. Both DC and AC pumps are available for
use. The distinguishing feature between DC and AC pumps is in the motor.
A DC pump system is the simplest SPWS configuration and consists of a
PV array directly connected to a pump assembly with a DC motor via a DC
controller. DC pumps have longer lifespans and are more efficient compared
to an equivalent size of AC (up to 90 per cent versus 50–70 per cent for AC)
as no power conversion is necessary. These pumps are, however, limited
in head and flow and are generally used for lower head, lower volume (i.e.
smaller) applications of up to 4 kW power demand. The pump design can be
positive displacement or centrifugal type. The motors can be either brushed or
brushless (both have permanent magnets).
The brushed motors have brushes that deliver current to the motor
windings through commutator contacts, while brushless motors have none of
these commutators. Brushed motors have the advantage of being less costly

to buy with simple installation as they can be wired directly to DC power

through a simple switch without the need of complicated electronics. Yet they
are less efficient (75–80 per cent), electrically noisy, and have a maintenance
cost due to wearing out of the brushes and commutators.
Brushless motors on the other hand, have a higher efficiency (85–90 per cent),
longer lifespan, and are less costly to maintain as they do not require
replacement of brushes. They do cost more than brushed motors and have an
additional cost of an encoder and a driver to control.
In an AC pump system, the PV array is connected to a pump assembly
with an AC motor. The motor is typically a brushless 3-phase induction
(asynchronous) motor. These motors have a robust design with standard or
enhanced insulation providing long, reliable service, minimum maintenance,
and ability to withstand the voltage stresses encountered with most inverter
drives. AC motors cannot operate with DC power and require a DC–AC
inverter to convert incoming DC supply to power the AC pump. The pump
design is commonly centrifugal due to their high flow capabilities.
An AC pump system is used for higher capacity applications that cannot be
handled by a DC system.

Positive displacement vs centrifugal pumps. Examples of positive displacement

pumps are helical rotor, diaphragm, or piston types. A helical design is used
in submersible pumps. It features a rotor cased inside a rubber stator that
spins with the motor, creating a vacuum that allows water into the cavity
and effectively squeezes water out as it rotates. They deliver water with
every rotation, with water output increasing with rotational speed, meaning
their efficiency and lift capacity remains high even at low rotational speeds.
Consequently they are appropriate for the varying solar radiation levels of
solar-direct water pumping. This means higher volumes of water can be
pumped per day in variable solar conditions. These pumps all fall within the
DC range of solar pumps and therefore have a limited capacity, suitable for
high heads and low-flow applications. Heads of up to 450 m are achievable
while maintaining high efficiency.
Centrifugal pumps feature one or more impellers inside a chamber
(referred to as a pump stage). Water enters the eye of the impeller and as the
impeller spins the water is subjected to centrifugal force that pressurizes
the water from one stage to another. To achieve high lift, multiple stages
are stacked together (multi-stage pumps) with the pressure of the water
increasing as it is pushed from one stage to the next. This is the reason
high-pressure centrifugal pumps are tall, (submersible pumps can have up to
100 stages with heights of up to 6 m!).

Centrifugal pumps require a minimum speed to start and deliver water. They
can achieve flows of up to 250 m3/hr with efficiency reducing at high
heads and low flows. For this reason, positive displacement pumps are
used for most systems that require high lift at low volumes. The efficiency
of centrifugal pumps deteriorates as the speed varies, whereas positive

displacement pumps can operate efficiently over a wide speed range.

Positive displacement pumps can also operate at fairly constant flow over
a wide pressure range.

Surface pumps vs submersible pumps. Submersible pumps are installed

completely submerged in water. They are predominantly used for deep-well
pumping. Submersible pumps are coupled to water-cooled or oil-cooled
motors and must never be operated without water otherwise they will burn
out due to dry running. They are available in both centrifugal and positive
displacement designs.
A surface pump is installed outside the water source – it cannot be submerged.
A surface pump has an air-cooled motor which should be installed in a well-
ventilated location protected from the weather. It is prone to failure if it is
submerged or splashed with water. Commonly, surface pumps are installed
inside a pumphouse. They are designed to draw water from a depth of 3–7 m
above the water-source surface level. If this vertical height (referred to as
suction lift) is exceeded, the pump experiences cavitation (as the water enters
the inlet of the impeller, low pressure causes it to vaporize, forming bubbles
which collapse and erode the impeller as they collapse), eventually leading to
pump failure. Surface pumps can be of centrifugal or positive displacement
(diaphragm or piston) design.
Surface pumps tend to be more efficient at high-flow pumping and are less
expensive than submersible pumps, but more complex to install and operate.
Manufacturer data sheets will state the type and name of pump.

Quality and performance considerations. Pumps are recommended to meet

EN 809 and EN 60034-1 or equivalent standards, stainless steel with a
minimum grade of AISI 304 or higher.
Centrifugal pumps may be constructed of other materials, such as cast iron
and plastic, the choice of which will depend on various factors, such as the
quality of water to be pumped. For example, water that has a lot of silt is better
pumped with a pump of plastic internal construction, whereas corrosive
water or hot water is better pumped with pumps of higher grades of steel.
Importantly, the material used for pump construction should be corrosion
resistant, permanently lubricated, and maintenance free, as well as able to
handle the water temperature.
The pump motor is the piece of equipment most prone to failure and
should be constructed with corrosion-resistant material, all stainless-
steel exterior construction, stainless-steel shaft, ceramic bearings, NEMA
mounting dimensions, hermetically sealed windings, water lubrication, and
pressure-equalizing diaphragm, and able to withstand a certain maximum
temperature.
The pump set must be of modular design to allow for replacement of
individual parts (pump end, pump motor, and electronics) if failure occurs.
The pump must have dry-run protection to protect it in the event of low
water levels.

3.3.2 Controllers
Solar panels produce DC power and the controller acts as a power conditioner,
meaning it improves the quality of power that is delivered to the pump from
the PV modules. It acts in one or more ways to deliver a voltage of the proper
level and characteristics to enable the pump to function properly. Another
important function of the controller is to start the pump slowly (soft start)
and adjust its speed according to the pumping load and power available from
the solar array. Maximum power point tracking optimally matches the power
output from the solar array to the load throughout all conditions.
Solar pump controllers are rated in watts or kilowatts. Selection of the
appropriate size to power the pump is based on the allowable input power
(minimum and maximum DC voltage and current), controller power output
(voltage, current), and the power rating of the pump motor (voltage, current).
The controller influences the series/parallel configuration of the modules.
Manufacturer data sheets or design software can be used to determine each of
these. A full explanation is provided in Annex B.

DC controllers. DC pumps utilize DC solar controllers, which come in two

forms, depending on the type of motor used in the pump.
Brushed DC motors can be wired directly to DC power through a simple
switch without complicated electronics. A brushed helical pump will have a
linear current booster (LCB) that reduces the voltage from the PV array while
it boosts the current. This starts the pump motor and prevents it from stalling
during low-light conditions. The brushed centrifugal pump is often supplied
without an LCB because it starts easily, and its current draw diminishes with
speed. An LCB will increase the pump’s efficiency during low-sun periods, but
the performance gain is relatively small.
Brushless DC motors require an external drive to control the voltage and
current applied to the motor, perform the LCB function, and match the pump
speed to the available power. The controller varies the motor speed by varying
its own frequency. A brushless DC pump is normally sold with a controller
that is engineered specifically for it, for example, Lorentz Brushless DC motors
have an external driver that is mounted on the surface to control the pump.
Controllers for brushless motors sometimes come integrated into the motor,
such as the Grundfos SQFlex, and Nastec solar pumps. The disadvantage of
integrated controls is that if there is a problem with the electronics in the
motor, the entire pump and pipe assembly must be removed from the well and
the entire motor assembly replaced. The above-ground controls are versatile
and easier to access for repairs and servicing.
Solar DC controller ratings are typically up to 4 kW and the rated power is
DC voltage and current.

AC inverters. For AC pumps, a solar inverter is needed to convert DC power

output from the PV array to AC power for the pump. The inverter outputs
a variable frequency depending on the energy available from the sun,

and consequently enables the pump motor to run at variable speed with
varying flow output depending on energy availability. It also works to
smooth the sinusoidal AC wave form and maintain a constant voltage over
varying loads. Ratings of up to 150 kW are available. Most inverters for
pumping are of 3-phase AC power output, the reason being that single-phase
inverters have little relevance in pumping due to the availability of direct
DC-powered solar pumps.
Inverters are now available with power blending or dual power supply
capability. The specific requirements of such inverters, such as isolation
switches to prevent both powers being present at the same time, are usually
provided by the manufacturer. The technical specification gives detailed
information on how they should be mounted, protected, and operated.

Quality and performance considerations. A good solar controller must meet

EN 61800-1, EN 61800-3, EN 60204-1, or internationally recognized equivalent
standards that are indicators of equipment safety and quality. Design and use
of a controller must follow IEC 62109-1 and IEC 62109-2.
DC solar controllers and AC inverters should also have the following
features for control, monitoring, and protection to make pumping practical
and efficient:

• integrated MPPT which tracks the maximum power point of the modules
to provide a constant voltage to the pump, as discussed in section 2.10;
• provisions for various control inputs, such as dry-run sensors (to prevent
dry running) and level control/pressure switch (high-level/low-level
tank automation);
• capability to control the pump system and provide diagnostic indicators
to show status;
• simple system health indicators that are user visible for troubleshooting
purposes – typically pump status, pump speed, well dry, tank full,
amperage, power, voltage, temperature;
• easy to service and unit replaceable by a trained person with modest skills;
• protections for over current, under voltage, over speed, over temperature,
reverse polarity, and dry running;
• protection against overload, such as when the pump/pipe becomes
clogged with dirt (such occurrences cause an increase in the current
consumed, which could lead to motor failure);
• direct solar connection as standard and the ability to add on an optional
power backup;
• suitable for outdoor installation (IP54 and higher – sealed, weatherproof,
insect proof, rodent proof);
• designed for >10 years lifespan under harsh environmental conditions
and have a high efficiency, typically >97 per cent.

Other optional features include data logging of operating parameters

which can be recalled for reference and troubleshooting.

3.3.3 Solar modules

To generate usable power, PV cells are connected in series and parallel to produce
solar modules with varying current, voltage, and power outputs. The cells are
connected in series, grouped, laminated, and packaged between sheets of plastic
and glass, forming a PV module as shown in Figure 3.5. The number of cells in a
module depends on the application for which it is intended. Modules can have
12, 24, 36, 60 or 72 cells with the power rating of the module increasing with
the increase in number of cells. The module has a frame (usually aluminium)
that gives it rigidity and allows for ease of handling and installation. Junction
boxes, where conductor connections are made to transfer power from the
modules to loads, are found on the backs of the PV modules.
Module efficiencies have increased over the years with commercially
available modules that are 15–22 per cent efficient, and research laboratory
cells that demonstrate efficiencies above 40 per cent.

Types of solar module. There are four main types of photovoltaic module:
mono-silicon (mono-Si), poly-silicon (poly-Si), amorphous silicon (a-Si), and
thin-film (Figure 3.6).
Mono-silicon (monocrystalline, mono-Si) contains a higher purity silicon
(a single continuous crystal structure), resulting in the highest efficiency
(15–20 per cent). It is consequently the most space efficient and produces more
power for an equivalent surface area, but is also the most expensive. Mono-Si
cells are easily recognizable by an external even colouring and uniform look
with rounded edges. They have guarantees of up to 25 years.

Aluminium frame

Tempered glass

Encapsulant - EVA

Solar cells

Encapsulant - EVA

Back sheet

Junction box

Figure 3.5 Illustration of a solar module construction

Source: Trina solar

Poly-silicon (multicrystalline, poly-Si) is made from various silicon crystals

formed from an ingot and is simpler to produce and therefore slightly cheaper
than mono-Si, however it tends to have lower output efficiency (13–18 per cent).
Poly-Si cells look perfectly rectangular without rounded edges. They have
guarantees of up to 20 years.
Amorphous silicon (a-Si) lacks a geometric cell structure. Amorphous
modules do not have the ordered pattern characteristic of crystals as in the
case of crystalline silicon. Commercial modules typically have conversion
efficiencies from 5 per cent to 10 per cent. Most product guarantees are for
10 years, depending on the manufacturer.
Thin-film photovoltaic cells (TFPV) use a semiconductor such as cadmium
telluride (CdTe) or copper indium gallium selenide (CIGS or CIS) that is
applied as a thin film or layer onto a substrate (such as glass, plastic, metal,
ceramics). The modules have a solid black appearance. The thin layer allows
thin film modules to be flexible, lightweight, and portable. They are cheaper
to produce but much less space efficient, therefore needing a larger support
structure and more cabling. A monocrystalline module of equivalent area
can typically produce four times the amount of electricity produced by a
thin-film module.
The energy consumption during the production process in a-Si and
TFPV is lower than that needed for c-Si (mono-Si and poly-Si) modules. The
influence of the temperature on the output power of TFPV is also the lowest
of all PV technologies. Since 2010 some thin-film technologies (CIS, CIGS,
and CdTe) have been used in large-scale grid-connected PV systems, with
the same warranties as the c-Si modules. Smaller efficiencies (10–18 per cent)
are compensated for with a reduction in the price. The main drawbacks of
the low efficiency are the larger dimensions of the PV plant, cost of the
structure, and assembly time.
Thin-film technologies are evolving and they have enormous potential
in the future as efficiency improves and costs reduce. One thing to note is
that some thin-film modules, such as cadmium telluride, use toxic cadmium
which, if not recycled, poses an environmental concern.
The choice of which module to use usually depends on what is available
in the local market (all quality considerations taken into account), cost, and
space efficiency. The recommended modules for water pumping applications
are mono-Si and poly-Si because of their higher performance, space, and cost
efficiencies.

Module characteristics. After testing PV modules at STC (section 2.7),

manufacturers will rate the modules and label them. It is important to select
modules that are clearly labelled and permanently marked with a data plate.
The plate will contain the following information: manufacturer’s name and
physical address, type/model number, the watt-peak power rating, open-circuit
voltage, short-circuit current, voltage and current at maximum power point,
tolerance, temperature coefficient, country of manufacture, and certification

Figure 3.6 Different types of solar modules (clockwise from top left: mono-Si, poly-Si, a-Si and TFPV)

Table 3.2 Example of module characteristics

Characteristic Term Unit Value
Peak power Pmax Wp 250
Power tolerance % 0 to +5
Maximum power point current Imp A 8.23
Maximum power point voltage Vmp V 30.4
Short circuit current Isc A 8.81
Open circuit voltage Voc V 37.6
Temperature coefficient for Pmax %/°C –0.42
Temperature coefficient for Voc %/°C –0.34
Temperature coefficient for Isc %/°C 0.06
Maximum system voltage VDC 1,000
Module efficiency % 17.12
All values at STC (AM = 1.5, E = 1,000 W/m2, cell temperature = 25 °C

(e.g. UL listing, IEC 61215, ISO certification). Table 3.2 gives characteristics for
a typical 250 W module.
These characteristics are important for designing the required solar
generator size and determining the module arrangement (series and parallel),
according to the voltage, current, and power limits of the pump and controller
(see section 5.3.5 and Annex B).
The cable terminals at the back of the module must also be clearly
labelled with positive and negative markings. The terminals come with
male (positive) and female (negative) quick connectors for easy, fool-proof
interconnection.
The number of modules required to power a pumping system, together
with their arrangement in series/parallel, is based on the power requirement
of the pump and is influenced by the controller characteristics (explained
in Annex B). The modules should be arranged to provide enough current,
voltage, and power to the pump, taking into consideration the envisaged
losses discussed in Chapter 4 (cloud, dirt, degradation, temperature, etc.).
It is critical to get the series/parallel wiring correct. This is a common
problem that can lead to suboptimal pump performance or damage to
equipment. The completely wired PV generator should always be checked
against the design specification before connecting to the controller/inverter
and the pump.

Quality and performance considerations. The key criteria for checking the quality
of solar modules is the certification. Crystalline PV modules must be approved
to IEC/EN 61215 and 61730, while thin-film modules must be approved to
IEC/EN 61646, or all types must be UL 1703 certified and listed, as indicators
of quality and adherence to safety standards.
Optional standards apply depending on the actual conditions the modules
will be installed in. For example, IEC/EN 61701 is required for modules that
will be used in coastal areas; it is an indicator that the module will be able
to withstand the salty mist conditions of coastal installations.
IEC/EN 61215 involves the examination of all parameters which are
responsible for the ageing of PV modules and describes the various quali-
fication tests based on the artificial load of the materials. As the modules
cannot be tested over a period of 25 years, accelerated stress is performed
which involves radiation testing, thermal testing, and mechanical testing.
IEC 61730 Part I and II is a testing for safety qualification.
There are many brands of PV modules worldwide, some of the leading
manufacturers being Canadian Solar, Trina Solar, First Solar, Jinko Solar,
JA Solar, Sunpower, Yingli Green Energy, Sharp Solar, Renesola, Hanwha
SolarOne, Kyocera, and SolarWorld. While all these manufacturers have
their modules properly approved to the above-mentioned manufacturing
certifications the industry is competitive and dynamic. Being the largest
manufacturer does not necessarily guarantee the highest quality module
and some of the smaller manufacturers may also offer premium products.

However, a company’s proven ability to produce and sell a large number of

solar modules is testimony to its brand credibility.
In general, a good brand should have a quality manufacturing process,
a good reputation, be free of defects in the manufacturing process, and
have a replacement warranty (see more on the quality of solar modules in
section 10.6).

3.4 SPWS balance-of-system components

Balance of system (BoS) components in an SPWS refers to all the components
required for the sound installation and operation of the PV system other
than the photovoltaic modules, pump, and solar controller. As the name
suggests, it provides a ‘balance’ between the solar modules, controller,
and pump. In a PV pumping system, BoS components include disconnect
switches, PV combiners, mounting structures, enclosures, wiring to connect
different hardware components, sensors to automate or protect the system,
meters to monitor the performance and status of the system, flow meters,
and so on.

3.4.1 Module mounting structure

The module mounting structure is a critical part of any solar installation.
It holds the solar modules and provides safety and security for them. Different
structure configurations exist, namely ground mount, pole mount, roof
mount, and ground screws, as discussed in section 6.2.5.
A structure can be made of stainless steel, galvanized mild steel (with
stainless-steel hooks/bolts), or aluminium. The configuration and material to
deploy is determined by factors such as environmental conditions, system
size, area topography, land availability, and security concerns.
The mounting structure should be designed to bear the weight of the
solar array and to withstand wind loading, snow loading, storms, and/or
earthquakes as per local conditions. The footing of the structure should be
made of reinforced concrete according to the soil type, with adequate bracing
provided to prevent swaying. The structure can be designed using computer-
based software to come up with the right sizes of reinforcement, poles,
runnings, struts, and ties, in compliance with structural design standards and
local building codes.

3.4.2 DC disconnection/isolation switches

DC electricity is generated though the photovoltaic effect of solar PV modules.
If PV modules are exposed to sunlight, they will produce electricity. Large
amounts of power (voltage and current) will be present in a PV array during
daylight hours and caution should be taken when handling the PV array.
The power present in the PV array should be isolated before attempting to

work on the PV pumping system. A DC disconnection switch (also known

as a disconnect switch or isolator switch) provides for this isolation and
for subsequent isolation during future maintenance. Some DC disconnect
switches also allow for safe and professional paralleling of multiple strings
coming from the PV generator. The DC isolator switch is installed between the
PV array and the solar controller.
The DC isolation/disconnection switch should be rated for the maxi-
mum possible DC current (short-circuit current) in the system and the maximum
possible DC voltage (open-circuit voltage). It should also be double pole to
effectively isolate both negative and positive inputs from the PV array.

3.4.3 Surge protector

A surge protector (or arrestor) provides enhanced protection for the controller
from electrical surges, such as indirect lightning, current surges, and voltage
spikes. It is installed on the DC input line between the PV generator and
controller, and close to the pump controller.
Lightning arrestors can also be installed in lightning-prone areas to arrest
surges due to lightning. A surge arrestor requires a reliable ground connection
to operate, as discussed in section 6.3.

3.4.4 Cables
Electrical cables are the carriers of electrical power to the pump. They must
therefore be able to deliver enough power to the pump for both the sound
functioning and safety of the pumping system. Cable selection should be
considered both on the DC side and the AC side.
Two types of insulated multiconductor cable are used in pumping applica-
tions: submersible pump cable and underground cable (commonly referred
to as UG cable). The submersible pump cable runs from the pump up to the
surface of the borehole (wellhead) in submersible applications. It is designed
to safely carry electrical loads under water as long as it is sized properly.
UG cable, on the other hand, is used between the wellhead and the pump
controller. Typically, UG cable is armoured and can be buried in the ground.
If it is not armoured it should be run in an electrical conduit. Submersible
pump cable can still be used between the wellhead and the controller so long
as it is run in an electrical conduit.
A pump cable will usually have the following parts, as shown in Figure 3.7:

• Conductors – these are the copper wires that conduct the electricity.
• Insulation – this is the plastic or rubber material covering the copper
conductors to keep the conductors from shorting between themselves
or to ground.
• Jacket – this is a rubber or PVC material covering the insulated conductors,
protecting them from abrasion.

Cable jacket
Cable jacket

Wire insulation
Wire insulation

Stripped wire
Stripped wire

Figure 3.7 Parts of a cable

Source: Wikipedia <https://creativecommons.org/licenses/by-sa/3.0/deed.en>

The correct cross-sectional dimension (or thickness) of the cable is critical

for sound operation and long life of the pumping system. Voltage drop or
loss occurs when too much current passes through a very small (undersized)
conductor. Voltage loss can be reduced by using thicker wires (lower resistance
conductors), reducing wire length, and/or increasing voltage (often not
practical) (see also section 2.9).
The maximum allowable voltage drop between the source and the load should
be 1–3 per cent of the source voltage. For DC power this refers to the maximum
power point (MPP) of the string. A suitable cable cross-section should be
selected to ensure the voltage loss does not exceed the permissible drop. A cable
of insufficient cross-section will convert the current flow into heat, leading to
overheating which could cause a fire or progressive failure of the system.
In summary, when selecting electrical cable consider:

• suitability of the cable to the environment (e.g UV strength, ambient

temperature, water temperature). All exposed cables should be approved
for outdoor use or installed in an electrical conduit;
• suitability of the cable to the application (water-resistant cables for
submerged installations, armoured cables for surface installation);
• current carrying capacity of the cable. This is dictated by the cable size
or cross-sectional area of the cable;
• allowable voltage drops across the cable. Voltage drop increases with
smaller cable thickness and longer cable lengths. Excessively long cables
should be avoided where possible to minimize the risk of voltage drop;
• characteristics of the load (voltage and current).

A guide on how to select a suitable cable size is provided in Annex D.

3.4.5 Sine-wave filter

As the external controller/inverter adjusts the incoming voltage for AC
motors, their sine wave is altered and in turn taxes the motor lifetime and

increases noise. Sine-wave filters have a high degree of filtering and are used for
reducing the voltage stress on the motor windings and the stress on the motor
insulation system as well as for decreasing acoustic noise from a frequency-
controlled motor. Motor losses are reduced since a sine-wave filter converts
the output pulses of the frequency converter into a sine-wave shape. The result
is a sine-wave-shaped current and reduced motor noise. The sine-wave filter is
installed between the inverter and the pump.
In addition to peak voltage effects, total motor cable length should
be considered in the context of instantaneous current peaks, which can
cause stress on the motor. Filters may be used to extend the maximum cable
length according to the technical specifications of the particular inverter
type. For example, Grundfos sine-wave filters extend the maximum cable
length to 300 m.

3.4.6 Other components

Combiner box. This can be used to wire incoming strings in parallel or to

combine two or more PV disconnect switches in parallel.

Dry-run sensor. Dry-run protection is mandatory for any pumping installation.

For submersible pumps this is provided in the form of a well probe that is
connected to the low-level sensor input of the controller. For a surface pump
it comes in the form of a low-level float switch or a water sensor. The purpose
of dry-run protection is to stop the pump in the event of low or no water in
the source. It prevents dry running which can lead to pump failure.
Float switch. This is a mechanical device used for automation of the pumping
system to a tank. It works by stopping the pump when the tank is full and
restarting it when the tank water level drops to a pre-set level (see more in
section 7.2).

Pressure switch/sensor. This is installed on the delivery pipe to automate

delivery to the tank where long delivery pipes are involved and a float switch
cannot be used. It works by sensing the pressure build-up of water in the pipe
and switching the pump on and off according to the pre-set cut-in and cut-out
system pressure. It is installed together with a ball valve at the tank (see more
in section 7.2).

Irradiation sensor. Some equipment manufacturers, such as Lorentz, provide

this sensor to cut off the pump when the sun irradiation drops below a pre-set
level. It plays the important role of avoiding pump idling where the pump
runs without delivering any flow, as this would cause the pump to wear out
due to lack of internal lubrication and will eventually cause failure.

Water meter. Installed on the delivery pipe to measure and display the water
flow output from the pump, the water meter is sized according to the pump
flow and the delivery pipe size.

PV generator Irradiation PV Controller Float switch

sensor disconnect
module

Water meter
Pressure sensor
Grounding rod Surge protector
Safety rope
Submersible pump

Splicing kit
Well probe
Level sensor
Figure 3.8 The components of a solar water pumping system

Splicing kit. The connection between the motor tail cable and the submersible
drop cable must be made watertight as it can be the weakest point on
the pumping system. The splicing kit needs to be appropriate for the cable
size and should be done by an experienced technician.

Chlorine doser. These are used to inject appropriate amounts of chlorine into
the delivery line to sanitize the water (see more in section 7.1).

Advanced controls. Some brands of inverter (e.g. Lorentz) feature advanced

controls for digital remote/contactless monitoring of certain parameters that
can be collected for long-term monitoring such as:

• water flowrate/output, through the connection of a pulse cable from the

water meter to the digital input of the controller;
• water level, through the installation of a liquid level sensor in the well to
determine the actual level of water in the well at any given time;
• liquid pressure, through installation of a liquid pressure sensor in the
pipe to measure pressure relative to the atmosphere.

Figure 3.8 is an example of a solar water pumping system showing balance

of system components.

3.5 SPWS equipment manufacturers

Solar-powered pumps, controllers, inverters, and accessories are available
from various suppliers globally. As discussed in Chapter 10, regard should be
given to high-quality products supplied by certified suppliers/manufacturers.

Suppliers/manufacturers should be asked to provide certifications that

demonstrate the quality and safety of the equipment. Some manufacturers of
solar pumping equipment are:

• Lorentz – German technology with a factory in China. Reliable and

high-quality range of solar pumps and inverters from 0.15 kW to 75 kW
of pump motor power (www.lorentz.de);
• Grundfos – Danish company with multiple manufacturing locations
around the world. Has a reliable solar pumping range of up to 37 kW
pump motor power (www.grundfos.com);
• Well Pumps – Belgian company with solar range up to 110 kW
(https://wellpumps.eu/en/homepage);
• Solartech –inverters of up to 150 kW manufactured in China and
distributed through regional suppliers, such as Davis & Shirtliff
Ltd (https://www.davisandshirtliff.com) and Solargen Technologies
(https://solargentechnologies.com) in Africa;
• ABB – drives for solar pumps with a range of 0.37 kW to 45 kW (https://new.
abb.com/drives/low-voltage-ac/machinery/ABB-solar-pump-drives);
• Franklin – solar pumps and drives from 0.55 kW to 37 kW (https://solar.
franklin-electric.com/products/high-efficiency/6-inch-high-efficiency-
solar-system/)
• Fuji – solar drives (https://www.fujielectric-europe.com/en/drives_
automation/products/solutions/frenic_ace_for_solar_pumping).

3.6 Importance of quality considerations in SPWSs

Solar pumping technology is a robust and reliable technology that can
provide many years of reliable water supply. Evidence (UNICEF, 2016;
GLOSWI, 2016) shows that where failure (non-functionality or breakdown)
of SPWSs has occurred, it is mainly because of pipe and pump-related issues,
such as motor failure, broken pipes, pipe bursts, or wiring – issues that are also
present with traditional grid or diesel-powered pumping systems and which
can be averted at the design and procurement stage. This is only possible if
the following conditions are met. First, the design is based on accurate and
reliable data, matching the right equipment to the water source.
Second, high-quality components with genuine certifications should be
selected. During the design stage the proposed equipment should be fully
specified in terms of material of construction, protection rating, and cable
insulation gauge so it matches the operating conditions. The quality of SPWSs
is discussed in Chapter 10.
Third, careful attention should be given to the entire implementation
process, including selection of the intake point in the river, the borehole
siting, full borehole development, the casing of the borehole, the dimensions
of the equipment, and the operating conditions of the equipment, such as
water temperature, ambient temperature, and snow.

Figure 3.9 Worn-out conduit due to high temperatures in Iraq

The selection of good BoS components is as important as the selection of

pump, controller, and PV modules. Low-quality BoS components are often
responsible for many avoidable maintenance problems for SPWSs in camps
and remote villages which can lead to premature failure and non-functionality
of the whole system. The goal of any SPWS design is to match its operational
life to that of the PV modules, that is, a minimum of 25 years. BoS components
should therefore be selected with a long operational life in mind.
Figure 3.9 shows what can happen to a piece of equipment poorly matched
to its operating environment. Even the smallest piece of equipment (such as
a cable gland or conduit), if the wrong size, of poor quality, and not matched
to the operating conditions, can be damaged, leading to premature failure and
disuse of the system.

Copyright practicalactionpublishing.com
CHAPTER 4
Energy losses in solar photovoltaic
energy production
The amount of electricity produced by solar panels and therefore the amount of water
pumped, changes during the day and over the year depending on a number of factors.
Some of the factors that induce energy losses in the system can sometimes be minimized
by designers (e.g. shadows on the solar modules), while others are due to the context
and the components used (e.g. losses in cables) and can only be taken into account
when sizing a solar pumping scheme. The origin and effect of each of these factors are
explained in this chapter, together with the calculation of the performance ratio of a
solar pumping scheme as the overall indicator of the efficiency of the system.

Keywords: cell temperature losses, soiling, module shadowing, solar

mismatching, angular and spectral reflectance, solar performance ratio.

4.1 Calculating energy losses

In standard test conditions (STC), the energy generated by a PV module can
be determined by the product of its power rating multiplied by the time
of exposure to sunlight. However, in real field conditions there will always
be energy losses that PV modules and the wider solar PV pumping system
will experience that need to be factored in. Understanding these losses and
how to minimize them will be of paramount importance in ensuring that
solar pumping systems provide the expected amount of water.
For any type of PV system, the energy generated (Egenerated), or energy
available for consumption (e.g. to power water pumps), can be estimated by
the following expression:
Egenerated Ppk PS
PSHHP
PR
R

where

• Ppk is the peak power of the PV field, obtained as the product of the
PV module’s power rating and the number of modules used in the
construction of the PV field (e.g. 10 modules of rated power at 300 Wp
will have a peak power of 300 × 10 = 3,000 Wp);
• PSH (or peak sun hours) is equal to the equivalent number of hours per
day when solar irradiance averages 1,000 W/m2;
• PR (or performance ratio) is defined as the ratio between the generated
energy and the theoretical energy that would be generated by the PV
field if the modules converted the irradiation received into useful energy
according to their rated peak power.

http://dx.doi.org/10.3362/9781780447810.004
Copyright practicalactionpublishing.com
50 SOLAR PUMPING FOR WATER SUPPLY

In other words, PR express the reduction of solar energy generation due to

different losses in the system including: in the PV modules, due to high PV
module cell temperature, low irradiance efficiency reduction, power converter
efficiency, power converter downtime, wiring, shading, and soiling, among
others. The energy loss factors in a PV system are diverse and sometimes
difficult to quantify.
Losses can be classified according to what they are related to:

• sun irradiance: soiling (dust and dirt on PV modules), shading, light

incident angle, air pollution, orientation and tilt, snow, and others;
• PV module: cell temperature, power tolerance, low irradiance efficiency,
mismatch, module quality, light-induced degradation, ageing and
other degradation factors, and module mounting conditions are the
main ones;
• power conversion and balance of system: voltage drops in the wiring,
power inverter efficiency, errors in tracking the maximum power
point, protections, downtime periods for maintenance, breakdowns or
malfunctions, and power curtailment are the main ones.

Most of these loss factors are estimated for the usual conditions found in
PV systems, being corrected and refined as new developments appear in the
market and experimental results are published worldwide. Others, like the
losses in the wiring or due to the PV module temperature, are estimated by
formulas, taking into account technical characteristics of the components and
specific conditions where the PV plant is located.
The closer the PR of a PV system is to 1, the more efficient the PV system
is and, therefore, fewer PV modules will be needed to meet the required water
needs. In order to estimate the PR of the system, estimates of the losses due
to each of the factors mentioned above are needed. In a well-designed and
mounted PV system, typical losses are as estimated in Table 4.1.

Table 4.1 Table of estimated losses as a percentage of total energy produced

Losses due to Estimated losses Losses due to Estimated losses
(as % of total (as % of total
energy produced) energy produced)
Module temperature 8–15% Tolerance 0–5%
Wiring 1–3% Mismatching1 1–2%
Soiling2 (dust, dirt on modules) 2–15% Low irradiance 1–4%
Shading3 0–2% Light-induced 3–20%
degradation
Reflectance 2–6% Power converter 1–5%
Module orientation 0–2% Availability 1–3%
1
Can be much higher if PV modules of different power ratings are connected
2
Can be much higher in dusty environments if modules are not cleaned regularly
3
Can be higher if modules are regularly shadowed

While different solar design software packages take into account some
or most of the losses explained in this chapter, it will be of paramount
importance that designers and field practitioners understand the different
factors that affect the efficiency of a solar PV pumping system so they can
act on them.
The following sections describe the most common loss factors, starting
with the losses that can be calculated with precision through mathe-
matical formulas: losses due to temperature and losses in the wiring.
Recommendations to minimize losses whenever possible are given at the
end of each section.

4.2 Cell temperature energy losses

The peak power of the PV modules is rated at STC, with PV cell temperature
at 25 °C. However, in real field conditions, PV cells (or modules) easily reach
temperatures over 25 °C when exposed to sunlight. The hotter a PV module
gets, the less voltage is produced and therefore power output is also reduced.
The more the PV module temperature exceeds 25 °C, the higher the losses due
to temperature.
As can be seen in Figure 4.1, the difference between the PV module
and ambient temperature can reach 20 °C during the central hours of the
day, and even higher depending on the PV module characteristics and
location.
Figure 4.2 shows the irradiance (in W/m2, in the right axis) and the PV cell
efficiency (in per cent, in the left axis). There can be seen a small decrease
in the cell efficiency at midday due to the high level of irradiance, which
produces an increase in the cell temperature and therefore more losses.
The low efficiency at the beginning and end of the day is related to the
optical losses and the low irradiance efficiency, detailed in section 4.5.4.
The power losses due to a module temperature different from the standard
test conditions (25 °C in STC) depend on the cell type and encapsulation,
wind, and the type of installation carried out. They are quantified by the
term (Ltemp). Using the temperature coefficient (g in 1/ °C or 1/K) given by
the manufacturer for each PV module and the PV cell temperature (Tcell), Ltemp
can be approximately determined by the following expression:
Ltemp g(
g (Tcell 25)

The value of g determines the dependence of the PV output power with

Tcell. Due to negative sign of g, the output power of the PV module decreases
as the Tcell increases. The cell temperature can be estimated for a known
ambient temperature (Tamb) and for a known sun irradiance (E, measured in
W/m2 with an irradiance meter) using the following expression:

E
Tcell Tam
ambb ( NOCT
NOCT 2 )
800

0:00:00
0:45:00
1:30:00
2:15:00
3:00:00
3:45:00
4:30:00
5:15:00
6:00:00
Source: Polytechnic University of Valence, Spain

6:45:00
7:30:00
8:15:00
9:00:00
9:45:00
c-Si ambient temp.

10:30:00
11:15:00
12:00:00
12:45:00

Figure 4.1 Temperature difference for a c-Si plant with a fixed-tilt angle of 30° in Valencia, Spain
13:30:00
14:15:00
15:00:00
15:45:00
16:30:00
17:15:00

c-Si module temp.

18:00:00
18:45:00
19:30:00
20:15:00
21:00:00
21:45:00
22:30:00
23:15:00
SOLAR PUMPING FOR WATER SUPPLY 52
14.00% 1000
900
12.00%

8.00% 600
500
6.00% c-Si efficiency 400
4.00% Irradian ce (W/m2) 300
200
2.00%
100
0.00% 0

7:00:00
7:35:00
8:10:00
8:45:00
9:20:00
9:55:00
10:30:00
11:05:00
11:40:00
12:15:00
12:50:00
13:25:00
14:00:00
14:35:00
15:10:00
15:45:00
16:20:00
16:55:00
17:30:00
18:05:00
18:40:00
19:15:00
19:50:00
20:25:00
21:00:00

Figure 4.2 Effect of sun irradiance in efficiency of c-Si PV modules

Source: Polytechnic University of Valence, Spain
ENERGY LOSSES IN SOLAR PHOTOVOLTAIC ENERGY PRODUCTION
53
54 SOLAR PUMPING FOR WATER SUPPLY

Table 4.2 NOCT, g, and efficiency factors for different PV module technologies
Technology c-Si (silicon-based Thin-film CISG HIT
modules) technology
s-Si p-Si a-Si/µc-Si CdTe CIS
(monocry- (polycry- (amorphus (cadmium (copper
stalline stalline silicon) telluride) indium
silicon) silicon) selenide)
NOTC (°C) 41 (±3) 41 (±3) 45 45 47 42 44
g (%/K) −0.37 −0.38 −0.35 −0.32 −0.33 −0.3 −0.26
Module efficiency (%) 20.4 17.6 9.8 10.6 15.1 16 20.3

Manufacturers of PV modules state in their data sheets the nominal operating

temperature of a cell (NOTC), which is defined as the temperature that is reached
by photovoltaic cells when the module is subjected to an irradiance of 800 W/m2
with a spectral distribution AM of 1.5 G, ambient temperature of 20 °C, and a
wind speed of 1 m/s. Some typical values for the NOTC and g are detailed in
Table 4.2 for some commercial PV modules with different PV technologies.

Application note

Considering a monocrystalline c-Si module with g = −0.45%/K and NOTC = 45 °C on a

summer day with a maximum ambient temperature equal to 20 °C and E = 1,000 W/m2,
the estimated Tcell is equal to:
1000
Tcell 23 ( 45 20 ) 54.25 C
800
And the corresponding Ltemp value is equal to:
Ltemp g (Tcell 25) 0.45 % k (54.25 25) 13.16%
The measurement of the ambient temperature should be carried out with a thermometer,
in the shade, in an area close to the photovoltaic modules.

Due to the variations of the temperature and irradiance during the day
and through the year for the specific PV system location, the value of Ltemp is
commonly calculated with the average daytime temperature of the period under
study. Most solar design software from the most popular pump manufacturers
will estimate this loss by considering ambient temperature data for every month
of the year, making the estimation closer to reality. Annual Ltemp losses between
8 per cent and 15 per cent are common for monocrystalline c-Si modules,
depending on the temperature characteristics of the PV system location.

4.3 Wiring energy losses

PV systems convert sunlight into electrical energy that flows as electric
current through wires that have an electric potential between terminals.
As explained in section 2.9, the flow of a current (I) through a wire produces

Box 4.1 Minimizing losses due to temperature

Installations done in places with good wind levels can have less Ltemp losses due to the
better cooling of the PV modules. Similarly, installing spacers to allow some 15–20 mm
of space between PV modules (see photo below) will allow better air circulation, cooling
down the PV plant. In roof-mounted PV modules, allowing separation of 10 cm between
PV modules and the roof would allow air flow and reduce thermal losses.

Figure 4.3 Spacers between modules to increase cooling

a voltage drop (∆Vwire) between the wire terminals due to the resistance of
the wire (Rwire).
Voltage drop is the reduction in electrical current that occurs as electricity
travels through wires. The international standard recommends that voltage
drop in the wires connecting solar arrays and pumps not exceed 3 per cent,
but it is acceptable to exceed this slightly in order to site the array in a
secure location.
This voltage drop causes a power loss (∆Pwire) along all the wire that overheats
the conductor. Losses due to wiring are represented by the term Lwires, where
Lwires =
∆Pwire ÷ Ppk
with Ppk being the peak power of the PV field.

The power loss in a wire is calculated as the product of the current and the
voltage drop:
∆Pwire =
∆Vwire I

Wiring losses in PV systems are classified as:

• DC wiring losses, due to cables used to connect the DC components

of the system – modules, combiner boxes, DC protections, monitoring
systems, DC pumps, etc.;
• AC wiring losses, due to cables used to connect the AC components of
the system – output circuit of inverters, AC pumps, protections, etc.

Wiring losses (for copper cables) are calculated with the following expression:
lwire 2 1 lwire 2
∆Pwire = Rwire ⋅ I 2 = ρ ⋅ ⋅I = ⋅ ⋅I
Swire γ Swire
Where lwire is the total wire length in metres (equal to twice the length
of the cable for DC cables), Swire is the wire cross-section in mm2, ρ is the
resistivity of the conductor in Ω mm2/m and γ is the conductivity of the
cooper in m/Ω mm2. The value of ρ (or γ) must be calculated for the operating
temperature of the wire. As an initial recommendation, a wire temperature
of 40 °C must be considered for any conductor in a PV system due to the
overheating produced by the power loss in the wire. Wires exposed to
sunlight will reach greater temperatures which, in some cases, can be near
90 °C (the maximum temperature supported by wires can get to 120 °C for
some wire types). Table 4.3 gives the values of the cooper resistivity and
conductivity for several wire temperatures.
The typical average value for Lwires is in the range of 1 to 3 per cent,
depending on the national codes and regulations applicable to each
country. Most solar design software from the most popular pump manufac-
turers will factor in this loss in their proposed designs.

4.4 Sun irradiance energy losses

Sun irradiance is defined as the solar power incident on a surface. There are
several sources of losses related to sun irradiance reaching the PV surface: dirt
and dust on the modules (also referred to as soiling); near or far shadows;
orientation and tilt of the PV module’s surface; level of air pollution in the

Table 4.3 Variation of resistivity and conductivity with temperature

Temperature 20 °C 40 °C 50 °C 60 °C 70 °C 80 °C 90 °C
Resistivity 0.01786 0.01926 0.01996 0.02066 0.02136 0.02206 0.02276
(Ω mm2/m)
Conductivity 55.9910 51.9205 50.0994 48.4017 46.8153 45.3295 43.9352
(m/Ω mm2)

Box 4.2 Minimizing wiring losses

To minimize Lwires it is important that, as far as possible, the cables supporting the
highest current are the shortest possible in length; placing the PV modules as close as
possible to the water pump will ensure that. Due to the large variations in the technical
conditions of each pumping installation it is not possible to determine whether it is
best to minimize the length of the cable on the DC side (PV modules to controller) or
on the AC side (inverter to pump, in case the pump is AC). The use of a spreadsheet
to evaluate the different options will allow a decision in each case as to which one
provides the least total losses in wiring. However, minimizing the length of the cables
on both sides of the inverter, by placing the inverter and the PV modules as close to
the water pump as possible, will bring down power losses due to wiring. In addition,
protecting the cables from direct sun exposure will reduce their resistivity and therefore
the wiring losses.

surroundings of the PV installation; light incident angle; and weather charac-

teristics of the location (snow, atmospheric humidity, rain).
Specific weather conditions of the region where the PV plant is installed
can produce a reduction of the irradiance reaching the PV surface. Some
of these factors can have a seasonal pattern, so the effects vary throughout
the year:
• The presence of snow in winter months will cause the PV system to
disconnect until the modules are cleared or the snow disappears.
The presence of the snow is related to days with low availability of sun
hours, so the impact on energy production is minimal. These losses are
included in the availability losses (Lavailability) together with other terms
that are described later.
• Rain over PV installations can naturally clean the PV modules, reducing
losses due to soiling. At the same time, in cities and industrial regions,
the air pollution will be reduced, so more direct radiation will reach
the PV modules. In regions near deserts, rain is scarce and may be
accompanied by dust, which will lead to increased soiling losses.
• The existence of a high level of humidity in the atmosphere can cause
fog and clouds, reducing the irradiance that reaches the PV surface.
Sun radiation will contain a greater diffuse part and PV plant yield
will be smaller. Condensation of humidity in the first hours of the
day can affect the dust deposited on the module and increase the
soiling losses.

