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TRAINING REPORT ON

QUALITY ASSURANCE AND

DESIGNING OF SOLAR

PHOTOVOLTAIC SYSTEMS

Submitted by:

JATIN

B-TECH (3RD YEAR)

ELECTRONICS AND

COMMUNICATION

ENGINEERING (ECE)

DELHI TECHNOLOGICAL

UNIVERSITY (DTU)

FORMERLY DELHI

COLLEGE OF

ENGINEERING

1

ABSTRACT

This training report is an extract of lessons learned during training at Solar Lighting Lab, The Energy and

Resources Institute [TERI]. The report aims at explaining the basics and details of the engineering

involved in Solar Photovoltaic Systems.

The training report describes the work flow that is followed to get the project and within the

departments to complete the job. It highlights the main components of the Solar Lighting Lab including

the IV characteristic Test, Battery Test and Designing of Solar Photovoltaic Systems.

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Acknowledgement

I would like to thank The Energy and Resources Institute (TERI) for giving me this opportunity for

undergoing this Internship programme.

I place on record and warmly acknowledge the continuous encouragement, invaluable supervision, timely

suggestions and inspired guidance offered by Mr. Richie Brian Stephen, Research Associate, Center for

Distributed Generation (CDG), TERI, in bringing this project report to a successful completion.

I wish to express my deep sense of gratitude and respects to Mr. Arvind Sharma, Research Fellow,

CDG, TERI, for stimulating discussions and constant encouragement during the course.

JATIN

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Contents INTRODUCTION ....................................................................................................................................... 6

Solar Energy ............................................................................................................................................ 6

The Sun .................................................................................................................................................... 7

Solar Radiation in Space ........................................................................................................................ 8

Solar Radiation Outside the Earth's Atmosphere................................................................................ 9

Solar Radiation at the Earth's Surface ............................................................................................... 10

Atmospheric Effects .............................................................................................................................. 10

Absorption in the Atmosphere ............................................................................................................. 11

Direct and Diffuse Radiation Due to Scattering of Incident Light ................................................... 11

Effect of clouds and other local variations in the atmosphere .......................................................... 12

Air Mass ................................................................................................................................................. 12

Comparision Of Different PV Technologies ....................................................................................... 12

Crystalline silicon PV........................................................................................................................ 13

Thin-film PV ...................................................................................................................................... 13

Performance parameters of solar PV module .................................................................................... 15

Outdoor photovoltaic module I-V characteristics test ........................................................................... 17

Background ........................................................................................................................................... 17

I-V Characteristics of solar PV module .............................................................................................. 17

Test outcomes ........................................................................................................................................ 19

Procedure ............................................................................................................................................... 20

Equipment requirements .................................................................................................................. 20

Test prerequisites .............................................................................................................................. 20

Apparatus .......................................................................................................................................... 20

Procedure ........................................................................................................................................... 21

Back-mounted thermocouple ........................................................................................................... 21

Generating an I-V Curve ...................................................................................................................... 21

Outdoor I-V Curve Tester .................................................................................................................... 22

Calculations ........................................................................................................................................... 23

Battery Test ............................................................................................................................................... 25

Background ........................................................................................................................................... 25

Purpose of the test and outputs ............................................................................................................ 25

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Battery chemistries ............................................................................................................................... 25

Battery Chemistry Comparison ........................................................................................................... 26

C-Rate Terminology ............................................................................................................................. 26

Battery Capacity Effected by C-Rate and Temperature ................................................................... 27

Recommended Battery Testing Details ............................................................................................... 27

Test outcomes ........................................................................................................................................ 28

Procedure ............................................................................................................................................... 28

Sealed lead-acid battery test..................................................................................................... 28

Equipment requirements .......................................................................................................... 28

Test prerequisites ...................................................................................................................... 28

Procedure ................................................................................................................................... 28

Calculations ....................................................................................................................................... 29

Battery Testing Operations .................................................................................................................. 30

Measurement Of Temperature Coefficients ........................................................................................... 33

Purpose .................................................................................................................................................. 33

Apparatus .............................................................................................................................................. 33

Solar simulator ...................................................................................................................................... 33

Classification of Solar Simulators: .................................................................................................. 33

Types of lamps ................................................................................................................................... 34

Equipment Details: ........................................................................................................................... 34

Temperature Compensation: ........................................................................................................... 35

System description: ........................................................................................................................... 35

Effect of temperature ............................................................................................................................ 35

Effect of Irradiance ............................................................................................................................... 36

Procedure with a solar simulator ........................................................................................................ 37

Calculation of temperature coefficients .............................................................................................. 37

Test Outcomes ....................................................................................................................................... 38

Experimental Data ................................................................................................................................ 39

Designing of Solar PV System .................................................................................................................. 45

Basic Principles to Follow When Designing a Quality PV System ................................................... 45

Basic Steps to Follow When Installing a PV System .......................................................................... 45

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SYSTEM DESIGN CONSIDERATIONS .......................................................................................... 45

Grid-Interactive Only (No Battery Backup)................................................................................... 45

Grid-Interactive With Battery Backup ........................................................................................... 46

Designing using PVsyst (Photovoltaic Systems Software) ................................................................. 48

References .................................................................................................................................................. 52

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INTRODUCTION

Solar Energy

Solar energy in one form or another is the source of nearly all energy on the earth. Humans, like all other

animals and plants, rely on the sun for warmth and food. However, people also harness the sun's energy in

many other different ways. For example, fossil fuels, plant matter from a past geological age, is used for

transportation and electricity generation and is essentially just stored solar energy from millions of years

ago. Similarly, biomass converts the sun's energy into a fuel, which can then be used for heat, transport or

electricity. Wind energy, used for hundred of years to provide mechanical energy or for transportation,

uses air currents that are created by solar heated air and the rotation of the earth.

Today wind turbines convert wind power into electricity as well as its traditional uses. Even

hydroelectricity is derived from the sun. Hydropower depends on the evaporation of water by the sun, and

its subsequent return to the Earth as rain to provide water in dams. Photovoltaics (often abbreviated as

PV) is a simple and elegant method of harnessing the sun's energy. PV devices (solar cells) are unique in

that they directly convert the incident solar radiation into electricity, with no noise, pollution or moving

parts, making them robust, reliable and long lasting. Solar cells are based on the same principles and

materials behind the communications and computer revolutions.

