Solar Photovoltaics: Principles, Application and case study

7/24/2019 Solar Photovoltaics: Principles, Application and case study

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SOLAR PHOTOVOLTAICS

PRINCIPLES AND CASE STUDY


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ABSTRACT

We all are aware of the exhausting energy sources and its time that we

think about alternative solutions for our day to day

requirements since we cannotcurb down our needs and ourdependency on the energy sources. It is peak time that

we need

to start reaching out for the alternative ways before we completely

run out of

the resources. Some of the renewable energy alternatives are wind

energy, solar energy,

tidal energy, thermal energy, geo-thermal energy. But most of these cannot be

harnessed at all locations. Hence, the best alternatives we can think of is the solar

energy which is never exhausting and also pollution free. Solar energy can be

harnessed at any location without any hindrance. One can install

them for the street

lights, on the rooftops, fields, etc. So why not we

go eco-friendly and harness the solar

energy which has less maintenance and presents easy installation on roof-tops or

ground.

There are many players in India manufacturing and providing a wide

range of solar energy products and solutions. The following report gives technical

details of a solar cell, module manufacturing procedure and also detailed description

of 1MW and 10MW solar power plants. Report concludes with a live Case Study on

off-grid solar power plant design.


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CONTENTS

1. INTRODUCTION

2.

SOLAR CELL AND ELECTRICAL PARAMETERS

3. MANUFACTURING OF SOLAR CELLS

4. MANUFACTURING OF SOLAR MODULES

5. INVERTERS

5.1 STRING INVERTER

5.1 CENTRAL INVERTER

6.

TRACKERS

6.1 SINGLE AXIS TRACKERS

6.2 DUAL AXIS TRACKERS

7. MAXIMUM POWER POINT TRACKING

8. GRID SYNCHRONIZATION

9. MOMINPET POWER PLANT VISIT

10.MIDJIL POWER PLANT VISIT

11.

ANALYSIS OF SOLAR POWER PLANT

11.1 SOLAR PLANT PERFORMANCE INDEX

11.2 POTENTIAL INDUCED DEGRADATION

11.3 FILL FACTOR IMPACT

12.CASE STUDY

13.CONCLUSION


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1.INTRODUCTION

The shortage of power, rapid consumption of non-renewable energy, ever-

increasing demand for power supply, daily warnings about our environment are enough

signs to tell us that it is time we need to do something. So, what can we do? How aboutharnessing solar energy?? Some of the advantages of plugging into sun are:

Reduces dependence on exhausting resources.

Solar energy is renewable.

Making way for a healthier environment.

Solar panels help protect the atmosphere by generating electricity without the

greenhouse gases that traditional power plants produce. 1 kWh produced from coal

emits 0.33 kg of CO2. 1 kWhproduced by the combination of all sources of renewableenergyemits0.04 kg of CO2.

If we build a solar power plant that produces 40,500 kWh peryear, we would save

7.3 tons of CO2 at no longer producethose watts in a carbon plant. So for every 1MWh

per year, we wouldsave 0.18 tons of CO2.

Under JNNSM (Jawaharlal Nehru National Solar Mission),Government of India

has taken steps to develop and deploy solar energy for supplementing the energy

requirements of the country. JNNSM was launched on 11th

January, 2010 by the PrimeMinister and has set the ambitious target of deploying 20,000 MW of grid connected

solar power by 2022 is aimed at reducing the cost of solar power generation in the

country through (i) long term policy; (ii) large scale deployment goals; (iii) aggressive

R&D; and (iv) domestic productionof critical raw materials, components and products,

as a result toachieve grid tariff parity by 2022. Solar mission will create an enablingpolicy

framework to achieve this objective and make India a globalleader in solar energy.


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Another such program is Clean Development Mechanism (CDM) which allows a

country with anemission-reduction or emission-limitation commitment to implement

an emission-reduction project in developing countries. Such projectscan earn saleable

certified emission reduction (CER) credits, eachequivalent to one tonne of CO2. The

mechanism is seen by many as a trailblazer. It is the first global, environmental

investment and credit scheme of its kind, providing a standardized emissions offset

instrument, CERs. A CDM project activity might involve, for example, a rural

electrification project using solar panels or the installation of more energy-efficient

boilers. The mechanism stimulates sustainable development and emission reductions,

while giving industrialized countries some flexibility in how they meet their emission

reductionorlimitation targets.

The solar cell is the basic building block of solar photovoltaics. The cell canbe considered as a two terminal device which conductslike a diode in the dark and

generates a photovoltage when chargedby the sun. These solar cells are then made into

solar photovoltaic (SPV) modules by sequence of processes. The prepared solar

modulesare then arranged into series connection to form a completePV array. These

arrays are then fixed in ground or roof-top. The supply from PV arrays is DC in nature,

but most of the electrical appliancesneed AC supply. Hence, inverters are used for the

conversion fromDC to AC. Inverters can be either central or string in naturedepending

on our need. The power so obtained is later sent to the substation following the

synchronization of the power with thegrid.


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2. SOLAR CELL AND ELECTRICALPARAMETERS

The sunrays falling on earth have two componentslight and heat. The heat

component has the solar Joules energy and the light component has the solar photon

energy.

Photons in, electrons out: The Photovoltaic effect

Solar photovoltaic energy conversion is a one-step conversion process which

generates electrical energy from light energy. The explanation relies on ideas from

quantum theory. Light is made up of packets of energy, called photons, whose energy

depends only upon the frequency, or colour, of the light. The energy of visible photons

is sufficient to excite electrons, to higher energy levels where they are free to move.

An extreme example of this is the photoelectric effect, which was explained by

Einstein in 1905, where blue or ultraviolet light provides enough energy for electrons

to escape completely from the surface of a metal. Normally, when light is absorbed by

matter, photons are given up to excite electrons to higher energy states within the

material, but the excited electrons quickly relax back to their ground state. In a

photovoltaic device, however, there is some built-in asymmetry which pulls the excited

electrons away before they can relax, and feeds them to an external circuit. The extra

energy of the excited electrons generates a potential difference, or electro-motive force(emf). This force drives the electrons through a load in the external circuit to do

electrical work.

The photovoltaic effect was first reported by Edmund Becquerel in 1839 when he

observed that the action of light on a silver coated platinum electrode immersed in

electrolyte produced an electric current.


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The solar cell is the basic building block of solar photovoltaics. The cell can be

considered as a two terminal device which conducts like a diode in the dark andgenerates a photovoltage when charged by the sun.

In reality cells dissipate power through the resistance of the contacts and through

leakage currents around the sides of the device. These effects are equivalent electrically

to two parasitic resistances in series (Rs) and in parallel (Rsh) with the cell.

Fig: Equivalent circuit of solar cell including series and shunt resistances.