4.4.1 Soiling (dust and dirt)

Losses due to dirt, bird droppings, dust or sand accumulation on the
modules (see Figure 4.4) are included in the soiling loss factor (Lsoiling).
Typical values for Lsoiling are in the range of 2 to 15 per cent but can reach up
to 80 per cent or more in deserts or dusty locations if PV modules are not
cleaned regularly enough.

Figure 4.4 Sand on PV modules limiting power output

Figure 4.5 Shading of PV modules limiting power output

New developments in the glass surface of PV modules are aimed at reducing

the accumulation of dust. A similar effect is obtained with an increase of
the tilt angle, so that there is less accumulation of sand on the PV modules,
where the better Lsoiling compensates the losses due to a non-optimized tilt
(see more on tilt angle in section 5.3).

Box 4.3 Minimizing losses due to soiling

It is important to ensure regular cleaning of PV modules (clean water and cloth, no soap
needed) by the community of users or an external party (from several times per week to
once a month, depending on level of dust and rainfall frequency) as otherwise excessive
dust/dirt on modules might significantly reduce water output or even bring it to zero.

4.4.2 Shading
Losses due to shading are represented by the term Lshading (Figure 4.5). Several
areas of shading are present in PV installations:

• shading between rows of modules;

• shading due to nearby obstructions, such as vegetation, bushes, trees,
buildings, poles, railings, antennas, signals, power lines, or overhead wiring;
• shading due to obstructions on the far horizon, such as mountains
or buildings.

If enough space is available, inter-row spacing will be calculated to avoid

PV modules casting shadow on others at any moment of the year. If space does
not allow, specifications would detail the number of hours of sunlight in the
PV plant, free of shadow in winter solstice around noon.
Nearby shading should be avoided as much as possible, since electrical
production of PV modules is non-linear, so a small shadow can produce a
large power loss in the system.
Obstructions on the far horizon produce shadow mainly during sunrise
and sunset, when irradiance levels are lower. Losses can be elevated in deep
valleys between high mountains.
The analysis of shading effects on PV modules is complex due to the
non-linear behaviour of PV modules. The impact of shading on PV arrays can
be evaluated by representing the obstructions on a sun position chart for the
latitude of the PV installation location. The reduction in the number of peak
sun hours due to shadow is calculated comparing the shadowed area with the
area of the complete solar window. There are some software programs and
devices that can provide a derating shading factor, simplifying the shading

Box 4.4 Minimizing losses due to shading

The structure supporting the PV modules must be elevated over the terrain in ground-
mounted PV installations if vegetation and bushes grow quickly. Other common elements
in buildings (poles, cables, antennas, etc.) should be installed on the north side of
the building, so that the PV modules can be installed facing south (in the northern
hemisphere), free of shadow. Including the absence of inter-row shading as a condition in
the contract with the installer will help to minimize such events. Involving the community
of users (or third parties) for regular clearing of the area around the PV plant (e.g. trimming
of nearby trees) and ensuring no future construction overshadows the PV modules will
decrease the likelihood of losses due to shading.

losses evaluation. In a first approximation Lshading= 0 per cent unless a shadow

study is carried out for the particular conditions of the installation.

4.4.3 Angular and spectral reflectance

Electrical characteristics of PV modules are obtained by the manufacturer
during a flash test with a light perpendicular to the PV module surface.
Yet the sun moves from east to west due to the rotation of the Earth and,
therefore, in fixed-tilt PV systems, the light incident angle on the PV module
varies throughout the day. The difference between the reflectance of a PV
module under real operating conditions and the reflectance in the flash test
is quantified by the term Lref or losses due to angular and spectral reflectance
(also denoted as optical losses).
Advancements in the front glass are aimed at increasing light transmission
using a thinner glass, improving surfaces to reduce dust accumulation, and
reducing light reflection with anti-reflective glass coatings. Similar advances
are being applied at the PV cell level, with new PV cell surfaces and new anti-
reflective coatings intended to reduce optical losses by catching the maximum
amount of solar radiation.
Typical values for Lref are in the range of 2 to 6 per cent in fixed-tilt
crystalline PV modules, depending on the quality of the materials used in the
construction of the PV module.
The irradiance incident on the PV surface is reduced when the air is
polluted. Air pollution is mainly produced by human activity and can reach
significant levels in the proximity of urban and industrialized locations.
Polluted air can contain fine solid particles, liquid droplets, and gases. These
substances reduce the total solar radiation reaching the PV modules due to
part of the direct solar radiation being diffused or reflected. These losses are
highly dependent on the particular characteristics of each location and there
are no typical values to quantify them.

4.4.4 Incorrect azimuth orientation and tilt angles of PV modules

Losses due to an incorrect orientation (Lori) or tilt angle (Ltilt) of the PV plant are
related to the energy yield that can be obtained with the optimum PV azimuth
orientation and tilt angle that generates the maximum energy (see more on
tilt and azimuth orientation angles in section 5.3)
In general, the two loss factors are calculated together with the following
expression:

PS orii ttilt
PSH
Loriittilt 1
PS optimum
PSH

The term PSHoptimum corresponds to the irradiation for the orientation and
tilt angle that maximizes the energy produced in a period and PSHori+tilt is the

irradiation for the orientation and tilt angle of the PV array. Lori+tilt is commonly
calculated on a yearly basis and is highly dependent on the particular charac-
teristics of each PV installation (see example in Annex C). Losses due to tilt
angle not being the optimum value or azimuth orientation (deviation from
south) are usually non-existent in most
installations as it is simple to find out Box 4.5 Minimizing losses due to incorrect
azimuth and tilt angle
the best angles for a given location.
As an approximation, for every 1 degree Define clearly in the tendering,
bidding, and/or installation specifi-
off the optimum tilt angle, the losses
cation documents the azimuth and
will be of around 0.1 per cent. Most tilt angle that is desired. When PV
design software from reputed manufac- modules are being installed, check in
turers will take into consideration the the field with the help of a compass
losses due to non-optimal azimuth since this is commonly the moment
when most errors are made.
orientation and tilt angles.

4.5 PV module energy losses

There are several energy loss factors related to the PV module. The cell
temperature during the normal operation of the PV plant is the most important
one, as explained in section 4.2. Other factors are: power tolerance, mismatching,
ageing and light-induced degradation, and low irradiance efficiency.

4.5.1 Power tolerance

PV module manufacturers guarantee the module’s peak power at STC within
a given tolerance range. Not reaching peak power is related to the power
tolerance detailed in the PV module datasheet and is influenced by the
quality of the module (and the manufacturing process). The power tolerance
of commercial PV modules varies greatly depending on the manufacturer:
0 per cent to +3 per cent; −3 per cent to +5 per cent; ±3 per cent; ±5 per cent;
etc. The power loss due to power tolerance (Ltolerance) corresponds to the
minimum tolerance detailed in the datasheet and determines the possible
loss of energy yield of the PV installation in the worst case scenario.

4.5.2 Mismatching
The values of IMPP and VMPP (section 2.10) may vary slightly from one PV module
to another, even when they are the same model of PV module. The connection
of modules with a lower IMPP will reduce the peak power of the PV field, since
the IMPP in a string of modules connected in series will be equal to the lowest
IMPP of any individual module in the string.
Mismatch losses (Lmismatching) appear due to differences in the parameters of
the modules used in the installation. For losses due to mismatching, a value of
2 per cent is used in the design of PV installations that use crystalline modules.
Manufacturers of thin-film photovoltaic modules claim that their technologies

have fewer mismatch losses, with values that are close to zero. This value can
vary substantially depending on the quality of the modules used in the PV
installation, so it is important to connect in series those modules with very
similar characteristics.
A bigger problem appears when PV modules of different manufacturers
or different power ratings are mounted in the same PV plant (for example,
when a contractor has run out of stock of PV modules in the middle of an
installation and brings other models in, or when a PV module is broken
in an existing installation and it is not possible to find the same model in
the market). This situation, especially when a new PV module with lower IMPP
and VMPP is mounted in a PV plant with modules that have larger IMPP and VMPP
values, is to be avoided at all costs as it might affect the entire PV plant output
and considerably reduce energy production and water output.
Finally, differences in cable length or cross-section among parallel strings
can introduce differences in voltage drop and therefore contribute to an
increase in mismatching losses.

Box 4.6 Minimizing mismatching losses

All PV modules must be from the same manufacturer and be of the same type and
model when constructing PV fields. When some modules break down and need to be
replaced by new modules the strings should be reorganized using the same model of
modules in as many strings as is possible, adding the new modules to complete the
incomplete strings.
The new modules must be of the same PV technology (whether mono-Si or poly-Si),
must have the same number of cells, and must have an IMPP and VMPP of the same value or
greater than the modules they are replacing.
In addition, cable of the same length and cross-section should be used as much as is
possible to connect strings in parallel.

4.5.3 Ageing and light-induced degradation

Ageing is one of the common names given to the long-term losses caused by the
PV modules being exposed to light, also known as light-induced degradation
(LID). It is important to distinguish between the long-term degradation of PV
modules and the initial stabilization that appears after the beginning of light
exposure. Initial stabilization reduces the PV module efficiency in values in
the range of −2 to −4 per cent in the first weeks of operation. The maximum
losses for long-term light-induced degradation, denoted as LLID, are limited by
the power warranty given by the manufacturer, which can be considered as a
conservative estimate for LLID.
In Figure 4.6, the initial stabilization of the PV cell entails a 3 per cent
decrease and the maximum annual degradation rate is equal to 0.68 per cent
during the 25 year lifespan. It is important to note that the most common
solar pumping design software does not consider losses due to ageing and
degradation over time of PV modules.

100%
Guaranteed power

97% Additio
nal va
lue fro
m Trin
90% a Sola
r ’s line
ar war
ranty
80%

Years 5 10 15 20 25
Trina linear warranty Standard step warranty

Figure 4.6 Example of warranty given by Trina Solar for Tallmax monocrystalline modules

Box 4.7 Minimizing ageing losses

When designing the PV installation, the power output from the PV plant at the end of the
design period can be estimated taking ageing into account (e.g. looking at the manufac-
turer’s PV warrantied power output graph). The PV field can now be oversized to ensure
the required power output will be available at the end of the design period despite ageing.
Care should be taken not to go beyond the maximum voltage input of the inverter when
oversizing the PV field.

4.5.4 Low irradiance efficiency

The low irradiance efficiency loss depends on the technology and characteristics
of the PV module and the irradiance level. Some manufacturers of thin-film
modules state that their technologies have a better low-light performance
than crystalline modules, producing more power at the nominal values at
STC. Locations with fog or overcast skies have an increased portion of diffuse
light reaching the PV module surface. Some crystalline module manufacturers
establish in their datasheets a 4.5 per cent reduction in the module efficiency
for irradiance equal to 200 W/m2.

4.6 Module mounting energy losses

In addition to the above-mentioned losses, the mounting of the PV modules,
whether in portrait or landscape orientation, influences energy loss.
Further to the inter-row shading losses explained in section 4.4.2, when
a shadow occurs on a PV module, the shadowed cells will start dissipating
the power generated by non-shadowed cells, getting hot to the point that the
whole PV module may malfunction. In order to avoid the appearance of
these hot spots, when PV module shadowing occurs, the bypass diodes in the
junction boxes at the back of each PV module will act as a switch, discon-
necting the shadowed cells from the rest of the PV module.
Usually one bypass diode protects a group of 18, 20, or 24 PV cells, which
are short-circuited and do not contribute to the generation of energy. PV
modules mounted in landscape configuration will typically experience less

Activation of
1 diode bypass
Activation of by partial
2 diodes shading
bypass by
partial
shading

Figure 4.7 Bypass diode activation in shadowed PV modules

inter-row shading losses than modules installed in portrait configuration due

to the internal connection of the bypass diodes, meaning that only one, rather
than two, diodes will activate, as shown in Figure 4.7.
Thin-film modules respond differently to shading. The difference in PV cell
construction means that losses due to shading will be proportional to the
area shadowed, no matter whether in portrait or landscape orientation.

4.7 Power converters and the balance-of-system energy losses

Balance of system, or BoS, describes all the components of the system other
than the PV modules, power converters (DC/DC control boxes or DC/AC
inverters), and water pumps. The BoS includes wiring, electrical safety
elements, auxiliary equipment and sensors, the supporting structure, and
mounting hardware. The most significant loss factors related to power
conversion and BoS elements are:
• wiring (explained in section 4.3);
• energy efficiency of the electronic power converters;
• errors in tracking the MPP;
• PV plant downtime for maintenance, breakdowns, or malfunctions;
• transformers (for grid-connected systems);
• other losses, such as those due to safety elements and auxiliary
equipment.

Several power converters can be used in PV systems: grid-connected

inverters, off-grid inverters, DC/DC or DC/AC converters, and so on. The main
losses related to power converters are MPP tracking losses, represented by
LMPPT, and losses in the conversion, represented as Lconv.
Some power converters are needed in order to establish the PV operating
point in the MPP of the PV field. The MPP tracking algorithm allows the
generation of the maximum power (and energy) from the PV field, optimizing
the overall performance of the system. Nowadays the losses due to MPP
tracking (LMPPT) are very small, less than 0.1 per cent.

During the operation of the power converters some losses appear in the
semiconductors that switch high voltages and currents. The efficiency in the
conversion (ηconv) varies with the characteristics of the pump connected to
the output and the input power source. Depending on the power converter
type, manufacturers can provide the efficiency profile of the converter.
The losses in the conversion, represented as Lconv, are calculated as:
Lconv= (1 − ηconv )

Typical values of Lconv vary in the range of 1 to 5 per cent.

In addition, there are sometimes intervals in which the PV plant is not
generating energy due to a failure in some part of the system: inverter discon-
nection, operation and maintenance (O&M) works on the PV plant, problems
in the grid connection (grid availability and disruption of grid-connected
systems), inverter or pump failure, and so on.
The typical availability losses (Lavailability) related to grid functionality in grid-
connected systems in developed countries are in the range of 1 to 3 per cent.
This can get much higher for areas where the grid is unstable or where
specialized technical assistance is needed but not immediately available.

Box 4.8 Minimizing losses due to availability

The functionality of the PV pumping scheme and expected maximum downtime and repair
times should be stated in an O&M contract. O&M services could be an integral part of the
installation contract with the private contractor selected for the works, and would detail
the time to respond to the different failures that can appear in a PV system. See more on
O&M services in section 11.2.

In some PV–grid hybrid systems it is necessary to use a transformer to

adjust the levels of the AC voltages between the inverter and the electrical
grid. Losses in the transformers (Ltransf) vary depending on the quality of the
materials used in the construction of the transformer, with typical values
between 1 and 5 per cent, or even greater than 7 per cent in poor-quality
transformers.
These days, due to the falling prices of PV modules and the need for
pumped water in times of low sun irradiance, it is common to oversize the PV
plant. In these cases, when the sun irradiance levels are high, the PV plant is
able to produce more energy than the pump requires to work at 100 per cent
of its capability. The power converter will only ‘take’ the energy needed by the
pump, and the rest is not used or ‘wasted’; that is called a curtailment of power
generation. The curtailment of the power generation reduces the performance
ratio of the installation, since the PR is calculated against the peak power of
the PV field.
Different electrical devices are commonly used in PV installations for the
protection of the installation (safety elements) or for the electrical connection:
string fuses, array over-current protective devices, automatic circuit breakers,

switches, and others. Losses due to these parts are difficult to calculate and are
not usually considered in the estimation of the energy generated by a photo-
voltaic system.

4.8 Estimation of the energy yield

The estimation of the production of a PV system is carried out using the
performance ratio of the installation using the following expression:
Egenerated Ppk PS
PSHHP
PR
R

The estimated value of PSH can be obtained using the PVGIS calculation
tools available at the European Commission’s Photovoltaic Geographical
Information System1 or other websites. The PR of an installation takes into
account all the power losses that can be determined for the PV system, such as
the factors described in the previous sections, calculated as:

(1 − Ltem ) × (1 − Lwires ) × (1 − Lsoiling ) × (1 − Lshading ) × (1 − Lref ) × (1 − Lori ) 

 
 (1 − Ltilt ) × (1 − Ltolerance ) × (1 − Lmismatching ) × (1 − LLID ) × (1 − LMPPT )
PR =× 
 
× (1 − L ) × (1 − L ) × ( 1 − L ) 
 conv availability trans 
A plant with a high PR converts solar radiation more efficiently into
electrical energy. PR is usually expressed as a percentage and presents seasonal
variations according to environmental conditions through the year. In addition,
a degradation factor of −0.5 per cent/year (approx.) must be taken into account
over the lifetime of the installation. The PR of PV systems depends strongly
on the type of installation and the components used in it.
The PR in a well-designed off-grid PV system is in the range of 0.5 to 0.75
a value closest to 1 is preferable (excluding energy losses in the water pump).
Equating the Egenerated with the Erequired by the pump to operate for a defined
number of hours (P1 of pump motor x no. of pump working hours, see example
in Annex B), it will be possible to get the required Ppk of the solar PV scheme.
Conversely, the PR can be calculated in real PV installations if the other
terms of the expression are known:
Egenerated
PR =
Ppk ⋅ PSH
Monitoring systems included in PV installations allow the measurement
and recording of the energy generated and the irradiance. PSH is calculated
from the irradiance values. The PR allows the comparison of PV plants over a
given time independent of PV plant peak power or solar resource. A high PR is
representative of a well-built and well-functioning installation.

Note
1. https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html

Copyright practicalactionpublishing.com
CHAPTER 5
Design of a solar-powered water scheme
The high variability of factors influencing water output in solar-powered schemes
makes it difficult to optimize sizing when solar design software is not used.
Solar software developed by different manufacturers is increasingly popular and
available. Yet the clarity of the data required beforehand and good design criteria
are key to coming up with an efficient design. These are explained in detail in this
chapter together with the different secondary energy options whenever a design
leads to hybrid configurations.

Keywords: solar design software, module orientation, solar pumping layout,

parallel and series configuration, solar design month, solar tracking

5.1 Solar pump design

As explained in previous chapters, there are numerous factors that
influence the production of electricity through solar modules, and
therefore the water output in a solar pumping scheme. Most of those
factors are variable with the time of day and season, making it complicated
and imprecise to proceed to design a solar pumping scheme using manual
calculations.
Numerous software packages that will facilitate this process are
available (e.g. Grundfos, Lorentz, Wellpumps), computing all factors for
the chosen components and geographical locations, and proposing designs
including solar module layout and power, cable sizes, inverter or control
box models, pumps, and balance-of-system components. Software-based
solutions will also match performance and electrical characteristics of
the components, to ensure expected electrical and water outputs as much
as possible.
Whether a field technician decides to come up with the design or
commissions a private contractor, the authors of this book believe the
design should always be carried out through a reputable software design
package.
However, no matter how good and user-friendly the software is, it is
always of paramount importance to understand what data are needed for
the design, and how different choices will affect the system performance.
Most of the steps involved and data needed to design a solar water pumping
scheme are common with those needed to design a generator-powered water
scheme. A summary of the data required is given in Table 5.1.

http://dx.doi.org/10.3362/9781780447810.005
Copyright practicalactionpublishing.com
68 SOLAR PUMPING FOR WATER SUPPLY

Table 5.1 Data needed to design a solar-powered water scheme

Data Comments
GPS location (degrees) of water source Precision of seconds or more than one
decimal is not needed
Maximum daily water requirements (m3/day) Bear in mind that demand may grow over
the design period of the water scheme and
the seasonality of water needs
Safe yield of water source (m3/hour) To be determined after pumping test (or
pumping yield to match if retrofitting an
existing system)
Expected maximum drawdown (m) Determined from nearby water sources
(seasonal drawdown) and/or hydrogeological
reports
Static and dynamic water levels (m) Determined from pumping test
Inside casing borehole diameter (inches) From borehole drilling report
Depth of pump installation (m) Needed to calculate losses in pump to
inverter cable
Distance from water source to solar Typically, this should be no more than a few
modules (m) metres from the water source
Distance from water source to tank (m) From topographical assessment
Elevation difference between water source From topographical assessment
outlet and tank inlet (m)
Space available for solar modules (m2) Field visit to the area
Pipe type from pump to tank (metal, plastic) Also pipe size if already existing
A list of equipment characteristics (in Generator size, water pumping yield, pump
addition to the above) in case of solarizing type and model, motor power rating, cable
an existing water scheme wire size, pump depth installation, pipe
materials and size, size of tank

5.2 Important design concepts and considerations

In designing a solar pumping system, there are several important concepts to
take into consideration.
• Design is based on water pumped per day as opposed to water pumped
per hour. Unlike traditional pumping, which is possible 24 hours a
day, with solar pumping there is a limited number of hours in a day
available for pumping, a period typically called the solar day. With
this concept, the total water requirement for the whole day is factored
in and a pumping system that will meet that requirement during the
solar day is selected.
• Batteries to store energy are to be avoided. Batteries introduce inefficiencies
(power losses), are expensive (increased system costs), heavy (difficult
delivery), have a relatively short life (replacement costs), and introduce
complexity, such as how to dispose of them at the end of their life

cycle. Instead of storing energy in batteries, it is recommended to store

water in elevated tanks (which is another form of storing energy),
making water available when needed and keeping the system simple
and efficient.
• The tank storage capacity must be factored in. The size of the storage tank
should be determined by the daily demand and should be large enough
to store as much water as possible during daylight hours. In areas that
have significant seasonal variations in solar radiation (due to weather)
the tank would be larger than in areas where there is less variation
(see more in section 5.3.8).
• Solar tracking is discouraged. Due to the cost of tracking systems, their
operation and maintenance requirements, and plummeting PV module
prices, solar tracking is not considered especially useful. It is more
common and easier to oversize a fixed PV generator to cater for losses
due to orientation of the PV array relative to the sun than to incur
the cost of more complex PV tracking (see more on tracking in sections
5.3.5 and 7.3).

5.3 Steps to design a solar-powered water scheme

In order to obtain the required data, a number of steps need to be taken to
ascertain whether a stand-alone solar system can meet the required water
demand from the selected water source or a hybrid (solar + one or more
additional power sources) is needed. These steps are:

1. Water-demand assessment and design period.

2. Water-source assessment, borehole construction, and pumping test.
3. Design month and flowrate.
4. Calculation of total dynamic head and pump selection.
5. Solar PV array sizing, layout, inverter and module selection, and
orientation of solar panels.
6. Location of main components.
7. Size and location of water storage tank.
8. System layout: stand-alone solar vs hybrid systems.
9. Balance-of-system minimum requirements.

5.3.1 Water-demand assessment and design period

As for any other water-scheme design process (not specifically solar), the
water demand of the target population must be estimated. In order to do
so, a project design period will need to be established. This is the period of
time in which the solar system must provide the amount of water set as the
target. Water demand typically grows over time as population and other needs
(e.g. irrigation, livestock) increase.
Ideally the system will be designed to meet water demand in any given
month of the design period. The longer the selected design period is, the

higher the water requirement to be met typically will be and therefore the
more oversized (compared to the current situation) and the more expensive
the whole water-scheme system will be. In practical terms, the length of
the design period will mostly depend on the budget available and will be a
question of investment priority.
The typical lifetime of quality components can serve as an additional
reference and these are given in Table 5.2:

Table 5.2 Expected lifetime of solar components

Component Expected lifetime (years)
Borehole 20–25
Pump 5–10
Inverter/control box 5–7
Solar module 25
Civil infrastructure (water tower, module supports) 20–25
Water tank – cement 15–20
Water tank – plastic 5–10

Since it is difficult to know how the water demand, population, and other
factors will grow and influence the system, it is often argued that it is impractical
to have very long design periods (over 20 years), which might be especially true
for humanitarian operations where donors have short funding periods, funding
is often restricted, and where contexts are volatile and might dramatically change
over the years. It also has to be taken into account that a design period of 10 or
15 years will not mean that the water system will stop working after that time.
In light of the expected component lifetimes, a resizing of the system may
be possible every 5 to 10 years, when the pump and inverter will typically
need to be changed and could be replaced by larger models if necessary (since
it will normally be possible to add more modules and increase water storage).
Therefore, design periods longer than 5–10 years may be difficult to justify in
humanitarian contexts.

5.3.2 Water-source assessment, borehole construction, and pumping test

While both surface and submersible pumps can be solarized, this chapter
will largely consider groundwater since it is more widely used due to wider
availability and better quality of water. Surface sources (rivers, ponds, lakes)
can also be exploited through solar pumping technology and the application
principles explained in this chapter remain the same.
Before installing any water pumping scheme, an understanding of the water
resource is needed; for groundwater aquifers, it will be the work of hydroge-
ologists to rigorously assess groundwater availability, storage and recharge of
the aquifer as well as water quality. This will be particularly relevant in areas

where an increasing number of boreholes are drilled, in order to ensure a

sustainable use of the resource.
Once borehole siting and drilling (or rehabilitation of an existing one)
is done (for more detail, see ICRC, 2010), a test pumping is carried out to
determine the unique characteristics of the water source, including the tested
yield and the dynamic water level that are critical for properly designing a
pump to match the borehole. Test pumping includes a 4-hour step-down
test followed by a constant rate test for 24–72 hours. The point at which the
rate of pumping out of the borehole remains constant even with continued
pumping is recorded as the tested yield. This is also the point at which the
water level in the borehole does not change and is recorded as the dynamic
water level (also known as pumping water level).
The safe yield is the maximum amount of water that can be safely extracted
from the borehole without compromising its integrity. It is a percentage
of the tested yield of the borehole and is a value between 60 and 70 per cent
of the tested yield.
Many aspects affect the safe yield of a borehole, namely:

• borehole siting and groundwater exploration (the ‘natural’ geological/

hydrogeological conditions);
• borehole construction and development (the ‘human-made’ conditions
acting on the hydraulic behaviour of the well);
• drilling and pump test (see more at MOAIWD, 2012) supervision and
documentation (which act on the resulting ‘safe yield’ interpretation).

In the absence of clear, detailed documentation of borehole characteristics

and pumping test results, the design and equipping of a pumping scheme
should not be done as there is a high chance of over or underestimating yields,
leading to malfunction, over-pumping,
the borehole drying up, and a number Assessment of the water point, including
of other problems. This is a critical pumping test results, must be carried
mistake that is often encountered in out before any design takes place.
field humanitarian projects.
In these cases, measures should be taken to find out the main characteristics
of the borehole, including carrying out a pumping test for which a contractor
might be hired.
In the case of retrofitting an existing water scheme to solar, assessment
of the borehole and its characteristics and safe yield (following the above-
mentioned studies and tests, especially pumping tests in case of doubt) must
be done before proceeding to any solar design or installation.
Finally, it should be kept in mind the date at which studies and tests
are carried out and how seasonality may affect the water-source level (e.g.
through monitoring water levels in other boreholes situated in the same
aquifer). For example, in some areas of the Middle East, drawdown during
a dry season might be over 100 metres; not taking this into consideration at
the time of designing a pumping scheme might lead to undersized equipment

being installed and other problems, resulting in the required water not being
provided during part of the year.

5.3.3 Design month and flowrate

In solar pumping schemes, and since solar irradiation will vary over the course
of the year, it is necessary to define a design month (the month taken as a
reference to size the system).
Typically, the design month when the water is for human consumption
will be the one with the lowest ratio between solar irradiation at a predeter-
mined tilt angle (see more about tilt angles in section 5.3.5) and water needs,
also called the worst month. The principle behind taking the worst month
as a reference point in designing the solar pumping scheme is that if it is
possible to provide the water required in that month, then it is ensured that
the solar system will be able to provide the required water during any other
month of the year.
In order to identify the worst month for a particular location and water
scheme, two situations are possible: 1) that daily water required is constant
during the year; or 2) that the water required changes from month to month.
When the water required is constant throughout the year, the month
with the lowest PSH/water required ratio will always be that with the lowest
solar irradiation (lowest number of peak sun hours). In the example given in
Table 5.3, it is the month of July.
In the example of variable requirements given in Table 5.4, more water is
needed during the dry season (water use per person is typically higher, there

Table 5.3 Example of worst-month calculation where constant water required: Yumbe, Uganda
(3N, 31E)
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Peak sun 6.8 6.8 6.0 5.4 5.0 4.5 4.2 4.6 5.4 5.5 5.9 6.5
hours (PSH)
Water required 120 120 120 120 120 120 120 120 120 120 120 120
(m3/d)
PSH/water .057 .057 .050 .045 .042 .038 .035 .038 .045 .046 .049 .054
required

Table 5.4 Example of worst-month calculation where variable water required: Yumbe,
Uganda (3N, 31E)
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Peak sun hours 6.8 6.8 6.0 5.4 5.0 4.5 4.2 4.6 5.4 5.5 5.9 6.5
Water required 154 165 140 120 110 105 98 110 120 120 130 155
(m3/d)
PSH/water .044 .041 .043 .045 .045 .043 .043 .042 .045 .046 .045 .042
required

might be irrigation schemes connected). Therefore, the worst month (the

lowest ratio of solar irradiation to water required) is February.
Most of the design software available will allow the introduction of design
month or give an option to proceed with the design considering the worst
month as the design month.
Once the design month is known, the required pumping rate can be
roughly estimated by dividing the water required by the PSH.
For example, in the case presented in Table 5.3 this is 120/4.2 = 28.5 m3/h.
If the safe yield of our well is higher than 28.5 m3/h, then it will be possible to
provide all the water required during the whole year with a stand-alone solar
pumping scheme, and this could be the selected layout.
Other considerations beyond the technical may factor in selecting
stand-alone or hybrid configuration, as discussed in section 5.3.8.
Even if safe yield is below 28.5 m3/hr, for most parts within the sun belt
(the area between latitudes 40 °N to 40 °S) it will be possible to pump water
between 6 and 9 hours per day by oversizing the solar PV array (design software
can provide this precise information). This would mean that for our example
of constant requirements, if the safe yield is between 13 m3/hr (120/9) and
20 m3/hr (120/6), it is still possible to provide the water required for the worst
month (depending on solar irradiation at the geographical location) and
hence for all the other months and, therefore, the selected layout could still
be a stand-alone solar system. For safe yields under 13 m3/h, another power
source (grid, generator) would be needed (or a second borehole drilled) in
order to meet the required water needs.

5.3.4 Calculation of total dynamic head and pump selection

Calculation of total dynamic head (TDH) and subsequent pump selection is a
step that can be done independent of the power source to be selected and is
essentially no different than if the pump is powered with a diesel generator.
Once the desired hourly pumping flow has been defined and the TDH of
the system calculated, H-Q curves for different pumps will be reviewed in order
to find a suitable one (numerous pump manufacturers’ catalogues are found
online with H-Q graphs for all their pumps). Care should be taken to select a
pump with a nominal flow for the given TDH that is close to the desired flow.
A step-by-step example of this process can be found in Annex A.
Whenever field conditions and requirements to be met allow, the choice of
a DC pump over an AC pump is recommended for solar stand-alone pumping
schemes. While DC pumps will generally be a bit more costly than their
equivalent AC ones, they have a longer lifespan, they are more efficient (so
fewer PV modules are needed to power them), and they don’t need DC/AC
electricity conversion, making their control box a cheaper accessory than DC/
AC inverters.
When selecting a pump, ensure that the nominal flow of the pump is close
to the required design flow. If a greatly oversized pump is selected, while it

will still supply the water required, it will also need a greater PV generator and
inverter increasing the total cost of the system. Moreover, pumps working at
a small fraction of their capacity will have their lifespan shortened and will
also compromise the life of the borehole, therefore increasing the capital and
replacement costs of the system.
Most solar pumping design software will size the pump and offer different
solutions even when TDH has not been computed, by providing other field data
(e.g. dynamic water level, tank elevation, and pipe material to be used).

5.3.5 Solar PV array sizing, layout, inverter and module selection,

and orientation of solar panels

Solar PV array sizing. Once the pump has been selected it will be possible to
estimate how much energy needs to be generated to power it.
Section 4.1 showed that for any type of PV pumping system the
energy generated by the PV generator can be estimated by the following
expression:
Egenerated =Ppk × PSH × PR

Section 4.8 showed that the energy required by the pump (Epump = P1 × hours
of operation of the pump) can be equated to Egenerated to get the required Ppk of
the solar PV scheme
E pump =Egenerated = Ppk × PSH × PR =P1 × hours of operation of the pump

Once the power of the pump (and hence the energy requirements), the PSH
in the location, and an estimated PR are known, it will be possible to calculate
the Ppk (peak power of the solar array) and therefore the minimum number of
PV modules needed (considering the models available in the local market).
An example is given in Annex B.
The higher the power rating of modules, the fewer will be needed. Silicon
crystalline modules of up to 500 Wp can be found on the market and power
ratings are constantly growing.

Solar PV array layout and inverter selection. Once the number of modules is
known it will be important to define the configuration; (deciding how many
are to be mounted in series and how many in parallel) so that not only the
power, but also the voltage, and current provided by the solar array are right
for the inverter and pump.
When PV modules of same model and ratings are mounted in series,
voltage adds up and current remains the same, and vice versa when mounted
in parallel.
PV modules are connected in series (connecting the positive terminal of the
first to the negative terminal of the second module and so on, as shown in
Figure 5.1) to generate greater voltage. A series connection increases voltage
but the current remains unchanged. In other words, the output voltage, Vmp

of a series connection is the sum of each individual module voltage in that

connection, while the output current is that of a single module.

Figure 5.1 Series connection

Referring to the module characteristics given in Table 3.2 where

=Pmax =
250 W , Vmp 30.4 V , and I mp = 8.23A

Power =
250 × 6 modules =1,500 W, Voltage =
30.4 × 6 modules
= 182.4= V, and Current 8.23 A
PV modules are connected in parallel to generate greater current. A parallel
connection means connecting all the positive terminals together and all the
negative terminals together, as shown in Figure 5.2. A parallel connection
increases current, but the voltage remains unchanged. In other words, the
output current of a parallel connection is the sum of each individual module
current in that connection, while voltage is that of a single module.

Figure 5.2 Parallel connection

Power =
250 × 6 modules = 1,500 W, Voltage =30.4 V,
Current = 8.23 × 6 modules = 49.38 A
Parallel and series connections can be combined to increase both the voltage
and the current according to what is required by the pumping system.

Figure 5.3 Combination of series and parallel connections

Power = 250 × 12 modules = 3,000 W, Voltage = 30.4 × 6 modules

= 182.4 V, Current = 8.23 × 2 strings = 16.46 A
Note that the power output of the connection is the sum of the power
of each individual module in the connection regardless of whether the
connection is in series or in parallel.
These calculations are only valid if all the modules have the same voltage
and the same current. If the panels in series do not have the same current, the
array will be limited to the lowest current value of the individual modules.
Likewise, if the modules in parallel do not have the same voltage, the array
will be limited by the lowest voltage value of the individual panels.
Parallel connections increase the current in the system, hence requiring
thicker cables to carry the current (refer to sections 2.9 and 3.4.4).
Deciding how many modules are mounted in series and in parallel will be
of paramount importance since it is not only the total power of the PV array

Example 5.1

Eighteen PV modules with characteristics as given in Table 3.2 have been interconnected
to operate a water pumping system. The array consists of six modules in series and three
strings in parallel (6s × 3p). The PV array will have the following parameters:
I mp= 8.23 × 3= 24.69 A, Vmp= 30.4 × 6= 182.4 V, Ppeak= 250 × 18= 4,500 Wp

maximum array current ( I sc =

) 8.81 × 3= 26.43 A
maximum array voltage (Voc =
) 37.6 × 6= 225.6 V
These values correspond to the electrical characteristics under standard test conditions –
AM 1.5, irradiance = 1.0 kW/m2 – and the operating temperature (T) of each module is
25 °C. In the real world, array output is expected to drop, as discussed in section 2.7 and
Chapter 4.

N number of strings Strings cables

(connected in
parallel)

M number of modules per string

(connected in series)

(Main DC cable)

Figure 5.4 Module array layout

that matters, but also the voltage and current that the pump will get from the
PV modules. A poor layout may mean that the pump will give less water (or
none at all in extreme cases).
The controller/inverter to be used influences the series/parallel configu-
ration. The selection of an appropriate controller/inverter is based on the
pump selected and the PV generator size. The controller/inverter should be
able to handle the incoming DC power from the PV generator and condition
it to that which is required by the pump.
A manually calculated example can be found in Annex B. Fortunately, the
recommended layout of the PV generator (number of modules to be connected
in series and parallel) for a predefined PV module and the appropriate
inverter size are provided by most reputable solar design softwares on the
market (including Lorentz and Grundfos), ensuring optimum configuration
and matching of PV module electrical characteristics for the given pump and
water needs.

Solar PV module selection. There are several kinds of solar modules that could
be incorporated in a solar water pumping design (see more in section 3.3.3).
As long as the brand of the module meets the required quality certifications
(see section 10.6), the module can be considered fit for purpose. Having
PV modules with quality manufacturing certifications should always be the
first aspect to consider and those without certifications should not progress
through the procurement process.
In the great majority of cases, mono or polycrystalline modules will be used
for the solar generator as they account for around 95 per cent of the market
and are available in nearly all national markets around the world. Choosing
one or the other will be a question of space for installation, price, and stock
availability. In cases where ambient temperatures are high, modules with a
lower temperature coefficient will have fewer losses and are preferred (see
more in sections 4.2 and 7.8.1), so monocrystalline will behave slightly better
in hot climates.
For average temperatures maintained over 40 °C, amorphous silicon
modules can also be considered; these will take up to three times more space

because their efficiency is significantly lower, but the losses due to heat are
also considerably lower than mono or polycrystalline modules.
Some design software (e.g. Wellpumps, Grundfos, Lorentz) allows users to
manually introduce the characteristics of any module and would generate a
design using that particular module.
Other considerations at the design stage are the mounting of the solar
modules (ground, on poles, on rooftops). The advantages and disadvantages,
and consideration of orientation and inclination of modules are given in the
next subsection and in section 6.2.5.
If for any reason, the ideal orientation and inclination of modules cannot
be ensured (e.g. modules are mounted on the roof of an existing building
and therefore mounting angles are predetermined by the roof), oversizing the
solar array may be necessary. Some design softwares (e.g. Lorentz) allow for
inserting different tilt and orientation angles and will propose different solar
generators depending on those.
Modules could be given another orientation if the designer decides that
is a better option for a particular site. For example, if more water is needed
during the mornings the designer might opt to orient the modules more
towards the east, knowing that in the afternoon water output will be reduced.
The more modules oriented to the east, the more water will be pumped
during the morning.

Orientation of solar panels. Available PSH will vary (be higher or lower)
depending on how the PV module is oriented with respect to the sun. The sun’s
path in the sky changes over the year; during summer, when days are longer,
the sun’s path is higher in the sky, while in winter, with shorter days, the sun’s
path is lower in the sky, as illustrated in Figure 5.5.
The sun’s position in the sky with respect to the earth’s surface is defined by
three angles: azimuth angle, zenith angle, and elevation angle.
The azimuth defines the daily movement of the sun from east to west
and is the angle on the horizontal plane between the projection of the
beam radiation and the north–south direction line. The elevation angle
defines the north–south trajectory of the sun through the seasons and is
measured in degrees from the horizon of the projection of the radiation
beam to the position of the sun. The zenith angle is the angle of the sun
relative to a line perpendicular to the earth’s surface. These angles are
represented in Figure 5.5.
Maximum energy of the sun will be obtained on a PV module oriented
at right angles with the sun (see Figure 5.6). This can only be achieved if
the module’s mounting structure follows the movement of the sun, that
is, it tracks the sun. Sun trackers follow the daily and seasonal sun path
to maximize the energy yield. Trackers can follow a single axis (seasonal
changes) or two/dual axes (daily and seasonal). Trackers are rarely used for
solar water pumping, as their absence is easily compensated for by oversizing

Sun

Zenith angle

West North
Solar panel

Elevation Tilt angle

angle

South Y East
Azimuth
angle

Figure 5.5 Sun’s position in the sky with respect to the earth’s surface

the solar PV array to account for losses due to non-optimal tilt (see Annex C
for an example). Their use is discouraged as they also introduce additional
complexity, involve extra costs and need specilized regular maintanence
(mechanical tracking).
When trackers are not used the PV generator is mounted on a fixed
structure at a fixed azimuth and tilt angle aligned so that the PV generator
is at right angles to the sun. The PV array tilt angle represents the angle the
array surface makes with the horizontal plane/earth. The PV array azimuth
angle represents the angle between true north and the direction the array
faces. With fixed structures the maximum energy – as a yearly average – is
generated when the PV array tilt is equal to the latitude of the location

Application note

As a general rule for water pumping, the configuration that will yield the highest amount
of energy and therefore the highest amount of water – as a yearly average – is the one
where PV arrays are tilted to an angle equal to the latitude of the location where it is being
installed (with a tolerance of +/–50, which won’t have a significant impact). It is also
common practice to allow for a minimum tilt angle of 15° in locations of lower latitudes to
allow for self-cleaning of the modules when it rains.
With regard to azimuth angle, the modules should be inclined to face towards the
equator; in the northern hemisphere, modules should be inclined to face south, and in the
southern hemisphere, modules should incline to face north.

PV
m
od
ul
e
or
ar
le ra
y
ng
Tilt A

Horizontal (Ground level)

Figure 5.6 Effect of tilt on solar energy capture

where the PV array is located, and the azimuth angle is oriented so that the
PV array faces the equator.
Since the height of the sun in the sky changes during the year (lower in
winter, higher in summer) the tilt angle can be chosen so that maximum
energy production is guaranteed in the critical season (for example,
a flatter tilt to maximize water pumping in the summer when needs might
be higher).

5.3.6 Location of main components

While the location of the pump will follow the same principles as in generator-
powered systems (see section 6.2.2) and BoS component locations will be
given by their function (e.g. dry-run sensors will be located in the borehole

Figure 5.7 PV modules in Sheikhan, Iraq, facing south at 36 ° tilt

just above the pump), the location of other system parts are often up to the
designer to choose.

Location of solar PV modules. PV modules should be located as close as

possible to the water pump (typically a few metres away from the borehole
in a submersible system) in order to minimize cable losses. In all cases,
they should be easily accessible for cleaning (see Figure 5.7). Modules should
generally be situated in a secure and safe location as they are typically the
component that is most prone to theft or vandalism.

Location of the inverter/control box. For the same reason as above, the controller
should be placed as close as possible to the modules and the pump, though
not in the sun as higher temperatures will lower their efficiency. Typically,
it will be placed beneath modules or in a building a few metres away in order
to keep it in the shade.

