978-1-4673-0934-9/12/$31.
00 2012 IEEE
Renewable Energy based Small Hybrid Power system
for Desalination Applications in Remote locations
R. Nagaraj
Bhabha Atomic Research Centre
Nuclear Desalination Demonstration Project
Kalpakkam, India
rnagaraj@igcar.gov.in
AbstractWater, energy and environment are essential
inputs for sustainable development of society. It is a common
phenomenon that certain packets of the country that are water
stressed are also power stressed at the same time. There is a huge
potential for utilizing renewable energy sources, for example
solar energy, wind energy, or micro hydropower to provide a
quality power supply to remote areas. The abundant energy
available in nature can be harnessed and converted to electricity
in a sustainable way to supply the necessary power to elevate the
living standards of the people without access to the electricity
grid. The advantages of using renewable energy sources for
generating power in remote areas are obvious such as the cost of
transported fuel are often prohibitive fossil fuel and that there is
increasing concern on the issues of climate change and global
warming. The disadvantage of standalone power systems using
renewable energy is that the availability of renewable energy
sources has daily and seasonal patterns which results in
difficulties in regulating the output power to cope with the load
demand. Combining more than one form of the renewable energy
generation and also conventional diesel power generation will
enable the power generated from a renewable energy sources to
be more reliable and affordable. This kind of electric power
generation system, which consists of renewable energy and fossil
fuel generators together with an energy storage system and
power conditioning system, is known as a hybrid power system.
This paper elaborates on the analysis of small capacity hybrid
power system for supplying electricity and clean water demand in
rural and remote areas by using mini-grid hybrid power system
consisting of renewable energy (Solar Photovoltaic cells &
Windmill) and battery with a reverse osmosis desalination plant
as a primary / deferrable load.
Keywordsrenewable energy; hybrid power system;
desalination; RO; solar; wind
I. INTRODUCTION
The provision of fresh water is becoming an increasingly
important issue in many areas of the world. Water and energy
are two basic commodities that rule human lives and promote
civilization [3]. The ocean is the only perennial source of
water. Their main problem is obviously their high salinity. The
removal of salinity is accomplished by several desalination
methods. Desalination processes require significant quantities
of energy. There are many parts of the country which does not
have conventional source of power and costs of extending the
electricity grid to these places are very high. Fortunately,
there are many parts of the country that have water shortage
but have exploitable renewable sources of energy that could be
used to drive desalination processes.
Renewable energy systems utilize sources available locally
and freely for production of energy. Production of fresh water
using desalination technologies driven by renewable energy
systems is thought to be a viable solution to the water scarcity
at remote areas characterized by lack of potable water and
conventional energy sources like heat and electricity grid.
Also they are environmentally friendly [4]. Desalination
systems cannot be compared with conventional systems in
terms of cost without taking site specific factors into
consideration. They are suitable for certain locations and will
certainly emerge as widely feasible solutions in due course of
time.
This paper elaborates on the analysis of small capacity
hybrid power system for supplying electricity and clean water
demand in rural and remote areas by using mini-grid hybrid
power system consisting of renewable energy (Solar
Photovoltaic cells & Windmill) and battery with a reverse
osmosis desalination plant as a primary / deferrable load.
II. RENEWABLE ENERGY SYSTEMS
There are a variety of renewable energy sources identified
and utilized in various levels. These cover solar energy which
includes thermal collectors, solar ponds and photovoltaic,
wind energy and geothermal energy. Major share being from
Solar Photo voltaic and Wind energy, we shall discuss only
these systems.
A. Solar Photovoltaic
Photovoltaic effect was discovered in selenium way back
in 1839. The photovoltaic (PV) process converts sunlight
directly into electricity. A PV cell consists of two or more thin
layers of semiconducting material, most commonly silicon.
When the silicon is exposed to light, electrical charges are
generated and this can be conducted away by metal contacts as
direct current (DC). The electrical output from a single cell is
small, so multiple cells are connected together and
encapsulated (usually glass covered) to form a module (also
called a panel). The PV panel is the principle building block
of a PV system and any number of panels can be connected
together to give the desired electrical output. Photovoltaic
(PV) cells are made of various semiconductors, which are
materials that are only moderately good conductors of
electricity. These cells are packed into modules which produce
a specific voltage and current when illuminated. PV modules
are connected in series / parallel arrangement to meet voltage /
current requirements.