Figure 1: Solar powered light house

Photovoltaics is the process of converting sunlight directly into electricity using solar cells. Today it is a

rapidly growing and increasingly important renewable alternative to conventional fossil fuel electricity

generation, but compared to other electricity generating technologies, it is a relative newcomer, with the

first practical photovoltaic devices demonstrated in the 1950s. Research and development of

photovoltaics received its first major boost from the space industry in the 1960s which required a power

supply separate from "grid" power for satellite applications. These space solar cells were several thousand

times more expensive than they are today and the perceived need for an electricity generation method

apart from grid power was still a decade away, but solar cells became an interesting scientific variation to

the rapidly expanding silicon transistor development with several potentially specialized niche markets. It

took the oil crisis in the 1970s to focus world attention on the desirability of alternate energy sources for

terrestrial use, which in turn promoted the investigation of photovoltaics as a means of generating

terrestrial power. Although the oil crisis proved short-lived and the financial incentive to develop solar

cells abated, solar cells had entered the arena as a power generating technology. Their application and

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advantage to the "remote" power supply area was quickly recognized and prompted the development of

terrestrial photovoltaics industry. Small scale transportable applications (such as calculators and watches)

were utilized and remote power applications began to benefit from photovoltaics.

In the 1980s research into silicon solar cells paid off and solar cells began to increase their efficiency. In

1985 silicon solar cells achieved the milestone of 20% efficiency. Over the next decade, the photovoltaic

industry experienced steady growth rates of between 15% and 20%, largely promoted by the remote

power supply market. The year 1997 saw a growth rate of 38% and today solar cells are recognized not

only as a means for providing power and increased quality of life to those who do not have grid access,

but they are also a means of significantly diminishing the impact of environmental damage caused by

conventional electricity generation in advanced industrial countries.

The increasing market for, and profile of photovoltaics means that more applications than ever before are

"photovoltaically powered". These applications range from power stations of several megawatts to the

ubiquitous solar calculators.

The Sun The sun is a hot sphere of gas whose internal temperatures reach over 20 million degrees kelvin due to

nuclear fusion reactions at the sun's core which convert hydrogen to helium. The radiation from the inner

core is not visible since it is strongly absorbed by a layer of hydrogen atoms closer to the sun's surface.

Heat is transferred through this layer by convection[1].

The surface of the sun, called the photosphere, is at a temperature of about 6000K and closely

approximates a blackbody. For simplicity, the 6000 K spectrum is commonly used in detailed balance

calculations but temperatures of 5762 ± 50 K Backus1976 and 5730 ± 90 KParrott1993 have also been

proposed as a more accurate fit to the sun's spectrum.

Figure 2: Structure Of Sun

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The total power emitted by the sun is calculated by multiplying the emitted power density by the surface

area of the sun which gives 9.5 x 1025 W.

The total power emitted from the sun is composed not of a single wavelength, but is composed of many

wavelengths and therefore appears white or yellow to the human eye. These different wavelengths can be

seen by passing light through a prism, or water droplets in the case of a rainbow. Different wavelengths

show up as different colours, but not all the wavelengths can be seen since some are "invisible" to the

human eye.

Solar Radiation in Space

Only a fraction of the total power emitted by the sun impinges on an object in space which is some

distance from the sun. The solar irradiance (H0 in W/m2) is the power density incident on an object due to

illumination from the sun. At the sun's surface, the power density is that of a blackbody at about 6000K

and the total power from the sun is this value multiplied by the sun's surface area. However, at some

distance from the sun, the total power from the sun is now spread out over a much larger surface area and

therefore the solar irradiance on an object in space decreases as the object moves further away from the

sun.

The solar irradiance on an object some distance D from the sun is found by dividing the total power

emitted from the sun by the surface area over which the sunlight falls. The total solar radiation emitted by

the sun is given by σT4 multiplied by the surface area of the sun (4πR2sun) where Rsun is the radius of the

sun. The surface area over which the power from the sun falls will be 4πD2. Where D is the distance of

the object from the sun. Therefore, the solar radiation intensity, H0 in (W/m2), incident on an object is:

where:

Hsun is the power density at the sun's surface (in W/m2) as determined by Stefan-Boltzmann's

blackbody equation;

Rsun is the radius of the sun in meters as shown in the figure below; and

D is the distance from the sun in meters as shown in the figure below.

Figure 3: At a distance, D, from the sun the same amount of power is spread over a much wider area so

the solar radiation power intensity is reduced.

The table below gives standardised values for the radiation at each of the planets but by entering the

distance you can obtain an approximation.

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Table 1: Mean Solar Irradiance of different planets of Solar system

Planet Distance (x 109 m) Mean Solar Irradiance (W/m2)

Mercury 57 9116.4

Venus 108 2611.0

Earth 150 1366.1

Mars 227 588.6

Jupiter 778 50.5

Saturn 1426 15.04

Uranus 2868 3.72

Neptune 4497 1.51

Pluto 5806 0.878

Solar Radiation Outside the Earth's Atmosphere

The solar radiation outside the earth's atmosphere is calculated using the radiant power density (Hsun) at

the sun's surface (5.961 x 107 W/m2), the radius of the sun (Rsun), and the distance between the earth and

the sun. The calculated solar irradiance at the Earth's atmosphere is about 1.36 kW/m2. The geometrical

constants used in the calculation of the solar irradiance incident on the Earth are shown in the figure

below.

Figure 4: Geometrical constants for finding the Earth's solar irradiance. The diameter of the Earth is not

needed but is included for the sake of completeness.

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The actual power density varies slightly since the Earth-Sun distance changes as the Earth moves in its

elliptical orbit around the sun, and because the sun's emitted power is not constant. The power variation

due to the elliptical orbit is about 3.4%, with the largest solar irradiance in January and the smallest solar

irradiance in July. An equation[2] which describes the variation through out the year just outside the

earth's atmosphere is:

where:

H is the radiant power density outside the Earth's atmosphere (in W/m2);

Hconstant is the value of the solar constant, 1.353 kW/m2; and

n is the day of the year.

These variations are typically small and for photovoltaic applications the solar irradiance can be

considered constant. The value of the solar constant and its spectrum have been defined as a standard

value called air mass zero (AM0) and takes a value of 1.353 kW/m2.

Solar Radiation at the Earth's Surface

While the solar radiation incident on the Earth's atmosphere is relatively constant, the radiation at the

Earth's surface varies widely due to:

atmospheric effects, including absorption and scattering;

local variations in the atmosphere, such as water vapour, clouds, and pollution;

latitude of the location; and

the season of the year and the time of day.

The above effects have several impacts on the solar radiation received at the Earth's surface. These

changes include variations in the overall power received, the spectral content of the light and the angle

from which light is incident on a surface. In addition, a key change is that the variability of the solar

radiation at a particular location increases dramatically. The variability is due to both local effects such as

clouds and seasonal variations, as well as other effects such as the length of the day at a particular

latitude. Desert regions tend to have lower variations due to local atmospheric phenomena such as clouds.