Location of the water tank. Locating the water tank close to the water point
will minimize the number of PV modules needed to power the pump
because the total dynamic head in the pumping side of the water scheme
will be lower. However, this might imply the construction of a higher
water tank tower if taps are located far from the water point, and vice versa
if the water tank tower is far from the water point but close to the taps.
A design for the same water point with the water tank located near or far
from the water point could easily be run with any solar design software
to appreciate the difference. Cost implications and ease of operation and
maintenance of the system should be taken into account by the designer
to decide the location.

Figure 5.8 Inverter box located under modules in Somali Region, Ethiopia

5.3.7 Size of water storage tank

The capacity of water storage for a solar pumping system depends on daily
water use, demand, and daily and seasonal variations of solar radiation.
The storage capacity should be designed to ensure water system adequacy,
reliability, and compatibility with existing and future demand.
Traditionally, the size of a water tank is calculated according to the largest
difference between accumulated hourly supply and demand for the month
when this difference is the largest. For generator or grid-connected systems,
as water can be pumped at any time (supposing grid and/or fuel supply is
reliable), the volume of the water tank tends to be minimized, accounting
typically for 0.5 to 1 times the daily water supply.
In solar-powered systems, however, since the time of pumping is limited
to certain hours during the day, larger water tanks are normally needed.
The largest amount of water pumped will normally occur during the central
hours of a solar day, when radiation is highest, but during that time, water
demand is commonly lower.
A larger water tank will store all the water pumped during the central
part of the day so it is available when water demand is higher than supply,
usually in the early morning and late afternoon. An even larger tank would
help to cater for deficiency in the normal expected values for solar radiation
(e.g. with longer than expected cloudy periods), adding extra security to
the system.
Field survey data indicates that many SPWS storage tanks are too small,
leading to water tank overflows, wasting water in the daytime and leaving
shortages in the evening.

Table 5.5 Quick guidance for water tank capacity

Water scheme type Water reservoir capacity
Generator/grid powered 0.5–1 × daily water requirement
Hybrid (solar + generator/grid) 0.5–3 × daily water requirement
Stand-alone solar 1–3 × daily water requirement

A tank that is too small may also force the operator to stop the solar
pumping system during the afternoon, when the highest amounts of water
could be pumped.
In a hybrid (solar plus generator) system, if more water pumped from the
solar source can be stored, the generator will be needed for less pumping.
In practical terms, investing in larger tanks for hybrid systems is considered
cost-efficient as capital costs are quickly recovered by shorter generator
operating times and hence lower fuel consumption.
There is no clear formula to arrive at the water tank volume for a solar
water system and an engineer will have to decide based on a compromise
between present and future water demand and supply, physical space, and
budget available as well as practical aspects concerning the operation of
the water scheme (e.g. absence of other water points in the area, criticality of
the system, and water collection patterns).
As an indication and in the absence of previous experience or data from
similar projects, the values given in Table 5.5 could be considered.
From field experience, a tank more than three times the volume of the daily
water requirement is normally considered impractical, mainly for reasons of
budget, physical space, and/or the adverse effects of keeping chlorinated water
stored for longer than three days.
Sometimes the number of consecutive no-sun days at a particular location,
data that can be retrieved from solar databases such as NASA’s, is taken as a
reference to size water tanks. The largest number of consecutive no-sun days
during the year is then taken as the water tank volume needed to cater for that
worst case scenario. Since most of the time, even in countries and locations
with high solar radiation, the number of consecutive no-sun days is higher
than three (and in many cases between 4 and 6), the authors consider this
impractical and difficult to justify, especially in the context of humanitarian
operations.

5.3.8 System layout: stand-alone solar vs hybrid systems

As explained in section 5.3.3, whenever the safe yield of the water source
is higher than the required yield to meet the daily water needs in the least
favourable (worst) month of the year by simply pumping during the solar day,
then the system layout could be a stand-alone solar system. This layout is the
most cost-effective, easy to operate and maintain.

If, on the other hand, the selected water pumping rate needed to meet
the water needs by just pumping during the solar day is higher than the safe
yield of the water source, a stand-alone solar system won’t be able to meet the
demand. In this case, there are three actions that can be taken:

1. Reassess the water needs and the design period of the scheme; consider
the possibility of including water-saving measures (e.g. drip irrigation)
and evaluate the criticality of not meeting the required water quantity
together with the community of users.
2. Have a hybrid system by including a second energy source in the water
scheme (e.g. diesel generator, grid if existent) which can complement
pumping beyond the solar day or for the cloudier months or days when
solar pumping cannot meet needs (see Annex A for generator selection
process). This can also be the case if extra security is needed to ensure
daily provision water a second energy source is introduced as a back-up.
3. Evaluate the use of a second water source (e.g. drilling another borehole)
that could complement the water supply. This option is especially
advisable if a second energy source cannot be introduced or it is too
complex or costly (e.g. in some places introducing a diesel generator
may not be feasible if the community cannot pay for diesel, or diesel has
to be transported from long distances).
The different pumping technologies that could be used with solar for a
hybrid system are briefly discussed below.

Solar and diesel generator. This is a common layout in humanitarian operations

(see Figure 5.9), especially for high-yielding boreholes or critical ones. The
installation of a diesel generator will not only provide the opportunity to
increase pumping whenever needed, but it also makes the system more robust
if the solar parts or generator develop technical problems.
In locations with highly marked seasonality, the solar PV array needed to
meet water demand in the cloudiest months of the year will have to be greatly
oversized. For those locations, sometimes the installation of a generator is
chosen instead. However, the way to optimize cost-efficiency in the design of
a hybrid solar–generator scheme is to reduce fuel consumption by minimizing
hours of generator run time. This will reduce fuel costs as well as maintenance
costs for the generator.
Furthermore, since the cost of solar modules has decreased considerably
over the last few years, it is technically and economically justified to design
a system for 100 per cent operation from the photovoltaic array and use the
generator only during certain weeks of the year where cloudy periods and bad
weather are more prominent.
The final recommendation should be made based on system optimization
and detailed economic analysis together with users’ preferences.

Solar and grid. Grid-connected solar systems are an optimal solution for hybrid
configuration. Moreover, in some locations this configuration may offer the

Figure 5.9 Hybrid solar-generator scheme at Adjumani refugee settlement in Uganda

Source: Oxfam, 2016

possibility to sell back to the grid the excess solar power generated, using the
solar array as a cash crop that may result in higher financial sustainability of
the whole system.
In many places where relief projects are carried out however, the grid is
either non-existent or unstable, leading to strong voltage variations that could
damage equipment or power cuts that could suddenly leave users with no
access to water. Unless water can be supplied to communities in alternative
ways whenever the grid is not functional or stable, the hybrid solar–grid
option should be carefully considered.

Solar and wind power. Apart from the high unpredictability of wind power,
wind technology requires specialized knowledge and spare parts with regular
maintenance which are hard to find and sustain in many places where relief
operations take place. Although this technology came to be highly popular at
one time, these days it is less and less utilized for water pumping purposes,
with its use in relief operations found to be marginal.

Solar and handpump. When borehole size allows, small solar pumps can be
installed together with handpumps (both in the same borehole, one below the
other). This solution saves users the burden of hand pumping and still offers
the possibility to get water if the solar technology develops problems or water
is needed beyond the solar day.
Care should be taken to know the safe yield of the borehole as solar pumps
will typically end up extracting more water than handpumps.

5.3.9 Balance-of-system minimum requirements

The balance of system is explained in section 3.4, which details the
components any solar pumping system should incorporate. Other BoS
components are optional and will depend on the degree of security,
monitoring, and control over the system that the designer wants the user
to have.

Copyright practicalactionpublishing.com
CHAPTER 6
Electrical and mechanical installation
of solar-powered water systems
The use of quality components is essential to get the expected water outputs.
This chapter identifies the different electrical and mechanical parts of a solar
pumping scheme and their correct installation sequence. In addition, it describes
the basic electrical protection measures required to ensure safety of the water
scheme and operators. Finally, a set of quality control measures together with the
different options for solar module mounting are discussed.

Keywords: solar installation checklist, module mounting, solar pole

mounting, Lightning Protection, Surge Protection, cable splicing, dry run
protection

6.1 Pumping system installation

Quality equipment will be supplied in original manufacturer packaging
and the cartons well labelled with brand names and models. The packaging
should be checked for damage and to ensure it contains all the contents
as ordered.
As a standard, the equipment must have a nameplate which can be counter-
checked against what was ordered (see Figure 6.1). The nameplates will contain
all the important data such as equipment model and power rating. A packing
list comes in handy for verifying delivery of all the required equipment.
As discussed in Chapter 10, it is important to vet equipment suppliers.
Nameplates and barcodes can be forged and if suppliers are not vetted to
ensure they represent and supply genuine manufacturer products there is a
risk of buying counterfeit equipment.
It is mandatory that before commencing the installation all supplied
components be inspected to ensure they do not have any obvious damage
(damage can occur in transit) and that they correspond to the design
parameters. Mistakes can occur when suppliers are loading the goods in their
warehouses, for example, dispatching the wrong inverter, and if not checked
beforehand this could lead to avoidable accidents, including equipment
failure, which is expensive in both time and money.
Even quality components can fail if they are not correctly installed and
maintained. The installation should only be carried out by qualified and trained
personnel following all the basic safety precautions, ensuring a safe and profes-
sional installation. The corresponding equipment operation and installation

http://dx.doi.org/10.3362/9781780447810.006
Copyright practicalactionpublishing.com
88 SOLAR PUMPING FOR WATER SUPPLY

Figure 6.1 Sample nameplates for (left) PV module, and (right) solar controller
Source: Davis & Shirtliff Ltd

manual should be used. These will usually be supplied by the manufacturer

together with the equipment. The instructions and recommendations in the
manual should be followed strictly to avoid unnecessary mistakes that could
lead to failure. Even experienced technicians who have undertaken similar
installations before should be keen
An installation checklist developed for to read the instructions provided as
water technicians to monitor instal- manufacturers will often update their
lation by private-sector contractors can products, incorporating new instruc-
be found in Annex J. tions in the manual that experienced
technicians are not aware of.
Reputable manufacturers provide a warranty for the equipment but this
warranty can be voided if failure is caused by installation mistakes, that
is, installation carried out contrary to manufacturer instructions. Besides
that, installation mistakes are a safety risk to those involved in the instal-
lation through electrical shocks, which can be fatal in addition to being a
hazard to the environment.
The equipment installation instructions should be used together with
local/national regulations for solar-powered water systems, electrical safety
codes, codes of practice, appraisal of local conditions (theft, flooding,
lightning, etc.), and other institutional minimum standards from the imple-
menting organization. As a minimum, all SPWS installations must reference
IEC 60364-7-712.
Equipment failure occurring shortly after installation is often due to trivial
mistakes, such as faulty cable splicing, loose cable connections, or wrong PV

module wiring delivering a high voltage, leading to inverter burn out, which
if careful attention was paid could have been easily avoided.
To support with supervision of installation, an installation control checklist
can be found in Annex J, on the Global WASH Cluster ‘Resources’ webpage
(GLOSWI, 2018f) or on Energypedia (2020). This checklist will help with
controlling installation quality and ensuring compliance with design require-
ments and standards.
Finally, after installation is complete the site should be left free of clutter, all
forms of debris, tools, and equipment, which can be a hazard to the operators
and negatively affect the performance of the system.

6.2 Installation sequence and process

From field experience the recommended sequence of installing the pumping
system is to begin with pump installation, followed by installation of all controls
(disconnection switch, combiner boxes, controller) together with all cabling,
and lastly installation of the support structure and the solar modules.
The installation team should be equipped with the correct tools that
guarantee professional work. These tools include DC and AC clamp meter,
multimeter (minimum 1,000 VDC), array tester (minimum 1,000 VDC), wire
stripper, crimping tool, and compass. Optional tools include inclinometer and
irradiance meter.

6.2.1 Cable splicing and dry-run protection

A splicing kit that is rated for underwater use and matched to the cable size
should be used to connect the submersible cable to the motor tail cable.
This splicing kit is not unique to
SPWSs and is used in traditional Cable splicing is one of the most critical
pumping systems. The manufacturer tasks of the entire installation. Sloppiness
will provide labelling or colour coding in workmanship can lead to an immediate
or future failure.
on the motor cables to allow for correct
wire sequencing.
The contracted supplier/installer should be asked to make the cable splice
in their workshop and test the pump unit before delivery to site. Since damage
can occur in handling and in transit, cable connections and splices should also
be checked onsite before lowering the pump by conducting continuity and
resistance tests on the motor and cable. It is also often possible to test small
pump units in a drum/bucket of water connected to one string of unmounted
modules laid out on the ground. This helps to detect any problems prior to
installation and avoid the time-wasting exercise of installing a faulty pump.
Submersible pumps must be operated while completely submerged in
water. Surface pumps must be operated with water in the suction pipe.
A critical sensor that must be installed with every pumping unit is a dry-run
protection sensor. This works by disconnecting power supply to the pump

when the source water level drops below a pre-set level. Different dry-run
protections are available, including well probes and water sensors/electrodes.
These sensors are connected through a cable to the corresponding sensor
input in the solar controller. Failure to install a dry-run protection can lead to
premature failure of the pump.

6.2.2 Pump installation

Submersible pumps. Beginning with pump installation is especially important
for solar retrofitted submersible pumping systems where it is necessary
to remove the existing pump in order to fit a dry-run probe. It is not
uncommon to find that the specifications of the existing pump are different
from what had been reported during the design stage. If the pump is found
to be smaller than envisioned, for example, this would call for a smaller
solar PV generator and a smaller controller, which can be exchanged from
the contractor.
Even for new pumping systems it is possible to encounter surprises, such
as a smaller borehole casing than what was thought, necessitating a reduced
size of pump, PV modules, and inverter, or a non-plumb casing that restricts
the pump from entering the borehole, or a dry borehole which would mean
the project has to be abandoned.
When such discrepancies are encountered, because the installation started
with the pump they can be corrected relatively easily, which would not be
possible if extensive PV installation works had already been undertaken.
As far as the choice of a new system versus a retrofitted system is concerned,
sound judgement should be made having all the information about the
system and considering the benefits to be realized. In some cases the existing
pump is a new pump, thus negating the need for a new pump. In other cases,
the pump is old and its soundness questionable, requiring a new pump to
be bought. An important consideration in this case is to ensure that the
pump to be powered with solar is adequate for variable-speed operation, is
the right size for the required demand as per the design, provides an optimal
design relative to the number of modules and inverter size required, does not
jeopardize the equipment warranty (e.g. some suppliers may not warrant their
inverters if they are installed with third-party pumps), and does not jeopardize
the performance warranty of the system.
Last-minute decisions on the size of the pump relative to the well diameter
have been a source of anguish (because of additional transport costs, project
delays, unhappy users, and embarrassment) for many agencies that fail
to give it prior consideration. Pump dimensions should be checked before
procurement to ensure that both the pump (including the cable guard) and
the motor can fit into the well. The minimum allowance between the pump
and the well casing is usually provided by the manufacturer.
Any submersible pump installation is usually done using a hydraulic winch
that lowers the pump into the well (Figure 6.2). Small pumps can be installed

Figure 6.2 Pump installation using a hydraulic winch

Source: Davis & Shirtliff Ltd

into shallow wells by hand or by using a simple pulley-and-rope system.

For deep boreholes, the installation work is more complex and problems
such as hitting the sides of the well, abrasion of the cable, and in the worst
case getting stuck or dislodging in the well, have been encountered. To avoid
such problems, professional installers or people who are conversant with the
process should be engaged as they are familiar with what care should be taken
to ensure a well-aligned installation free of damage.
The pipe size and type used during the design stage to compute head
losses must be used in the installation. If a smaller or rougher pipe is used, it
will result in reduced pump performance. The submersible cable should be
secured onto the pipe using plastic cable ties to prevent it from sagging and
being strained.
Importantly, the position of the submersible pump in the well has an impact
on the longevity of the pump. The submersible pump must be installed:

• suspended in the well to prevent contact with sand and mud at the
bottom of the well;

• below the dynamic water level to avoid the pump cutting out on low
water during prolonged pumping;
• above the main aquifer to ensure efficient motor cooling as the water
flows around the motor;
• within a plain casing for proper cooling, to avoid turbulence on the
inlet, and to prevent sand from entering the pump.

Effective circulation of water around the motor during operation is particu-

larly important for submersible pumps as this provides the needed cooling of
the motor that prolongs its life.
Submersible pumps are sometimes installed with a stainless-steel safety
rope for additional safety, to avoid it falling into the well when pipes corrode
or when an unexpected weakness in the piping system occurs. Plastic drop
pipes must always be installed with
A cooling sleeve can be used to provide a safety rope. The complete borehole
proper cooling in cases where the pump installation should be fitted with a
cannot be installed above the main high-quality steel wellhead cover
aquifer and within a plain casing. that is strong enough to support the
complete installation.
As a standard, submersible pumps come fitted with a non-return valve at
their outlet to prevent the water in the pipe from flowing back into the well
when the pump stops.

Surface pumps. Surface pumps are mounted/bolted on a concrete plinth

(platform) of appropriate dimensions and strong enough to withstand
the pump weight and vibration during operation (see Figure 6.3). Since
surface pumps are air cooled, enough ventilation should be provided for
good air circulation. The exterior of surface pumps should not get into
contact with water and when installed outside should be protected from
rain and direct sunlight to prolong their lifetime and reduce maintenance
requirements.
Surface pumps should be installed close to the water source within the
suction lift limit of the pump (see Annex A). Bends, valves, and fittings
should be minimized on the suction side of the pump as they compromise
the pump suction capability. Sharp bends and constrictions (e.g. pipe
reductions) must be avoided too on the suction side. As a general rule,
surface solar pumps should be installed as close to the water source as
possible, despite their potential capacity to lift water from deeper sources.
A low suction head significantly improves daily flowrate and operational
reliability. A surface pump must be primed before operation, that is, the
suction pipe must be full of water for the pump to operate. To prevent
water from running back into the well when the pump is switched off, a
foot valve or non-return (check) valve is fitted at the end of the suction
pipe. The valve keeps the suction full of water. In the absence of the foot/
check valve, the suction pipe will need to be manually primed (filled with
water) each time the pump is started.

Figure 6.3 Horizontal surface pumps installed on a concrete plinth in Itang Water Supply,
Ethiopia

To prevent cavitation in a surface pump (see section 3.3.1, ‘Surface

pumps vs submersible pumps’) the following should be observed on the
suction side:

• The maximum suction lift limit of the pump should be observed

(Annex A) with reference to the net positive suction head (NPSH)
requirement of the pump from the manufacturer’s datasheet. The NPSH
available in the pump location should always be higher than the
NPSH required by the pump for cavitation to be avoided.
• Friction on the suction side should be minimized. Sharp bends should
be avoided (45° elbow instead of 90° elbow, long radius instead of
short radius elbow); the suction pipe should be kept short (maximum
10–20 m); the number of bends should be kept to a minimum
(preferably only one bend or none at all if possible); and the suction
pipe should be large enough and never smaller than the pump inlet
diameter.
• The suction pipe should be kept air tight, i.e. no water leakages should
be present.

Cavitation and minimum suction lift issues are not discussed in detail here
as they are common to all mechanized pumps regardless of the power source.
However, these two issues are highly volatile in solar pumping because power,

pressure, and flowrate are varying constantly. The application of solar surface
pumps calls for computer-aided system design, which allows the designer to
analyse the behaviour of the system under all operating conditions.

6.2.3 Installation of controls

Installing controls before installing the PV modules is also recommended.
This is because the controls, specifically the DC disconnection/isolation
switch (see section 3.4.2), provides a way to manage the high voltage and
current produced by the modules which would otherwise be impossible and
dangerous to handle (see Figure 6.4).
The solar controller should be well ventilated and depending on its
enclosure/protection rating, be shielded from the elements such as rain, dust,
and sunlight. Some manufacturers provide controllers that are rated IP66,
which means they are protected from splashes of water and dust. They should
not however ever be immersed in water.
Controllers should be installed as close as possible to the PV generator
to keep cable losses (voltage drop) on the DC side at a minimum.

Figure 6.4 Installed controls (left to right): AC changeover switch, inverter, surge protector, PV
disconnection switch

Increased distance between the controller and the motor causes harmonics
that require a filter to avoid damage to the pump and the controller (see
sine-wave filter in section 3.4.5). Commonly, they are installed under the
solar module structure, which provides good protection against rain and
direct sunlight, or in a small control room close to the solar panels, fixed at
a minimum height from the ground of about 1.5 m. When installed inside
a room, enough ventilation should be ensured for air circulation that will
provide efficient cooling of the inverter.
Controllers must never be installed in a fully enclosed cage as this
will cause them to overheat and perform non-optimally. Where theft or
vandalism is a concern the inverter can be mounted inside a lockable
meshed cage, as shown in Figure 6.5. The cage should also be perforated
at the top and bottom to allow for an effective cooling stream of air
flowing behind the controller. Refer to the manufacturer manuals in case
of uncertainty.

Figure 6.5 Inverter installed in a lockable meshed enclosure under the PV array at Turkana, Kenya
Source: Oxfam

One solar pump controller is designed to power one pumping system.

No other load should be connected to the solar controller except the pump.
In addition, the PV generator discussed in this book is designed to power
the pump alone and hence no other load should be connected to the PV
generator.

6.2.4 Cabling
Cables between the pump, controls, and PV generator should be appropriately
sized, as explained in Annex D. For correct cable termination at the motor
and in the controller, refer to the motor and inverter manual to ensure correct
sequencing. Reference should also be made specifically to IEC 60364-7-712,
60947-1, and 62253.
DC cable terminations should be carried out in such a way that it should
never be necessary for an installer to work in any enclosure or situation featuring
simultaneously accessible live PV string positive and negative parts.
A watertight submersible cable should be used inside the well and should be
protected from physical damage especially at the point where it is in contact
with the borehole casing. It should be secured onto the drop pipe using cable
ties to relieve strain. The right type and size of cable splicing should be used
to connect the submersible cable to the motor tail cable and should be done
by an experienced technician to ensure a secure connection. The manufac-
turers’ splicing instructions should be followed carefully. The weight of the
pump should be supported on a rigid pipe (e.g. steel pipes) and not on the
electrical pump cable. A separate corrosion-resistant safety rope should be used
to support the pump when plastic pipes are used. The pump cable should never
be used to pull the pump out of the well because this will damage the cable.
Surface cables should be approved for external use (e.g. armoured type)
or for running the cable inside an electrical conduit. Surface cables should
always be buried in the ground to a minimum depth of 0.5 mm for electrical
safety, away from flood-prone areas. Cable glanding should be the right size
to ensure a good seal, which will prevent entry of dust, insects, rodents, and
moisture which can cause damage.
All connections should be made in easy-to-access junction boxes where
they can be inspected, repaired, and mechanically secured. All electrical
connections should be protected against water, dust, and insect intrusion.
Good cable management is important in a professional installation.
It also helps with preventing physical accidents (e.g. tripping on cables) and
electrical accidents (e.g. short-circuits when cables overlap). See Figures 6.6
and 6.7 for examples of poor and good cable management.

6.2.5 Module mounting structures

Different types of module mounting structure are available commercially
or can be fabricated locally. Ground mount and pole mounts are the most

Figure 6.6 Examples of poor cable management in South Sudan

Figure 6.7 Examples of good cable management in South Sudan and Tanzania respectively

common structures for off-grid applications, especially in rural contexts,

where most humanitarian and development work is done.

Ground mount. The structure is directly anchored onto the ground either
in cast concrete or bolted onto a reinforced concrete block. It is the most
robust configuration as it is mounted not more than 1 m from the ground
and hence is less affected by wind. Orientation and tilt can also be optimized.
Ground mounts have the advantage of easy access for cleaning but expose the
modules to theft and vandalism. (See Figure 6.8 and Figure 5.9 for an example
of a ground mount structure.)

Pole mount. These are anchored into the ground on a high support pole
(usually more than 1.5 m high on the lower side) and filled with reinforced
concrete (See Figure 6.9). This structure is most affected by wind loading

Figure 6.8 Ground mount structure in Kawrgosk refugee camp, Iraq

Figure 6.9 Pole mounted PV modules in Bidibidi refugee settlement, Uganda

which should be factored in when designing the structural member sizes.

Pole mounts provide security against theft and vandalism but are more
expensive and more difficult to access for cleaning. This configuration is
adaptable as it can be constructed on almost any terrain, orientation and tilt
can be optimized, and modules can be raised high as an anti-theft measure.
Cleaning can be difficult as the modules are often raised high above the

Figure 6.10 Roof mount on a flat tank roof in Gaza

ground. Due to the wind effect, this structure is most prone to failure if it is
not correctly designed and installed. Adequate bracing should be provided
to prevent swaying. The concrete for the pole support foundation should
be mixed and allowed to cure properly to provide adequate support against
wind and rain. Most failed structures encountered in the field are pole
mount structures.

Roof mount. The structure is mounted on an existing roof, either sloping or

flat, often in the same direction and tilt as the roof (see Figure 6.10). A roof
mount has the advantage of requiring less land (or no extra land at all if the
existing roof is enough) but on the flipside its feasibility depends on the roof
and it is not always possible to optimize the orientation/inclination, resulting
in energy losses which must be factored into the solar power calculations.
Roof mounts are difficult to access for cleaning.

Ground screw. This structure is a relatively new concept which does not require
excavation, concreting, or refilling. The support poles (ground screws)
are simply hammered into the ground, resulting in minimal disturbance on
the soil and vegetation (See Figure 6.12). They are advantageous in the sense
that they are easy to install, easy to remove, and reusable; however, they can
only be installed on stable soil types and in non-rocky areas.

Elevated tank mounting. Sometimes modules are mounted on an elevated tank

for security, reduced cost, and efficient space utilization (See Figure 6.13).

Solar tracking systems are discussed in section 7.3 and are installed only
on pole mounts, which allow the modules to be manoeuvred to follow the
daily and seasonal path of the sun in order to maximize the energy yield.

Figure 6.11 Combined roof and pole mount installation at IOM water scheme, Kutupalong
Balukhali Expansion Site refugee camp (Cover photo)
Source: IOM-Bangladesh

Trackers can be a single axis (seasonal changes) or two axes (daily and
seasonal). Trackers were previously common in higher altitude locations and
less common in the tropics, where they have become less popular due to
the affordability of PV modules, such that the benefit attained by installing
trackers can now be realized more economically by oversizing the PV generator.
Trackers are also undesirable as they are expensive and require maintenance,
which is difficult in remote locations.

Factors to be considered in the structure installation include:

• Location. The tilt angle of the structure should be set equal to the latitude
of the location (with 15 degrees being the minimum tilt angle for self-
cleaning of the modules when it rains) and facing the equator. In instances
where there is great risk of modules being blown off by strong winds the
tilt angle should favour module survival under strong winds.
• Shading. The structure should be installed away from any shadowing,
such as that cast by nearby trees, buildings, or overhead cables.
• Soil conditions. The soil should be firm enough to carry the weight of
the whole system. Foundation depth and concrete casting should be
sufficient to provide support according to the soil type.
• Rain. For pole mount and ground mount structures the metallic support
poles should be cast in concrete to a height above the flood level to
prevent corrosion due to flood waters.
• Temperature. Spacing between the modules should accommodate the
expansion and movement of the modules with changing temperature
(see section 6.2.6).

Figure 6.12 Example of ground screw structure

Figure 6.13 Tank-mounted structure in an IDP camp near Maiduguri, Nigeria

• Corrosion. Anti-corrosion measures, especially for mild steel structures,

should be put in place, and stainless-steel hooks and bolts should be
used to prevent corrosion at the contact point. The structure should
be properly coated and protected against environmental factors,
such as rain, humidity,and salinity, as failure to do so will affect its
structural integrity.

Assessments done in several countries in equatorial regions have found

that mounting structures, if not properly designed and installed, are
prone to failure. Such failures (tilting or complete tipping) can happen
under normal loading if inadequate foundation depth (especially for the
pole-mount structure) is provided (Figure 6.14). To reduce the likelihood
of such disastrous failures the foundation must be designed to carry the
expected point and wind loads, as determined using the relevant structural
design standards and codes.

6.2.6 Solar module installation

Mounting the solar modules onto the support structure is the last step of the
mechanical installation of the PV system. All DC controls and wiring should
be completed prior to this step. This will allow effective electrical isolation
of the DC system (via the DC disconnection switch and PV module cable
connectors) while the array is being installed, and effective electrical isolation
of the PV array while the inverter is installed.
Solar modules should be mounted onto the support rail and then firmly
fastened using bolts, j-hooks or one-way screws through the mounting holes.
Clamps can also be used but must not come into contact with the front glass
of the module or shadow it. Modules must be installed in the clear open
without any shading above. A minimum space of about 10 mm should be
kept between modules to allow for expansion and aeration. The module must
be fastened on all four corners to prevent it from being blown off the support
due to inadequate bolting (see Figure 6.14).
Once all the modules are firmly secured on the structure, the home-run
negative and positive terminals from the PV array are connected to the
DC disconnection switch and/or combiner box but omitting the module
interconnections. Note that while the installer will be handling live
cables during the subsequent module interconnection, because the circuit
is broken at the DC disconnection switch, there is no possibility of an
electric shock current flowing from the partially completed PV string.
The maximum electric shock voltage that should ever be encountered is
that of one individual PV module.
The interconnection is done using the male/female cable terminals at
the back which must be pushed in all the way to make a tight connection
(see Figure 6.15). The connector can be MC3 or MC4 type although the former

Figure 6.14 Failed pole mount in Yida, South Sudan (left), modules blown off in Fafen,
Ethiopia (right)

Module output cable + (positive)

Waterproof connector

Module output cable – (negative)

y
e wa
all th
n
s hi
Pu

Figure 6.15 A tight connection of solar module MC3 quick connectors

is mostly obsolete. Before connecting modules, check the contacts are corrosion
free, clean, and dry. Modules are connected in series to increase the operating
voltage by plugging the positive plug of one module into the negative socket
of the next (discussed in section 5.3.5). The system voltage is defined by the
DC controller or inverter, as discussed in Annex B, but must be less than the
maximum system voltage allowable for the module, which is typically 1,000 V.
Some recent modules have a maximum system voltage of 1,500 V.

Homeruns
out to
disconnect Mod.1 Mod.2 Mod.3 Mod.18 Mod.19 Mod.20
switch

String 1

String 2

Figure 6.16 Leap-frog connection of modules

The voltage of each individual string should be verified before making a

parallel connection. A difference of more than 10 V between strings should be
checked and rectified before making the parallel connection.
The interconnection adopts the leap-frog style of connecting modules
whereby one terminal of the first module goes into one terminal of the
third module, while the remaining terminal of the first module goes into
one terminal of the second module. The remaining terminal of the second
module goes into the first terminal of the fourth module, while the remaining
terminal of the third module goes into one terminal of the fifth module.
This is repeated until the end of the string (See Figure 6.16). The purpose
of this leap-frog connection is to achieve a free positive and free negative
terminal (home-run terminals) on the same side of the string as opposed to
having the two terminals on opposite sides, thereby reducing the DC cable
and distance required to run to the disconnection box.
The most optimal sequencing should be adopted depending on the location
of the controls, for example, if the inverter is positioned midway under the
panels then the connections will be done so that the positive and negative
terminals meet in the middle of the array.
During installation of solar modules, it should be ensured that:

• no module is damaged, e.g. the module covering glass is not broken, the
cable terminals have no cuts or scratches;
• all the modules are of the same rating (same model, current, voltage,
and power);
• each string should have an equal number of modules;
• the voltage in each string is the same. This helps to show if there are any
module wiring mistakes and to ensure the right voltage goes to the inverter;
• the terminals cables are not hanging or caught on plants but are neatly
secured using plastic cable ties onto the metallic structure. The cables

Figure 6.17 Example of untidy and tidy module cables

should not touch the back of the modules as they can overheat and melt
(see Figure 6.17);
• the positive and negative home-runs are clearly labelled with positive
and negative markings, or by using colour coding;
• the angle bars that hold the modules should be installed in such a way
that they do not obstruct or cast a shadow on the solar cells.

A maintenance walkway should be provided for cleaning and other

maintenance activities such as module replacement and cable inspection
(see figures 6.18 and 6.19 for examples). This is especially important for dusty
environments and locations where self-cleaning cannot be guaranteed.

Figure 6.18 Walkway on a roof mount at Strathmore University, Kenya

Figure 6.19 Walkway on a ground mount in Koboko, Uganda

6.3 Earthing, lightning protection, and surge protection

High voltage peaks induced by lightning are one of the most common causes
of electronic failures in outdoor installations. Lightning surges are also a
common cause of controller failure in SPWSs.
The probability of lightning striking a PV installation depends on the
size and location of the system as well as prevalence of thunderstorms in
the area. Installation of a PV system does not increase the likelihood of a
lightning strike.
A PV system can produce large amounts of current and voltage that can be
dangerous if not well handled and managed. To arrest such dangers and ensure
the safety of the system all exposed or accessible PV equipment and circuits
must be properly connected to earth (grounded). Properly grounding PV
systems reduces the risk of electrical shock to personnel and the effects of
lightning and surges on equipment.
Earthing and grounding should be referenced to IEC 60347-7-712 and
62548 as well as complying with the requirements of the country electrical
codes. Briefly, the general considerations for protecting PV systems from
surges are:

• Lightning arrestor. A lightning arrestor should be installed at the highest

point on the SPWS site and be connected to a conductive 2.5 m-long,

16 mm copper grounding rod safely connected to the ground using an

insulated copper cable. Lighting arrestors should not be installed in
physical contact with the PV module structure.
• Bonding. All exposed metal components (including PV module frames,
metallic mounting structures, metallic enclosures), ground terminals of
the disconnection switch, and the controller should be interconnected
using a grounding conductor, such as a copper wire of minimum size
6 mm2 (AWG#8), and the conductor connected to a protective earth
connection.
• Grounding. One or more 2.5 m-long, 16 mm conductive copper grounding
rods should be driven into the ground and one end connected to the PV
array and controller using a cable of sufficient size. The rod should be
driven into sufficient depth that most of its area contacts conductive
soil (moist soil), so that when a surge comes down the line, the electrons
can drain into the ground with minimal resistance. Low earth contact
resistance can be improved by adding soda ash or activated charcoal to
the area surrounding the rod.

A properly grounded conductive structure will guide the lightning surge

or voltage spike into the earth (divert the surge) and reduce the potential for
damage.
Grounding is a complex issue that should always be referenced to manufac-
turer installation manuals as well as other, more detailed documents, such as
the Solar America Board for Codes and Standards (SABCS, 2015).
Surge protection devices (SPDs) provide additional protection for electronic
equipment (see Figure 6.20). They are used to reduce the risk of lightning
damage entering from the cables to the equipment. Though SPDs greatly reduce
the risk of damage, they do not eliminate it completely. It is recommended
that one SPD unit is installed at every sensor input in a PV pumping system.
Sensor inputs include dry-run input, low/high level input, and pressure
switch inputs.

Figure 6.20 Lorentz surge protection device

Source: Lorentz

In addition, the probability of damage caused by far-range lightning strikes

can be minimized by keeping the cable distance between the PV array and
the controller short, as well as by burying all exposed wires into the ground
instead of running them overhead.

6.4 Electrical safety

Electrical safety when installing a PV pumping system should be given proper
attention by minimizing potential hazards and risks. That said, long-term
safety of the system begins at the point of correct design followed by proper
installation, operation, and maintenance.
As PV power cannot be switched off, a means of isolating the power before
attempting to work on the PV pumping system should be provided (as a
minimum, a DC switch of the right rating will always be present between the
PV modules and the inverter). Failure to take precaution can lead to injuries
to personnel and damage to equipment.
Labelling of DC cables is important to make it easy to distinguish between
different pairs of negative and positive circuits. Danger signs should also be
put up at points where high voltage is a risk. All labels must be clear, easily
visible, and constructed and affixed to last and remain legible for the lifetime
of the system.
Additionally when solar modules are installed on poles or rooftops,
working at heights poses risks for the installers and operators of the system.
Appropriate measures should be taken to protect human life, such as through
training and mitigating against the risk of falling.
The most important safety measure in any PV installation is the human
factor which, if neglected, can lead to avoidable failures and injuries.
This requires that only personnel who are acquainted with the voltages
present in a PV pumping system be allowed to work on any live components
of the system (see more at section 11.2.6).

Copyright practicalactionpublishing.com
CHAPTER 7
Specific considerations and limitations
for solar-powered water pumping
This chapter analyses a number of issues specific to solar pumping which often
lead to misconceptions and design errors. These relate to variable chlorination, solar
tracking pumping in hot water contexts, tank sizing, theft-avoiding measures, and
overpumping related to the use of solar energy sources. An example of solar emergency
kits and a selection of some of the most frequently asked questions received on the
solar helpline run by the authors is shown at the end of the chapter.

Keywords: solar tracking, water chlorination, vandalism, theft, solar

pumping schemes, dosing pumps, hot water pumping, aquifer overpumping,
solar emergency kits

7.1 Chlorination
Water treatment with chlorine or chlorine compounds is a usual measure
taken in humanitarian operations to ensure bacteriological safety of drinking
water. Water chlorination entails the addition of a fixed amount of chlorine
per volume of water to be treated. The amount of chlorine to add is determined
based on the quality and quantity of the water to be treated (see more on
chlorination in Skinner, 2001).
When water is pumped at a fixed rate, as happens when the water pump is
connected to a constant and stable energy source, such as a diesel generator
or a stable grid, it is easy to calculate how much chlorine needs to be added in
order to achieve bacteriological safety.
In solar pumping schemes, the solar radiation that hits the panels will
change in value several times per second. As a consequence, the water
flowrate delivered (m3/hr) will change all through the day. Therefore, in
solar-powered water schemes, the fact that water flowrate varies during the
day and daily water pumped varies during the year needs to be taken into
account.
There are four different solutions commonly found in the field in order
to solve this problem: tank chlorination, in-line mechanical dosers, variable
dosing pumps, and valve-regulated chlorine dosers.

7.1.1 Tank chlorination

The chlorine dosing is done at the water tank. Since the water volume of a
full tank is known, it is easy to calculate the amount of chlorine to be added.

http://dx.doi.org/10.3362/9781780447810.007
Copyright practicalactionpublishing.com
110 SOLAR PUMPING FOR WATER SUPPLY

Tank chlorination is a basic approach yet it does require more constant

monitoring and additional human resources.

7.1.2 In-line mechanical dosers (water powered)

A device is installed in the pipeline between the pump and the water tank
which basically consists of a valve which opens at intervals, dosing in a fixed
amount of chlorine that can be manually adjusted. The higher the water
flowrate, the more times the valve will be opened, releasing a higher amount
of chlorine, and vice versa, so the chlorination is proportional to the water
flow. An operator will need to regularly refill the doser with chlorine.
While these devices are easy to install and use, reports from the field
indicate that they tend to get stuck at the seal level from time to time. Mixing
the chlorine (fully dissolved granules) and positioning the screen of the pickup
hose so it does not touch the bottom of the chlorine container ensures longer,
trouble-free use.

7.1.3 Variable dosing pumps (electric powered)

There are a whole range of chemical dosing pumps in which the chemical
dose rate (e.g. chlorine) is varied in direct proportion to changes in flow,
measured with a water flowmeter. This method of control maintains a
chlorine/water ratio constant (mg/l) and does not make any allowances for
variations in the incoming water quality (see more at Brandt et al., 2017).
While an operator will be needed to start and stop the pump and refill the
chlorine tank, as for in-line water-powered chlorinators, an extra inconvenience
comes from the fact that an electrical power supply will be needed for the dosing
pump to function. As typically solar water pumping is used where no reliable
grid is present, an alternative energy source (typically a small panel and battery,
since the energy demand for these pumps is normally very low) will need to be
provided to ensure proper functioning. Note that in case of hybrid systems and
water pump functioning beyond the solar day, another power source for the
dosing pump will be needed to ensure proper water treatment.

7.1.4 Valve-regulated chlorine doser (manually operated)

More traditional solutions found in the field consist of a parallel pipe
connection conducting part of the water flow through a chlorine container
(see Figure 7.1). A valve mounted on the pipe going through the chlorine
container is manually regulated to limit the flow of water and therefore the
amount of chlorine going to the main pipeline. After some iteration and
careful monitoring of chlorine residual, an experienced operator will be able
to know whether the valve should be almost closed (cloudy days with lower
water flows) or more open (for sunnier days).
Variations are systems using tablets and/or a venturi restriction (see more
in Skinner, 2001, pp. 22–24) on the pumping main, or on a bypass to it that

Key
Flow of water
Chlorine tablets are placed
Way to wash out the
Chlorine tablet system when needed

Figure 7.1 Valve-regulated bypass chlorinator

takes some of the flow so that a small hose at the venturi can be used to suck
the solution into the pipe. Valves can be used to adjust the flowrate in the
bypass pipe and/or in the small pipe to get the right dose.

7.2 Full-tank detection at long distances

Pressure switches are control devices that open or close electrical contacts
in response to changes in pressure. Float switches are mechanically actuated
devices for water-level detection.
In applications where water tanks are just a few metres away from the water
point, a float switch can be easily installed within the tank to detect water
levels. When the water tank is full, an electrical signal is sent via a cable to the
controller of the pump to stop pumping and vice versa.
However, when the water tank is hundreds of metres away from the water
point this configuration becomes impractical since such a long cable would
be too expensive and could potentially, in some contexts, attract lightning,
which would put the whole water scheme in danger.
A more practical solution for these contexts is to install a pressure switch in
the pipeline together with a simple ball valve in the tank. As the water tanks

get full, the ball valve starts closing and pressure increases in the pipeline.
When the pressure reaches a certain pre-established threshold, the pressure
switch sends an electrical signal to the pump controller (located just a few
metres away) to stop the pump. The system switches back on automatically
when the switch-on pressure is reached. With this configuration, there is no
cable from the ball valve to the pump controller, which avoids long cables and
the problems that come with it.

7.3 Solar tracking

Because of the different position of the sun in the sky during the day and
through the seasons, the only way to have solar panels at a right angle with
the sun at all times, and therefore maximize electricity production and
water output, is to move the panels to follow the sun’s path (see Figure 7.2).
This is the function of mechanical tracking devices installed in a solar array.
A tracking device can increase electricity output up to around 30 per cent.
As mentioned in section 5.2, while tracking devices have been used
extensively in the past they are used infrequently now in solar pumping
applications, for reasons of both high cost and complexity to maintain and
repair versus the more economical and simpler option of adding more solar
panels to the array. A tracking device is therefore discouraged, especially in
humanitarian operations and in places where operation and maintenance of
these trackers cannot be guaranteed.

South

East West

Solar panel
tracking the sun

Figure 7.2 Solar trackers: double-axis tracking (left) and single-axis tracking (right)

7.4 Emergency solar pumping kits

Emergency solar pumping kits are modular, making them quick and easy to
install at any moment, which is especially useful in contexts where fuel supply
is limited or irregular, the grid is unstable or non-existent, and emergency
water supply systems need to be installed (so no time for normal procurement
procedures).

