Solar Energy Book 2011-2012

8/11/2019 Solar Energy Book 2011-2012

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Benha University

Shoubra Faculty Of Engineering

Mech. Power Eng. Dep.

PVSolar Systemwith Cooling

Supervised By:

Prof. Dr /. Osama E. Abd Ellatif

2012


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PROJECT TEAM :( 2012)

Bola George Abd El Mesieh Farag

Hany Boshra Gerges Ghatas

John Salah Hanna Amgad

Saber Tawfik Sidhom Noaman

Wagdy Wagih Daoud


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ACKNOWLEDGEMENT

We owe a great many thanks to a great many people who helped

and supported us during working in that project. Our deepest thanks to

Professor Osama Ezzat the guide of the project for guiding and

correcting various information and documents of ours with attention

and care. He has taken pain to go through the project and make

necessary correction as and when needed.

We would also thank our Institution and our faculty members

without whom this project would have been a distant reality. We also

extend our heartfelt thanks to our family and well-wishers.

Your Sons,

Project Team


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ABSTRACT

The aim from this research is to study the behavior

of a photovoltaic monocrystalline cell under

cooling system to reach maximum efficiency.

The design of photovoltaic system and its

components will be illustrated with complete

details provided with computational experimentsand experimental work to study the whole system

and to get the optimum utilization in this study,

with mentioning the advantages of this system and

the difficulties facing the applying of this hopeful

project if we take all economical and technicalparameters into account.

These difficulties are owing to the little interest

here in Egypt towards this promising source of

clean energy, which easily can change the shape of

the future in Egypt and the lack of the available

financial resources.


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TABLE OF CONTENTS

Chapter One: Renewable Energy

1.1

Uses of Renewable Energy..1

1.2The Ultimate Renewable Energy...2

1.3 Forms & Types of Renewable Energy................3

1.3.1 Wind Energy.....4

1.3.2 Geothermal Energy6

1.3.3 Hydroelectricity......7

1.3.4 Biomass Energy......8

1.3.5 Waste Renewable Energy ......9

1.3.6 Solar Energy.....10

1.4 Uses of Solar Energy......10

1.5 Solar Energy Applications..11

1.6 WaterTreatment.14

Chapter Two: Solar Energy

2.1 Electricity Generation from Sun. .19

2.2 Sun Energy Reaches Earth ...20

2.3 Solar Constant Calculation.... 23

-Emissivty26


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-Solar angle27

Chapter Three: Photovoltaic System

3.1 How do Photovoltaics Work?...31

3.2 The photovoltaic effect...32

3.3. Electricity Generation.34

3.4. The Photovoltaic System .36

3.4.1. Photovoltaic System Components ...36

3.4.2. Photovoltaic Arrays Connections ..36

3.5.Type of Solar Panels....39

3.5.1 Monocrystalline Silicon Cells..40

3.5.2 Polycrystalline Silicon Cells..40

3.5.3 Thick -film Silicon...41

3.5.3 Amorphous Silicon.42

3.6. Charge Controller..43

3.7. Solar Batteries .44

3.8. Inverter ...45

3.9. Types of PV Systems ..46

3.9.1. Stand Alone Systems....46

3.9.2. Hybrid System ...47

3.9.3. Grid-Connected Systems ..47

3.10. Photovoltaic Benefits..49

3.11. Photovoltaic Limitations .....49


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Chapter Four: Tracking system

-What are solar trackers?......................................................................................................50

4.1How do solar trackers work?...........................................................................................51

4.2.Advantage of solar trackers.51

4.3. Disadvantages of solar trackers ....52

4.4. Types of Solar Trackers ...52

4.4.1. Single Axis Solar Tracker 53

4.4.2. Dual Axis Solar Tracker..56

4.3.5 Tracker type selection..58

4.5. Drive types ..59

4.5.1. Active tracker59

4.5.2 Passive tracker. 60

- Disadvantages ..61

4.6. What is the difference between a passive tracking system and an active tracking

system ? ..62

4.7. Choosing Solar Trackers.62

Chapter Five: Computational Fluid Dynamics

4.1. Operation ...64

4.2. Operating Equations...66

4.2.1. Navier-Stokes Equations .67

4.2.2. Incompressible Navier-Stokes Equations .68

4.2.3. Euler Equations ..69

4.2.4. Discrete Phase Modeling .70


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4.3. CFD Applications ...71

- Aerospace Applications .....71

-Automotive Applications 72

- Marine Applications ..73

4.4. Advantages of CFD...74

4.5. Limitations of CFD .75

Chapter SIX Experimental Work

6.1. Experiment component .80

6.2.cooling system description .86

6.3 The cooling system component..88

Chapter Seven: ExperimentAL Result

7.1. Experimental Results ....92

7.2. Computational

Results.....100

7.1.1Gambit work.......100

7.2.2Modeling parameters....102

7.2.3 Modeling solving .102

7.2.4 CFD Rusult ...103

Conclusion ......105

4. Multimeters .88

...89

6. DC Motor with Gear Box .89


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7. 12 Volts Lamp. 90

8. Tracking System ......90

9. Phynometer .91

Chapter: Results and Conclusion

7.1. Experimental

Results....95

7.2. Computational Results...105

8. Conclusion .....107


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` V Solar System With cooling

Graduation project 2012 Page 1

IIInnntttrrroooddduuuccctttiiiooonnn

Renewable Energy Generally, renewable energy projects are used on alarge scale, however, this does not mean that renewable energy cannot be

used in smaller areas such as villages or more generally rural areas. A

clear example can be seen in Kenya, where it is estimated that roughly

30,000 small solar power units with a capacity of 20 to 100 watts are sold

every year. This is the largest solar ownership rate in the world for

residential communities. There are some renewable energy technologies

that are disliked for being unreliable but at the same time if you are to look

at the renewable energy market it seems to be growing every day.

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Renewable energy is of many uses and it can support small as

well large applications. Renewable energy from wind, sun and

geothermal is used to produce electricity and heat for use. The

solar power plants are used to generate electricity and steam

for industrial projects. The energy form the geothermal heat is

used to heat radiators in the homes. Thus the renewable

energy sources can viably help users to their heat homes.

Some other applications of renewable energy sources include

heating space, ventilation, day lighting, space cooling, water

heating, mechanical energy to cut woods and grinding grains.

The renewable energy sources and the technologies

associated with them are equally important to households and

industry.


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Of all the renewable energy sources, solar energy holds the most

promise for providing a sustainable energy source. The GermanAdvisory Council on Global Change is forecasting that by 2100 solar

power will be the largest source of global energy.

Scientists estimate that our Sun will continue producing solar energy

for another 5 billion years! Talk about a sustainable energy source!

We definitely do not have to worry about running out of solar energy.

It is the ultimate renewable energy available to us.

In one hour enough sunlight reaches the Earth to supply its energy needsfor an entire year. So not only is it sustainable, but it provides more than

enough energy for our needs. We just need to continue improving our solar

technology so that we can capture more of this energy and put it to

productive use.

Reduced Dependence on Fossil Fuels

Solar energy production does not require fossil fuels and is therefore less

dependent on this limited and expensive natural resource. Although there isvariability in the amount and timing of sunlight over the day, season and

year, a properly sized and configured system can be designed to be highly

reliable while providing long-term, fixed price electricity supply.

