printable rse slides

8/13/2019 Printable RSE Slides

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and theGreenhouse ffect

1. The impact of the greenhouse effect on planet

Earth

2. Greenhouse gases and their effects

3. Human activities have contributed to global

warming

4. The effects of global warming on people and

the land

OBJECTIVES:

What is the Greenhouse effect?

The greenhouse effect is the rise in temperature

that the Earth experiences because certain gases in

the atmosphere trap heat from the Suns rays.

Have you seen a greenhouse?

Most greenhouses look

like small glasshouses.

Green houses are used

to grow plants,especially in the

winter.

How do greenhouses work?

Greenhouses work by

trapping heat from the

sun.

The glass panels of the

greenhouse let in light

but keep heat from

escaping.


This causes the

greenhouse to heat up

much like the inside of

a car parked in

sunlight, and keeps the

plants warm enough to

live in the winter.


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The Greenhouse Effect

The Earthsatmosphere is all

around us. It is the air

we breathe.

Greenhouse gases in

the atmosphere behave

much like the glass

panes in a greenhouse.

The Greenhouse Effect

Sunshine enters the Earths atmospherepassing through the blanket of greenhouse

gases.

As it reaches the Earths surface, land,

water, and biosphere absorb the sunlights

energy! Once absorbed this energy is sent

back into the atmosphere.


Some of the energy

passes back into space.

Much of it remains

trapped in the

atmosphere by the

greenhouse gases,

causing our world to

heat up.

The greenhouse effect is important.

Without the greenhouse effect, the Earth would

not be warm enough for humans to live.

But if the greenhouse effect becomes stronger, it

could make the Earth warmer than usual.

Even a little warming

causes problems for

plants and animals.

Greenhouse Effect

Without these gases, heat would escape back into

space and Earths average temperature would be

about 60 F colder.

Because of how they

warm our world, these

gases are referred to

as greenhouse gases.

What are these gases?

The greenhouse gases

are:

Water Vapour

Carbon dioxide

Nitrous Oxide

Methane

CFCs


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Water Vapour

There is more water in the atmosphere than carbon

dioxide so most of the greenhouse heating of the Earths

surface is due to water vapour.

The water vapour content in the atmosphere is constant

which means it hasnt changed.

Water Vapour

Water vapour is the biggest contributor to the

natural greenhouse effect

Human activities have little impact on the level of

water vapour.

Carbon Dioxide

Our atmosphere contains many natural gases other

than ozone. One of these natural gases is carbon

dioxide.

Our atmosphere needs a

certain amount of this gas.It is carbon dioxide that helps

to keep the Earth warm.

Carbon Dioxide

This gas holds in just enough heat from the

sun to keep animals and plants alive.

If it held in more heat than it does the

climate on Earth would grow too hot for

some kinds of life.

If it held in less heat, Earths climate wouldbe too cold.

Carbon Dioxide

Carbon Dioxide is probably the most important of

the greenhouse gases and is currently responsible

for 60 % of the enhanced greenhouse effect

Enhanced

Human activities, not natural.

Global carbon dioxide emissions

Carbon Dioxide

For the past 100 years,

the amount of carbon

dioxide in our

atmosphere seems to

have been increasing.

Why is this happening?

What is it doing to the

Earths atmosphere?


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Where do all the carbon dioxide gases come

from?

Carbon dioxide

Human respiration.

Industrialization

Burning of fossil fuel to generate electricity

Burning of f orest (lesser trees) CO2 is now 1/3more than before Industrial

Revolution

Carbon Dioxide

Burning fossil fuels release the carbon dioxidestored millions of years ago.

We use fossil fuels to run vehicles (petrol, diesel,

and kerosene), heat homes, businesses, and power

factories.

Nitrous Oxide

Nitrous oxide makes up an extremely small

amount of the atmosphere It is less than

one-thousandth as abundant as carbon

dioxide.

However it is 200 to 300 times moreeffective in trapping heat than carbon

dioxide.

Nitrous Oxide

Nitrous Oxide has one of the longest atmosphere

lifetimes of the greenhouse gases, lasting for up to

150 years.

Since the Industrial Revolution, the level of nitrous

oxide in the atmosphere has increased by 16%.

Nitrous Oxide

The impact of

human activities

Burning fossil fuels and

wood

Widespread use of

fertilizers

Sewage treatment

plants

Where do all nitrous oxide gases comefrom?

Nitrous Oxide

Vehicle exhaust Nitrogen based fertili sers


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Methane

The importance ofmethane in thegreenhouse effect isits warming effect.

It occurs in lowerconcentrations thancarbon dioxide but itproduces 21 times asmuch warming ascarbon dioxide.

Methane

Methane accounts for20%of the enhanced

greenhouse effect.

It remains in the

atmosphere for 10-12

years. (Less than other

greenhouse gases)

Methane

Human Activities

An increase in livestock farming and rice growing has ledto an increase in atmospheric methane. Other sourcesare the extraction of fossil fuels, landfill sites and theburning of biomass.

Methane concentration in the atmosphere has more thandoubled during the last 200 yr. Some of this methane isproduced by ricefields

Where do all the methane gases come from?

Methane Produced by bacteria living in swampy areas.

Wet rice cult ivation

Waste in landfil ls

Rearing of l ivestock

When cows belch (burp)

Each molecule can trap 20 times as muchheat as a CO2molecule.

Where do all the CFCs comefrom?

CFCs (Chlorofluor ocarbons)

Aerosol sprays

Making foam packaging

Coolants in fridge and air cons

Cleaning solvents

Each CFC molecule can trap as much heat as

100 000 CO2molecule. Can remain in t he atmosphere for a long time

(up to 20 000 years)

Global Warming

The average global temperature has increased by

almost 1 F over the past century.


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Global Warming

Even a small increase in temperature over a long

time can change the climate.

When the climate changes, there may be big changes

in the things that people depend on.

Global Warming

These things include the level

of the oceans and the places

where we plant crops. They

also include the air we breathe

and the water we drink.

Global Warming

Days and nights would

be more comfortable

and people in the area

may be able to grow

different and better

crops than they could

before.

Global Warming

Changes in some

places will not be good

at all.

Human Health

Ecological Systems

(Plants and animals)

Sea Level Rise

Crops and Food Supply

Human Health

Heat stress and other heat related health problems

are caused directly by very warm temperatures and

high humidity.

Ecological Systems

Plants and animals

Climate change may alter the worlds habitats.

All living things are included in and rely on these places.

Most past climate changes occurred slowly, allowingplants and animals to adapt to the new environment ormove someplace else.

Plants and animals may not be able to react quicklyenough to survive if future climate changes occur asrapidly.


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Sea Level Rise

Global Warming may make the sea levelbecome higher. Why?

Warmer weather makes glaciers melt.

Melting glaciers add more water to the

ocean.

Warmer weather also makes water expand.

When water expands in the ocean, it takes

up more space and the level of the sea rises.

Rising Sea Levels

When earths t emperature rises, sea level is likely t o

rise too: Higher temperature sea water to expand in

volume

Ice caps at poles to melt

Sea Level Rise

Sea level may rise between several inches and as

much as 3 feet during the next century.

Coastal flooding could cause saltwater to flow into

areas where salt is harmful, threatening plants

and animals in those areas.

Oceanfront property would be affected by

flooding.

Coastal flooding may also reduce the quality of

drinking water in coastal areas.

Crops and Food Supply

Global warming may make the Earth warmer in cold

places.

People living in these areas may have the chance to

grow crops in new areas.

But global warming might bring droughts to other

places where we grow crops.

What Might Happen?

This warming trend is expected to bring

droughts and flooding of low lying coastal areas

as the polar ice caps melt and raise sea level.

Climatic Change Global warming will lead to an increase in the

evaporation of water more water vapour.

With more water vapour, more rain fall is expected.

But it is not evenly distributed:

Dry areas severe drought conditi on, water

shortage and heat waves occur s

Wet areas floods (landslides)


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Climatic Change

Other problems may arise:

Destroy food crop rice, wheat and corn Aff ect animals need to migrate

Encourage growth of weed and pests may

lead to diseases l ike dengue fever, cholera

which are deadly.

What can we do about it?