Table 7.1 Summary of Global Solar and Water Initiative specifications for small, medium-
sized, and large solar pumping kits for rapid deployment
Kit Flow Daily flow TDH Lorentz pump Grundfos Solar panels
range range range model pump model (W)
(m3/h) (m3/day) (m)
Small 1.0–2.8 10–30 40–120 PS1800 HR-14H SQF 2.5-2 615–4100
1.7 kW pump 1. 4kW pump
Medium 3.5–7.0 30–70 60–140 PS4000 C-SJ5-25 SP5A-33 3 kW 2460–9840
4 kW pump pump
Large 6.0–12.0 50–100 80–180 PSk2-9 C-sj8-44 SP9-32 6560–15580
7.5 kW pump 7.5 kW pump

TDH = total dynamic head

A few WASH agencies with in-house technical expertise have developed

their own kits. While it is strongly recommended to use quality design
software to get the right dimensioning of the solar system for each individual
water system, the Global Solar and Water Initiative team has developed
guides for small, medium-sized, and large emergency solar pumping kits, with
technical specifications (GLOSWI, 2018e).
This provides a quick reference for emergency deployment. The performance
ranges indicated on each kit are meant to be a rough guide and should not
be taken to be the actual installed performance. These estimated performance
ranges are summarized in Table 7.1.
The terms small, medium, and large do not refer to the solar water pumping
system sizes available in the industry, but rather to the emergency kit sizes
relative to each other.
These kit sizes are based on what was most widely encountered in field
assessments of 160 water schemes in 55 refugee camps and communities,
mostly located in Sub-Saharan Africa. Smaller and larger solar water
pumping solutions are available from different manufacturers. Off-the-
shelf solutions of up to 75 kW (motor size) are available from some good-
quality manufacturers.
The performance estimations of each kit (shown in Table 7.1) are based
on the Lorentz and Grundfos sizing software. These software programs
use long-term estimates of solar and meteorological data from accredited
sources, such as NASA.

7.5 Power range for pump motors and inverters

There are widespread misconceptions about the limitations of pumps
powered with solar energy in terms of water volume and depth of boreholes
(or total dynamic heads – TDH).
In the past, the term ‘solar pumps’ was used to describe water pumps that
could be directly coupled with solar panels. Those solar pumps were equipped

with DC motors, which for a number of reasons were limited in most cases to
4 kW of pump motor power. From this came the association of ‘solar pumps’
with small pumps.
Technical developments in inverter technology have allowed solar panels
to power AC pumps with higher motor power ratings, making it possible to
pump higher water volumes from larger TDHs. The higher the input power
of the inverter, the bigger the pump motor power can be. Manufacturers of
inverters specifically designed for water pumping have been increasing the
sizes of inverters offered in recent years.
Several reputable solar pumping inverter manufacturers now offer
solutions for water pump motor powers up to 37 kW. In this range,
submersible centrifugal pumps can deliver water volumes of up to 240 m3/h
and TDH of up to 200 m.
For helicoidal water pumps, while the water output is quite limited to a few
cubic metres per day, TDHs are up to 450 m, making it possible to pump small
volumes from deep water. For surface pumps in the same range of motor size,
volumes of up to 2,000 m3/day are easily possible.
Today, larger fit-for-purpose inverters (standard inverters with in-built
software designed for solar water pumping) are available off the shelf, allowing
pumps from 75 kW (e.g. SolarTech, Lorentz) up to 280 kW (Fujielectric)
of motor power to function with solar power (with hydraulic potential
(flowxTDH) from 15,000 m4/h up to 50,000 m4/h).
Moreover, since inverters for large solar power plants for electricity
production exist in the market, some solar pump manufacturers and private
contractors offer the possibility to use these utility-scale inverters for solar
water pumping applications. For example, WellPumps manufacturer uses
standard Schneider inverters with its own solar water pumping software,
allowing up to 220 kW of motor power.
The largest solar water pumping scheme of such kind visited by the Global
Solar and Water Initiative team was found in Lebanon, using a pump motor
power of 150 kW.
While this is not a complete list of brands and manufacturers of various
inverter types and sizes, what is clear is that the use of the already existing
inverters on the market make it possible to literally solarize any water scheme
found in humanitarian operations today.
On the other end of the spectrum, pumps as small as 150 W of motor
power that work with a single solar panel are now also common on
the market.

7.6 Vandalism and theft

Theft of PV modules has become less common in recent years due to their
low cost. Yet, as the majority of PV pumping systems for humanitarian
and development work are implemented in rural, marginalized locations,
solar modules are attractive commodities because they can meet the energy

needs of communities. Theft and vandalism of solar modules can be a

concern where:

• there is a lack of ownership;

• systems are installed at remote locations and near public places or roads;
• users have not been consulted and the energy system installed does not
meet their needs;
• there is disparity in water provision with some communities feeling
underserved, leading to sabotage of the others’water systems;
• systems fall into disrepair (and the energy service ceases).

Certain measures can be taken to deter or prevent theft and vandalism

including:

• welding the bolts onto the structure, making it difficult to remove the
panels;
• using pop rivets to fasten the modules onto the structure which require
special tools to remove that will not be readily available to potential thieves;
• using elevated pole-mount structures that are hard to reach or mounting
the modules on an elevated water tank (see Figure 7.3);
• fencing the perimeter of the PV module area and securing it with a lock;
installing barbed wire/razor wire; installing an electric fence; fitting a
motion-sensitive siren; and/or lighting the PV module area (see Figure 7.4);
• installing the PV modules close to populated areas, such as near
the users;

Figure 7.3 Fenced SPWS with a solar light for security in Turkana, Kenya

Figure 7.4 Extreme module security measures in Burao, Somalia

• staffing the PV module area with a guard, especially at night; having

someone living at the water point; or having a vigilance plan where
community members take turns to guard the system;
• painting the name of the village/owner on the back of the solar modules
with non-removable paint;
• raising awareness among the users on the value of protecting and
keeping the system safe (community ownership, see Figure 7.5);
• engaging security forces (such as police, army) in extreme security
situations.

It has been observed that communities that are well aware of the value
of keeping the system working will pull together to protect it, including
taking disciplinary action against perpetrators, reporting to authorities,
and charging the cost of repair to the families of people who damage
the modules.
Preventing theft and vandalism cannot always be achieved, especially for
locations that are generally insecure due to conflict or war. Consider such
security concerns at initial design stage as PV water pumping may not be
suitable and should be discouraged in such circumstances (see video from
World Bank, 2017).

Figure 7.5 Awareness raising of the value of the SPWS to avoid theft and vandalism

7.7 Overpumping of aquifers

While the authors could not find rigorous studies showing the relationship
between solar pumping adoption and overextraction of water there is a genuine
concern that solar pumping could lead to water wastage and overpumping
of water sources.
This is mostly based in the perception by many communities of users (but
common also among implementing organizations and other water stake-
holders) that, where water can be supplied by solar-powered schemes, water is
free. The absence of rigorous groundwater assessments looking at the available
water resource (i.e. storage plus recharge) with clear and enforced recommenda-
tions for water extraction, especially in places where an increasing number of
new boreholes are being drilled and/or retrofitted to solar (see more on this in
section 5.3.2), may lead to overexploitation of the available water resource.
While solar-powered water schemes will typically suffer fewer breakdowns
and have much less intensive maintenance than generator or handpump
schemes, solar systems can and will experience problems at some point.
The absence of a plan to have funds available for the maintenance of the system
will undoubtedly lead to systems falling into disrepair and abandonment. It is
therefore critical that communities of users understand the limitations of
solar pumping solutions so that, wherever possible, water is provided at a fee,
even if supplied through solar pumping. This will be an important measure to
ensure greater sustainability but also the best way to limit the feared wastage
and/or overextraction of water.
Another way to limit overextraction of water, especially relevant for water
schemes with multiple uses (e.g. water-for-people and water-for-food), is to

transform the economy to low water use or/and to support actions that will
lead to a switch from excess water use to a low water agro-economy (see for
example Delegation of the European Union to Pakistan, 2018).
As the solar pump is in many cases driven by a microprocessor, it is possible
to limit the daily flow to a certain agreed amount to be set at the control box/
inverter level.
In addition, new liquid level sensors (vs simple dry-run sensors) measure
water levels in the well (static and pumping levels) and record the data in the
pump controller, allowing for proper and simpler follow-up of water levels
and tracking of seasonal and long-term well behaviour to better support
monitoring of water resource use. As the data recording is, depending on the
manufacturer, done in the pump controller (and therefore can be accessed
remotely from a central office), this is a logical addition to solar pumps –
especially at critical water points – at minimal incremental cost.
Finally, there are situations where excess electricity produced can be used as
a remunerative crop or for purposes other than water extraction (e.g. electricity
sold via the grid; see more in Shah et al., 2018), which in turn will incentivize
the rational use of solar pumping, limiting overpumping of aquifers.

7.8 Hot climate zones and hot water pumping

7.8.1 Solar panel considerations for hot climate zones
Contrary to what intuition would dictate, there are important challenges
when using solar PV panels in areas with high levels of sun irradiation
and increased air temperatures. Solar panels are normally tested and rated
for cell temperatures of 25 °C (STC). The temperature of the cell can reach
25 °C with ambient temperatures well below that value. In real conditions,
and especially in many places within the sun belt, ambient temperatures
will easily reach values over 20 °C, 30 °C and even 40 °C during the day,
meaning that cell temperatures will increase over the 25 °C at which the
panels were tested and will start experiencing losses, with voltage output
decreasing and peak energy output dropping as cell temperature rises (see
sections 2.10 and 4.2).
The loss of energy output due to temperature is expressed by the
temperature coefficient of the panel, which should appear in the datasheet
of the product and depends on the kind of panel (mono or polycrys-
talline, amorphous, thin film) and the manufacturer. If, for example, the
temperature coefficient is –0.5 per cent per degree Celsius, this would mean
that for every 1 °C over 25 °C of cell temperature, the energy output of the
panel will be reduced by 0.5 per cent. The higher the ambient temperature,
the more losses induced. At an ambient temperature of 30 °C, it would not
be rare to find panels at around 60 °C.
The way to compensate these losses (which are computed and accounted
for in good-quality solar pumping design software) is to oversize the solar

generator by adding a few more panels. In order to minimize this oversizing,

it is important to try to minimize losses due to temperature. Two measures can
be typically taken to do so:

1. Allow space at the back of the panels and between panels for air to
circulate, cooling the panels down.
2. Chose panels with a lower temperature coefficient (typically monocrys-
talline will have slightly lower temperature coefficients than polycrys-
talline, and thin film will have the lowest of all).

7.8.2 Inverter considerations for hot climate zones

Reputed manufacturer inverters will be able to operate within temperatures
of up to 60 °C. However, as for solar panels, an inverter’s AC output reduces
as temperature rises. Starting from the rated continuous AC output at 25 °C,
the continuous output of inverters decreases, for example, at 40 °C by
6–15 per cent, depending on the model.
In the same manner as with solar panels, a way to mitigate performance
losses at high air temperatures is to oversize the inverter. The indications on
the datasheets of inverter models are to be referred to for calculating how
much oversizing of the inverter’s capacity would be required to provide
sufficient AC output at consistently elevated air temperatures.
Furthermore, the technical room where the inverter is located should
have enough air inlets to ensure maximum air flow to cool down the system.
Depending on the size of the solar PV system, a ventilating system may be
considered to support the air flow in the technical room and keep tempera-
tures in check (see more at Energypedia, 2019). Finally, where inverters are
mounted in a casing inside a control room it is considered good practice to
leave the door cover of the enclosure open during working hours, allowing for
cooling and air flow.

7.8.3 Hot water pumping

Submersible pumps may be affected in hot working conditions, either under-
performing or having their working life shortened when the water to be
pumped surpasses a certain temperature (e.g. in areas with volcanic activity).
For helical rotor pumps, hot water may damage the rubber stator; for
other centrifugal submersible pumps, it may be rubber parts that are affected.
In addition, the motor in the borehole may have insufficient cooling, which
could compromise the whole water scheme.
Some manufacturers, such as Grundfos, in order to protect pump and
motor rubber parts, offer the possibility that pumps be fitted with bearings
made of FKM material, which is resistant to liquid temperatures of up to 90 °C
(see Grundfos, 2012). Other manufacturers will clearly indicate the maximum
water temperature at which the pump is expected to work (30 °C to 40 °C is

a typical threshold for many pumps), and may offer alternative models for
temperatures above 30 °C or 40 °C.
As for insufficient cooling, similar to inverters and solar panels, oversizing
the pump is a way to compensate for efficiency losses or, in other words,
derating the motor power. Manufacturers will provide derating factors. What
is important to keep in mind is that the solar generator will have to be
reviewed, and probably oversized, in order to power a bigger pump.

Example 7.1 Derating motor power for hot water pumping

A pumping scheme to provide 50 m3/day is designed for a village. It is estimated that a

pump with a motor power (P2) of 4 kW will suffice to provide the required water. The water
temperature is checked and found to be 40 °C, while the pump temperature threshold is
30 °C. At 40 °C water temperature and for that size of motor, the manufacturer provides
a derating factor of 0.9. What motor size will be needed in order to provide the expected
amount of water?
The 4 kW motor will produce 4 kW x 0.9 = 3.6 kW of power. In order to have the
expected 4 kW, the motor power is divided by the derating factor: 4 kW/0.9 = 4.4 kW.
The nearest higher motor size available in the market is 5.5 kW, so a pump of 5.5 kW will
have to be installed. The solar generator will have to be resized for that power.

7.9 Frequently asked questions

Can I precisely predict water outputs in a solar pumping scheme since solar
conditions are so variable?
You cannot predict exactly what the water output will be in any given day.
Typically, the most reputed solar design software will provide average water
output per day for different months of the year (e.g. 30 m3/day during the
month of June). Based on this, your location, and your experience, you will be
able to predict a range of values per day quite accurately.
For example, you may not be able to ascertain that a certain solar
pumping scheme will provide 35 m3/day exactly, but you may find that it
will provide between 24 and 42 m3/day. If your needs for that particular
location are below 24 m3/day, you can be certain your solar system will
meet those needs.

Can I get enough water during cloudy days and in the rainy season?
Normally, if the system has been rightly sized, you will be able to get
water on rainy or cloudy days too. The questions is how much water
you can get and whether that will be enough to meet your needs. As
explained in the question above, you can predict a range of values for
water output and whether your water needs will be met. Typically, for
systems intended to provide water for drinking purposes, the size of
the solar arrays will be designed for the worst meteorological conditions
of the year in order to ensure water needs are met even during cloudy days
and rainy seasons.

Is the capital cost of solar still prohibitive, especially when compared to

equivalent diesel-based solutions?
This used to be the case. However the price of solar panels has dropped
80 per cent in the last 10 years, making the technology more affordable.
Typically for small schemes, the solar capital cost can be compared to that
for diesel generators. What is important, however, is to look at costs over the
life of the equipment. As good solar panels have a lifespan of 25 years and
the running costs are so low, the cost advantages are clear when looking at
it over time. On average, the return on investment period ranges between
0 and 4 years, and cost savings are of 40–90 per cent when compared to
equivalent diesel systems (see more in Chapter 9).

Do I need to hire an electrical engineer to deal with my solar pumping project?

Although an electrical engineer with knowledge in solar technology would
give you an additional advantage it is not strictly needed. A water engineer with
a few days of training could get the necessary knowledge to deal with the main
issues of a solar pumping project. Knowledgeable private-sector contractors
will most likely be present in capital cities, meaning your water technician will
have to monitor only some critical steps at each stage of the project.

Is there any point thinking about solar pumping in countries where

fuel prices are low?
The economic case for solar may still be made (depending on national solar
market conditions) since the running costs of solar pumping schemes are so
low. The Global Solar and Water Initiative has run several economic analyses
to compare solar with diesel systems in Sudan and Iraq (where diesel can be as
cheap as US$0.3 /litre), finding that solar pumping solutions made economic
sense in most cases. However, apart from technical and economic feasibility,
other factors have to be considered, such as social and environmental aspects,
access to sites linked to security and logistical constraints, and reliability of fuel
supplies or the electrical grid (if any). A holistic analysis will be required before
hand to see the added value of using solar technology versus other options.

Can solar schemes work well under very high temperatures?

Solar panel efficiency decreases with high temperatures (see more in sections 4.2
and 7.8). This factor is taken into account at the design stage and is therefore
not a problem as such. With ambient temperatures of over 55–60 °C, resins and
epoxies within the solar panel itself could start melting, affecting the function-
ality of the equipment. However, those temperatures are rarely reached on earth.
In summary, solar panels perform sufficiently under high temperatures.

How long is it before solar pumping schemes develop technical problems?

And can local communities be trained to carry out repairs?
A well-designed and maintained solar pumping scheme can last a long time
(10 years or more) without any major technical issue. However, at some point,
these systems can and will develop problems that community technicians
won’t be able to solve, regardless of the training provided to them. This is why

it is important to consider and put in place from the start a model that links
users/owners of the system with technical offices or providers with enough
technical expertise to solve such issues. It is not recommended to focus on
technology alone without taking into account maintenance aspects when it
comes to important failures.

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CHAPTER 8
Solar-powered water pumping
for agriculture
While technology considerations are similar regardless of how water is used, design
and operation of solar irrigation schemes come with their own specific challenges.
This chapter explains different irrigation techniques and matches them to solar
pumping considerations. In addition, it sets out a range of models to help in the
financing of solar irrigation schemes, together with a set of the most common risks
and problems encountered when using solar pumping for agricultural purposes.

Keywords: irrigated agriculture, solar irrigation, irrigation policy, solar

financing, irrigation techniques

8.1 Water for irrigated agriculture

Irrigation is the science of providing water to crops. Irrigation allows farmers
to reduce the uncertainty of rainfed farming. With irrigation, farmers can
provide the right amount of water needed by the plant depending on the plant
growth stage. Reducing uncertainty increases yield and improves livelihoods
of farmers (see Figure 8.1).
Agriculture accounts for around 70 per cent of water withdrawals
(91 per cent of which is for irrigation) from rivers, lakes, and aquifers (FAO &
WWC, 2015). The industrial and municipal sectors account for 20 per cent
and 10 per cent respectively (Aquastat, 2019).
Farming activities are usually performed in rural areas where grid connection
is non-existent or unreliable. In 2017, an estimated 1.1 billion people –
14 per cent of the global population – did not have access to electricity (IEA,
2017). Many more households experience power outages. Almost 84 per cent
of those without electricity access live in rural areas in Sub-Saharan Africa
and developing Asia. For this reason, the main energy source for irrigation
is fossil fuel (diesel, gas, or petrol). Both liquid fuels and electricity require
infrastructure between the producer and consumer.

8.2 The influence of pressure on energy requirements in irrigation

Irrigation techniques can be summarized as six main types:

• Flood irrigation delivers water to the crop by flooding the base of the
plant. Also known as furrow irrigation, it is achieved by digging a trench
between plant rows to deliver water using gravity.

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124 SOLAR PUMPING FOR WATER SUPPLY

8000
Cereal production (kg/ha)

7000
6000
5000
4000
3000
2000
1000
0
1000 2000 3000 4000 5000 6000 7000
Water availability (m /ha)
3

High-yielding varieties, high inputs High-yielding varieties, low inputs

Traditional varieties, high inputs Traditional varieties, low inputs

Figure 8.1 Yield response of crops to water availability in China

Source: Smith et al., 2001

• Drip irrigation uses pipes installed at the plant base along the plant rows,
delivering water drop by drop to the plant.
• Sprinkler irrigation sprays water into the air to irrigate the crops using
spray heads. It irrigates the entire soil surface.
• Micro-sprinkler is a mix of drip and sprinkler irrigation. The micro-
sprinkler heads are set up close to the plant base and spray water locally
in small water drops. They require the same amount of piping as drip
irrigation but use different sprinkler heads. Furthermore, the pipes are
elevated off the ground.
• Pivot irrigation uses the sprinkler irrigation method but with the spraying
head fixed to a machine rotating around a pivot. Circular patterns are
created with this technique.
• Travelling guns are also derivatives of the sprinkler technology. They
operate parallel to the field which needs to be irrigated and at higher
pressure than a classic rotating sprinkler.

The estimated pressure requirements for each irrigation technique are:

Irrigation technique Estimated pressure requirement

Flood 0 bar
Drip 0.5–3 bar
Micro Sprinkler 0.5–2 bar
Pivot 1–3 bar
Sprinkler 2–5 bar
Travelling gun 2–8 bar
Source: FAO & GIZ, 2018b

Pressurized irrigation systems need a tank to operate. The tank height

provides the pressure need of the irrigation technique. One bar represents an
increase of total dynamic head of 10 m and irrigation tanks are usually set up
close to the fields and not higher than 10 m. For this reason, for irrigation
techniques requiring pressure of more than 1 bar it could be necessary to add
a water booster in the system. Water boosters require electricity to operate.
Therefore, solar energy is recommended for low-pressure irrigation techniques,
such as flood, drip, micro-sprinkler, and some pivot systems.

8.3 Greenhouse gas emissions from agriculture

and climate-change adaptation
The three main sources of greenhouse gas (GHG) emissions in agri-food
systems are carbon dioxide from food processing and food waste degradation,
methane from ruminants, and nitrous oxide from manure left on pastures.
It is estimated that irrigation accounts for 10 per cent of GHG emissions from
the agri-food sector (see Figure 8.2). If solar is to replace existing fuel-based
energy sources for irrigation this will have a clear impact on the mitigation of
GHG emissions in agri-food systems. Once installed, solar irrigation does not
produce GHG emissions
The more common solar-powered irrigation systems (SPISs) become, the
less greenhouse gases will be released into the atmosphere compared to
fossil fuel or grid irrigation. SPISs do not only offer an opportunity for
mitigating GHG emissions, but also for adaptation. Irrigating farmers are
more resilient against erratic rainfall patterns caused by climate-change
effects and as they produce their own electricity they do not depend on
an external energy provider (fuel or erratic grid) (FAO, 2017). The main

POST-HARVEST BEHIND THE FARM GATE

Cooking/retail
Transport Manure Nitrous
oxide

Food Fertilizer
processing
Paddy rice
Carbon
dioxide
Methane
Ruminants

Irrigation
Machinery

Figure 8.2 Approximate shares of greenhouse gas emissions (in CO2 equivalent) emitted by
the global agri-food sector in 2010
Source: FAO, 2015

benefit of SPISs compared to grid pumping is the reliability of the system,

if well maintained. Solar energy farmers become independent energy
producers and can schedule their irrigation needs instead of depending on
an external energy source.

8.4 Financing solar-powered irrigation systems

One of the main differences between solar pumping for drinking and for
agriculture is the nature of the investment. Drinking water is a human right
and pumping usually benefits a whole community. Therefore, the group could
collectively invest in the pumping system. Individual farmers or coopera-
tives invest in irrigation systems to support their activity and increase their
revenues. Therefore, investment costs are strong drivers for the adoption of
SPISs because individual farmers or groups of farmers support them.
The agriculture sector represents 63 per cent of the employment in
low-income countries and 55 per cent in Sub-Saharan Africa (World Bank,
2018). Low-income countries are countries with a gross national income per
capita of less than US$996 per year (World Bank, 2018). The cost of energy
for irrigation (investments and operational costs) is an important parameter
for farmers.
The cost of SPIS pumping equipment has been brought down by the
plummeting of solar PV prices. Though solar equipment is only one of the
elements of an SPIS, it represents one of the most important drivers for
adoption by farmers. Investment costs for SPISs remain higher than fuel-based
pumping (FAO, 2018). Since SPISs do not require fuel, operational costs are
limited to maintenance and replacement at the end of life of the different
components. In the fuel-based pumping model, the fuel cost will increase
the operational costs over the short to medium term (see more on cost in
Chapter 9). These operational costs make fossil fuel–based pumping more
expensive than SPISs.
Payback periods for SPISs differ around the world and according to the
different subsidy schemes in place (FAO, 2018). Some country examples are:

• Senegal. Payback periods for solar pumps in the belt between Dakar and
Saint Louis are given as 2–2.5 years (three cropping seasons, 1 ha irrigation
with a 15 per cent interest rate on equipment) (Hagenah, 2017).
• Chile. The payback period for solar pumps for small farmers (2–4 ha) in
northern Chile is around 4 years (three cropping seasons of tomatoes,
paprika, and green beans) (R. Schmidt, Africa Solar, pers. comm., 2017).
• Kenya. Suppliers of SPISs in Kenya claim a payback period of between
1 and 2 years, sometimes even less (at non-subsidized prices) for SPISs
irrigating 1–2 ha of fruit and vegetables (S. Ibrahim, SunCulture, Kenya,
pers. comm., 2017).
• India. The payback period depends on the state subsidy, ranging from
0 years in Bihar with subsidy for 8 ha of rice, wheat, maize, and lentils

to 19 years without the subsidy. The payback period in West Bengal,

where there is no subsidy, is 8 years for 7 ha of rice and vegetables
(Mukherji et al., 2017a).
• Pakistan. The payback period is 6 years for 32 ha of rice, wheat, and
cotton. There is no subsidy on the cost of equipment.
• Nepal. A payback period of 2.5 years is reported with subsidy and 8 years
without subsidy for 5 ha of rice, wheat, and vegetables. The financing
mechanism entails a subsidy (up to 70 per cent of the total cost for a
female farmer compared to 60 per cent for a male farmer) and a loan
with 15 per cent interest rate (Mukherji et al., 2017b).

SPISs are economical thanks to the short payback period. The systems
are dependable because farmers do not rely on the grid or on fuel delivery.
However, a number of risks and challenges persist.

8.5 Financing instruments to develop solar irrigation

Farming revenues depend on seasonality and SPISs may require a high initial
capital investment, which implies:

• long repayment periods (5–10 years);

• the need for high profit margins on agricultural products or associated
services;
• the need for a grace period at the beginning of the repayment plan.

Irrigation brings higher revenues to farmers but the investment and

collateral needed to invest in SPISs may be too high for small-scale farmers.
For this reason, farmers need to perform an economic analysis of their
farm and to run scenarios without irrigation, with fossil or grid irrigation, and
with an SPIS. Based on actual investment costs and potential revenues with
irrigation, farmers can define the investment needed as well as the type of
financing instrument to use.
Different financing instruments for solar irrigation, discussed in Annex I, are:

• commercial bank loans;

• rural/development bank loans;
• microfinance
• leasing or repurchase agreements;
• financing through agrarian cooperatives;
• informal saving groups;
• pay-per-use business models;
• SPIS subsidy mechanisms;
• matching grants mechanisms.

A blend of different instruments (a loan and a grant, for instance) can

also support farmers in designing, acquiring, operating, and maintaining
their SPIS.

8.6 The risks and challenges of solar irrigation

One of the main challenges for small-scale farmers are the capital investment
costs of SPISs, as farmers typically lack the funds to invest in the system and
the collaterals requested by traditional banking. In some cases, a company
may be granted a subsidy with a loan component on behalf of a group
of farmers and sell water to them using a fee-for-service or a pay-as-you-
go model.
The second challenge is related to nature of solar power. Where most
electric and fuel pumps deliver a set quantity of water (in m3/h) from
a predefined depth, most solar pumps deliver a set quantity of water
according to solar irradiation (unless there is a second energy source in
a hybrid configuration). During the day, solar pumps will deliver more
water at noon when solar irradiation is at its maximum, whereas it is not
recommended to irrigate at midday since evapotranspiration is also at its
maximum (FAO, 1998). It is recommended to irrigate when evapotrans-
piration is lowest, in the morning and evening, at which time the solar
pump output is lowest. For farmers, irrigation experts, and extension staff,
it is a complete change of paradigm where they have to think in quantity
per day instead of hour. This can have an impact on investment costs
because farmers may need to install a storage system to be able to irrigate
at the right time for their crops.
Another challenge is related to the risk of overpumping since operating
costs of SPISs are minimal. State control may play a big role here, in the form
of water withdrawal permits or in subsidizing SPISs with water-efficiency
equipment. For instance, in Tunisia, subsidies for SPISs are granted only
if the farmer is using drip irrigation (FAO & GIZ, 2019). State control also
depends on the land and water tenure regime. In cases where landowners are
also water owners, the state cannot exert control over groundwater pumping.
The absence of state control, low operating costs, and the importance of
agricultural water withdrawal may lead to an increase in water consumption
and a decrease in sustainable water resources.
An additional challenge of solar irrigation is to operate and maintain the
solar components of irrigation systems. These challenges are not different from
the ones observed in other chapters of this book. SPISs are usually operated and
maintained by irrigation experts, whose energy knowledge may be basic.
As part of the global initiative Powering Agriculture, GIZ together with
FAO and Energypedia developed the
SPIS toolbox (see FAO & GIZ, 2018b.)
Training farmers, extension services, and
irrigation boards has the potential to in English, French, and Spanish,
reduce the misconception of ‘more water – in order to help find solutions to
more yield’ (FAO & ICIMOD, 2019). technical, economic, and sustain-
ability challenges.
To support the use of the toolbox, FAO and GIZ run capacity-building
programmes. GIZ also maintains a list of trainers and has developed
the community of trainers on solar irrigation. The objective of these

activities is to reinforce local capacity on all aspects of SPISs: environ-

mental, technical, and financial, and to cover sustainability aspects of the
water-energy-food nexus.
Finally, national and regional dialogues between the different public and
private actors or the water-energy-food nexus are necessary.

8.7 Recommendations for solar irrigation challenges

Globally, agriculture is the largest use of water (FAO & WWC, 2015; Aquastat,
2019). By reducing the energy costs of pumping, farmers may not link a price
to water and could overpump. This can have important consequences on
water resources. For this reason, a number of policy recommendations for
solar irrigation can be made.
Solar-powered irrigation has many facets and a wide variety of stakeholders
in the areas of agriculture, energy, and groundwater management. There is
a lack of understanding and coordination between the different national
ministries in charge of the water-energy-food nexus (FAO, 2014), which could
lead to competing and conflicting decisions and to suboptimal solutions.
To address this issue, government should establish strategies for sustainable
energy and water use, and monitor and control water use (through allocations
and quotas) in line with the subsidy mechanism, particularly in water-scarce
areas. It is also recommended that policymakers develop a map of operating
pumps to identify both the farmers that exploit common water resources and
the agricultural wells in operation.

8.7.1 Existing water laws

Solar irrigation has become a reliable and affordable technology. A certain
number of agricultural water policies have preceded the technology and all
stakeholders should ensure compliance with existing water laws, policies, and
frameworks. For instance, the development of SPISs must respect existing water
allocations, water quotas, water abstraction permits, and well licensing. It is
necessary to ensure the means of control (staff number and quality) and legal
provisions for illegal wells equipped with SPISs and abstraction rates higher
than allocation. It is also essential to ensure the payment of irrigation fees.

8.7.2 Subsidy leverage

Authorities have a strong role to play in controlling the sector and can use
the subsidy leverage to reinforce their position. Premiums paid by users could
support efficient water management and community systems, and subsidies
can also be made conditional on:

• a water management plan;

• a national or federal directory of solar irrigation systems, featuring GPS
coordinates, clear description of components, flowrate, and power of
the solar components;

• water abstraction permits corresponding to the water allocation of the

subsidized SPIS and the type of crops irrigated or agricultural products;
• water and energy metering;
• electronic control devices that transmit real-time information on
reservoir levels, pump flows, and water drilling;
• training of subsidy recipients on water efficiency and crop water
requirements;
• community or cooperative-owned systems based on volume delivery
since collective water abstraction tends to be more efficient than
individual water abstraction;
• different subsidy mechanisms according to the type of water source.
It should be easier for farmers to access subsidies if they withdraw surface
water (easier to monitor decreasing availability) and more difficult if
they withdraw groundwater (difficult to monitor depletion).

Policymakers could also establish a register of controllers and make the sale of
variable speed drive controllers conditional on the existence of an authorized
well and licensing.

8.7.3 Licensing suppliers of SPIS components

Governments are in charge of quality control of solar products for irrigation
and other uses. However, in some countries, commercial providers of cheap,
low-quality solar-irrigation components are entering the market without
proper licensing. Policymakers can limit this through different measures;
for instance, the Infrastructure Development Company Limited (IDCOL),
a government-owned non-bank financial institution of Bangladesh, has
developed a list of approved service providers. Another solution is to establish
working groups on solar irrigation within solar industry associations to ensure
products comply with minimum quality standards.
In addition, regulatory bodies must ensure companies manage SPIS
components at their end of life by setting up schemes for collection, repairs,
recovery, recycling, and safe disposal of SPIS products present on the market.
As an example, India started a pilot in April 2019 to define and implement a
regulatory framework to manage PV module waste (Bridge to India, 2019).

8.7.4 Integrating other uses for solar energy

Agriculture requires energy (electricity or fuel) for different uses, be it
machinery, equipment, heating, cooling, or lighting spaces, and indirectly
through fertilizers and chemicals (Schnepf, 2006). Solar energy produced in
excess of requirements for water pumping could have other on-farm uses:

• drying, milling, milking, husking, grinding, threshing, or pressing of

crops as a complementary activity when the water pump is not in use
(GIZ, 2016);

• cold storage and lighting if the system is equipped with batteries (FAO,
2018b);
• charging batteries for agricultural machinery;
• household uses (mobile charging, lighting, entertainment, water
heating, etc.).

Planning alternative electricity uses supports the valuation of produced

electricity to reduce the overuse of pumps and increase revenue streams to
invest in SPIS capital expenditure. It could also ensure optimal use of the solar
equipment and empower farmers to make rational decisions on the use of
energy and water at farm level.

8.7.5 Solar irrigation service providers

Another potential solution to reduce the challenge of financing SPISs is to
establish solar irrigation service providers (IWMI, 2018). In this scheme, small
companies have their own portable panels, pumps, and solar equipment, and
sell water to farmers for a fee. This model exists in Bangladesh, Bihar state
(India), and south of Nepal (Terai). It is aimed at replacing existing irrigation
water providers that use diesel pumps. In this case, the farmer does not
have to invest in the technology and the service provider is maximizing the
return on their pump and solar equipment, therefore reducing the payback
period of their investment. India also has a different model for grid-tied
solar pumping systems, where a cooperative is established to manage the
SPIS. This cooperative is registered as an independent power producer and
can contract a power purchase agreement with the utility based on the
negotiated feed-in tariff (FiT). Farmers are able to make informed decisions
on either watering their crops or injecting renewable energy to the grid.
They base their decisions on potential cash flow from the produced food or
from the FiT.
Solar energy has the potential to revolutionize irrigation. As such, raising
the awareness of agricultural experts and farmers on the potential and
impacts of solar irrigation is urgent, notably on water stress. Strengthening
the capacity of agricultural extension services and vocational training centres
on SPISs will lead to improved maintenance and contribute to managing the
risks of water stress.

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CHAPTER 9
Economic analysis: life-cycle cost
of different pumping technologies
Economic considerations, beyond capital costs, are essential when considering
different water pumping solutions. This chapter explains life-cycle cost analysis step
by step as a way to properly compare costs over time of different pumping technol-
ogies. This analysis is presented as a decision-making tool for implementers and
communities of users to work out the most cost-efficient way over time to supply
water. Examples and tools are given and/or referenced throughout the chapter to
facilitate understanding. Finally, different business models suited to financing solar
pumping schemes are shown.

Keywords: life cycle cost analysis, payback period, financing models for
solar pumping, lease to own, discount rates

9.1 The importance of economic considerations

Economic considerations are important when comparing alternative pumping
methods. In many cases, hydrological or climatological factors will limit the kind
of pumping system that can be used. Where equivalent performance alternatives
exist, their evaluation must include both economic and technical analysis.
Energy for water supply is, in a large number of humanitarian contexts,
partially or totally dependent on generators and fuel. Pumping of water is a
high energy-consumption activity, resulting in high recurrent costs, particu-
larly for fuel supply and maintenance of equipment. Depending on the local
setting, the provision of fuel can be extremely costly and energy-intensive.
While the capital costs for solarizing water points are normally higher
than those of other technologies, such as diesel pumping systems, it has been
established that adoption of solar energy systems translates to higher savings
with time.
The Global Solar and Water Initiative (2018) has analysed the life-cycle
economics of 160 water schemes in 55 refugee camps and communities, estab-
lishing return-on-investment periods (solar vs generator) of 0 to 4 years and
cost reductions over time ranging from 40 to 90 per cent.
These financial estimations vary from water scheme to water scheme
however. What will the capital costs be for a solar system, how quickly will
the investment be compensated by the savings produced, and how much of
the costs will be reduced over time?
These are questions that need to be answered before starting any work on
the ground in order to know how worthwhile, from the financial point of

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134 SOLAR PUMPING FOR WATER SUPPLY

view, it is to invest in solar equipment, as well as to prioritize those schemes

that produce higher savings more quickly.

9.2 Life-cycle cost analysis

9.2.1 Main concepts
The most complete approach to economic appraisal when comparing
different pumping technologies is the life-cycle cost analysis (LCCA). In this
analysis all future costs and benefits are calculated in today’s money value.
Because the value of money changes over time it would be unrealistic to add
up costs incurred in different years. Instead, those costs need to be converted
into money value at the same point in time, normally the present time.
A life-cycle cost analysis considers the following concepts.

Life-cycle costs. The sum of all costs and benefits associated with the pumping
system over its lifetime (or over a selected period of analysis), expressed in present-
day money. This is called the present worth or the net present value of the system.

Payback period. The length of time required for the initial investment to be
repaid by the benefits gained.

Total cost saving. The difference in total costs incurred between two different
investments at the end of the appraisal period.

Discount factor (also called real interest rate). An index that expresses the change in
value of money over time in a certain country for a certain product. This is
not the change due to general inflation, but the difference in return between a
chosen investment and another that is not chosen (e.g. if a lender is receiving
9 per cent from a loan and the inflation rate is 8 per cent, then the real interest
rate = nominal interest rate – real inflation rate = 9 – 8 = 1 per cent).

9.2.2 Present worth

The present worth is a calculation of all costs and benefits incurred in today’s
money value. For a payment of Cr($) to be made in the future, the present
worth (PW) is found by multiplying the payment Cr by a factor Pr:

( formula 1.1) PW 1/(1 + d)

N
=
Cr × Pr, with Pr =

with time for the payment (N, in years) and discount rate (d) as the main
variables (note: if d = 12 per cent, d = 0.12 in formula 1.1).
In an ideal situation, there would be a real interest rate difference for every
product, since the price of solar PV panels, pumps, generators, diesel, and the like
will increase or decrease over time in different ways. However, as it is difficult to
have this intimate knowledge of the national market and its price evolution for
different products it is common to apply a general discount rate to all products.
Therefore, the real interest rate is calculated by subtracting the real
inflation rate from the nominal interest rate, both taken for the country

where we are considering the investment (for more values of real interest
rates per country see World Bank, 2019.)
In the case that no information can be found for a particular country,
a good approximation to the real interest rate would be the commercial bank
lending interest rate of the country of work.
So overall the total present worth will be then,
( formula 1.2 ) Total PW ∑
N
=
I+ n=1
Cr × [(1/(1 + d)N ]

with I = initial or capital costs and Cr = all other costs incurred over time.

Example 9.1: Calculating the present worth

A bicycle is bought for US$125. After two years of use, the front wheel needs to be
changed at a cost of $15. In the third year, changing the brakes costs $10. What is the
total cost incurred to buy and maintain the bicycle in today’s money value if the real
interest rate is 12 per cent?
The costs in different years cannot simply be added together, since the value of money
changes over time. Instead, all future costs will be brought to today’s value so that they
can be added together.
Following formula 1.2,

I = $125; d = 0.12; Cr for Year 1 = 0; Cr for Year 2 = $15; Cr for Year 3 = $10

PW = 125 + 0 + 15 × [(1/(1+0.12)2] + 10 × [(1/(1+0.12)3]

= 125 + 12 + 7 = $144, in today’s value.

This formula can be added to an Excel sheet, making it easy to consider as

many costs and benefits as needed for as many years as needed (see Economic
analysis Excel tool at GLOSWI, 2018).
As explained earlier, it is also possible to consider different discount rates for
different costs. This might be useful when there is a good understanding about
price variation over time for different costs incurred. In Example 9.1, if it is known
that bicycle wheel prices are increasing while brakes are decreasing, different real
interest rates could be used in the formula for each of them in order to get the
present worth. When this is not known (as is often the case) or for the sake of
simplicity, a discount rate for the country is found and applied to all the costs, as
in the example.

9.3 Life-cycle costing for water pumping

9.3.1 Types of cost to be considered
For every pumping system for which a present worth LCCA will be carried out,
all related costs will need to be identified first. These can be generally divided
into the following four categories:

• initial capital costs (including installation);

• operation and maintenance (minor and major services and fuel);

• overhaul;
• replacement of equipment during lifetime of the water scheme.

Once the economic appraisal is done for each of the pumping technologies
that could be used for a particular water point, these will be compared in order
to establish which one offers more cost savings over time.
A rural water supply system will have five main components: water
point (drilling, fencing etc.), power source (solar, generator), pump, water
tank, and distribution system (i.e. piping system). Since the point of the
LCCA is to establish a comparison between technologies, costing elements
that are common for all the different pumping options (e.g. distribution
system, drilling, fencing, and others) can be excluded from the analysis in
order to simplify it, since they will have the same effect for the different
options.
Cost can be divided into capital and future or recurrent costs:

Capital cost. These are the costs of buying the different components of the
system, transporting them to the site, and installing them.

Future or recurrent costs. These are the operating costs (e.g. diesel), maintenance
or repair costs (e.g. replacement of parts, carrying out repairs), and replacement
costs (e.g. components that are replaced when they reach the end of their
lifetime).
Figure 9.1 describes the steps for an economic appraisal. Steps 1 to 3
have to do with the technical design of the pumping system, as explained
in Chapter 5. These steps are necessary in order to determine the different
technologies and equipment sizes that could be used for a particular
water point.
Once the possible technical designs have been established, the capital cost
of each item needs to be determined by asking suppliers, partner organiza-
tions or others for quotations. Similarly, O&M, replacement, and other costs
can be estimated through past project experience.
The data required for the last three steps (steps 4 to 6) are given in
Table 9.1.

Table 9.1 Data required for life-cycle analysis

Economic Period of analysis (typically all systems are taken to the longest lifespan of
any of the components, which is 25 years for solar panels)
Discount rate (= nominal interest rate – inflation rate)
Relative inflation rate (typically zero)
Cost of each Capital cost1
component
Annual O&M, overhaul, and replacement costs
Labour costs
Technical Lifetime of each component

Calculate Size pump Determine Get PW of Life-cycle

and different costs and unit
head of Determine capital future costs
power cost of water
system design costs for for each
sources for each
and safe month each power power
(solar, diesel,
yield source source power source
hybrid …)

Steps 1 to 3: Technical design Steps 4 to 6: Economic appraisal

Figure 9.1 Steps for technical design and economic appraisal

9.3.2 Guidance costs and values

In case the manufacturer does not state lifetime information clearly on their
datasheets, the following can be used as a guide as to when different system
components will likely need to be replaced, based on good-quality products in
compliance with manufacturing certifications:

• solar panels: 25 years;

• pump ends and motor: 10 and 7 years respectively;
• inverter / control equipment: 7 years;
• civil structure and frames: 25 years;
• mechanical and electrical fittings: 25 years.

Similarly, for diesel generators, where field information is not available

regarding replacement frequency and costs, Table 9.2 provided by a good-
quality generator manufacturer (and considered from experience as a conser-
vative estimate) can be used as a reference.
Finally, fuel consumption for a generator will need to be established in
order to estimate running costs. Again, the best way to get this data is from
previous field experience. Where this is not available, Table 9.3, provided by a
good-quality generator manufacturer, can be referred to.
Once the LCCA is performed between diesel, solar, and any other pumping
option being considered, a choice will have to be made. Of course, the least
cost solution may not be the final choice once other factors are taken into
account; reliability or ease of maintaining equipment, for example, could be
the most important considerations and users may be prepared to pay the extra
cost. However, as said earlier, a cost comparison is a necessary step before
making a choice of technology.