Equatorial regions have low variability between seasons.

The amount of energy reaching the surface of the Earth every hour is greater than the amount of energy

used by the Earth's population over an entire year.

Atmospheric Effects

Atmospheric effects have several impacts on the solar radiation at the Earth's surface. The major effects

for photovoltaic applications are:

a reduction in the power of the solar radiation due to absorption, scattering and reflection in the

atmosphere;

a change in the spectral content of the solar radiation due to greater absorption or scattering of

some wavelengths;

the introduction of a diffuse or indirect component into the solar radiation; and

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local variations in the atmosphere (such as water vapor, clouds and

pollution) which have additional effects on the incident power,

spectrum and directionality.

These effects are summarized in the figure.

Figure 5: Typical clear sky absorption and scattering of incident sunlight [3]

Absorption in the Atmosphere

As solar radiation passes through the atmosphere, gasses, dust and aerosols absorb

the incident photons. Specific gasses, notably ozone (O3), carbon dioxide (CO2), and

water vapor (H2O), have very high absorption of photons that have energies close to

the bond energies of these atmospheric gases. This absorption yields deep troughs in

the spectral radiation curve. For example, much of the far infrared light above 2 µm is

absorbed by water vapor and carbon dioxide. Similarly, most of the ultraviolet light

below 0.3 µm is absorbed by ozone (but not enough to completely prevent sunburn!).

While the absorption by specific gasses in the atmosphere change the spectral content of the terrestrial

solar radiation, they have a relatively minor impact on the overall power. Instead, the major factor

reducing the power from solar radiation is the absorption and scattering of light due to air molecules and

dust. This absorption process does not produce the deep troughs in the spectral irradiance, but rather

causes a power reduction dependent on the path length through the atmosphere. When the sun is

overhead, the absorption due to these atmospheric elements causes a relatively uniform reduction across

the visible spectrum, so the incident light appears white. However, for longer path lengths, higher energy

(lower wavelength) light is more effectively absorbed and scattered. Hence in the morning and evening

the sun appears much redder and has a lower intensity than in the middle of the day.

Direct and Diffuse Radiation Due to Scattering of Incident Light

Light is absorbed as it passes through the atmosphere and at the same time it is subject to scattering. One

of the mechanisms for light scattering in the atmosphere is known as Rayleigh scattering which is caused

by molecules in the atmosphere. Rayleigh scattering is particularly effective for short wavelength light

(that is blue light) since it has a λ-4 dependence. In addition to Rayleigh scattering, aerosols and dust

particles contribute to the scattering of incident light known as Mie scattering.

Scattered light is undirected, and so it appears to be coming from any region of the sky. This light is

called "diffuse" light. Since diffuse light is primarily "blue" light, the light that comes from regions of the

sky other than where the sun is, appears blue. In the absence of scattering in the atmosphere, the sky

would appear black, and the sun would appear as a disk light source. On a clear day, about 10% of the

total incident solar radiation is diffuse.

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Effect of clouds and other local variations in the atmosphere The final effect of the atmosphere on incident solar radiation is due to local variations in the atmosphere.

Depending on the type of cloud cover, the incident power is severely reduced. An example of heavy cloud

cover is shown below.

Figure 6: [4]

Relative output current from a photovoltaic

array on a sunny and a cloudy winter's day in

Melbourne with an array tilt angle of 60°

Air Mass

The Air Mass is the path length which light takes through the atmosphere normalized to the shortest

possible path length (that is, when the sun is directly overhead). The Air Mass quantifies the reduction in

the power of light as it passes through the atmosphere and is absorbed by air and dust. The Air Mass is

defined as:

AM=1/cos(θ) where θ is the angle from the vertical (zenith angle). When

the sun is directly overhead, the Air Mass is 1.

Figure 7:

The air mass represents the proportion of

atmosphere that the light must pass through before

striking the Earth relative to its overhead path

length, and is equal to Y/X.

Comparision Of Different PV Technologies

There are a number of photovoltaic (PV) technologies available for converting sunlight into electrical

energy. For building applications, technologies that are commercially available are predominately silicon-

based and can be categorized as either crystalline silicon or thin film. Each has different operating

characteristics, conversion efficiencies and costs.

Conversion efficiency is an important PV characteristic commonly used to compare PV technologies.

Conversion efficiency provides a measure of how effectively a PV device converts sunlight into

electricity. Conversion efficiency is calculated as the ratio of the peak power produced by a PV device in

watts (W) to the power of the sunlight incident on that device in watts. Since the output of a PV device

depends on a number of variables such as the spectral distribution of the sunlight and cell temperature,

standard test conditions (STP) have been established for measuring PV conversion efficiency. PV

conversion efficiency is measured in a laboratory with the PV device at 25 C and using a light source with

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an intensity of 1,000 watts per meter at the PV device and a spectral distribution that corresponds to air

mass (AM) 1.5 global standard.

PV conversion efficiency is reported for both cells and panels. The conversion efficiency is greater for

cells because of the inherent losses that result from assembling a number of cells into a panel. Since PV

panels are installed on buildings, the conversion efficiency of panels should be considered when

comparing PV technologies and not individual cell conversion efficiency.

Crystalline silicon PV

Crystalline silicon is the most common type of PV cell used in building applications today. Crystalline

silicon has a conversion efficiency that ranges between 10 and 13 percent. In general, crystalline silicon

PV panels are usually opaque and have either a dark blue or black antireflective coating. Some

manufacturers will provide crystalline silicon PV panels in custom colors, but there is usually a

minimum-order size, loss of efficiency, and price premium for this option. Additionally, crystalline

silicon PV panels can be built with space between individual cells to allow light to pass through the panel

for skylight and similar applications.

Crystalline PV cells can be further categorized as either monocrystalline cells or polycrystalline cells.

The difference is in the manufacturing process. Monocrystalline silicon is grown from a silicon seed and

results in a uniform crystalline structure. Polycrystalline silicon is produced from pouring molten silicon

into a mold. As a result, polycrystalline silicon PV cells do not have a uniform crystal structure and their

conversion efficiency is typically less than monocrystalline PV cells. However, the cost per square foot to

manufacture polycrystalline silicon PV is less than monocrystalline silicon PV, which can offset the

difference in conversion efficiency.