There are many little things that we can do to

make a difference to reduce the amount ofgreenhouse gases that we put into theatmosphere.

Many greenhouse gases come from things we doevery day.

Driving a car or using electricity is not wrong.We just have to be smart

Eg. Try carpooling

Ways you can help make our planet better.

Read Learning about

the environment is

very important.

Save Electricity

Whenever we use

electricity, we help put

greenhouse gases into

the air.Turn off lights, the

television and the

computer.


Bike, Bus and Walk-

You can saves energy

by sometimes taking

the bus, riding a bike

or walking.


Recycle When you recycle, you send less trash to

the landfill and you help save natural resources like

trees and elements such as aluminum.

Recycle cans, bottles,

plastic bags and newspapers.


When You Buy, Buy

Cool Stuff

Buy Products that

dont use as much

energy

Buy recyclable

products instead of

non-recyclable ones.

Solar Energy can be

used to heat homes,

buildings, water and to

make electricity.


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Cars cause pollution and release a lot ofgreenhouse gases into the air.

Some cars are better for the environment

They travel longer on a smaller amount of fuel.

They dont pollute as much.

Using these cars can help reduce can help

reduce the amount of greenhouse gases in the

air.

What else can we do?

To reduce the emissio n of g reenhouse gases

International efforts: Kyoto treaty (1997) was started to reduce

emission of greenhouse gases by 5% of

1990s levels by 2012.

Worlds major polluters

Summary / Conclusion

Environmental Crisis will affect us:

Health

Air pol lu tion asthma o r other

respiratory problems

Water pollutio n poison our food source

e.g fish

Destruction of forest lost of possible

medical solutions

Property Floods property lost

Pollution destroy streets and beaches

Soil erosion desertification, lost of farm

lands

Summary / Conclusion

Environmental Crisis will affect us: Economic Costs

Lost in terms of monetary values, industry

and businesses.

Money need to be spent to r estore the

original

Public Health Services need to be

provided by the government.


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Renewable and NonrenewableResources

Environment and EcologyStandards 4.2 A

1. Natural Resources

All of the Earths organisms, air, water,and soil, as well as materials such asoil, coal, and ore that are removed fromthe ground.

Separated into two broad categories:

Renewable resources

Nonrenewable resources

2. Renewable Resources

Are any resourcethat cycles or can bereplaced within ahuman life span.

Examples include:

water, crops, wind,soil, sunlight,animals, etc

a. Food and fiberare renewableagriculturalresources that canbe harvested orraised indefinitely

unless their use

exceeds the ratethey can bereplaced.

b. Soil a mixture ofliving organismsand dirt.

Even though itinitially takesthousands of yearsto form, the rate atwhich soil can

regeneratedepends on theclimate of an area.

c. Wind caused bythe uneven heatingof the Earth. Notonly renewable butinexhaustible.

d. Sun light fromthe sun supportsall the life on Earthas we know it.Also consideredinexhaustible. (atleast for the next 5billion years)

e. Water constantlyrenewed/replenishedby the water cycle.

However, fresh waterresources aresomewhat limited.

The use and quality ofwater must becarefully monitoredto ensure future use.

f. Biomass fuels areorganic matter(wood, plants,animal residues,etc) that containstored solarenergy.

Used to supply energyto 15% of theworlds supply.

g. Geothermal energy the heatgenerated deepwithin the Earth.

Fueled by thedecay ofradioactiveelements. Used toheat water.


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3. Nonrenewable Resources

Any resource that cannot be replacedduring the time of a human life span.

Took millions of years to form and existin fixed amounts in the Earth.

They need to be conserved before theybecome depleted.

a. Ores mineraldeposits fromwhich valuablemetals andnonmetals can berecovered forprofit.

Metallic ores include:gold, silver,copper, aluminum,zinc, etc

Nonmetallic oresinclude: salt, sand,gravel, clay,diamonds,gemstones, etc..

The major nonmetallicores mined are coal,limestone, granite,

slate, sand, andgravel.

b. Fossil Fuels

Are nonrenewable because they takemillions of years to form.

In developing countries, the fossil fuels

are fossilized wood, charcoal, and peat.In developed countries, the fossil fuelsare mainly coal, natural gas, and oil.

i. Coal the remainsof wetland plantsthat have beencompressed overmillions of years.

Different types

Peat about 50%carbon. The rest iswater andcontaminants.

Lignite (brown coal) about 70%carbon.

Bituminous (softcoal) about 85%carbon.

Anthracite (hardcoal) greatly than90% carbon. This isthe cleanest burningand least abundant.

ii. Petroleum andNatural Gas arethe remains ofmainly marineorganisms.

Typically found inundergroundformations calledtraps with thenatural gas trappedon top and oil onthe bottom.


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4. Global Energy Use andProduction.

Energyconsumptionincreased by 50%from 1973-1993.

Expected tocontinue toincrease in thefuture mainly indeveloping orthird worldcountries.

Remember that using more fossil fuelsaccelerates the global warming trenddue to more greenhouse emissions andpollution.

What other effects will a growth inglobal energy use produce?

5. Alternative EnergyResources.

a. These are energy resources that aremore renewable or moreenvironmentally friendly in comparisonto fossil fuels.

b. Currently include the following: solar,wind, geothermal, hydropower,nuclear, and biomass.

i. Solar energy canbe used to heatbuildings andwater and provideelectricity

Solar cells can

collect and convertthe suns energyinto electricity forresidential use.


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ii. Wind turns giantwind turbines that

produce electricity. iii. Hydropower theenergy of waterstored behind damscan be turned intoelectricity.

iv. Nuclear Power uses the process of fissionto release energy to make electricity.

Availability of Resources

Environment and EcologyStandards 4.2.B

Almost every resource needs to beremoved from the Earth andprocessed in some way before it canbe used.

What ultimately determines theavailability of resources are the costsinvolved in removing/extracting itfrom the Earth and the costs involvedin processing/refining them intoproducts.

1. Removing/Extracting

Earths Resources Over time, technologyhas increased theefficiency of obtainingour natural resources.

A. Farming practices changed from manyhuman/animal laborto increased use offarm machinery.


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SOLAR CELLThe devices used in photovoltaic conversion

are called solar cell.

Photovoltaic conversion sunlight is directly

converted to electricity

When solar radiation falls on these devices

,it is converted directly into dc electricity.

Silicon is the material used for making most

cells

Single crystal silicon cells are thin wafers

about 300 m in thickness sliced from p type

doped silicon

A shallow junction is formed at one end by

diffusion of n type impurity.Metal electrodes made from a Ti-Ag solder

are

attached to front and back side of the cell

On the front side the electrode is in the form

of metal grid with fingers which permit the

sunlight to go through

The back side the electrode completely

covers the surface

An anti reflection coating of SiO,having a

thickness of about ,.1 m and a thintransparent encapsulating sheet are also put

on the top surface.

Cell vlotage .5-1V

Current density 20-40 mA/cm2

To obtain higher voltages and currents

individual cells are fixed side by side on a

suitable back up board and connected in

series and parallel to form a module

No of modules are inter connected to form

an array

Solar cells are available in circular or

rectangular shape

Silicon solar cells are also available from poly

crystalline silicon and amorphous silicon


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Two important steps 1.Creation of pairs of Positive and negative

charges(called electron hole pairs) in the

solar cell by absorbed solar radiation.

2.Separation of positive and negative charges

by a potential gradient within the cell

E=hc/

Where h=planks constant=6.62x10-27erg-s

C=velocity of light=3x108m/s

= wave length in m

So E=1.24/eV

The only materials suitable for absorbing the energy of

the photons of sunlight are semiconductor like silicon,

cadmium sulphide, gallium arsenide,etc.

In a semiconductor, the electrons occupy one of two

energy bands-the valence band and the conduction

band.

The valence band has electrons at a lower energy level

and is fully occupied, while the conduction band has

electrons at a higher energy level and is not fully

occupied.

The difference between the energy level of theelectrons in the two bands is called the band gapenergy Eg.

Photons of sunlight having energy E greater than theband gap energy Eg are absorbed in the cell materialand excite some of the electrons

These electrons jump across the band gap fromvalence band to conduction band leaving behind holes

in the valence band. Thus electron hole pairs arecreated

The electrons in the conduction band and the holes inthe valence band are mobile.

