Adel A.

Elbaset
M.S. Hassan

Design and
Power Quality
Improvement
of Photovoltaic
Power System
Chapter 1
Introduction and Background of PV
Systems

1.1 Concept of Research Work

Increasing environmental concerns regarding the inefficient use of energy, climate

change, acid rain, stratospheric ozone depletion, and global dependence on elec-
tricity have directed attention to the importance of generating electric power in a
sustainable manner with low emissions of GHGs, particularly CO2. In Egypt, total
GHG emissions were estimated at 137.11 Mt of CO2 equivalent, out of which more
than 70 % was emitted from energy sector including about 35 % attributed to the
electricity sector [1]. In the context of addressing environmental issues and climate
change phenomena, Egypt signed Kyoto Protocol in 1997 and approved it in 2005.
According to the Kyoto Protocol, the developed and industrialized countries are
obliged to reduce their GHG emissions by 5.2 % in the period of 2008–2012 [2].
To achieve this, many industrialized countries seek to decarbonize electricity
generation by replacing conventional coal and fossil fuel fired plants with renew-
able technology alternatives [3].
Due to the shortage of inexhaustible resources and environmental problems
caused by the emissions, the traditional power generations, which are based on
fossil fuel are generally considered to be unsustainable in the long term. As a result,
many efforts are made worldwide and lots of countries have being introducing more
renewable energies, such as wind power, solar photovoltaic (PV) power, hydro-
power, biomass power, and ocean power, etc. into their electric grids [4]. Currently,
a significant portion of electricity is generated from fossil fuels, especially coal due
to its low prices. However, the increasing use of fossil fuels accounts for a large
amount of environmental pollution and GHG emissions, which are considered the
main reason behind the global warming. For example, the emissions of carbon
dioxide and mercury are expected to increase by 35 % and 8 %, respectively, by the

© Springer International Publishing AG 2017 1

A.A. Elbaset and M.S. Hassan, Design and Power Quality Improvement
of Photovoltaic Power System, DOI 10.1007/978-3-319-47464-9_1
2 1 Introduction and Background of PV Systems

year 2020 due to the expected increase in electricity generation. Furthermore,

possible depletion of fossil fuel reserves and unstable price of oil are two main
concerns for industrialized countries [5].
While the prices for fossil fuels are skyrocketing and the public acceptance of
these sources of energy is declining, PV technology has become a truly sensible
alternative. Solar energy plays a major role since it is globally available, flexible
with regard to the system size and because it can fulfill the needs of different
countries since it offers on-grid and off-grid solutions [6]. The boundless supply of
sunlight and wind and their zero emission power generation become a driving force
in the fast growth of PV and Wind systems technology. Unlike the dynamic wind
turbine, PV installation is static, does not need strong high towers, produces no
vibration, and does not need cooling systems. In addition, it is environmentally
friendly, safe, and has no gas emissions [6]. The use of PV systems in electricity
generation started in the seventies of the twentieth century and today is currently
growing rapidly around worldwide in spite of high capital cost [5].
PV systems convert the sun’s energy directly into electricity using semicon-
ductor materials. They differ in complexity, some are called “stand-alone or
off-grid” PV systems, which signifies they are the sole source of power to supply
building loads. Further complicating the design of PV systems is the possibility to
connect the PV system generation to the utility “grid connected or on-grid” PV
systems, where electrical power can either be drawn from grid to supplement
system loads when insufficient power is generated or can be sold back to the utility
company when an energy surplus is generated [7, 8]. Based on prior arguments,
grid-connected, or utility-interactive systems appear to be the most practical
application for buildings where the available surface is both scarce and expensive.
Grid-connected PV systems currently dominate the PV market, especially in
Europe, Japan, and USA. With utility interactive systems, the public electricity grid
acts as an energy store, supplying electricity when the PV system cannot. The
performance of a PV system largely depends on solar radiation, temperature and
conversion efficiency. Although, PV systems have many advantages, they suffered
from changing of system performance due to weather variations, high installation
cost, and low efficiency that is hardly up to 20 % for module [9]. An interesting
problem associated with PV systems is the optimal computation of their size. The
sizing optimization of stand-alone or grid connected PV systems is a convoluted
optimization problem which anticipates to obtain acceptable energy and economic
cost for the consumer [10].
The main aim of this chapter is to present the introduction and concept of
research work done in this book. First, the chapter studies the energy situation in
Egypt and discusses Egypt goals and policies regarding their Renewable Energy
Sources (RESs) especially solar energy resource. Secondly, solar PV energy
applications share in Egypt are demonstrated and development of rooftop PV
technologies are discussed. Then, an overview of PV systems are presented.
Finally, the research motivation, objectives, and book outlines are introduced.
1.2 Energy Situation in Egypt 3

1.2 Energy Situation in Egypt

Energy plays a significant role in any nation’s development, and securing energy is
one of the most important challenges facing any developmental plans. While Egypt
has limited fossil fuels, their RESs abound. Nevertheless, RESs currently represent
just a small fraction of the energy mix. They appears to be great potential for the
utilization of Egypt’s renewable resources to generate electricity, thereby boosting
exports and economic development [11]. Recently, Egypt has adopted an ambitious
plan to cover 20 % of the generated electricity by RESs by 2022, including 12 %
contribution from wind energy, translating more than 7200 MW grid-connected
wind farms. The plan includes also a 100 MW Solar thermal energy concentrated
solar power with parabolic trough technology in Kom Ombo city, and two PV
plants in Hurgada and Kom Ombo with a total installed capacity 20 MW each [2].
In order for Egypt to achieve these goals, policies must be aimed at localizing the
Renewable Energy (RE) supply chain and strengthening technological capabilities
at various levels. Egypt is also still in the developmental phase of legislation
supporting the use of RE. A proposed electricity law is currently under construction
and development. It would include some legislation supporting RE in terms of
obligations or commitments on both energy consumers and producers to assign a
part of their production capacity and/or consumption to be from RESs.
The long-term security requirement of Egypt is to reduce the dependence on
imported oil and natural gas and move toward the use of RESs. Egypt’s current
captive-market electricity structure, with the government being a sole buyer, is not
conducive to the rise of a new RE regime. However, a new proposed electricity law,
now in the process of being approved. The anticipated new electricity law tackles
the issue by providing market incentives for private investors, along with those in
RE. Competitive bidding for a determined share of the Egyptian network from RE
is supposed to build a guaranteed market demand for renewable bulk-energy pro-
ducers. Additionally, based on decentralization trend, anticipated new law and
market structure, it seems likely that electricity prices will rise considerably,
including peak-demand figures. Subsidies, as a policy tool, will be used selectively,
especially for low-income and low-consumption residential consumers.

1.3 Solar Energy Resource in Egypt

Favorable climate conditions of Upper Egypt and recent legislation for utilizing
RES provide a substantial incentive for installation of PV systems in Egypt. Egypt
possesses very abundant solar energy resources with sunshine duration ranging
from 9 to 11 h/day with few cloudy days over the year or ranging between 3285
and 4000 h/year. Egypt lies among the Sun Belt countries with annual global solar
4 1 Introduction and Background of PV Systems

Fig. 1.1 Solar atlas of Egypt (annual average direct solar radiation) [1]

insolation, as shown in Fig. 1.1 ranging from 1750 to 2680 kWh/m2/year from
North to South and annual direct normal solar irradiance ranging from 1970 to
3200 kWh/m2/year also from North to South with relatively steady daily profile and
small variations making it very favorable for utilization [1].
El-Minia has a high solar energy potential, where the daily average of solar
radiation intensity on horizontal surface is 5.4 kWh/m2, while the total annual
sunshine hours amounts to about 3000. These figures are very encouraging to use
PV generators for electrification of the faculty as it has been worldwide success
fully used.
1.3 Solar Energy Resource in Egypt 5

Lighting Systems Cell Phone Networks

Systems
20% 12%

Communication
Systems
32%

24%
Advertising Lighting
Systems Cathodic
Protection Systems
Water Pumping 1%
2%
Systems Desalination
9% Systems

Fig. 1.2 PV applications share in Egypt [1]

1.3.1 Photovoltaic Applications in Egypt

Most of solar PV energy applications share in Egypt were demonstrated in Fig. 1.2,
including water pumping, desalination, refrigeration, village electrification, light-
ing, telecommunication, and other solar PV applications. It is estimated that the
solar PV systems installed capacity is presently more than 5.2 MW peak with
around 32 % of that capacity is in telecommunications sector due to the rapid
expansion of mobile telephones repeater stations where the desert represents more
than 90 % of Egypt’s area [1].

1.4 Rooftop Photovoltaic System Technology

In the next years, there will be an explosion of solar PV rooftops across the world,
big and small. Fifteen or 20 years from now, a “bare” rooftop will seem very
strange to us, and most new construction will include PV as routine practice. This
will lead to a parallel explosion in micro-grids (both residential and commercial),
community-scale power systems, and autonomous-home systems. The grid will
become a much more complex hybrid of centralized and distributed power, with a
much greater variety of contractual models between suppliers and consumers [4].
Development of rooftop PV technologies has received much attention and
introduction of a subsidy for the system cost and energy production especially in
Germany and Japan has encouraged the demand for rooftop PV systems [12], where
German PV market is the largest market in the world, and Germany is a leading
country in terms of installed PV capacity. One of the most suitable policies for
introducing rooftop PV systems to the market is Feed-in Tariff mechanism.
According to this approach, eligible renewable power producers will receive a set
6 1 Introduction and Background of PV Systems

price from their utility for all the electricity they generate and deliver to the grid,
where grid interactive PV systems derive their value from retail or displacement of
electrical energy generated. The power output of a PV system depends on the
irradiance of Sun, efficiency and effective area of PV cells conducted. Therefore, it
is compulsory to choose the optimal size of PV system according to the application.
Egypt has abundant solar energy resource, which is extensively applied to
buildings. Therefore, solar energy utilization in buildings has become one of the
most important issues to help Egypt optimize the energy proportion, increasing
energy efficiency, and protecting the environment. Solar PV system can easily be
installed on the rooftop of education, governmental as well as on the wall of
commercial buildings as grid-connected solar PV energy application. Energy effi-
ciency design strategies and RE are keys to reduce building energy demand.
Rooftop solar PV energy systems installed on buildings have been the fastest
growing market in the PV industry. The integration of solar PV within both
domestic and commercial roofs offers the largest potential market for PV especially
in the developed world [12].

1.5 Photovoltaic Systems Overview

Photovoltaic systems can be grouped into stand-alone systems and grid-connected

systems as illustrated in Fig. 1.3. In stand-alone systems the solar energy yield is
matched to the energy demand. Since the solar energy yield often does not coincide

Fig. 1.3 PV systems classifications [13]

1.5 Photovoltaic Systems Overview 7

in time with the energy demand from the connected loads, additional storage sys-
tems (batteries) are generally used. If the PV system is supported by an additional
power source, for example, a wind or diesel generator this is known as a PV hybrid
system. In grid-connected systems the public electricity grid functions as an energy
store [13].

1.5.1 Stand-alone Systems

The first cost-effective applications for photovoltaics were stand-alone systems.

Wherever it was not possible to install an electricity supply from the mains utility
grid (UG). The range of applications is constantly growing. There is great potential
for using stand-alone systems in developing countries where vast areas are still
frequently not supplied by an electrical grid. These systems can be seen as a
well-established and reliable economic source of electricity in rural areas, especially
where the grid power supply is not fully extended [14]. Solar power is also on the
advance when it comes to mini-applications: pocket calculators, clocks, battery
chargers, flashlights, solar radios, etc., are well-known examples of the successful
use of solar cells in stand-alone applications.
Stand-alone PV systems generally require an energy storage system because the
energy generated is not usually required at the same time as it is generated (i.e.,
solar energy is available during the day, but the lights in a stand-alone solar lighting
system are used at night). Rechargeable batteries are used to store the electricity.
However, with batteries, in order to protect them and achieve higher availability
and a longer service life it is essential that a suitable charge controller is also used as
a power management unit. Hence, a typical stand-alone system comprises the
following main components [13]:
1. PV modules, usually connected in parallel or series-parallel;
2. Charge controller;
3. Battery or battery bank;
4. Loads;
5. Inverter (i.e., in systems providing AC power).

1.5.2 Grid-Connected Photovoltaic Systems

The basic building blocks of a grid-connected PV system are shown in Fig. 1.4.
The system is mainly composed of a matrix of PV arrays, which converts the
sunlight to DC power, and a power conditioning unit (PCU) that converts the DC
power to an AC power. The generated AC power is injected into the UG and/or
utilized by the local loads. In some cases, storage devices are used to improve the
8 1 Introduction and Background of PV Systems

Fig. 1.4 Main components of grid-connected PV systems [5]

availability of the power generated by the PV system. In the following subsections,

more details about different components of the PV system are presented.
A grid connected PV system eliminates the need for a battery storage bank
resulting in considerable reduction of the initial cost and maintenance cost. The PV
system, instead, uses grid as a bank where the excess electric power can be
deposited to and when necessary also withdrawn from. When the PV system is
applied in buildings, the PV modules usually are mounted on rooftop, which can
reduce the size of mounting structure and land requirements.