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I-V characteristics of a solar cell is shown in the figure below

Effect of resistances on I-V characteristics of a solar cell

Effect of (a) increasing series and (b) reducing parallel resistances.

Like all other semiconductor devices, solar cells are sensitive totemperature. In a

solar cell, the parameter most affected by an increase in temperature is the open-circuit

voltage (Voc). The impact of increasingtemperature is shown in the figure below.


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Open-circuit voltage decreases with increase in temperaturewhereas short-circuit

current increases slightly. In a solar cell the rate of change of open-circuit voltage and

short-circuit current with respect to temperature is given by

Solar cells convert the photon light around the pn-junction directly into electricity

without any moving or mechanicalparts. PV cells produce energy from sunlight,

not from heat. In fact,they are most efficient when they are cold.

When exposed to sunlight (or other intense light source), thevoltage produced

by a single solar cell is about 0.58V DC, with thecurrent flow being proportional to thelight energy (photons).In most solar cells, the voltage is nearly constant, and the

current is proportional to the size of the cell and the intensity of the light.

Some of the key concepts regarding the solar cells are the StandardTest Conditions

(STC) which are as follows:

1.

AM (Air Mass Index) =1.5

2.

Temp= 25oC

3.

Irradiance= 100mW/cm2

Key performance characteristics:

1.

Jsc = q bs(E)QE(E)dE

Jsc = Short-circuit current density q= is the electron charge

bs= Incident spectral photon flux density QE (E) = Quantum efficiency

2.

Voc= (kT/q) ln(Jsc/Joc +1)

Jo c= Open circuit current density k=Boltzmann constant

T= temperature

3. FF (fill factor) = (Jm Vm)/ (Jsc Voc)

Voc= Open circuit Voltage Jm = Maximum current density

Vm = Maximum voltage

4.

(efficiency) = (Jm Vm)/Ps Ps= input solar power


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3. MANUFACTURING OF SOLAR CELLS

Silicon is the eighth most common element in the universe bymass, but very rarely

occurs as the pure free element in nature. It is most widely distributed in dusts, sands,

planetoids, and planets asvarious forms of silicon dioxide (silica) or silicates. Over 90% oftheEarth's crust is composed of silicate minerals, making silicon the second most abundant

element in the Earth's crust (about 28% by mass) after oxygen. More modern silicon

compounds such as silicon carbide form abrasives and high-strength ceramics. Siliconis the

basis of the widely used synthetic polymers called silicones.

The process of solar cells manufacturing, first starts with the mining of quartz from

the earth and then conversion of that quartz into Mg-Si by carbothermic reaction. Mg-Si

is processed into poly-silicon by Siemens process. The poly-silicon is then made into ingot

with the help of a seed of the silicon. The circular ingot obtained is then cut into particular

shape at the edges. This structure is then cut into very thin slices to give wafers which are

processed to give solar cells. The upper surface of the module is n-type and the bottom

part needs to be made into p-type by diffusing POCl3at 800C. The edges are then made

proper by the process of plasma edging and it removes the excess of the p-type material.


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Extraction of metallurgical grade Silicon:

Metallurgical grade Silicon is commercially prepared by the reaction ofhigh-purity silica

with wood, charcoal, and coal in an electric arc furnace using Carbon electrodes. At

temperatures above 1900 C (3450 F), Carbon in the above mentioned materials and the

Silicon undergo the chemical reaction SiO2 + 2C Si + 2CO.Liquid Silicon collects in the

bottom of the furnace, which is thendrained and cooled. The silicon produced in this manner

is called metallurgical grade silicon and is at least 98% pure. Using thismethod, Silicon Carbide

(SiC) may also form from an excess of Carbonin one or both of the following ways:

SiO2 + C SiO + CO

SiO + 2C SiC + CO.

However, provided the concentration of SiO2 is kept high,the Silicon Carbide can be

eliminated by the chemical reaction as:-

2SiC +SiO2 3Si + 2 CO

Mono-crystalline silicon ingot grown by the Czochralski processPolycrystalline silicon rod made by the Siemens process


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Methods of manufacturing ingot:

a)

Czochralski method: Used to create a monocrystalline cell. A single monocrystalline

silicon seed crystal is slowly pulled from the high-heat molten Silicon. As it is drawn

upwards, the Silicon cools and solidifies as a single ingot. This cylindrical ingot is then

sliced into thin pieces that are then cut into the cell shapes as visible on a monocrystalline

solar panel.

b)

Siemens Process: This technique grows high-purity Silicon crystallites directly on the

surface of (pre-existing) pure Silicon seed rods by a chemical decomposition that takes

placewhen the gaseous Trichlorosilane (HSiCl3) is blown over the rod'ssurface at 1150C.

This technique is called Chemical Vapour Deposition (CVD) and produces high-purity

Polycrystalline Silicon, also known as polysilicon. Whilethe conventional Siemens process

produces electronic grade polysilicon at typically 9N11N purities, that is, it containsimpurity levels of less than one part per billion , themodified Siemens process is a dedicated

process-route for the production of solar grade silicon (SoG-Si) with purities of 6N

(99.9999%) and less energy demand.

c)

FBR Method: A more recent alternative for the production ofpolysilicon is the fluidized

bed reactor (FBR) manufacturing technology. Compared to the traditional Siemens

process, FBRfeatures a number of advantages that lead to cheaper polysilicon demanded

by the fast-growing photovoltaic industry.Contrary to Siemens batch process, FBR runscontinuously,wasting fewer resources and requires less setup and downtime.It uses about

10% of the electricity consumed by aconventional rod reactor in Siemens process, asitdoes

not waste energy by placing heated gas and silicon incontact with cold surfaces. In the FBR,

silane (SiH4) is injected into the reactor from below and forms a fluidized bed together

with the silicon seed particles that are fed from above. Thegaseous silane then decomposes

and deposits silicon on theseedparticles. When the particles have grown to larger granules,

they eventually sink to the bottom of the reactor where they arecontinuously withdrawn.

The FBR technology produces polysilicon at 6N to 9N, apurity still higher than the 5N

to 6N of upgraded metallurgical silicon (UMG-Si), a third technology used by the

photovoltaic industry, that dispenses altogether with chemical purification, using

metallurgical techniques instead. Solar grade purity is 99.999% (5N) and electronic grade

purity is99.9999999(9N)


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The two types of PV crystalline cells mono and multi are compared in the table below.Monocrystalline

(Single crystalline)Multi-crystalline

(Polycrystalline)

1.

Composed of single crystal of silicon

2.

Czochralski method is employed.

Cylindrical shaped ingot is obtained

with the help of a seed crystal.

3.

Can function in low light conditions

also.

4.

More expensive

5.

More efficient in real life conditions.

1.

Composed of many crystals of silicon

2.