They can be separated and made to flow through anexternal circuit if a potential gradient exists within thecell


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X intercept of the curve is Voc

Y intercept of the curve is Isc The maximum useful power corresponds to

the point which yields the rectangle with

largest area

The voltage yielding maximum power Vm

The current yielding maximum power Im

Fill factor =VmIm/IscVoc

Conversion efficiency=VmIm/ItAc

=FFxVocIsc/ItAc

It =Incident solar flux

Ac =area of cell

It depends on climatic conditions where system is

placed

Appropriate spatial placement of modules

The availability of a concentrator/solar tracking

mechanism in the system.The tracking solar

modules collect higher solar energy than those of

fixed solar modules

Efficiencies from a few percent up to 20-30%

MWp of a photo voltaic device is the nominal

output of a solar panel measured as maximum

power output under standard test conditions

(STC) in a laboratory with light intensity

1000W/m 2

Solar cells can be electrically connected in

series (voltages add) or in parallel (currents

add) to give any desired voltage and current

(or power) output since P = I x V.

Photovoltaic cells are typically sold in

modules (or panels) of 12 volts with power

outputs of 50 to 100+ watts. These are thencombined into arrays to give the desired

power or watts.

Dc

Ac l

ac

dc Load

control

switches

Grid

Pv

array

To ac

loads

inverter

Photo voltaic array

Inverter/Converter

Appropriate switches and circuit

breakers

Load

They have no moving parts

Require little maintenance

Work quite satisfactorily with beam or

diffuse radiations

They are readily adapted for varying

requirements

No noise

Lifetimes of 20-30 years or more


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Cell efficiency depends on Natural climaticconditions where it is used

Optimal matching of the system with load

High cost

Pumping water for irrigation and drinkingElectrification for remote villages for

providing street lighting and other

community services

Telecommunication for the post and

telegraph and railway communication

network

Grid connected application

Corrosion protection such as cathodic

protection for bridges,pipe line protection

Satelite communication


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ntypesemiconductor

ptypesemiconductor

+ + + + + + + + + + + + + + +

PhysicsofPhotovoltaicGeneration

DepletionZone

PhotovoltaicSystem

Typicaloutputofamodule(~30cells)is 15V,with1.5Acurrent

PVTechnologyClassification

SiliconCrystallineTechnology ThinFilmTechnology

MonoCrystallinePVCells AmorphousSiliconPVCells

MultiCrystallinePVCells PolyCrystallinePVCells

(NonSiliconbased)

SiliconCrystallineTechnology

Currentlymakesup86%ofPVmarket

Verystablewithmoduleefficiencies1016%

MonocrystallinePVCells

MadeusingsawcutfromsinglecylindricalcrystalofSi

Operatingefficiencyupto15%

MultiCrystallinePVCells

Castefromingotofmeltedandrecrystallisedsilicon

Cellefficiency~12%

Accountsfor90%ofcrystallineSimarket

MonocrystallinePVCells

ProsEfficient flat solar panels due to

their ability to convert highestamount of solar energy into

electricity

Long life and durability

Not hazardous to environment

ConsMore expensive

ThinFilmTechnology Silicondepositedinacontinuousonabasematerialsuchasglass,

metalorpolymers Thinfilmcrystallinesolarcellconsistsoflayersabout10mthick

comparedwith200300mlayersforcrystallinesiliconcells

PROSLowcostsubstrateandfabricationprocess

CONSNotverystable


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AmorphousSiliconPVCells

Themostadvancedofthinfilmtechnologies

Operatingefficiency~6%

Makesupabout13%ofPVmarket

PROSMaturemanufacturingtechnologiesavailable

CONSInitial2040%lossinefficiency

PolyCrystallinePVCells

CopperIndiumDiselinide

CISwithbandgap 1eV,highabsorptioncoefficient105cm1

Highefficiencylevels

PROS 18%laboratoryefficiency >11%moduleefficiencyCONS Immaturemanufacturingprocess Slowvacuumprocess

NonSiliconBasedTechnology

PolyCrystallinePVCells

CadmiumTelluride(CdTe)

lCdTeexhibitsdirectbandgapof1.4eVandhighabsorptioncoefficient

PROS

16%laboratoryefficiency

69%moduleefficiency

CONS

Immaturemanufacturingprocess

NonSiliconBasedTechnology

SemiconductorMaterialEfficiencies

EmergingTechnologies

UltraThinWaferSolarCells

Thickness~45m

CellEfficiencyashighas20.3%

Anti ReflectionCoating

Lowcostdepositiontechniquesuseametalorganictitaniumortantanummixedwithsuitableorganicadditives

Applications@PV

WaterPumping:PVpoweredpumpingsystemsareexcellent,simple,reliable life20yrs

CommercialLighting: PVpoweredlightingsystemsarereliableandlowcostalternative.Security,billboardsign,area,andoutdoorlightingareallviableapplicationsforPV

Consumerelectronics: Solarpoweredwatches,calculators,andcamerasarealleverydayapplicationsforPVtechnologies.

Telecommunications

ResidentialPower:AresidencelocatedmorethanamilefromtheelectricgridcaninstallaPVsystemmoreinexpensivelythanextendingtheelectricgrid

(Over500,000homesworldwideusePVpowerastheironlysourceofelectricity)


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Solarthermalenergy

Gomathy.S

.Electricity

generated

by

burning

fossil

fuels

suchascoal,oilandnaturalgas,emits

carbondioxide,nitrogenoxidesandsulfur

oxides gasesscientistsbelievecontribute

toclimatechange.Solarthermal(heat)

energyisacarbonfree,renewable

alternativetothepowerwegeneratewith

fossilfuelslikecoalandgas.

SizeofMarket

Source:Emerging EnergyResearch

WhatisSolarThermalPower? Freeandsecureresource,

widelyavailableandhighlypredictable

Usesreflectorstoconcentratesunsenergyandcreateheat

Uniquelysuitedforansweringpeakdemands

AdvantagesandDisadvantages

Advantages

Allchemicalandradioactivepollutingbyproductsofthethermonuclearreactionsremainbehindonthesun,whileonlypureradiantenergyreachestheEarth.

Energyreachingtheearthisincredible. Byonecalculation,30daysofsunshinestrikingtheEarthhavetheenergyequivalentofthetotalofalltheplanetsfossilfuels,bothusedandunused!

Disadvantages

Sundoesnotshineconsistently.

Solarenergyisadiffusesource. Toharnessit,wemustconcentrateitintoanamountandformthatwecanuse,suchasheatandelectricity.

Addressedbyapproachingtheproblemthrough:

1)collection,2)conversion,3)storage.

Therearetwomainwaysofgeneratingenergyfromthesun.

Photovoltaic(PV)andconcentratingsolarthermal(CST),alsoknownasconcentratingsolarpower(CSP)technologies.

PVconvertssunlightdirectlyintoelectricity.Thesesolarcellsareusuallyfoundpoweringdevicessuchaswatches,sunglassesandbackpacks,aswellasprovidingpowerinremoteareas.


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Solar

thermal

technology

is

large

scale

by

comparison.

OnebigdifferencefromPVisthatsolarthermalpowerplantsgenerateelectricityindirectly.

Heatfromthesun'sraysiscollectedandusedtoheatafluid.

Thesteamproducedfromtheheatedfluidpowersageneratorthatproduceselectricity.

It'ssimilartothewayfossilfuelburningpowerplantsworkexceptthesteamisproducedbythecollectedheatratherthanfromthecombustionoffossilfuels

There

are

two

types

of

solar

thermal

systems:

passiveandactive.

Apassivesystemrequiresnoequipment,likewhenheatbuildsupinsideyourcarwhenit'sleftparkedinthesun.

Anactivesystemrequiressomewaytoabsorbandcollectsolarradiationandthenstoreit.

Solarthermalpowerplantsareactivesystems,

andwhilethereareafewtypes,therearea

fewbasicsimilarities:Mirrorsreflectand

concentratesunlight,andreceiverscollect

thatsolarenergyandconvertitintoheat

energy.

Ageneratorcanthenbeusedtoproduce

electricityfromthisheatenergy.