Table 9.2 Estimated cost for maintenance of a good-quality diesel generator

Maintenance Frequency of change Price
and replacement (in working hours of generator) (US$)
Minor service 250 20
Major service 1,000 180
Overhaul 10,000 30 per cent of new generator
Replacement 35,000 Buy new generator

Table 9.3 Estimated generator fuel consumption at different loads

Generator fuel consumption chart – average for good quality engines
kVA kW Load 25% Load 50% Load 75% Load 100%
25 20 2.3 3.4 4.9 6.0
38 30 4.2 6.8 9.1 11.0
50 40 6.0 8.7 12.1 15.1
75 60 6.8 11.0 14.4 18.1
94 75 9.1 12.9 17.4 23.1
125 100 9.8 15.5 21.9 28.0
156 125 11.7 18.9 26.8 34.4
169 135 12.5 20.4 28.7 37.0
188 150 13.6 22.3 31.8 41.2
219 175 15.5 25.7 36.7 48.0
250 200 17.1 29.1 41.6 54.4

Note: A quick rule of thumb for estimating fuel consumption is 0.3–0.5 litres per kWh
consumed at pump level.
Source: Genset

9.4 Comparing LCCA of solar and generator systems

9.4.1 Stand-alone generator vs stand-alone solar system: a worked example
A new borehole is drilled and it is calculated that a diesel generator of 15 kVA
with a pump of 5.5 kW could supply the daily water needed. However, a solar
system of 11 kWp of solar panels working with the same pump could supply
the same amount of water.
A present worth life-cycle cost analysis is performed in order to determine
the most cost-efficient option. In order to simplify the analysis, costs that
are common to both systems are not considered (e.g. the cost of replacing the
water pump, cost of fencing the water point, cost of water point guards).
The cost of buying and installing the generator-powered pumping system is
$8,450. The generator should work seven hours a day in order to provide the
water needed; the costs of operating and maintaining the generator are taken
from Table 9.2. The cost of 1 litre of diesel is $1.10 while the discount rate for
the country where the system is to be installed is 12 per cent (d = 0.12).
All the associated costs are added up and multiplied by the corresponding Pr
factor for each year. The Pr factor expresses not only the increase of price due
to inflation, but measures the weight in our budget for paying costs now and
in the future. A high discount rate (d) would mean that costs in the first years
will weigh more in the budget than future costs, and vice versa. The LCCA for
the scheme with a diesel generator is given in Table 9.4.
The capital cost of the solar pumping system is given in Table 9.5.
Repeating the analysis for the solar option, where no fuel is used, the only
replacement to be done is that of the inverter/control box, every seven years

Table 9.4 LCCA for the given water scheme with a diesel generator
Year Capital Gene- Minor Major Fuel Cost Overhaul Replace- Pr = Total
(N) cost of rator service service consum- of fuel 30% ment New 1/(1+d)N costs in
gene- working $20 $180 ption ($) generator genset present
rator time every every (litres/h) cost every every worth
system (h/year) 250 h 1,000 h 10,000 h 35,000 h ($)
($) ($) ($)
0 8,450 2,555 204 460 3.5 9,837 1.000 18,951
1 2,555 204 460 9,837 0 0 0.893 9,376
2 2,555 204 460 9,837 0 0 0.797 8,371
3 2,555 204 460 9,837 1,350 0 0.712 8,435
4 2,555 204 460 9,837 0 0 0.636 6,674
5 2,555 204 460 9,837 0 0 0.567 5,959
6 2,555 204 460 9,837 0 0 0.507 5,320
7 2,555 204 460 9,837 1,350 0 0.452 5,361
8 2,555 204 460 9,837 0 0 0.404 4,241
9 2,555 204 460 9,837 0 0 0.361 3,787
10 2,555 204 460 9,837 0 0 0.322 3,381
11 2,555 204 460 9,837 1,350 0 0.287 3,407
12 2,555 204 460 9,837 0 0 0.257 2,695
13 2,555 204 460 9,837 0 4,500 0.229 3,438
14 2,555 204 460 9,837 0 0 0.205 2,149
15 2,555 204 460 9,837 0 0 0.183 1,919
16 2,555 204 460 9,837 0 0 0.163 1,713
17 2,555 204 460 9,837 1,350 0 0.146 1,726
18 2,555 204 460 9,837 0 0 0.130 1,366
19 2,555 204 460 9,837 0 0 0.116 1,219
20 2,555 204 460 9,837 0 0 0.104 1,089
21 2,555 204 460 9,837 1,350 0 0.093 1,097
22 2,555 204 460 9,837 0 0 0.083 868
23 2,555 204 460 9,837 0 0 0.074 775
24 2,555 204 460 9,837 0 0 0.066 692
Total cost in present worth $104,007

as standard lifetime. An additional annual cost of $1,500 is included to cater

for the cost of preventive maintenance, regular cleaning of the solar panels,
and any small repairs that may be needed over time. The LCCA for a solar
scheme is given in Table 9.6.
Additional costs that need to be factored in can be added in a new column
with the analysis proceeding in the same way. Remember, this is a comparison
between technologies and therefore costs that are similar to both solutions
(e.g. salary of the water point operator) can be disregarded in order to simplify
the analysis.

Table 9.5 Capital cost of the main components of the given solar PV pumping system
Component Unit Quantity Unit price ($) Total price ($)
Pump W 5,500 0.58 3,200
Inverter W 5,500 0.33 1,800
Solar modules W 11,000 0.80 8,800
DC accessories W 11,000 0.12 1,320
Cables and low-level sensors m 60 7.00 420
PVC pipes and wellhead cover m 90 5.00 450
Support structure W 11,000 0.35 3,850
Subtotal 19,840
Add 10% for installation 1,984
Total 21,824

Table 9.6 LCCA for the given water scheme with a solar PV pumping system
Year Capital Preventive Major Fuel Cost Overhaul Replace- Pr = Total
(N) cost ($) and minor service consum- of ($) ment cost 1/(1+d)N costs in
service NA ption fuel Change present
and (litres/h) ($) invertor worth
cleaning every 7 ($)
($) years ($)
0 21,824 1,500 0 0 0 1.000 23,324
1 1,500 0 0 0.893 1,339
2 1,500 0 0 0.797 1,196
3 1,500 0 0 0.712 1,068
4 1,500 0 0 0.636 953
5 1,500 0 0 0.567 851
6 1,500 0 0 1,800 0.507 1,672
7 1,500 0 0 0.452 679
8 1,500 0 0 0.404 606
9 1,500 0 0 0.361 541
10 1,500 0 0 0.322 483
11 1,500 0 0 0.287 431
12 1,500 0 0 0.257 385
13 1,500 0 0 1,800 0.229 756
14 1,500 0 0 0.205 307
15 1,500 0 0 0.183 274
16 1,500 0 0 0.163 245
17 1,500 0 0 0.146 218

Year Capital Preventive Major Fuel Cost Overhaul Replace- Pr = Total

(N) cost ($) and minor service consum- of ($) ment cost 1/(1+d)N costs in
service NA ption fuel Change present
and (litres/h) ($) invertor worth
cleaning every 7 ($)
($) years ($)
18 1,500 0 0 0.130 195
19 1,500 0 0 0.116 174
20 1,500 0 0 0.104 156
21 1,500 0 0 1,800 0.093 305
22 1,500 0 0 0.083 124
23 1,500 0 0 0.074 111
24 1,500 0 0 0.066 99
Total cost in present worth 36,492

Figure 9.2 plots the cumulative costs for both systems. As shown, there is a
considerable cost reduction over the lifetime of the equipment (65 per cent)
when the generator is replaced by a solar solution at that particular water
point. It is also common to look at shorter periods of time when considering

$120,000
Cumulative costs solar vs diesel gnerator

$100,000

Break-even Total cost saving

$80,000
period, 65% OR 67,515 USD
1.5 years

$60,000
Cost saving after 10 years,
58% OR 44,247 USD
$40,000

$20,000 Cost saving after 5 years,

46% OR 23,927 USD

$0
Capital costs
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25

Generator
Solar

Figure 9.2 Comparison over time of costs for solar vs generator

solar investment. Figure 9.2 shows that savings incurred grow quickly and in
year 5 they are already 46 per cent.
Since there are a number of variable factors (e.g. working hours of
generator, size of the systems, daily water requirements) and there may be
a wide difference in terms of potential cost savings and break-even periods
among the different water schemes in the same area of work, it is always useful
to perform a similar LCCA for all water points to prioritize intervention in
contexts where funding is limited. Table 9.7, compiled during a visit by the
authors to South Sudan illustrates these variations, with a wide range in cost
savings and break-even periods.
In addition, it is not uncommon to find break-even points of solar compared
to diesel generators of one year or less, making the investment worthwhile
even for donors with narrow funding windows. Another point to bear in mind
and not considered in the analysis
Although not quantified in economic is that, in many contexts, diesel is
analysis, solarizing boreholes minimizes considered a commodity and therefore
or eliminates the cost linked to diesel theft is widespread during transport and
theft, a widespread problem in many storage, a problem that is minimized
humanitarian contexts.
or eliminated through the adoption of
stand-alone solar solutions.
A final consideration is that the more remote the water point is,
the more expensive it will be to transport fuel, increasing the cost of
running a generator, while solar costs would remain more or less the same
over time.

9.4.2 Stand-alone generator vs hybrid (solar and generator) systems

As discussed in other chapters, sometimes a stand-alone solar system
cannot provide the total daily water required. It may then be necessary
to consider either a stand-alone generator or a hybrid system that would
be solar powered during the solar day and powered by generator for some
night hours.
In order to find which of these two options is more cost-effective, an
LCCA can be performed, calculating on one side the cost over time of
pumping all the water required with a stand-alone generator and, on the
other, the cost of pumping during the solar day with a solar system plus
the cost of using a generator for some additional hours to provide all the
water required.
If for any reason a diesel generator cannot be considered (e.g. difficult to
transport diesel to the site because of security reasons, or bad roads) and a
stand-alone solar system cannot provide all the water needed, drilling a second
borehole equipped with solar panels could be considered.
In Figure 9.3 the three options are considered for a refugee camp in
Tanzania in 2016. Normally, a diesel-free option will be more cost-effective in
the medium and long term.

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Table 9.7 Cost comparison between existing generator stand-alone systems in South Sudan and equivalent solar or hybrid systems
Site details Water output Economic/life cycle analysis
Generator stand Solar stand alone Hybrid/Solar - Diesel

Copyright practicalactionpublishing.com
alone or Hybrid Comparison
No. Camp BH ID Managing Average daily Daily output Daily Initial Cost over Initial Cost over Reduction Break-even
agency output of of proposed output of cost life cycle cost life cycle of expenses point
prposed solar generator to current (USD) (USD) (USD) (USD) hybrid/solar
(m3/day) work with generator vs Genset
solar, m3/d (m3/day)

1 Bentiu Sector 1 Mercy 71.1 56.1 127.2 $10,013 $357,425 $12,858 $238,688 −33% 0.7 years
Block 7 Corps
2 Bentiu Sector 2 IOM 120.0 0.0 120.0 $12,468 $371,939 $30,767 $194,943 −48% 1.6 years
Block 9
3 Bentiu Sector 3 Concern 151.1 146.0 297.1 $18,895 $660,400 $22,696 $467,750 −29% 1.2 years
Block 1 Worldwide
4 Ajuong Market Samaritan 72.0 0.0 72.0 $17,200 $272,981 $21,500 $34,515 −87% 0.2 years
Thok Purse
ECONOMIC ANALYSIS: LIFE-CYCLE COST OF DIFFERENT PUMPING
143
144 SOLAR PUMPING FOR WATER SUPPLY

1,400,000

1,200,000

1,000,000
Cost- in USD

800,000

600,000

400,000

200,000

0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
Years
Diesel generator Hybrid (Solar + generator)
100 per cent Solar (2 boreholes)

Figure 9.3 LCCA of stand-alone generator vs hybrid vs solar at Nyarugusu, Tanzania

9.5 Cost of ownership

Different business models can be adopted to finance solar-powered water
projects making them affordable to more people and therefore accessible
(see Figure 9.4).

9.5.1 Direct cash or financed purchase

The organization in charge hires a contractor to design, procure, and install
the system. Costs are paid at once in cash; a financing partner may be

Upfront sales Direct cash

Perpetual Lease-to-own
Rental with financing sales
lease
partner

Consumer Consumer
buys a buys a
service product

Figure 9.4 Business models for financing solar-powered water systems

involved if cash is only partially available. Once installed, the ownership

and management remains with the organization in charge or is transferred
to the users or local government entity. Any of those stakeholders can take
in hand the operation and maintenance of the system or outsource it to a
third party for a fee.

9.5.2 Upfront sales with financing partner

The organization in charge partners with a financial entity that provides
funds to interested partners to build a solar scheme; these funds can then be
reimbursed in a pre-negotiated way so that the burden of upfront costs are
eased for all parties involved.

9.5.3 Lease to own

The organization in charge leases (or rents out) the solar pumping system
from a solar service company and pays a monthly fee. The solar service
company will finance design, installation, and operation and maintenance
of the system. The ownership of the system is transferred to the organization
in charge when the lease ends, which can then outsource the operations and
maintenance of the system for a fee. Typically lease agreements can last from
two to three years up to ten years.

9.5.4 Perpetual lease or power (or water) purchase agreement

The organization in charge buys solar energy (or water) and pays a monthly
bill. A power purchase agreement (PPA) will cover only the energy generated
(or water pumped) by the solar system. The solar service company will finance
design, installation, and operation and maintenance of the system. At the end
of the PPA, the organization can renew or cancel the agreement with the solar
service company remaining as the owner of the equipment in any case. PPAs
can last from two to three years up to ten years.

9.5.5 Rental
The organization in charge rents the equipment from a solar service company
for a fixed monthly amount. The solar service company will finance design,
installation, and possibly operation and maintenance of the system. At the
end of the rental period agreement the organization can renew or cancel
the agreement with the solar service company remaining the owner of the
equipment in any case.

Copyright practicalactionpublishing.com
Copyright practicalactionpublishing.com
CHAPTER 10
Calls for proposal and bidding
Quality considerations in the selection of solar components are critical to achieve
the water outputs expected. Manufacturing certification criteria are the best way to
ensure quality components are selected. This chapter also describes other aspects
of solar pumping purchasing and bidding, including warranty, deliverables, and
tender evaluation. A template for solar pumping bidding is provided. In addition, the
chapter explains the procedures and tools available online to ensure manufacturing
certification conformity.

Keywords: solar quality performance, IEC/EN 61215 and 61730, solar bidding,
linear performance warranty, solar pumping toolkit, certification database,
supplier selection, solar product authenticity

10.1 Selection criteria for solar pumping products and services

Quality is a key criterion in equipment selection and can be defined as the
ability of a product or service to consistently fulfil defined requirements over
a defined period. Quality is an integral part of a product or service and should
be a key consideration in solar pumping equipment selection.
Selection of products of dubious quality (especially related to solar
modules) may result in declining performance of the pumping system that
may erroneously cast doubt over the overall suitability and sustainability of
the project. On the other hand, carefully selected quality products will ensure
value for money while contributing to the sustainability of the project.
Some dimensions of product quality that should be considered to establish
the desired characteristics of a solar water pumping system are described in
Box 10.1.

10.2 Desired features of key components

Table 10.1 summarizes the key minimum or desirable characteristics of solar
pumping equipment.
All equipment should be inspected in the supplier’s warehouse before
delivery onsite to identify and eliminate poor-quality and damaged goods.
They should also be inspected and verified on delivery to site. The authen-
ticity of the product should also be checked by looking at equipment serial
numbers and certifications and sending these to the original manufacturer for
verification. Solar modules can be verified on certificate databases, discussed
in section 10.6.

http://dx.doi.org/10.3362/9781780447810.010
Copyright practicalactionpublishing.com
148 SOLAR PUMPING FOR WATER SUPPLY

Durable

Robust

Reliable

Figure 10.1 Quality of solar panels matters

Box 10.1 Dimensions of product quality

Performance The selected product must meet the specified water demand and
head during the design month, which can be the month with the
least irradiation, the driest month etc. The design provided by the
bidders should show the monthly pumped outputs in line with the duty
requirements.
Efficiency Efficiency defines the amount of water that will be pumped with the
available power and it impacts the cost of ownership. The payback
period for the solar system with the expected cost savings over the
life cycle of the system will be a differentiating factor of systems with
similar performance. With an efficient system you either spend less
for the same amount of water or get more water from the same power
source. (see more at Lorentz, 2020a).
Reliability The desired product should not fail within a specific period. Evidence
that the product has worked in the past without failure from field
examples will be a good indicator of reliability. References provided
by the supplier and actual site visits will confirm this. Manufacturer
warranty is also a display of manufacturer confidence in the reliability of
the product.
Conformity The product should meet the specified standards of quality and
safety such as IEC/EN certifications, UL/MET listing, or other local
and internationally recognized standards. The supplier should provide
verifiable certificates of conformity.
Durability Different components will be able able to exist for a long time
without significant deterioration. Solar modules will be typically
warrantied for 25 years. Quality pumps and controllers have 7 to
10 year life span.

Robustness The system should be designed for use in remote locations without
failure. The particular environment the system will be installed in should
be accommodated for at the design stage, e.g. an enclosure rating for
high temperature conditions, or coastal salt mist conditions. Attention
should be paid to the specifications given by the supplier.
Serviceability All components should be subject to minimal servicing and without
expensive parts. Parts should only need to be replaced infrequently to
reduce replacement costs. The expected time and skill level required for
replacement of parts should be such that downtime is reduced.
Aesthetics Even though it has no bearing on performance, the installed system
should be pleasing to the eye as this can enhance community acceptance.

Table 10.1 Minimum recommended characteristics of solar components

Criteria Equipment characteristics
Solar module Pump and motor Controller
Performance PV modules to Positive displacement or Maximum power point
meet the power centrifugal pumps tracking and current
demand of the boosting function
Variable-speed induction
pump
motor that can overcome Rated to meet the
harmonics (motor current, voltage, and
insulation PE2/PA) power demand of the
pump
Duty point of the pumping
system should meet the
requirement
Efficiency >14 per cent Motor: >80 per cent >95 per cent

Reliability Prior successful Used previously in other Used previously in

off-grid use sites without failure other sites without
failure
Conformity IEC/EN 61215 IEC/EN 809, 60034-1, IEC/EN 61800-1,
& 61730 for 62253, 61702 61800-3, 60204-
crystalline 1, 61683, 62109,
ISO certifications
modules 62093

IEC 61646 for ISO certifications

thin-film PV
modules

UL 1703 listed

IEC/EN 61701
(for coastal areas)
Durability 25 year 7 years for motor 7 years
performance
10 years for pump
guarantee

20 year product
warranty

(Continued)

Table 10.1 Continued

Robustness Quality Constructed of non- Environmental
encapsulation corrodible material, such protection of IP54 or
as stainless steel (AISI higher
Do not break 304 or higher)
easily Closely matched to
Permanently lubricated actual conditions
Sturdy frame (e.g. ambient
Closely matched to temperature, humidity,
groundwater temperature air salinity, altitude)
and water quality
Serviceability Terminal/junction Modular design i.e. Preferably keep
box on the detachable pump and electronics above
module should motor ground (not
have a provision submerged)
Maintenance free where
for ‘opening’ for
possible (e.g. brushless Low replacement cost
replacing the
motors) for spare parts
cable, if required
Low frequency of repair

10.3 Supplier selection

Besides products, selecting a good supplier is critical to having a sustainable
solar-powered water system. The right supplier will not only provide the
right product but also provide sound installation and workmanship as well
as after-sales support, which will contribute to system longevity. Some criteria
that may be applied in selecting a good supplier are presented in Box 10.2.

Box 10.2 Criteria for supplier selection

Product quality Operate a quality management system that is ISO 9000 or

equivalent and have recognized third-party verification. Have UL/
MET listed products for supply
Delivery Reliable supplier that can deliver within the required time frame
Experience Relevant experience of designing, installing, and maintaining solar
pumping solutions of a similar size, scope, and application
Reputation Good international standing in the industry. Provide references from
previous customers and peers
Capacity Staff, tools, and equipment to satisfactorily execute the project
Technical Certified trained staff who can successfully install the system and
capability service the project
Warranty and after- Policies that support post-installation replacements and repairs.
sales service Must have access to spare parts supply with backing from the
equipment manufacturer
Training Certified trained staff who can provide training to the organization,
operators, and users

Potential suppliers should be visited to gauge the quality and quantity of

the products they stock, to discuss their delivery lead times for non-stock
items, and to gauge their overall capability and capacity to deliver the project
in a timely manner. It is also advisable to get in touch with their referees and,
where possible, visit project sites that they have implemented previously as all
this will reveal unscrupulous suppliers.

10.4 Bidding process

Most SPWS projects will require multiple bidders to bid before a contract
is awarded. Usually, potential bidders will be asked to submit a proposal
according to the requirements set out on a bidding document. The bidding
document will state the statutory legal requirements, financial require-
ments, and technical requirements. This section focuses on bidding for the
technical side.
There are two approaches to carrying out the technical bidding process.

1. One involves the buying organization carrying out the technical

design of the project and issuing bidders with a list of preferred
equipment to be supplied, including brands/models (or equivalents),
specific equipment sizes, power ratings, and quantities. This approach
is simple and allows supplier selection to be done quickly, though it
should be used only where the organization’s technical expertise is
good enough to do the design and to properly evaluate bids, or where
an experienced consultant or private contractor can be engaged to carry
out the design. This approach is especially useful when procurement
needs to be done speedily, such as in emergency response situations
where water supply systems need to be installed within the shortest
time. The emergency kits mentioned in section 7.4 can be used for
such emergency contexts (a full list of equipment required for each
kit is provided at GLOSWI, 2018e).
2. The second approach involves the organization providing information
about the project, location, water demand, and other requirements, and
asking bidders to submit proposals (including solar scheme designs) to
meet those requirements. This approach may result in a lengthy, tedious,
and complex process of filtering through the different proposals to
identify the ones that match the requirements. The clearer the require-
ments are explained and the more accurate the data provided is, the
easier and fairer the bidder selection process will be. The bidder that
provides a proposal which most closely matches the requirements is
selected. This approach also requires the organization to have some
reasonable level of technical expertise to be able to evaluate the different
proposals, but less so than in the first case.

Internal procurement guidelines will also dictate which approach is

acceptable. For example, some organizations require that equipment brands

are not mentioned in the request for proposal which can hinder the first
approach, although care can be taken to comply with such rules while still
providing a full list of the required equipment.
The bidding template in section 10.5 is a guideline on using the second
approach, where bidders are asked to provide proposals in response to the
provided requirements.

Box 10.3 A reference guide for the SPWS procurement process

The bidding process can be complex and difficult, which, if not well managed, can result
in project delays and unsatisfactory delivery of the project. The World Bank document
‘Photovoltaics for Community Service Facilities’ highlights common issues encountered in
the procurement process and how to address them (World Bank, 2010). This document
should be referred to during the procurement process for SPWS projects.

10.5 Bidding template: technical terms of reference

The terms of reference for the technical requirements of a bid are outlined here.

10.5.1 General information

Location. Location is a critical requirement when an SWPS is being designed
as it is the basis for having the correct solar resources data, such as irradiation,
peak sun hours, and temperature. The location should be provided in the form
of GPS coordinates.

Background information. This section should give the bidders background

information on the project. It lays out the context of the project so that
bidders can conceptualize the needs, the current situation, the requirements
of the proposed project, and the targeted achievements.

Objectives. The objectives of the project should be clearly laid down here, for
example, ‘the project aims to provide a power system for water pumping in
order to maximize the reduction of diesel fuel demand by pumping as much
water as possible through a solar pumping solution’.

System planning and design. Information on system planning and design

should be provided, such as what design tools should be used, the design
factors to be applied (e.g. losses factored into the design), whether a cost–
benefit analysis is required with the proposal, and whether datasheets are
required to be submitted with the proposal.

10.5.2 Project information

Scope of work. The scope of work description entails delivery schedule,
installation, and commissioning guidelines. It should state in detail what is

expected of the supplier, from what the extent of the work will be to what
will constitute a completed installation. Details such as workmanship,
training, documentation, and lifetime requirements need to be clearly
explained.

Water requirements. Water demand requirements will be specified, stating the

design approach to be used, such as the worst month method discussed in
section 5.3.3.

Water source. The water source and other environmental factors should be
well detailed such that the bidder has the complete information required for
a sound system design. This includes water-source characteristics and site
information, such as distances and tank size.

Other design parameters. Hours of operation and water collection patterns,

among other things, are useful for the design process.

System configuration. The bid should provide the configuration design of the
system, such as stand-alone solar or hybrid solar–diesel.
A schematic layout of the site can also be provided, such as the one shown
in Figure 10.2.

Tank height

Riser, pipeline
Well to tank
diameter
elevation
Cable length Riser, pipeline length

Dynamic
water level Static level

Drawdown

Drop pipe diameter Pump intake

depth

Well diameter
Depth of well

Figure 10.2 Example of a solar-powered water system layout provided to bidders

As a minimum, the information about the project listed in Table 5.1 must
be provided for a comprehensive technical design to be carried out.

10.5.3 Equipment specifications

Servicing requirements. The bidders should be asked to state clearly the
servicing requirements of the equipment proposed, i.e. the service intervals,
cost of parts, time required for replacement, and skill level required for
such service.

Spare parts requirements. The bidders should be asked to list the spare parts
required, frequency of replacement, and how readily available these parts are.

User friendliness. The equipment must be user friendly for ease of operation
and fault finding.

Solar PV modules. The selection of PV modules needs to be given critical attention

due to the market proliferation of modules of poorer quality in recent years.
Selecting a quality module can only be achieved by meeting the criteria discussed
in sections 10.2 and 10.6. The quality requirements for the modules should be
provided to the bidders, who are then expected to clearly and in a detailed
manner provide a statement of conformity to the quality criteria. Module
power rating can also be included. Protection provisions against theft should
also be requested, such as permanent marking on the back of the module.

System protection. Include requirements for protection against dry running,

surge protection, lightning protection, cable protection, and so on in the
equipment specifications.

Control equipment. The equipment controller is the heart of any solar pumping
system and should be carefully selected to suit the application. This can
be achieved by clearly defining the controller requirements, such as power
conversion from DC to AC, efficiency, display interface, quality standards,
control inputs, protection features, data logging for remote monitoring,
servicing requirements, and environmental protection.

Ancillary control. This is required for a professional installation, such as

disconnection switches, combiner boxes, and junction boxes.

Electric pump and motor. Specifications for the required pump will be provided
here, such as pump type (AC vs DC, submersible vs surface), pump design
(helical vs centrifugal), motor features, pump construction, motor construction,
variable-frequency requirements (e.g. PE2/PA motors), efficiency, and quality
standards, as stated in section 10.2.

Module support structure. Bidders should be asked to either provide a support

structure according to the specifications set out in the bid or to design a
support structure that is suitable for the conditions set out in the bid. Bidders
will be expected to submit a drawing showing the various sections of the
support structure. Provisions for anti-theft/vandalism should be stated.

10.5.4 Warranty, defects liability, service, and maintenance

Warranty and defects liability period. The bidder should be required to state as
part of the technical proposal the warranty period and defects liability period
(DLP), repairs/replacement covered by the warranty, and the extent and terms
of the warranty.

After-sales support. The support expected after installation should be stated

and bidders encouraged to give explicit details and commitment to providing
such support in case the scheme develops a problem.

Service proposal. The bidders can be requested to provide a priced proposal

with their bid for a two-year service agreement after expiry of the warranty
and DLP.
The bidder should also detail as part of the technical proposal their avail-
ability and capacity to provide backup support from within the country,
preferably through their physical presence in the country.
More of this is discussed in section 11.2.4.

10.5.5 Deliverables
This section defines what constitutes the indicators of project completion,
which could include: a signed goods received note provided by the supplier;
signed test certificate; delivery, installation, and commissioning report to the
contracting agency and users; and/or a training report.

10.5.6 Bidder qualification

The criteria listed in section 10.3 should be provided to the bidders so they
are aware of the requirements for qualifying as a bidder, including reputation,
experience, and capacity.

10.5.7 Evaluation of tender and other considerations

Evaluation criteria. The evaluation criteria for the bids should be provided
here. This will help the bidders in knowing how they will be scored so that
they can provide complete and comprehensive bids meeting all requirements.
Those who cannot meet these requirements will not submit a bid, saving time
and effort for both parties.

Activity timeline. The activity timeline is useful for bidders to know whether
they can work within the timelines given and to plan properly, thus ensuring
timely delivery of the project. The bidders should also be asked to provide a
work plan that fits within the stated timelines.

Obligations. The obligations of both the buying organization and the

bidding organization (selected contractor) should be clearly stated, including
information such as provision of site access, site handover, payment obligations,
contract signing, ethical standards, logistics, delivery, and reporting.

Submission of bid. Submission guidelines should be provided to the bidders

indicating the closing day and time of the tender, the submission means
(email, tender box, etc.), and any other requirements, such as separation of
technical and financial proposals.

Annexes. Under the annexes, documents to be attached include technical

evaluation checklist, deliverables checklist, any technical drawings such as the
module support structure, and a list of all equipment that should be supplied
(if applicable).
A sample terms of reference document can be accessed on the Global
WASH cluster under the Solar Pumping Toolkit (GLOSWI, 2018f). This sample
document is provided as a simple guide that can be used to quickly and easily
tailor a tender document for the specific context.

10.6 Quality of solar modules

Conformity to specified standards is one of the first, obvious indicators of
quality of system components.
The quality of solar modules is worth special consideration as people often
do not know how to make a choice between different modules due to so many
different types being available. Besides that, many markets in developing countries
are flooded with cheap, low-quality modules that are difficult to distinguish with
the naked eye. Differentiating a good-quality module from a bad one is indeed
difficult, yet module quality has a huge impact on system sustainability. Following
is some guidance for choosing a module of good quality and performance.

10.6.1 Checking conformity and authenticity

As mentioned in section 10.2, certification is an important indicator of
module quality. Certification to IEC/EN 61215, IEC/EN 61730 (for crystalline
modules), IEC/EN 61646 (for thin-film modules) and UL 1703 is mandatory
for any module to be considered a quality module. Modules that meet these
standards provide a better assurance of prolonged life.
Optional standards can also be considered depending on the actual conditions
the modules will be installed in, for example, IEC/EN 61701 is required for
modules that will be used in coastal areas. This is an indicator that the module
will be able to withstand the salty mist conditions of coastal installations.
Certifications are either marked on the module nameplate or on the module
datasheet. Modules that are not marked with certification numbers introduce
uncertainty as to their quality and genuineness.
Bidders should be asked to provide module certification identification
numbers corresponding to the quoted certifications, whose genuineness can
be verified on certification databases, with the applicable database depending
on the certifying organization. The authenticity of the panel brand (and
therefore its quality) should be called into question when bidders are unable
to provide such certification identification numbers.

For example, in Figure 6.1, the SolarWorld module is certified to IEC 61215
and IEC 61730, traceable to TÜV Rheinland (the certifiying agencies for this
case). The applicable database to check the authenticity of this certification is
TÜV Rheinland.
A few certifying bodies and their validity-checking databases are:

• TÜV Rheinland; https://www.certipedia.com/

• TÜV SÜD Group; https://www.tuvsud.com/en/services/product-
certification/ps-cert
• TÜV Rheinland; - DIN CERTCO; https://www.dincertco.tuv.com/?locale=en
• TÜV NORD; https://www.tuev-nord.de/en/company/certification/
certificate-database/
• VDE Institute; https://www2.vde.com/en/Institute/OnlineService/VDE-
approved-products/Pages/Online-Search.aspx

On some of these databases the certification can be searched using the

company or product name.

Checking certification using company module name. Referring to the SolarWorld

module in Figure 6.1:

1. Identify the certifying organization from the module datasheet. In this

case the certifying organization is TÜV Rheinland.
2. Go to the certification database corresponding to the certifying organi-
zation. In this case it is <https://www.certipedia.com/>.
3. Enter the name of the module brand or the name of the manufacturer
(e.g. SolarWorld) and click the ‘Start Search’ tab.
4. The displayed results show the SolarWorld products, including modules
that are certified by TÜV Rheinland.

Checking certification using certificate number. Trinasolar is a global solar module

manufacturer. On its website are listed the different types and sizes of solar
module that it makes. The datasheet for Allmax multicrystalline module 265–
285 W indicates that it is IEC 61215 and IEC 61730 certified.

1. Identify the certifying organization from the module datasheet. In this

case the certifying organization is TÜV Rheinland.

2. Identify the certification certificate ID number from the module. In this

case the certificate ID is 0000024632.

3. Go to the certification database corresponding to the certifying organi-

zation: in this case it is <https://www.certipedia.com/>.
4. Enter the certification ID number and click the ‘Start Search’ tab.
5. The displayed results show that the certification is genuine and lists all
the certified products so that the particular certified product (model
type) can be verified.

A lack of proper import controls in many developing countries has

led to the flooding of markets with low-quality products and the entry
of counterfeit modules. To counter this some world-leading manufac-
turers mark each solar module with a serial number that can be found
on a sticker inside the glass of the PV module. At procurement point the
serial number can be emailed to the original manufacturer for verification
of the module as a genuine product from their factory. Serial numbers
help to reveal counterfeits that come marked with fake stickers of leading
brands.
Panels without proper manufacturing certifications with their corre-
sponding ID number should be avoided.

10.6.2 Additional evaluation of solar module quality and performance

Additional criteria for evaluating the quality and performance of a solar
module include:

Power rating. The higher the power rating of a module, the higher the power
it will generate. This criterion can be used to compare different module sizes
on offer.

Efficiency. A module with higher efficiency can produce more power

than a similar module with lower efficiency. This criterion is particularly
useful for comparing modules of the same type and size, for example,
two polycrystalline modules of the same power rating but with different
efficiencies.

Power tolerance. This is an indicator of how much the power output from a
module in operation will differ from the power indicated on the nameplate.
It is typically expressed as a plus or minus percentage. For example,
a 300 Wp module with tolerance of ±5
Box 10.4 Checking module quality
per cent means it has a power output
range of 285–315 W under STC. As a
• Certification selection criterion, a smaller tolerance
• Power Rating
• Efficiency
range is preferable as it represents a
• Power tolerance lower deviation from the actual and
• Temperature coefficient gives a higher certainty of getting the
actual output.

Temperature coefficient. The effect of cell temperature on the power output

of the module is discussed in sections 2.10, 4.2 and 7.8.1. The temperature
coefficient quantifies how the output from a module decreases per unit
increase in cell temperature above the STC temperature of 25°C. It is
expressed as a percentage having different values for power, voltage, and
current. For example, a 300 Wp module with a temperature coefficient for
power of –0.45 per cent/°C means for every unit increase in cell temperature
above 25°C, the power output from the module reduces by 1.35 W. Modules
with lower temperature coefficients are preferable because they translate
into less power loss at higher temperatures.

10.7 Practical aspects of equipment and supplier selection

Many implementing agencies and organizations use limited donor funds
to implement solar pumping projects. There will be a tendency to want
to minimize the procurement costs often at the expense of quality. This is
further exacerbated by institutional procurement procedures which require
that consideration be given to the price, such that the award is given to
the lowest bidder. Often engineers abdicate the responsibility of equipment
selection to the procurement department which is likely not familiar with the
technical aspects of the product. They will therefore give preference to price

over technical specifications under the assumption that the products are
similar in specification. It is advised that engineers oversee the technical
selection of products, giving priority
to quality over price. The choice of equipment should not
Private-sector contractors/suppliers be left to procurement personnel without
are often constrained to provide satis- a technical review from knowledgeable
factory support when they bid at the engineers.
lowest price point. While cut-throat
competition has the benefit of introducing competitive prices and challenging
monopolies, it could also lead to declining service levels that could compromise
longevity and sustainability. This is to say that initial price should not be the
sole determinant of a suitable supplier, but the support that will be provided
thereafter should be used to differentiate between several suppliers. This support
will likely come at a higher price. Suffice to say, goodwill as well as long-term
relationships between the buyer and supplier are important for guarantee of
quality and long-term support.
Another occurrence that has been observed is the direct engagement
of foreign-based suppliers/manufacturers without a physical presence in
the country of implementation to install the SPWS at field level. While
this works at the installation stage it will usually not work in the long
run. This is due to the unreachability of these suppliers in case a problem
is encountered and the high costs in terms of time and money to send
parts and knowledgeable technicians from abroad. Installations have been
encountered that have taken months to repair, or have been abandoned
altogether due to the unavailability of parts and lack of support from
the international supplier. Commonly, these international suppliers will
be brought in due to bilateral agreements between governments and
while such engagements cannot always be avoided, measures can still be

Low price Low quality Premium Good

price quality

No support After sales Quality

support service
Figure 10.3 Cheap will become expensive with time

introduced to have local dealers, spare parts, and technicians in place for
the future.
Finally, a single supplier policy should be favoured as opposed to buying
different components from different suppliers. Besides it being easier to
manage a single supplier it will add confidence to the warranty as a single
supplier will take full responsibility for every component in the system
without passing blame to others for failure. It is strongly discouraged to buy
different products from different suppliers and engage another party for the
installation in order to save costs, without considering the implications for
the warranty when failure occurs.
A final point here is the prudence of using equipment that is familiar in the
market, that is, equipment which is well known by local providers/technicians
and which they can support with spare parts and repair. Where possible,
organizations should standardize their solar pumping equipment by having
one or two brands which they use across their programmes and for which
they can stock spare parts or even have personnel dedicated to supporting
the equipment. It is easier to institutionalize the SPWS knowledge of a few
brands than multiple brands.

Copyright practicalactionpublishing.com
CHAPTER 11
Testing and commissioning, operation
and maintenance
The handing over of solar pumping schemes from installers to users involves specific
testing and commissioning procedures. This chapter reviews those processes together
with the necessary documentation that should be provided with every scheme.
The different maintenance categories, ranging from routine to preventive, reactive,
predictive, and extraordinary maintenance, are explained. The importance of having
dependable after-sale specialized technical support to ensure proper functioning
of solar pumping schemes over time is discussed together with health and safety
considerations.

Keywords: inverter programming, solar testing report, PV module

cleaning, maintenance for solar systems, open-circuit voltage, short-circuit
current

11.1 Testing and commissioning

11.1.1 Inspections and functionality tests
Before the solar-powered water system is put into use it should be tested by
the contractor/installer for proper function and safety. The various checks and
tests recommended are outlined in Table 11.1.

11.1.2 System performance tests

Once the preliminary checks have been done the working system should
be tested, performance monitored, and recorded. The testing should be
done for a prolonged period of two to three days over the full solar day to
monitor performance, which can help in revealing any discrepancies from the
expected/design values. These test results act as a benchmark for monitoring
future performance. The various components of the SPWS should be subject
to the tests outlined in Table 11.2.

11.1.3 Testing report

Upon satisfactory testing of the SPWS by the contractor, the contractor
should prepare a testing report detailing the results of the tests and stating
information on the installation as below. A detailed hourly report of the pump
performance should also be provided, as shown in Table 11.3.

http://dx.doi.org/10.3362/9781780447810.011
Copyright practicalactionpublishing.com
164 SOLAR PUMPING FOR WATER SUPPLY

Table 11.1 Inspections and functionality tests for solar-powered water systems
Item/component Description of action/test
PV generator Visual inspection of modules for damage during installation

General orientation of the modules

Support structure mechanical check e.g. stability, obvious swaying

Measurement of the rated value of modules, i.e. open-circuit

current and short-circuit current at solar peak hour (when the sun
is strongest)

Disconnection switch check for polarity, insulation, cable

connection, etc.

Output voltage and current measurement at each string

inside the disconnection switch at solar peak hour (a digital
multimeter can be used). These should match the design values
or deviate by the factor of tolerance discussed in sections 4.5.1
and 10.6.2
Inverter/control box Visual check

Environmental protection check

Start-up sequence

Maximum power point tracking

Inverter programming
Pump and motor Continuity test

Insulation test

Priming for surface pumps

Cables Visual inspection of cables, e.g. loose connections, hanging wires,
abrasions, correct dimensions, insulation

Voltage and megger (insulation-resistance) tests

PV grounding system Continuity of ground connection

Measurement of ground resistance

Protective earth tests

Pipework and fittings Visual inspection of wellhead and pipes, e.g. loose connections,
broken pipes, bent pipes, correct sizes

Check for closed valves

11.1.4 Commissioning, acceptance, and system handover

After practical completion of the installation, the client should request
commissioning, followed by acceptance, and system handover, at which stage
the risk and liability passes over to the client (or implementing agency or
community of users). Warranty and maintenance periods usually commence
after satisfactory handover by the contractor and acceptance by the client.

Table 11.2 System performance tests for a solar-powered water system

Item/component Description of action/test
PV generator Measurement of the system current and voltage on load and
record of PV power generated
Inverter Output frequency, voltage, and current

Functionality of all sensor inputs, such as low-water sensor, high-

level sensor, pressure sensor, irradiation sensor
Pump and motor Start-up sequence (reverse rotation is a common problem that can
result in reduced pump output)

Flowrate and pressure

Motor current and speed

Cables Obvious signs of failure, such as overheating, peculiar smells
Pipework and fittings Check for leaking pipes and fittings, blockages, etc.

During the commissioning and handover process, the installer should

provide the following documents to the client:

• signed goods received note;

• wiring diagram of the control components, including wire sizes and
ratings;
• wiring diagram of the PV generator;
• operation and maintenance manual (easy to read and preferably in a
local language), including troubleshooting procedures;
• technical equipment manuals, such as equipment datasheets, specific
equipment operation and installation manuals;
• signed warranty document;
• capacity-building plan for the first 1 to 2 years;
• testing and commissioning report, including the testing and performance
results (Table 11.3);
• other documents identified in Table 11.4.

Usually the implementing agency will in turn hand over the water scheme
to the users at the end of the project implementation period. As mentioned,
a complete, well thought-out and well-executed handover procedure should
be conducted, involving:

• training users on basic operation and maintenance of the system;

• the provision of complete warranty information;
• the provision of all relevant documents and information regarding the
operation of the system;
• linking to a technically knowledgeable third party (e.g. private contractor)
to provide routine preventive and corrective maintenance.

Despite complete training and handover there are still certain aspects of
the system which the users will not be able to resolve on their own if a problem

Client name/implementing agency

Installing company/contractor name, contact person, and contact details
Installation completion date
Borehole details 1. Site name 5. Water rest level (m)
2. Location name and GPS coordinates 6. Pumping water level (m)
3. Borehole depth (m) 7. Total dynamic head (m)

Copyright practicalactionpublishing.com
4. Borehole diameter (mm) 8. Depth of pump (m)
Equipment specifications 1. Pump brand and model 6. Controller name, brand, and model
2. Motor brand, model, and rating 7. Controller serial number
3. Motor serial number 8. PV module brand, model, and size
4. Pump cable type and size 9. No. of modules in series
5. Piping size and type 10. No. of modules in parallel
SOLAR PUMPING FOR WATER SUPPLY

Pump performance Morning Afternoon/evening

0600 0700 0800 0900 1000 1100 1200 1300 1400 1500 1600 1700 1800
Irradiation (W/m2)
System pressure (m)
Pump output (m3/hr)
Motor current (A)
Pump speed (Hz)
Input power (kW)
Input voltage (VDC)
Output voltage (VAC)
Input current (A)
Output current (A)
TESTING AND COMMISSIONING, OPERATION AND MAINTENANCE 167

occurs. In such cases, coordination with knowledgeable local government

entities or water offices and/or technically competent private companies
should be a prerequisite for project handover.