Siemens method or Fluidized Bed

reduction method is employed. Cube

shaped ingot is obtained

3.

Function better under high heat

conditions

4.

Less expensive

5.

More efficient in lab conditions.


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4. MANUFACTURING OF SOLAR MODULES

Before getting into manufacturing process of solar modules let ushave a look at some of

the IEC standards.

IEC TC 82 Working Groups

WG1: Glossary

Task: To prepare a glossary of terms relevant to PV.

WG2: Modules, non-concentrating

Task: To develop international standards for non-concentrating,terrestrial

photovoltaic modules -crystalline & thin-film.

WG3: Systems

Task: To give general instructions for photovoltaic system designand

maintenance.

WG6: Balance-of-system (BOS) components

Task: To develop international standards for BOS components forPV systems.

WG 7: Concentrator modules

Task: To develop international standards for photovoltaicconcentrators and

receivers.

WG 8: Solar cells and wafers (new group to be formed in 2013)

Task: To develop international standards for photovoltaic cells andwafers.

JWG 21/TC 82 Batteries

Task: To draw up standard requirements for battery storagesystems intended for use

in photovoltaic systems.

JWG 1-TC 82/TC 88/TC21/SC21A

Task: To prepare guidelines for Decentralized Rural Electrification(DRE) projectswhich are now being implemented.

Here are some of the IEC TC 82 standards

IEC 60891:2009 Edition 2.0 (2009-12-14)

Photovoltaic devices - Procedures for temperature and irradiance corrections to measured

I-V characteristics


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IEC 60904-1:2006

Edition 2.0 (2006-09-13)

Photovoltaic devices - Part 1: Measurement of photovoltaic current-voltage characteristics

IEC 60904-2:2007

Edition 2.0 (2007-03-20)

Photovoltaic devices - Part 2: Requirements for reference solar devices

IEC 60904-3:2008

Edition 2.0 (2008-04-09)

Photovoltaic devices - Part 3: Measurement principles for terrestrial photovoltaic (PV)

solardevices with reference spectral irradiance data

IEC 60904-4:2009

Edition 1.0 (2009-06-09)

Photovoltaic devices - Part 4: Reference solar devices - Procedures for establishing

calibration traceability

IEC 60904-5:2011

Edition 2.0 (2011-02-17)

Photovoltaic devices - Part 5: Determination of the equivalent cell temperature (ECT) of

photovoltaic (PV) devices by the open-circuit voltage method

IEC 60904-7:2008

Edition 3.0 (2008-11-26)

Photovoltaic devices - Part 7: Computation of the spectral mismatch correction for

measurements of photovoltaic devices

IEC 60904-8:2014

Edition 3.0 (2014-05-08)

Photovoltaic devices - Part 8: Measurement of spectral responsivity of a PV device

Complete standards published by TC 82 can be found on at this link:

http://www.iec.ch/dyn/www/f?p=103:23:0::::FSP_ORG_ID,FSP_LANG_ID:1276,25


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The process of manufacturing solar modules involves the followingsteps:

1.

Segregation and Cell testing

2.

Tabbing

3.

Stringing

4.

Lamination

5.

Testing with sun simulator and tagging with RFID reader

6.

Silicone taping and Framing

7.

Bypass diode connections

1.

Segregation and Cell Testing

The incoming solar cells are already processed with anti-reflective coating, screen

printing and BSF (Back Surface Field=250m) coating. The incoming cells with silver

lining are first tested. The silver lining on the cells has very less thickness sincemore open

area is needed to capture the sunlight. The front part of the cell is made n-type by using

phosphorous metal on silicon and therear surface is made p-type diffusing boron.

2.

Tabbing:

Tabbing wire is used to connect the solar cells in series to get the desired voltage. The

tabbingwire should be 18-20 mm thick to get better current. A good tab wireis made out of

copper coated with solder for easy flow.


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Bus Wire (Connecting wire): Similar to tab wire but it is muchwider and used to carry

the current across the cell and can rangefrom 2.5mm to 5mm depending on the power and

size of the cell. It ismade out of copper coated with solder. At the end of the tabbingprocess,

2 pairs of positive and negative terminals are left out forfurther connection into the bypass

diodes which are fixed at the endof the whole process.

3.

Stringing:Process where the solar cells are connected inseries. Standard module sizes are 6 x 3,

6 x 6, 6 x10 and 6 x12. At the end of the process weget a cell module. After this process the

module is sent for lamination.

4.

Lamination:

The cell module so obtained is covered with Ethylene Vinyl Acetate (EVA) sheetsat

the top and bottom which reduces the loss of electrical conductivity and also reducing the

CTM (cell to module) loss. High transmission glass (having low iron content) is fixed onthe top EVA and the bottom EVA is covered with a back cover which is made up of PVF

(Poly Vinyl Fluoride) made of TPT (Tedlar Polyester Tedlar). The TPT is made up of

multi-laminated sheets andpossesses highdurability, impermeability, insolubility, erosion

durability, mechanical stability, hydrophobic property.


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In the laminator, renise sheets are used to avoid sticking of the EVA sheets. The

elasticity of EVA and toughness of TPT gives the solar cell better astigmatic property and

comprehensive protections. The laminator is a double vacuum chamber with temperature

around 100C which melts EVA in about 8-10 mins. Once the lamination is completed, the

structure so obtained is sent to the curing oven where the cross-linking of the EVA sheettakes place. After curing, the edges of module are sharpened and sent for testing.

5.Testing with Sun Simulator and RFID reader

The module is placed on a sun simulator. A beam is made incident on the module

which has a spectrum similar to the sun spectrum. This simulates the IV characteristics

(upside down characteristics of a forward biased diode) and provides the specifications

about the modules.

Radio Frequency Identification (RFID)

RFID is a method for Automatic Identification and Data Capture (AIDC). It is

wireless use of electromagnetic fields to transfer data for automatically identifying and

tracking purpose. The tags contain electronically stored data. The RFID reader and writer

feeds the data related to the module to RFID tag placed on the solar module. Unlike a

barcode, the tag does not necessarily need to be within line of sight of the reader, and may

be embedded in the tracked object.


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Data sheet of an SPV module of 60 cells

6.

Silicone Taping and Framing

Once the modules are cleared from testing, they are sent for silicone taping and framing.

Silicone taping is done to protect the modules fromwater.


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Silicones:

Alternating silicon-oxygen chains with hydrogen attached to the remaining silicon

bonds form the ubiquitous silicon-based polymeric materials known as silicones. These

compounds containing silicon-oxygen and occasionally silicon-carbon bonds have thecapability to act as bonding intermediates between glass and organic compounds, and to

form polymers with useful properties such as impermeability to water, flexibility and

resistance to chemical attack. Silicones are often used in waterproofing treatments,

moulding compounds, mould-release agents, mechanical seals, high temperature greases

andwaxes, and caulking compounds.