ParabolicTroughCollectors

ParabolicTroughSystemSchematic

Becauseofitsshape,thistypeofplantcan

reachoperatingtemperaturesofabout750

degreesF(400degreesC),concentrating the

sun'sraysat30to100timestheirnormal

intensityontoheattransferfluidor

water/steamfilledpipes.Thehotfluidisused

toproducesteam,andthesteamthenspinsa

turbinethatpowersageneratortomake

electricity.


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SolarPowerTowers Solarpowertowersystemsareanothertypeofsolarthermalsystem.Powertowersrelyonthousands

of

heliostats,

which

are

large,

flat

sun

trackingmirrors,tofocusandconcentratethesun'sradiationontoasingletowermountedreceiver.

Likeparabolictroughs,heattransferfluidorwater/steamisheatedinthereceiver(powertowers,though,areabletoconcentratethesun'senergyasmuchas1,500times),eventuallyconvertedtosteamandusedtoproduceelectricitywithaturbineandgenerator.

090211

SolarPowerTowers:SandiaCRTF

Flatmirrorsareaimedtofocussunatthereceivertargettomeltsalt

ParabolicDishSystem

Theparabolicdishsystemusesaparabolicdishshapedmirrororamodularmirrorsystemthatapproximatesaparabolaandincorporatestwoaxistrackingtofocusthesunlightontoreceiverslocatedatthefocalpointofthedish,whichabsorbstheenergy

andconverts

it

into

thermal

energy.

Thiscanbeuseddirectlyasheatforthermalapplicationorforpowergeneration.

PARABOLIC DISH SYSTEM

Thethermalenergycaneitherbetransportedto

acentralgeneratorforconversion,oritcanbe

converteddirectlyintoelectricityatalocal

generatorcoupledtothereceiver

ThePDCs(parabolicdishcollector)trackthesun

ontwoaxes,andthustheyarethemostefficient

collectorsystems.Theirconcentrationratios

usuallyrangefrom600to2000,andtheycan

achievetemperaturesinexcessof1500oC.92%

TechnologyComparisonParabolicTroughtheDominantTechnology

525KW (perdish)1064(MW)50600(MW)SizeScale

Dishfocusessunlightto single

point,wherethermalcollector

captures theheat.Engineconverts

heatintomechanicalenergywhich

drivesgenerator toproduce

electricity.

Circulararrayofmirrors

concentrate ssunlighton

receiverplacedattopof

centraltower. Heatcreates

steamtopower generator.

Curvedtroughreflectssolar

radiationonto tubeandheats

theoilinsideit.Aheat

exchangercreatessteam

whichrunsasteamturbine.Mechanism

Negligible5%7%Marketshareby2012

(MW)

Embryonic Pilotunderway ProofofconceptMature technology, 20yr

commercial trackrecordCommercialStatus

25 30161814 18Cost(cent\kWh)

DishTowerParabolicTrough


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4

SolarThermalHeat

Solarthermal

systems

are

apromising

renewable

energysolution thesunisanabundantresource.Exceptwhenit'snighttime.Orwhenthesunisblockedbycloudcover.Thermalenergystorage(TES)systemsarehighpressureliquidstoragetanksusedalongwithasolarthermalsystemtoallowplantstobankseveralhoursofpotentialelectricity.Offpeakstorageisacriticalcomponenttotheeffectivenessofsolarthermalpowerplants.

In

a

two

tank

direct

system,

solar

thermal

energy

is

stored

rightinthesameheattransferfluidthatcollectedit. Thefluidisdividedintotwotanks,onetankstoringitatalowtemperatureandtheotheratahightemperature.

Fluidstoredinthelowtemperaturetankrunsthroughthepowerplant'ssolarcollectorwhereit'sreheatedandsenttothehightemperaturetank.

Fluidstoredatahightemperatureissentthroughaheatexchangerthatproducessteam,whichisthenusedtoproduceelectricityinthegenerator.

Andonceit'sbeenthroughtheheatexchanger,thefluidthenreturnstothelowtemperaturetank.

Atwotankindirectsystemfunctionsbasically

thesameasthedirectsystemexceptitworks

withdifferenttypesofheattransferfluids,

usuallythosethatareexpensiveornot

intendedforuseasstoragefluid.

Toovercomethis,indirectsystemspasslow

temperaturefluidsthroughanadditionalheat

exchanger.

Unlikethetwotanksystems,thesingletankthermoclinesystemstoresthermalenergyasasolid,usuallysilicasand.

Insidethesingletank,partsofthesolidarekeptatlowtohightemperatures,inatemperaturegradient,dependingontheflowoffluid.

Forstoragepurposes,hotheattransferfluidflowsintothe

top

of

the

tank

and

cools

as

it

travels

downward,

exitingasalowtemperatureliquid.

Togeneratesteamandproduceelectricity,theprocessisreversed.

SolarthermalsystemsthatusemineraloilormoltensaltastheheattransfermediumareprimeforTES,butunfortunatelywithoutfurtherresearch,systemsthatrunonwater/steamaren'tabletostorethermalenergy.

Otheradvancementsinheattransferfluidsincluderesearchintoalternativefluids,usingphasechangematerialsandnovelthermalstorageconceptsallinanefforttoreducestoragecostsandimproveperformanceandefficiency.

SolarThermalGreenhouses

Theideaofusingthermalmassmaterials materialsthathavethecapacitytostoreheat tostoresolarenergyisapplicabletomorethanjustlargescalesolarthermalpowerplantsandstoragefacilities.

Theideacanworkinsomethingascommonplaceasagreenhouse.

Allgreenhousestrapsolarenergyduringtheday,usuallywiththebenefitofsouthfacingplacementandaslopingrooftomaximizesunexposure.

Butoncethesungoesdown,what'sagrowertodo?Solarthermalgreenhousesareabletoretainthatthermalheatanduseittowarmthegreenhouseatnight.

Stones,cementandwaterorwaterfilledbarrelscanallbeusedassimple,passivethermalmassmaterials(heatsinks),capturingthesun'sheatduringthedayandradiatingitbackatnight.


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Solarthermalchimneys

Justas

solar

thermal

greenhouses

are

away

to

applysolarthermaltechnologiestoan

everydayneed,solarthermalchimneys,or

thermalchimneys,alsocapitalizeonthermal

massmaterials.

Thermalchimneysarepassivesolar

ventilationsystems,whichmeanstheyare

nonmechanical.

Examples

of

mechanical

ventilation

include

wholehouseventilationthatusesfansandductstoexhauststaleairandsupplyfreshair.

Throughconvectivecoolingprinciples,thermalchimneysallowcoolairinwhilepushinghotairfromtheinsideout.

Designedbasedonthefactthathotairrises,theyreduceunwantedheatduringthedayandexchangeinterior(warm)airforexterior(cool)air.

Thermalchimneysaretypicallymadeofablack,hollowthermalmasswithanopeningatthetopforhotairtoexhaust.

Inletopeningsaresmallerthanexhaustoutletsandareplacedatlowtomediumheightinaroom.

Whenhotairrises,itescapesthroughtheexterior

exhaust

outlet,

either

to

the

outside

or

intoanopenstairwell.

Asthishappens,anupdraftpullscoolairinthroughtheinlets.

Inthefaceofglobalwarming,risingfuelcostsandanevergrowingdemandforenergy,energyneedsareexpectedtoincreasebynearlytheequivalent of335millionbarrelsofoilperday,mostlyforelectricity.

Whetherbigorsmall,onoroffthegrid,oneofthegreatthingsaboutsolarthermalpoweristhatitexistsrightnow,nowaiting.

Byconcentratingsolarenergywithreflectivematerialsandconverting itintoelectricity,modernsolarthermalpower

plants,if

adopted

today

as

an

indispensable

part

of

energy

generation,maybecapableofsourcingelectricitytomorethan100millionpeopleinthenext20years.

Allfromonebigrenewableresource:thesun.

Conclusion:SolarThermal Solarthermalsystemsarecosteffectiveatlowtemperaturesforwaterheatingorcooking

Waterheatersareenergysavers,butinitialcostdissuadesmanyfromusingthesame.