Global warming and solar energy

The use of fuels like oil and gas in homes, cars and industry has brought us

to the problem of global warming. The extreme production of harmful gases

like carbon monoxide has destroyed the ozone layer hence we receive both

the harmful and harmless sunrays. The extreme pollution in our planet has

disturbed the smooth working of our echo system. This has resulted in

lower rainfalls and dries weather. The use of sun to support industrial

processes can help us overcome the worst situation of global warming. It


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can also help us stop destroying our fertile land from the harmful waste

resulting from industrial processes.

Flexible Locations

Solar power production facilities can be installed at the customer site which

reduces required investments in production and transportation

infrastructure.

Matching Peak Time Output with Peak Time Demand

Solar energy can effectively supplement electricity supply from an

electricity transmission grid, such as when electricity demand peaks in the

summer.

Modularity and Scalability

As the size and generating capacity of a solar system are a function of the

number of solar modules installed, applications of solar technology are

readily scalable and versatile.


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111...333...111WWWiiinnndddEEEnnneeerrrgggyyy

The first major form of renewable energy is wind power. Wind has

been an energy source for a very long time. It was used by the

Renewable Energy.

Fig. 1.1 Wind Turbine


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Chinese about 4000 years ago to pump water for their crops and by

sailors to sail around the world. The energy in wind can be used by

making a tower which stands high above the sea level with a large

propeller at the top. What the wind does is it basically blows the

propeller round and round which in turn helps produce electricity. Bybuilding not just one but multiple of these towers you can produce

more electricity at once. The most suitable area to build these wind

turbines would be in coastal areas, tops of hills, open fields or

basically anywhere the winds are strong and continuous.

Wind energy is a teeming energy source which never seems to

expire. Hence human race cannot go out of it unless we exist. This

plentiful and powerful natural resource can replace conventional

electricity production procedures.

Moreover the power generation from wind turbines does not pollute

the air. It is one of the worlds fastest emerging energy sources for

electricity production.

The traditional methods of producing electricity have resulted in

climate changes because of high rate pollution it discharges. Wind

power turbines can provide clean electricity which can cover its cost

in 5 to 6 months easily.

Wind turbines have been most popular energy source in

Europe because of its environment nature and no harm to

animals and human beings. Wind mills are also liked by their

aesthetic features, because they tend to increase the beauty of

the land.

A windmill gives us great impression, even If we observe it

from miles. This is the only power plant that has so far killed no

human being during the process of electricity. The design and

structure of wind mills is equally sturdy and beautiful.


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They are designed so well that they can even withstand

tornadoes. Thus we need to build more wind mills in suitable

regions as a substitute for conventional and expensive

electricity power houses to rectify and recover the climate

disasters.

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As its name refers geo thermal energy is the energy which is

extracted from the heat of the sun that is why it falls under the

renewable energy. This energy is present into the earth due to the

decay of minerals and absorption of sunlight by earth. Geothermal

heat has innumerable applications form the ancient times it wasearlier used for bathing and space heating. However, now this

immense source of energy is used for producing electricity mostly.

Geothermal energy is a reliable, cost effective and inexhaustible

energy reservoir. Geothermal electric energy can be extracted from

the earth by installing heat exchangers into the earth. This

geothermal energy can or cannot be used with electricity in order to

support heating applications. The energy for the geothermal heat

pumps can be pulled out by earth tubes and heat exchangers. Theheat from the earth can be directly transferred to the radiators for

heating homes.

Fig.1.2 Binary Cycle Power Plant


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Hydroelectricity is the production of electricity from the falling water.Hydroelectricity power plant is the renewable energy source and itdoes not generate any harmful chemicals and gases during theprocess of electricity generation. This electricity accounts forapproximately 20% of the world electricity and it comprises total 88%of the renewable energy sources.

The different types of hydroelectricity come from the water stored indams; these dams convert the potential energy present in the water

to the electricity with the support of generators. The amount of energywhich can be pulled out from water depends upon the working ofHead (difference of height between the source and water flow).

Fig.1.3 Hydroelectric Power Plant


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Biomass energy is another form of renewable energy source and it is

derived from living or dead organisms like plants, waste and alcohol

mostly. Biomass energy is getting widespread popularity nowadays.

Biomass energy source is most often derived from plants either to

generate electricity or to produce heat.

Sources of Biomass Energy

Biomass energy is derived form various sources which help ingenerating sufficient energy for use. The various source of generatingenergy from biomass are wood, waste, alcohol, garbage, landfillgases. Wood is either taken from trees or from the waste of industrialprocesses. The waste material of industry like paper making is reallyhelpful in providing pulping liquor. The second major source of

deriving biomass energy is from the solid waste. This solid waste iseither provided by municipality waste or industrial waste. Whenenergy is extracted either from alcohol or from the fiber present in thecorn, it is termed as ethanol fuel. This ethanol fuel is really helpful inproviding fuel to the cars and farm tractors.

Biomass energy can also be extracted from various kinds of plantslike polar, willow, hemp, corn, miscanthus, sugar cane, spice trees,eucalyptus, palm oil, switch grass and sorghum.

Advantages and Disadvantages of Biomass Energy

The biomass is used and produced throughout the world. It is themost inexpensive way of producing electricity. So far it looks like aninexhaustible natural resource. Biomass energy as a renewableenergy source is capable of replacing fossil fuels.


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On this earthly planet, human beings are busy to spend their lives.They need energy to perform their daily activities. This energy comesfrom food, oxygen in the air and water. After consuming theseresources there is a lot more production of waste material. This wastematerial if not disposed properly would surely harm the environmentwhich ultimately is dangerous for human beings. With the evergrowing population, there is need to not only disposed this wasterather by taking some advantage out of waste renewable energy

Fig.1.4 Energy Production from Waste Process


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Solar power ( or ) Solar Energy:

is the energy we derive form from rays and heat of sun. It is in usefrom the time immemorial. However it is now that mankind hasrealized its importance as a safe and inexpensive energy source. Theenergy from the sun can be used to overcome the energy crisisgenerated by the scarcity of resources like oil and gas. Solar energy

is free and it is everywhere. That is why now more and morecountries have switched to processes which help them conserve theheat and light from sun.

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*Residential*

The number of PV installations on buildings connected to the electricity grid

has grown in recent years. Government subsidy programs (particularly in

Germany and Japan) and green pricing policies of utilities or electricity

service providers have stimulated demand. Demand is also driven by the

desire of individuals or companies to obtain their electricity from a clean,

non-polluting, renewable source. These consumers are usually willing to

pay only a small premium for renewable energy. Increasingly, the incentive

is an attractive financial return on the investment through the sale of solarelectricity at premium feed-in tariff rates.

In solar systems connected to the electricity grid, the PV system supplies

electricity to the building and any daytime excess may be exported to the

grid. Batteries are not required because the grid supplies any extra


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demand. However, to be independent of the grid supply, battery storage is

needed to provide power at night.

Holiday or vacation homes without access to the electricity grid can use

solar systems more cost-effectively than if the grid was extended to reachthe location. Remote homes in sunny locations can obtain reliable

electricity to meet basic needs with a simple system comprising of a PV

panel, a rechargeable battery to store the energy captured during daylight

hours, a regulator (or charge controller), and the necessary wiring and

switches. Such systems are often called solar home systems (SHS).

*Commercial*

On an office building, roof areas can be covered with glass PV modules,which can be semi-transparent to provide shaded light. On a factory or

warehouse, large roof areas are the best location for solar modules. If the

roof is flat, then arrays can be mounted using techniques that do not

breach the weatherproofed roof membrane. Also, skylights can be partially

coveredwith PV.