Once the silicone taping is done, the modules are framed withaluminium metal and

the name plate with the specifications is alsoplaced.

7.

Bypass diodeconnections

While selecting bypass diodes or blocking diodes, Imaxis taken into consideration. Bypass

diodes are used in parallel with either a single or a number of photovoltaic solar cells to

prevent the current(s) flowing from unshaded solar cells overheating and burning out

weaker or partially shaded solar cells. Bypass diode hence provides current path around the

weaker cell. Bypass diodes in solar panels are connected in parallel with a photovoltaic cell

or panel to shunt the current around it, whereas blocking diodes are connected in series

with the PV panels to prevent current flowing back into them.


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Two types of diodes are available as bypass diodes in solar panels and arrays: the pn-

junction Silicon diode and the Schottky diode. Both are available with a wide range of

current ratings. The Schottky barrier diode has a much lower forward voltage drop of

about 0.4V as opposed to the PN diodes 0.7Vdrop for a Silicon device.

This lower voltage drop allows a savings of one full PV cell in eachseries branch of

the solar array therefore; the array is more efficient since less power is dissipated in the

blocking diode. Mostmanufacturers include both blocking diodes and bypass diodes in

their solar panels simplifying the design.

SPV Modules:


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Special Features:

High energy conversion efficiency because of high fill factor.

Cells sorted by power and current to minimize field mismatch losses.

Electroluminescence test carried out for micro-cracks.


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5. INVERTERS

Inverter converts DC output of PV panels into a clean AC current for AC appliances

or fed back into grid line. Inverter is a critical component used in any PV system where

alternative current (AC) power output is needed.Basically there are two types of inverters, they are:

String inverter

Central inverter

5.1

STRING INVERTER:

A string inverter is commonly used in home and commercial solar power systems and

is often situated some distance away from the solar array. Depending on the size of the

installation, there may be more than one string inverters for a solar power plant.


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5.1 CENTRAL INVERTER:

Central inverters are designed for applications such as large arrays installed on buildings,

industrial facilities as well as field installations - they are basically just a very large string

inverter.


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6. TRACKERS

A solar tracker is a device that orients a payload toward the sun. Payloads can be

photovoltaic panels, reflectors, lenses or otheroptical devices.

In concentrated photovoltaic (CPV) and concentrated solar thermal (CSP)

applications, trackers are used to enable the optical components in the CPV and CSP

systems. The optics in concentrated solar applications accepts the direct component of

sunlight light and therefore must be oriented appropriately to collect energy. Tracking

systems are found in all concentrator applications because such systems do not produce

energy unless pointed at the sun.

The sun travels through 360 East to West per day, but from the perspective of any

fixed location the visible portion is 180 during an average 1/2 day period (more in spring

and summer; less, in fall and winter). Local horizon effects reduce this somewhat, making

the effective motion about 150. A solar panel in a fixed orientation between the dawn and

sunset extremes will see a motion of 75 to either side, and thus, according to the table

above, will lose 75% of the energy in the morning and evening. Rotating the panels to the

east and west can help recapture those losses. A tracker rotating in the East-West direction

is known as a single-axis tracker.

The sun also moves through 46 North and South during a year. The same set of

panels set at the midpoint between the two local extremes will thus see the sun move 23on either side, causing losses of 8.3%. A tracker that accounts for both the daily and seasonal

motions is known as a dual-axis tracker. Generally speaking, the losses due to seasonal angle

changes are complicated by changes in the length of the day, increasing collection in the summer

in northern or southern latitudes. This biases collection toward the summer, so if the panels are

tilted closer to the average summer angles, the total yearly losses are reduced compared to a system

tilted at the spring/fall solstice angle (which is the same as the site's latitude).

The primary benefit of a tracking system is to collect solar energy for the longest period ofthe day, and with the most accurate alignment as the Sun's position shifts with the seasons.

In addition, the greater the level of concentration employed, the more important accurate

tracking becomes, because the proportion of energy derived from direct radiation is higher, and

the region wherethat concentrated energy is focused becomes smaller.


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There are mainly two types of trackers:

1. Single-Axis tracker: Single axis trackers have one degree of freedomthat acts as an axis

of rotation. The axis of rotation of single axistrackers is typically aligned along a true North

meridian.

2. Dual-Axis tracker: Dual axis trackers have two degrees of freedom that act as axes of

rotation which are normal to oneanother. The axis that is fixed with respect to the ground

can be considered a primary axis. The axis that is referenced to the primary axis can be

considered a secondary axis.

6.1 SINGLE AXIS TRACKERS:

1.

HSAT: Horizontal Single Axis TrackerThe axis of rotation for horizontal single axis tracker is horizontal with respect to the

ground. The posts at either end of the axis of rotationof a horizontal single axis tracker can

be shared between trackers tolower the installation cost.

Field layouts with horizontal single axis trackers are very flexible. Thesimple geometry

means that keeping all of the axes of rotationparallel to one another is all that is required for

appropriatelypositioning the trackers with respect to one another.

Appropriate spacing can maximize the ratio of energy production to cost, this beingdependent upon local terrain and shading conditions and the time-of-day value of the

energy produced. Backtracking is onemeans of computing the disposition of panels.

Horizontal trackers typically have the face of the module orientedparallel to the axis of

rotation. As a module tracks, it sweeps acylinder that is rotationally symmetric around the

axis of rotation.


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2.

HTSAT: Horizontal Tilt Single Axis Tracker

In HSAT, the modules are mounted flat at 0, while in HTSAT;the modules are installed at

a certain tilt. It works on same principleasHSAT, keeping the axis of tube horizontal in N-S

line and rotating the solar modules E-W throughout the day. These trackers are usually

suitable in high latitude locations but do not take as much land space as consumed by

Vertical single axis tracker (VSAT).


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3.VSAT: Vertical Single Axis Tracker

The axis of rotation for vertical single axis trackers is vertical withrespect to the

ground. These trackers rotate from East to West overthe course of the day. Such trackers

are more effective at highlatitudes than are horizontal axis trackers.Field layouts must consider shading to avoid unnecessary energy losses and to

optimize land utilization. Also optimization for dense packing is limited due to the

nature of the shading over the course ofa year.

Vertical single axis trackers typically have the face of the module oriented at an

angle with respect to the axis of rotation. As a module tracks, it sweeps a cone that is

rotationally symmetric around the axisof rotation.

4.

TSAT: Tilted Single Axis Tracker

All trackers with axes of rotation between horizontal and vertical areconsidered

tilted single axis trackers. Tracker tilt angles are often limited to reduce the wind profile

and decrease the elevated endheight.