Massivepowertoweryields10MW,whileatypicalutilityplantis5001500MW

Powertowersarentlikelytobeeconomicallypracticalforsometime

Solardryers,cookers,andovensarerelativelyinexpensiveandavailableforremotecooking

090211


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UNIT-I

SOLAR ENERGYCONTENTS TO BE DISCUSSED

Solar radiation Estimation and Measurements

WHY SOLAR ENERGY

Solar energy is the most readily available source of

energy.

Solar energy received in the form of radiation, can be

converted directly or indirectly into other forms of

energy, such as heat and electricity.

It is free.

It is also the most important of the non-conventional

sources of energy because it is non-polluting.

WHAT IS SOLAR ENERGY

Originates with the

thermonuclear reactions

occurring in the sun.

Represents the entire

electromagnetic

radiation (visible light,

infrared, ultraviolet, x-

rays, and radio waves).

FACTS ABOUT SOLAR ENERGY

Energy is radiated by the sun as the electromagnetic waves of

which 99 percent have wavelengths in the range of 0.2 to 4.0

micrometers.

Energy supplied by the sun in one hour is almost equal to the

amount energy required by the human population in one year.

Most if the other source on renewable energy have their in

sun.

SOLAR CONSTANT

The rate at which Solar energy arrives at the top of the

atmosphere is called the Solar Constant Isc.

It is the amount of energy received in unit time on a unit area

perpendicular to the Suns direction at the mean distance of

the earth from the Sun.

The standard value (NASA)-1353 watts/sq.metre


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WAVELENGTH VERSUS ENERGY

Wavelength() 0-0.38 0.38-0.78 0.78-4.0

Approximate

energy(W/m2)

95 640 618

Approximate

Percentage of

total energy

7% 47.3% 45.7%

SOLAR RADIATION

Beam Radiation (Direct radiation) Reaches directly to

the earth surfaces, which produces the shadow effect.

Diffused Radiation Solar radiation from the sun after its

direction has been changed.

Variation in Solar Radiation due to

REFLECTION,ABSROPTION AND SCATTERING

Reflection: by surface and clouds

Absorption : Short wave Ultra-violet rays by ozone and

long wave infra red by Co2 and moisture in the

atmosphere.

Scattering : As Solar radiation passes through the earths

atmosphere the components of the atmosphere, such as

water vapor, dust in the atmosphere causes scattering.

Solar Radiation = Beam Radiation + Diffuse Radiation

Also called Insolation: total solar radiation received on a

horizontal surface of unit area on the ground in unittime (1 day)

Insolation varies with date, time, altitude of sun and with

weather conditions (clouds,humidity)

Solar Radiation Measurements

Must measure both direct and diffuse radiation.

Solar Radiation measured by two basic type of instruments

Pyrheliometer-Collimates the radiation(parallel rays) to

determine the beam intensity as a function of incident angle

Pyranometer-It measures the total hemispherical solar

radiation.

Types of Pyrheloimeters

Pyrheliometers measures beam radiation, blocks diffuse

radiation.

Used for routine measurements.

Types :

Angstrom pyrheliometer

The Abbot Silver disc pyrheliometer

Eppley pyrheliometer


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Angstrom Compensation Pyrheliometer

A thin blackened shaded manganin strip is heated

electrically upto the same strip exposed to solar

radiation.

The thermocouples on the back of each strip connected

in opposition through a galvanometer to check the

equality of temperature.

Angstrom Compensation

Pyrheliometer

Abbot Silver Disk Pyrheliometer It consist of blackened silver disk positioned at the lower end of tube with

diaphragms to limit to the aperture to 5.7deg .

A Mercury-in-glass thermometer is used to measure the temperature of

the disk and shutter made of 3 polished metal leaves is provided at the

upper end of tube to allow solar radiation to fall on the disk at regular

intervals.

The thermometer stem is bend through 90 deg so that it lies along the

tube to minimize its exposure to the sun.

Used as calibrating instruments.

Eppley Pyrheliometer

Bismuth-silver thermopile with 15 junctions mounted atthe base of a brass tube, the limiting diaphragms subtend

an angle of 15 degrees

A thermopile is basically a series arrangement ofthermocouples used to develop a much greater voltage

than it is possible using only one.

The tube is filled with dry air and sealed with crystalquartz window which is removable.

The instrument has found wide acceptance within theU.S.A and many parts of the world.

Pyranometers

Measures total or hemispherical or global radiationover a hemispherical point of view.

Hot and cold junctions of a thermopile.

Emf proportional to solar radiation is received.-range of 0 to 10mV

Types: Eppley pyranometer

Yellot solarimeter(photovoltaic solar cell)

Thermoelectric pyranometer

Moll-Gorczyheski solarimeter

Eppley PyranometersThe temperature is sensed on the

concentric silver ring ( 0.25 mm thick )

consist of black (absorb radiation) andwhite surface (reflect radiation) with a

thermopile

10 or 50 thermocouple junctions todetect the temperature difference

between the coated rings and it is

enclosed in hemispherical glass cover.


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Eppley Pyranometers

Yellot Solarimeter

Used on photovoltaic detectors.

Silicon cells are used to measure solar radiations.

The incident radiations are converted to the

equivalent electrical energy.

Sunshine Recorder

Measures duration of bright sunshine in a

day

The duration of sun shine is measured

by means of suns rays are focused by a

glass sphere to point on a card strip

held in a groove in a spherical bowl

concentrically with the sphere.

Burnt space with length equal to

duration of sunshine is obtained on

the strip.

Estimation of Average Solar radiation The monthly average horizontal solar radiation Hav was given by

Angstrom which is

where a and b are constants

a=0.35

b=0.61

Ho=monthly average horizontal solar radiation for a clear day

= average daily hours of bright sunshine for same period

N=maximum daily hours of daily sunshine for same period

A better form of the above equation suggested by Page(1964)

where Ho=the average monthly insolation at the top of the atmosphere.

a and b are modified constants depending upon the location. Their valuesfor various locations and climate conditions can be obtained fromstandard tables

SOLAR ENERGY COLLECTORS

Solar collector is a device for collecting solar radiation

and transfer the energy to a fluid passing in contact with

it.

Two types of solar collectors ;

Non-concentrating (or) Flat plate type

Concentrating (focusing type) type flat type

Principle of heat conversion is green

house effect


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Flat plate collectors Temperatures below about 90 degrees are adequate, as they

are for space and service heating flat plate collectors, which

are of the non-concentrating type, are particularly convenient.

They are made in rectangular panels, from about 1.7 to 2.9

sq.m,in area and are relatively simple to construct and erect.

Flat plates can collect and absorb both direct and diffuse

radiation.

Flat plate collectors

Flat-plate solar collectors may be divided into two main

classifications based on the type of heat transfer fluid

used.

Liquid heating collectors are used for heating water and

non-freezing aqueous solution and occasionally for non-

aqueous heat transfer fluids.

Air or gas heating collectors are employed as solar air

heaters.

Main components

1. Transparent cover which maybe one or moresheets of glass or radiation transmitting plasticfilm or sheet

2. Tubes, fins, passages or channels to carry

water, air or other fluid.

3. The absorber plate, normally metallic or black

surface4. Insulation at the back and sides to minimize

heat losses. Standard insulating materials likefiber glass can also be used.

5. Casing or container for protection.

Typical liquid collector

Advantages of second glass

Heat transport system-water, air

Solar air heaters

Advantages anddisadvantages of air asmedium

Porous and non-porousabsorber

Advantages of Flat plate collectors

They have the advantages of using both beam and diffuse solar

radiation.

They do not require orientation towards the sun.

They require little maintenance.

They are mechanically simpler than the concentrating

collectors, absorbing surfaces and orientation devices of

focusing collectors.


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Applications of Solar Air Heaters

Heating buildings.

Drying agricultural produce and lumber.

Heating green houses.

Air conditioning buildings utilizing desiccant beds or a

absorption refrigeration process.

Using air heaters as the heat sources for a heat engine

such as a Brayton or Stirling cycle.

Concentrating Collectors: Focusing Type

Focusing collector is a device to collect solar energywith high intensity of solar radiation on the energy

absorbing surface.

Such collectors generally use optical system in the form

of reflectors or refractors.

These type of collectors can have radiation increase low

value of 1.5-2 to high values of the order of 10,000.

Optical Efficiency The combined effect of all loses is indicated through the

introduction of a term called the optical efficiency.