1.5.3 The Photovoltaic Cell/Module/Array

The PV cell is the smallest constituent in a PV system. A PV cell is a specially

designed P-N junction, mainly silicon-based semiconductor and the power input is
made possible by a phenomenon called the photoelectric effect. The characteristic
of photoelectric effect was discovered by the French scientist, Edmund Bequerel, in
1839, when he showed that some materials produce electricity when exposed to
sunlight. The photons in the light are absorbed by the material and electrons are
released, which again creates a current and an electric field because of charge
transfer. The nature of light and the photoelectric effect has been examined by
several scientists the last century, for instance Albert Einstein, which has led to the
development of the solar cell as it is today [15].
1.5 Photovoltaic Systems Overview 9

In most practical situations the output from a single PV cell is smaller than the
desired output. To get the adequate output voltage, the cells are connected in series
into a PV module. When making a module, there are a couple of things that need to
be considered.
• No or partly illumination of the module
During the night, when none of the modules are illuminated, an energy storage
(like a battery) connected directly in series with the modules makes the cells
forward biased. This might lead to a discharge of the energy storage. To prevent
this from happening a blocking diode can be connected in series with the
module. But during normal illumination level this diode represents a significant
power loss.
• Shading of individual cells
If any of the cells in a module is shaded, this particular cell might be forward
biased if other unshaded parts are connected in parallel. This can lead to heating
of the shaded cell and premature failure. To protect the system against this kind
of failure, the modules contain bypass diodes which will bypass any current that
cannot pass through any of the cells in the module.
If the output voltage and current from a single module is smaller than desired,
the modules can be connected into arrays. The connection method depends on
which variable that needs to be increased. For a higher output voltage the modules
must be connected in series, while connecting them in parallel in turn gives higher
currents. It is important to know the rating of each module when creating an array.
The highest efficiency of the system is achieved when the MPP of each of the
modules occurs at the same voltage level. Figure 1.5 shows the relation between the
PV cell, a module and an array.

Fig. 1.5 Relation between the PV cell, a module and an array

10 1 Introduction and Background of PV Systems

1.5.4 Power Conditioning Units

Power conditioning units are used to control the DC power produced from the PV
arrays and to convert this power to high-quality AC power before injecting it into
the UG. PV systems are categorized based on the number of power stages. The past
technology used single-stage centralized inverter configurations. The present and
future technology focus predominantly on the two-stage inverters, where a DC–DC
converter is connected in between the PV modules and the DC–AC inverter as
shown in Fig. 1.6.
In single-stage systems, an inverter is used to perform all the required control
tasks. But, in the two-stage system, a DC–DC converter precedes the inverter and
the control tasks are divided among the two converters. Two-stage systems provide
higher flexibility in control as compared to single-stage systems, but at the expense
of additional cost and reduction in the reliability of the system [16]. During the last
decade, a large number of inverter and DC–DC converter topologies for PV sys-
tems were proposed [16, 17], In general, PCUs have to perform the following tasks:

(a)

Controlled
LC
DC-AC
Filter
Inverter

Utility Grid
Solar PV
Arrays

(b)

DC-DC Controlled
LC
Boost DC-AC
Filter
Converter Inverter

Utility Grid
Solar PV
Arrays
Fig. 1.6 Classification of system configurations a single stage b two stages
1.5 Photovoltaic Systems Overview 11

1.5.4.1 Maximum Power Point Tracking (MPPT)

One of the main tasks of PCUs is to control the output voltage or current of the PV
array to generate maximum possible power at a certain irradiance and temperature.
There are many techniques that can be used for this purpose [17–20] with the
Perturb-and-Observe (P&O) and Incremental Conductance (IC) techniques being
the most popular ones [7].

1.5.4.2 Control of the Injected Current

Power Conditioning Units should control the sinusoidal current injected into the
grid to have the same frequency as the grid and a phase shift with the voltage at the
point of connection within the permissible limits. Moreover, the harmonic contents
of the current should be within the limits specified in the standards. The research in
this field is mainly concerned with applying advanced control techniques to control
the quality of injected power and the power factor at the grid interface [21–23].

1.5.4.3 Voltage Amplification

Usually, the voltage level of PV systems requires to be boosted to match the grid
voltage and to decrease the power losses. This task can be performed using step-up
DC–DC converters or MLIs. 3L-VSIs can be used for this purpose as they provide a
good tradeoff between performance and cost in high voltage and high-power sys-
tems [24].

1.5.4.4 Islanding Detection and Protection

Islanding is defined as a condition in which a portion of the utility system con-

taining both loads and distributed resources remains energized while isolated from
the rest of the utility system [25].

1.5.4.5 Additional Functions

The control of PCUs can be designed to perform additional tasks such as power
factor correction [26], harmonics filtering [27], reactive power control [28], and
operating with an energy storage device and/or a dispatchable energy source such as
diesel generator as an uninterruptible power supply [29].
12 1 Introduction and Background of PV Systems

1.6 Connection Topologies of Photovoltaic Systems

PV systems have different topologies according to the connection of the PV

modules with the PCU. Some of the common topologies are discussed below.

1.6.1 Centralized Topology

This is one of the well-established topologies. It is usually used for large PV

systems with high-power output of up to several megawatts. In this topology [16,
30], a single inverter is connected to the PV array as illustrated in Fig. 1.7. The
main advantage of the centralized topology is its low cost as compared to other
topologies as well as the ease of maintenance of the inverter. However, this
topology has low reliability as the failure of the inverter will stop the PV system
from operating. Moreover, there is significant power loss in the cases of mismatch
between the modules and partial shading, due to the use of one inverter for tracking
the maximum power point. Since the maximum power point of each module varies
depending on the solar radiation (changing with tracking, shading, cloud cover,
etc.), module material, etc. Thus, a local maximum power point of a module may
not correspond with the global maximum power point of the whole system resulting
in under-operation of some PV modules.

1.6.2 Master–Slave Topology

This topology aims to improve the reliability of the centralized topology [31]. In
this case as shown in Fig. 1.8, a number of parallel inverters are connected to the
array and the number of operating inverters is chosen such that if one inverter fails,
the other inverters can deliver the whole PV power. The main advantage of this

AC Voltage
Bus

AC
DC

Fig. 1.7 Central inverter configuration of PV systems

1.6 Connection Topologies of Photovoltaic Systems 13

AC Voltage
AC
Bus
DC

AC
DC

Fig. 1.8 Master–slave configuration of PV systems

topology is the increase in the reliability of the system. Moreover, the inverters can
be designed to operate according to the irradiance level, where for low irradiance
level some of the inverters are shut down. This technique of operation extends the
lifetime of inverters and overall operating efficiency. However, the cost of this
topology is higher than that of the centralized topology and the power loss due to
module mismatch and partial shading is still a problem with this topology.

1.6.3 String Topology

In the string topology, each string is connected to one inverter as depicted in

Fig. 1.9; hence, the reliability of the system is enhanced [16, 30, 32]. Moreover, the

AC Voltage
Bus
AC
DC

AC
DC

AC
DC

Fig. 1.9 String inverter configuration of PV systems

14 1 Introduction and Background of PV Systems

losses due to partial shading are reduced because each string can operate at its own
maximum power point. The string topology increases the flexibility in the design of
the PV system as new strings can be easily added to the system to increase its power
rating. Usually, each string can have a power rating of up to 2–3 kW. The main
disadvantage of this topology is the increased cost due to the increase in the number
of inverters.

1.6.4 Team Concept Topology

This topology is used for large PV systems; it combines the string technology with
the master–slave concept as shown in Fig. 1.10. At low irradiance levels, the
complete PV array is connected to one inverter only. As the irradiance level
increases, the PV array is divided into smaller string units until every string inverter
operates at close to its rated power. In this mode, every string operates indepen-
dently with its own MPP tracking controller [33].

1.6.5 Multi-String Topology

In this topology, every string is connected to a DC–DC converter for tracking the
MPP and voltage amplification [16, 32]. All the DC–DC converters are then con-
nected to a single inverter via a DC bus as shown in Fig. 1.11. This topology
combines the advantages of string and centralized topologies as it increases the
energy output due to separate tracking of the MPP while using a central inverter for
reduced cost. However, the reliability of the system decreases as compared to string

AC Voltage
Bus
AC
DC

AC
DC

AC

DC

Fig. 1.10 Team concept configuration of PV systems

1.6 Connection Topologies of Photovoltaic Systems 15

AC Voltage
DC Bus
DC

DC AC

DC DC

DC

DC

Fig. 1.11 Multi-inverter configuration of PV systems

topology and the losses due to the DC–DC converters are added to the losses of the
system.

1.6.6 Modular Topology

This is the most recent topology. It is also referred to as “AC modules,” because an
inverter is embedded in each module as described in Fig. 1.12. It has many
advantages such as reduction of losses due to partial shading, better monitoring for
module failure, and flexibility of array design [16, 32]. However, this topology is
suitable only for low power applications (up to 500 W) and its cost is relatively
high. Moreover, the lifetime of the inverter is reduced because it is installed in the
open air with the PV module, thus increasing its thermal stress.

Fig. 1.12 Module inverter AC Voltage

configuration of PV systems
Bus
AC

DC

AC
DC

AC

DC
Chapter 3
Optimum Design of Rooftop
Grid-Connected PV System

3.1 Introduction

Egypt is experiencing one of its most considerable energy crises for decades. Power
cuts in Egypt have been escalated in recent years due to the shortage of fuel
necessary to run power plants—due to the rapid depletion of fossil fuels and
continual instability of their prices—and overconsumption of loads especially in
summer season, which negatively affected various levels of social and economic
activities. On the other hand, Egypt has some of the highest GHG emissions in the
world. To solve problems of power cuts and emissions, Egypt is taking impressive
steps to rationalize consumption and optimize the use of electricity in addition to
develop and encourage PV system projects that can be deployed on rooftop of
institutional and governmental buildings. As a result, Egypt government intends to
implement about one thousand of grid-connected PV systems on the roof of gov-
ernmental buildings. As a case study, this book presents a new approach for
optimum design of 100 kW rooftop grid-connected PV system for Faculty of
Engineering buildings. In order to ensure acceptable operation at minimum cost, it
is necessary to determine the correct size of rooftop grid-connected PV system
taking into account meteorological data, solar radiation, and exact load profile of
consumers over long periods. The next limitation to consider is the area available
for mounting the array. For the majority of grid-connected PV systems, this area is
the roof of the house or any other building.
This chapter presents a new approach for optimum design of rooftop
grid-connected PV system installation on an institutional building at Minia
University, Egypt as a case study. The new approach proposed in this chapter is
based on optimal configuration of PV modules and inverters according to not only
MPP voltage range but also maximum DC input currents of the inverter. The
system can be installed on the roof of Faculty of Engineering buildings' B and C.
The study presented in this chapter includes two scenarios using different brands of
commercially available PV modules and inverters. The first scenario includes four

© Springer International Publishing AG 2017 27

A.A. Elbaset and M.S. Hassan, Design and Power Quality Improvement
of Photovoltaic Power System, DOI 10.1007/978-3-319-47464-9_3
28 3 Optimum Design of Rooftop Grid-Connected PV System

types of PV modules and three types of inverters while the second scenario includes
five types of PV modules and inverters. Many different configurations of rooftop
grid-connected PV systems have been investigated and a comparative study
between these configurations has been carried out taking into account PV modules
and inverters specifications. Energy production capabilities, COE, SPBT, and GHG
emissions have been estimated for each configuration using proposed MATLAB
computer program.

3.2 Site Description

Faculty of engineering which located in Upper Egypt was established in the late of
1976s. It is comprised of three buildings A, B, and C, with approximately 200 staff,
3500 undergraduate students, and 400 employees. Location is selected as it has
many of the typical attributes of an education building, since it contains classrooms,
offices, computer laboratories, and engineering laboratories. An important limita-
tion to consider in the design of rooftop PV system is the area available for
mounting the arrays on the buildings. To determine the amount of space available
for the system, a site survey was performed leading to net roof areas available of
2100 and 3100 m2 for buildings B and C, respectively. Coordinate of selected site
is 28.1014 (28° 6′ 5″) °N, 30.7294 (30° 43′ 46″) °W. Electrification of faculty of
engineering is often realized through an electric distribution network via three
transformers with rated 1000, 500, and 500 kVA from Middle Egypt for Electricity
Distribution Company (MEEDCo.). There are three energy meters M1, M2, and M3
with numbers 16947, 59310007, and 59310857, respectively, put on each trans-
former to indicate the total energy consumed by faculty loads. Figure 3.1 shows a
Google Earth™ image of the selected site.