11.2 Operation and maintenance of equipment

Solar-powered water schemes will suffer fewer breakdowns and require much
less intensive maintenance than generator or handpump schemes. However,
solar-powered schemes can and will experience problems at some point that
cannot be solved at community level (or which the managing agency/entity
will probably need specialized technical support), regardless of the training
provided at user level.
As such it is important that where possible, some kind of operation and
maintenance (O&M) service agreements (see section 11.2.4) are established
prior to any installation and renewed over the years, with a quality private
contractor, water utility, water service provider, relevant government technical
office, and/or any other stakeholder with sufficient technical knowledge and
means to timely respond when needed.
A well-thought and professional O&M service package, ideally negotiated
together with the construction contract/tender, will ensure that an SPWS
maintains high levels of functionality; it will also ensure extended life of the
equipment.
In addition, and especially where spare parts and knowledgeable technicians
are mostly located in capital cities, as is still often the case, clustering of SPWSs
in a geographical area will facilitate preventive maintenance and repairs being
carried out in an easier and more effective way for everyone.
Solar-powered water schemes have been found to work without any major
issues for over 10 years in communities where O&M procedures have been
clear, well designed, and followed. Yet this is not often the case in humani-
tarian operations where time pressure tends to lead to an excessive focus
on solar technology design and installation, often at the expense of a well-
structured O&M plan (in terms of the plan itself and the funds dedicated
to it). This puts the functionality of the solar pumping scheme at risk in the
short and medium term.
Typically, technical faults might develop and repairs might be needed
within the first 12 to 18 months of operation of the scheme (due often to
some wrong design data or some faulty component or installation errors
not detected during the short testing period prior to commissioning).
Therefore, it is critical to ensure a proper O&M service programme is
in place at the very least during that period, and that it is renewed and
adapted to contextual situations over the years.
In the life of a solar-powered water scheme, the O&M phase is by far the
longest, as shown in Figure 11.1. Therefore, increasing the quality of O&M
services is important and neglecting O&M is risky, counterproductive, and
more expensive in the long term.

Construction Operation & Maintenance

(1–8 weeks) (typically 20–30 years)

Planning Dismantling
(1–6 months) or repowering
(1–2 months)

Figure 11.1 Duration of different phases in the life of a solar pumping scheme

11.2.1 Operation
Operation is about onsite daily management, supervision, and control of the
solar pumping scheme (see Annex F – Routine Inspection and Maintenance
Sheets) and may also involve remote monitoring (see more on remote moni-
toring in Chapter 12). It may also involve coordination of maintenance
activities, depending on the model chosen for doing so.
SPWS documentation is crucial for an in-depth understanding of the design,
configuration, and technical details of the system. It is the asset owner’s
responsibility to provide these documents; if not available, they should, as
best practice, be recreated at the asset owner’s cost (also in the local working
language where appropriate).
Before assuming any maintenance and/or operational activities, it is
important that the actors involved understand the characteristics of the PV
scheme. Moreover, for quality/risk management and effective operations
management, good and clear documentation of contract information, scheme
information, maintenance activities, and PV scheme management are needed
over the lifetime of the equipment.
In general, for optimum service provision and as a best practice, the
contractor in charge of more technical specialized maintenance will have
access to all possible documents.
The contractor or agency in charge of construction and installation of
the solar pumping equipment will develop a site operating plan which gives
a complete overview of the scheme location, layout, electrical diagrams,
components in use, and references their operating manuals, health and safety
rules for the site, and further topics as needed and agreed. This plan will have to
be handed over to the party in charge of O&M and be stored (electronically and
physically) safely for immediate access in case of solar pumping scheme issues.
A list of documents to be included in the as-built documentation set accom-
panying the SPWS is given in Table 11.4.

Table 11.4 Documentation set accompanying the solar water-pumping scheme

Item Description
Site information Location, GPS coordinates, detailed map

Spare parts storage/warehouse (if any)

Stakeholder list and contact information (e.g. maintenance

and repair service provider)
Project technical studies Plant layout and cable drawings and sizes
and drawings
PV module configuration and connection

Earth/grounding system layout drawing

Lightning protection system details (if any)

Water yield simulation

Water pump and inverter study

List of balance-of-system components

Drawing and location of water reservoir and pipe sizes,

material, and lengths
PV modules and Inverters PV module datasheets

O&M inverter manual

Inverter setting and location

Warranties and certificates

Switchgear (disconnection Type of switchgear
switch)/Controls
Switching procedure to operate and stop pumping system
Mounting structure Mechanical assembly drawings and material

Warranties and certificates

Security, anti-theft, and Security and alarm system layout
alarm system
PV scheme controls PV scheme control system and meter descriptions
Communication system Installation and O&M manual

Working agreement and communication to remote-

monitoring operators
Other documentation Test and commissioning report from installation company

As best practice for the operations team, when the system is out of service
and maintenance performed the maintenance tasks should be documented
and linked back, if applicable, to failures that may have triggered the respective
maintenance activity. This will allow the team to learn from past and ongoing
operation and maintenance, and to then be able to improve performance via,
for example, predictive maintenance in the following years.
Records of service and maintenance activities should include the input
records listed in Table 11.5.

Table 11.5 Records of service and maintenance activities at site level

Activity type Input record and information type
Routine onsite maintenance List of activities and person responsible
Alarms/operation incidents Date and time, affected equipment, number of days,
external visits/inspections from third parties
Preventive maintenance Preventive maintenance plan and activities to undertake

Tasks performed, date, technician name, and function

Corrective maintenance Detailed failure, problem resolution description, and start
and repairs and end dates of the intervention
Inventory management Inventory stock and management
Monitoring and supervision Water production, inverter readings, start and stop
pumping times, weather conditions

Records of visits
Warranty management Registration of claims

11.2.3 Maintenance
Maintenance is usually carried out onsite either by trained personnel,
specialized technicians, or subcontractors. Maintenance can be of five different
types, depending on the kind of activities, frequency, and level of technical
skills required.

Routine maintenance. Once the solar pumping scheme has been installed
and commissioned, several simple actions are to be followed by the owners
of the system in order to maximize water production and minimize the
likelihood of system breakdowns (typically carried out by non-specialized
staff who have received some kind of training, e.g. operator, community
members, NGO staff).
While these activities are simple and easy to do it is not unusual to find
numerous schemes where they are not carried out either because the personnel
onsite have not been trained or advised to do so, tools have not been provided,
and/or the community of users and water committee are not aware of the
importance of these activities and their
Being consistent in the performance influence on the amount of daily water
of routine maintenance activities will supplied by the system.
strongly influence the daily amounts of A list of the activities involved in
water supplied. routine maintenance at field level can be
found in Table 11.6 and in Annex F, and
main ones are illustrated in Figure 11.2 (as a best practice, a similar poster to this
can be placed by the water point to act as a reminder over the years).

Preventive maintenance. A core element of maintenance services,

preventive maintenance involves regular visual and physical inspections
as well as verification activities to comply with the operating manuals.

Table 11.6 Routine maintenance activities for solar-powered water systems

Activity Frequency
Solar pumping PV module cleaning Weekly to monthly, depending on
maintenance the level of dust
Vegetation trimming and As needed to avoid shadows on PV
management modules
Maintenance of PV supporting As needed and monthly check of
structure bolting of panels to the structure
Inspect water piping, repair or Weekly to monthly
report leakages
General site Pest control, waste disposal Weekly
maintenance Perimeter fencing repair As needed
Maintenance of buildings As needed
Maintenance of security equipment Test functionality once a month
(if any)
Onsite Water readings Daily
measurement Recording of pumping hours, Daily
weather conditions
Inverter readings, fault recording Daily
and reporting

Regular cleaning of solar panel Regular cleaning of inverter

Use clean water & polyester cloth Clean dust using a dry
to avoid dust & moulds cloth and soft broom

General compound maintenance Check and record faults

Repair fence, slash grass and trim Check faults from inverter &
vegetation to give enough light report to the technician

Inspect water piping system Check and cover up all the inverter holes
Report leakages to a plumber to To avoid rodents and lizards
tighten all loose sections from entering the inverter

Check water tank Yield

Check if water tank is full and Call a qualified technician if
system yields less water or pump
stop pumping if overflowing makes strange noises

Figure 11.2 Routine maintenance activities to ensure proper daily functionality

Application note: suggested method for cleaning PV modules

Cleaning PV modules is perhaps the single most important regular maintenance

activity to be carried out. For proper cleaning, use only water (as pure and absent
of suspended solids as possible) and cloth; no soap or other elements are needed.
Pressure washing modules is not an acceptable cleaning method and may invalidate
the warranty on the panels.
For panels mounted on elevated poles or roofs, cleaning is made easier when a ladder
and a telescopic handle is provided. Health and safety must be considered to keep workers
safe onsite. This will involve some form of specific training for solar module cleaning,
including working at height if cleaning elevated mounted modules.

The preventive maintenance plan details a list of inspections that should

be performed at predetermined intervals (typically quarterly, biannually,
or annually depending on context) by a technician with specialized
knowledge (e.g. technical staff from a private contractor). Tracking records
of preventive maintenance carried out will optimize activities further.
(See Annex G for a preventive maintenance plan template.)
The maintenance contract (section 11.2.4) should include this scope of
services and each task frequency. Ideally, such a contract will be negotiated
together with (and even be an integral part of) the installation contract.
It is the responsibility of the contractor in charge of maintenance to prepare
the preventive maintenance plan for the duration of the contract period,
following the frequencies specified in the contract. These activities should be
reported to the asset owner or asset manager.

Corrective maintenance. Corrective maintenance covers activities aimed

at restoring a faulty solar pumping scheme, equipment, or component to
a status where it can perform the required function. Agreeing beforehand
on maximum response time to minimize downtime of the solar pumping
scheme should be stated in the O&M service agreement. A system of financial
penalties could be put in place to ensure that technicians will be deployed
onsite when called in a reasonable amount of time (one to three days).
When a system falls into disrepair it is critical that non-qualified staff do
not tamper with the equipment as this can aggravate the problem and/or
lead to electric shocks or other accidents as well as void the warranty. In any
case, modifications should not be carried out on the solar pumping scheme
without technical guidance from the system supplier, the contractor in charge
of maintenance, or a qualified technician. Box 11.1 describes the scenarios
when a technician should be called.

Box 11.1 When to call a technician

• When the pump is making unusual noises.

• When there is any change in the rate of pumping (the system is pumping less water
than it used to yet the solar modules are clean).
• When biannual maintenance checks need to be performed.

Corrective maintenance takes place after a failure is detected either by onsite

operators and users, remote monitoring and supervision staff, or during regular
inspections and specific measurement activities. Operators should be clear
about the occasions when it is necessary to call a qualified technician onsite.
Only when a qualified technician has arrived should corrective maintenance
take place, which will involve the following three activities:

1. fault diagnosis, also called troubleshooting, to identify the cause of the

fault and isolate it;
2. temporary repair to restore the required faulty item for a limited time,
until a full repair is carried out;
3. full repair to restore the required function permanently.

In cases where the PV plant or segments need to be taken offline, the

execution of scheduled corrective maintenance during the night or low
irradiation hours would be considered best practice as the overall power
generation is not affected.

Predictive maintenance. Predictive maintenance is a special service

provided by contractors in charge of maintenance who follow best practice
principles. It is defined as a condition-based maintenance carried out
following a forecast derived from the analysis and evaluation of the significant
parameters of the solar-powered water scheme.
A prerequisite for good predictive maintenance is that information can be
retrieved from the devices onsite in such a way that the contractor in charge
of maintenance can evaluate trends or events that signal deterioration of
the different devices, especially the PV modules or water pumps.
For efficient predictive maintenance a certain level of maturity and
experience is required, which is at best a combination of knowledge of the
system’s performance, related equipment design, operation behaviour, and
relevant accumulated experience and track record from the service provider.
Normally, it is a process that starts after the implementation of an
appropriate monitoring system and the creation of a baseline. The baseline
will represent the entire SPWS operation as well as how different pieces of
equipment interact with each other, and how this system reacts to environ-
mental changes.
Although predictive maintenance is rare to find in the humanitarian
context, it has several advantages, including:

• maintenance activities (both corrective and preventive) are anticipated;

• some maintenance activities can be delayed, eliminated, or optimized;
• time for repairs is reduced;
• spare parts replacement costs are reduced;
• emergency and non-planned work is reduced;
• predictability is improved.

Extraordinary maintenance. Extraordinary maintenance, usually not

covered by the O&M service agreement and fee, may be necessary after

major unpredictable events occur in the solar pumping scheme that require
substantial repair works (e.g. damage after theft, fire, vandalism, or caused
by design mistakes).

11.2.4 Service contract framework

One of the key challenges facing SPW systems is the lack of locally available
technical expertise to provide troubleshooting, repairs, and specialized
maintenance services to the users. This is more so once the after-sales
service period has ended, where all liability for service and maintenance
shifts to the user/owner of the system. This commonly also corresponds with
the time when the system is being handed over to the community/users
by the implementing entity. This results in uncertainty of getting the help
needed in case of system failure which could lead to prolonged periods of
system downtime and non-functionality.
A service contract plays a key part in tackling this challenge. It is
signed between the users and the installer (or other qualified maintenance
contractor) for a period of one to two years post system handover to the
users or within the critical first 18–24 months of the system’s operation.
It will be an agreement with specific terms (including annual fees)
between the asset owner and the contractor in charge of maintenance.
This agreement defines in detail the maintenance services, both remote
operations services and onsite maintenance activities, the management
and interface of those services, and the responsibilities of each party.
Liquidated damages, penalties, and bonus schemes are also part of the
contractual commitments.

Example 11.1 Preventive maintenance service contract with Solar Pumping Ltd in Kenya

Under service agreements with Solar Pumping Ltd the private contractor is mandated to
visit the system at least four times a year to conduct regular maintenance checks. They are
also required to visit the system when a problem arises.
Clients in the service contract are charged annually. Consumers are charged based on
their distance from the nearest Solar Pumping Ltd branch, at $0.90 per kilometre, for
each routine check and a technician cost of $100 per day.
In case of equipment breakdown, the client pays for repair/replacement of
components at a discounted rate. This expense is in addition to the annual service and
maintenance fee.

It is considered best practice to define and agree a maintenance

framework before starting construction of the SPWS. As some installers
will void the equipment warranty if they are not engaged to provide
the maintenance service, it is advisable to consider the repercussions of
engaging a different maintenance contractor from the original system
installer. The agreement is renewable on an annual basis upon both parties
meeting their obligations.

Box 11.2 Example of essential provisions in a maintenance service agreement

Communication line

• Reporting to asset owner on solar pumping scheme performance, O&M performance,

incidents, and warranty management
Solar pumping scheme operation
• Scheme documentation management
• Scheme operation and/or supervision
• Performance monitoring and documentation
• Issue detection/diagnostics
• Security incidents monitoring interface
Solar pumping scheme maintenance
• Maintenance scheduling
• Solar pumping scheme and site maintenance activities, and contact details for
preventive and corrective maintenance
Spare parts management
• Spare parts list for two to five years
• Spare parts replenishment
• Spare parts storage (optional)

The scope of services to be provided by the contractor in charge of

maintenance should include:

• quarterly, biannual (twice a year) or annual checking up and record-

keeping for proper operation of the system;
• scheduled/routine visits by the contractor to site according to the
agreement (commonly every two or three months) to carry out preventive
maintenance, address impending failures before they happen (such as
replacing overheating breakers that could cause inverter or pump failure,
checking tightness of connections), replace any components or subcompo-
nents of the SPWS as needed, and ensure optimal operation of the system;
• prompt response by the contractor to address any reported faults by the
client, with turnaround time for such repairs not exceeding three days
(or as stipulated in the service agreement);
• continuous training of the users/operators by the installer on the
operation and maintenance of the system;
• submission to the client of a report of the works carried out during every
visit and the state of the system, including performance (flow, pressure)
and electrical data (current, voltage, power).

In most cases the service contract fee covers the cost of labour and
transport for carrying out such works with the replacement parts being
paid for by the client.
One challenge of putting in place such a plan is the shortage of funds,
though donors can support this by extending funding windows to cover one

to two years of maintenance fees after project handover. The implementing

body should put in its funding proposal the maintenance cost for one to two
years after system handover.
This kind of maintenance plan is beneficial as it contributes towards overall
success, functionality, and sustainability of the system. It provides a link
between the community/users and the private sector so that the community
is not left in limbo and is guaranteed of system functionality in the long run.
Further, on expiry of the initial NGO-funded maintenance agreement, the
community should be aware of its value and be encouraged to renew the
contract using water fee collections or other funding sources.
Suffice to say, a robust maintenance plan is absolutely essential for a
successful and sustainable SPWS. This includes but is not limited to an
operation and maintenance plan, a service contract, and continuous capacity-
building of the users.

11.2.5 Training
Training of operators and other personnel (e.g. water committee members,
NGO technical staff) in the running and daily maintenance of the solar
pumping system is critical.
As shown in the previous section, it is strongly recommended that this
training be a contractual condition so that it is provided by the installation
contractor before leaving the site and on an ongoing basis according to the
contractual agreements.
Components of the training may cover all relevant aspects of the O&M of
the solar plant as well as basic plumbing (useful in repairing leakages) and the
daily running of the water scheme, including being able to manage finances
accrued from water sales if relevant.
As solar pumping solutions are rapidly expanding in many countries,
NGOs, UN agencies, and other parties should consider utilizing the technical
expertise of private contractors to provide regular technical and awareness
training. Given the business opportunity, some contractors may offer such a
service for free.
Finally, everyone who enters a solar pumping scheme site, regardless of their
skills and experience, needs to be trained in the dangers present in addition
to the individual skills and experience that are required for the tasks they
normally perform. Awareness of the necessary health and safety regulations
is a must.

11.2.6 Health and safety

Solar pumping schemes are electricity-generating power stations and pose
significant hazards which can result in permanent injury or death. It needs
to be remembered that PV modules cannot be switched off and as long as
there is sunlight, even if the pump is not in operation, electrical shock hazards

are present. Risks can be mitigated through proper hazard identification,

careful planning of works, regular briefing of procedures to be followed, and
well-documented inspection and maintenance practices.
The dangers of electricity are well known and can be effectively managed
through properly controlled access and supervision by the contractor in
charge of maintenance. Any person accessing an SPWS location should be
briefed on hazards and risks.
Staff working on electrical equipment must be appropriately trained,
experienced, and supervised, but it is also key that others working around the
equipment, for example module cleaners, are equally aware of the potential
risks and have safe methods of working.
Hazardous areas and equipment should carry appropriate signage to warn
personnel of the hazards and wiring sequence. Such markings should be clear
and evident to all personnel and third parties (and intruders) entering the
scheme premises.
Besides workers of the solar plant, it is not unusual for other parties to require
access to it. This may be the asset owner, or their representative, the landlord, or
in some situations members of the public. It is important that the plant access
control and security system keeps people away from areas of danger and that
they are appropriately supervised and inducted as necessary.
The asset owner is ultimately responsible for compliance with health and
safety regulations within the site/plant.

11.2.7 Security
It is important that the solar pumping scheme site, or key areas of it,
are protected from unauthorized access. This serves the dual purpose of
protecting the equipment (from theft or vandalism) and keeping members
of the public safe.
Together with the contractor in charge of maintenance and the security
service provider, the asset owner will put in place a security protocol in case
an intrusion is detected.
A security system may be formed of simple fencing or barriers, or may
include other measures as listed in section 7.6.
As well as the general security of the site over the lifetime of the
scheme, particular attention should be paid to periods of construction
or maintenance when usual access arrangements may be different. It is
important that security is always maintained, particularly when there are
activities that may be of more interest to members of the public, children,
or potential thieves.

11.2.8 Spare parts management

Spare parts management can be an inherent and substantial part of O&M
that should ensure spare parts are available in a timely manner for corrective

maintenance in order to minimize the downtime of a solar-powered water

scheme (or a part of it).
Generally, it is not economically feasible to stock spare parts for every
possible failure in the water scheme. Therefore, the contractor in charge of
maintenance together with the asset owner should define a list and stocking
level of specific spare parts that make economic sense.

Copyright practicalactionpublishing.com
CHAPTER 12
Warranties, social models
for management, and monitoring
This chapter describes warranties related to products, installation, and services for
solar pumping schemes. As important as the technical considerations, social models
of management adapted to the specificities of solar pumping schemes are essential
to ensure its functioning in the long term; the different models are presented here
together with commonalities in well-managed schemes. Finally, remote operation
and maintenance is briefly explained, along with the different range of tools to
monitor electrical parameters in a solar PV generator.

Keywords: solar component warranty, electrical monitoring tools, solar key

performance indicators, remote monitoring, thermal image, solar checker

12.1 Warranties
Reputable equipment manufacturers provide product warranties for their
equipment. The supplier of the equipment must provide to the asset owner
a warranty document clearly detailing and explaining the terms of warranty,
including the start date and the period of warranty (see Annex E).
The terms generally include repair, replacement, or refund of salvage value
of the defective equipment due to failures caused by manufacturer fault.
Warranty does not cover failure that is due to external causes.
The warranty period starts from the time of either collection, delivery of
equipment or commissioning, in the
case of installation by the manufac- Warranty is voided when installation
turer’s local representative/distributor/ instructions are not followed and
supply agent/installer. The warranty is when repairs are attempted without
claimed through the supplier/installer, the manufacturer’s authorization.
who should extend the manufacturer’s
warranty to the buyer or end user.
Often the installation contractor will combine the manufacturer’s component
warranty with their own warranty terms to include workmanship, quality
of installation and after-sales support under what is known as a comprehensive
warranty. The warranty provided should therefore cover both the product and
workmanship. Proof of purchase must be provided for a warranty claim to be
honoured.
Incomplete handover procedures (such as when the community/users/
committees are not provided with warranty documents) can create issues

http://dx.doi.org/10.3362/9781780447810.012
Copyright practicalactionpublishing.com
180 SOLAR PUMPING FOR WATER SUPPLY

if there are problems with the system within the critical two-year mortality
period (a system that lasts the first two years of operation has a much greater
probability of lifetime functionality). It is therefore paramount that during
the handover process the users are educated on the warranty claim process,
provided with warranty documents, linked with the right contact in case
of a problem, shown where to access technicians, and given all relevant
information regarding the warranty. Field evaluations have revealed systems
that have remained non-functional for long periods of time (within the
warranty period) with obvious consequences, and which could have been
quickly and easily rectified had the users known the avenues for warranty
and repair. Provision of warranty certificates to the users and education on
warranty procedures helps to avoid such occurrences.

12.1.1 Warranty management

The technical asset manager or the asset owner will be focal points for any
warranty claims to the contractor or manufacturers of SPWS components.
During the warranty period (or at least the first two years), it should be
mandatory, as far as possible, for the contractor to enter into a comprehensive
maintenance contract with the asset owners, and this should be well stated in
the contract documents.
For any warranty claims the formal procedure provided by the warranty
provider should be followed; therefore, it is important that warranty terms and
conditions are made clear and are well understood at the time of equipment
purchase and installation.
All malfunctions or failures of equipment should be reported to the
manufacturer or contractor promptly as the warranty validity is considered at
the date of reporting, not when the problem was observed.
The warranties typically requested by implementing agencies are component,
quality of installation and workmanship, and system performance warranties.

Component warranty. The length of the warranty period varies with the type
of equipment and the manufacturer. The standard warranties provided by
the manufacturers of the individual components, usually against defective
components or workmanship, are:

• Solar modules; 10-year product warranty and 25 years power output

guarantee based on light-induced degradation (see section 4.5.3);
• Controller/inverters; 2–5 years;
• Pump and motor; 2–5 years;
• All other balance of system components; 1–2 years.
Unless the warranty specifies that these are covered onsite (i.e. within
the defects period, or under an extended maintenance contract), then they
are assumed to be on an exchange basis and the labour and costs of transport
are excluded, that is, the equipment must be returned by the client to the

supplier/contractor for diagnosis of the problem. In case the installer needs

to visit the site for diagnosis, the cost of the visit is charged to the client,
although this also depends on the goodwill extended by the supplier and
other contractual obligations stipulated in the contract. Where it is found
that the failure was due to the fault of the installer, all costs are borne by the
installer. This can be a point of contention which should be discussed and
documented during the contract signing/negotiation stage. It is advisable to
look for more than individual component warranties.

Quality of installation and workmanship warranty. The minimum defects

liability period or after-sales service support commits the installer to
provide backup support onsite (typically within the first six months to one
year), without additional charge, in case the system develops a problem
after installation. It requires that any items which fail or are not installed
to standard are corrected and resolved onsite at cost to the supplier. Issues
arising from poor quality of installation are also dealt with onsite at a cost
to the supplier and this also covers corrosion of materials used onsite, such
as the support structure.
An after-sales warranty follows the same principle as the component
warranty in that only failures that are caused by contractor fault, workmanship,
or quality issues are covered.

System performance warranty. Although rarely encountered in humanitarian

contexts, the supplier may guarantee that the PV system will meet or exceed
the design performance for several years.
A system performance warranty may be based more generally on monthly
average or annual average figures for insolation and water delivery, or on actual
instantaneous outputs. Performance can be assessed initially during commis-
sioning via the system performance test benchmarking and the supplier
should warranty that future system performance tests, when corrected back to
design conditions, will exceed the design performance.
As long-term system performance is subject to many onsite and environ-
mental conditions as well as requisite maintenance, such warranties would
need to go hand in hand with a long-term maintenance contract.

12.1.2 Activities typically covered and not covered by warranties

During the warranty, the following maintenance will be required to be carried
out by the contractor/supplier/installer:

1. repair/replacement of all defective components and subcomponents

of the system as per the requirement to ensure the system is in good
working order;
2. repair/replacement of the SPWS to make the system functional
within the warranty period whenever a complaint is lodged by the
user. The contractor shall attend within a reasonable period of time

and, in case of breakdown, fix issues within a period not exceeding

three days of being reported;
3. repair/replacement of components damaged due to negligence or fault
of the client (users and/or asset owner), theft, or vandalism, at the
clients’ cost.

The safety and security of the system will be the sole responsibility of the
user/asset owner.

12.2 Social models for management

As discussed in section 11.2, operation and maintenance of solar water systems
is crucial to their long-term sustainability and inadequate O&M is a frequent
cause of system failure.
When an NGO or UN agency takes over the full management of a solar-
powered water scheme, as is often the case in camp settings, management
(including O&M) becomes simple and straightforward because it is assumed
that those organizations will make provisions in their budgets and keep in
contact with competent technical partners to respond to any issues regarding
the operation and functionality of the water scheme.
For solar pumping schemes at community level things are normally
more complex. Different management models work in different settings
and the authors do not advocate for or discourage any particular model.
Different studies have tried to analyse the strengths and weaknesses of a
number of management models at community level (see for example WSTF,
2017). However, because a model is working in one setting does not mean
it will work in all settings; and that a model is not working in one setting
does not mean it’s a bad idea for another. Good concepts may sometimes
not work because they are either not executed well, their execution was
wrongly timed, or they are not suited to the particular environment.
Several evaluations and field visits carried out within the Global Solar and
Water Initiative have found that there are three key factors which should be
incorporated into any management model to ensure its sustainability:

• financial accountability of water committees collecting water fees (e.g.

legally registered water committees, with an open bank account, keeping
registers of contributions);
• dedicated personnel (e.g. salaried water operators);
• involvement of government technical offices and private companies for
repairs and services.

Other commonalities observed in successful community-managed water

schemes are described in Box 12.1.
Financial sustainability models found at community level for solar-powered
water schemes are like those found for other technologies, namely: pay as you
go, metered monthly payments, and flat monthly payments.

Box 12.1 Commonalities between successful community-managed water schemes in Kenya

At least one individual who is highly committed to the success of the project
For instance, in Adamasija, Wajir County, the committee chairman has taken it upon
himself to ensure that meters are read, has set up a shop where people can settle their
water bills, ensures that electricity bills are paid, and oversees the system’s water distri-
bution schedule.

Absence of alternative sources of water

Lack of alternatives, especially during the dry season, causes communities to be better
stewards of their water systems. This may mean a higher willingness to pay for water to
ensure availability of funds for maintenance. This is especially the case where the main
source of livelihoods (e.g. livestock) is highly dependent on availability of water.

High sense of community responsibility

A general perception that water collections by the committee are community funds. Some
of these committees had contributed towards the construction of classrooms in schools
within their communities, extended distribution networks to key institutions, or provided
water at subsidized costs during the dry season.

Community awareness of recurrent costs

Communities with diesel or solar–diesel hybrid systems were seen to have a higher under-
standing of financial management, which is key to the sustainability of water schemes.
These schemes also saw that consumers had a higher sense of willingness to pay for water
services, unlike in stand-alone solar systems, where there was a general wrong perception
that water should be free as the energy is free. See also Box 12.2.

Source: GLOSWI, 2018f

Box 12.2 For local community projects, should solar water be free?

Given the nature of implementation of solar-powered water systems for communities,

which are often through aid or government projects (at no cost to the benefitting
communities), and as there is no cost for the energy required for water pumping, this
tends to be interpreted as ‘water for free’, thus negating creating a perception that water
should not be paid for.
There needs to be a complete shift in the community narrative of SPWSs, from
‘tapping into a cost-free source of energy to pump water’ to ‘cumulating funds for
system replacement’. Communities need to understand that while there are minimal
recurrent costs in operating solar systems, there are significant one-off costs
to ensuring their continued long-term operation. For long-term sustainability of
systems, water must be provided at a fee to ensure funds for repairs, maintenance,
and replacement of parts, and implementing agencies need to be very deliberate in
altering this viewpoint.

12.3 Monitoring
12.3.1 Remote monitoring
Monitoring on a system-wide basis is very important; it can help to further
develop the installation, evaluate overall performance, and reduce costs.

The main things to be monitored at the solar pumping side of a water

scheme are:

• discharge from the borehole, amount of water pumped;

• operating pressure;
• static and dynamic water level;
• pump operation trends e.g. current, frequency;
• solar radiation on the array plane, voltage, and current.
Solar pumping technology allows monitoring of those parameters either
onsite with the use of specific tools or through remote monitoring solutions
(see Figure 12.1).
Remote monitoring allows for distant, computer-based operation and
monitoring of a solarized water scheme in areas where a telephone network
is present. In humanitarian operations, remote monitoring is useful to run
and monitor water schemes that are distant from the humanitarian organiza-
tion’s operational base, when schemes are many and staff is stretched, where
tight controls are needed (e.g. critical boreholes supplying a large number of
people), and/or where security or other logistic constraints make it difficult to
access the scheme when required.
In addition, remote monitoring is useful to better understand aquifer
behaviour and anticipate maintenance needs through recording and observing
actual and historical data. Actual data collected may be live monitoring,
system status, ‘pump off’ reasons, and advanced information (e.g. faults),
while historical data includes running time; water amounts, and static and
dynamic levels; voltage, current, flow, and so on.

Figure 12.1 Lorentz communication system for monitoring from phone via Bluetooth or from
computer via Internet
Source: Lorentz

12.3.2 Key performance indicators

Key performance indicators should reflect the performance of the SPWS
and assess the O&M service provided by the O&M contractor.
SPWS KPIs include:

• water supplied vs the water forecast;

• performance ratio (the energy generated divided by the energy obtainable
under ideal conditions expressed as a percentage);
• uptime/availability, parameters that represent, as a percentage, the
time during which the plant operates over the total time it is possible
to operate. While uptime reflects all downtime regardless of the cause,
availability involves certain exclusion factors to account for downtime
not attributable to the O&M contractor (such as force majeure), an
important difference for contractual purposes.

O&M contractor KPIs may include:

• acknowledgement time (the time between a problem being reported and

the contractor acknowledging it);
• intervention time (the time between acknowledgement and a technician
reaching the SPWS site);
• resolution time (the time to resolve the fault, starting from the moment
the technician reaches the PV plant);
• response time (acknowledgement time plus intervention time), an
indicator used for contractual guarantees.

12.3.3 Monitoring and diagnosis tools

Clamp meter. Unless a more specialized monitoring and maintenance service
for a considerable number of solar pumping stations is required as simple
clamp meter of the right category (see Figure 12.2), able to measure both
voltage and current (AC and DC) to the required scale, should be enough to
perform basic electrical checking.

Solar meter. Solar radiation levels in the panel can be easily measured by placing
a solar meter on top of a panel (in order to ensure the same orientation and tilt
angle). By measuring solar radiation levels and water supplied and comparing
them with expected values according to the design provided it is possible to get an
idea of the accuracy of the design and outputs expected and act in consequence.

Thermography. Thermography cameras are used to spot high temperature

points and cells in panels with a temperature difference of more than 15 °C
(normally indicating some kind of defect or problem). Thermography can also
be used to locate bad connections in cable boxes or inverters.
Other problems that can be typically spotted with thermal imagery are:

• welding defects;
• impurities in silicon cells of panels;

Figure 12.2 Fluke clamp meter

• defects in connection box of solar modules;

• reverse polarization of solar cells;
• loose cable connection in inverter/control boxes;
• cooling or overload issues at any solar equipment part.

Solar checker. Solar checkers are a more complete, complex, and expensive
testing and monitoring device that can be used to provide PV panel, array,
or whole generator measurements onsite. Especially used to trace I-V curves
for output measurement and spotting differences with expected values, these
tools are useful to locate potential problems at solar generator level but need
specialized training for their use.

Copyright practicalactionpublishing.com
ANNEX A
Pump and generator design basics
This annex provides a quick guide for determining a duty point for pump
design together with the design of a diesel generator.
Two components are required to select a suitable pump: the design yield
(m3/hr) and the total head. These two parameters define the duty point of the
required pump.

Design yield
There are two ways of determining the design yield.

1. Based on the daily water needs of the population to be served. The daily
demand is converted to an hourly flow by dividing by the hours of
pumping. (For stand-alone SPWSs, the hours of pumping are equivalent
to the peak sun hours but for hybrid systems this is the total number
of hours of combined pumping.)
Daily demand m3/day
Design yield m3/hr
Hours of operation
2. Based on extraction of the maximum potential of the borehole. In this
case the design yield is matched to the safe yield (see section 5.3.2)
of the borehole so that the maximum potential of the borehole
is pumped.

Design yield (m3/hr) = Safe yield (m3/hr)

In both cases, the design yield should never exceed the safe yield of the
borehole (60–70 per cent of the tested yield).

Total head calculation

For boreholes,
Total dynamic head (TDH) H DWL H elev H friction H residual

Where,
HDWL = dynamic water level, i.e. the water level after completion of test
pumping measured from the borehole surface
Helev = elevation/vertical height from borehole surface/wellhead to the tank
inlet

Hfriction = friction loss, i.e. pressure drop due to friction in the pipe expressed
as a coefficient of friction per 100 m. The coefficient of friction is
obtained from friction loss tables
Hresidual = residual head, i.e. additional pressure required at the delivery point.
For pumping to tank it is a value between 0 m and 10 m

Friction Loss +
Residual Head (m)

Water Tank
Total dynamic head (m)

Tank height (m)

Running distance/riser
pipe length (m)

Well head

Ground elevation (m)

Drop
pipe
Water rest level (m)
Drawdown
Dynamic water level (m)

Pump intake level (m)

P
u
m
p

Total borehole depth (m)

Figure A1 Layout of total dynamic head calculation

For surface pumps,

Total head (TD) H suction H static H friction H residual

Where,
Hsuction = vertical height from water level to pump inlet where the water level
is below the pump inlet, i.e. negative suction. Where the water
level is above the pump inlet, this is a positive suction
Hstatic = elevation/vertical height from pump inlet to the tank inlet
Hfriction = friction loss, i.e. pressure drop due to friction in the pipe expressed
as a coefficient of friction per 100 m. The coefficient of friction is
obtained from friction loss tables
Hresidual = residual head, i.e. additional pressure required at the delivery
point. For pumping to tank it is a value between 0 m and 10 m

Pressure loss due to friction loss is affected by various factors:

1. Length of the pipe – the longer the pipe, the greater the pressure drop
will be due to friction.
2. Diameter of the pipe – the smaller the pipe, the greater the pressure drop.
3. Flow of water through the pipe – the greater the flow, the greater the
pressure drop.
4. Pipe roughness – the rougher the interior surface of the pipe, the greater
the pressure drop. PVC pipe is smoother than galvanized iron pipe and
has less friction in comparison.
5. Fittings and joints – each bend, elbow, union, flow meter, valve, strainer
etc. introduces an additional pressure drop that must be considered.

All these factors increase the resistance to the flow of water through the pipe,
thus increasing the pressure drop leading to higher pumping power requirements.
Pipe friction is determined by using friction factors (coefficients of friction),
which are available in pipe friction tables. To use these tables the following
must be known: the flow to be pumped through the pipe, the total running
distance of the pipe, the inner diameter of the pipe, the pipe type (whether
PVC or GI) and the pipe class (class C, class D etc.). The friction tables give
head loss per 100 m which is then worked out for the entire length, as
explained in the worked example below.
The residual head refers to the additional pressure requirement at the
delivery point. For delivery to a tank the value can be zero. For delivery to an
irrigation scheme the residual head will be the pressure requirement of the
irrigation nozzle/head (refer to Chapter 8, Box 8.1).
For surface pumps, besides the total head, due consideration should also be
given to the suction capability of the pump under the conditions in which it is
installed. This suction capability is called the maximum suction lift of the pump.
Lorentz provides a good step-by-step process for calculating the maximum
suction lift (https://partnernet.lorentz.de/files/lorentz_psk2-cs_manual_en.pdf).
In other sources this maximum suction lift is also explained using the net
positive suction head (NPSH) required verses the NPSH available.

Generator sizing
It is common for WASH engineers to size the generator by multiplying the
pump motor size by a factor of two to three. This section seeks to explain why
this is done with the aim that engineers will pay better attention to correct
sizing and avoid the common problem of oversizing generators, which leads
to higher fuel consumption and running costs.
Engine-driven generators are tested, rated, and offered by manufacturers
according to standard conditions of:

• maximum altitude above sea level of 150 m;

• maximum air inlet temperature of 30 °C;
• maximum humidity of 60 per cent.

Operating generators in conditions that exceed these results in reduced

power from the same generator. Generators will often be installed in locations
that are outside the standard conditions, which leads to power losses because
of higher altitude, higher temperature, and higher humidity.
What this means is that to determine how much power the generator will
produce (or working in reverse, what size of generator should be selected to
meet the power demand of the pump), deration of the generator has to be
done using the power loss values provided here:

• altitude: loss of 3.5 per cent for every additional 300 m above the
maximum recommended 150 m above sea level (2.5 per cent for turbo-
charged engines);
• air inlet temperature: loss of 2 per cent for every 5.5 °C above 30 °C
(3 per cent for turbo-charged engines);
• humidity: loss of 6 per cent at 100 per cent humidity.

In addition, the efficiency of the alternator is taken into consideration

together with voltage reduction during start-up.
The formula for calculating the generator size is:
Generator size ( kVA ) =
Motor size × efficiency factor × start-up factor
× deration for altitude × deration for temperature
× deration for humidity × 1.25

Worked example
Parameter Value
Borehole depth 118
Tested yield 13 m3/h
Water rest level 31
Dynamic water level 41
Safe yield 7.8–9.1 m3/hr
Pump intake level 93 m, using 2-inch steel pipe
Distance to tank/running distance 1350 m, using 2-inch PVC pipe, class E

Parameter Value
Ground elevation 3m
Tank height 6m
Number of elbows in the pipeline 3No. x 63 mm
Number of gate valves 1No. x 2 inch
Number of non-return valves 1No. x 2 inch
Location and altitude 30N 380E, 540 m
Temperature and Humidity 380C, 80 per cent

Water Tank

Tank
height
(6 m)

Running distance/riser
pipe length (1350 m)

Well head/borehole
surface
Ground 3m
elevation

Drop
pipe Water rest level (31 m)

Dynamic water level (41 m)

Pump intake level (93 m)

P
u
m
p

Total borehole depth (118 m)

Figure A2 Layout of worked example

Design yield
Based on maximum extraction of the borehole’s potential, the design yield =
safe yield = 7.8–9.1 m3/hr

TDH calculation
First we need to determine the length of pipe equivalent to the fittings in
the system as these also introduce losses into the system. The equivalent
length of pipe for the various 2-inch fittings and valves can be computed
using tables available from different sources such as https://powderprocess.
net/Tools_html/Piping/Pressure_Drop_Key_Piping_Elements.html or https://
www.engineeringtoolbox.com/resistance-equivalent-length-d_192.html

3 elbows: 3 × 3.0 = 9 m
1 gate valve: 0.6 m
1 non-return valve: 5.2 m
Total equivalent length = 14.8 m

Total effective riser pipe length for friction computation is therefore:

1350 m + 14.8 m = 1364.8 m
Friction tables are used to pick the corresponding coefficient of friction (such
as the one available here titled TABLE 1: PVC AND GI FRICTION LOSS TABLE
https://dayliff.com/media/com_hikashop/upload/safe/technical_reference.pdf)

• The coefficient of friction for a flow of 9 m3/hr through a 2-inch steel

drop pipe is 4.7 m per 100 m.
• The coefficient of friction for a flow of 9 m3/hr through a 2-inch PVC
class E riser pipe is 3.4 m per 100 m.

=
Therefore, total friction loss ( 4.7/100 × 93) + ( 3.4/100 × 1364.8 )
=4.37 m + 46.38 m =50.77 m
Total dynamic head = H DWL + H elev + H friction + H residual
= 41 + ( 6 + 3) + 50.77 + 10 = 110.77 m

Pump selection
From the design yield and TDH determined above, the duty point for this
system is 9 m3/hr at 110 m head. This is used to select a suitable pump.
Referring to the pump performance curves in Figure B4 (in Annex B),
a submersible borehole pump (a Grundfos SP9-21 4.0 kW 3 × 400 V 50Hz) can
be used to meet this duty point.

Generator selection
To size a generator for the 4 kW pump, the following steps should be followed.

Step 1: Allow for losses due to efficiency of alternator (80 per cent)

= 4 kW ÷ 0.8 = 5 kW

Step 2: Oversize for voltage reduction during start-up (35 per cent)

= 5 kW × 1.35 = 6.75 kW

Step 3: Compute deration factors

Altitude: 3.5 per cent for every 300 m above 150 m above sea level

540 − 150
× 3.5% =
0.0455 (4.55%)
300
Temperature: 2 per cent for every 5.5 °C above 30 °C

38 30
2.0% 0.0290 2.9%
5.5
Humidity: 6 per cent at 100 per cent humidity
At 80 per cent humidity, deration factor is 3 per cent

Step 4: Apply the deration factors to get the generator size

6.75 kW 6.75
= = 7.508 kW
(1 − 0.0455) × (1 − 0.0290 ) × (1 − 0.03) 0.9545 × 0.971 × 0.97

Step 5: Convert kW to KVA (Cosq = 0.8)

7.508 × 1.25 = 9.385 kVA

A generator that is at least 9.385 kVA is required. In this case select the next
nearest size that can be found in the market i.e. 10 kVA.

Copyright practicalactionpublishing.com
Copyright practicalactionpublishing.com
ANNEX B
Manual calculation of solar system
Chapter 5 explained why it is preferable to use computer-based software to
design the PV generator of a water scheme over manual design. While the
manual process does not produce precise results and cannot accurately predict
the actual performance of the SPWS, it is useful in cases where computer-
based software is not available, as with some solar pumping brands that do
not provide design software for sizing.
The method for selecting a pump discussed in Annex A results in a pump
brand and model, with a factory-defined motor size. In other scenarios, there
could be an existing pump with a known motor rating. The motor needs
to be powered to drive the pump that delivers water to the tank or to the
point of use. In the case of an SPWS, the motor is powered using electricity
generated by the PV generator. The process of estimating the energy to be
generated by the PV generator is discussed below. This process details how
many solar modules should be installed to power the pump motor to deliver
the desired pump performance. It should be kept in mind that the process can
result in either an undersized or oversized PV generator, leading to suboptimal
performance of the system.
For any pump, the power absorbed by the motor from the power source, P1,
can be calculated in either of two ways.