The introduction of more optical losses is compensated

for by the fact that the flux incident on the absorber

surface is compensated for by the fact that the flux

incident on the absorber surface is concentrated on

smaller area.

Types of Concentrating Collectors Parabolic trough collector

Mirror strip reflector

Fresnel Lens collector

Flat plate collector with adjustable mirrors

Compound parabolic concentrator

Parabolic Trough Reflector The principle of the parabolic trough collector, which

is often used in concentration collectors.

Solar radiation coming from the particular direction is

collected over the area of the reflecting surface and is

concentrated at the focus of the parabola.

It can be vary over a wide range the length of a

reflector unit may be roughly 3 to 5m,and the width

about 1.5 to 2.4m.

Cross section of

Parabolic Trough Reflector


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Parabolic trough reflectors have been made of highly polished

aluminium,of silvered glass or of a thin film of aluminized

plastic on a firm base.

For the solar radiation to be brought to a focus by parabolic

trough reflector, the sun must be in such a direction that it lies

on the plane passing through the focal line and the vertex.

Trough type of collectors are generally oriented in the east-

west or north-south directions.

Typical cylindrical parabolic system


For the east-west orientation, the collectors are laid flat

on the ground.

The north-south orientation permits more solar energy

to be collected than the east-west arrangements, except

around the winter equinox.

The choice of orientation in any particular instance

depends on the foregoing and other considerations.

Mirror Strip Reflector In another kind of focusing collector, a number of plane or slightly curved

mirror strips are mounted on a flat base.

The angles of the individual mirrors are such that they reflect solar

radiation from a specific direction on to the same focal line.

The angles of the mirrors must be adjusted to allow for changes in the

suns elevation, while the focal line remains in a fixed position.

Fresnel Lens Collector For a trough-type collector, the lens is rectangle about

4.7m in overall length and 0.95m in width.

It is made in sections from cost acrylic plastic and can

probably be produced in quantity at low cost.

To be fully effective, the Fresnel lens must be

continuously aligned with the sun in 2 directions

namely, both along and perpendicular to its length.

Fresnel Lens Collector In Fresnel lens collector, the solar radiation is focused into the

absorber from the top, rather than from the bottom as in the

parabolic type.

Insulation at the bottom and sides of the absorber pipe and a

flat-plate over the top reduce thermal losses.

A stainless steel reflector adjacent to the pipe reflects back

emitted thermal radiation.


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Point Focusing Collector

A dish 6.6m,in diameter has been made from about 200

curved mirror segments forming a paraboloidal surface.

The absorber, located at the focus, is a cavity made of

zirconium-copper alloy with a black chrome selective

coating.

The dish can be turned automatically about two

axes(up-down and left-right)so that the sun is always

kept in a line with the focus and the base of the

paraboloidal dish.


The concentration ratios is the ratio of the area of the

concentrator aperture to the energy absorbing area of

the receiver, it determines the effectiveness of a

concentrator, are very high .

In case of Parabolic system and therefore can be used

where high temperatures are required.

In cylindrical parabolic system, the concentration ratio is

lower than parabolic counter parts.


Concentration ratios of about 30 to 100 or higher would be

needed to achieve temperatures in the range of 300 to 500

degree Celsius or higher.

Central receiver collector- tower power plant using heliostat

mirrors.

Point Focusing Solar Collector

Central Receiver Collector Concentrating Collectors-Flat PlateCollector Augmented With Mirrors


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Compound Parabolic Concentrator CPC is non-focusing-but solar radiation from many

directions is reflected toward the bottom of the trough.

CPC provides moderately good concentration, although

less than a focusing collector in an east-west direction

without adjustment for sun tracking..

Compound Parabolic Concentrator

CPC reflectors can be designed for any absorber shapes.

Flat one sided absorber

Flat two sided absorber

Wedge-like absorber

Tubular absorbers

They are suitable for the temperature range of 100-150

degree Celsius even if the absorber is not surrounded by a

vaccum.

Compound Parabolic ConcentratorAdvantages of Compound Parabolic

Concentrator

There is no need of tracking ,as it has high acceptance

angle, only essential adjustments are required.

The Efficiency for accepting diffuse solar radiation is much

larger than conventional concentrators.

Its Concentration ratio is equal to the maximum value

possible for given acceptance angle.

The Maximum concentration ratios are available with

parabolic system, is of the order of 10,000.

Advantages and Disadvantages of

Concentrating collections overFlat-plate Type Collectors

Reflecting surfaces required less material and are

structurally simpler than flat-plate collectors. For aconcentrator system the cost per unit area of solar

collecting surface is therefore potentially less than that for

flat-plate collectors.

The absorber area of a concentrator system is smaller

than that of a flat-plate system for same solar energycollection and therefore the isolation intensity is greater.

Advantages and Disadvantages of Concentrating

over Flat-plate Type Collectors Concentrating systems can be used for electric power

generation when not used for heating or cooling. The total

useful operating time per year can therefore be large for a

concentrator system than for a flat-plate collector and the

initial installation cost of the system can be regained by saving

in energy in a shorter period of time.

Little or no anti-freeze is required to protect the absorber in a

concentrator system whereas the entire solar energy

collection surface requires anti-freeze protection in a flat-plate

collector.


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Disadvantages

Out of the beam and diffuse solar radiation components,only beam component is collected in case of focusingcollectors because diffuse component cannot be reflected.

Additional requirements of maintenance particular to

retain the quality of reflecting surface against dirt, weather,oxidation etc.

Non- uniform flux on the absorber whereas flux in flat-

plate collectors is uniform.

Additional optical losses such as reflectance loss and theintercept loss

High initial cost.

1. Direct Thermal Application

Direct use of Heat resulting in absorption of solar radiation

Space heating of residences, buildings

Hot water service

Curing of agricultural industrial products

2. Solar Electric Application

Converts Solar energy directly or indirectly to electrical energy

a. Solar Thermal Electric Conversion

Includes production of high temperature

To boil water or working fluid required to run turbines of

electric generator

b. Photovoltaic Conversion

solar cells convert solar energy to electrical energy

c. Thermo Electric Conversion

Conversion of solar energy to electrical energy using

thermo electric effect

d. Ocean Thermal Energy Conversion

* Difference in temperature between solar heated surface

and cold deep ocean to operate a vapour expansion turbine

n electric generator.

Solar Energy Storage

Permits solar energy to be captured when

insolation is highest and used later whenneeded.

Makes it possible to deliver short peaks of

power for exceeding the rated power

capacity of the plant.

Improve reliability.

Permit a better match between solar energy

input and load demand than without storage.

Solar Energy Storage System Thermal Energy Storage

Energy can be stored by heating, melting or vaporization of

material, and the energy becomes available as heat, when the

process is reverse.

Storage by causing a material to rise in temperature is called

Sensible Heat Storage.

Storage by phase change, the transition from solid to liquid or

from liquid to vapor is another mode of thermal storage,

known as Latent Heat storage.


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Applications

Thermal energy storage is essential for both domestic

water and space heating application.

For the high temperature storage system needed for

thermal power application.

Used in industries and horticultural

Sensible Heat storage

Sensible heat storage involves a material that

undergoes no change in phase over the

temperature domain encountered in the

storage process.

Water tank storage unit

Energy is added by

circulating water through

collector and is removed

by circulating water

through load

Water tank storage unit

Qs = (mCp)s (T1 T2)

Where

Qs Total thermal energy capacity

Cp Specific heat

The ability of store thermal energy in a given containerof volume V is,

Q/V=Cp T

- density of the storage medium

Storage

The materials used for this type of storage are

Water

Rock, gravel or crushed stone

Iron, red iron oxide or iron ores

concrete

Water storage Most common heat transfer fluid for a solar system is

water and the easiest way to store thermal energy is by

storing the water directly in a well insulated tank.

The optimum tank size for flat plate collector system is

about 70kg/m2


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Characteristics of water for use as storage medium

It is an inexpensive, readily available and useful

material to store sensible heat.