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We have always used solar energy as far back as humans have existed onthis planet. We know today, that there are multiple uses of solar energy. We

use the solar energy every day in many different ways. When we hang

laundry outside to dry in the sun, we are using the solar heat to do work,

drying our clothes. Plants use the solar light to make food. Animals eat

plants for food.

Solar energy refers primarily to the use of solar radiation for practical ends.However, all renewable energies, other than geothermal and tidal, derive

their energy from the sun.

Solar technologies are broadly characterized as either passive or activedepending on the way they capture, convert and distribute sunlight. Active


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solar techniques use photovoltaic panels, pumps, and fans to convert

sunlight into useful outputs. Passive solar techniques include selecting

materials with favorable thermal properties, designing spaces that naturally

circulate air, and referencing the position of a building to the Sun. Active

solar technologies increase the supply of energy and are considered supply

side technologies, while passive solar technologies reduce the need for

alternate resources and are generally considered demand side technologies.

Solar Thermal

Solar thermal technologies can be used for water heating, space heating,

and space cooling and process heat generation.

Water Heating

Solar hot water systems use sunlight to heat water. In low geographical

latitudes (below 40 degrees) from 60 to 70% of the domestic hot water use

with temperatures up to 60 C can be provided by solar heating systems.

The most common types of solar water heaters are evacuated tube.

Fig 1. 5

Solar Water Heaters


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Collectors (44%) and glazed flat plate collectors (34%) generally used for

domestic hot water; and unglazed plastic collectors (21%) used mainly to

heat swimming pools.

Heating, Cooling and Ventilation

Fig. 1.5.1 Solar House

Solar House: of Massachusetts Institute of Technology in the United

States, built in 1939, used seasonal thermal storage for year-roundheating. In the United States, heating, ventilation.

1.

A solar chimney (or thermal chimney, in this context) is a passive solar

ventilation system composed of a vertical shaft connecting the interior

and exterior of a building. As the chimney warms, the air inside is

heated causing an updraft that pulls air through the building.

Performance can be improved by using glazing and thermal mass


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materials in a way that mimics greenhouses. Deciduous trees and

plants have been promoted as a means of controlling solar heating

and cooling. When planted on the southern side of a building, their

leaves provide shade during the summer, while the bare limbs allow

light to pass during the winter with winter solar availability.

1.6Water Treatment

Fig.1 .6 Small Scale Solar Powered Sewerage Treatment

Plant

2. Solar distillation

Can be used to make saline or brackish water potable. The first recorded

instance of this was by 16th century Arab alchemists. A large-scale solar

distillation project was first constructed in 1872 in the Chilean mining town

of Las Salinas. The plant, which had solar collection area of 4,700 m2, could


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produce up to 22,700 L per day and operated for 40 years. Individual still

designs include single-slope, double-slope (or greenhouse type), vertical,

conical, inverted absorber, multi-wick, and multiple effect. These stills can

operate in passive, active, or hybrid modes. Double-slope stills are the most

economical for decentralized domestic purposes; while active multiple effect

units are more suitable for large-scale applications.

Fig.1 .7 Compare between solar and wind energy in kwh


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Fig.1 .8 System Availability and Capacity Factor


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Fig.1 .9 Compare between solar and wind energy in kwh


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VSolar System W ith cooling


SSSuuunnn:::

Is the star at the center of the Solar System. It is almostperfectly spherical and consists of hot plasma interwoven withmagnetic fields. It has a diameter of about 1,392,000 km, about109 times that of Earth, and its mass (about 21030 kilograms,330,000 times that of Earth). The Sun is by far the largestobject in theolar system. It contains more than 99.8% of thetotal mass of the Solar System (Jupiter contains most of therest). Chemically the Sun is, at present, about 70% Hydrogen,and 28% Helium by mass, everything else (Metals") is lessthan 2%. This changes slowly over time as the Sun converts

hydrogen to helium in its core.

Fig. 2.1 Sun Properties


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The Sun radiant power comes from nuclear fusion processes, duringwhich the sun loses 4.3 million tons of mass each second. This massis converted into radiant energy; each square meter of the sunssurface emits a radiant power of 63.1 MW, which means that just afifth of a square kilo-meter of the suns surface emits an amount ofenergy equal to the global primary energy demand on earth.

Fig. 2.2 Sun internal Layers


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The Sun's energy output in each second is the result of

conversion of about 700,000,000 tons of hydrogen into

695,000,000 tons of helium and 5,000,000 tons of energy (386

billion billion megawatts) is produced by Nuclear Fusion

reactions. As it travels out toward the surface, the energy is

continuously absorbed and re-emitted at lower and lower

temperatures so that by the time it reaches the surface of the

Sun, it is primarily visible light. For the last 20% of the way to

the surface, the energy is carried more by Convection than by

radiation. The surface of the Sun, called the photosphere, is at

a temperature of about 5800 K.

A small region known as the chromospheres lies above the

photosphere, the highly rarefied region above the

chromospheres, called the corona, extends millions of

kilometers into space but is visible only during a total solar

eclipse (left). Temperatures in the corona are over 1,000,000 K.

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The sun fusion process generates intense energy that travels

outwards as electromagnetic radiation. Electromagnetic

radiation from the Sun takes the form of visible light (41%),

Ultra violet, X rays, and Gamma rays (9%), and shortwave

infrared energy (50%).

The heat energy received by a surface perpendicular to the

sun's rays, outside the atmosphere would be a relatively

constant 1365 watts per square meter. This is called the solar

constant.


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Isolation refers to incoming solar radiation.

The total dai ly is olat ion at a place on th e earth's

sur face is determined by:

a. The angle of the sun's rays.

b.The amount of time a place is exposed to the sun's rays.

c. The amount of clouds, dust, and water vapor in the

atmosphere.

Isolation also varies with latitude and the seasonal changes produced

by the tilt of earths axis in its orbit around the sun.

For the earth as a whole, insolation must equal long-wave radiation to

space.

However*low latitudes (0 - 40 North and South) receive more insolation

than they emit to space (energy surplus). Higher latitudes (40 - 90 North

and South) emit more radiation to space than they receive (energy deficit).

The electromagnetic radiation emitted by the sun shows a wide range of

wavelengths. It can be divided into two major regions with respect to the

capability of ionizing atoms in radiation-absorbing matter:

a) Ionizing radiation (X-rays and gamma-rays) and

b) Non-ionizing radiation (UVR, visible light, and infrared

radiation)


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Fig. 2.3 Solar electro spectrum

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Fig. 2.4 Solar irradiance Calculation


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S = (E 4 R2) / (4 r

2) = E (R

2/ r

2)

S = Solar Constant

E = 6.4 x 107 W/m2 = Surface Irradiance of the sun

R = 6.96 x 105 km = Radius of the sun

r = 1.51 x 108 km =Average Sun Earth Distance

Then S = 1367 W/m2


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SSSooolllaaarrrAAAnnngggllleeesss

The geometric relationships between a plane of any - particular

orientation relative to the earth at any time (whether that plane is

fixed or moving Relative to the earth) and the incoming beam solar

radiation that is, these Angles and the relationships between them

are as follows:


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LLLaaatttiiitttuuudddeee,,,

That is the angular locat ion north o r sout h of the

Equator no r th po s i t ive -90 < < 90

DDDeeecccllliiinnnaaatttiiiooonnn,,,

That is the angular posit ion of the sun at solar

noon With respect to the plane of the equator ,

north p osit ive.