3.2.1 Load Data

First, the load demand of faculty of engineering has been gathered. The main
electrical loads for faculty are represented in lighting, fans, Lab devices,
air-conditioners, and computers with accessories. Table 3.1 provides most electrical
appliances used in the faculty, while Table 3.2 provides energy consumption and
their bills values for the faculty of engineering during a recent year, 2013 which
have been taken from MEEDCo. These values actually have been gotten from
electricity bills paid by the university, where university is the largest customer of its
energy supplier. It can be seen that the yearly energy consumption reaches 980.33
MWh during 2013 year. According to energy bills, it was noticed that energy
consumed continues to increase due to the increasing loads that faculty added
during the recent period. Also it was found that the faculty pays 25 piaster/kWh
(3.57 cent/kWh) up to 2012 year as an energy tariff, it is considered as power
3.2 Site Description 29

Fig. 3.1 Google Earth™ image of faculty of engineering buildings’ layout

Table 3.1 Typical electrical appliances

Floor Load type Total
Lights Fans Air-conditions (3 power/floor
(40 W) (80 W) HP)
No. of Ground 565 36 4 34,432
units First 510 37 11 47,978
Second 435 33 3 26,754
Third 426 32 4 28,552
Fourth 416 20 2 22,716
Sum 2352 158 24 –
Total power 94,080 W 12,640 W 53,712 W 160,432 W

service on low voltage according to the tariff structure of the Egyptian Electricity
Holding Company. Starting from January 2013, the energy tariff increased by about
13.8 % to be 29 piaster/kWh (4.14 cent/kWh). It is expected that tariff structure
continues to increase to reduce governmental subsides.
 30
3

Table 3.2 Typical energy consumption in the faculty for a recent year (2013)
Month Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec.
Energy (MWh) 71.88 54.78 50.04 67.44 62.04 76.26 80.40 97.44 110.278 98.46 113.76 105.04
Bills (EGP) 20,845 15,886 14,512 18,494 17,992 22,115 23,316 28,258 29,806 28,553 32,990 30,462
Optimum Design of Rooftop Grid-Connected PV System
3.2 Site Description 31

3.2.2 Climate Data

Strength of solar radiation is the primary consideration in selecting location for PV

installation. The generated output power of a PV array is directly proportioned to
the input solar radiation. So, to get an optimum design of rooftop PV system, it is
important to collect the meteorological data for site under consideration. Hourly
data of solar direct irradiance and ambient temperature are available for 1 year.
Table 3.3 shows monthly average radiation on the horizontal surface which has
been obtained from Egyptian Metrological Authority for El-Minia site, Egypt.
El-Minia and Upper Egypt region have an average daily direct insolation between
7.7 and 8.3 kWh/m2/day [1, 75].
It is clear from Table 3.3 that solar energy in this region is very high during
summer months, where it exceeds 8 kWh/m2/day, while the lowest average
intensity is during December with a value of 3.69 kWh/m2/day and the actual
sunshine duration is about 11 h/day. So, solar energy application is more and more
considered in El-Minia and Upper Egypt as an RES compared to conventional
energy sources. Figure 3.2 shows the hourly solar radiation over the year seasons as
a sample data.

3.3 Methodology

3.3.1 Radiation on Tilted Surfaces

Solar irradiance data provide information on how much of the sun’s energy strikes a
surface at a location on the earth during a particular period of time. Due to lack of
measured data of irradiance on tilted surfaces, mathematical models have been
developed to calculate irradiance on tilted surfaces.

3.3.1.1 Estimation of Monthly Best Tilt Angle

The new approach is presented based on monthly best tilt angle tracking. Hourly
solar radiation incident upon a horizontal surface is available for many locations.
However, solar radiation data on tilted surfaces are generally not available [76]. The
monthly best tilt angle, b (degrees) can be calculated according to the following
equations [76]:

b¼;d ð3:1Þ
 32
3

Table 3.3 Monthly average climate data (kW/m2/day) for El-Minia, Egypt
Month Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec.
Radiation (kWh/m2) 4.7 5.78 6.58 7.87 8.03 8.25 7.9 7.70 7.20 6.50 5.59 4.77
Temp. T (oC) 14.3 16.9 17.95 34.3 23.7 30.15 33.3 30.6 31.1 26.7 21.55 18.2
Optimum Design of Rooftop Grid-Connected PV System
3.3 Methodology 33

1.20
January
April

Solar Radiation kW/m2

1.00
July
October
0.80

0.60

0.40

0.20

0.00

Time, hr.

Fig. 3.2 Hourly solar radiation on horizontal surfaces at El-Minia site

Table 3.4 Number of the average day for every month and its value [77]
For the average day of the month
Month n, for the i day of the month Recommended n, Recommended day per
date year
Jan. i 17/1 17
Feb. 31 + i 16/2 47
March 59 + i 16/3 75
April 90 + i 15/4 105
May 120 + i 15/5 135
June 151 + i 11/6 162
July 181 + i 17/7 198
Aug. 212 + i 16/8 228
Sept. 243 + i 15/9 258
Oct. 273 + i 15/10 288
Nov. 304 + i 14/11 318
Dec. 334 + i 10/12 344

If calculations are made based on monthly average variables, it is recommended

to use the average number of days for each month and the number n of the day
presented in Table 3.4.
The declination angle can be calculated for the Northern hemisphere in terms of
an integer representing the recommended day of the year, n, by
 
 ð284 þ nÞ
d ¼ 23:45  sin 360  ð3:2Þ
365
34 3 Optimum Design of Rooftop Grid-Connected PV System

3.3.1.2 Calculation of Radiation on Tilted Surfaces

Average daily solar radiation on horizontal surface, H for each calendar month can
be expressed by defining, K T the fraction of the mean daily extraterrestrial radia-
tion, H o as [76]

H
KT ¼ ð3:3Þ
Ho

The average daily radiation on the tilted surface, H T , can be expressed as follows:

HT ¼ R  H ¼ R  KT  Ho; ð3:4Þ

where R is the ratio between radiation on tilted surfaces to radiation on horizontal

surfaces. R can be estimated individually by considering the beam, diffuse, and
reflected components of the radiation incident on the tilted surfaces toward the
equator. Assuming diffuse and reflected radiation can be isotropic then R can be
expressed as follows [76]:
       
HT Hd Hd ð1 þ cosðSÞÞ ð1  cosðSÞÞ
R¼ ¼ 1  Rb þ þq 
H H H 2 2
ð3:5Þ

Hd
2
3
¼ 1:39  4:027  K T þ 5:531  K T 3:108  K T ; ð3:6Þ
H

where H d is the monthly average daily diffuse radiation. However, Rb can be

estimated to be the ratio of the extraterrestrial radiation on the tilted surface to that
on horizontal surface for the month, thus [76]:


sinðdÞ sinð;  dÞðp=180Þx0s þ cos d cosð;  dÞ sin x0s
Rb ¼ ; ð3:7Þ
sinðdÞ sinð;Þðp=180Þ þ cosðdÞ cosð;Þ sinðxs Þ

where

xs ¼ cos1 ð tanð;Þ tanðdÞÞ ð3:8Þ

 
x0s ¼ min xs ; cos1 ð tanð;  SÞÞ tanðdÞ ð3:9Þ
3.3 Methodology 35

3.3.2 Mathematical Modeling of PV Module/Array

Most studies related to the performance of PV systems require the use of a model to
convert the irradiance received by the PV array and ambient temperature into the
corresponding maximum DC power output of the PV array. The performance of PV
system is best described using single-diode model [78−81] or two-diode model
[82]. These models are used to establish I-V and P-V characteristic curves of PV
module/array to obtain an accurate design, optimum operation, and discover the
causes of degradation of PV performance. The models recorded in the literature
[78−81] vary in accuracy and complexity, and thus, appropriateness for different
studies. PV cells essentially consist of an interface between P and N doped silicon.
Therefore, they can be mathematically evaluated in a manner akin to that employed
when dealing with basic P-N junctions. The single-diode model, shown in Fig. 3.3,
is one of the most popular physical models used in the analysis to represent the
electric characteristics of a single PV cell [83].
The mathematical equation describing the IV characteristics of a PV solar cells
array is given by the following equations where the output current can be found by
   
qðV ðtÞ  I ðtÞ  Rs Þ V ðtÞ þ I ðtÞ  Rs
I ðtÞ ¼ Iph ðtÞ  Io ðtÞ exp 1  ð3:10Þ
AKT ðtÞ Rsh

The hourly reverse saturation current, Io ðtÞ varies with temperature as follows:
    
TðtÞ 3 1 1
Io ðtÞ ¼ Ior  exp q  Ego =Ki  ð3:11Þ
Tr T r T ðt Þ

The hourly generated current of solar cells module, Iph ðtÞ varies with tempera-
ture according to the following equation:

H T ðt Þ
Iph ðtÞ ¼ ðIsc þ Ki ðT ðtÞ  298ÞÞ  ð3:12Þ
100

Fig. 3.3 Equivalent circuit of

a PV module
I
Rs
+
ID
D Rsh V
Iph -
36 3 Optimum Design of Rooftop Grid-Connected PV System

The output power of a PV module can be calculated by the following equation:

Ppv;out ðtÞ ¼ V ðtÞ  I ðtÞ ð3:13Þ

3.3.3 Calculation of Optimal Number of PV Modules

The number of subsystems, Nsub depends on the inverter rating, Pinverter and size of
PV system, Psystem . To determine the number of subsystems, inverter rating and
module data must be known.

Psystem
Nsub ¼ ð3:14Þ
Pinverter

Series and parallel combination of each PV subsystem can be adjusted according

to not only the MPP voltage range but also maximum DC input current of the
inverter. Estimation of the initial total number of PV modules for each subsystem
can be calculated as follows:

Pinverter
NPV sub i ¼ ð3:15Þ
Pmax

Most manufacturers of inverters for PV systems make a wide range between
the
maximum and minimum values of MPP voltage range Vmpp max ; Vmpp min , where
inverters act properly and have no problem to find the maximum power point in
where the module is working. Minimum and the maximum number of PV modules
that can be connected in series in each branch, Ns min and Ns max , respectively, are
calculated according to the MPP voltage range as follows:
 
Vmpp min
Ns min ¼ ceil ð3:16Þ
Vmpp
 
Vmpp max
Ns max ¼ ceil ; ð3:17Þ
Vmpp

where Vmpp is the maximum power point of PV module. The optimal number of
series modules, Ns sub is located in the range of

Ns min \Ns sub \Ns max

Minimum and the maximum number of PV modules that can be connected in

parallel in each subsystem, Np min and Np max , respectively, are calculated as
follows:
3.3 Methodology 37

 
NPV sub i
Np min ¼ ceil ð3:18Þ
Ns max
 
NPV sub i
Np max ¼ ceil ; ð3:19Þ
Ns min

where optimal number of parallel modules Np sub is located in the range of

Np min \Np sub \Np max

Number of PV modules connected in parallel Np sub may be set to Np min but

cannot be set to Np max , because the DC current results from all parallel strings may
be higher than the maximum DC input of the inverter which may damage the
inverter. For each number of series modules, Ns sub in the series range calculated
previously, estimation of the corresponding parallel modules for each subsystem
can be calculated as follows:
 
NPV sub i
Np sub ¼ ceil ð3:20Þ
Ns sub

Then, recalculate the total number of PV module, NPV sub according to each
resulted series and parallel combination

NPV sub ¼ Ns sub  Np sub ð3:21Þ

Assuming that inverter is operating in the MPP voltage
range, the operating
input voltage and current of the inverter Vmpp sub ; Impp sub can be calculated as
follows:

Vmpp sub ¼ Ns sub  Vmpp ð3:22Þ

Impp sub ¼ Np sub  Impp ð3:23Þ

From previous calculations, a database containing probable series and parallel

combinations, PV modules, DC input voltage and current for each subsystem is
formed. Optimal total number of PV modules for each subsystem is selected
according to minimum number of PV modules which satisfies not only the MPP
voltage range but also the maximum DC input current of the inverter. The total
number of PV modules, NPV for the selected site can be calculated from the
following:

NPV ¼ Nsub  NPV sub ð3:24Þ

38 3 Optimum Design of Rooftop Grid-Connected PV System

Fig. 3.4 PV modules with several stacked arrays [84]

3.3.4 Optimal Orientation and Arrangement of PV Modules

Photovoltaic arrays are usually tilted to maximize the energy production of the
system by maximizing the direct irradiance that can be received. Optimal placement
of PV array is often somewhat elevated, which reduces not only direct beam
radiation in the winter, but also to some extent diffuse radiation all year round. In
cases of single-row PV system, this loss of diffuse radiation is partially offset by
additional reflected radiation from the building. But in most cases, PV array is
installed in multiple rows or in stacks, which reduce the impact of reflected radi-
ation. So, to increase output capture power from PV array, the clearance distance as
shown in Fig. 3.4 between the rows of the various arrays can be calculated as
follows [84]:

a ¼ d cos b þ h cot a1 ¼ d ðcos b þ sin b cot a1 Þ ð3:25Þ

PV arrays are usually tilted to maximize the energy production of the system by
maximizing the direct irradiance that can be received. Horizon elevation angle can
be determined as follows [84]:

a1 ¼ 66:5  ;

3.3.5 Economic Feasibility Study

The most critical factors in determining the value of energy generated by PV system
are the initial cost of the hardware and installation, and the amount of energy
produced annually [85]. Commonly calculated quantities are SPBT and COE.
3.3 Methodology 39

A grid-connected PV system is economically feasible only if its overall earnings

exceed its overall costs within a time period up to the lifetime of the system. The
time at which earnings equal cost is called the payback time and can be evaluated
according to SPBT.