Thin-film PV

Thin-film PV cells are manufactured by depositing layers of semiconducting materials a few micrometers

thick on a substrate such as glass or stainless steel. Thin-film PV cells are categorized based on the type

of semiconducting material used. Amorphous silicon is the most common material used to produce thin

film PV cells today. Amorphous silicon has no crystalline structure and has a PV panel conversion

efficiency of between 5 and 8 percent. This conversion efficiency under STP is significantly less than

crystalline silicon PV, but continuing research and development is improving thin-film PV conversion

efficiency. In addition, thin-film PV conversion efficiency is better than crystalline silicon PV in low or

diffuse light making it more efficient on cloudy days. Thin-film PV is also better in very hot desert

regions because its cell temperature remains lower than crystalline silicon PV.

Even without significant improvements in conversion efficiency, thin-film PV has a number of

advantages over crystalline silicon PV that make it preferable for a number of building applications. Thin-

film PV is significantly less expensive to manufacture. Its PV cells require between 1 and 5 percent of the

materials and energy required to manufacture crystalline silicon PV cells. More important, the

manufacture of thin-film PV is much more automated and efficient than crystalline silicon PV. As a

result, its lower conversion efficiency is offset by its lower cost per square foot.

Thin-film PV is also much better suited for building integrated PV (BIPV) applications. Thin-film PV can

be deposited on vision glass and appear as an architectural tint as well as on spandrel glass, effectively

turning the entire building curtain wall into a power generator. It can also be integrated with roofing

materials on commercial flat roofs or shingles on sloped residential roofs.

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Figure 8: Classification of Solar PV technologies

Figure 9: Space requirements of different PV modules

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Performance parameters of solar PV module

There are various factors affecting the performance of solar PV module:

1. Mismatch effect

Mismatch losses are caused by the interconnection of solar cells or modules which do not

have identical properties or which experience different conditions from one another.

Mismatch losses are a serious problem in PV modules and arrays under some conditions

because the output of the entire PV module under worst case conditions is determined by the

solar cell with the lowest output.

Mismatch in PV modules occurs when the electrical parameters of one solar cell are

significantly altered from those of the remaining devices. The impact and power loss due to

mismatch depend on

–the operating point of the PV module;

–the circuit configuration; and

–the parameter (or parameters) which are different from the remainder of the solar cells.

2. Shading effect

Figure 10: Types of Shading

3. Temperature effect Solar PV module are sensitive to temperature. Increases in temperature reduce the band gap of a semiconductor, thereby effecting most of the semiconductor material parameters. The parameter most affected by an increase in temperature is the open-circuit voltage. Figure 11: Effect of Temperature on PV module

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4. Irradiance effect

The light intensity incident on a solar PV module is directly proportional to the current.

Figure 12: Effect of Irradiance effect on PV module

5. Degradation and ageing

The performance of a PV module will decrease over time. The degradation rate is typically

higher in the first year upon initial exposure to light and then stabilizes.

Factors affecting the degree of degradation include the quality of materials used in

manufacture, the manufacturing process, the quality of assembly and packaging of the cells

into the module, as well as maintenance levels employed at the site.

The extent and nature of degradation varies among module technologies.

Amorphous silicon cells the degrade can cause reductions of 10-30% in the power output of

the module in the first six months of exposure to light.

6. Soiling

The accumulation of dust on the surface of a photovoltaic module decreases the radiation

reaching the solar cell and produces losses in the generated power.

The mean of the daily irradiation losses in a year caused by dust deposited on the surface of a

photovoltaic module is around 5%. After long periods without rain, daily irradiation losses

can be higher than 20%.

Figure 13: Effect of soiling on PV module

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Outdoor photovoltaic module I-V characteristics test

Background

The purpose of the outdoor photovoltaic (PV) module I-V characteristics test is to validate the DUT

manufacturer’s PV module data (if available) and determine the PV module’s I-V characteristic curve

under standard test conditions (STC) and typical module operating temperatures (TMOT).

Solar LED lamp units are often powered by PV modules having a power range from approximately 0.3

watts (W) to 10 W. When selecting a measurement instrument, it is important to ensure that it is able to

make accurate measurements of modules in the desired size range. This is particularly important for

modules rated at less than 3,0 W since most measurement equipment is not designed for very small

modules.

The PV module may be measured with a solar simulator in accordance with standard IEC 60904-1 and

corrected for TMOT with standard IEC 60891. This is the preferred technique for characterizing PV

modules and laboratories with access to a solar simulator should use this procedure.

The test may also be performed with an instrument that is designed to make outdoor performance

measurements of small solar modules.

I-V Characteristics of solar PV module

The I-V curve of an illuminated PV module has the shape shown in figure below, as the voltage across the

measuring load is swept from zero to VOC.

Many performance parameters for the solar module can be determined from this data, such as Voc, Isc

and Pmp.

Figure 14: I-V Characteristics of solar PV module

Standard Test Condition (STC) creates uniform test condition which make it possible to

conduct uniform comparisons of photovoltaic (PV) modules by different manufacturers. This

condition defines performance at an solar radiation of 1000 W/m2, temperature 25°C and air

mass 1.5 G.

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NOCT coefficient (Nominal Operating Cell Temperature) is usually specified by most of PV

module manufacturers, which is the temperature attained by the PV modules with standard

conditions defined as solar radiation at 800 W/m2, ambient temperature 20°C, wind velocity 1

m/s and open-circuit PV module.

Short-circuit current (Isc) is the current through the solar module when the voltage across the

solar module is zero (i.e., when the solar module is short circuited).

Open-circuit voltage (Voc) is the maximum voltage available from a solar cell, and this occurs

at zero current.

Figure 15: IV curve showing Isc and Voc

Maximum power point (Pmp or Pmax) provided by the PV module is achieved at a point on

the I-V curve, where the product Imp (or Imax) and Vmp (or Vmax) is maximum

Pmp = Imp x Vmp

Figure 16: IV curve showing maximum power point

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Fill factor (FF) is also known as the curve factor, is a measure sharpness of the knee in an I-V

curve. It indicates how well a junction was made. The maximum value of the fill factor is 1.0,

which is not possible. Its maximum value in Silicon is 0.88.

Solar cell efficiency (ηec or ηeff) is the solar cell power conversion efficiency and may be given

as

where Imax and Vmax are the current and voltage for maximum power, corresponding to solar

ntensity I(t) and AC is the area of the solar cell.