PV equipment has no moving parts and as a result requires
minimal maintenance and has a long life. It generates
electricity without producing emissions of greenhouse or any
other gases, and its operation is virtually silent.
B. Wind energy
Wind energy is basically by the pressure differences in
atmosphere due to solar power. The wind turbine technology
is highly mature and available in commercial scale. The
production can be improved by using novel control strategies
and better energy storage systems.
C. Reverse Osmosis (RO) desalination using Solar PV and
Wind Energy
The photovoltaic technology can be connected directly to a
RO system. The factors that determine economics are the
plant capacity, cost of extending electricity grid and the
concentration of the salt in raw water [7] [8].
RO is the desalination process with the minimum energy
requirements. Wind power is abundant in coastal areas. Hence
wind power desalination is a promising option [1] [5] [6].
D. Problems with renewable energy based desalination
plants
The disadvantage of wind energy and solar energy is that
they are intermittent (stochastically varying) source. This
reduces the reliability of power output and hence the water
output also. The second major disadvantage is its capital cost.
III. HYBRID SOLAR PV-WIND POWER
The complementary features of wind and solar resources make
the use of hybrid windsolar systems to drive a desalination
unit a promising alternative as usually when there is no sun the
wind is stronger and vice versa [2]. It should be noted,
however, that there will be conditions when both solar and
wind energy is not available. This implies that the process
operates only partially when the energy is available unless
some storage device is used. Batteries are one such storage
devices but are usually expensive.
A RO renewable desalination plant can be designed to
operate coupled to the grid or off-grid (standalone-
autonomous system). For grid connected systems, the
renewable source is just a substitute. But for off-grid systems,
the design of both power and desalination systems should
permit intermittent operation due to the nature of renewable
source.
Desalination systems are generally designed to operate
with a constant power input. But with varying power input, the
plant operates in non-optimal points and hence creates
operational difficulties. Such problems are specific to the
renewable source connected with the plant. For instance, the
reverse osmosis (RO) system has to withstand such conditions
that can deteriorate their membranes due to scaling, fouling by
these intermittent operations because of varying power supply.
A. Analysis of Hybrid Power System with RO Plant
The intermittent nature of renewable sources, use of any
particular renewable energy resource based system may lead
to component over-sizing and unnecessary operational and
lifecycle costs. Such limitations can be overcome by
combining one or more renewable energy resources in a form
of a hybrid system. Hybrid systems improve load factors
plants and save maintenance and replacement costs, as the
renewable resource components complement each other.
For optimal combination of different renewables, various
types of hybrid systems and methods of techno economic
analysis are used. Excel based linear programming, artificial
intelligence; LINGO and HOMER are the most commonly
used methods of hybrid system optimization techniques.
B. Basic Components and Model of Hybrid System
The basic components of the hybrid system are the hydro
system, the wind plant and the PV system. Others are
additional/auxiliary components which help for full time
functioning of the hybrid system. Fig. 1 shows schematic of
the hybrid system.
Fig. 1. Schematic Diagram of a typical small Hybrid powered
Desalination Plant
The power conditioners are set of power electronics
converters which enable to handle the variability of wind and
solar resources. They are composed of DC/DC, AC/DC,
DC/AC converters. The AC output of the hydropower, diesel
and generator are integrated and controlled in such a way that
the output can be directly supplied to the connected AC load.
When there is excess of energy (mainly from the wind, PV and
hydro), it is directed to the battery through the converter and
DC center. In addition, frequency and voltage regulation
control circuitry is to be included in the operation and control
center. Similarly, the DC output of the PV panel is connected
to the system via the DC center. The DC center is integrated
with the system through DC/AC and AC/DC converters. It is
also connected to PV and battery components.
C. Data
The hybrid power system design options are analyzed for
the project site, Kalpakkam. Kalpakkam is situated in South
India and has the following latitude and longitude:
Latitude: 12
o
34 North
Longitude: 80
o
10 East
The daily solar irradiance data in kWh/m2/day is given in Fig
2. In this study, wind turbine (type, cost, hub height, life time
and number), Solar PV (size, cost, slope, ground reflectance,
de rating factor, life time), converter (cost, efficiency, size and
life time), battery (type, cost and number of strings, life time),
primary load (hourly data for the year, daily and hourly noise)
are considered as inputs for analysis. Details of solar and
wind, resources are defined. The monthly averaged daily solar
radiation data, location and time zones are used to calculate
the hourly incident solar radiation on the PV panel. Similarly,
the monthly averaged wind speed data, altitude, anemometer
height, variation with height, hour of peak wind speed etc. are
used by to estimate the wind distribution and output power.