3.3.5.1 Cost of Electricity (COE)

The economical aspect is crucial for PV systems because of their high cost, which is
reflected on price of kWh generated by them. COE is a measure of economic
feasibility, and when it is compared to the price of energy from other sources
(primarily the utility company) or to the price for which that energy can be sold, it
gives an indication of feasibility [86]. Initial capital investment cost is the sum of
the investment cost of parts of PV system, i.e., PV array, DC/AC inverter, and
miscellaneous cost (wiring, conduit, connectors, PV array support, and grid
interconnection)

Ccap ¼ CPV þ Cinverter þ Cm ð3:27Þ

Miscellaneous cost, Cm can be determined as follows:

Cm ¼ Clabor þ Cwiring þ Cracks þ Cgrid ð3:28Þ

The COE ($/kWh) is primarily driven by the installed cost and annual energy
production of system which can be calculated form the following equation:

Ccap þ Cmain
COE ¼ ð3:29Þ
AEP

Economic parameters considered in the proposed rooftop grid-connected PV

system are shown in Table 3.5.

Table 3.5 Economic parameters considered for the proposed system

Description Value Notes
Installation labor cost ($/h) [87] 16.66 0.43 h/unit
Installation Materials cost [wiring, conduit, connectors] ($/module) 3.60
[87]
Mounting structure cost ($/Wp) [88] 0.080
O&M costs, ($/year) [89] 425.60
Grid Interconnect cost ($) [87] 2,000
Life time, N (years) 25
Tracking system Monthly
40 3 Optimum Design of Rooftop Grid-Connected PV System

3.3.5.2 Simple Payback Time (SPBT)

A PV system is economically feasible only if its overall earnings exceed its overall
costs within a time period up to the lifetime of the system. The time at which
earnings equal cost is called the payback time. In general a short payback is
preferred and a payback of 5–7 years is often acceptable. SPBT provides a pre-
liminary judgment of economic feasibility, where SPBT calculation includes the
value of money, borrowed or lost interest, and annual operation and maintenance
costs can be calculated as follows [85]:

Ccap
SPBT ¼ ð3:30Þ
AEP  P  Ccap  i  Cmain

3.3.6 GHG Emissions Analysis

Concerning to the environmental effects that can be avoided using PV systems. CO2
emission is the main cause of greenhouse effect, so that the total amount of CO2 at
the atmosphere must be minimized in order to reduce the global warming. Amount
of tCO2 can be calculated according to the following equation:

CO2ðemissionÞ ¼ FE  AEP  N ð3:31Þ

3.4 Applications and Results

A new computer program has been developed based on proposed methodology for
design and economic analysis of rooftop grid-connected PV system. The total load
demand of the faculty is about 160.432 kW as shown from Table 3.1. However,
these loads do not work all at one time, on the contrary working for a short time.
Assuming demand load of 60 % of the total load demand, so a capacity of 100 kW
rooftop grid-connected PV system is proposed. According to the Egyptian legal-
ization, the feed-in rates vary depending on usage. Households will receive 84.8
piaster/kWh, commercial producers will receive 90.1 piaster/kWh (under 200 kW)
and 97.3 piaster/kWh for producers of 200−500 kW [90]. Rooftop PV system
operational lifetime period has been set to 25 years, which is equal to guaranteed
operational lifetime period of PV module. According to Ref. [89], an hourly salary
of $26.60 for a facility services engineer to maintain the system is considered. The
projected maintenance costs will be 16 h/year ($425.60) for a medium system (less
than 100 kW). Also to mount the panels on the roof, a solar panel rail kit is applied.
The rail kit is sized based on the assumption that PV modules will be mounted on
the roof inclined with monthly best tilt angle to optimize the energy output. The
3.4 Applications and Results 41

proposed computer program includes two scenarios using different brands of

commercially available PV modules and inverters.

3.4.1 Scenario No. 1

Four different types of PV modules with three different types of inverters have been
used in this scenario. Many different configurations have been investigated and a
comparative study among these configurations has been carried out taking into
account PV modules and inverters specifications. Flowchart of proposed MATLAB
computer program is shown in Fig. 3.5.

Start

Input Radiation, Temperature, PV

module spec. and Site Latitude

For i = 1 : 12
No. of months

For j = 1 : 24
No. of hours/day

Modification of radiation on surfaces tilted by

monthly best tilt angle & Ambient Temp.
Eqns. (3.1) : (3.9)

Input inverter specifications from Table (3.6)

Pinveter, Vmpp_min, Vmpp_max and Iinv_max

For m = 1 : 4
PV module Types

Input module specifications from Table (3.5)

Pmax , Voc , Isc , Vmpp , Impp & Dimensions
NPV & Capital cost calculations PV
Calculation of energy generated power for each modules Eqn. (3.26):(3.28)
module Eqns. (3.10) : (3.15)
COE, SPBT and GHG emission reduction
Calculate Nsub & NPV_sub_i calculations Eqns. (3.29) : (3.31)
for each subsystem Eqns. (3.16), (3.17)
End
Calculate Ns_min, Ns_max, Np_min & Np_max Eqns. (3.18) : (3.21)

For k = Ns_min : Ns_max

Estimation of corresponding parallel and total

modules for each subsystem Eqns. (3.22), (3.23)

Calculate operating input voltage and current of the

inverter Eqns. (3.24), (3.25)

Fig. 3.5 Flowchart of proposed computer program in scenario no. 1

42 3 Optimum Design of Rooftop Grid-Connected PV System

Table 3.6 Technical characteristics of selected PV modules in scenario no. 1

Item Module
Mitsubishi Suntech ET-P672305WB/WW 1Sol Tech
PV-UD190MF5 STP270S-24/Vb 1STH-350-WH
Pmax (W) 190 270 305 350
VOC (V) 30.8 44.8 45.12 51.5
Isc (A) 8.23 8.14 8.78 8.93
Vmpp (V) 24.7 35.0 37.18 43.0
Impp (A) 7.71 7.71 8.21 8.13
Dimensions, m 1.658 * 0.834 1.956 * 0.992 1.956 * 0.992 1.652 * 1.306
Efficiency (%) 13.7 15 15.72 16.2
Number of 50 cell 72 cell 72 cell 80 cell
cells
Cell type Polycrystalline Monocrystalline Polycrystalline Monocrystalline
(Silicon)
Price/unit $340 $753 $305 $525

3.4.1.1 Selected PV Modules in Scenario No. 1

Depending on the manufacturing process, most of PV modules can be of three types:

Monocrystalline Silicon, Polycrystalline Silicon, and Amorphous Silicon. Two
different Silicon solar cell technologies (Monocrystalline and Polycrystalline) with
four different selected types of commercially available PV modules (i.e., 190, 270,
305, and 350 W) have been used in the first scenario as illustrated in Table 3.6.

3.4.1.2 Inverter Selection in Scenario No. 1

Inverters are a necessary component in a PV system generation used to convert

direct current output of a PV array into an alternating current that can be utilized by
electrical loads. There are two categories of inverters, the first category is syn-
chronous or line-tied inverters which are used with utility connected PV systems.
While the second category is stand alone or static inverters which are designed for
independent utility-free power systems and are appropriate for remote PV instal-
lation. Three different types of commercially available line-tied inverters (i.e., 20,
50, and 100 kW) have been used associated with capital costs as revealed in
Table 3.7.
3.4 Applications and Results 43

Table 3.7 Characteristics of different inverters used in scenario no. 1

Specification Inverter
Sunny Tripower HS50K3 HS100K3
20000TL
Manufacturer SMA Solar Han’s Inverter & Grid Han’s Inverter & Grid
Technology Tech. co. Ltd. Tech. co. Ltd.
Pinverter (kW) 20.45 55 110
Max. DC 36 122 245
current (A)
MPP voltage 580–800 450–800 450–820
range (V)
Max. AC power 20 50 100
(kW)
Max. AC 29 80 160
current (A)
Frequency (Hz) 50 50 50
Price/unit $3870 $8060 $14,500

3.4.1.3 Configurations of PV Modules for Each Subsystem

in Scenario No. 1

The configuration details for each subsystem in scenario no. 1 are shown in
Table 3.8, while AEP resulting from proposed PV system is calculated in
Table 3.9. The optimal configuration with two subsystems (HS50K3 inverter)
consists of 182 Polycrystalline silicon PV modules (ET-P672305WB). The PV
modules are arranged in 14 parallel strings, with 13 series modules in each. From
this table, although, the combination of ET-P672305WB PV module and HS100K3
inverter has the minimum price for kWh generated (0.6725 $/kW), this is not the
best combination due to system reliability. Also, it can be seen that the maximum
generated energy from HS50K3 with two subsystem is equal to 208.83 MWh,
meanwhile the optimal system configuration consists of ET-P672305WB PV
module and HS50K3 inverter based on lowest cost of kWh generated (0.6792 $/
kWh) and system reliability. Figure 3.6 shows the rooftop grid-connected PV
system layout proposed in scenario no. 1
The electric characteristics of a PV module depend mainly on the irradiance
received by the module and the module temperature. Figures 3.7 and 3.8 demon-
strate the electrical characteristics of optimal PV module in scenario no. 1 at specific
hour over the day at different levels of irradiance and constant temperature for 2
days, one during a day in March and the other during a day in December. The
amount of energy generated by the solar PV panel depends on peak sun hours
available where peak sun hours vary throughout the year. It can be seen that the
peak power generation during a day in March is about 298.57 W which occurs
between 12:00 and 1:00 p.m., while that for a day in December is about 222.13 W
and occurs between 1:00 and 2:00 p.m. The difference depends on the intensity of
 44

Table 3.8 Specifications for each subsystem in scenario no. 1

Inverter type Details Module
Mitsubishi Suntech ET-P672305WB/WW 1Sol Tech
PV-UD190MF5 STP270S-24/Vb 1STH-350-WH
Sunny Tripower 5 Ns sub 27 19 17 15
20000TL subsystem Np sub 4 4 4 4
3

NPV sub 108 76 68 60

Vsub (V) 666.9 665.0 632.06 645.0
Isub (A) 30.84 30.84 32.84 32.52
HS50K3 2 Ns sub 29 17 13 16
subsystem Np sub 10 12 14 10
NPV sub 290 204 182 160
Vsub (V) 716.3 595.0 483.34 688.0
Isub (A) 77.1 92.52 114.94 81.30
HS100K3 1 Ns sub 20 17 19 15
subsystem Np sub 29 24 19 21
NPV sub 580 408 361 315
Vsub (V) 494.0 595.0 706.42 645.0
Isub (A) 223.59 185.04 155.99 170.73
Optimum Design of Rooftop Grid-Connected PV System
 3.4 Applications and Results

Table 3.9 AEP and COE results in scenario no. 1

Parameter Inverter Module
Mitsubishi Suntech ET-P672305WB/WW 1Sol Tech
PV-UD190MF5 STP270S-24/Vb 1STH-350-WH
AEP Sunny Tripower 20000TL 228.8893 228.5928 195.0641 238.2875
(MWh/yr.) HS50K3 245.8443 245.4365 208.8333 254.1732
HS100K3 245.8443 245.4365 207.1121 250.2018
COE ($/kWh) Sunny Tripower 20000TL 0.9565 1.3988 0.7017 0.7984
HS50K3 0.9370 1.3793 0.6792 0.7804
HS100K3 0.9304 1.3727 0.6725 0.7756
45
46 3 Optimum Design of Rooftop Grid-Connected PV System

Fig. 3.6 Rooftop grid-connected PV system layout proposed in scenario no. 1

Fig. 3.7 P-V characteristics of ET−305 W PV module during a day in March

3.4 Applications and Results 47

Fig. 3.8 P-V characteristics of ET−305 W PV module during a day in December

sun radiation incident on the PV modules. Also, noticed that, the characteristics of
PV module appear every hour in March due to the presence of irradiance, unlike in
December due to the weather clouds that occasionally scatter some of the sun’s
energy preventing it from reaching the ground. Clearly, the change in irradiance has
a strong effect on the output power of the module, but negligible effect on the
open-circuit voltage.
The annual energy production is estimated to be 208.83 MWh with $0.6792 for
each kWh generated. Also, the scenario estimates that, 145.97 tons of CO2-eq
annually will be avoided as the rooftop grid-connected PV system replaces the need
of some electricity from the existing UG. Table 3.10 shows the generated output
power during each month for optimal PV module (ET-P672305WB/WW) selected
in scenario no. 1.