High thermal storage capacity

Energy addition and removal from this type of

storage is done by medium itself, thus eliminating

any temperature drop between transport fluid and

storage medium

Pumping cost is small

Packed Bed Exchanger Storage

For sensible heat storage with air as the energytransport mechanism, rocks, gravel or crushed

stone in a bin has the advantage of providing a

large, cheap heat transfer surface

Its thermal capacity is only half that of water and

the bin volume will be about 3 times the volume

of a water tank

Advantages of Rock over Water

Rock is more easily contained than water

Rock acts as its own heat exchanger, which reduces total

system cost

The heat transfer coefficient between the air and solid is high

Cost of the storage material is low

Conductivity of the bed is low when air flow is not present

Schematic of Packed Bed Storage Unit

Latent Heat Storage

Heat is stored in a material when it melts and extracted

from the material when it freezes.

Material that undergo a change of phase in a suitable

temperature range may be useful for energy storage if the

following criteria can be satisfied

The phase change must be accompanied by high latent heat

effect

The phase change must occur with limited super cooling

Cost of materials and its containers must be reasonable

Its phase change must occur close to its actual melting

temperature

Material must be available in large quantities

A small volume change during the phase change


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A sodium acetate heating pad. When the

sodium acetate solution crystallises, it

becomes warm.

Glaubers salt Na2SO4.10H2O-soduim

sulphate decahydrate

Salt eutectics

Some organic compound

like paraffin or fatty acids

Refractory materials (MgO, Al2O3, SiO2)

Electrical Storage

Capacitor storage:

At high voltage low current capacitor storage isused

Where V volume of dielectric

- constant

E electric field strength

Electric field strength is limited by breakdown

strength of the dielectric

The electrical energy storable in a dielectric is

limited

Mica is the best dielectric material

Inductor storage:

At low voltage and high current inductor storage

is used

where - permeability of the material

Hm- magnetic flux density

Battery storage:

A battery is the combination of individual cells.

A cell is the elemental combination of materials and

electrolyte constituting the basic electrochemical energy

stored

Secondary batteries are rechargeable and primary batteries

are non rechargeable

Secondary batteries- lead acid, nickel cadmium, iron air,

nickel-hydrogen, zinc air, sodium sulpur, sodium chlorine etc.

Working of Battery Storage System

A cell consists of two electrodes called anode and cathode

immersed in a suitable electrolyte

When an electrical load is connected between the electrode charge

separation occurs at the interface between the electrode and

electrolyte, freezing both an electron and an ion.

The electron flows through the external load and ion through the

electrolyte, recombining at the other electrode


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Chemical Storage

Storage in the form of fuel: A storage battery in which the

reactant is generated by photochemical reaction brought about

by solar radiation

In this case converter itself acts as a storage battery

The battery is charged photochemically and discharged

electrically whenever needed

Some of the reactions that could potentially be useful

for the storage of solar energy:

2NACl + photons 2NO+Cl2

AgCl (s) + photons Ag(s) + Cl2

NO2 + photons NO + O2

H2C + O2 H2O2

Thermo-chemical energy storage: Thermochemical storage

systems are suitable for medium and high temperature

applications only

Advantage of thermochemical storage include high energy

density storage at ambient temperatures for long periods

without thermal losses

This type of storage is illustrated by a hypothetical reaction

A+B AB

The forward reaction takes place with absorption of heat and

heat is stored in the form of products, when heat is desired

the products are to be remixed to allow the reversible reaction

to take place with liberation of heat

Both forward and reverse reactions takes place at constant but

different temperature

Hydrogen Storage: Energy can be stored and transport as

hydrogen, which serves as a secondary fuel.

On wind electric or photovoltaic system the dc output power

can be fed directly into a electrolyzer tank which produces

hydrogen and oxygen from ordinary water

The hydrogen and oxygen gas produced can bestored either in gas or liquid form for a long time

The system thus effectively stores the suns energy

as hydrogen and oxygen, and from this storage a

smooth reliable power output may be taken for a

limited time set by the hydrogen storage capacity


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Mechanical Energy Storage

Pumped Hydroelectric Storage:Electric power in excess of the immediate

demand is used to pump water from a supply at a

lower level to a reservoir at a high level

When the power demand exceeds the supply, the

water is allow to flow back down through a

hydraulic turbine which drives a generator

The overall efficiency of the pumped storage, that is the

percentage of the electrical energy used to pump the water is

recovered as electrical energy is about 70%

The pumped hydroelectric storage is the most economical

means presently available to electric utilities, hence solar and

wind energy in electrical form can be used by this system

Schematic Diagram for Pumped Hydroelectric

storage system

Compressed Air Storage:

A wind turbine can directly pump air into a suitable pressurized

storage tank

Then later when the wind is not blowing the energy stored in the

air could be utilized to drive an air turbine, whose shaft would

then drive a generator

Thus supplying the needed electrical power when the wind is not

blowing

Flywheel Storage:

The rotation of flywheel can be used to operate a generator to

produce electricity when required

The same machine serves as both a motor, when electricity is

supplied and as a generator, when the armature is rotated by the

flywheel

The energy recovery efficiency is estimated to be upto 90%

Electromagnetic Energy StorageHere energy storage is via super conducting magnet

An electromagnetic field is produced by an electric

current flowing through a wire can store energy

If the coil were made of super conducting material and

kept at the required low temperature, resistance losses

are small and once initiated, an electric current would

remain constant


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Electrical energy supplied as direct current towire coil would be stored in the

electromagnetic field

By attaching coil to load, the stored energy

could be recovered as electrical energy.

Applications of solar energy

Direct thermal applications Solar electric applications

Solar thermal electric conversion

Photovoltaic methods

Thermoelectric conversion

Wind energy, Ocean energy

Energy from biomass and bio-gas

Solar Thermal Electric Conversion

Heat can be converted directly into electrical energy by solar

cell or thermoelectric methods, but these techniques may not

be suitable for use with the sun-generated heat.

The most practical thermal electric procedure for solar

energy is to utilize the energy to heat a working fluid.

The heat energy is then converted into mechanical energy ina turbine and finally into electrical energy by means of

conventional generator coupled to the turbine.

Power cycles-low, medium and high temp.

Arrangements-

Central Receiver Collector-large scale

generation

Distributed collector-smaller capacity-

2kW

Thermo Electric Conversion systems Low temperature using flat plate collectors or

solar pond.

Concentrating collectors for medium and high

temperature.

Power tower concept or central receiver

system

Distributed collector system

Low temperature systems Temperature range of 60-100 degree Celsius

Rankine cycle is used

Organic fluid is Freon or butane

Flat plate collectors or solar pond

arrangement


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Solar pond A natural or artificial body of water for

collecting and absorbing solar radiationand storing it as heat.

Dissolved salts to create stable density

gradient.

Medium temperature systems

Temperature above 100 degree Celsius

250-500 degrees Celsius

Parabolic cylindrical collector is used

High temperature Systems

Central Receiver Collector

Distributed collector systems (solarfarms)

Central receiver systems (Tower Power plant) Principle and working A large field of mirrors, called heliostats, track the sun.

A tower collects light concentrated by the heliostats onto a centralreceiver on top of a tower. Tower heights range from approximately 300to 650 feet.

HTF, composed of either water or molten nitrate salt, moves through thereceiver and is heated to temperatures over 500 C.

The heated HTF is then sent to a heat exchanger where water is turnedinto steam, which then drives a turbine generator.


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Description of the system

Tower with the central receiver on top Heat conversion subsystem

Heat storage device

Field of oriented mirrors

Distributed Collector system (Solarponds)

Solar Electric Power Generation Direct conversion of solar energy into electricity

by means of photovoltaic effect, i.e. conversion oflight into electricity.

Photovoltaic effect

-generation of an electromotive force as a resultof the absorption of ionizing radiation.

Solar cells- Energy conversion devices which areused to convert sunlight to electricity by the useof photovoltaic effect.

Solar cell animation

Solar cell working

What is a solar cell? Solid state device that converts incident solar

energy directly into electrical energy

Efficiencies from a few percent up to 20-30%

No moving parts

No noise

Lifetimes of 20-30 years or more


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Cross Section of Solar CellSchematic view of Typical Solar Cell

How Does It Work?

The junction of dissimilar materials (n and p typesilicon) creates a voltage

Energy from sunlight knocks out electrons, creatinga electron and a hole in the junction

Connecting both sides to an external circuitcauses current to flow

In essence, sunlight on a solar cell creates a smallbattery with voltages typically 0.5 V DC

How solar cells Generate electricity

A PV system consists of : Photon interaction in a semi conductor three processes

are required :

The photons have to be absorbed in the active part of the material

and result in electrons being excited to a higher energy potential.