-23. 450 < < 23 450

SSSlllooopppeee,,,

That is, the angle between the plane surface in

quest ion

And the horizontal 0 < 90 mean that

the sur face has a down ward fac ing component .

SSSuuurrrfffaaaccceeeaaazzziiimmmuuuttthhhaaannngggllleee,,,

that is, the deviat ion o f the project ion o n a

ho r izon tal plan of the norm al to the surface from

the local meridian With zero due sou th, east

negat ives west posit ive -180 < < 180


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HHHooouuurrraaannngggllleee,,,

That is, the angular disp lacement of the sun east

or west of the local meridian due to rotat ion o f the

earth on its axis at 150 per hour morn ing negat ive

afternoon pos it ive Pract ical Work 18 .

AAAnnngggllleeeooofffiiinnnccciiidddeeennnccceee,,,

That is the angle between the beam radiat ion on a

Surface and the no rmal to that su rface.

os = Sin Sin Cos - Sin Cos Sin Cos

+ Cos Cos Cos Cos + Cos Sin Sin Cos

Cos + Cos Sin Sin Sin


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PPPhhhoootttooovvvooollltttaaaiiicccSSSyyysssttteeemmm


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IIINNNTTTRRROOODDDUUUCCCTTTIIIOOONNN

Photovoltaics (PV),offer consumers the ability to generate electricity in a

clean, quiet and reliable way.

Photovoltaic systems are comprised of photovoltaic cells, which converts

sunlight otni electricity using solar cells. Because the source of light is

usually the sun, they are often called solar cells.

The word photovoltaic comes from photo, meaning light, and voltaic,

which refers to producing electricity. Therefore, the photovoltaic process is

producing electricity directly from sunlight. Photovoltaic are often referred

to as PV.

Semiconductor materials such as silicon, gallium arsenide, cadmium

telluride are used in these solar cells. The crystalline Solar cell is the most

commonly used variety. During 2006, these had a worldwide market share

of 95 per cent.

Fig.3.1 Photovoltaic Array


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Photovoltaics is the direct conversion of light into electricity at the atomic

level. Some materials exhibit a property known as the photoelectric effect

that causes them to absorb photons of light and release electrons.

Fig.3.2 How solar cell work


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The photoelectric effect was first noted by a French physicist,

Edmund Bequerel, in 1839, who found that certain materials would

produce small amounts of electric current when exposed to light. In

1905, Albert Einstein described the nature of light and the

photoelectric effect on which photovoltaic technology is based, for

which he later won a Nobel prize in physics. The first photovoltaic

module was built by Bell Laboratories in 1954. It was billed as a solar

battery and was mostly just a curiosity as it was too expensive to gain

widespread use. In the 1960s, the space industry began to make the

first serious use of the technology to provide power aboard

spacecraft. Through the space programs, the technology advanced,its reliability was established, and the cost began to decline. During

the energy crisis in the 1970s, photovoltaic technology gained

recognition as a source of power for non-space applications.

Fig.3.3 Photovoltaic Array


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The diagram above illustrates the operation of a basic photovoltaic cell,

also called a solar cell. Solar cells are made of the same kinds of

semiconductor materials, such as silicon, used in the microelectronicsindustry. For solar cells, a thin semiconductor wafer is specially treated to

form an electric field, positive on one side and negative on the other. When

light energy strikes the solar cell, electrons are knocked loose from the

atoms in the semiconductor material. If electrical conductors are attached

to the positive and negative sides, forming an electrical circuit, the

electrons can be captured in the form of an electric current -- that is,

electricity. This electricity can then be used to power a load, such as a light

or a tool.

A number of solar cells electrically connected to each other and mounted in

a support structure or frame is called a photovoltaic module. Modules are

designed to supply electricity at a certain voltage, such as a common 12

volts system. The current produced is directly dependent on how much light

strikes the module.

Fig.3.3 Difference between a Cell, Module and Array


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Multiple modules can be wired together to form an array. In general,

the larger the area of a module or array, the more electricity that will

be produced. Photovoltaic modules and arrays produce direct-current

(dc) electricity. They can be connected in both series and parallel

electrical arrangements to produce any required voltage and current

combination.

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Fig.3.4 Operation of Photovoltaic Cell


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Light, including sunlight, is sometimes described as particles called"photons." As sunlight strikes a photovoltaic cell, photons move into

the cell. When a photon strikes an electron, it dislodges it, leaving an

empty "hole". The loose electron moves toward the top layer of the

cell. As photons continue to enter the cell, electrons continue to be

dislodged and move upwards.

If an electrical path exists outside the cell between the top grid and

the Backplane of the cell, a flow of electrons begins. Loose electronsmove out the top of the cell and into the external electrical circuit.

Electrons from further back in the circuit move up to fill the empty

electron holes. Most cells produce a voltage of about one-half volt,

regardless of the surface area of the cell. However, the larger the cell,

the more current it will produce.

Current and voltage are affected by the resistance of the circuit thecell is in. The amount of available light affects current production. The

temperature of the cell affects its voltage. Knowing the electrical

performance characteristics of a photovoltaic power supply is

important, and is covered in the next section.


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a PV system consists of a number of interconnected components

designed to accomplish a desired task, which may be to feed

electricity into the main distribution grid, to pump water from a well, topower a small calculator or any of possible uses of solar generated

electricity, the design of the system depends on the task it must

perform, the location and other site conditions under which it must

operates.

333...444...111...PPPhhhoootttooovvvooollltttaaaiiicccSSSyyysssttteeemmmCCCooommmpppooonnneeennntttsss:::

1. Solar Panel (module).

2. Charge Controller.

3. Storage (Solar Batteries).

4. Inverter.

Fig.3.5 Photovoltaic System Components

333...444...222...PPPhhhoootttooovvvooollltttaaaiiicccAAArrrrrraaayyysssCCCooonnnnnneeeccctttiiiooonnnsss

In many applications the power available from one module is

inadequate for the load. Individual modules can be connected in

series, parallel, or both to increase either output voltage or current.

This also increases the output power.


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When modules are connected in parallel, the current increases. For

example, three modules which produce 15 volts and 3 amps each,

connected in parallel, will produce 15 volts and 9 amps.

Fig.3.6 Parallel Connection

If the system includes a battery storage system, a reverse flow of

current from the batteries through the photovoltaic array can occur at

night. This flow will drain power from the batteries. A diode is used to

stop this reverse current flow. Diodes are electrical devices which

only allow current to flow in one direction.


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If the same three modules are connected in series, the output voltage

will be 45 volts, and the current will be 3 amps.

Fig. 3.7 Series Connection

If one module in a series string fails, it provides so much resistancethat other modules in the string may not be able to operate either. A

bypass path around the disabled module will eliminate this problem.

Many modules are supplied with a bypass diode right at theirelectrical terminals. Larger modules may consist of three groups ofcells, each with its own bypass diode.

Isolation diodes are used to prevent the power from the rest of anarray from flowing through a damaged series string of modules. Theyoperate like a blocking diode.


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They are normally required when the array produces 48 volts or

more. If isolation diodes are used on every series string, a blocking

diode is normally not required.