3.4.2 Scenario No. 2

Five different brands of commercially available PV modules and inverters have

been conducted in this scenario as shown in Tables 3.11 and 3.12. Many different
configurations of rooftop grid-connected PV systems have been investigated and a
comparative study among these configurations has been carried out taking into
account PV modules and inverters specifications. Flowchart of proposed MATLAB
computer methodology, used in scenario no. 2, is shown in Fig. 3.9. From the
proposed computer program, it can be seen that the ST25000TL inverter is not
suitable for those selected PV modules in this scenario due to its low DC input
 48

Table 3.10 Generated output power for one module of ET-P672305WB/WW

Hour Month
Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec.
01:00 AM 0 0 0 0 0 0 0 0 0 0 0 0
02:00 AM 0 0 0 0 0 0 0 0 0 0 0 0
03:00 AM 0 0 0 0 0 0 0 0 0 0 0 0
04:00 AM 0 0 0 0 0 0 0 0 0 0 0 0
05:00 AM 0 0 0 0 0 0 0 0 0 0 0 0
06:00 AM 0 0 0 0 0 0 0 0 0 0 0 0
07:00 AM 0.2418 11.7741 4.6065 7.2977 8.2353 0 2.0918 2.0996 0.4404 13.1777 3.3355 0
3

08:00 AM 24.4655 61.7912 59.6002 25.1291 52.1722 11.0664 20.8252 35.5297 24.4066 49.3103 49.4647 22.5759
09:00 AM 83.3111 94.8623 129.7234 42.4925 99.8702 54.4898 64.2239 86.8332 83.8088 85.8805 114.7261 104.4056
10:00 AM 151.1045 131.9372 177.3813 70.2066 111.4648 111.0428 135.1924 140.7313 142.979 124.2075 187.6101 157.0487
11:00 AM 186.4208 201.4572 230.0969 144.1673 138.5558 167.9091 192.6576 175.3098 180.5782 205.6089 235.2146 166.5365
12:00 AM 218.6747 250.9574 246.0327 173.1991 190.371 204.7407 228.9464 218.5693 224.7353 172.0633 250.0235 158.7423
01:00 PM 229.8822 244.2047 243.6301 202.309 230.5426 222.8717 247.1432 234.6135 249.6875 180.6353 237.6825 183.0456
02:00 PM 218.6747 247.9235 238.1043 212.0242 221.455 228.2437 246.5853 234.6135 243.3155 172.0633 207.3271 112.1367
03:00 PM 193.1365 244.9876 151.6879 174.8146 207.4793 229.2902 227.3432 211.5964 219.5043 130.0866 149.0073 37.4054
04:00 PM 124.5951 178.9874 110.8437 127.5986 163.1074 215.9664 188.4135 187.5583 177.0993 65.8824 71.0328 24.2797
05:00 PM 39.607 111.8641 43.5743 60.2103 143.349 185.9995 135.1924 143.3647 122.221 31.6332 10.6772 5.1297
06:00 PM 0.3278 36.3876 7.7319 6.9857 92.4348 145.5496 89.282 86.2857 60.5862 0.9847 0 0
07:00 PM 0 0.5885 0 0 34.1938 95.7708 41.5669 31.425 7.6333 0 0 0
08:00 PM 0 0 0 0 3.0698 42.6708 0.5901 1.6933 0 0 0 0
09:00 PM 0 0 0 0 0 6.2578 0 0 0 0 0 0
10:00 PM 0 0 0 0 0 0 0 0 0 0 0 0
11:00 PM 0 0 0 0 0 0 0 0 0 0 0 0
12:00 PM 0 0 0 0 0 0 0 0 0 0 0 0
Optimum Design of Rooftop Grid-Connected PV System
Table 3.11 Technical characteristics of the selected PV modules in scenario no. 2
Item Module
3.4 Applications and Results

Mitsubishi Suntech ET-P672305WB/WW 1Sol Tech Solar panel Heliene 96 M

PV-UD190MF5 STP270S-24/Vb 1STH-350-WH 420
Pmax (W) 190 270 305 350 420
VOC (V) 30.8 44.8 45.12 51.5 60.55
Isc (A) 8.23 8.14 8.78 8.93 9.0
Vmpp (V) 24.7 35.0 37.18 43.0 49.53
Impp (A) 7.71 7.71 8.21 8.13 8.48
Dimensions, m 1.658 * 0.834 1.956 * 0.992 1.956 * 0.992 1.652 * 1.306 1.967 * 1.310
Efficiency (%) 13.7 15 15.72 16.2 16.4
Number of cells 50 cell 72 cell 72 cell 80 cell 96 cell
Cell type Polycrystalline Monocrystalline Polycrystalline Monocrystalline Monocrystalline
(Silicon)
Price/unit $340 $753 $305 $525 $420
49
50 3 Optimum Design of Rooftop Grid-Connected PV System

Table 3.12 Characteristics of the different inverter ratings used in scenario no. 2
Specification Inverter
GCI-10 k-LV Sunny ST25000TL HS50K3 HS100K3
Tripower
20000TL
Manufacturer B&B Power SMA Solar B&B Han’s Inverter Han’s Inverter
co. Ltd. Technology Power co. & Grid Tech. & Grid Tech.
Ltd. co. Ltd. co. Ltd.
Pinverter (kW) 10.2 20.45 26.5 55 110
Max. DC 30 36 32 122 245
current (A)
MPP voltage 150–500 580–800 450–800 450–800 450–820
range (V)
Max. AC 10 20 25 50 100
power (kW)
Max. AC 25 29 40 80 160
current (A)
Frequency 50/60 50 50/60 50 50
(Hz)
Price/unit $1500 $3870 $2650 $8060 $14,500

current, where the common feature of selected PV modules is that, they have a high
current at different voltage level to supply a high power with a minimum instal-
lation area.

3.4.2.1 Configurations of PV Modules for Each Subsystem

in Scenario No. 2

The configuration details of PV modules for each subsystem in this scenario are
shown in Table 3.13. From this table, it can be seen that the outputs of the proposed
MATLAB computer program are the optimum total number of PV modules for
each subsystem, NPV sub , number of modules per strings Ns sub , number of strings,
Np sub , and finally the output voltage and current of each subsystem.
Figure 3.10 displays the electrical characteristics of selected PV module
(Heliene 96M 420) at different levels of irradiance and constant temperature over a
day in July. The amount of energy generated by the solar PV panel depends on peak
sun hours available where peak sun hours vary throughout the year. It is clear that
the change in irradiance has a strong effect on the output power of the module, but
negligible effect on the open-circuit voltage. Also, it can be seen that the maximum
power generated during a day in July occurs at 1:00–2:00 p.m. Table 3.14 shows
the generated output power for optimal PV modules (Heliene 96 M 420) selected in
scenario no. 2.
3.4 Applications and Results 51

Start

Input Radiation, Temperature, PV

module spec. and Site Latitude

For i = 1 : 12
No. of months

For j = 1 : 24
No. of hours/day

Modification of radiation on surfaces tilted by

monthly best tilt angle & Ambient Temp.
Eqns. (3.1) : (3.9)

Input inverter specifications from Table (3.11)

Pinveter, Vmpp_min, Vmpp_max and Iinv_max

For m = 1 : 5
PV module Types

Input module specifications from Table (3.10)

Pmax , Voc , Isc , Vmpp , Impp & Dimensions
Select Ns_sub , Np_sub , & NPV_sub that
Calculation of energy generated power for each satisfies MPP voltage range and max. DC
module Eqns. (3.10) : (3.14) input current of inverter Table (3.14)

Calculate Nsub & NPV_sub_i Calculate optimal number of PV module

for each subsystem Eqns. (3.15), (3.16) NPV Eg. (3.25)

Calculate Ns_min, Ns_max, Np_min & Np_max Eqns. (3.17) : (3.20) Optimal orientation & Capital cost
calculations of PV modules
Eqns. (3.26):(3.29)
For k = Ns_min : Ns_max
COE, SPBT and GHG emission reduction
Estimation of corresponding parallel and total calculations Eqns. (3.30) : (3.32)
modules for each subsystem Eqns. (3.21), (3.22)

Calculate operating input voltage and current of the Detailed Calculations

inverter Eqns. (3.23), (3.24)
End

Fig. 3.9 Flowchart of proposed computer program in scenario no. 2

3.4.2.2 Optimal Configuration as a Detailed Calculation

in Scenario No. 2

Many calculations have been done for many subsystems. A database containing
probable series and parallel combinations, PV modules for each subsystem, and DC
input voltage and current is formed. Detailed calculations for optimal configuration
of selected module (Heliene 96 M 420) and inverter (GCI-10 k-LV) based on
minimum price of kWh generated can be done as follows. Input data are given in
Tables 3.5, 3.11, and 3.12.
 52

Table 3.13 Specifications for each subsystem in scenario no. 2

Inverter Type/sub systems Type Mitsubishi Suntech ET-P672305WB/WW 1Sol Tech Solar panel Heliene
Details PV-UD190MF5 STP270S-24/Vb 1STH-350-WH 96 M 420
GCI-10 k-LV 10 Ns sub 18 13 12 10 9
subsystem Np sub 3 3 3 3 3
NPV sub 54 39 36 30 27
Vsub (V) 444.6 455.0 446.16 430.0 445.77
Isub (A) 23.13 23.13 24.63 24.39 25.44
Sunny Tripower 5 Ns sub 27 19 17 15 17
3

20000TL subsystem Np sub 4 4 4 4 3

NPV sub 108 76 68 60 51
Vsub 666.9 665.0 632.06 645.0 842.01
(V)
Isub (A) 30.84 30.84 32.84 32.52 25.44
HS50K3 2 Ns sub 29 17 13 16 11
subsystem Np sub 10 12 14 10 12
NPV sub 290 204 182 160 132
Vsub (V) 716.3 595.0 483.34 688.0 544.83
Isub (A) 77.1 92.52 114.94 81.30 101.76
HS100K3 1 Ns sub 20 17 19 15 11
subsystem Np sub 29 24 19 21 24
NPV sub 580 408 361 315 264
Vsub (V) 494.0 595.0 706.42 645.0 544.83
Isub (A) 223.59 185.04 155.99 170.73 203.52
Optimum Design of Rooftop Grid-Connected PV System
3.4 Applications and Results 53

Fig. 3.10 P-V Characteristics of solar panel Heliene 96M 420 over day times in July

   
Psystem 100; 000
Nsub ¼ ceil ¼ ceil ¼ ceilð9:8039Þ ¼ 10 subsystems
Pinverter 10; 200
   
Pinverter 10; 200
NPV sub i ¼ ceil ¼ ceil ¼ ceilð24:2857Þ ffi 25 modules
Pmax 420
   
Vmpp min 150
Ns min ¼ ceil ¼ ceil ¼ ceilð3:0284Þ ffi 4 modules
Vmpp 49:53
   
Vmpp max 500
Ns max ¼ ceil ¼ ceil ¼ ceilð10:0948Þ ffi 11 modules
Vmpp 49:53

So, in order to stay within the voltage range at which the inverter will track the
MPP of each subsystem, the number of modules in each string, Ns sub must not be
fewer than 4 and not be more than 11 as shown in column 2 from Table 3.15.