Field layouts must consider shading to avoid unnecessary losses andto optimize

land utilization. With backtracking, they can be packed without shading perpendicular

to their axis of rotation at any density. However, the packing parallel to their axes of

rotation is limited by the tilt angle and the latitude.

Tilted single axis trackers typically have the face of the moduleoriented parallel to

the axis of rotation. As a module tracks, it sweepsa cylinder that is rotationally symmetric

around the axis of rotation.


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5.

PASAT: Polar Aligned Single Axis Tracker

This method is scientifically well known as the standard method of mounting a

telescope support structure. The tilted single axis is aligned to the polar star. It is

therefore called a polar aligned single axis tracker (PASAT). In this particularimplementation of a tiltedsingle axis tracker, the tilt angle is equal to the site latitude.

Thisaligns the tracker axis of rotation with the earths axis of rotation.

6.2

DUAL AXIS TRACKERS:

1.

TTDAT: Tip Tilt Dual Axis Tracker

A tip-tilt dual axis tracker is so-named because the panel array ismounted on the

top of a pole. Normally the E-W movement isdriven by rotating the array around the top

of the pole. On top of therotating bearing is a T- or H-shaped mechanism that provides

verticalrotation of the panels and provides the main mounting points for thearray. The

posts at either end of the primary axis of rotation of a tip-tilt dual axis tracker can be

shared between trackers to lowerinstallation costs.

Other such TTDAT trackers have a horizontal primary axis and a dependent

orthogonal axis. The vertical azimuthal axis is fixed. Thisallows for great flexibility of the

payload connection to the groundmounted equipment because there is no twisting of

the cablingaround the pole.

Field layouts with tiptilt dual axis trackers are very flexible.


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2.

AADAT: Azimuth Altitude Dual Axis Tracker

An azimuthaltitude dual axis tracker has its primary axis (the azimuthaxis) vertical

to the ground. The secondary axis (often called elevationaxis) is normal to the primary

axis. They are similar totip-tilt systems in operation, but they differ in the way the arrayis rotated for daily tracking. Instead of rotating the array around the top of the pole,

AADAT systems can use a large ring mounted on theground with the array mounted on

a series of rollers. The mainadvantage of this arrangement is the weight of the array is

distributedover a portion of the ring, as opposed to the single loading point of the pole

in the TTDAT. This allows AADAT to support much largerarrays.


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7. MAXIMUM POWER POINT TRACKING

Maximum Power Point Tracking (MPPT) is a technique used to get the maximum

power from one or more power plants. It is the purpose of the MPPT system to sample

the output of the cells and apply the proper resistance (load) to obtain maximum powerfor any given environmental conditions. MPPT devices are typically integrated into an

electric power converter system that provides voltage or current conversion, filtering, and

regulation for driving various loads, including power grids, batteries, or motors.

Solar inverters convert the DC power to AC power and may incorporate MPPT: such

inverters sample the output power (I-V curve) from the solar cell and apply the proper

resistance (load) so as to obtain maximum power.

Maximum power point is the product of the maximum voltage (Vmpp) and maximumcurrent (Impp). Some solar panels have a higher maximum power than others.

In the above graph, the line which intersects the IV-curve givesthe maximum power

transfer point.


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8. GRID SYNCHRONIZATION

Inverters are used in grid synchronization with the solar power plant. Special protective

devices are used to prevent the risk of danger in the event of mains interference. The more

the PV plants feed into the grid, greater are the demands placed on the grid services.If the feed-in power of the PV plants is greater than the capacity of the local grids, then

adjustable local grid transformers are used to regulate the voltage and prevent the upper

limit from being exceeded. This task can be performed by power storage systems.

When a large amount of power is being consumed, then the line voltage in these weak

grid lines decreases, thus the act of feeding in solar power counteracts this voltage drop and

in turn, supports the grid. Measures need to be taken to avoid excessive increasing in

voltage during the period when the feed-in is high and the consumption is low. Also, in thissituation the currents may also flow in reverse direction. Disconnection devices are used in

between the PV generating plant and the grid, which can disconnect the plant from the grid

in cases of repair, failure, etc. In smaller plants, ADD or manual disconnection is done.

ADD (Automatic Disconnecting Device):

ADD device monitors the energy feedback into the 230/400 V grid. If mains power is

switched off by the electricity supply company, or by a protective device, it is vital for small-

scale power plants to be disconnected within a few milliseconds. Monitoring the voltageand frequency and recognizing isolated (off-grid) operation are essential requirements for

any ADD.

MSD (Mains Switching Devices): Similar to the ADD; itmeasures the grid

impedance and is able to recognize power failure and cut-offs on the basis of

impedance jumps.


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9. MOMINPET POWER PLANT - 1 MW

Location: Mominpet, Sangareddy, Telangana.Production - 1 MW

Types of tracker system-Single axis, Single axis horizontal tiltand Dual axis

In single axis tracking system 19 modules are connected inseries to form one string.

Inverters used here are string inverters of capacity 17kW, for every 4 strings (76 modules)

one inverter is used.

Readings of an inverter at the time of visit:

Day: 16th

Dec 2014Time: 2:16 PM

Power 9771 W

Day 41.72 kWh

Total 76350 kWh

DC input current 13.6 A

DC input voltage 511 V

AC output current 12.6 AAC output voltage 236 V


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AC supply from inverters is stepped up to 11kV using transformer and finally

connected to the grid.

Transformer Specifications:

Rated kVA 1250Rated voltage HV 11000 V

LV 400 V

Rated current HV 65.6 A

LV 1804.2 A

Phases 3

Frequency 50 Hz

Switchyard which gives extra protection to the system contains components like

auxiliary relay, vacuum switch gear,over current and earth fault relay, trip circuit supervisionrelay, under voltage relay and master trip relay.

Vacuum switchgear:

Remote Terminal Units (RTU) are installed in all inverters and any fault at inverter level can

be identified by theoperator sitting in the control room with the help of SCADA system.

Number of lightning arrestors used - 1

PV arrays are earthed using GI Flat material.


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10.MIDJIL POWER PLANT - 10 MW

Each block with 12 rows has a motor for single axis tracking. Each row contains two

strings and each string contains 24modules in series. For every 8 strings i.e. 4 rows there

is one AJB (Array Junction Box). Number of inputs for AJB is 8 (+)inputs and 8 (-) inputsfrom total 8 strings

Fig: Internal circuit diagram of AJB

Fig: Internal circuit of AJB


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Fig: Single axis tracking setup

DC supply from AJBs is given to inverter. In this plant centralized inverters are

used. Inputs from 16 AJBs are connected to one AJB. Inverter consists of three parts.

(i) DC section

(ii)

IGBT section(iii)AC section

In total there are 9 inverters. Capacity of each inverter is630kW.