Fig. 3.8 Series and Parallel Modules Connected Together

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All PV cells consist of two or more thin layers of semi-conducting material,

most commonly silicon. When the semiconductor is exposed to light,

electrical charges are generated and this can be conducted away by metal

contacts as direct current (DC). The electrical output from a single cell issmall, so multiple cells are connected together to form a "string", which

produces a direct current.


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333...555...111MMMooonnnooocccrrryyyssstttaaalllllliiinnneeeSSSiiillliiicccooonnnCCCeeellllllsss

These are made using cells sliced from a single cylindrical crystal of

silicon, this is the most efficient photovoltaic technology, typically

converting around 15% of the sun's energy into electricity. The

manufacturing process required to produce monocrystalline silicon is

complicated, resulting in slightly higher costs than other technologies.

Fig.3.9 Monocrystalline silicon cell

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Also sometimes known as multicrystalline cells, these are made

from cells cut from an ingot of melted and recrystallised silicon.

The ingots are then saw-cut into very thin wafers and

assembled into complete cells; they are generally cheaper to

produce than monocrystalline cells, due to the simpler

manufacturing process, but they tend to be slightly less

efficient, with average efficiencies of around 12%.


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Fig.3.10 Polycrystalline Silicon Cells

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This is a variant on multicrystalline technology where the silicon is

deposited in a continuous process onto a base material giving a fine

grained, sparkling appearance. Like all crystalline PV, it is normally

encapsulated in a transparent insulating polymer with a tempered

glass cover and then bound into a metal framed module.

Fig.3.11 Thick film Silicon


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Amorphous silicon cells are made by depositing silicon in a thin

homogenous layer onto a substrate rather than creating a rigid crystal

structure. As amorphous silicon absorbs light more effectively than

crystalline silicon, the cells can be thinner - hence its alternative

name of "thin film" PV. Amorphous silicon can be deposited on a wide

range of substrates, both rigid and flexible, which makes it ideal for

curved surfaces or bonding directly onto roofing materials. This

technology is however less efficient than using crystalline silicon, with

typical efficiencies of around 6%, but it tends to be easier and

cheaper to produce. If roof space is not restricted, an amorphousproduct can be a good option; but if the maximum output per square

metre is required, specifiers should choose a crystalline technology.

Fig.3.12 Amorphous Silicon


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333...666...CCChhhaaarrrgggeeeCCCooonnntttrrrooolllllleeerrr

A Solar Charge Controller is a device that is installed directly in

between your solar panel and battery bank and it helps protect your

batteries from overcharging/discharging, and also helps to prevent an

overload or short circuit in your system. They are great for helping

you keep your batteries working to their optimal level. Additionally, a

good solar charge controller can also help to prevent the battery bank

from reverse charging a solar panel acting as a blocking diode if

your solar panel system does not have a one-way diode already

installed. Most Solar Charge Controllers can be used with a 12volt or

24volt battery bank system and can handle anywhere from 50 watts

to 400 watts of power.

Fig.3.13 Charge Controller


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333...777...SSSooolllaaarrrBBBaaatttttteeerrriiieeesss

Solar energy systems use a lead-acid deep cycle battery or

accumulator. This type of battery is different from a conventional car

battery, as it is designed to be more tolerant of the kind of ongoing

charging and discharging you would expect when you have variable

sun from day to day. Deep cycle batteries last longer but they also

cost more than a conventional battery. The major difference between

lead acid batteries and other batteries is that they have solid lead

plates; in conventional car batteries, the plate is made of a sponge-

like material. This difference is not easily seen, but is internal, the

units rating and electrical properties for discharging will indicate the

needed information.

Fig. 3.14 Solar Batteries


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Inverter The purpose of a solar inverter is to convert the DC output poweroutput from photovoltaic modules into a clean 50 or 60 Hz AC current sine

wave. This DC output is then directly applied to the commercial electrical

grid or to a local off grid electrical network. Communication to the inverter

can also be included in order to monitor the operating conditions, provide

firmware updates, to control the inverter grid connections and report on the

output power.

Fig.3.15 Inverter to Convert DC to AC


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333...999...111...SSStttaaannndddAAAlllooonnneeeSSSyyysssttteeemmmsss

As its name suggests this type of PV system is a separate electricity

supply system. It supplies electricity to a single system and is connected

only to that system. This means that it is not linked to the mains

electricity supply. Usually a standalone system includes one or more

batteries, used to store the electricity.

Fig.3.17 Stand Alone Direct Coupled System

Fig.3.16 Stand Alone System with A Battery Operating DC and AC Loads


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A hybrid system combines PV with other forms of power generation,

usually a diesel generator. Biogas is also used. The other form of

power generation is usually a type which is able to modulate power

output as a function of demand. However more than one form of

renewable energy may be used e.g. wind and solar. The photovoltaic

power generation serves to reduce the consumption of non-

renewable fuel.

Fig.3.17 Hybrid Power System

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A large number of photovoltaic systems installed in industrial nationstoday are grid connected. An inverter converts the direct current (DC)

voltage of the modules to the two-phase or three-phase AC voltage of

the public grid. The inverter usually has an integrated MPP tracker

which operates the PV generator at the maximum power point.


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However, the voltage and current generated by the PV modules must

fit within the inverter range. If PV modules are connected in series,

their voltage adds to the total voltage, whereas the current of parallel

PV modules adds to the total current. Photovoltaic inverters only

operate at rated power for a very few hours in any year, as, due to

changes in solar irradiance, they work predominantly at part load.

Therefore, it is very important that inverters have high efficiencies,

even when operating at these part loads. A representative efficiency

is used to compare different inverters, the so-calledEuro efficiency.

This is clearer than the term average efficiency, and is the average

efficiency for typical European irradiance conditions.

Fig.3.18 Grid Connected System


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Solar electric systems offer many advantages,

including the following: They are safe, clean and quiet to operate;

They are highly reliable;

They require virtually no maintenance;

They operate cost-effectively in remote areas and for many

residential and commercial applications.

They are flexible and can be expanded at any time to meet your

electrical needs.

They give you increased autonomy independence from the grid or

backup during outages.

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You should also be aware of the practical limitations of PV systems:

PV systems are not well suited for highly energy-intensive uses such

as heating. If you wish to use solar energy for this purpose, consider

other alternatives such as a solar water heater, which produces heat

much more efficiently.

- Grid-connected systems are rarely economical, primarily because

the current cost of the PV technology is much higher than the cost ofconventional energy. Since these systems can be expensive,

choosing a solar electric power system often comes down to a

personal lifestyle decision just like the type of house or car you

might own.


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WWWhhhaaatttaaarrreeesssooolllaaarrrtttrrraaaccckkkeeerrrsss???

Solar trackers are racks for photovoltaic modules that move to point

at or near the sun throughout the day. Trackers add to the efficiency

of the system, reducing its size and the cost per KWH.

A tracking system can increase the output of your PV system by up to

30 in the summer and 15 in the winter over non-tracked systems.

Tracking systems are usually classified as being either passive or

active. In a passive system the tracker follows the sun from east to

west without using any type of electric motor to power the movement.

Instead the system rotates from a combination of heat and gravity.

Because no external source of electricity is needed such systems are

ideal for remote off-the-grid scenarios or use with water pumping

systems where peak the peak demand is in the summer.

Tracking systems are also sometimes classified as to the number of

axis they track against. Simple one axis systems rotate only left to

right rather than in an arch. A two axis tracking system will track both

left to right and up and down. This allows it more accurately to follow

the true arch of the sun throughout the day.