4\Ns sub \11

   
NPV sub i 25
Np min ¼ ceil ¼ ceil ¼ ceilð2:2727Þ ¼ 3 modules
Ns max 11
   
NPV sub i 25
Np max ¼ ceil ¼ ceil ¼ ceilð6:25Þ ¼ 7 modules
Ns min 4

Optimal number of parallel modules Np sub is located in the following range as

shown in column 3 from Table 3.15:
Table 3.14 Generated output power for one module of solar panel Heliene 96 M 420
54

Hour Month
Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec.
01:00 AM 0 0 0 0 0 0 0 0 0 0 0 0
02:00 AM 0 0 0 0 0 0 0 0 0 0 0 0
03:00 AM 0 0 0 0 0 0 0 0 0 0 0 0
04:00 AM 0 0 0 0 0 0 0 0 0 0 0 0
05:00 AM 0 0 0 0 0 0 0 0 0 0 0 0
06:00 AM 0 0 0 0 0 0 0 0 0 0 0 0
07:00 AM 0.3869 19.3269 7.5326 12.1424 13.5776 0 3.4555 3.4596 0.7194 21.8332 5.463 0
3

08:00 AM 40.2037 102.1675 98.6208 42.036 86.7179 18.378 34.7779 59.3259 40.7083 82.1584 82.0466 37.2135
09:00 AM 137.6023 157.1019 215.2645 71.2331 166.3914 91.0967 107.7298 145.465 140.4422 143.3796 190.8788 173.1567
10:00 AM 250.1059 218.7582 294.6442 117.9044 185.7772 186.0997 227.3243 236.1198 240.0051 207.6215 312.6241 260.8263
11:00 AM 308.7587 334.4683 382.4907 242.6693 231.0913 281.7559 324.2758 294.3231 303.322 344.1976 392.1934 276.6345
12:00 AM 362.3424 416.8962 409.0517 291.6883 317.8104 343.7468 385.5264 367.1668 377.7117 287.899 416.9499 263.648
01:00 PM 380.964 405.6504 405.0471 340.8543 385.0717 374.2697 416.2453 394.1888 419.7569 302.2836 396.319 304.145
02:00 PM 362.3424 411.8436 395.837 357.2656 369.8541 383.3138 415.3035 394.1888 409.0194 287.899 345.5775 186.0261
03:00 PM 319.9144 406.9542 251.8427 294.4165 346.4533 385.0758 382.8202 355.4236 368.898 217.4805 248.1239 61.7924
04:00 PM 206.0947 297.0598 183.835 214.7024 272.1748 362.6444 317.1134 314.9453 297.4624 109.8888 117.984 40.0349
05:00 PM 65.2221 185.3697 72.0128 101.0626 239.1108 312.2011 227.3243 240.5515 205.0627 52.6133 17.5918 8.3949
06:00 PM 0.5256 60.0357 12.6774 11.6208 153.9625 244.1347 149.9307 144.5447 101.4119 1.6095 0 0
07:00 PM 0 0.9498 0 0 56.7396 160.4276 69.6143 52.4465 12.6659 0 0 0
08:00 PM 0 0 0 0 5.0357 71.272 0.9678 2.7869 0 0 0 0
09:00 PM 0 0 0 0 0 10.3647 0 0 0 0 0 0
(continued)
Optimum Design of Rooftop Grid-Connected PV System
Table 3.14 (continued)
Hour Month
Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec.
10:00 PM 0 0 0 0 0 0 0 0 0 0 0 0
11:00 PM 0 0 0 0 0 0 0 0 0 0 0 0
12:00 PM 0 0 0 0 0 0 0 0 0 0 0 0
3.4 Applications and Results
55
56 3 Optimum Design of Rooftop Grid-Connected PV System

3\Np sub \7
   
NPV sub i 25
Np sub ¼ ceil ¼ ceil ¼ ceilð2:7777Þ ¼ 3 modules
Ns sub 9
NPV sub ¼ Ns sub  Np sub ¼ 9  3 ¼ 27 modules

Assuming that the inverter is operating in the MPP voltage range, the operating
input voltage and current of the inverter can be calculated as follows as shown in
columns 5 and 7 in Table 3.15, respectively:

Vmpp sub ¼ Ns sub  Vmpp ¼ 9  49:53 ¼ 445:77 V

Impp sub ¼ Npsub  Impp ¼ 3  8:48 ¼ 25:44 A

Each nine modules will be connected in series to build three parallel strings.
Considering open-circuit voltage ðVoc ¼ 60:55 VÞ and short-circuit current
ðIsc ¼ 9:0 AÞ of Heliene 96 M 420 solar module at standard conditions, the
open-circuit voltage and short-circuit current for resultant PV array.

Voc a ¼ 60:55  9 ¼ 544:95 V

Isc a ¼ 9  3 ¼ 27 A

Which also satisfy the voltage and current limits of selected inverter. MPP
voltage range of the (GCI-10 k-LV) inverter is 150−500 V, as can be seen from
Table 3.15, all configurations can be implemented according to operating voltage
except the last one (case 8) because the voltage exceeds the maximum value of
MPP voltage range. On the other hand, maximum DC input current of selected
inverter is 30 A, so cases 1−5 from Table 3.15 cannot be implemented where
resultant current is higher than maximum DC input current of selected inverter.
Although the minimum number of PV modules for a subsystem is 25 as revealed in
column 4 in Table 3.15, this number is not the optimal number of PV modules for a

Table 3.15 Optimal configuration of PV module and inverter in scenario no. 2

Case Ns sub Np sub Nsub Vsub (V) Voltage Isub (A) Current Optimal
condition condition
1 4 7 28 198.12 Satisfied 59.36 Not Satisfied
2 5 5 25 247.65 Satisfied 42.40 Not Satisfied
3 6 5 30 297.18 Satisfied 42.40 Not Satisfied
4 7 4 28 346.71 Satisfied 33.92 Not Satisfied
5 8 4 32 396.24 Satisfied 33.92 Not Satisfied
6 9 3 27 445.77 Satisfied 25.44 Satisfied Selected
7 10 3 30 495.30 Satisfied 25.44 Satisfied
8 11 3 33 544.83 Not Satisfied 25.44 Satisfied
3.4 Applications and Results 57

subsystem because the resultant current is 42.4 A, which is higher than the maxi-
mum DC input current of the inverter (30 A). Optimal total number of PV modules
for each subsystem is selected according to minimum number of PV modules which
satisfies not only MPP voltage range but also maximum DC input current of the
inverter. So the optimal number of PV modules from the remaining cases 6 and 7 is
27 modules. The total number of PV modules can be calculated from the following
equation as shown in Table 3.16:

NPV ¼ Nsub  NPV sub ¼ 10  27 ¼ 270 modules

Finally, layout of the PV system is illustrated in Fig. 3.11. The PV system is

mainly composed of 270 Heliene 96 M 420 monocrystalline silicon PV modules.
The PV modules are arranged in three parallel strings, with nine series modules in
each. A power diode, called bypass diode, is connected in parallel with each
individual module or a number of modules. The function of this diode is to conduct
the current when one or more of these modules are damaged or shaded. Another
diode, called blocking diode, is usually connected in series with each string to
prevent reverse current flow and protect the modules. The diodes are physically
mounted into a junction box on the rear side of the panel and are normally inactive.
Each subsystem is connected to GCI-10 k-LV inverter which has the feature of
controlling the MPP of PV array through a built-in DC–DC converter. Failure of
one distributed inverter does not stop the operation of the entire PV system, because
they operate separately. The generated AC power from the inverter is injected into
the grid through a distribution transformer and/or utilized by the local loads.
From the proposed computer program shown in Fig. 3.9, the daily generated
power for each module and the total number of PV modules for each subsystem can
be calculated. To determine the total generated power for each month multiply the
generated power for each module/month by the total number of modules for each
type of PV modules. The generated power for each type of PV modules under
GCI-10 k-LV inverter is shown in Table 3.17 and the reaming results of other
inverters are given in Appendix A. Figure 3.12 shows the monthly generated PV
power for the GCI-10 k-LV inverter under different PV modules.

3.4.2.3 Maximum Clearance Distance Between PV Rows

From Table 3.11 the width of selected PV module is about 1.31 m, where there are
three parallel strings so the width of each PV array is

d ¼ 3 ðmodulesÞ  1:31 ðmÞ ¼ 3:93 m

 58

Table 3.16 Optimal total number of PV modules for each system

3

Inverter Module
Mitsubishi Suntech ET-P672305WB/WW 1Sol Tech Solar panel Heliene
PV-UD190MF5 STP270S-24/Vb 1STH-350-WH 96 M 420
GCI-10 k-LV 540 390 360 300 270
Sunny Tripower 540 380 340 300 255
20000TL
HS50K3 580 408 364 320 264
HS100K3 580 408 361 315 264
Optimum Design of Rooftop Grid-Connected PV System
3.4 Applications and Results 59

DC Side AC Side
Subsystem #1
PV Array #1
Bl ocking St ri ngs
DC Bus
Diode
Inverter Block #1 AC Bus
1
9 Modules/ string

2 DC DC
3 DC AC
Bl ocking Bui lt-in DC/DC
Inverter #1
9 Diode Converter #1

Subsystem Details
P_sub : 10.2 kWp
Utili ty
V_sub : 445.77 V Ns_sub: 9 modules
Gri d
I_sub : 25.44 A Np_sub : 3 modules
No. of subsystems : 10 Subsystem #10
PV Array #10
St ri ngs
DC Bus PV System Details
Inverter Block #10 P_system : 102 kWp
1
9 Modules/ string

V_system : 445.77 V
2 I_system : 254.4 A
DC DC Total no. of strings : 30 strings
3 DC AC No. of modules/string : 9 modules
Bui lt-in DC/DC No. of strings/invert er : 3 string
Inverter #10
9 Converter #10

PV Module Details Inverter Details

Type : Sol ar panel Heliene 96M 420 Max. DC power : 10.2 kWp
Pm ax : 420 W Max. DC current : 30 A
Vmp : 49.53 V Imp : 8.48 A MPP voltage range : 150~500 V
Voc : 60.55 V Is c : 9.00 A Max. AC output : 10 kW
Dimensions : 1.967 *1.310 m2

Fig. 3.11 Rooftop grid-connected PV system layout proposed in scenario no. 2

The horizon elevation angle can be calculated as follows:

a1 ¼ 66:5  ; ¼ 66:5  28:1 ¼ 38:4

From proposed computer program, the monthly best tilt angles are shown in
Table 3.18. From Table 3.18 it can be concluded that the maximum clearance
distance between PV rows is 6.326 m (Fig. 3.13).

3.4.2.4 Detailed Calculations for ST25000TL Inverter

ST25000TL inverter is not selected where the output DC current of subsystems

exceed the maximum DC input current of the inverter according to the following
calculations:
 60

Table 3.17 Monthly generated PV power for the GCI-10 k-LV inverter at different modules
Power (MWh) Module
Mitsubishi Suntech ET-P672305WB/WW 1Sol Tech Solar panel Heliene 96 M
PV-UD190MF5 STP270S-24/Vb 1STH-350-WH 420
January 18.3541 18.8494 16.1013 18.5173 19.9930
February 22.5449 23.1328 19.9040 22.9430 24.7736
3

March 20.3224 20.8509 17.9910 20.7359 22.4107

April 14.7427 15.0863 13.6484 15.7505 17.2265
May 20.6593 21.1859 18.5745 21.3905 23.2394
June 23.0249 23.5827 21.0444 24.3313 26.4835
July 21.6247 22.1305 19.9295 23.0833 25.15
August 21.4202 21.9373 19.6029 22.6637 24.678
September 20.7607 21.2569 19.0201 22.0116 23.9573
October 14.8668 15.2379 13.4853 15.5108 16.9084
November 18.5825 19.0549 16.6013 19.1593 20.7427
December 11.9861 12.3031 10.6358 12.1903 13.2375
Total generated 228.8893 234.6086 206.5385 238.2875 258.8006
power
Optimum Design of Rooftop Grid-Connected PV System
3.4 Applications and Results 61

30

Monthly Generated Power, MW

28
26
24
22
20
18
16
14
12
10
8
6
4
2
0
1 2 3 4 5 6 7 8 9 10 11 12
Time, Month
190 W module 270 W module 305 W module 350 W module 420 W module

Fig. 3.12 Monthly generated PV power for the GCI-10 k-LV inverter at different modules

   
Pinverter 26; 500
NPV sub i ¼ ceil ¼ ceil ¼ ceilð63:0952Þ ffi 64 modules
Pmax 420
   
Vmpp min 450
Ns min ¼ ceil ¼ ceil ¼ ceil ð9:0854Þ ffi 10 modules
Vmpp 49:53
   
Vmpp min 800
Ns min ¼ ceil ¼ ceil ¼ ceilð16:1518Þ ffi 17 modules
Vmpp 49:53

Optimal number of series modules Ns sub is located in the following range as

shown in column 2 from Table 3.19:

10\Ns sub \17

   
NPV sub i 64
Np min ¼ ceil ¼ ceil ¼ ceilð6:4000Þ ffi 7 modules
Ns max 10
   
NPV sub i 64
Np max ¼ ceil ¼ ceil ¼ ceilð3:7647Þ ffi 4 modules
Ns min 17

Optimal number of parallel modules Np sub is located in the following range as

shown in column 3 from Table 3.19:

4\Np sub \7
   
NPV sub i 64
Np sub ¼ ceil ¼ ceil ¼ ceil ð6:4Þ ffi 7 modules
Ns sub 10
 62
3

Table 3.18 Clearance distance between rows

Month Jan. Feb. March April May June July Aug. Sep. Oct. Nov. Dec.
Best tilt angle (degree) 49.48 42.02 31.48 19.65 10.27 5.98 7.88 15.61 26.85 38.66 47.98 52.12
Distance, a (m) 6.322 6.238 5.940 5.368 4.751 4.425 4.572 5.119 5.745 6.166 6.314 6.326
Optimum Design of Rooftop Grid-Connected PV System
3.4 Applications and Results 63

Fig. 3.13 PV modules with

several stacked arrays

Assuming that the inverter is operating in the MPP voltage range, the operating
input voltage and current of the inverter can be calculated as follows as shown in
columns 4 and 6 in Table 3.19, respectively:

Vmpp sub ¼ Ns sub  Vmpp ¼ 10  49:53 ¼ 495:3 V

Impp sub ¼ Np sub  Impp ¼ 7  8:48 ¼ 59:36 A

It is noticed that the DC output current of subsystem (59.36 A) is higher than the
maximum DC input of the inverter (32 A) which makes ST25000TL inverter not
suitable for this application as revealed in Tables 3.19 and 3.20.
Detailed calculations of subsystems with ST25000TL inverter which is not
suitable for the proposed rooftop grid-connected PV systems are shown in

Table 3.19 Subsystems with ST25000TL inverter and Heliene 96 M 420 PV module
Case Ns sub Np sub Nsub Vsub (V) Voltage Isub Current Optimal
condition (A) Condition
1 10 7 70 495.30 Satisfied 59.36 Not There is no optimal
Satisfied configuration
2 11 6 66 544.83 Satisfied 50.88 Not
Satisfied
3 12 6 72 594.36 Satisfied 50.88 Not
Satisfied
4 13 5 65 643.89 Satisfied 42.40 Not
Satisfied
5 14 5 70 693.42 Satisfied 42.40 Not
Satisfied
6 15 5 75 742.95 Satisfied 42.40 Not
Satisfied
7 16 4 64 792.48 Satisfied 33.92 Not
Satisfied
8 17 4 68 842.01 Not 33.92 Not
Satisfied Satisfied
64 3 Optimum Design of Rooftop Grid-Connected PV System

Table 3.20, where the case in column 2 from Table 3.20 refers to the number of
probable system configurations with each module type.