1. Obtained from pump curves

P1 = Shaft power, P2 ÷ Motor efficiency, ηm (i)

2. Calculated using the duty point (flow and head)

First, Shaft power, P2 = Hydraulic power, Ph ÷ Pump efficiency, ηp and
hence;

P1 =Hydraulic power , Ph ÷ Pump efficiency, η p ÷ Motor efficiency , ηm (ii)

Shaft power is the power transferred from the motor to the shaft of the
pump (power absorbed by the pump shaft at a given flow rate) and depends
on the efficiency of the pump. The efficiency of the pump is specified by the
pump manufacturer.
Hydraulic power is the theoretical power transferred from the pump to
the water.

Q ×ρ ×g×H
Hydraulic power, Ph = kW
( 3.6 × 106 )

Where, Q = flow capacity (m3/h)

ρ = density of fluid (1000 kg/m3)
g = gravity (9.81 m/s2)
H = total head (m)
Total energy demand of the pump is given by:

= P1 × Hours of operation
E pump (iii)

From chapter 4, the energy generated by the installed PV generator is:

Egenerated = Ppeak × PSH × PR (iv)

Where,

• Ppeak is the peak power of the PV generator at STC (obtained as the

product of the PV module’s peak power multiplied by the number of
modules used)
• PSH (peak sun hours) is the equivalent number of hours per day when
solar irradiance averages 1000 W/m2.
• PR (performance ratio) quantifies the reduction in solar energy generated
due to system losses.

Equating the two equations (iii) and (iv) gives Epump = Egenerated and hence,

P1 × Hours of operation = Ppeak × PSH × PR (v)

The performance ratio (PR) is discussed in detail in Chapter 4 and includes

all the losses in the system.
Once the power of the pump (P1), hours of operation on solar, the PSH
in the location and an estimated PR are known, it will be possible to calculate
the Ppeak (or the PV generator size to be installed).

P1 × hours of operation
PPeak = (vi)
PSH × PR
Since P1, PSH and PR are all constant, it means that increasing the PV
generator size increases the hours of operation. It should, however, be noted
that the energy provided by solar is only available during sunlight hours.
This means that the solar PV generator cannot be increased infinitely to
improve the hours of pumping. As mentioned in sections 3.2.1 and 5.3.8,
pumping beyond the solar day should be done using an alternative power
source, such as grid or diesel power.
From the peak power, the quantity of modules required based on the
models available in the market can be determined.
PPeak
Quantity of modules, P = (vii)
Module rating
Once the number of modules has been determined, their arrangement in
series and parallel is then determined. The inverter to be used influences the
series/parallel configuration.

The selection of an appropriate inverter is based on the pump selected

and the PV generator size. The inverter should be able to handle the incoming
DC power from the PV generator and condition it to that which is required
by the pump.
The system voltage of the PV system is defined by the inverter voltage.
Every inverter has a maximum input voltage (Vmax_input) and a minimum MPPT
voltage (Vmin_mppt) which is provided on the inverter data sheet. The inverter
will also have a maximum current and power input.
In addition, every solar module has a maximum voltage (Voc) and peak
voltage (Vmp) which is marked on the module and used to determine how
many modules will be connected in series to be within the minimum and
maximum system voltage.

If M =
the number of modules in series (one series arrangement is
commonly referred to as a string)
N = the number of strings in parallel

Then,

Total quantity of modules, P = M × N (see Figure B1) (viii)

N number of strings
(connected in
parallel) Strings cables

M number of modules per string

(connected in series)

(Main DC cable)

Figure B1 Number of modules arranged in series and parallel

The number of modules in series (M) is determined using the following

limits.
Vmin _ mppt (system) Vmax _ input (system)
< M< (ix)
Vmp ( panel ) Voc ( panel )

The value of M should be as big as possible to provide the maximum

voltage possible. In other words, the value of M chosen should be as close as
possible to the upper limit.
Since P and M are now known, the value of N (number of parallel strings)
can be determined by plugging into formula viii.

Worked example
Step 1: Determine the water demand and calculate the required duty point
(design yield and head)
Determination of duty point is explained in Annex A. Assuming the water
demand is 60 m3/day, and using a duty point of 8.8 m3/hr at 110 m head, it
means that the pump must be operated for approximately 7 hours at peak
pumping to meet the demand using solar alone.

Step 2: Select a suitable pump for the duty point

Using a submersible borehole pump, a Grundfos SP9-21 4.0 Kw 3 × 400 V 50Hz
can be used to meet this duty point. See pump head-flow curve (Figure B4) and
pump data (Figure B5) below.

Step 3: Determine the pump power demand, P1

From the P2/Q curves (see power-flow curve below in Figure B6) at 8.8 m3/hr
the power absorbed by the pump shaft is P2 = 3.77 kW.
Grundfos SP9-21 is fitted to a 4 kW motor and so the loading on the
motor is 3.8/4 = 95 per cent. The efficiency of the motor at this loading
level can be obtained from the motor data sheet (Figure B7) by interpo-
lating between ηm = 78.4 per cent (at 75 per cent loading) and ηm = 78.0 per
cent (at 100 per cent loading). Interpolating between the two values yields:
at 95 per cent loading, motor efficiency, ηm = 78.08 per cent.

Note: For simplicity, the motor efficiency at the nearest loading (in this case 78.0 per
cent) can also be used instead of interpolating.

Therefore, power absorbed by the motor from formula (i) is

P2 ÷ ηm which is 3.77 ÷ 0.7808 =

P1 = 4.828 kW

Or alternatively using formulae (ii) and referring to Figure B3 below, ηp = 0.7

P1 = Ph ÷ η p ÷ ηm = ( 8.8 × 9.8 × 1000 × 110 ) ÷ ( 3.6 × 106 × 0.7 × 0.7808 )

= 4.821 kW ( close to 4.828 )

Step 4: Determine the available solar resource

Assuming the installation will be done in Sub-Saharan Africa (10N 390E in
Kenya, see irradiation map in Figure B8), the average solar irradiation is
2190 kWh/m2 (equivalent to 6 peak sun hours) (source: Solargis, Kenya
solar resource map).

Company name:
Created by:

98699059 SP 9-21
Input - summary Products
Pump: SP 9-21, 1 x 98699059
Water volume (max): 60 m³/day
Solar module: 36 x Trinasolar 270
Month for sizing: June
Switch box / control unit: RSI 3x380-440V IP66 5.5kW 12A, 1 x
Static lift above ground: 110 m 99044351
Dynamic water level: 0 m
Switch box / control unit: OTDCP16, Circuit Breaker, 16Amp, 2 x
Sun tracking: No (fixed) 98341686
Location: 603, Sericho, Isiolo, Kenya
Latitude: 1 DD, Longitude: 39 DD Switch box / control unit: OVR PV 40-1000 P, Surge Protection, 1 x
98341687
Others: Sine-wave filter, 1 x 96754976

Sizing results - summary

Water production, Peak flow and Price Typical performance at solar radiation 800 W/m²
Total water production per year: 24500 m³ Flow: 8.3 m³/h
Avg. water production per day: 67.2 m³/day Total head: 110.0 m
Average water production per watt per day: 6.9 l/Wp/day
Cables and pipes:
Solar module configuration: Pump cable length: 120 m
Number of solar modules in series: 18, in parallel: 2 Pump cable size: 4 mm²
Solar array rated power: 9.72 kW Total cable loss: 2.2 %
Solar array rated volts: 556.2 V
Sun tracking: No (fixed)
Pipe diameter: DN50(44)
Tilt angle: 15 deg.
Friction loss: 0.0 m

System performance - monthly average

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Water production [m³/day] 69.6 70.1 68.4 66.5 64.8 62.6 63.3 67 69.6 69.4 67 68.2
Energy production [kWh/day] 44.2 44.5 43.4 42.3 41.2 40.1 40.5 42.5 44.0 44.0 42.7 43.4
Radiation horizontal [kWh/m² day] 6.8 7.4 7.1 6.9 7.0 6.6 6.6 7.2 7.7 7.2 6.1 6.2
Radiation tilt [kWh/m² day] 7.2 7.6 6.9 6.4 6.1 5.7 5.8 6.5 7.4 7.2 6.4 6.6
Avg. Temp. [K] 28. 29. 30. 28. 28. 27. 26. 26. 27. 28. 27. 27.
Solar data location: Latitude: 1 DD, Longitude: 39 DD

Water production - monthly Water production - daily: June

m³/day m³/h
70
8

60 7

50 6

5
40

4
30
3
20
2

10
1

0 0
J F M A M J J A S O N D 0 2 4 6 8 10 12 14 16 18 20 22
Month Time of Day

Printed from Grundfos Product Centre [2019.08.002] 10/11

Figure B2 Grundfos sizing result

BERNT LORENTZ GmbH

Wednesday, 03 July 2019

New project

Solar pumping project

Parameter
Location: , (1° North; 39° East) Water temperature: 25 °C
Required daily output: 60 m³; Sizing for June Dirt loss: 5.0 % Motor cable: 120 m
Pipe type: - Total dynamic head: 110 m Pipe length: -

Products Quantity Details

PSk2-7 C-SJ8-30 1 pc. Submersible pump system including controller with DataModule, motor and pump end
Trinasolar 270 40 pc. 10,800 Wp; 20 x 2 modules; 15 ° tilted
Motor cable 120 m 6 mm² 3-phase cable for power and 1-phase cable for ground
Accessories 1 set Surge Protector, PV Disconnect 1000-40-5, PV Protect 1000-125, SmartPSUk2, SmartStart, Well
Probe V2

SunSwitch setting in PumpScanner min. 200 W/m²

Daily output in June 61 m³
Daily values Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Av.

Output [m³]

Energy [kWh] 59 60 54 48 47 44 45 49 55 54 50 53 52
Irradiation [kWh/m²] 6.6 6.8 6.1 5.4 5.3 4.9 5.0 5.5 6.2 6.0 5.4 5.8 5.7
Rainfall [mm] 0.37 0.27 1.2 3.2 1.2 0.10 0.10 0.067 0.13 1.3 2.4 1.1 0.93
Ambient temp. [°C] 28 29 29 27 27 27 26 26 27 27 26 27 27

Hourly values 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00

Output [m³/h]

Energy [kWh] 0 1.2 2.9 4.2 5.3 5.8 6.0 5.7 5.1 4.0 2.7 1.2 0
Irradiation [kWh/m²] 0 0.12 0.29 0.45 0.58 0.65 0.68 0.65 0.58 0.45 0.29 0.12 0
Ambient temp. [°C] 22 22 23 25 27 29 31 32 32 32 32 31 31

Created by LORENTZ COMPASS 3.1.0.135

1/5 All specifications and information are given with good intent, errors are possible and products may be subject to change
without notice.

Figure B3 Lorentz sizing result

SP 9
Performance curves

ηpump = 70 per cent

TM06 1424 2414

NPSH: Minimum inlet pressure 0.5 m.

Figure B4 Grundfos SP 9 head-flow curve

Dimensions and weights

Mot or Di m e n s io ns [ m m ]
Rp 2 Net
Pump type weight
Power
Type C B A D E [kg]
[kW]
Single-phase, 1 x 230 V / 1 x 240 V
SP 9-4 MS 402 0.75 438 306 744 95 101 15.9
SP 9-5 MS 402 1.1 488 346 834 95 101 18.3
SP 9-8 MS 402 1.5 638 346 984 95 101 20.0
SP 9-10 MS 4000 2.2 738 577 1315 95 101 31.6
SP 9-11 MS 4000 2.2 788 577 1365 95 101 32.2
Three-phase, 3 x 220-230 V / 3 x 380-400-415 V
SP 9-4 MS 402 0.75 438 276 714 95 101 14.7
SP 9-5 MS 402 1.1 488 306 794 95 101 16.5
SP 9-8 MS 402 1.5 638 346 984 95 101 20.0
SP 9-10 MS 402 2.2 738 346 1084 95 101 22.5
SP 9-11 MS 402 2.2 788 346 1134 95 101 23.1
SP 9-4 MS 4000 0.75 438 402 840 95 101 19.2
SP 9-5 MS 4000 1.1 488 417 905 95 101 20.7
TM06 5396 0818

SP 9-8 MS 4000 1.5 638 417 1055 95 101 22.5

SP 9-10 MS 4000 2.2 738 457 1195 95 101 25.6
SP 9-11 MS 4000 2.2 788 457 1245 95 101 26.2
SP 9-13 MS 4000 3 888 497 1385 95 101 29.3
SP 9-16 MS 4000 3 1038 497 1535 95 101 31.0
SP 9-18 MS 4000 4 1138 577 1715 95 101 36.2
E Rp 21 1/2
RP
SP 9-21 MS 4000 4 1288 577 1865 95 101 37.9
SP 9-23 MS 4000 5.5 1388 677 2065 95 101 44.1
SP 9-25 MS 4000 5.5 1488 677 2165 95 101 45.2
SP 9-29 MS 4000 5.5 1688 677 2365 95 101 47.7
SP 9-32 MS 4000 7.5 1838 777 2615 95 101 53.4
SP 9-36 MS 4000 7.5 2038 777 2815 95 101 55.7
SP 9-40 MS 4000 7.5 2238 777 3015 95 101 58.0
SP 9-23 MS 6000 5.5 1451 547 1998 139.5 139.5 55.0
C

SP 9-25 MS 6000 5.5 1551 547 2098 139.5 139.5 562

SP 9-29 MS 6000 5.5 1751 547 2298 139.5 139.5 58.6
A

SP 9-32 MS 6000 7.5 1901 577 2478 139.5 139.5 63.4

SP-9-36 MS 6000 7.5 2101 577 2678 139.5 139.5 65.8
SP-9-40 MS 6000 7.5 2301 577 2878 139.5 139.5 68.1
SP 9-44 MS 6000 9.2 2501 607 3108 139.5 139.5 78.2
SP 9-48 MS 6000 9.2 2701 607 3308 139.5 139.5 80.6
SP 9-52 MS 6000 11 2901 637 3538 139.5 139.5 86.1
SP 9-56 1) MS 6000 11 3396 637 4033 139.5 140 110.0
B

1)
SP 9-60 MS 6000 13 3596 667 4263 139.5 140 116.5
SP 9-65 1) MS 6000 13 3846 667 4513 139.5 140 120.9
D SP 9-69 1) MS 6000 13 4046 667 4713 139.5 140 124.3
TM07 3068 4618

Pump in sleeve SP 9-75 1) MS 6000 15 4346 702 5048 139.5 140 133.6
SP 9-79 1) MS 6000 15 4546 702 5248 139.5 140 137.1
1)
SP 9-86 MS 6000 18.5 4896 757 5653 139.5 140 147.6
SP 9-93 1) MS 6000 18.5 5246 757 6003 139.5 140 153.7
1) SP 9-56 to SP 9-86 are mounted in sleeve for R2 connection.
The pump types above are also availabl e in N- and R-versions. See page 6.
E = Maximum diameter of pump inclusive of cable guard and motor.

Figure B5 Grundfos SP 9 pump data sheet

Power curves

P2 = 3.77 kW
TM06 1425 2414

Figure B6 Grundfos SP 9 power-flow curves

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204 SOLAR PUMPING FOR WATER SUPPLY 7
3 x 230 V, submersible rewindable motors "MMS"
E le c t ri c a l d a t a D i me n s i o n s

Motor Motor efficiency [%] Power factor Build

Full-load Ist Diameter in Weight
Power current
Type Size η50 % η75 % η100 % Cos φ 50 % Cos φ 75 % Cos φ 100 % In [mm] length [kg]
[kW] In [A]
[mm]
MMS 6 (N, R) 6" 5.5 25.0 71 75 76 0.61 0.72 0.78 3.5 144 807 50
MMS 6 (N, R) 6" 7.5 33.5 72 76 77 0.59 0.71 0.78 3.5 144 837 53
MMS 6 (N, R) 6" 9.2 40.5 74 77 78 0.59 0.71 0.78 3.6 144 867 55
MMS 6 (N, R) 6" 11 50.0 74 78 79 0.53 0.66 0.74 3.8 144 897 60
MMS 6 (N, R) 6" 13 56.0 77 80 80 0.57 0.69 0.77 3.9 144 927 65
MMS 6 (N, R) 6" 15 62.5 79 82 82 0.58 0.71 0.79 4.3 144 997 77
MMS 6 (N, R) 6" 18.5 75.0 80 82 82 0.61 0.75 0.81 4.2 144 1057 83
MMS 6 (N, R) 6" 22 87.0 82 84 83 0.61 0.74 0.81 5.3 144 1087 95
MMS 6 (N, R) 6" 26 106 81 83 83 0.57 0.7 0.78 5.6 144 1157 105
MMS 6 (N, R) 6" 30 118 82 83 82 0.63 0.76 0.82 4.8 144 1212 110
MMS 6 (N, R) 6" 37 148 82 84 83 0.59 0.72 0.81 5.4 144 1312 120
MMS 8000 (N, R) 8" 22 82.5 80 84 84 0.71 0.80 0.84 5.3 192 1010 126
MMS 8000 (N, R) 8" 26 95.5 81 84 84 0.76 0.83 0.86 5.1 192 1050 134
MMS 8000 (N, R) 8" 30 110 83 85 86 0.71 0.80 0.84 5.7 192 1110 146
MMS 8000 (N, R) 8" 37 134 83 86 86 0.73 0.82 0.85 5.7 192 1160 156
MMS 8000 (N, R) 8" 45 168 84 87 88 0.62 0.74 0.81 6.0 192 1270 177
MMS 8000 (N, R) 8" 55 214 84 87 88 0.57 0.70 0.77 5.9 192 1350 192
MMS 8000 (N, R) 8" 63 210 87 89 89 0.81 0.87 0.90 5.7 192 1490 218
MMS 10000 (N, R) 10" 75 270 84 86 86 0.72 0.81 0.85 5.4 237 1500 330
MMS 10000 (N, R) 10" 92 345 83 85 86 0.65 0.77 0.82 5.6 237 1690 385
MMS 10000 (N, R) 10" 110 385 85 86 86 0.80 0.86 0.88 5.7 237 1870 435

3 x 400 V, submersible motors "MS"

E l e c t r ic a l d a t a Di m e ns io ns

Motor Motor efficiency [%] Power factor

Build
Full-load current Ist Diameter in Weight
Power In [A] [mm] length [kg]
Type Size η50 % η75 % η100 % Cos φ 50 % Cos φ 75 % Cos φ 100 % In
[kW] [mm]
MS 402 4" 0.37 1.40 51.0 59.5 64.0 0.44 0.55 0.64 3.7 95 229 5.5
MS 402 4" 0.55 2.20 48.5 57.0 64.0 0.42 0.52 0.64 3.5 95 244 6.3
MS 402 4" 0.75 2.30 64.0 69.5 73.0 0.50 0.62 0.72 4.7 95 279 7.7
MS 4000R 4" 0.75 1.84 68.1 71.6 72.8 0.69 0.79 0.84 4.9 95 401 13.0
MS 402 4" 1.1 3.40 62.5 69.0 73.0 0.47 0.59 0.72 4.6 95 309 8.9
MS 4000R 4" 1.1 2.75 70.3 74.0 74.4 0.62 0.74 0.82 5.1 95 416 14.0
MS 402 4" 1.5 4.20 68.0 73.0 75.0 0.50 0.64 0.75 5.0 95 349 10.5
MS 4000R 4" 1.5 4.00 69.1 72.7 73.7 0.55 0.69 0.78 4.3 95 416 14.0
MS 402 4" 2.2 5.50 72.5 75.5 76.0 0.56 0.71 0.82 4.7 95 349 11.9
MS 4000 (R) 4" 2.2 6.05 67.9 73.1 74.5 0.49 0.63 0.74 4.5 95 456 16.0
MS 4000 (R) 4" 3.0 7.85 71.5 74.5 75.2 0.53 0.67 0.77 4.5 95 496 17.0
MS 4000 (R) 4" 4.0 9.60 77.3 78.4 78.0 0.57 0.71 0.80 4.8 95 576 21.0
MS 4000 (R) 4" 5.5 13.0 78.5 80.1 79.8 0.57 0.72 0.81 4.9 95 676 26.0
MS 4000 (R) 4" 7.5 18.8 75.2 78.2 78.2 0.52 0.67 0.78 4.5 95 777 31.0
MS 6000 (R) 6" 5.5 13.6 78.0 80.0 80.5 0.55 0.67 0.77 4.4 139.5 547 35.5
MS 6000 (R) 6" 7.5 17.6 81.5 82.0 82.0 0.60 0.73 0.80 4.3 139.5 577 37.0
MS 6000 (R) 6" 9.2 21.8 78.0 80.0 79.5 0.61 0.73 0.81 4.6 139.5 607 42.5
MS 6000 (R) 6" 11 24.8 82.0 83.0 82.5 0.65 0.77 0.83 4.7 139.5 637 45.5
MS 6000 (R) 6" 13 30.0 82.5 83.5 82.0 0.62 0.74 0.81 4.6 139.5 667 48.5
MS 6000 (R) 6" 15 34.0 82.0 83.5 83.5 0.64 0.76 0.82 5.0 139.5 702 52.5
MS 6000 (R) 6" 18.5 42.0 83.5 84.5 83.5 0.62 0.73 0.81 5.1 139.5 757 58.0
MS 6000 (R) 6" 22 48.0 84.5 85.0 83.5 0.67 0.77 0.84 5.0 139.5 817 64.0
MS 6000 (R) 6" 26 57.0 84.5 85.0 84.0 0.66 0.77 0.84 4.9 139.5 877 69.5
MS 6000 (R) 6" 30 66.5 84.5 85.0 84.0 0.64 0.77 0.83 4.9 139.5 947 77.5

Figure B7 Grundfos motor data sheet

Figure B8 Solar resource map for Kenya

Source: Solargis

Step 5: Compute the system losses/performance ratio

Considering only the following losses:
Losses due to temperature, Ltemp = 10 per cent
Wiring losses, Lwire = 3 per cent
Losses due to soiling/dirt, Lsoiling = 5 per cent
Losses due to reflectance Lref = 3 per cent
Losses due to incorrect orientation, Lorientation = 2 per cent
Losses due to incorrect tilt, Ltilt = 3 per cent
Loss due to power tolerance, Ltolerance = 3 per cent
Losses due to mismatching, Lmismatch = 2 per cent
Losses due to conversion = 3 per cent
Losses due to light-induced degradation, LLID = 3 per cent

Then PR = (1 – 0.1) × (1 – 0.03) × (1 – 0.05) × (1 – 0.03) × (1 – 0.02) × (1 – 0.03)

× (1 – 0.05) × (1 – 0.02) × (1 – 0.03) × (1 – 0.03)
= 0.90 × 0.97 × 0.95 × 0.97 × 0.98 × 0.97 × 0.97 × 0.98 × 0.97 × 0.97
= 0.684

Step 6: Calculate the PV peak power to be installed

From formula (vi)

P1 × Hours of operation
PPeak =
PSH × PR
4.828 × 7 33.796
=
PPeak = = 8.23 kW
6 × 0.684 4.104

Step 7: Select a suitable inverter/controller

Using electrical data for Grundfos inverters, shown below and matching to the
Grundfos SP9-21, 4 kW, 9.75-9.6-9.8A, 3 × 400 V (see motor electrical data below),
the appropriate inverter is the 5.5 kW inverter (see under controller data below)
with rated output current of 12 A 3 × 380−415 V. The system voltage is Vmin_mppt =
400 VDC (recommended Vmin_mppt = 530–61 5 V), Vmax_input system = 800 VDC.

Note the 4 kW inverter with a rated output of 9.6A has not been selected as it is right
on the edge of the required motor current.

Grundfos otor Electrical data:

Motor type: MS4000
Rated power - P2: 4 kW
Power (P2) required by pump: 4 kW
Mains frequency: 50 Hz
Rated voltage: 3 × 380-400-415 V
Rated current: 9.75-9.60-9.80 A

Grundfos otor Electrical data:

Starting current: 460-500-530 per cent
Cos phi - power factor: 0.85-0.80-0.77
Rated speed: 2850-2865-2875 rpm
Start. method: direct-on-line
Enclosure class (IEC 34-5): IP68
Insulation class (IEC 85): F
Built-in temp. transmitter: no
Motor No: 79194510

Grundfos controller data

Voltage 3 × 208-240 V 3 × 380-440 V
Installation Min. ambient temperature [°C (°F)] −10 (14) −10 (14)
environment Max. ambient temperature [°C (°F)] 60 (140) 60 (140)
Max. relative humidity [%] 100 100
Electrical DC minimum MPP voltage [VDC] 230 400
data DC recommended MPP voltage [VDC] 290−336 530−615
DC maximum input voltage [VDC] 400 800
AC input voltage [VAC] 208−240 380−460
AC rated output voltage [VAC] 220 380−440
Min. frequency [Hz] 5 5
Max. frequency [Hz] 60 60
Phases 3 3
Enclosure class IP66 IP66

Grundfos high voltage range

Power Product number Electrical data
[kW (hp)] Max. P2 Rated output Frame size
[kW (hp)] current [A]

2.2 (3) 99044348 2.2 (3) 5.6 A

3.0 (4) 99044349 3.0 (4) 8 A
4.0 (5) 99044350 4.0 (5) 9.6 A
5.5 (7.5) 99044351 5.5 (7.5) 12 A
7.5 (10) 99044352 7.5 (10) 16 B
11 (15) 99044363 11 (15) 23 B
15 (20) 99044364 15 (20) 31 B
18.5 (25) 99044365 18.5 (25) 38 C
22 (30) 99044366 22 (30) 46 C
30 (40) 99044367 30 (40) 61 C
37 (50) 99044368 37 (50) 72 C

Step 8: Determine the quantity of modules and module configuration

Using a multicrystalline 270 W module (Trinasolar) with electrical data shown
below, Vmp = 30.9 V, Voc = 37.9 V

Electrical data (STC)

Peak Power Watts-PMAX (Wp)* 265 270 275 280 285
Power Output Tolerance-PMAX (W) 0 ~ +5
Maximum Power Voltage-VMPP (V) 30.8 30.9 31.1 31.4 31.6
Maximum Power Current-IMPP (A) 8.61 8.73 8.84 8.92 9.02
Open Circuit Voltage-VOC (V) 37.7 37.9 38.1 38.2 38.3
Short Circuit Current-ISC (A) 9.15 9.22 9.32 9.40 9.49
Module E_ciency m (%) 16.2 16.5 16.8 17.1 17.4

Temperature ratings
NOCT(Nominal Operating Cell Temperature) 44°C (±2°C)
Temperature Coe_cient of PMAX −0.41%/°C
Temperature Coe_cient of VOC −0.32%/°C
Temperature Coe_cient of ISC 0.05%/°C

PPeak 8.23 × 1000 ( W )

Number=
of modules, P =
Module rating 270 ( W )
= 30.4 minimum number of modules
Using formula ix the number of modules in series is calculated using the
two limits:

Vmin _ mppt ( system ) Vmax _ input ( system )

= = 17
530/30.9 = 800/37.9= 21
Vmp ( panel ) Voc ( panel )

The number of modules per string is a value between 17 and 21, but the
number should be as high as possible while keeping the number optimal.
The number of modules in all strings must also be equal.
Since P = M × N, two parallel strings of between 17 and 21 modules will give
a PV generator of between 9.18 kW and 11.34 kW.
Check: Using Grundfos sizing software (a step-by-step process for using the
Grundfos sizing tool can be found at GLOSWI, 2018f), the sizing gives the
results shown in Figure B2. The proposed configuration is 18 panels in series
in two strings (9.72 kW)

Alternatively, using a Lorentz inverter with the electrical data yields shown:

Lorentz controller data

Power max. 8.0 kW
Input voltage max. 850 V
Optimum Vmp** > 575 V
Motor current max. 13 A
Efficiency max. 98 per cent
Ambient temp. –30 … 50 °C
Enclosure class IP54

Vmin _ mppt ( system ) Vmax _ input ( system )

= = 18.6
575/30.9 = = 22.4
850/37.9
Vmp ( panel ) Voc ( panel )

Two parallel strings of between 19 and 22 modules will give a PV generator

of between 10.26 kW and 11.88 kW.
Check: Using the Lorentz Compass software (a step-by-step process for
using the Lorentz Compass sizing tool can also be found at GLOWSI, 2018f)
the sizing results are shown in Figure B3. The proposed configuration is
20 panels in series in two strings (10.8kW)
In both cases, the check done using sizing software give designs that produce
more water than the required daily amount of 60 m3/day. Using computer-based
software takes into consideration the hydraulic and electric load, the available
solar resource, the power losses and the module characteristics to give a more
precise, predictable and optimal design than the manual process discussed here.

Step 9: Determine if alternative power source is required

In the case where the water demand is higher than what solar alone can
provide, an alternative source of power will be required to prolong pumping.
In this example, extended pumping is not necessary as solar alone is sufficient
to meet the demand of 60 m3/day.
For illustration, if the water demand in this case was, say, 100 m3/day,
considering the worst month, it would be necessary to prolong pumping for
4–5 hours with either a generator or grid power (if present) to provide the deficit
of 40 m3/day. The additional pumping would be done in the early morning, late
evening, or at night when solar pumping cannot be achieved.

Estimation of daily pumped flow

The amount of water pumped is dependent on the available solar resource,
day by day and month by month, as well as the pump power. Estimation

of pumped water can be done by applying previous formulas and working

in reverse.

P1 = P2 ÷ ηm and P2 = Ph ÷ η p Hence; P1 = Ph ÷ (η p × ηm )

Also,
P1 × Hours of operation Ph × Hours of operation
=PPeak =
PSH × PR η p × ηm × PSH × PR

Q × ρ × g × H × Hours of operation
=
η p × ηm × PSH × PR × 3.6 × 106
It is known that Daily flow = Q × Hours of operation, and using ρ =
1000 kg/m3, g = 9.81 m/s2

Daily flow × ρ × g × H Daily flow × H × 2.725–03

PPeak =
η p × ηm × PSH × PR × 3.6 × 106 η p × ηm × PSH × PR

Ppeak × η( p , m ) × PSH × PR
Thus, daily flow can be estimated as: Daily flow =
H × 2.725 × 10 −3

Daily flow (m3/day) = Ppeak (Wp) x η(p,m) x PSH x PR ÷ H(m) x 2.725

Quick reference of combined pump and motor efficiency (ηp,m) is between

25 per cent and 60 per cent. All other factors in the formulas are known
from previous workings. Therefore, by knowing the different PSH values
month by month, one can work backwards to estimate the daily flow for
each month or season for the installed SPWS. Likewise, by estimating the
required duty point, the required PV generator can also be calculated by
rearranging the formulas.

Copyright practicalactionpublishing.com
ANNEX C
Example of calculation of losses due
to non-optimum tilt angle of PV modules
Question: How can more energy be obtained with 1 kWpk of PV modules
mounted in Valencia (Spain)?

1. With the modules mounted horizontally on the roof.

2. With the modules mounted in the south face of the same building.

Use the PVGIS calculation tools available from the European Commission
(2019) to solve the question.

Remember that in PV systems the azimuth orientation is defined as the

deviation from south (for the northern hemisphere).

Solution: With the default values given by the program for the location
‘Valencia, Spain’, and selecting the option ‘Optimize slope and azimuth’, the
value of PSHoptimum = 2070 PSH (yearly in-plane irradiation in kWh/m2) can
be obtained:

Summary

Provided inputs:
Location [Lat/Lon]: 39.470, −0.376
Horizon: Calculated
Database used: PVGIS-CMSAF
PV technology: Crystalline silicon
PV installed) [kWp]: 1
System loss [%]: 14

Simulation inputs:
Slope angle [0]: 36 (opt)
Azimuth angle [0]: −1 (opt)
Yearly PV energy production [kWh]: 1610
Yearly in-plane irradiation [kWh/m2]: 2070
Year to year variability [kWh]: 43.10
Changes in output due to:
Angle of incidence [%]: −2.5
Spectral effects [%]: 0.6
Temperature and low irradiance [%]: −7.8
Total loss [%]: −22.2

The PV modules mounted horizontally on the roof are 0° tilted and the
orientation doesn’t matter. The modules mounted on the south face have a
tilt angle equal to 90°. Using the program for these two cases the following
results are obtained:

Simulation inputs:
Slope angle [0]: 0
Azimuth angle [0]: 0
Yearly PV energy production [kWh]: 1360
Yearly in-plane irradiation [kWh/m2]: 1770
Year to year variability [kWh]: 27.00
Changes in output due to:
Angle of incidence [%]: −3.6
Spectral effects [%]: 0.4
Temperature and low irradiance [%]: −7.7
Total loss [%]: −23.2

Simulation inputs:
Slope angle [0]: 90
Azimuth angle [ ]: 0
0
Yearly PV energy production [kWh]: 1050
Yearly in-plane irradiation [kWh/m2]: 1370
Year to year variability [kWh]: 38.80
Changes in output due to:
Angle of incidence [%]: −5.4
Spectral effects [%]: 0.8
Temperature and low irradiance [%]: −6.5
Total loss [%]: −23.4

The irradiation for the horizontal modules is PSH0° = 1770 and for the
modules on the facade is PSH90° = 1370. It is evident that the horizontal config-
uration produces more energy than with the modules mounted on the facade.
The Lori+tilt factor for each case are the following:

 1770 
0° =
Ltilt0° 1 − =0.145 → 14.5%
 2070 

 1330 
90° =
Ltilt90° 1 − =0.375 → 35.7%
 2070 

In the parameters given by the PVGIS tool is detailed the ‘system loss’,
which corresponds to the performance ratio defined previously. It can be seen
that, with a small variation, the three values of PR only vary by 1.1 per cent,
with an important variation of the losses due to angular and spectral
reflectance in the different configurations.

Copyright practicalactionpublishing.com
Copyright practicalactionpublishing.com
ANNEX D
Cable sizing
For pumping systems, the right dimension of the cable cross-section can be
found using any of the following four ways:
Method 1: Computer-based pumping design simulations will give
recommended cable size
Method 2: Manual calculation of the allowable voltage drop, followed by
selection of the right cable size from voltage drop charts such as the one
in Figure D1. In this method, the voltage drop permissible is computed in
millivolts per amp per metre (mV/A/m). Alternatively for DC cables, the
allowable voltage drop can also be calculated using the formula
Voltage drop = Lc × R × I

Where Lc = Length of a two-core cable (back and forth) in metres, I =

Nominal current in Amps, R = Electrical resistance of a two-core cable in
ohms/metre.
Method 3: Using tables provided by pumping equipment providers. These
tables will usually have a list of cable sizes with the maximum length of
each cable size that can be run from the motor to the power source for each
motor size, based on a maximum voltage drop (1–3 per cent). An example of
a submersible cable sizing chart provided by Grundfos is shown in Figure D2
(for AC motors at maximum water temperature of 30°C). Different tables are
available for DC motors and DC cables.
Method 4: Using the formulas provided in section 4.3. It should be noted that
for DC cables, the current flows all the way through the negative and positive
circuit and therefore voltage drop is considered for double the length of cable.
∆Pwire =
∆Vwire I

lwire 2 1 lwire 2
∆Pwire = Rwire ⋅ I 2 = ρ ⋅ ⋅I = ⋅ ⋅I
Swire γ Swire

Example 1: AC cable sizing using method 2

11 kW 3 × 400 VAC, 24.6 A motor, 200 m AC cable

Note that the entire cable length should be considered from the pump all the way to
the AC controller e.g. 150 m submerged + 50 m on the surface = 200 m.

Step 1 – Permissible voltage drop calculation: 3 per cent × 400 V × 1000

= 12,000 mV
Step 2 – Computation of permissible voltage drop per amp per metre
through the cable
= 12,000 mV ÷ (24.6 A × 200 m) = 2.44 mV/A/m
Copyright practicalactionpublishing.com
216

Conductor or Multicore amoured pvc insulated cable (PVC-SWA) Twin and multicore pvc insulated cable
size (mm2) Two core cable Three or four core cable Two core cable Single Three or four core cable
Single phase supply Three phase supply phase supply

Copyright practicalactionpublishing.com
Max current Voltage drop Max current Voltage drop Max current Voltage drop Max current Voltage drop
capacity per amp per capacity (A) per amp per capacity (A) per amp per capacity (A) per amp per
(A) meter (mv) meter (mv) meter (mv) meter (mv)
1.5 22 29.00 19 25.00 19.5 29.00 17.5 25.0
2.5 31 18.00 26 15.00 27 18.00 24 15.0
SOLAR PUMPING FOR WATER SUPPLY

4.0 41 11.00 35 9.50 36 11.00 32 9.5

6.0 53 7.30 45 6.40 46 7.300 41 6.4
10.0 72 4.40 62 3.80 63 4.40 57 3.8
16.0 97 2.80 83 2.40 85 2.80 76 2.4
25.0 128 1.75 110 1.50 112 1.75 96 1.5
35.0 157 1.25 135 1.10 138 1.25 119 1.1
50.0 190 0.94 163 0.81 168 0.94 144 0.81

Figure D1 Table of cable current capacity and voltage drop

Source: Davis & Shirtliff Ltd
CABLE SIZING 217

Cable dimensions at 3 x 400 V,

V 50 Hz, DOL
V ltage drop: 3 per cent
Vo

Dimensions
Motor kW In [A] Cos φ 100 % [mm2]

1.5 2.5 4 6 10 16 25 35 50 70 95 120 150 185 240 300

4" 0.37 1.4 0.64 462 767
4" 0.55 2.2 0.64 294 488 777
4" 0.75 2.3 0.72 250 416 662 987
4" 1.1 3.4 0.72 169 281 448 668
4" 1.5 4.2 0.75 132 219 348 520 857
4" 2.2 5.5 0.82 92 153 244 364 602 951
4" 3 7.85 0.77 69 114 182 271 447 705
4" 4 9.6 0.8 54 90 143 214 353 557 853
4" 5.5 13 0.81 39 66 104 156 258 407 624 855
4" 7.5 18.8 0.78 28 47 75 112 185 291 445 609 841
6" 4 9.2 0.82 55 91 146 218 359 566 867
6" 5.5 13.6 0.77 40 66 105 157 258 407 622 850
6" 7.5 17.6 0.8 29 49 78 117 193 304 465 637 882
6" 9.2 21.8 0.81 23 39 62 93 154 243 372 510 706 950
6" 11 24.8 0.83 34 53 80 132 209 320 440 610 823
6" 13 30 0.81 28 45 68 112 176 270 370 513 690 893
6" 15 34 0. 82 39 59 97 154 236 324 449 604 783 947
6" 18. 5 42 0. 81 48 80 126 193 265 366 493 638 770 914
6" 22 48 0. 84 41 67 107 164 225 313 422 549 665 793 927
6" 26 57 0. 84 57 90 138 189 263 355 462 560 667 781 937
6" 30 66. 5 0. 83 49 78 11 9 164 227 30 7 398 482 574 670 803 926
6" 37 85. 5 0. 79 63 97 133 183 246 317 382 452 525 624 714
8" 22 48 0. 84 41 67 107 164 225 313 422 549 665 793 927
8" 26 56. 5 0. 85 57 90 138 189 263 356 464 563 672 787 947
8" 30 64 0. 85 50 79 122 167 233 314 409 497 593 695 836 968
8" 37 78. 5 0. 85 65 99 136 190 256 334 405 483 567 682 789
8" 45 96. 5 0. 82 54 83 11 4 158 213 276 334 396 462 553 636
8" 55 11 4 0. 85 68 94 131 177 230 279 333 390 469 544
8" 63 132 0. 83 83 11 5 155 201 243 289 338 404 466
8" 75 152 0. 86 70 97 132 171 208 249 292 353 409
8" 92 186 0. 86 79 107 140 170 204 239 28 8 335
8" 110 224 0.87 89 116 141 169 198 240 279
10" 75 156 0. 84 69 96 130 169 205 244 285 343 396
10" 92 194 0. 82 79 106 137 166 197 230 275 316
10" 110 228 0.84 89 116 140 167 195 234 271
10" 132 270 0.84 98 118 141 165 198 229
10" 147 315 0.81 103 122 142 169 194
10" 170 365 0.81 105 122 146 168
10" 190 425 0.79 106 125 144
12" 147 305 0.83 105 125 146 175 202
12" 170 345 0.85 92 110 129 155 180
12" 190 390 0.84 98 114 137 158
12" 220 445 0.85 100 120 139
12" 250 505 0.85 106 123
Max. current for cable [A]* 23 30 41 53 74 99 131 162 202 250 301 352 404 461 547 633

* At particularly favourable heat dissipation conditions. Maxi mum cable length in metres from motor starter to pump.
For motors with star-delta starting, the cable length can be calculated
by multiplying the relevant cabl e length from the above table by .3

Figure D2 Table of cable sizes

Source: Grundfos

Step 3 – Selection of the cable size from appropriate cable chart. From
Figure D1 (for multicore armoured PVC insulated cable >> three
or four core cable three phase supply) a 16 mm2 cable will have
a voltage drop of 2.4 mV/A/m which is within the permissible
maximum of 2.44 mV/A/m computed above.

Example 2: AC cable sizing using method 3

11 kW 3 × 400 VAC 24.6 A motor, 200 m AC cable.

From Figure D2, 2.5 mm2 connected to an 11 kW motor can be run up to

34 m, 4 mm2 up to 53 m, 6 mm2 up to 80 m, 10 mm2 up to 132 mand 16 mm2

up to 209 m. Therefore, 16 mm2 should be selected as it accommodates the

distance of 200 m.

Example 3: DC cable sizing using method 2

649 VDC, 18.4 A, 200 m DC cable

Step 1 – Permissible voltage drop calculation: 3per cent × 649 V × 1000 =

19,470 mV
Step 2 – Computation of permissible voltage drop per amp per metre
through the cable
= 19,470 mV ÷ (18.4 A × 200 m
= ) 5.29 mV/A/m
Step 3 – Selection of the cable size from appropriate cable chart. From
Figure D1 (for twin and multicore PVC insulated cable >> two
core cable single phase supply) a 10 mm2 cable will have a voltage
drop of 4.4 mV/A/m, which is within the permissible maximum of
5.29 mV/A/m computed above.

Note since the cable is two core, it will be stripped so that one core carries positive
and the other core carries negative.
In general, the thicker the cable, the lower the voltage drop and conse-
quently to reduce operating losses the cable cross-section can be increased if it
is economical and the conditions are favourable to do so.