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DC to AC conversion happens in IGBT section. AC output from inverter is given to

380V/33kV transformer. Output from transformer is given to Ring Main Unit (RMU). Each

RMU has 1input and 2 outputs. Input terminal is connected to output of a transformer and one

of the output terminals of RMU isconnected to HT panel and the other is connected to RMU

of other transformer. The purpose of RMU is to form a ring busproviding an alternate path to

supply from transformer in case of any faulty condition that effects the connection between

transformer output and grid.

Fig: Ring Main Unit

HT panel is connected to switch yard which is installed withswitching devices and CTs

and PTs to measure energy being supplied to the grid.

Fig: Switchyard


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Protecting devices:

Lightning arrestors are installed for protection from lightning. In total there are 7

lightning arrestors.

Earthing is done to every AJB with GI Flat material andconnected to earth pit. Theseearth pits are internally connected to form a loop.

Fencing is done for protection from intruders.

SCADA system is also installed for identification of faults.

As of now generation of the plant is 6.5MW and construction for generation of

remaining 3.5 MW is under progression. PR of the plant is 82.07% and PLF is 24.56%- 30%.

The total area of plant is 68 acres.

Fig: Transformer


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Specifications:

kVA 2400

HV -33kV

Voltage at no-load LV1-380V

LV2-380V LV3-380 VRated current HV- 41.98ALV1- 1215.47ALV2- 1215.47ALV3-

1215.47A

Remote Terminal Units (RTU) are installed in all inverters and any fault at

inverter level can be identified by theoperator sitting in the control room with the help of

SCADA system.

Readings on SCADA monitor at the time of visit:

Day: 22 Dec 2014Time: 12:40 PM

Fig: Plant generation on the time of visit

Fig: Readings of one of the inverters


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11. ANALYSIS OF SOLAR POWER PLANT

11.1 SOLAR PLANT PERFORMANCE INDEX

Evaluating technical performance of a solar power plant is veryimportant for the

growth of solar PV industry. There are two solarplant performance indices. They are:

1.

Plant Load Factor

2.

Performance Ratio

1.

PLANT LOAD FACTOR:

The ratio of the total number of kWh supplied by a generator orgenerating station to the

total number of kWh which would havebeen supplied if the generator or generating station

had been operated continuously at its maximum continuous rating is called Plant Load

Factor. This is also known as Capacity Utilization Factor (CUF). PLF of a plant will

generally be around 22%.

2.

PERFORMANCE RATIO:

The performance ratio is a measure of the quality of a PV plant that is independent of

location and it therefore often described as a qualityfactor. The performance ratio (PR) is

stated as percentage and describes the relationship between the actual and theoretical

energy outputs ofthe PV plant. It thus shows the proportion of the energy that is actuallyavailable for export to the grid after deduction of energy loss (e.g. due to thermal losses and

conduction losses) and of energy consumption for operation.

The closer the PR value determined for a PV plant approaches 100%,the more efficiently

the respective PV plant is operating. In real life, a value of 100% cannot be achieved, as

unavoidable losses always arisewith the operation of the PV plant (e.g. thermal loss due to

heating of the PV modules). High-performance PV plants can however reach a

performance ratio of up to 80%.

Performance Ratio (PR) of a plant for a period of time = Energy

measured (kWh)/

(Irradiance (kWh/m2) on the panel x Active area of

PV module (m2) x PV module

efficiency)


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In the Indian solar context, CUF is perhaps the most overused word when it comes to

measuring a solar power plant performance. The interesting thing is, not many people

outside India understand the CUF because most of them use a much better metric

Performance Ratio (PR).

How CUF is calculated and how different it is from the globally accepted standard

of Performance Ratio (PR).

CHROSIS, a Germany based consulting firm, has published this excellent whitepaper on

the subject that gives some good insights on the subject.

Some of the highlights of the whitepaper are as follows:-

Capacity Utilisation Factor (CUF) =Energy measured (kWh) / (365*24*installed

capacity of the plant).So on one side, PR is a measure for the performance of a PV system taking into

account environmental factors (temperature, irradiation, etc.) and on the other side is

CUF that completely ignores all these factors and also the de-rating or degradation of the

panels.

Some more factors that can also be important when comparing PR vs. CUF:

PR will take into account the availability of the grid, CUF will not.

PR will take into account the minimum level of irradiation needed to generateelectrical energy, CUF will not.

PR will take into account irradiation levels at a given period of time, CUF will not

PR can be used as a tool to compare different solar PV systems with each other even

if they are located at different locations since all environmental factors will be taken into

account. Therefore only the design and the ability of the system to convert solar energy

into electrical energy will be compared with each other.

Therefore it is not convincing that the CUF is a good tool to provide insights into asolar PV system.


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An example of calculating PR:

To calculate the Performance Ratio (PR) of the installed 127 kWp SPVplant for January

Analysis period: Jan-2012

Measured total solar irradiation intensity in Jan-2012: 171 kWh/m2(Calculation below)

Generator area of the PV plant: 889 m2

Efficiency factor of the PV modules: 14.4%

Electrical energy actually exported by plant to grid: 16,833 kWh

PR= Actual reading of plant output in kWh p.m. / Calculated nominalplant output in

kWh p.m.

Calculated nominal plant output= Annual incident solar irradiation atthe generator surface

of the PV plant x relative efficiency of the PVplant modules=171 x 889 x 14.4%

=21,890 kWh

=> PR=16,833/21,890

=76.8%

Solar radiation data:

Jan-2012 Daily average solar intensity in W/m2

Day Average solar intensity in W/m2

1 251

2 258

3 257

4 242

5 171

6 221

7 242

8 184

9 251

10 225

11 105

12 241

13 244

14 243


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15 209

16 220

17 229

18 247

19 239

20 229

21 233

22 238

23 256

24 255

25 252

26 250

27 241

28 245

29 194

30 227

31 230

Daily Average 230 W/m2

Jan Total- 230 x 24 hrs x 31 days=171 kWh/m2


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11.2 POTENTIAL INDUCED DEGRADATION

Potential Induced Degradation is a very recent phenomenonthat has taken the solar

industry by surprise.

Introduction:Potential Induced Degradation (PID) is an undesirable property of some solar

modules. The factors that enable PID (voltage, heat andhumidity) exist on all photovoltaic

(PV) systems, but the effect doesnot occur on all or even most PV systems. According to

Dr. Peter Hacke of the National Renewable Energy Laboratory (NREL), All c-Si

[crystalline silicon] modules have elements of reversible and non- reversible [PID]

mechanisms. The key is to understand the extent towhich modules experience these

mechanisms.