3.4.3 Economic Study Calculations

Using data from Tables 3.5, 3.11, and 3.12 and results from Tables 3.13 and 3.16,
economic calculation of PV system can be done. Solar PV array is the most
expensive component in the proposed system where system cost is determined
primarily by the cost of PV modules as shown in Fig. 3.14. Thus, most of the
research activities performed in this area are concerned with manufacturing
low-cost solar cells with acceptable efficiencies. In the proposed approach, batteries
are not considered, so the capital cost is reasonable. Detailed calculations for each
system are given in Table 3.21.
According to methodology for COE shown in item 3.3.5.1., the COE can be
calculated as follows:
1. Total cost of PV modules can be calculated as follows:
 
$
CPV ¼ PV module cost  NPV ðmodulesÞ ¼ 420  270 ¼ $113; 400
module

Table 3.20 ST25000TL inverter under different PV modules

Module type Case Ns sub Np sub Nsub Vsub Isub Condition
(V) (A)
Mitsubishi Start (1) 19 8 152 469.30 61.68 Not
PV-UD190MF5 Satisfied
End 33 5 165 815.10 38.55 Not
(15) Satisfied
Suntech STP270S-24/Vb Start (1) 13 8 104 455.00 61.68 Not
Satisfied
End 23 5 115 805.00 38.55 Not
(11) Satisfied
ET-P672305WB/WW Start (1) 13 7 91 483.34 57.47 Not
Satisfied
End 22 4 88 817.96 32.84 Not
(10) Satisfied
1Sol Tech Start (1) 11 7 77 473.00 56.91 Not
1STH-350-WH Satisfied
End (9) 19 4 76 817.00 32.52 Not
Satisfied
Heliene 96M 420 Start (1) 10 7 70 495.30 59.36 Not
Satisfied
End (8) 17 4 68 842.01 33.92 Not
Satisfied
3.4 Applications and Results 65

350000
Grid interconnect
300000 PV racks
Wiring
250000 Labour

Cost, US $
Inverters
200000 PV modules

150000

100000

50000

PV module type

Fig. 3.14 Cost analysis for GCI-10 k-LV inverter under different types of PV modules

2. Total cost of inverters can be calculated as follows which depends on the

number of subsystems:
 
$
Cinverter ¼ inverter cost  No: of subsystems ¼ 1500  10 ¼ $15000
unit

3. The miscellaneous cost which include labor cost, installation materials cost,
mounting hardware cost, and grid interconnection cost:
3-a Labor cost can be estimated as
   
$ hr
Clabor ¼ installation labor cost   NPV ðmodulesÞ
hr module
¼ 16:66  0:43  270 ¼ $1934:226

3-b Wiring cost can be estimated as

 
$
Cw ¼ installation materials  NPV ðmodulesÞ ¼ 3:6  270 ¼ $972
module

3-c PV racks cost can be estimated as

 
$
Cracks ¼ mounting structure  Pinverter  No:of subsystems
Wp
¼ 0:08  10200  10 ¼ $8160

3-d grid interconnection cost which assumed to be $2000 as in Ref. [87].

Table 3.21 Detailed economic calculations for each system
66

Inverter Cost ($) Module

Mitsubishi Suntech ET-P672305WB/WW 1Sol Tech Solar panel
PV-UD190MF5 STP270S-24/Vb 1STH-350-WH Heliene 96 M
420
GCI-10 k-LV PV cost Assume Grid 183,600 293,670 109,800 157,500 113400
Inverters interconnection 15,000 15,000 15,000 15,000 15000
cost cost = 2000 $ [87]
Labor 3868.452 2793.882 2578.968 2149.14 1934.226
cost
Wiring 1944 1404 1296 1080 972
3

cost
PV rack 8160 8160 8160 8160 8160
cost
Capital 214572.452 323027.882 138834.968 185889.14 141466.226
cost
Sunny PV cost 183,600 286,140 103,700 157,500 107,100
Tripower Inverters 19,350 19,350 19,350 19,350 19,350
20000TL cost
Labor 3868.452 2722.244 2435.692 2149.14 1826.769
cost
Wiring 1944 1368 1224 1080 918
cost
PV rack 8180 8180 8180 8180 8180
cost
Capital 218942.452 319760.244 136889.692 190259.14 139374.769
cost
HS50K3 PV cost 197,200 307,224 111,020 168,000 110,880
(continued)
Optimum Design of Rooftop Grid-Connected PV System
Table 3.21 (continued)
Inverter Cost ($) Module
Mitsubishi Suntech ET-P672305WB/WW 1Sol Tech Solar panel
PV-UD190MF5 STP270S-24/Vb 1STH-350-WH Heliene 96 M
420
Inverters 16,120 16,120 16,120 16,120 16,120
cost
Labor 4155.004 2922.8304 2607.6232 2292.416 1891.2432
cost
3.4 Applications and Results

Wiring 2088 1468.8 1310.4 1152 950.4

cost
PV rack 8800 8800 8800 8800 8800
cost
Capital 230363.004 338535.6304 141858.0232 198364.416 140641.6432
cost
HS100K3 PV cost 197,200 307,224 110,105 165,375 110,880
Inverters 14,500 14,500 14,500 14,500 14,500
cost
Labor 4155.004 2922.8304 2586.1318 2256.597 1891.2432
cost
Wiring 2088 1468.8 1299.6 1134 950.4
cost
PV rack 8800 8800 8800 8800 8800
cost
Capital 228743.004 336915.6304 139290.7318 194065.597 139021.6432
cost
67
68 3 Optimum Design of Rooftop Grid-Connected PV System

According to Eq. (3.28), the miscellaneous cost can be estimated as follows:

Cm ¼ Clabor þ Cwiring þ Cracks þ Cgrid

¼ $1934:226 þ $972 þ $8160 þ $2000 ¼ $13066:226

According to Eq. (3.27), the capital investment cost can be determined as

follows:

Ccap ¼ CPV þ Cinverter þ Cm ¼ $113400 þ $15000 þ $13066:226 ¼ $141466:226

3.4.3.1 Estimating AEP, Cash Flows, and COE

For each combination of input system device types, the yearly PV system energy
production and the corresponding cash inflows resulting from the generated electric
energy purchased to the UG are calculated by simulating the system operation for
the lifetime period. According to the Egyptian legalization, the selling price of
energy produced by the PV system has been set to P = 84.0 piaster/kWh (12.53
cent/kWh) for systems with installed peak power up to 100 kW. Figure 3.15 shows
generated power for each PV module. From this figure, the monthly generated
power can be calculated. AEP and corresponding cash inflows resulting from
electric energy purchased to the UG for each configuration of PV system are shown
in Table 3.22. It can be concluded that the optimal system configuration consists of
PV module (Heliene 96 M 420) and inverter (GCI-10 k-LV) based on minimum
cost of kWh generated which is equal to 0.5466 $/kWh. The monthly generated
power for selected system is shown in Fig. 3.16. The COE can be determined from
Eq. (3.30) as follows:

450
400
Generated Power, Watt

350
300
250
200
150
100
50
0
0 50 100 150 200 250
Time, Hour
420 W module 350 W module 305 W module 270 W module 190 W module

Fig. 3.15 Generated power for each PV module over the year
Table 3.22 AEP, selling price, and COE
Parameter Inverter Module
Mitsubishi Suntech ET-P672305WB/WW 1Sol Tech Solar panel Heliene
PV-UD190MF5 STP270S-24/Vb 1STH-350-WH 96 M 420
AEP GCI-10 k-LV 228.8893 234.6086 206.5385 238.2875 258.8006
3.4 Applications and Results

(MWh/year.)
Sunny Tripower 228.8893 228.5928 195.0641 238.2875 244.4227
20000TL
HS50K3 245.8443 245.4365 208.8333 254.1732 253.0494
HS100K3 245.8443 245.4365 207.1121 250.2018 253.0494
Selling price GCI-10 k-LV 27466.71 28153.03 24784.62 28594.50 31056.07
($/year)
Sunny Tripower 27466.71 27431.13 23407.69 28594.50 29330.72
20000TL
HS50K3 29501.31 29452.38 25059.99 30500.78 30365.92
HS100K3 29501.31 29452.38 24853.45 30024.12 30365.92
COE ($/kWh) GCI-10 k-LV 0.9374 1.3768 0.6721 0.7801 0.5466
Sunny Tripower 0.9565 1.3988 0.7017 0.7984 0.5702
20000TL
HS50K3 0.9370 1.3793 0.6792 0.7804 0.5557
HS100K3 0.9304 1.3727 0.6725 0.7756 0.5493
69
70 3 Optimum Design of Rooftop Grid-Connected PV System

30
25
20

MWh
15
10
5
0

Month

Fig. 3.16 Monthly generated PV power for the proposed system

Ccap þ Cmain $141466:226 þ $425:6

COE ¼  ¼ ¼ 0:5466 $=kWh
AEP kWhyear
258800:6

3.4.3.2 SPBT Estimation

SPBT for the rooftop grid-connected PV system can be calculated according to

Eq. (3.30):

Ccap
SPBT ¼
AEP  Ccap  i  Cmain
141466:226
¼ ¼ 6:958 years
258:8006  10  0:1253  141466:226  0:0825  425:6
3

The cost of proposed rooftop grid-connected PV system can be recouped in

6.958 years, where systems with larger PV output always achieve a shorter payback
period due to the lower cost.

3.4.4 GHG Emissions Reduction

The emission factor, FE is set to be 0.699 kg CO2-eq/kWh [91]. Annual GHG

reduction income for a rooftop PV system is calculated using prices for tCO2
reduction credits. Prices for CO2 reduction credits differ based on many factors such
as how the credit is generated and how it will be delivered. The model estimates
that the PV system will reduce GHG emissions by 180.9016 tons of CO2-eq
3.4 Applications and Results 71

annually. Approximately 4522.54 tons of CO2 emissions will be avoided as the

rooftop grid-connected PV system replaces the need of some electricity from the
existing power grid. At an assumed emission cost factor of about US$30/ton CO2 as
in Ref. [91], the emissions of 0.699 kg CO2/kWh give a CO2-revenue of 2.097
cent/kWh (14.68 piaster/kWh). Annual CO2 emission reduction can be estimated as
follows:

CO2ðemissionÞ ¼ FE  AEP
 
kgCO2eq
¼ 0:699  258:8006  103 ðkWhÞ ¼ 180:9016 t CO2eq =year
kWh

CO2 emission reduction during the lifetime of the project

CO2ðemissionÞ ¼ FE  AEP  N
 
kgCO2eq
¼ 0:699  258:8006  103 ðkWhÞ  25ðyearsÞ
kWh
¼ 4522:54tCO2eq
Estimating PV System
Size and Cost
SECO FACT SHEET NO. 24

yp pp
Appliance
Appliance AC
AC or
or Hours
Hours Watt-
Watt
HIGHLIGHTS DC
DC
Watts
Used/
Used/
Day
hours/
Hours/
Day
Watts Day Day
◆ Off-grid photovoltaic (PV)
Ceiling Fan 100 x 8.0 = 800
systems can be affordable.
Coffee Maker 600 x 0.3 = 180
◆ Estimating the size and cost Clothes Dryer 4,856 x 0.8 = 3,885
of a PV system to meet your Computer 75 x 2.0 = 150
needs is easy. Computer Monitor 150 x 2.0 = 300
Dishwasher 1,200 x 0.5 = 600
Lights, 4 Compact Fluorescents 4x15 x 5.0 = 300
INTRODUCTION Microwave Oven 1,300 x 0.5 = 650
Photovoltaic (PV) energy generating sys- Radio 80 x 4.0 = 320
tems (or PV systems) convert the sun’s Refrigerator 600 x 9.0 = 5,400
energy directly into electricity using Television 300 x 8.0 = 2,400
state-of-the-art semiconductor materials. Vacuum Cleaner 600 x 0.2 = 120
VCR 25 x 8.0 = 200
PV systems vary in complexity. Some are
Washing Machine 375 x 0.5 = 188
called “stand-alone” or “off-grid” sys-
Total 15,493
tems, which means they are the sole
source of power to a home, water pump Table 1 Typical household electrical appliances and run times
or other load. Stand-alone systems can
be designed to run with or without bat- PV system exceeds the customer’s loads, PV system ultimately depends on the
tery backup. Remote water pumps are excess energy is exported to the utility, PV array size, the battery bank size, and
often designed to run without battery turning the customer’s electric meter on the other components required for
backup, since water pumped out of the backward. Conversely, the customer can the specific application.
ground during daylight hours can be draw needed power from the utility
stored in a holding tank for use any when energy from the PV system is This fact sheet is designed to generate
time. In contrast, stand-alone home insufficient to power the building’s an estimate for the PV array size, bat-
power systems often store energy gener- loads. Under this arrangement, the cus- tery bank size, and total cost of a stand-
ated during the day in a battery bank for tomer’s monthly electric utility bill alone PV system. (It can be used for
use at night. Stand-alone systems are reflects only the net amount of energy grid-connected systems, too, but with
often cost-effective when compared to received from the electric utility. several caveats that are identified in the
alternatives such as utility line extensions. step-by-step instructions.) This will
Each type of system requires specific help you converse knowledgably with a
Other PV systems are called “grid-con- components besides the PV modules. professional PV designer or installer
nected” systems. These work to supple- Generating AC power requires a device should you decide to purchase a system.
ment existing electric service from a called an inverter. Battery storage To obtain a more complete system
utility company. When the amount of requires special batteries and a battery design that takes into consideration
energy generated by a grid-connected charge controller. The final cost of any your particular power needs, site loca-

SECO FACT SHEET NO. 24 ESTIMATING PV SYSTEM SIZE AND COST P.1
 Of course, for grid-connected systems,
you can simply review your monthly
utility bills to get an accurate idea of
monthly energy consumption.

RENEWABLE ENERGY
THE INFINITE POWER
1.b. Determine Available Sunlight.
OF TEXAS 5.0 The amount of useful sunshine avail-
4.4 3.3 able for the panels on an average day
during the worst month of the year is
3.9 called the “insolation value.” (We use
the worst month for analysis to ensure
tion, local weather conditions, and spe- the system will operate year-round.) In
cific equipment used, it is suggested most of Texas, average solar insolation
that you work with a qualified PV values range from about 3.3 to 5.0
designer or installer. hours per day in December, with the
Figure 1 Solar Insolation Map for lowest values in east Texas and the
Texas This shows the average number of
ESTIMATING PV SYSTEM highest values in the Panhandle and far
hours of useful sunlight available in
SIZE AND COST December for a PV module at latitude tilt. west Texas (see Figure 1). The insola-
The worksheet presented here will help tion value also can be interpreted as the
you estimate the size and cost of a PV kilowatt-hours per day of sunlight
system. The worksheet is adapted from energy that fall on each square meter of
a method developed by Sandia National and voltage only; to obtain watts, just solar panels at latitude tilt.
Laboratories, and the analysis is con- multiply amps by the voltage). Then
ducted in two sections. In the first sec- multiply by the number of hours it is 1.c. Determine PV Array Size. For a
tion, we derive the system specifications expected to operate on an average day PV system powering loads that will be
by determining the load, available sun- to obtain watt-hours (Wh). used every day, the size of the array is
light, and the size of the PV array and determined by the daily energy require-
battery bank needed. In the second sec- For more complex loads, such as power- ment (1.a.) divided by the sun-hours
tion, we convert the system specifica- ing a whole house, you will need to per day (1.b.). For systems designed for
tion into a cost for the PV system. Let’s estimate all the different loads in the non-continuous use (such as weekend
walk through the analysis, step by step. house on a typical day and sum them. cabins), multiply the result by the days
Table 1 provides an example calculation per week the loads will be active divid-
STEP 1. DETERMINE LOAD, for a household using this method. ed by the total number of days in the
AVAILABLE SUNLIGHT, PV ARRAY week. For example, for a weekend
SIZE, AND BATTERY BANK SIZE For complex loads like households, it is cabin, multiply by 2/7. Generally, grid-
1.a. Determine Load. The preferred sometimes difficult to anticipate every connected systems are designed to pro-
method for determining PV system electric load. Electric clocks, TVs, stere- vide from 10 to 60% of the energy
loads is a “bottom-up” approach in os and other appliances sometimes draw needs with the difference being sup-
which every daily load is anticipated small amounts of power even when they plied by utility power.
and summed to yield an average daily are turned off. For this reason, we rec-
total. For PV systems designed to power ommend multiplying your estimated 1.d. Determine Battery Bank Size.
simple loads, such as a single water daily load by a “fudge factor” of 1.5. Most batteries will last longer if they are
pump, electric light or other appliance, Some other elements accounted for by shallow cycled–discharged only by
this method is easy. Simply look at the this factor are all the system efficiencies, about 20% of their capacity–rather
nameplate power rating on the appli- including wiring and interconnection than being deep-cycled daily. A conserv-
ance to calculate its power consumption losses, as well as the efficiency of the ative design will save the deep cycling
in watts (some labels show amperage battery charging and discharging cycles. for occasional duty, and the daily dis-

SECO FACT SHEET NO. 24 ESTIMATING PV SYSTEM SIZE AND COST P.2
 The average Texas household uses can buy in bulk. When purchasing mod- systems the inverter should be sized to
approx. 1,100 kilowatt-hours (kWh) of ules, look for a UL listing (which certi- provide 125% of the maximum loads
electricity per month, or about 36,000 fies that the modules meet electrical safe- you wish to run simultaneously at any
Wh of electricity per day. In contrast, a ty standards) and long-term warranties. one moment. For example, if the total
Some manufacturers offer modules with loads you wish to run will be 1,600
home designed to be energy efficient
10-20 year warranties. watts (a dishwasher, television and ceil-
can use as little as 6,000-10,000 Wh
ing fan from Table 1) choose an invert-
per day. As you might guess, a PV
2.b. Estimate Battery Bank Cost (if er with a rated continuous power out-
system designed to power an energy put of 2,000 watts. For grid-connected
needed). Many flooded lead acid batter-
efficient home will cost much less. ies designed for use with PV systems systems the maximum continuous input
can be purchased at retail for under $1 rating of the inverter should be about
per amp-hour. 10% higher than the PV array size to
charge should be about 20% of capaci- allow for safe and efficient operation.
ty. This implies that the capacity of the 2.c. Estimate Inverter Cost (if needed). The input rating of the inverter should
battery bank should be about five times An inverter will be needed for systems never be lower than the PV array rating.
the daily load. It also suggests that your that output AC power. For stand-alone For more information contact an
system will be able to provide power
continuously for five days without
recharging (such as during a winter WORKSHEET – ESTIMATING THE COST OF PHOTOVOLTAIC SYSTEMS

storm). Multiply the daily load (1.a.) by Step 1. Determine the load, available sunlight, array size, battery bank size:
5, and then divide the result by the a. Determine the energy load required in watt-hours (Wh) per day. Multiply the number of watts the load will
voltage of the battery bank you will use consume by the hours per day the load will operate (see Table 1). Multiply your result by 1.5.
(typically 12 volts). The result is the
Total Wh per day required: _______Wh
recommended amp-hour rating of the
b. Determine the hours per day of available sunlight at the site (see Figure 1).
battery bank. If you wish to be more
secure and design for more days of Total available sunlight: ______ hrs/day
cloudy weather multiply by a number c. Determine the PV array size needed. Divide the energy needed (1.a.) by the number of available sun hours per
greater than 5. However, it is generally day (1.b.). Total array size required: ______ Watts
not recommended to design for more d. Determine the size of the battery bank (if one is desired). Multiply the load (1.a.) by 5 (result is watt-hours, Wh).
than 12 days of cloudy weather unless it Then divide by the battery voltage (for example, 12 volts) to get the amp-hour (Ah) rating of the battery bank.
is a highly critical load. Of course, you
Total Battery Bank Required: ______ Ah
can skip this step entirely if your system
does not incorporate a battery bank, Step 2. Calculate the cost of the PV system needed for this application:
such as a water pump, or is grid-con- a. Multiply the size of the array (1.c.) by $5 per watt.
nected since the availability of grid
Cost estimate for PV array: $ _________
power obviates the need for storage.
b. If a battery bank is used, multiply the size of the battery bank (1.d.) by $1 per amp hour.
STEP 2. CALCULATE PV SYSTEM Cost estimate for battery bank: $ _________
COSTS c. If an inverter is used, multiply the size of the array (1.c.) by $1 per rated watt.
2.a. Estimate PV Array Cost. Many PV Cost estimate for Inverter: $ _________
modules can be purchased at retail for Subtotal: $ _________
about $5 per watt for most small systems d. Multiply the subtotal above by 0.2 (20%) to cover balance of system costs (wire, fuses, switches, etc.).
in the 150 – 8,000 watt range. Of
Cost Estimate for Balance of System: $ _________
course, there are opportunities to pur-
Total Estimated PV System Cost: $ _________
chase modules for a lower price, especial-
ly when your system is larger and you

SECO FACT SHEET NO. 24 ESTIMATING PV SYSTEM SIZE AND COST P.3
 F i n a n c i a l A ck n ow l e d g e m e n t This publication was developed as part of the Renewable Energy

InfinitePower.org Demonstration Program and was funded 100% with oil overcharge funds from the Exxon settlement as provided
by the Texas State Energy Conservation Office and the U.S. Department of Energy. Mention of trade names or
commercial products does not constitute endorsement or recommendation for use.

inverter supplier. Inverters designed for Other alternatives include on-site diesel RESOURCES
residences and other small systems can generators, hybrid wind-solar systems, FREE TEXAS RENEWABLE ENERGY
be purchased at retail for about $1 per or simply making energy improvements INFORMATION
rated watt. such as installing energy-efficient appli- For more information on how you can put
ances, improving insulation and sealing Texas’ abundant renewable energy resources
to use in your home or business, visit our
2.d. Estimate Balance of System Cost. ducts. Each alternative comes with its
website at www.InifinitePower.org or call
Besides PV modules and batteries, com- own benefits and drawbacks, many of us at 1-800-531-5441 ext 31796. Ask about
plete PV systems also use wire, switches, which are difficult to quantify. For our free lesson plans and videos available to
fuses, connectors and other miscella- example, the cost of purchasing and teachers and home schoolers.
neous parts. We use a factor of 20% to delivering diesel fuel to a remote genera-
cover balance of system costs. tor should be considered in an econom- ON THE WORLD WIDE WEB:
ic analysis of alternatives, as well as the
COMPARE TO noise and exhaust generated as byprod- Center for Renewable Energy and
ALTERNATIVES ucts of the energy production. Sustainable Technology (CREST)
A final step in an economic feasibility www.solstice.crest.org
study is to compare estimated costs of STICKER SHOCK? THE
the PV system to other alternatives. The IMPORTANCE OF NREL’S National Center for
most common alternative to off-grid PV EFFICIENCY
Photovoltaics
is a line extension from an electric utili- If you’ve just completed the worksheet
www.nrel.gov/ncpv
ty company. Utilities in Texas typically to estimate the cost of a PV system for
charge anywhere from $5,000 to your home, chances are the price may
$30,000 per mile for line extensions, so seem a bit high. This is why most peo- Florida Solar Energy Center
for many small- or medium-sized loads ple who use PV to power their homes www.fsec.ucf.edu
in remote locations PV systems are the design them to be energy efficient. This
economically feasible choice. For this means they build their homes with Department of Energy Solar Site
reason, several rural electric cooperatives excellent insulation, take advantage of
www.eren.doe.gov/RE/solar.html
in the state now offer their customers energy efficient designs, and pay atten-
PV systems in lieu of more costly line tion to important factors such as site
extensions. Line extensions also may be selection, shading, and orientation. Sandia Laboratory photovoltaics with
prohibitively expensive even when the With some careful planning, it is possi- load calculation worksheets
distance traveled is short, such as in ble to reduce a home’s electrical loads by www.sandia.gov/pv
urban areas where pavement cuts are 50 to 80 percent without sacrificing
required. comfort and convenience.

STATE ENERGY CONSERVATION OFFICE

111 EAST 17TH STREET, ROOM 1114
AUSTIN, TEXAS 78774

PH. 800.531.5441 ext 31796

www.InfinitePower.org
RENEWABLE ENERGY
THE INFINITE POWER
OF TEXAS

SECO FACT SHEET NO. 24 ESTIMATING PV SYSTEM SIZE AND COST P.4