Lecture19-AlternativeEnergyResources-SolarPower

8/9/2019 Lecture19-AlternativeEnergyResources-SolarPower

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Page 1of 7Lecture 19

Lecture 19: Alternative Energy

Resources The Solar PowerThe Energy Resources

One of the greatest challenges facing mankind in the twenty-first century is energy. Starting withthe industrial revolution in the eighteenth century, fossil fuels such as coal, petroleum, and naturalgas have been the main energy resources for everything vital for human society: from steamengines to Otto and diesel engines, from electricity to heating and cooling of buildings, fromcooking and hot-water making, from lighting to various electric and electronic gadgets, as well asfor most of the transportation means. However, fossil fuel resources as stored energy accumulatedduring hundreds of millions of years are being rapidly depleted by excessive exploration. n

addition, the burning of fossil fuels has caused and is causing damage to the environment of!arth.

Alternative Energy Resources

"lternative energy is any energy source that is an alternative to fossil fuel. #hese alternatives areintended to address concerns about such fossil fuels. n a general sense, alternative energy as it iscurrently conceived is that which is produced or recovered without the undesirable conse$uencesinherent in fossil fuel use, particularly high carbon dioxide emissions, an important factorin global warming.

!xamples ncludes:

Solar

%ind

Hydro

&eothermal

'iomass

#idal

"ll of these are carbon free or actually carbon neutral, used almost exclusively to produce electricity

Solar Energy


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"ccording to well-established measurements, theaverage power density of solar radiation (ustoutside the atmosphere of the !arth is )*++%m, widely known as the solar constant. #hedefinition of the meter is one over ),, of!arth/s meridian, from the 0orth 1ole to the

e$uator. #his definition is still pretty accurateaccording to modern measurements. #herefore,the radius of !arth is 234 5 )6m.

#he total power of solar radiation reaching !arthis then

Solar power 7 )*++ 5 83 5 ))8 ).6* 5

))6%.

!ach day has 9+,8 s, and on average, each year has *+.8 days. #he total energy of solarradiation reaching !arth per year is

"nnual solar energy 7 ).6* 5 ))65 9+8 5 *+.8 .8+ 5 )8;.

Or ,8+, !;year. #o have an idea of how much energy that is, let us compare it with annualglobal energy consumption. n the years


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for producing electricity in a few rural areas. "lternate !nergy Aevelopment 'oard 2"!A'4electrified approximately * households with total 1C power generation of k% in districtsof Dohat 20%E14, A.&. Dhan, Fawalpindi 21un(ab4, #harparkar 2Sindh4, #urbatDalat2'alochistan4, etc. while providing 9 % panels with lighting system to each household. 1akistanGouncil of Fenewable !nergy #echnologies 21GF!#4 electrified more than schools,mos$ues, houses through 1C power with total generation capacity of more than 9 k%.

#he total installation appears to be much less than ) k% in 1C and ), solar thermal units2all kind4 in the country.

Solar Energy Systems

#hree different methods are used to utilie solar energy

Solar Heating Solar #hermal 1hotovoltaic


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Solar Heating

1roduces heat for hot water

'lack collector to maximie

absorption Betal tubes circulating in thermal

contact with collector

Aouble-pane glass to trap energy

radiated by glass. #he greenhouseeffect again.

Flat Panel Efficiency

#ransmission through glass panes: 9=

"bsorption by black sheet: >=

Fadioactive loss through double glass pane: *=

Gonvective conductive losses: )=

#otal efficiency: .9 x .> x .6 x .> 7 =

Some Interesting Facts

n the early )>9/s, high oil prices led the IS government to offer tax credits for

installation of solar panels, so they were essentially free.

Bany units were installed until the program was dropped in )>9. Bost were used to heat swimming pools.

n other parts of the world, solar water heaters are far more common.

o >= of homes in Gypress

o += of homes in srael

Solar Thermal

Concentrating Sunlight

" flat panel collector in the midday sun with 9 %m can only reach temperature of about )6o

E. So can/t use this to produce electricity with steam turbine and need to concentrate the Sun/senergy.

Fig. 19.3: Solar Water Heater

Fig. 19.4: Ea!ple of Solar Water Heating Syste!


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#wo approaches

"rray of many mirrors to focus sunlight on a boiler

mounted on a tower

Set of dishes or troughs to focus sunlight onto pipes

carrying a heated fluid that is then pumped to a boiler.

" parabolic reflector brings all parallel rays to a common focus

Goncentration factors of a few thousand are achievable.

#emperatures of over oE can be achieved

#he parabolic reflectors must be steered to

follow the Sun

#wo axis steering 2dish4 is best

#emperature goes like fourth root of the

concentration factor

Fecall the blackbody radiation law: power goes

like temperature to the fourth power

The Barstow Tower

)> ft x ft reflectors

Goncentration factor of few thousand

) B% of peak power produced with

less than B% average power

Fig. 19.": Solar Po#er $ro%g&s

Fig. 19.': Solar Po#er $o#er

Fig. 19.(: )a* $&e +arsto# $o#er, )-* $&e #orking principle


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Solar Photovoltaic

" certain amount of energy is needed to move an electron from thevalence band to the conduction band. %hen this happens, a JholeKabsence of an electron is left in the valence band.

One way to get some electrons into the conduction is by thermal2heat4 energy. "t a given temperature there will be a certain numberof electrons in the conduction band and the same number of holes inthe valence band.#he higher the temperature the more there will be.

f a photon of energy greater the band gap interacts with the silicon, it creates an electron-holepair. t puts an electron into the conduction band leaving a hole in the

valence band. #his produces an electric current that can be used to lightlamps etc.

" solar cell is somewhat like a battery but different in working. "battery puts out a constant voltage up to some maximum current. "silicon photovoltaic puts out a current that is proportional to theintensity of light shining on it up to a maximum voltage that for siliconis about .+ C.

Comining Cell Together

" single 1C cell in sun act like a battery. Stack cell in series to get

useful power. " typical panel has *+ cells for about ) C, but actuallydrops to L)+C at maximum power which is well suited to charge ) Cbatteries.

Baximum efficiency of silicon is *= with 8= loss as waste heat.!fficiencies greater than 8= have been achieved by using multiplelayers of different materials, but are expensive.

!ivingston Solar Farm

6 solar panels

)9 k% average power about homes

Fig. 19.: Silicon Crystal +an/ 0ap

Fig. 19.9: Silicon Crystal +an/ 0ap P&oton Ecitation

Fig. 19.1: Solar Panel Config%ration


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)= of the Mivingston Gampus

* tons of carbon savings per year

Gost: N) million, levelied cost over years:

* cents per k%h

Area "ee#e# to Power Pakistan

Gurrent power re$uirement of 1akistan L , B%1ower ield 2L* %m in 'aluchistan4 L 8 %m

2)=4"rea needed 7 km

Fig. 19.11: iingston Solar Far!

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Lecture19-AlternativeEnergyResources-SolarPower