Test outcomes

Table 2: Test outcomes of Outdoor photovoltaic module I-V characteristics test

Metric Reporting units Related aspects

Short-circuit current (Isc) at STC Amperes (A) These are the key

parameters describing

solar module

performance at

standard test

conditions (“STC” -

AM 1.5, 25 °C,

1000 W/m2) and

Normal operating cell

temperature

(“NOCT” - same as

STC except cell

temperature of 50 °C)

Open-circuit voltage (Voc) at STC Volts (V)

Maximum power point power (Pmpp) at STC Watts-peak (Wp)

Maximum power point current (Impp) at STC Amperes (A)

Maximum power point voltage (Vmpp) at STC Volts (V)

Short-circuit current (Isc,NOCT) at NOCT Amperes (A)

Open-circuit voltage (Voc,NOCT) at NOCT Volts (V)

Maximum power point power (Pmpp,NOCT) at

NOCT

Watts-peak (Wp)

Maximum power point current (Impp,NOCT) at

NOCT

Amperes (A)

Maximum power point voltage (Vmpp,NOCT) at

NOCT

Volts (V)

Temperature coefficient Per degree Celsius (1/°C)

STC I-V Curve dataset Volts (V), Amperes (A)

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Procedure

The PV module is tested outdoors to obtain its characteristic I-V curve, from which the maximum power

(Pmpp), open-circuit voltage (Voc), and short-circuit current (Isc) can be determined.

Equipment requirements

a) Outdoor I-V curve analyser

b) Fast-response (i.e., silicon PV-based) pyranometer with less than 5 % error

c) Voltage meter or multimeter with a basic measurement uncertainty less than or equal to 0,5 % of

the measuring range

d) Surface-mounted thermocouple(s) and a thermocouple reader with a precision less than 2 °C

Test prerequisites

a) Constant atmospheric conditions (i.e., a clear, sunny day with no clouds)

b) Incident solar radiation between 850 W/m2 and 1 150 W/m2 and an ambient temperature between

15 °C and 35 °C

c) Air mass less than or equal to 2

d) If the PV module is amorphous silicon or otherwise may be subject to degradation (e.g., because

it is thin film or of unknown technology), it must sun-soak for 30 days prior to performing this

test

Apparatus

There should be an appropriate stand to hold the PV module and pyranometer in the same plane, directly

normal to the sun. The PV module should be placed as close as possible to the pyranometer to ensure that

each device “sees” the same sky view. A sighting tube with bracket can be used to ensure the stand is

directly normal to the sun.

1 Pyranometer

2 Board or other flat surface

3 Bracket

4 Sighting tube

θ 90°

Figure 17: Apparatus used for outdoor photovoltaic

Module IV characteristic test

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Procedure

Determine the appropriate thermocouple mounting technique based on PV panel configuration. If the PV

module is separate from the lighting product or can be easily removed without damaging the active PV

material and the back of the PV module is accessible, use the back-mounted thermocouple procedure.

Otherwise, use the front-mounted thermocouple procedure.

Back-mounted thermocouple

a) Before the PV module is exposed to sunlight, do the following:

1) Cut the connector from the end of the PV module cable, leaving as much of the cable

connected to the PV module as possible, and strip the wire ends.

2) Connect a voltage meter or multimeter (DC voltage range) to the PV module.

3) Fix the thermocouple to the back of the PV module near the centre of the active area and affix

insulating material (e.g., foil-backed foam tape) over the thermocouple.

b) Expose the PV module to direct normal sunlight and immediately measure and record the open-

circuit voltage (Voc,1) and the PV module temperature (T1).

c) Leave the PV module in direct normal sunlight until thermal equilibrium is reached (i.e., the PV

module temperature is not changing by more than 1 °C/min).

d) Connect the PV module to the I-V curve analyser per the I-V curve analyser’s manufacturer’s

instructions.

e) Execute the I-V measurement per the I-V curve analyser’s manufacturer’s instructions and record

the PV module temperature (T) and incident solar radiation.

f) After the I-V curve measurement, measure and record the PV module temperature again (T2).

g) Measure the record the PV module’s open-circuit voltage at T2 (Voc,2) using the same instrument

that was used in step (a).

h) Connect the PV module to the lighting product and measure and record the typical operating

voltage (Vop) at the lighting product’s PV socket using a voltage meter or multimeter.

Generating an I-V Curve

Figure 18: generation of IV curve

22

Outdoor I-V Curve Tester

Figure 19: outdoor IV curve Tester Setup

Figure 20: IV curve generated by Tester

23

Calculations

a) Convert all of the current measurements to STC using the following formula:

GII

2

mmW 0001

where

I is the PV module’s current at STC, in amperes (A);

Im is the PV module’s measured current, in amperes (A);

G is the measured incident solar radiation during the I-V curve measurement, in watts per

square meter (W/m2).

b) Determine the temperature coefficient for the voltage (Tc,voc) using the following formula:

Tc,voc =Voc,1 -Voc,2( ) Voc,2

T1 -T2

where

Tc,voc is the PV module’s temperature coefficient for the voltage, per degree Celsius (1/°C);

Voc,1 is the PV module’s open-circuit voltage immediately after exposure to sunlight, in volts

(V);

Voc,2 is the PV module’s open-circuit voltage after the I-V measurement is taken, in volts (V);

T1 is the PV module’s temperature immediately before exposure to sunlight, in degrees

Celsius (°C);

T2 is the PV module’s temperature after the I-V curve measurement is taken, in degrees

Celsius (°C).

c) Convert all of the voltage measurements to STC using the following formula:

V =Vm ´ 1+Tc,voc ´ Tstc -T( )éë ùû

where

V is the PV module’s voltage at STC, in volts (V);

Vm is the PV module’s measured voltage, in volts (V);

Tc,voc is the PV module’s temperature coefficient for the voltage, per degree Celsius (1/°C);

Tstc is the temperature at STC, 25 °C;

T is the PV module’s temperature during the I-V curve measurement, in degrees

Celsius (°C).

d) The PV module’s short-circuit current at STC (Isc) is the current corresponding to 0 V on the

STC-adjusted I-V curve.

e) The PV module’s open-circuit voltage at STC (Voc) is the voltage corresponding to 0 A on the

STC-adjusted I-V curve.

24

f) Determine the PV module’s measured maximum power point power at STC (Pmpp) using the

following formula:

Pmpp = max I ´V( )

where

Pmpp is the PV module’s measured maximum power point power at STC, in watts-peak (Wp);

I is the PV module’s current at STC, in amperes (A);

V is the PV module’s voltage at STC, in volts (V).

g) The PV module’s maximum power point current at STC (Impp) is the current corresponding to

Pmpp on the STC-adjusted I-V curve.

h) The PV module’s maximum power point voltage at STC (Vmpp) is the voltage corresponding to

Pmpp on the STC-adjusted I-V curve.

25

Battery Test

Background

The battery test is used to determine a DUT’s actual battery capacity and storage efficiency. This

information is useful to determine if a battery is mislabelled or damaged. During the test the battery is

connected to a battery analyser, which performs charge-discharge cycles on the battery. The last charge-

discharge cycle data from the battery test is analysed to determine the actual battery capacity and battery

storage efficiency.