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4.1. How do solar trackers work?

A solar tracker automatically follows the sun during the course of a day and

throughout the seasons of the year.

Fig.4.1 solar tracking doing

4.2. Advantage of solar trackers

The main reason to use a solar tracker is to reduce the cost of the

energy you want to capture. A tracker produces more power over a

longer time than a stationary array with the same number of modules.

This additional output or gain can be quantified as a percentage of

the output of the stationary array. Gain varies significantly with

latitude, climate, and the type of tracker you chooseas well as the


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orientation of a stationary installation in the same location. (The

energy required to move the tracker is insignificant in these

calculations.) Climate is the most important factor. The more sun and

less clouds, moisture, haze, dust, and smog, the greater the gain

provided by trackers. At higher latitudes gain will be increased due to

the long arc of the summer sun. In the cloudiest, haziest locations the

gain in annual output

4.3. Disadvantages of solar trackers

Trackers add cost and maintenance to the system - if they add 25% to the

cost, and improve the output by 25%, the same performance can be

obtained by making the system 25% larger, eliminating associated

maintenance.

4.4. Types of Solar Trackers

Tracking systems are classified by the number and orientation of their

axes.

There are two basic tracker types:

Dual-axis trackers full tracking)

Move on two axes to point directly at the sun, taking maximum

advantage of the suns energy.


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Single-axis trackers

Follow the sun accurately enough that their output can be very close

to full tracking. Trackers need not point directly at the sun to be

effective. If the aim is off by ten degrees the output is still 98.5% of

the full-tracking maximum.

Photovoltaic trackers that operate with a single axis can increase

solar power output by approximately 30%, while a two axis tracker

can further increase output by up to 6% and possibly more when

compared to a fixed solar panel system.

Considering that the solar PV industry continually strives to improve

solar cell conversion performance by a single percentage point, or

less, an increase of 36% over fixed panel performance is impressive.

Solar trackers can boost daily energy production significantly.

Choosing what solar tracker to install simply comes down to

comparing the extra investment and cost of maintenance over time

against the increased solar energy and financial yield delivered by the

unit.

4.4.1. Single Axis Solar Tracker

The single axis tracker typically has one degree of freedom that acts

as an axis of rotation typically aligned along a true North meridian.

Most are programmed to automatically follow the sun throughout the

course of the day while compensating for the seasons of the year.

Some units permit manual adjustment of the tilt on the polar axis in


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response to seasonal changes in the sun's orbit.

There are several common types of single axis trackers:

Horizontal Single Axis Tracker (HSAT)

Fig. 4. 2 Horizontal Single Axis Trackers (HSAT)

The HSAT axis of rotation is horizontal to the ground with the face of the

solar panel array oriented parallel to the axis of rotation. As the system

tracks, it sweeps a cylindrical arc to track the visible motion of the sun

throughout the day.

The benefit of the one axis design is that support posts at either end of the

single axis of rotation can be shared between tracking systems to lower the


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cost of installation. Trackers can be easily positioned in close proximity for

commercial and utility scale solar power applications.

Vertical Single Axis Tracker (VSAT)

The VSAT axis of rotation is vertical to the ground with the face of the solar

panel array oriented at an angle with respect to the axis of rotation. As the

system tracks, it sweeps a cone-shaped arc to track the visible motion of

the sun throughout the day.

Tilted Single Axis Tracker (TSAT)

Fig. 4. 3 Tilted Single Axis Trackers (TSAT)


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The TSAT axis of rotation is neither horizontal nor vertical to the

ground; itsany angle between horizontal and vertical with the face of

the solar panel array oriented parallel to the axis of rotation. As the

system tracks, it sweeps a cylindrical arc to track the visible motion ofthe sun throughout the day.

4.4.2. Dual Axis Solar Tracker

Two axis trackers typically have two degrees of freedom that acts as

axes of rotation typically normal to one another. The axis that's fixed

with respect to the ground is its primary axis, while the axis that'sreferenced to the primary axis is its secondary axis. Most dual axis solar

trackers are programmed to automatically follow the sun throughout

the course of the day while compensating for the seasons of the year.

There are two common types of dual axis trackers:

Tip-Tilt Dual Axis Tracker (TTDAT)

Fig. 4. 4Tip-Tilt Dual Axis Tracker (TTDAT)


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The TTDAT has its primary axis of rotation horizontal to the ground with its

secondary axis normal to the primary axis. The axes of these trackers are

typically aligned either along a true north meridian or an east west line of

latitude, but they are very flexible and can be aligned in any cardinal

direction desired.

Azimuth-Altitude Dual Axis Tracker (AADAT)

Fig. 4. 5 Azimuth-Altitude Dual Axis Trackers (AADAT)

The AADAT has its primary axis of rotation vertical to the ground with its

secondary axis normal to the primary axis. Like a telescope mount, one

axis is vertical allowing the system to orient to a compass point while the

second axis is a horizontal pivot, enabling the solar panel array to point to

any sky location. As it's a non-precision orientation, this type of tracker only


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works best with solar panel systems rather than some types of

concentrating PV collectors.

4.3.5 Tracker type selection

The selection of tracker type is dependent on many factors including

installation size, electric rates, government incentives, land constraints,

latitude, and local weather.

Horizontal single axis trackers are typically used for large distributed

generation projects and utility scale projects. The combination of

energy improvement and lower product cost and lower installation

complexity results in compelling economics in large deployments. In

addition the strong afternoon performance is particularly desirable for

large grid-tied photovoltaic systems so that production will match the

peak demand time. Horizontal single axis trackers also add a

substantial amount of productivity during the spring and summer

seasons when the sun is high in the sky. The inherent robustness of

their supporting structure and the simplicity of the mechanism also

result in high reliability which keeps maintenance costs low. Since the

panels are horizontal, they can be compactly placed on the axle tube

without danger of self-shading and are also readily accessible for

cleaning.

A vertical axis tracker pivots only about a vertical axle, with the

panels either vertical, at a fixed, adjustable, or tracked elevation


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angle. Such trackers with fixed or (seasonally) adjustable angles are

suitable for high latitudes, where the apparent solar path is not

especially high, but which leads to long days in summer, with the sun

travelling through a long arc.

Dual axis trackers are typically used in smaller residential installations

and locations with very high government feed in tariff.

4.5. Drive types

4.5.1. Active tracker

Active trackers : use motors and gear trains to direct the tracker as

commanded by a controller responding to the solar direction.

In order to control and manage the movement of these massive structures

special slewing drives are designed and rigorously tested. The

technologies used to direct the tracker are constantly evolving and recent

developments at Google and Eternegy have included the use of wire-ropes

and winches to replace some of the more costly and more fragile

components.

Counter rotating slewing drives sandwiching a fixed angle support can be

applied to create a "multi-axis" tracking method which eliminates rotation

relative to longitudinal alignment. This method if placed on a column orpillar it will generate more electricity than fixed PV and its PV array will

never rotate into a parking lot drive lane. It will also allow for maximum

solar generation in virtually any parking lot lane/row orientation, including

circular or curvilinear.
http://en.wikipedia.org/wiki/Slewing_Drivehttp://en.wikipedia.org/wiki/Slewing_drivehttp://en.wikipedia.org/wiki/Slewing_drivehttp://en.wikipedia.org/wiki/Slewing_Drive


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Active two-axis trackers are also used to orient heliostats - movable

mirrors that reflect sunlight toward the absorber of a central power

station. As each mirror in a large field will have an individual

orientation these are controlled programmatically through a central

computer system, which also allows the system to be shut down

when necessary.