PID was first recognized in the 1970s, and has been studiedsince. The rapid growth

in PV plant deployments, combined withdramatic reduction in module prices (and in some

cases, modulequality), has brought renewed interest in the phenomenon. Andbecause the

issue is highly technical, requiring at least someunderstanding of chemistry and physics, the

renewed interest hasbeen accompanied by substantial fear, uncertainty and doubt in the

market today.

The Causes of PID:

Potential Induced Degradation, as the designation implies, occurswhen the modules

voltage potential and leakage current drive ion mobility within the module between the

semiconductor material andother elements of the module (e.g. glass, mount and frame), as

shown in Figure 1, thus causing the modules power output capacity todegrade. The ion

mobility accelerates with humidity, temperature andvoltage potential. Tests have revealed

the relationship of mobility to temperature and humidity: Planar contact with the panel

surfacealso causes a capacitive coupling to the cells, resulting in a capacitiveleakage current

of varying strength. The PV system and environment interact to cause PID. Theconditions necessary for the occurrence ofPID involve:-

(i)

Environmental factors

(ii) System

(iii)Module

(iv) Cells.


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While the environment is set for each individual installation, it ispossible to prevent PID

by properly controlling only one of the factors

JOINT PRESS RELEASE FOR EU PVSEC 2011

Initial test conditions for potential induced degradation (PID) of solar modules developed

German testing institutes and solar companies present first step toward specific,

relevant PID test conditions

Test conditions make it possible to clearly, easily and quickly distinguish between

crystalline silicon modules that are stabilised against PID and those prone to PID

PVSEC Hamburg, 5 September 2011 Potential induced degradation (PID) has recently

been identified as a key factor impacting the energyyield of solar modules. Output of a solar

module can be reduced if themodule is exposed to high negative voltage between solar cells

and the ground during operation, especially in major plants. Basically, this effect is

reversible. It can also be avoided by implementing additionalsystem design measures. The

more economical option, however, isusing a technology that provides for modules or cells

that areresistantagainst PID.

A broadly accepted or even standardized test for PID resistance, which would

facilitate quick and easy assessment, is not available at present, though couple of solar

companies have obtainedPID test reports.Four independent institutes the Fraunhofer Institute for Solar Energy Systems

(ISE), Photovoltaic Institute Berlin (PI-Berlin), TV Rheinland and VDE Testing and

Certification Institute and theGerman Solar companies Q-Cells, Schott Solar and Solon

have defined conditions to test crystalline PV modules for their PID sensitivity. These

conditions were comprehensively checked for applicability andaccuracy in separating PID-

free products from items that are prone toPID.

The inspection was carried out at room temperature (25 Celsius) to provide a

simple test that would not require expensive special equipment. According to the

established parameters, negativevoltage of 1,000 volts is to be applied to the cells of a

module forseven days (168 hours) through the junction box.


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The front panels of all modules are covered with aluminiumfoil or a continuous

film of water and grounded, ensuring fullcomparability. A module will be deemed resistant

against PID ifpower output decreases by less than 5% during the test. Solon hadproduced

special modules that were prone to PID to confirm the test conditions relevance.

Significant losses in output were observedwhen testing these modules.When they were inspected at the institutes laboratories, PID-protected glass-

foil standard modules from series production atQ-Cells, Solon and Schott achieved output

reductions of less than 5%,proving that they are resistant against PID. A cross check with

an unrepresentative sample of modules from other brand manufacturers procured in the

market revealed a loss of output of significantly more than 50% for some modules. This

means a preliminary test design has been developed, which assesses crystalline solar

modules sensitivityto PID in a simple, specific and relevant manner and separatesmodules

that are prone to PID from their PID-resistant counterparts.

However, it is not yet possible to draw conclusions on the long-term

performance of installed modules on the basis of these test conditions, as it will largely

depend on module wiring and climaticfactors. The involved institutes and companies are

committed tofurther developing PID tests into a general standard.

Conclusion:

Potential Induced Degradation can have profound adverse impact on the financingand operating of PV plants. While the entirePV system interacts to cause PID, the failure

mode occurs in themodules. Fortunately PID does not occur in all modules, and tests are

available to determine whether modules are susceptible or resistant to the effect. Many

module manufacturers have taken steps toproduce PID resistant modules. And for existing

c-Si modules that do experience PID, the effect is usually reversible with cost-effective

mitigation measures.

Because mitigating PID in the PV plant can increase initial system costs, a judiciouschoice of resistant modules and otherpreventative efforts, within the constraints of each

individual system, may be warranted. But it is also possible, of course, to intentionally

design a new PV plant with modules susceptible to PID if the savings from using such

modules is greater than the mitigation measures required. Refer to the Mitigating Panel

Polarization application notefor options using Advanced Energy inverters.


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The best solution for the industry long-term is to minimize or eliminate PID by

making design changes at the system, module and/or cell levels. Until then, it will remain

important for operators to overcome any fear, uncertainty, and doubt by becoming more

knowledgeable about PID, and hopefully the information and references provided here

help achieve that objective.

11.3 Fill Factor Impact

The short-circuit current and the open-circuit voltage are themaximum current and

voltage respectively from a solar cell. However,at both of these operating points, the power

from the solar cell iszero. The "fill factor", more commonly known by its abbreviationFF",

is a parameter which, in conjunction with Voc and Isc, determinesthe maximum power from

a solar cell. The FF is defined as the ratio ofthe maximum power from the solar cell to the

product of Voc and Isc.Graphically, the FF is a measure of the "squareness" of the solar celland is also the area of the largest rectangle which will fit in the IVcurve. The FF is illustrated

below.

Graph of cell output current (red line) and power (blue line) asfunction of voltage.

Also shown are the cell short-circuit current (Isc)and open-circuit voltage (Voc) points, as

well as the maximum power point (Vmp

, Imp

). Click on the graph to see how the curve

changes for acell with low FF.

As FF is a measure of the "squareness" of the IV curve, a solar cellwith a higher voltage

has a larger possible FF since the "rounded" portion of the IV curve takes up less area. The

maximum theoreticalFF from a solar cell can be determined by differentiating the power

from a solar cell with respect to voltage and finding where this isequal to zero.


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Hence:

However, the above technique does not yield a simple or closed formequation. Theequation above only relates Voc to Vmp, and extra equations are needed to find Imp andFF. A

more commonly usedexpression for the FF can be determined empirically as:

where Voc is defined as a "normalized Voc":

where n isIdeality factor

The above equations show that a higher voltage will have a higher possible FF.However, large variations in open-circuit voltage within a given material system are

relatively uncommon. For example, at onesun, the difference between the maximum open-

circuit voltagemeasured for a silicon laboratory device and a typical commercialsolar cell

is about 120 mV, giving maximum FF's respectively of 0.85 and 0.83. However, the

variation in maximum FF can be significant for solar cells made from different materials.

For example, a GaAs solarcell may have a FF approaching 0.89.