Purpose of the test and outputs

•Purpose: determine if battery is properly rated and determine battery efficiency

•Cycle batteries using specific procedures by chemistry

–SLA

–Li-ion

–LiFePO4

–NiMH/ NiCd

•Determine battery capacity and battery efficiency from final charge-discharge cycle data

Battery chemistries

Figure 21: different types of batteries

Nickel Cadmium (NiCd) — mature and well understood but relatively low in energy density. The NiCd

is used where long life, high discharge rate and economical price are important. Main applications are

two-way radios, biomedical equipment, professional video cameras and power tools. The NiCd contains

toxic metals and is not environmentally friendly.

Nickel-Metal Hydride (NiMH) — has a higher energy density compared to the NiCd at the expense of

reduced cycle life. NiMH contains no toxic metals.

Applications include mobile phones and laptop computers.

26

Lead Acid — most economical for larger power applications where weight is of little concern. The lead

acid battery is the preferred choice for hospital equipment, wheelchairs, emergency lighting and UPS

systems.

Lithium Ion (Li-ion) — fastest growing battery system. Li-ion is used where high-energy density and

light weight is of prime importance. The Li-ion is more expensive than other systems and must follow

strict guidelines to assure safety. Applications include notebook computers and cellular phones.

Lithium Ion Polymer (Li-ion polymer) — a potentially lower cost version of the Li-ion. This chemistry

is similar to the Li-ion in terms of energy density.

It enables very slim geometry and allows simplified packaging. Main applications are mobile phones.

Reusable Alkaline — replaces disposable household batteries; suitable for low-power applications. Its

limited cycle life is compensated by low self-discharge, making this battery ideal for portable

entertainment devices and flashlights.

Battery Chemistry Comparison

Table 3: comparison of different Battery Chemistries

C-Rate Terminology

C-rate: determines how quickly the battery is charged or discharged

The same C-rate can be written in many ways:

How can the C-rate be written for a 5Ah battery charged or discharged for 5 hours at 1A?

•C/X, where X = duration of charge or discharge (hours)

ex: C/5

•XC, where X = 1/duration of charge or discharge (hours)

ex: 0,2C

•X It A, where X = 1/duration of charge or discharge (hours)

ex: 0,2 It A

27

Battery Capacity Effected by C-Rate and Temperature

Required testing temperature: 20 °C ± 5 °C

Figure 22: Lead-Acid Battery Capacity VS Temperature

Recommended Battery Testing Details

Table 4: Recommended Testing details for different batteries

28

Test outcomes

Table 5: Test outcomes for Battery Test

Metric Reporting units Related aspects Note

Battery

capacity

(Cb)

Milliampere-hours

(mAh) at a

discharge current

(0,x It A)

This is a measure of the amount of

charge that can be stored in a battery,

which effects the run time of products.

--

Battery

storage

efficiency

(ηb)

Percentage (%) The input to battery circuit efficiency, or

generator-to-battery charging efficiency,

is a measure of how efficient the DUT

electronics are at feeding generated

energy into the battery.

At least two

complete charge-

discharge cycles are

required for the

calculation

Procedure

Sealed lead-acid battery test The DUT’s sealed lead-acid battery is cycled on a battery analyser and the data from the final charge-

discharge cycle is used to determine the DUT’s actual battery capacity and storage efficiency.

Equipment requirements Battery analyser with the voltage, current, and capacity measurement tolerances

± 1 % for voltage; ± 1 % for current; ± 1 % for capacity.

Test prerequisites The battery can be taken out of the lighting product for this test, if desired.

Procedure

a) Prime the battery using a charge rate of 0,1 It A, a discharge rate of 0,1 It A, and the

information in the battery cycling recommended practices.

Using the battery analyser, continuously cycle the battery until the maximum battery capacity

is reached (i.e., until the capacity improvement is less than or equal to 5 % over the previous

battery capacity).

b) Ensure the battery is charged using a charge rate of 0,1 It A and the information in the battery

cycling recommended practices. After charging, the battery shall be stored in an ambient

temperature of 20 °C ± 5 °C for not less than 1 h and not more than 4 h.

c) The battery shall be discharged at a rate of 0,1 It A, using the information in the battery

cycling recommended practices, and the battery capacity shall be measured.

d) Continue cycling the battery until the change in measured battery capacity between

subsequent cycles is less than or equal to 15 %, ensuring that the last two charge-discharge

cycles have identical charge and discharge rates.

e) If the battery will be stored after undergoing this test, charge the battery using a charge rate of

0,1 It A and the information in the battery cycling recommended practices.

29

Calculations

a) Determine the total energy input into the DUT’s battery during the final charge cycle (Ec) using

the following formula:

tIVE ccc

where

Ec is the energy entering the battery during the charge cycle, in watt-hours (Wh);

Vc is the voltage recorded during the charge cycle, in volts (V);

Ic is the current recorded during the charge cycle, in amperes (mA);

∆t is the time interval between subsequent data points, in hours (h).

b) Determine the total energy output from the DUT’s battery during the final discharge cycle using

the following formula:

tIVE ddd

where

Ed is the battery’s energy output during the discharge cycle, in watt-hours (Wh);

Vd is the voltage recorded during the discharge cycle, in volts (V);

Id is the current recorded during the discharge cycle, in amperes (mA);

∆t is the time interval between subsequent data points, in hours (h).

c) Determine the DUT’s battery capacity with data from the final discharge cycle using the

following formula:

tIC db

where

Cb is the measured battery capacity, in milliampere-hours (mAh);

Id is the current recorded during the discharge cycle, in amperes (mA);

∆t is the time interval between subsequent current data, in hours (h).

d) Determine the DUT’s battery efficiency using the following formula:

c

db

E

E

where

b is the battery storage efficiency;

Ed is the battery’s energy output during the discharge cycle, in watt-hours (Wh);

Ec is the energy input to the battery during the charge cycle, in watt-hours (Wh).

30

Battery Testing Operations

Figure 23: Flow Chart for Battery Testing Operations

Step 1 on Cadex

Figure 24: Step 1 on Cadex

31

Example for SLA battery

Figure 25: Example for SLA battery on Cadex for step 1

Step 2 on Cadex

C-code:

–Specify c-rates and other charging/discharging parameters

–Specific for each battery chemistry

Figure 26: C-code for SLA Battery

32

Step 3 on Cadex

Download Data as .csv File

Figure 27: Readings measured by Cadex during Battery Testing

33

Measurement Of Temperature Coefficients

Purpose

The purpose is to determine the temperature coefficient of current(α), voltage(β) peak power(δ) from

module measurements. The coefficients so determined are valid at the irradiance at which the

measurements were made.