Interest rate and project life time are considered for calculation
of cost economics.
The wind speed data is given in Fig. 3. The hybrid power
system shall be designed to feed power to a brackish water
desalination plant of 100 m3/day capacity. Fig. 4 gives the
proposed hybrid power system setup to feed power to the
above plant.
IV. RESULTS AND DISCUSSIONS
The feasibility study is carried out by optimization analysis.
A given system type may have many different configurations
based on the size combination of constituent elements. The
overall optimization table displays all feasible system
configurations (for any possible system type) ranked in their
cost effectiveness.
From the details of the optimization analysis the following
can be observed: size of different components in each system,
electric production of each component, capital, replacement
and operating and maintenance cost of each system,
Fig. 2. Solar Irradiance data
Fig. 3. Wind speed Data
Fig. 4. Hybrid Power System setup for RO Desalination Plant
Table 1. Partial list of different configurations of hybrid power systems along with their key performance indicators
annualized cost, cost of energy (COE), Cost of energy
(COE), and total NPC values. The above can be used as
parameter of selecting a given configuration among the
many possible configurations.
Table 1 lists the partial results of different configurations
of hybrid power systems along with their key performance
indicators. From the results obtained by simulation, we can
see that addition of capacities of PV panels or Wind turbines
or storage capacities does not help in reduction of the cost of
energy. On the other hand the cost increases.
But, when the capacities are supplemented with Solar PV
and Wind turbines, we find that we are able to meet the load
requirements at lower energy costs. This is mainly because
of the fact that when there is no sun, the wind is stronger and
vice versa. This complements each other and supplies
energy at lower costs.
V. CONCLUSION
In this paper, a review of renewable energy based
desalination systems with Solar PV and Wind turbines was
PV (kW) Aerogen(10KW) Battery
Converter
(kW) Initial Cost(Rs.) Net Present Value(Rs.)
Cost of
Energy/unit(Rs.)
1 1 5 950,000 1,141,750 20.9
1 1 10 1,100,000 1,329,550 23.65
2.5 1 1 5 1,150,000 1,392,750 15.5
1 2 5 1,250,000 1,469,850 26.85
1 1 15 1,250,000 1,517,400 27
2.5 1 1 10 1,300,000 1,580,600 17.1
5 1 1 5 1,350,000 1,652,750 13.55
1 2 10 1,400,000 1,657,700 29.45
2.5 1 2 5 1,450,000 1,720,850 19.1
2.5 1 1 15 1,450,000 1,768,450 19.15
1 3 5 1,550,000 1,797,950 32.75
5 1 1 10 1,500,000 1,831,650 14.45
1 2 15 1,550,000 1,845,500 32.75
2.5 1 2 10 1,600,000 1,908,700 20.6
1 3 10 1,700,000 1,985,800 35.2
5 1 2 5 1,650,000 1,986,500 16.25
7.5 1 1 5 1,550,000 1,997,500 13.65
5 1 1 15 1,650,000 2,019,450 15.95
2.5 1 3 5 1,750,000 2,049,000 22.7
2.5 1 2 15 1,750,000 2,096,550 22.65
1 4 5 1,850,000 2,126,050 38.65
7.5 1 1 10 1,700,000 2,126,750 13.6
5 1 2 10 1,800,000 2,159,750 17.05
1 3 15 1,850,000 2,173,650 38.55
2.5 1 3 10 1,900,000 2,236,800 24.15
10 1 1 5 1,750,000 2,304,650 14.35
1 4 10 2,000,000 2,313,900 40.95
presented. Then the hybrid power system comprising of
both of the above with storage batteries was introduced. The
above was subjected to optimization analysis to find the
configuration that gives least cost of energy for minimum
capital investment and net present value. It is found that a
combination of Solar PV modules, Wind turbines, battery
storage system and suitable power converter is capable of
supplying power at lower cost per unit of energy with
minimum capital investment without causing any damages
to the environmental system.
The typical values shown fairly hold well for scaling up
to larger systems as Solar PV and battery systems are
completely modular in nature. Hence, after a minimum
capacity, the increase in capacities of Solar PV systems has
got insignificant effect in the unit cost of energy. As for as
wind turbines are concerned, more economy can be
achieved at higher capacities depending upon the prevailing
wind data.
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