Light-sensing trackers typically have two photosensors, such as

photodiodes,configured differentially so that they output a null when

receiving the same light flux. Mechanically, they should be

omnidirectional (i.e. flat) and are aimed 90 degrees apart. This will

cause the steepest part of their cosine transfer functions to balance at

the steepest part, which translates into maximum sensitivity. For

more information about controllers seeactive daylighting.

Since the motors consume energy, one wants to use them only as

necessary. So instead of a continuous motion, the heliostat is moved

in discrete steps. Also, if the light is below some threshold therewould not be enough power generated to warrant reorientation. This

is also true when there is not enough difference in light level from one

direction to another, such as when clouds are passing overhead.

Consideration must be made to keep the tracker from wasting energy

during cloudy periods.

4.5.2Passive tracker

Passive trackers : use a low boiling point compressed gas fluid that

is driven to one side or the other (by solar heat creating gas pressure)

to cause the tracker to move in response to an imbalance. As this is a
http://en.wikipedia.org/wiki/Heliostathttp://en.wikipedia.org/wiki/Solar_power_towerhttp://en.wikipedia.org/wiki/Solar_power_towerhttp://en.wikipedia.org/wiki/Photosensorhttp://en.wikipedia.org/wiki/Photodiodeshttp://en.wikipedia.org/wiki/Active_daylightinghttp://en.wikipedia.org/wiki/Active_daylightinghttp://en.wikipedia.org/wiki/Active_daylightinghttp://en.wikipedia.org/wiki/Photodiodeshttp://en.wikipedia.org/wiki/Photosensorhttp://en.wikipedia.org/wiki/Solar_power_towerhttp://en.wikipedia.org/wiki/Solar_power_towerhttp://en.wikipedia.org/wiki/Heliostat


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non-precision orientation it is unsuitable for certain types of

concentrating photovoltaic collectors but works fine for common PV

panel types. These will have viscous dampers to prevent excessive

motion in response to wind gusts. Shader/reflectors are used to

reflect early morning sunlight to "wake up" the panel and tilt it toward

the sun, which can take nearly an hour. The time to do this can be

greatly reduced by adding a self-releasing tie down that positions the

panel slightly past the zenith (so that the fluid does not have to

overcome gravity) and using the tie down in the evening. (A slack-

pulling spring will prevent release in windy overnight conditions.)

The term "passive tracker" is also used for photovoltaic modules that

include a hologram behind stripes of photovoltaic cells. That way,

sunlight passes through the transparent part of the module and

reflects on the hologram. This allows sunlight to hit the cell from

behind, thereby increasing the module's efficiency. Also, the module

does not have to move since the hologram always reflects sunlight

from the correct angle towards the cells.

Disadvantages

Trackers add cost and maintenance to the system - if they add 25% to the

cost, and improve the output by 25%, the same performance can be

obtained by making the system 25% larger, eliminating associated

maintenance.


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4.6. What is the difference between a passive

tracking system and an active tracking system

?

An active tracking system is kind of ground mounted system

that actively moves to track the suns position throughout the

day with the use of special optic sensors. This ensures that

the panels achieve the maximum amount of energy

generation A passive tracking system uses the suns heat to

move a liquid inside the panel from side to side, physically

moving the dev ice towards the area of optimum sunlight.

4.7. Choosing Solar Trackers

Single axis tracking systems can be more cost-effective for large

commercial power installations. Their relatively simpler components result

in less maintenance and installation costs and their lower profile creates

less shadow thereby permitting closer positioning of solar modules. They

offer a definite energy yield advantage over fixed angle solar installations.

Double axis trackers are more cost-effective for smaller, residential solar

power installations when coupled with high Feed-in Tariff programs. Their

greater number of moving parts results in additional installation and

maintenance costs, and their higher profile requires greater space between

units, but this can be offset by the increased efficiency they offer, especially


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in northern climates.

Unfortunately, not all solar panel installers promote the benefits of solar

tracking systems claiming they are prone to breakdowns and over

expensive. Neither is the case! Today's tracker technology ensures near

trouble free operation and the significant increase in energy they

produce results in a quicker system payback.

Some solar installation companies that discourage tracking don't

have the know-how to install trackers, or they cannot supply them,

or they opt for quick profits by hurrying to their next job not willing

to spend the extra time connecting them. If you live in a northern

climate and the installer won't recommend solar trackers, dump

him and find one that's better-qualified who will. You'll benefit in

the long run.

The benefit of solar trackers like


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Chapter five

Computational Fluid

Dynamics

CFD


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Graduation project 2012 Page65

Simplifying assumptions are made in order to make the

problem tractable (e.g., steady-state, incompressible, in

viscid, two-dimensional).

Provide appropriate boundary and initial conditions for the

problem

CFD applies numerical methods (called discretization) to

develop algebraic equations to approximate the governing

differential equations of fluid mechanics in the domain tobe studied.

Governing differential equations to algebraic.

The collection of cells is called the grid or mesh.

The system of algebraic equations are solved numerically

(on a computer) for the flow field variables at each nodeor cell.

System of equations are solved (usually through iterations)

to provide solution.

The final solution is post-processed to extract quantities of

interest (e.g. lift, drag, heat transfer, separation points,

pressure loss, etc.).

In CFD we wish to solve mathematical equations which

govern fluid flow, heat transfer, and related phenomena

for a given physical problem.


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5.2.Operating EquationsNavier-Stokes equations

Most general.

Can handle wide range of physics.

Incompressible Navier-Stokes equations

Assumes density is constant.

Energy equation is decoupled from continuity and momentum

equations if all fluid properties are constant.

Euler equations

Neglect all viscous terms.

Reasonable approximation for high speed flows (thin boundary

layers).

Can couple with boundary layer equations to determine viscous

effects.


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Other equations and models

Turbulence modeling equations.

Thermodynamics relations and equations of state.

Discrete phase equations for particles.

5.2.1.Navier-Stokes Equations:

Conservat ion o f Mass

Conservation of Momentum

Conservation of Energy

Equation of State


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Property Relations

Navier-Stokes equations provide the most general model

of single-phase

fluid flow/heat transfer phenomena.

Five equations for five unknowns: , p, u, v, w.

The computation costs are high.

Requires additional turbulence model, i.e., additional

equation(s) in order to solve turbulent flows for practical

engineering problems.

5.2.2.Incompressible Navier-Stokes Equations:

Conservation of Mass

Conservation of Momentum


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Simple form of the Navier-Stokes equat ions w hich assume;

incompressible flow

constant properties

For isothermal flows, we have four unknowns: p, u, v, w.

Energy equation is decoupled from the flow equations in this case.

Can be solved separately from the flow equations.

Can be used for flows of liquids and gases at low Mach number.

Still require a turbulence model for turbulent flows.

5.2.3.Euler Equations

Neglecting all viscous terms in the Navier-Stokes equations yields

the Euler equations:

No transport properties (viscosity or thermal conductivity) are needed.

Momentum and energy equations are greatly simplified.

But we still have five unknowns: r, p, u, v, w.


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The Euler equations provide a reasonable model of compressible

fluid flows at high speeds (where viscous effects are confined to

narrow zones near wall boundaries).

5.2.4.Discrete Phase Modeling

We can simulate secondary phases in the flows (either liquid or solid) using

a discrete phase model.