The electron hole charge carrier created by the absorption must be

physically separated and moved to the edge of the cell.

The charge carriers must be removed from the cell and delivered to a

useful load before they loose their extra potential.


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A PV system consists of :

For completing the above processes a solar cell consists of

*Semiconductor in which electron hole pairs are created by

absorption of incident solar radiation

*Region containing a drift field for charge separation and

*Charge collecting front and back electrodes.

The photo-voltaic effect can be described easily for p-n junction in

semiconductor. Combination of n-type and p-type semiconductors

thus constitute a photovoltaic cells or solar cell. The electric field

which separates the charge created by the absorption of sunlight.

This p-n junction is usually obtained by putting a p-type basematerial into a diffusion furnace containing a gaseous n-type

doping such as phosphorous and allowing the n-dopant to

diffuse into the surface about 0.2m.

Each of the individual solar cells will produce power at about

0.5V with the current directly proportional to the cells area.

Current voltage relationship is given by

Ji = Jo [exp (Ve/KT) 1 ]

Jo saturation current

V- voltage across junction

E- electronic charge

K- boltzmanns constant

T- absolute temperature

Conversion Efficiency and Power Output

The equivalent circuit of a Solar Cell :

J=JL JI=JL- Jo [exp (Ve/KT) 1 ]

Photovoltaic semi-conductors with conversion

efficiencies up to about 25% or more are known, but it is

uncertain if the extra conversion efficiency can

compensate for the additional cost, except in special

circumstances.

The maximum power of a silicon cell occurs at an output

voltage of approximately 0.45 volt.

A Basic Photovoltaic System forPower Generation


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Solar array A Blocking diode

Battery storage

Inverter/Converter

Appropriate switches and circuit breakers

Combining Solar Cells

Solar cells can be electrically connected inseries (voltages add) or in parallel (currents

add) to give any desired voltage and current(or power) output since P = I x V.

Photovoltaic cells are typically sold in

modules (or panels) of 12 volts with power

outputs of 50 to 100+ watts. These are thencombined into arrays to give the desired

power or watts.

From Cells to Modules

The open circuit voltage of a

single solar cell is approx 0.5V.

Much higher voltage is required

for practical application.

Solar cells are connected inseries to increase its open circuit

voltage.

Cells, Modules, Arrays

Advantages of Solar Photovoltaic System

Direct room temperature conversion of light to electricity

Absence of moving parts

Highly reliable / No pollution / Long life

High power to weight ratio

Consume no fuel to operate as the suns energy is free

Amenable to on site installation

Disadvantages : High cost

Storage is required


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Applications of Solar PhotovoltaicSystem

Water pumping sets for micro irrigation and drinking watersupply.

Community radio and Television sets

Railway signaling equipments.

A PV array

Street Lighting

Weather monitoring

PV was developed for the spaceprogram in the 1960s

Photovoltaic Array for Lighting Telecommunications Tower

Remote Water Pumping in Utah

Recreation Vehicle Outfitted with

Solar Panels


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Solar Lanterns for Landscaping A Solar Driven Band

Pole Mounted PV Pole Mounted PV

Maximum Power Point Tracking Maximum power point tracking(MPPT) is a techniquethat grid tie inverters, solar battery chargers and similardevices use to get the maximum possible power from oneor more solar panels.

Solar cells have a complex relationship between solarirradiation, temperature and total resistance that produces

a non-linear output efficiency known as the I-V curve. It isthe purpose of the MPPT system to sample the output of

the cells and apply the proper resistance (load) to obtainmaximum power for any given environmental conditions.


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Photovoltaic cells have a complex relationship between

their operating environment and the maximum powerthey can produce. For any given set of operational

conditions, cells have a single operating point where thevalues of the current (I) and Voltage (V) of the cell resultin a maximum power output.

These values correspond to a particular load resistance,

which is equal to V / I as specified by Ohm's Law. The

power P is given by P=V*I. From basic circuit theory, thepower delivered from or to a device is optimized wherethe derivative (graphically, the slope) dI/dV of the I-V

curve is equal and opposite the I/Vratio (where dP/dV=0).This is known as the maximum power point (MPP)

and corresponds to the "knee" of the curve.

A load with resistance R=V/Iequal to the reciprocal ofthis value draws the maximum power from the device.

This is sometimes called the characteristicresistanceof the cell. This is a dynamic quantity which

changes depending on the level of illumination, as well asother factors such as temperature and the age of thecell. If the resistance is lower or higher than this value,

the power drawn will be less than the maximum

available, and thus the cell will not be used as efficientlyas it could be. Maximum power point trackers utilize

different types of control circuit or logic to search forthis point and thus to allow the converter circuit toextract the maximum power available from a cell.

Controllers usually follow one of three

types of strategies to optimize the poweroutput of an array. Maximum power point

trackers may implement differentalgorithms and switch between them

based on the operating conditions of the

array.

Perturb and observe

Incremental conductance

Constant voltage

Maximum Power Point Tracking, frequently referred to as

MPPT, is an electronic system that operates the Photovoltaic

(PV) modules in a manner that allows the modules to

produce all the power they are capable of.

MPPT is not a mechanical tracking system that physically

moves the modules to make them point more directly at the

sun.

MPPT can be used in conjunction with a mechanical tracking

system, but the two systems are completely different.

MPPT is a fully electronic system that varies the electrical

operating point of the modules so that the modules are ableto deliver maximum available power. Additional power

harvested from the modules is then made available as

increased battery charge current.

A MPPT solar charge controller is the charge controller

embedded with MPPT algorithm to maximize the amount of

current going into the battery from PV module.

MPPT is DC to DC converter which operates by taking DC

input from PV module, changing it to AC and converting it

back to a different DC voltage and current to exactly match

the PV module to the battery.


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MPPT Working To understand how MPPT works, lets first consider the operation of a conventional

(nonMPPT) charge controller. When a conventional controller is charging a discharged

battery, it simply connects the modules directly to the battery. This forces the modules to

operate at battery voltage, typically not the ideal operating voltage at which the modulesare able to produce their maximum available power. The PV Module

Power/Voltage/Current graph shows the traditional Current/Voltage curve for a typical75W module at standard test conditions of 25C cell temperature and 1000W/m 2 ofinsolation. This graph also shows PV module power delivered vs module voltage. For the

example shown, the conventional controller simply connects the module to the batteryand therefore forces the module to operate at 12V. By forcing the 75W module tooperate at 12V the conventional controller artificially limits power production to 53W.

MPPT Characteristics

146

The MPPT system in a Solar Boost charge controller

calculates the voltage at which the module is able toproduce maximum power Rather than simply connecting

the module to the battery, the MPPT system in a Solar

Boost charge controller calculates the voltage at which

the module is able to produce maximum power. In this

example the maximum power voltage of the module

(VMP) is 17V. The MPPT system then operates the

modules at 17V to extract the full 75W, regardless of

present battery voltage. A high efficiency DC-to-DC

power converter converts the 17V module voltage at

the controller input to battery voltage at the output.

Contd..

In this Example, the maximum power voltage of themodule (VMP) is 17V

The MPPT system then operates the modules at 17V toextract the full 75W, regardless of present battery voltage.

Actual charge current increase varies with operatingconditions. As shown in fig., the greater the differencebetween PV module maximum power voltage VMP and

battery voltage, the greater the charge current increasewill be.

147 148

MPP

Electrical Output Characteristic

Maximum Power depends on the environment:Insolation, clouds, mobile

applications, reflection and temperature

Maximum Power Point Tracking (MPPT) Algorithms:Constant voltage,

constant current, incremental conductance

Conclusions of MPPT

Power output of the module improves with

the MPPT system than it was with out the

MPPT system.

Conclusions of MPPT

Temperature of the module is an important parameter. The

power output of the module changes by about 0.5% for every

degree rise in temperature. So a 38W module gives only a

power of about 29W peak

The module placement also plays an important role in power

output. Module is kept in south facing. Buts its elevation angle

must be adjusted every month to get high power output.

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