Apparatus

The following apparatus is required to control and measure the test conditions:

a) A radiant source (natural sunlight or solar simulator,class B or better in accordance with IEC

60904-9) of the type to be used in subsequent tests;

b) A PV module having a known short circuit current versus irradiance characteristics determined

by calibrating against an absolute radiometer in accordance with IEC 60904-6;

c) Any equipment necessary to change the temperature of the test specimen over the range of

interest;

d) A suitable mount for supporting the test specimen and the reference device in the same plane

normal to the radiant beam;

e) A means for monitoring the temperature of the specimen and reference device to an accuracy of

±1 °C, and repeatability of ±0.5 °C;

f) Equipment for measuring the current of the test specimen and reference device toan accuracy of

±0.2 % of the reading;

g) Equipment for measuring the voltage of the test specimen and reference device toan accuracy of

±0.2 % of the reading;

Solar simulator

A solar simulator (also artificial sun) is a device that provides illumination approximating

natural sunlight. The purpose of the solar simulator is to provide a controllable indoor test facility under

laboratory conditions, used for the testing of solar cells, sun screen, plastics, and other materials and

devices.

Classification of Solar Simulators:

Table 6: classification of solar simulators[5]

34

Figure 28,29: Solar Simulators

Types of lamps

Several types of lamps have been used as the light sources within solar simulators.

Xenon arc lamp: this is the most common type of lamp both for continuous and flashed solar

simulators. These lamps offer high intensities and an unfiltered spectrum which matches

reasonably well to sunlight. However, the Xe spectrum is also characterized by many undesirable

sharp atomic transitional peaks, making the spectrum less desirable for some spectrally sensitive

applications. Xe arc lamps can be designed for low powers or up to several kilowatts, providing

the means for small- or large- area illumination, and low to high intensities.

Metal Halide arc lamp: Primarily developed for use in film and television lighting where a high

temporal stability and daylight colour match are required, metal halide arc lamps are also used in

solar simulation.

QTH: quartz tungsten halogen lamps offer spectra which very closely match black body

radiation, although typically with a lower color temperature than the sun.

LED: light-emitting diodes have recently been used in research laboratories to construct solar

simulators, and may offer promise in the future for energy-efficient production of spectrally

tailored artificial sunlight.

Equipment Details:

Table 7: Sun Simulator specifications (used in the Lab):

Software used INVSUN MT20-11

Max module dimension 2000mm x 1100mm

Measurement range voltage 100V

Current 30Amp

Variable insolation 50-100mW/cm2 calibrated by reference module and controlled

by micro-controller

Light source pulsed Xenon light source with AM 1.5 filter, closely matching

the solar spectrum avoiding modular heating

Illumination uniformity ± % 3 over 2000mm x 1100mm area

Reference cell calibrated Si Pyranometer mounted inside Xenon flash unit

coupled to electronic load to monitor illumination intensity ,

control pulse to pulse consistency and to trigger data acquisition

35

Temp is monitored and displayed by thermocouple.

Temperature Compensation:

Module testing temp is measured with the thermocouple assembly which is kept on the module sensing

the back surface temp during testing to allow optional temperature compensation of the IV data with the

help of voltage and current programmed co-efficient.

Flash unit area of 2300mm x 1500mm x 1000mm

Power phase I AC 220V /50Hz/15 Amps 3KVA rating.

System description:

The subsystems are:

Xenon Sun Simulator with Module Holder, Electronic Rack Unit, Flash Control Unit, Electronic Load, Pc

for Data Acquisition.

Effect of temperature

Like all other semiconductor devices, solar cells are sensitive to temperature. Increases in temperature

reduce the band gap of a semiconductor, thereby effecting most of the semiconductor material parameters.

The decrease in the band gap of a semiconductor with increasing temperature can be viewed as increasing

the energy of the electrons in the material. Lower energy is therefore needed to break the bond. In the

bond model of a semiconductor band gap, reduction in the bond energy also reduces the band gap.

Therefore increasing the temperature reduces the band gap.

In a solar cell, the parameter most affected by an increase in temperature is the open-circuit voltage. The

impact of increasing temperature is shown in the figure below.

Figure 30: The effect of temperature on the IV characteristics of a solar cell.

36

Effect of Irradiance

The light intensity incident on a solar PV module is directly proportional to the current.

Figure 31: Effect of irradiance[6]

Figure 32: IV curve showing effect of temperature and irradiance

37

Procedure with a solar simulator

a) Determine the short circuit current of the module at the desired irradiance at room temperature, in

accordance with IEC 60904-1.

b) Mount the test module in the equipment used to change the temperature. Mount the PV reference

device within the simulator beam. Connect to the instrumentation.

c) Set the irradiance so that the test module produces the short-circuit current. Use the PV reference

device to maintain this irradiance setting throughout the test.

d) Heat or cool the module to a temperature of interest. Once the module has reached the desired

temperature, measure Isc, Voc and peak power. Change the module temp in steps of

approximately 5 °C over a range of interest of atleast 30 °C and repeat the measurement of Isc,

Voc and peak power.

Calculation of temperature coefficients

Plot the value of Isc, Voc and Pmax as functions of temperature and construct a least-square-fit

curve through each set of data.

From the slopes of the least squares fit straight lines for current, voltage and Pmax. Calculate α,

the temperature coefficient of short circuit current, β, the temperature coefficient of open circuit

voltage, and δ, the temperature coefficient of Pmax, for the module.

38

Test Outcomes

Figure 33: Configuration Settings Of Solar Simulator

Figure 34: IV curve obtained from Solar Simulator

39

Experimental Data

Figure 35: IV and WV curve at irradiance of 1000W/m2

Figure 36: IV and WV curve at irradiance of 900W/m2

0

5

10

15

20

25

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0 5 10 15 20 25

Po

we

r (W

)

Cu

rre

nt

(A)

Voltage (V)

Current

Power

0

5

10

15

20

25

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0 5 10 15 20 25

Po

we

r (W

)

Cu

rre

nt

(A)

Voltage (V)

Current

Power

40

Figure 37: IV and WV curve at irradiance of 800W/m2

Figure 38: IV and WV curve at irradiance of 700W/m2

0

5

10

15

20

25

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0 5 10 15 20 25

Po

we

r (W

)

Cu

rre

nt

(A)

Voltage (V)

Current

Power

0

5

10

15

20

25

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0 5 10 15 20 25

Po

we

r (W

)

Cu

rre

nt

(A)

Voltage (V)