This model is applicable to relatively low particle volume fractions (< %10-

12 by volume)

Model individual particles by constructing a force balance on the moving

Particle.

Assuming the particle is spherical (diameter D), its trajectory is

governed by


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Applications of discrete phase modeling

Sprays.

Coal and Liquid Fuel Combustion.

Particle Laden Flows (Sand Particles in An Air Stream).

5.2.7.CFD Applications

Aerospace Applications

CFD methods are now widely used in most aerospace applications for the

purpose of predicting component performance and as an integral part of

the design cycle. The applications are numerous and we will only list few

examples

here.


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The first example

Is flow around an aircraft. Wind tunnel tests require substantial scaling

which leads to some difficulties of matching the important flow parameters.

If we attempt to model the correct Mach number, the Reynolds number willbe substantially lower than the full scale Reynolds number leading to errors

in the modeled shear stress and other flow features. It is also very

expensive to replicate altitude conditions within a wind tunnel.

Fig.5.1 Grid and flow solution for a civil aircraft with nacelles

Automotive Applications

In automotive applications CFD is nowadays used in a large number ofareas including engine components, auxiliary systems and also for

modeling the

aerodynamics of the car to minimize drag and optimize the down force

tidier


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various operating conditions. Figure shows two examples of

automotiveapplications. Figure shows the flow field around a family car

obtained using CFD

methods.

Fig.5.2 Flow around a car

Marine Applications


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Fig.5.3 Flow around marine ship

5.3.Advantages of CFD

Low Cost

Using physical experiments and tests to get essential engineering data for

design can be expensive.

Computational simulations are relatively inexpensive, and costs are likely to

decrease as computers become more powerful.

Speed CFD simulations can be executed in a short period of time.

Quick turnaround means engineering data can be introduced early in the

design process.

Ability to Simulate Real Conditions

Many flow and heat transfer processes cannot be (easily) tested - e.g.

hypersonic flow at Mach 20

CFD provides the ability to theoretically simulate any physical condition.

Ability to Simulate Ideal Conditions

CFD allows great control over the physical process, and provides the ability

to isolate specific phenomena for study.


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Example: a heat transfer process can be idealized with adiabatic, constant

heat flux, or constant temperature boundaries.

Comprehensive Information

Experiments only permit data to be extracted at a limited number of

locations in the system (e.g. pressure and temperature probes, heat flux

gauges, LDV, etc.)

CFD allows the analyst to examine a large number of locations in the region

of interest, and yields a comprehensive set of flow parameters for

examination.

5.4.Limitations of CFD

-Physical Models

CFD solutions rely upon physical models of real world processes (e.g.

turbulence, compressibility, chemistry, multiphase flow, etc.).

The solutions that are obtained through CFD can only be as accurate as the

physical models on which they are based.

Numerical Errors

Solving equations on a computer invariably introduces numerical errors

Round-off error - errors due to finite word size available on the computer

Truncation error - error due to approximations in the numerical models

Round-off errors will always exist (though they should be small in most

cases)

Truncation errors will go to zero as the grid is refined - so mesh refinement

is one way to deal with truncation error.


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EEExxxpppeeerrriiimmmeeennntttaaalllWWWooorrrkkk


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IIInnntttrrroooddduuuccctttiiiooonnn

The photovoltaic panel efficiency decreases further during the

operational period by increasing the cells temperature above a

certain limit. In addition, reflection of the suns irradiance from

the panel typically reduces the electrical yield of PV modules by 8-

15%. To increase the efficiency of PV systems one way is cooling

them during operation period. One method for cooling

photovoltaic module is to flow a film of water over the PV module

to decrease its temperature. By using this method reflection

would also be reduced and therefore the electrical efficiency will

improve.

In this chapter we deal with the solar radiation that incident on

photovoltaic cells. The cell plate has an area of 0.52 m2. The output

electric power generated from the cell is fed to the solar battery.

There is a film cooling system to decrease the cell temperature so

that cell output power increase.

The present wo rk was carr ied out on two solar cell

cases:

30 titledsolar cell with horizontal and faces to south without

cooling.

30 titled solar cell with horizontal and faces to south with cooling.


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For every posi t ion the fo l lowing readings areobtained:

Solar Flux Q in W/m2, this reading is taken every hour from the

sun rise to the sun set.

The Volt and Ampere output from the cell, with and without charge

controller these readings are obtained using the digital Voltmeter,

which reads the Volts and Ampere according to the position used.

Solar cell back surface temperature by using five thermocouple

types K inserted on the back surface.

Air ambient temperature by using thermocouple type K inserted in

a shadow area.

Calculation of solar cell surface temperature by taken the

temperature difference between the back and front surface into

consideration.

Calculation of the output power produced by multiplying the output

Volt V output Ampere I

Power= V I= watts

Calculations of the cell efficiency. This calculation is based on

the following formula:


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Where

V= Output Voltage of the cell in Volts.

I = Output Current of the cell in Amperes.

Q= Solar Flux in W/m2.

A = Area of the cell plate in m2.

These readings and calculat ion s are perform edevery ho ur from sun r ise to sun set. The output

resul ts wi l l b e shown later .

The following figure presents the experimental

system used in this project:


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6.1. Experimental Cad layout

Fig. 6.2. actual layout


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6.1. Experiment component

111...SSSooolllaaarrrPPPaaannneeelll

Fig. 6.2 Monocrystaline module inclined on a 30 alumital

Stand


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Mono-crystalline panel containing 40 cells.

Panel dimension (85.5 66) cm.

Panel Area = 0.52 m

Maximum output = 20 V

222...SSSooolllaaarrrBBBaaatttttteeerrriiieeesss

Fig. 6.2. actual layout

12 volt- acid lead solar battery.

24 ampere hour


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.

222...CCChhhaaarrrgggeeeCCCooonnntttrrrooolllllleeerrr

6.4 Fig. Charge Controller


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444...MMMuuullltttiiimmmeeettteeerrrsss

6.5 Fig. Multimeters


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555... 333000 dddeeegggrrreeeeeeAAAllluuummm...SSStttaaannnddd

AAAllluuummm...SSStttaaannndddwwwiiittthhhdddiiimmmeeennntttiiiooonnn:::

999444***111000333***555666cccmmm

Fig 6.6 30degree alumital Stand


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666... 111222 vvvooollltttssslllaaammmppp

Fig 6.7 12 volts lamp

777...solar power meter

It is used to measu re solar irradiance on

a surface


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Fig. 6.8. solar power meter

6.2.cooling system description


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Fig. 6.8. cooling system description

A cooling system was designed to reduce the solar cell

surface temperature and increase the cell out power. In

which closed loop cooling circuit was connected to take

water from water tank and pumping it by using 1.5 l/min

Dc pump through an holed hose that hold on alumital

Stand top. A film water flowing over the cell surface and

it then collected and discharged to the tank .and so on


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6.2. The cooling system component

1- Insulated galvanized steel tank

100 *91*20 water tank fabricated from galvanized steel mm and well

insulated by using 1 inch wool glass. The tank maximum capacity of

180 litters of fresh water .

Fig. 6.9. 180 littre water tank.


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2- 12-volt pump

6 watt dc pump connected on the tank outlet to pumping1.5 l/min fresh water.

Fig. 6.10. 12 v water pump.

3-Closed loop hoses & con

Documents

Solar Energy Book 2011-2012