The above equation also demonstrates the importance of the ideality factor, alsoknown as the "n-factor" of a solar cell. The ideality factoris a measure of the junction quality

and the type of recombination in a solar cell. For the simple recombination mechanisms,

the n-factorhas a value of 1. However, some recombination mechanisms,particularly if they

are large, may introduce recombinationmechanisms of 2. A high n-value not only degrades

the FF, but since itwill also usually signal high recombination, it gives low open-circuit

voltages.

A key limitation in the equations described above is that theyrepresent a maximum

possible FF, although in practice the FF will be lower due to the presence of parasitic

resistive losses. Therefore, theFF is most commonly determined from measurement of the

IV curveand is defined as the maximum power divided by the product ofIsc*Voc, i.e.:


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Influence of FF:

The picture below illustrates the I-V curves of both a high fill factorsolar panel and a

low fill factor panel.

As can be seen, both curves (solar panels) hold the same open circuitvoltage and

short circuit current, however, the lower fill factor panelactually produces less power at its

maximum power point comparedto the higher fill factor panel.

During the manufacture of commercial grade solar panels, each andevery single solar

cell is tested for its fill factor. If its fill factor is low(below 0.7), the cells are sold off as Grade-

B cells, then sliced, andused for hobbyist use.

To make things clearer, look at the picture below.


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We can see that the dummy power (or the theoretical power) is thearea in red, and

the actual power is the area in the blue. The fill factoris the ratio of the blue area to the red

area. The higher the fill factorofa solar panel, the closer the blue curve is to the red curve.

One can say that a higher FF solar panel has less parasitic losses, i.e.,losses due to theseries and parallel resistances within the cell itself.

When commercial solar panels are labelled, they take the FF intoaccount, and only

measure the real power. When hobby cells arelabelled, you will see that most of the time

they will just states theshort circuit current and open circuit voltage.


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12. CASE STUDY

OFF GRID SOLAR POWER PLANT DESIGN:

Location: Narketpally, Nalgonda Dist., Telangana.

Latitude and Longitude: 17.2 and 79.2 respectively.Area of the site: 8 acres.

Fig: Site layout


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Solar PV system includes different components dependedon your system type, site

location and applications. The major components for solar PV system are solar charge

controller, inverter, battery bank, auxiliary energy sources and loads (appliances).

Total watt hours per day required on an average by allappliances in the nearby industry to

which power is to be supplied is 572500

The lowest month solar has a daily average of 4.1 kWh/ m2

/day and is observed in the

month of august.

This is equivalent to 4.1 hours of 1000 W/m2sunlight every day. Each Wp of the panel

would therefore deliver 4.1Wh/day.

Corrections that have to be considered include:

15% for temperature above 25 C 5% for losses due to sunlight not striking the panelstraight on (caused by glass

having increasing reflectance at lower angles of incidence)

10% for losses due to not receiving energy at the maximum power point (not

present if there is a MPPT controller)

5% allowance for dirt

10% allowance for the panel being below specification and for ageing

Total power = 0.85 x .95 x .90 x .95x .90 = 0.62 of the originalWp rating.

Accounting for losses, Panel Generation Factor (PGF) can be calculated as

4.1*0.62=2.54 Wh/Wp/day

Losses that have to be addressed by panel are

Wiring and connection losses about 10%

Losses in the battery about 20%

Total losses around 30%, so the panel will need to produce enough Wh/day for theload plus enough to cover the losses. So it will have to produce about 130% of the energy

required by the load


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To calculate the Wh/day needed from the panel, multiply the load Wh/day times 1.3

Minimum Wp (peak wattage) of the plant needed to meet loadrequirement is

= 572500*1.3/PGF

= 572500*1.3/2.54

=293012

So capacity of solar plant can install is approximately293kW.

PV Module Specification:

Pmax (Wp) = 255.55

Vmax =31.42

Imax = 8.13A

Voc= 37.59 VIsc= 8.7116 A

FF= 78.04%

Efficiency= 15.7%

Total number of PV modules required = 293012/255.55

= 1146.82

= 1147 (approx.)

Two blocks can be designed each of 12 rows. Each row can be made of two strings

with each string comprising of 24 modules in series. This setup needs in total of 1152

modulesand it is always a better choice to use a bit more number of modules than required.

One motor can be used for each block for the purpose of single axis tracking. If we

consider 4 rows as a group, there are 6 groups in total and each group can be arranged with

oneAJB. So there are 6 AJBs in total. 8 strings connected to oneAJB are arranged in parallel

configuration.

ELECTRICAL CALCULATION

Output voltage of each string = 24*31.42 =754.08 V Output current of each string = 8.13 A

Output voltage of each group = 754.08 V Output current of each group = 8.13*8=65.04 A

Dc Output Calculation:

Output power of each string = 754.08*8.13=6130.67 W

Output power of each group = 754.08*65.04=49045.36 W Output power of 6 groups =

294.3 kW


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Battery Size:

If battery of 48V is used

Battery Size (Ah) = (572500*1.3*1)/ (0.85*0.6*48) = 30402.4

Since formula for battery size is:

'0.85' accounts for battery losses 0.6 accounts for depth of discharge

Solar Charge Controller Sizing:

Its function is to regulate the voltage and currentfrom the solar arrays to the battery

in order to preventovercharging and also over discharging. According to standard practice,

the sizing of solar charge controller is to take the short circuit current (Isc) of the PV array,

and multiply it by 1.3

Solar charge controller sizing = Short circuit current of PV Array*1.3Isc of a module or

string = 8.7116 A

Number of strings = 48

Solar charge controller rating = 48*8.7116*1.3 =543.6 A

Inverter sizing:

An inverter is used in the system where AC power output is needed. Inverter cantolerate input up to 120% of itscapacity so a central inverter of size 280kW is suitable for

thispurpose.


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13. CONCLUSION

Solar radiation data is available from several sources including satellite simulations.

The data collection and simulation is a complex procedure and can have inaccuracies

varying from 3-20%. The most reliable data isground measured with accurate instruments.Capacity utilization factor (CUF) depends on several factors including the solar

radiation,temperature, air velocity apart from the module type andquality, angle of tilt (or

tracking), design parameters to avoid cable losses and efficiencies of inverters and

transformers. There are some inherent losses which can be reduced through proper

designing but not completely avoided. It would be desirable to monitor the solar plant

installations and build updatabase for future work.

How to reasonably utilize green energy and keepsustainable development is themost important challenge. Solar Photovoltaic power plants will play an important role inthe

overall energy supply. The grid parity is likely to be achieved around 2017-2020. We should

grasp the opportunity to build the most suitable environmental friendly solar PV power

plants, and welcome a better tomorrow.

Solar Photovoltaics: Principles, Application and case study

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