Current

Power

41

Figure 39: IV and WV curve at irradiance of 600W/m2

Figure 40: IV Curve at different values of Irradiance for calculating Temperature Coefficient

0

5

10

15

20

25

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0 5 10 15 20 25

Po

we

r (W

)

Cu

rre

nt

(A)

Voltage (V)

Current

Power

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0.0 5.0 10.0 15.0 20.0 25.0

Cu

rre

nt

(A)

Voltage (V)

Current (1000W/m2)

Current (900W/m2)

Current (800W/m2)

Current (700W/m2)

Current (600W/m2)

42

Figure 41: IV curve at temperature 40.8 °C

Figure 42: IV curve at temperature 37.3 °C

43

Figure 43: IV curve at temperature 34.8 °C

Figure 44: IV curve at temperature 30.1 °C

44

Figure 45: IV curve at temperature 28.2 °C

Figure 46: IV curve at temperature 25.8 °C

45

Designing of Solar PV System

Basic Principles to Follow When Designing a Quality PV System

1) Select a packaged system that meets the owner's needs. Customer criteria for a system may

include reduction in monthly electricity bill, environmental benefits, desire for backup power,

initial budget constraints, etc. Size and orient the PV array to provide the expected electrical

power and energy.

2) Ensure the roof area or other installation site is capable of handling the desired system size.

3) Specify sunlight and weather resistant materials for all outdoor equipment.

4) Locate the array to minimize shading from foliage, vent pipes, and adjacent structures.

5) Design the system in compliance with all applicable building and electrical codes.

6) Design the system with a minimum of electrical losses due to wiring, fuses, switches, and

inverters.

7) Properly house and manage the battery system, should batteries be required.

8) Ensure the design meets local utility interconnection requirements.

Basic Steps to Follow When Installing a PV System

1) Ensure the roof area or other installation site is capable of handling the desired system size.

2) If roof mounted, verify that the roof is capable of handling additional weight of PV system.

Augment roof structure as necessary.

3) Properly seal any roof penetrations with roofing industry approved sealing methods.

4) Install equipment according to manufacturers specifications, using installation requirements and

procedures from the manufacturers' specifications.

5) Properly ground the system parts to reduce the threat of shock hazards and induced surges.

6) Check for proper PV system operation by following the checkout procedures on the PV System

Installation Checklist.

7) Ensure the design meets local utility interconnection requirements

8) Have final inspections completed by the Authority Having Jurisdiction (AHJ) and the utility (if

required).

SYSTEM DESIGN CONSIDERATIONS

Typical System Designs and Options

PV Electrical System Types

There are two general types of electrical designs for PV power systems for homes; systems that interact

with the utility power grid and have no battery backup capability; and systems that interact and include

battery backup as well.

Grid-Interactive Only (No Battery Backup)

This type of system only operates when the utility is available. Since utility outages are rare, this system

will normally provide the greatest amount of bill savings to the customer per dollar of investment.

However, in the event of an outage, the system is designed to shut down until utility power is restored.

46

Typical System Components:

PV Array: A PV Array is made up of PV modules, which are environmentally-sealed collections of PV

Cells—the devices that convert sunlight to electricity. The most common PV module that is 5-to-25

square feet in size and weighs about 3-4 lbs./ft2. Often sets of four or more smaller modules are framed or

attached together by struts in what is called a panel. This panel is typically around 20-35 square feet in

area for ease of handling on a roof. This allows some assembly and wiring functions to be done on the

ground if called for by the installation instructions.

Balance of system equipment (BOS): BOS includes mounting systems and wiring systems used to

integrate the solar modules into the structural and electrical systems of the home. The wiring systems

include disconnects for the dc and ac sides of the inverter, ground-fault protection, and overcurrent

protection for the solar modules. Most systems include a combiner board of some kind since most

modules require fusing for each module source circuit. Some inverters include this fusing and combining

function within the inverter enclosure.

DC-AC inverter: This is the device that takes the dc power from the PV array and converts it into

standard ac power used by the house appliances.

Metering: This includes meters to provide indication of system performance. Some meters can indicate

home energy usage.

Other components: utility switch (depending on local utility).

Figure 47: Grid-Interactive Only (No Battery Backup)

Grid-Interactive With Battery Backup

This type of system incorporates energy storage in the form of a battery to keep “critical load” circuits in

the house operating during a utility outage. When an outage occurs the unit disconnects from the utility

and powers specific circuits in the home. These critical load circuits are wired from a subpanel that is

separate from the rest of the electrical circuits. If the outage occurs during daylight hours, the PV array is

able to assist the battery in supplying the house loads. If the outage occurs at night, the battery supplies

the load. The amount of time critical loads can operate depends on the amount of power they consume

and the energy stored in the battery system. A typical backup battery system may provide about 8kWh of

energy storage at an 8-hour discharge rate, which means that the battery will operate a 1-kW load for 8

hours. A 1-kW load is the average usage for a home when not running an air conditioner.

47

Typical System Components:

In addition to components listed in Grid Interactive System, a battery backup system may include some or

all of the following:

1) batteries and battery enclosures

2) Battery charge controller

3) separate subpanel(s) for critical load circuits

Figure 48: Grid-Interactive With Battery Backup

48

Designing using PVsyst (Photovoltaic Systems Software)

PVsyst is a PC software package for the study, sizing, simulation and data analysis of complete PV

systems.

Figure 49: Photovoltaic Systems Software Interface

Figure 50: Stand alone system presizing at New Delhi

49

Figure 51: Selection of Project’s Location

Figure 52: Horizon (far shadings) at New Delhi and selection of Diffuse Factor

50

Figure 53: Daily use of energy (Daily consumptions)

Figure 54: System Specification(tilt and azimuth)

51

Figure 55: Sizing and Results (available solar energy and user needs)

Figure 56: Sizing and Results (average state of charge of batteries and probability of loss of load)

52

References

1. Hanasoge SM, Duvall TL, Sreenivasan KR. From the Cover: Anomalously weak solar

convection. Proceedings of the National Academy of Sciences. 2012 ;109(30):11928 - 11932.

2. Rai GD. Solar Energy Utilisation. In: Khanna Publishers; 1980. p. 44.

3. Hu C, White RM. Solar Cells: From Basic to Advanced Systems. New York: McGraw-Hill; 1983.

4. Mack M. Solar Power for Telecommunications. The Telecommunication Journal of Australia.

1979 ;29:20-44.

5. "Specification for Solar Simulation for Photovoltaic Testing". 2010. doi:10.1520/E0927-10.

6. Jump up^ "Tables for Reference Solar Spectral Irradiances: Direct Normal and Hemispherical

on 37 Tilted Surface". 2008. doi:10.1520/G0173-03R08.