Example 4: DC cable sizing using method 4

649 VDC, 18.4 A, 100 m DC cable (for DC double length will be considered
i.e. 200 m)

Step 1 – Permissible voltage drop calculation: 3 per cent × 649 V = 19.47 V

∆Pwire
= 19.47V × 18.4A
= 358.248 W

ρ × Lwire × I 2
=
Swire for cable at 70°C, the resistivity
= , ρ 0.021
0.02136
∆P
Pwire

= ( 0.02136 × 200 × 18.4 ) ÷ 358.248

2
= 4.04 mm 2 × 2 cores
= 8.08 mm 2 nearest cable size is 10 mm 2

Copyright practicalactionpublishing.com
ANNEX E
Product warranty card sample
Format of warranty card to be supplied with each solar water pumping scheme

Item description
Solar PV modules
Make
Type of cell
Date of installation of modules
No. of modules installed
Serial no.’s
Rating of each PV module
Output voltage (Vmpp) of each module
Max output voltage of PV array
Warranty validity date

Pump-motor assembly
Make
Model/Part number
Serial number
Rated hydraulic capacity
Manufacturer production date
Installation date
Commissioning date
Warranty validity date
DC-AC inverter/pump controller/drive
Make
Model/Part number
Rating
Serial number
Installation date
Commissioning date
Warranty validity date

Isolation, earthing, and surge protection

Commissioning date
Warranty validity date
Designation and address of firm and contact person for claiming of
warranty obligations

Plate and date (Signature)

Name and designation
Name & address of manufacturer/supplier
(SEAL/STAMP)

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Copyright practicalactionpublishing.com
ANNEX F
Routine inspection and maintenance
activity sheets
Weekly activity sheet
Regular inspection and preventative care activity sheet
System Preventative care and maintenance Activity
component
Pump Check area around pump for rubbish Remove and dispose of rubbish
(over and and debris and debris
above regular Is pump or discharge piping leaking? If yes, request technical support to
operations fix leaks
procedures
provided by Record pump pressure when running If there is a change from normal
operator) range in pressure, request
technical support
Pumphouse/ Check enclosure for cracks and If cracked, repair cracks with
Pump damage cement
enclosure Is the enclosure locked? If not, lock enclosure and/or repair
locking hardware as necessary
Controllers/ Record electrical discharge If there is a change in electrical
Inverters, etc. discharge, request technical
support to check panels
Solar Check for a source of shade on Trim or remove any vegetation
photovoltaic the panels, such as vegetation or around the solar panels as well
array structures as any structures that will block
sunlight
Check area around solar panels for Remove and dispose of rubbish
rubbish, debris, and spider webs or and debris. Carefully remove webs
any other insect nesting and nests
Wash panels Do during early hours when it is
not yet hot. Use a soft sponge and
water only
Are there any cracks in the panels? If yes, request technical support
Is there any exposed or loose or If yes, request technical support
disconnected wiring? Check for any
damage from rodents or animals
Is the panel mounting strong and well If yes, request technical support
attached? Are there cracks or any
other signs of weakening?

Regular inspection and preventative care activity sheet

System Preventative care and maintenance Activity
component
Pressure line Are any pipes exposed? If yes, bury pipe

Are any valves leaking? If yes, request technical support

Are any pipes leaking? If yes, request technical support

Are any connections leaking? If yes, request technical support

Are any valves stuck (cannot be If yes, request technical support

moved), loose, or missing?
Tank Has the tank lid been damaged or If the lid is missing, replace the
removed? lid. If the lid is damaged, request
technical support to fix the lid
or place a purchase order for a
new lid
Is the tank (itself) cracked or leaking? If yes, request technical support

Are connections to the tank leaking? If yes, request technical support

Is the tank stand (support) damaged If yes, request technical support

in any way?
Is the tank leaning? If yes, request technical support

Distribution Are any pipes exposed? If yes, bury pipe

line
Are any valves leaking? If the valve is loose, tighten the
fittings. If the fittings are still
leaking, remove valve and replace
gasket. Replace entire valve if
necessary
Are any pipes/connections leaking? If the pipe is leaking at a fitting,
tighten the fitting. If the leak
continues, request technical
support
Are any valves stuck (cannot be If yes, request technical support
moved), loose, or missing?
Taps and Are any taps loose? If yes, tighten tap
standpipes
Are any taps leaking? If yes, tighten tap. If it continues
to leak, replace gasket or entire tap
as necessary
Are any taps stuck or blocked? If yes, replace tap

Are any tap handles missing? If yes, replace handle/ tap

Are any standpipes leaning or Straighten and construct support

falling over? for tap stand or secure to existing

Daily activity sheet

Regular inspection and preventative care activity sheet
System Preventative care and Activity
component maintenance
General Follow the official pumping As indicated by scheme management
schedule of the scheme
Pump Maintain a clean facility at Remove and dispose of rubbish and
(over and above all times debris, sweep area
regular operation Record pump pressure Pressure_______Date______Time_______
procedures when running
provided by Pressure_______Date______Time_______
manufacturer’s
Pressure_______Date______Time_______
operating
manual) Record pumping times
Bulk water meter Record readings • If bulk water meter is not
working read power consumption
instead (daily)
• Report functionality problems
immediately
• Request for calibration if there are
doubts about the accuracy of the
readings or if the meter has not been
calibrated for more than five years
Read pressure gauge
Controllers/ Record electrical power
inverters, etc. Check any warning lights • Low water level in the well
or alarms • Intrusion
• Power outage
• Pump failure
• Low pressure
Read volt and
ampere meters
Solar array Check solar array for any • Leaves or sticks that have been blown
immediate needs or fallen onto the panels
• Bird droppings or major dirt build-up
• Breakages from storms or other means
• Wiring

Copyright practicalactionpublishing.com
Copyright practicalactionpublishing.com
ANNEX G
Preventive maintenance plan
Adapted from SolarPower Europe <www.solarpowereurope.org>
The abbreviations describe the importance and frequency of the main-
tenance tasks related to each component of the solar plant:
Q: quarterly
SA: semi-annual
Y: yearly
nYr: every n years.

Equipment Task Importance Frequency

Modules Integrity inspection and Minimum requirement Y
replacement
Check cleanliness of modules Minimum requirement Y
Electrical measurement Minimum requirement Y
inspections
Thermography inspection Recommendation Y
Checking clamps/bolts panel Minimum requirement Y
structure
Internal inspection of junction Recommendation Y
boxes
Electrical Integrity check and cleaning Minimum requirement SA or Y
boards and Check labelling and Minimum requirement Y
switches identification
Electrical protections (including Minimum requirement Y
fuses, surge and others) visual
and functional tests
Checking integrity of cables and Minimum requirement SA or Y
state of terminals
Measurement inspection Best practice Y
Thermography inspection Recommendation Y
Check cable tightening Minimum requirement Y
Monitoring operation test Best practice Y
Cables Integrity inspection Minimum requirement SA or Y
(DC and AC) Check labelling and Minimum requirement Y
identification
Check cable terminals Minimum requirement Y
Measurement inspection Best practice Y

Equipment Task Importance Frequency

Control box/ Integrity check and cleaning Minimum requirement SA or Y
Inverter Document inspection Best practice Y
Check labelling and Minimum requirement Y
identification
Check correct operation (on/off) Minimum requirement SA or Y
by operator
Check fuses and surge Minimum requirement Y
protections
Thermographic inspection Best practice Y
Sensor functional verification Minimum requirement Y
Generator Integrity check and cleaning According to manufacturer
(for emergency General maintenance recommendations
back-up or in
hybrid systems) Check correct operation
Replacement of filters
Lights and Integrity check and cleaning Minimum requirement Y
electrical Check correct operation Best practice Y
sockets
Check conformity to local Best practice Y
security standards
Water supply Integrity inspection of pipeline Minimum requirement SA or Y
system and reservoir (if any)
Check water meter correct Minimum requirement SA or Y
operation
Check water readings are Best practice SA or Y
properly taken by operator
Lighting Integrity inspection Minimum requirement Y
protection
(if applicable)
Fences and Integrity inspection Minimum requirement Y
gates
Vegetation Vegetation clearing According to local Q, SA or Y
conditions
Drainage General cleaning According to local Q, SA or Y
system conditions
Buildings Integrity check and cleaning According to local requirements
Documentation inspection Best practice Y
Check earthing Minimum requirement 3 Yr
PV support Integrity inspection Minimum requirement Y
structure Check tightening Minimum requirement Y
Irradiation Integrity check and cleaning According to Q
sensors Calibration manufacturer 2 Yr
specifications and local
Monitoring operational test conditions Y

Equipment Task Importance Frequency

Communication Functional communication Minimum requirement Q
board/Remote check
monitoring
Intrusion Integrity check and cleaning According to Y
detection Functional verification of manufacturer Y
system intrusion detection specifications

Functional verification of Q
alarms/cameras
Specific maintenance Y
Stock of spare Inventory of stock Minimum requirement Y
parts Visual inspection of stock Minimum requirement Y
conditions
Stock replenishment Minimum requirement Q

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Copyright practicalactionpublishing.com
ANNEX H
General troubleshooting for SPWSs
Troubleshooting of solar-powered water systems is unique to the system
components, which is dependent on the product brand and type. This table
is only a quick guide for common problems that may be encountered with
a solar pumping system and therefore reference should be made to the
manufacturer manuals for a complete troubleshooting procedure.

Fault Possible cause Check Remedy

The pump Power supply to the Check if the tank-full Tank is full – pump will
does not pump has been cut off light is red come on with water use
start/run by the tank-full switch
Check if the source-low Pump will come on
or dry-run protection
light is red when source recharges
No or low power Check if the solar Clean the modules
coming from the PV modules are clean
Rectify insecure/
generator
Check for failed unsealed wires, loose
connections cable connections,
failed cable joints
Check if wiring (series/
parallel) is correct Correct wrong wiring
No or low power Check if accessories Rectify wiring
reaching the controller are correctly wired
Rectify insecure/
Check for failed unsealed wires, loose
connections cable connections,
failed cable joints
The motor is not Check for loose Rectify loose
getting power on all connections and connections and wiring
three phases correct wiring
The dry-run protection Check if the dry-run Rectify dry-run sensor
is faulty sensor is working
correctly
The pump Solar power is not Check if the panels Clean the modules
light comes strong enough for the are clean
This does not indicate
ON and OFF pump to run
Check if there is a a problem. The pump
passing shadow should restart after
normal delay
Check if the weather is
overcast Wait for the weather
to improve

Fault Possible cause Check Remedy

Pump ON Excessive pressure Check if there is a Remove restriction,
light shows restriction in the pipe open valve
red instead such as a blocked pipe,
of green due closed valve
to system Insufficient motor Check for high running Confirm pump
overload cooling current position and match
to guidelines in
section 6.2.2
Blocked motor or pump Check for high running Switch off the pump
current and call the system
service provider/
technician to rectify
High water temperature Check for high running Switch off the pump
current and call the system
service provider/
technician to rectify
Pump Insufficient power Check if accessories Rectify wiring
attempts reaching the controller are correctly wired
Rectify insecure/
to start at
Check for failed unsealed wires, loose
intervals
connections cable connections,
(will start to
failed cable joints
turn or just
vibrate a Pump is running in Check if phases are Rectify wiring
little) reverse direction correctly connected
Motor is not getting Check for loose Tighten connections
power on all three connections
phases
Pump or pipe is Check if pipes or pump Clean pump and pipes
blocked are packed with mud,
sand, debris
Pump runs Surface valves are shut Check if any valves Open all valves
but no water are closed
delivery Broken downpipe Check pipes by Pull out the pump and
listening near borehole replace worn out pipes
Insufficient irradiation Check if irradiation Wait for the weather to
to deliver water threshold is enough for improve
water delivery
Pump running in Check if phases are Rectify wiring
reverse direction correctly connected
The non-return valve is Check non-return valve Clean or replace the
stuck in closed position valve
The suction strainer is Pull out the pump and
blocked clean the strainer
Pump/motor coupling Check for low running Switch off the pump
broken current and call the system
service provider/
technician

Fault Possible cause Check Remedy

Pump runs Leaking downpipe or Check pipes by Replace worn-out pipes
but there is delivery pipe listening near borehole and fittings
lower water
Check surface pipes
delivery than
for leakages
expected
Source water level Check if flow is Wait for source to
too low intermittent and if recharge
motor current is low
Pump or pipe chocked Check if water output Unclog pipes, pull out
with silt/mud, valves is discoloured and silt pump and unclog
partially closed laden

Check if any valves Open valves

are closed
The valves in the Clean or replace
discharge pipe are the valves
partly closed/blocked
Pump running in Check if phases are Rectify wiring
reverse direction correctly connected
Insufficient power Check if DC accessories Rectify wiring
reaching the controller are correctly wired
Rectify insecure/
Check for failed unsealed wires, loose
connections cable connections,
failed cable joints
Pump internal parts Call service centre for
worn out repair or replacement
Pump starts The water level sensors Check if sensor and Adjust sensor/switch
and stops or level switches in the switch intervals are too intervals
at frequent reservoir are installed close
intervals incorrectly

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Copyright practicalactionpublishing.com
ANNEX I
Financing instruments for solar-powered
irrigation systems

Commercial bank loan

The commercial bank loan is the most common instrument. The borrower
requests funds from a finance intermediary (the bank) and they both
agree on a repayment schedule and terms (interest rate). The intermediary
has the choice to finance different projects in all sectors of the economy.
The objective of the bank is to have the lowest default risk for the highest
return. Intermediaries would usually try to build their portfolio by mixing
high return (new technologies, for instance) with low risk (real estate)
investments. Agriculture is seen as a risky sector as it depends on external
parameters (climate variability). Unforeseen climatic events can drastically
reduce the revenues of farmers (crop failures). Chapter 8 demonstrated that
irrigation can reduce rainfall uncertainty. Bankers will ask for a lot of personal
data to assess the credit worthiness of potential clients: age, sex, marital status,
and bank and credit history. Finally, the intermediary will ask for collateral,
which usually takes the form of land titles, which many farmers do not possess.
The risk assessment of banks leads to different interest rates: 15 per cent in
Senegal and 20–30 per cent in Kenya, for example (FAO & GIZ, 2018a).

Rural or development bank loans

These are an alternative to commercial bank loans. The portfolio of these
banks is composed of only rural development projects in which agriculture
is the major share. As such, they operate in a riskier environment. They can
offer lower interest rates due to their knowledge of the sector but they have
a lower earning capacity and are subject to competition from minor and
more flexible institutions, such as microfinance actors. For this reason,
they would usually partially finance the investment (around 75 per cent),
meaning that farmers need to possess seed capital. The interest rates of
agricultural banks are lower than commercial banks. For instance, the
interest rate charged by the Agricultural Bank of Ghana for personal loans
is the base rate plus 4–8.5 per cent; for the agriculture and forestry sector,
it is the base rate plus 0–5 per cent (ADB, 2019). Finally, famers still need a
bank account and collateral. At this stage, it seems that neither commercial
nor agricultural banks are encouraged to finance SPISs: awareness is still

lacking on the specificities of the equipment and their advantage (in case of
default, solar systems could be used for other uses). International funding
agencies could refinance local banks with specific lines for clean energy to
encourage local banks to finance SPISs.

Microfinance
Microfinance institutions (MFIs) manage risk on their loan by reducing
the size of the investment and imposing frequent repayments (monthly,
weekly or even daily) with short contract durations. Typical loans from MFIs
range between US$100 and $300, which may not be sufficient for systems
pumping groundwater. However, this amount could complement farmers’
own investments to cover the purchase of a piston pump to lift water from
a surface source. In 2008, the global average microcredit interest rate was
35 per cent (Kneiding & Rosenberg, 2008) well above commercial and rural
development banks.

Value chain loans

Input providers (upstream) or traders (downstream) can provide value chain
loans. Input providers will provide inputs at a reduced cost before harvesting.
After harvest, the farmer will pay the intermediary the remaining costs of the
inputs plus a fee. Traders will lend money to farmers before harvest to purchase
inputs. After harvest farmers will receive a payment from traders for their
production minus the costs of inputs and a fee. In the case of SPISs, pump
providers could establish contracts with farmers for a delayed payment of part
of the equipment cost after harvest. Downstream value chain loans (traders) are
not specific to SPISs and might only be used if the SPIS has a shorter payback
period than other irrigation technologies. For the end users, the interest rate
can be as high as 30 per cent since financial intermediaries’ interest rates will be
summed up with the pump provider interest rate based on its risk analysis. For
instance, Futurepump in Kenya provides pumps to farmers. They can contract
a loan with a commercial bank at a reduced interest rate (14 per cent and two
years maturity) with a deposit corresponding to 30 per cent of the pump cost
and a 5 per cent set-up fee (FAO & GIZ, 2018a).

Leasing or repurchase agreements

These are financial instruments in which the farmer leases the pump and
linked solar system. At the end of the lease period, the farmer has the choice
to buy the equipment or not. The user pays the lessee two fees: a utilization
fee and a depreciation fee. The lessor pays the price of the equipment plus an
interest rate. The leasing fees are paid monthly. Leasing is cheaper for farmers
compared to loans. In the event of non-payment the financial intermediary
can claim the equipment back from the farmer.

Agrarian cooperatives
These can be financed by agricultural and commercial banks, and by govern-
mental and international development programs. They are legally registered
entities with a specific status in most countries. They are also financed by
contributions from their members. Thanks to their membership base and
their legal status, they usually appear to banks to be less risky than individual
farmers. Therefore, they are able to offer loans to their members for equipment,
including SPISs, with reasonable interest rates. In cooperatives, default is less
important than with commercial banking because cooperative members help
each other to reimburse the loan taken collectively by an individual farmer
(Huppi & Feder, 1990). Furthermore, in case of default, another member can
repurchase the equipment.

Informal saving groups

This category covers different types of organization and schemes, such as
village saving loan associations (VSLAa), tontines, table finance or informal
loans. The aim is to gather savings from individual group members to finance
investment for the whole group or for one of the members of the group.
For instance, in a VSLA project in Rwanda, the loan amount during the first
loan cycle ranged between US$200 and $1,000, which is similar to the amount
offered by microfinance institutions (CARE, 2007). VSLA and agrarian cooper-
atives could support financial and operational models where wells are drilled
in common, investments done by the group, and maintenance paid collec-
tively, or for small surface pumps irrigating communal fields.

Pay-per-use business models

Pay-per-use comes in two types of investment mechanism: the fee-for-service
model and the pay-as-you-go scheme (Moving Energy Initiative, 2018). In the
fee-for-service model, farmers make an initial payment to cover the instal-
lation costs of the SPIS. The consumer makes regular payments to unlock
the energy device. This could work either by time used, volume of water, or
amount of energy. In the pay-as-you-go model, the consumer does not make
the initial payment and makes regular payments to use the energy device and
linked water volume for a fixed period of time or fixed volume. There are
different ways to pay for the service: SMS or scratch top-up cards.

Subsidy mechanisms
Indirect subsidies exist on solar equipment when countries do not apply
value-added tax (VAT) on solar products. Specific subsidy mechanisms for
SPISs exist at national level in India, Nepal, and Tunisia (FAO, 2019). In India,
subsidies depend on the different states. They range from 100 per cent

of the total cost of equipment in Bihar to 60 per cent of the total cost in
Haryana. They represent 70 per cent of the total cost for a woman farmer
in Nepal. In Tunisia, the subsidy is 40 per cent of the total equipment cost
with a US$7,000 limit for the subsidy per project. The subsidy obtained could
be used as collateral to secure bank loans for SPISs. Subsidies can also be used
as leverage to support the development of the SPIS sector together with water
efficiency measures. For instance, different premiums could be offered to
farmers depending on their project. A higher percentage of the project could
be covered if the farmer implements drip irrigation or for collective use of the
SPIS, for example.

Matching grants mechanisms

These use the same principle as subsidy mechanisms but with a different
origin of fund: cooperation funds instead of national or federal state funds
(IWMI, 2018).

Copyright practicalactionpublishing.com
ANNEX J
Physical control installation
and maintenance checklists
In order to get a good-quality solar pumping installation, monitoring the
field work carried out by the private contractor selected is of paramount
importance. It is therefore strongly recommended to WASH officers to follow
up as much as possible this list of actions.

Introduction: 4 steps
1. Check the references of all components of the system to ensure that the
installed components are those provided in the design.
2. Check orientation and the inclination of the panels, and shadow on
the solar PV generator. The orientation and inclination values must be
close enough to those that were determined during calculation sizing.
The acceptable variations will be less than 5° for the inclination and 15°
with respect to the geographic north–south orientation.
3. Check the cleanliness and protection of the wiring, and its compliance
with the standards.
4. Finally inspect civil works (e.g. castle, basin, trough, fixing the solar
supports), piping, valves and all other important elements that can
compromise the sound operation of the system.

Modules and PV array

No. Subject Observations
1. Check the conformity of module specification in accordance with
the design simulation and that all installed modules are of the same
characteristics
2. Check the number of modules: number of modules in series and in
parallel and compare with design
3. Check with the help of a compass if the modules are well oriented in
south or north direction (according to the hemisphere), by positioning
the compass against the east or west edge of a module
4. Check the inclination of the modules (tilt angle) using the inclinometer
5. Check with a level if the east–west axis of the modules is properly
horizontal
6. Check that the height of the lowest point of the modules from the
ground is greater than or equal to the height in the specifications

No. Subject Observations

7. Check the cleanliness of the solar array (each cell)
8. Ensure that no module is damaged, e.g. broken glass, frame, twisted,
scratched
9. With the installer, measure the voltage output from each string and ensure
it’s consistent with the design and uniform across all the strings
10. Check and ensure that every module is fastened to the structure
at every bolt hole in a manner that is robust, acceptable, and will
deter vandalism

Electrical wiring
No. Subject Observations
1. Ensure cable conformity: compare cable specifications and sections
with those provided by the manufacturer for the power and the
distances measured on site
2. Check that all cable connections are inside the junction boxes provided
for this purpose; no connection between two cables should be visible
3. Ensure all cable glands and conduits match the cable size and are
properly sealed. All cable entries into the terminal box should be
through cable glands
4. Check that all housings connections are at a minimum height of 50 cm
from the ground
5. Choose a sample of the cable and test it by pulling a cable out of a
gland to ensure that it is sufficiently tight to hold the cable
6. Check that all cable terminals are properly fastened and
sufficiently tight
7. Check the cable interconnection between the modules is fastened to
the structure at regular intervals by use of suitable clips or cable ties
8. Check that all surface cabling is of armoured type. If not armoured,
it should be placed in electrical conduits and protected using
protective tiles to prevent damage from passing vehicles
9. Check that there are no overhead cables. All interconnecting cables
(e.g. connecting two support structures) should be guided to the
ground and conform to point 7 above
10. Verify the existence and proper connection of grounding rods for both
earthing and lightning surge protection

Solar support structure

No. Subject Observations
1. Check if all the members of the supporting structure are of the
material specified. Ensure that no parts are susceptible to corrosion.
Check for proper and uniform painting of the structure
2. Check the proper eye alignment of the support posts

No. Subject Observations

3. Check with a spirit level the verticality and horizontality of poles
and modules (this allows to check the general quality of the
completed work)
4. Check the bolting has been done at every hole
5. Check if the foundations are of sufficient size
6. Check for obvious weaknesses such as structures that are
grossly swaying or leaning

Inverter or other AC interface

Note: The pumps are equipped with an ‘inverter box’ also serving as a control
box. For those who work in DC, the control cabinet is often called ‘interface’
or power conditioner.

No. Subject Observations

1. Check the conformity of inverter specifications (or interface)
2. Check for varistors presence between positive terminal and earth; and
between terminal negative and earth (or between positive and negative
terminals if the terminal negative is connected to earth) on the
terminal block to the input of the inverter (or interface)
3. Check the inverter (or interface) is correctly mounted at more than
50 cm above the ground
4. Make sure inverter is well protected from adverse weather conditions
and is as close as possible to the PV array e.g. placed in the shade of
the modules. If mounted inside a room, sufficient ventilation should
be provided. The inverter must not be installed inside an additional
enclosure as this will lead to insufficient cooling
5. Check that the inverter is mounted directly on a solid wall or equipped
with a backplate, and that the wall/backplate can support the weight
of the inverter. Check to ensure that it is also mounted in accordance
with minimum spacing requirements provided by the manufacturer
6. Ensure protective devices have been installed between the PV array
and the inverter e.g. DC disconnection switches, DC breakers, surge
protectors

Pump unit
No. Subject Observations
1. Check the conformity of motor specifications
2. Check the conformity of pump specifications
3. Check that the splicing kit is of suitable type, quality, and
workmanship. Resin type joint (not heatshrink) is recommended for
deep installations. Check for obvious mistakes like air pockets on the
joint, uniformity of mould

No. Subject Observations

4. Check that the pump setting depth complies with the purchase order/TOR
5. During installation, check that the drop cable and well probe cable
are fastened to the pipe using suitable cable ties (tape or metallic
clips MUST NOT be used) and at intervals of 3 m. Ensure the cable
has been fastened with a stretching allowance as the delivery pipe is
subject to elongation when filled with water (about 2 per cent stretch)
6. During the test run:

Check that the protective control features are set in accordance with
the pump specifications e.g. speed, voltage, sensor settings

Check that the pump performance is in accordance with the design in

terms of flow and pressure (e.g. reversed phases will cause reduced flow)

Check that the current consumed by the pump is consistent with the
pump specification

Drill head
No. Subject Observations
1. Ensure that all the components of the drill/wellhead are of corrosion-
resistant material
2. Check that the gate valve meets the specifications and that it is fully
open. Valve handle should be removed to avoid accidental closure
3. Check the conformity of the water meter to the specifications
and mounting direction. Monitor compliance with the minimum
safety lengths: 20 times the nominal diameter upstream, 10 times
downstream

System monitoring and control

No. Subject Observations
1. System registered on remote monitoring platform
2. Controller registered/activated for data logging and remote access provided
3. Alerts and notifications activated to system owner’s email/SMS

General
No. Subject Observations
1. 2 days hands-on training of operators/users/NGO done on site
2. Testing, installation and commissioning report handed to NGO or asset
owner if other.

Copyright practicalactionpublishing.com
ANNEX K
Daily photovoltaic module and pump
operation/monitoring format
Adapted from World Bank

Daily PV array and pump performance data

Recorded by: _________ Date_________ Designation _________
Location __________ District__________ Region __________
Latitude _________ Longitude___________ Elevation ___________ (m)
Pump type _________ Pump duty point ____ (m /h) Motor type __________
3

Motor rating (kW) ____ PV array type_ PV cell type ______

PV array peak Watt _______ No. of panels _________ ( C) Inverter make __________
o

Inverter type _________ Inverter rating _______ (kW) Inverter rating ______(Amps)
Borehole depth _______ (m) Static water level ______(m) Dynamic water level_____ (m)
Pump setting ________ (m) Reservoir capacity ____(m3)

Hr of Weather Power Actual Actual Air Cell Solar Flow Pressure Actual Actual
the day (rainy, input PV inverter temp temp radiation meter reading PV inverter
cloudy, (solar, voltage voltage (oC) (oC) (W/m2) reading (Bar) current current
sunny) generator, (VDC) (VAC) (m3) (Amps) (Amps)
other)
0700
0730
0800
0830
0900
0930
1000
1030
1100
1130
1200
1230
1300
1330
1400
1430
1500
1530

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Glossary
alternating current (AC) – electric current in which the direction of flow
oscillates at frequent, regular intervals over time.

AM – air mass.

Ampere or Amps – a measure of electric current.

altitude – the angle between the horizon (a horizontal plane) and the sun,
measured in degrees.

amorphous silicon (a-Si) – a thin-film PV silicon cell having no crystalline

structure.

aquifer – a naturally occurring layer of water-bearing soil, rock, or sand.

asset owner – this can be the stakeholder who contributes to financing

of construction (donor or UN agency, NGO, government, or others) or the
community of users if equipment is handed over to them.

asset manager – aims at ensuring optimal functioning of the solar

pumping scheme (or a portfolio of schemes) by supervising energy and water
production, and O&M activities. Reports to asset owners.

azimuth – angle between true south and the point directly below the
location of the sun, measured in degrees.

balance of system (BoS) – components of a PV system other than the PV

array.

battery – two or more cells electrically connected for storing electrical

energy.

battery bank – an energy storage capacity (ampere-hour).

borehole – a hole drilled through the ground to reach water. Borehole

diameters vary depending on the required size of the system. Standard
borehole sizes are 4 to 12 inches (100 to 300 mm).

camp – a context of displaced persons living in a confined location managed

by a UN agency, such as UNHCR or IOM, and whose services ae provided by
implementing agencies, such as NGOs.

capital cost – initial investment of a project.

cavitation – phenomenon in which low pressure causes bubbles to be

formed at the suction inlet of the pump.

CdTe – a type of PV cell made from cadmium and telluride.

centrifugal pump – a pump that delivers water centrifugally using

impellers by producing a pressure difference.

CIGS – a type of PV cell made from copper, indium, gallium, and di-selenide.

CIS – a type of PV cell made from copper, indium, and selenide.

contractor – entity that is in charge of installation of the solar pumping

components, and/or operation and maintenance of the solar-powered
pumping system.

conversion efficiency – the ratio of the electric energy produced by a PV

to the energy from incident sunlight.

crystalline silicon (c-Si) – a type of PV cell made from a single crystal or

polycrystalline slice of silicon.

current – the flow of electric charge in a conductor between two points

having a difference in potential (voltage).

days of autonomy – the number of consecutive days a stand-alone system

will meet a defined load without energy input.

design month – the month having the lowest renewable energy production
to load ratio.

diffuse radiation – solar radiation scattered by the atmosphere.

direct radiation – solar radiation transmitted directly through the

atmosphere.

direct current (DC) – electric current flowing in one direction.

disconnect – switch gear used to connect or disconnect components in a

stand-alone system.

discount rate – rate at which the value of money changes relative to general
inflation.

drawdown – the distance below the water table that the water level in a well
falls to when steady state pumping is in progress.

duty point – the required flow and head of the operating pump.

efficiency – the ratio of output power to input power, expressed as a

percentage.

E-generated – energy generated and available for consumption in the AC

and DC loads.

electric circuit – a complete path followed by electrons from a power

source to a load and back to source.

electric current – the magnitude of the flow of electrons.

flatplate – an arrangement of solar cells in which the cells are exposed

directly to normal incident sunlight.

g – temperature coefficient of power of the PV module.

global solar radiation – the sum of diffuse and direct solar radiation
incident on a surface.

grid – the network of transmission lines, distribution lines, and transformers

used in central power systems.

HIT – heterojunction with intrinsic thin-film layer.

hydraulic equivalent load – the product of the daily amount of water

produced by the pumping head.

hydraulic energy – the energy necessary to lift water.

IEC – International Electrotechnical Commission

incidence angle – angle that refers to the sun’s radiation striking a surface.
A normal angle of incidence refers to the sun striking a surface at a 90°
(or perpendicular) angle.

irradiance – the instantaneous power per unit area received by a surface on

the earth’s surface (expressed in W/m2).

insolation – a measure of the cumulative irradiance received on a specific

area over a period of time, measured in Wh/m2 or kWh/m2.

inverter – a solid-state device that converts a DC input to an AC output.

kilowatt (kW) – one thousand watts.

kilowatt hour (kWh) – one thousand watt hours.

W/m2 – watts per square metre.

kW/m2 – kilowatt per square metre.

LID – light-induced degradation.

life-cycle cost – an estimate of the cost of owning and operating a system

for the period of its useful life, usually expressed in terms of the present value
of all costs incurred over the lifetime of the system. The sum of the capital cost
and the present worth of the recurrent, salvage, and replacement costs.

load – the amount of electrical power being consumed at any given

moment. Also, any device or appliance that is using power. In SPWSs the
load is the pump.

load matching – the process of matching the load with the input power
source to maximize the power transfer to the load.

load-matching factor – a non-dimensional factor defined by the ratio

of energy acquired by the hydraulic load to the maximum power extracted
from the power source in a one-day period. It can also be the ratio of the
actual power output used for water pumping to the power source output
capability.

maximum power point tracker (MPPT) – the impedance-matching

electronics used to operate a PV array output at its maximum power.

module (panel) – a predetermined electrical configuration of solar cells

laminated into a protected assembly.

monocrystalline silicon – a material formed from a single silicon crystal.

net present cost (NPV) – all project expenses converted into the current
value of money.

NOCT – nominal operating temperature of a cell.

nominal voltage – a reference voltage used to describe batteries, modules,

or systems (e.g. a 12-volt or 24-volt battery, module, or system).

orientation – placement according to the cardinal points (N, S, E, and W);

azimuth is the measure in degrees from true south.

O&M – operations and maintenance.

payback period – the number of years (periods) required for the income
(benefit) from a project to equalize its investment cost.

peak hour demand – the maximum amount of water required in an hour.

In most cases, peak hour can refer to noon and/or evening water consumption.

peak efficiency – the highest output efficiency level that a solar panel or a
solar inverter can achieve.

peak sun hours (PSH) – equivalent number of hours per day when solar
irradiance averages 1,000 W/m2.

peak watt (Wp) – the amount of power a PV device will produce during
peak solar radiation periods when the cell faces directly towards the sun
(value at STC).

performance ratio (PR) –the ratio between the generated energy and the
theoretical energy that would be generated by the PV field if the modules
converted the irradiation received into useful energy according to their rated
peak power.

photovoltaic (PV) – phenomenon of generation of electricity from the

sun’s energy.

photovoltaic (PV) cell – a cell that generates electrical energy when

incident solar radiation impinges on it.

photovoltaic (PV) system – an integrated system composed of a PV array,

power conditioning, and other subsystems, such as the motor–pump.

polycrystalline silicon – silicon that has solidified at a rate such that

many small crystals have formed.

positive displacement pump – a type of water pump that can lift water
from a borehole by means of a cavity or cylinder of variable size. Also called a
volumetric/helical rotor pump.

power conditioning – the electrical equipment used to convert power

from a PV array into a form suitable to meet the power supply requirements of
more traditional loads. It is a collective term for inverter, transformer, voltage
regulator, meters, switches, and controls.

present worth – the value of future costs or benefits expressed in the

current value of money (present-day money).

pumping head – the height of a water column that would produce the
pressure that the pump experiences.

PV array – a mechanically and electrically integrated configuration of PV

modules and support structure designed to form a DC power-producing unit.

PV field/PV plant/PV generator – the entire PV module arrangement

in a solar installation.

remote site (location) – a site that is not located near a utility grid.

renewable energy (RE) – energy produced by non-fossil fuel or nuclear

means. Includes energy produced from PV, wind turbines, hydroelectric,
and biomass.

rising main – the pipe used to lift water from the borehole or surface
pumping source.

rotor – the rotating central section of a motor or a pump.

solar collector – a horizontal or tilted surface on the earth’s surface that

captures the solar radiation.

solar controller – an electric device used for controlling and monitoring a

solar pumping system.

solar thermal electric – a method of producing electricity from solar

energy by concentrating sunlight on a working fluid that changes phase to
drive a turbine generator.

SPWS – solar-powered water system or solar-powered water scheme.

stand-alone system – a system that operates independently of utility

lines. It may draw supplementary power from the utility but is not capable of
providing power to the utility.

static head – the height over which water must be pumped. Static head
may vary due to seasonal changes in well recovery rates, fluctuations in
groundwater level, etc.

stator – the outer stationary component of a motor or a progressive cavity

pump.

standard test conditions (STC) – defined as irradiance of 1,000 W/m²,

solar spectrum of AM 1.5 and module temperature at 25 °C.
string – set of solar modules electrically connected in series.

switchgear – the switches and electrical controls in a solar-powered water

system.

tilt angle – angle of inclination of a PV array as measured in degrees

from the horizontal surface. Usually equal to the latitude of the PV array’s
location.

tilted factor – the ratio of the incidence solar radiation on a tilted PV array
surface to the global solar radiation.

TPV_cell – PV cell temperature.

volt (V) – a unit of measurement of the force given to electrons in an electric

circuit; electric potential (voltage).

water table (static water level) – the level below the ground at which
the natural water level can be found.

watt (W) – measure of electric power. Watts = volts x amps.

watt hour (Wh) – a quantity of electrical energy when one watt is used/
generated for one hour.

zenith angle – the incidence angle to a horizontal surface.

Copyright practicalactionpublishing.com
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Websites
Databases
POWER Data Access Viewer <https://power.larc.nasa.gov/data-access-viewer/>.
Solargis solar resource maps <https://solargis.com/maps-and-gis-data/overview>.
<https://solargis.com/maps-and-gis-data/download/kenya>. (Annex B)

Manufacturers of SPWS equipment (Chapter 3)

ABB solar drives: https://new.abb.com/drives/low-voltage-ac/machinery/ABB-
solar-pump-drives
Franklin solar pumps and drives: https://solar.franklin-electric.com/products/
high-efficiency/6-inch-high-efficiency-solar-system/
Fuji – solar drives: https://www.fujielectric-europe.com/en/drives_automation/
products/solutions/frenic_ace_for_solar_pumping
Grundfos company: www.grundfos.com
Lorentz pumps and controllers: www.lorentz.de
Solar service provider: https://www.davisandshirtliff.com
Solar service provider: https://solargentechnologies.com
Well pumps company: https://wellpumps.eu/en/homepage

PV module datasheets (accessed June 2019)

s-Si: Trina Solar Tallmax DE15M(II) 415 W (www.trinasolar.com)
p-Si: Trina Solar Honey PE06H 300 W(www.trinasolar.com)
a-Si/µc-Si: Kaneka Hybrid U-EA type 120 W (http://www.kaneka-solar.com/
product/thin-film/)
CdTe: First Solar Series 6 FS-6445 (http://www.firstsolar.com/Modules/Series-6)
CIS: Solar Frontier SFK185-S 185 W (http://www.solar-frontier.com/eng/)
CIGS: Solibro SL2 Generation 2.3 150 W (https://solibro-solar.com)
HIT: Panasonic VBHN340SJ53 340 W (https://eu-solar.panasonic.net/en/)
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Solar Pumping For Water Supply

Uploaded by

Solar Pumping For Water Supply

Uploaded by

Solar Pumping for Water Supply

‘This is a good reference book to be used by anybody – not just technicians –

Asenath W. Kiprono and Alberto Ibáñez Llario

© Asenath W. Kiprono and Alberto Ibáñez Llario, 2020

This open access article is distributed under a Creative Commons

Product or corporate names may be trademarks or registered trademarks, and

ISBN 978-1-78853-036-1 Paperback

Since 1974, Practical Action Publishing has published and disseminated

Cover design by RCO.design

1. Solar photovoltaic solutions for water pumping 1

2 Definitions and principles of solar energy production 9

3 Solar-powered water system configurations and components 27

4 Energy losses in solar photovoltaic energy production 49

5 Design of a solar-powered water scheme 67

6 Electrical and mechanical installation of solar-powered

7 Specific considerations and limitations for solar-powered

8 Solar-powered water pumping for agriculture 123

9 Economic analysis: life-cycle cost of different pumping

10 Calls for proposal and bidding 147

11 Testing and commissioning, operation and maintenance 163

12 Warranties, social models for management, and monitoring 179

Annex A Pump and generator design basics 187

Annex B Manual calculation of solar system 195

Annex C Example of calculation of losses due to non-optimum

Annex D Cable sizing 215

Annex E Product warranty card sample 219

Annex F Routine inspection and maintenance activity sheets 221

Annex G Preventive maintenance plan 225

Annex H General troubleshooting for SPWSs 229

Annex I Financing instruments for solar-powered irrigation systems 233

Annex J Physical control installation and maintenance checklists 237

Annex K Daily photovoltaic module and pump

Box 2.1 Solar PV components 13

Box 4.1 Minimizing losses due to temperature 55

Box 4.2 Minimizing wiring losses 57

Box 4.3 Minimizing losses due to soiling 59

Box 4.4 Minimizing losses due to shading 59

Box 4.6 Minimizing mismatching losses 62

Box 4.7 Minimizing ageing losses 63

Box 4.8 Minimizing losses due to availability 65

Box 10.1 Dimensions of product quality 148

Box 10.2 Criteria for supplier selection 150

Box 10.4 Checking module quality 160

Box 11.1 When to call a technician 172

Box 11.2 Example of essential provisions in a maintenance

Box 12.1 Commonalities between successful community-managed

Figure 1.1 Global map of appropriate locations for solar applications 2

Figure 1.2 Evolution of price of PV cells, 1977–2015 4

Figure 2.1 Sun and water: a perfect relationship 10

Figure 2.2 Global Horizontal Irradiation 11

Figure 2.3 Conversion of sunlight to electricity 12

Figure 2.4 The ‘PV effect’ process 13

Figure 2.5 Illustration of PV cell, module, array, and generator 14

Figure 2.6 A typical solar-powered water system 15

Figure 2.7 Weekly irradiation in Valencia in the month of July 16

Figure 2.8 Time-based solar irradiance in Valencia during summer

Figure 2.9 Graph of daily insolation 18

Figure 2.10 Solar irradiance during two days of July and

Figure 2.11 Air mass for different sun positions 20

Figure 2.12 PSH map for Jordan 22

Figure 2.13 Typical I-V and power curves for a crystalline PV

Figure 2.14 I-V curve under varying irradiance and temperature 26

Figure 3.1 Typical flow output profile of a solar-powered pump 29

Figure 3.2 Stand-alone solar installation 30

Figure 3.3 Hybrid installation 30

Figure 3.4 Stand-alone surface Installation 31

Figure 3.5 Illustration of a solar module construction 38

Figure 3.6 Different types of solar modules (clockwise from

Figure 3.7 Parts of a cable 44

Figure 3.8 The components of a solar water pumping system 46

Figure 3.9 Worn-out conduit due to high temperatures in Iraq 48

Figure 4.1 Temperature difference for a c-Si plant with a fixed-tilt

Figure 4.2 Effect of sun irradiance in efficiency of c-Si PV modules 53

Figure 4.3 Spacers between modules to increase cooling 55

Figure 4.4 Sand on PV modules limiting power output 58

Figure 4.5 Shading of PV modules limiting power output 58

Annex C Example of calculation of losses due to non-optimum

Annex K Daily photovoltaic module and pump

Box 11.2 Example of essential provisions in a maintenance

Box 12.1 Commonalities between successful community-managed

Figure 2.8 Time-based solar irradiance in Valencia during summer

Figure 2.10 Solar irradiance during two days of July and

Figure 2.13 Typical I-V and power curves for a crystalline PV

Figure 3.6 Different types of solar modules (clockwise from

Figure 4.1 Temperature difference for a c-Si plant with a fixed-tilt

Figure 4.6 Example of warranty given by Trina Solar for Tallmax

Figure 5.8 Inverter box located under modules in Somali

Figure 5.9 Hybrid solar-generator scheme at Adjumani refugee

Figure 6.1 Sample nameplates for (left) PV module, and (right)

Figure 6.3 Horizontal surface pumps installed on a concrete plinth

Figure 6.4 Installed controls (left to right): AC changeover switch,

Figure 6.5 Inverter installed in a lockable meshed enclosure under

Figure 6.6 Examples of poor cable management in South Sudan 97

Figure 6.7 Examples of good cable management in South Sudan and

Figure 6.9 Pole mounted PV modules in Bidibidi refugee settlement,

Figure 6.11 Combined roof and pole mount installation at

Figure 6.13 Tank-mounted structure in an IDP camp near

Figure 6.14 Failed pole mount in Yida, South Sudan, modules

Figure 7.2 Solar trackers: double-axis tracking (left) and single-axis

Figure 7.5 Awareness raising of the value of the SPWS to avoid theft

Figure 8.2 Approximate shares of greenhouse gas emissions (in CO2

Figure 9.3 LCCA of stand-alone generator vs hybrid vs solar at

Figure 10.2 Example of a solar-powered water system layout

Figure 11.1 Duration of different phases in the life of a solar

Figure 11.2 Routine maintenance activities to ensure proper daily

Figure 12. 1 Lorentz communication system for monitoring from

Table 1.1 Advantages and disadvantages of solar PV water

Table 4.1 Table of estimated losses as a percentage of total

Table 4.2 NOCT, g, and efficiency factors for different PV module

Table 5.3 Example of worst-month calculation where constant water

Table 5.4 Example of worst-month calculation where variable water

Table 7.1 Summary of Global Solar and Water Initiative specifications

Table 9.2 Estimated cost for maintenance of a good-quality