Solar Energy Presentation 0220

8/2/2019 Solar Energy Presentation 0220

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Solar Energy:

The Ultimate Renewable

Resource

Xiangfeng Duan


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What is Solar Energy?What is Solar Energy?

Originates with theOriginates with thethermonuclear fusionthermonuclear fusionreactions occurring in thereactions occurring in thesun.sun.

Represents the entireRepresents the entireelectromagnetic radiationelectromagnetic radiation(visible light, infrared,(visible light, infrared,ultraviolet, xultraviolet, x--rays, and radiorays, and radio

waves).waves).

Radiant energy from the sunRadiant energy from the sunhas powered life on Earth forhas powered life on Earth formany millions of years.many millions of years.


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Advantages and DisadvantagesAdvantages and Disadvantages AdvantagesAdvantages

All chemical and radioactive polluting byproducts of theAll chemical and radioactive polluting byproducts of thethermonuclear reactions remain behind on the sun, while only purethermonuclear reactions remain behind on the sun, while only pureradiant energy reaches the Earth.radiant energy reaches the Earth.

Energy reaching the earth is incredible. By one calculation, 30 daysEnergy reaching the earth is incredible. By one calculation, 30 days

of sunshine striking the Earth have the energy equivalent of the totalof sunshine striking the Earth have the energy equivalent of the totalof all the planets fossil fuels, both used and unused!of all the planets fossil fuels, both used and unused!

DisadvantagesDisadvantages

Sun does not shine consistently.Sun does not shine consistently.

Solar energy is a diffuse source. To harness it, we must concentrate itSolar energy is a diffuse source. To harness it, we must concentrate it

into an amount and form that we can use, such as heat and electricity.into an amount and form that we can use, such as heat and electricity. Addressed by approaching the problem through:Addressed by approaching the problem through:

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


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Solar Energy toSolar Energy to Heat Living SpacesHeat Living Spaces

Properdesign of a building is for it to act as a solarProperdesign of a building is for it to act as a solarcollectorand storage unit. This is achieved throughcollectorand storage unit. This is achieved throughthree elements: insulation, collection, and storage.three elements: insulation, collection, and storage.


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Solar Energy to Heat WaterSolar Energy to Heat Water

A flatA flat--plate collector is usedplate collector is usedto absorb the suns energy toto absorb the suns energy toheat the water.heat the water.

The water circulatesThe water circulatesthroughout the closed systemthroughout the closed systemdue to convection currents.due to convection currents.

Tanks of hot water are usedTanks of hot water are usedas storage.as storage.


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PhotovoltaicsPhotovoltaics

PhotoPhoto++voltaicvoltaic = convert= convert lightlight toto electricityelectricity


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Solar Cells BackgroundSolar Cells Background

18391839 -- French physicist A. E. Becquerel first recognized the photovoltaicFrench physicist A. E. Becquerel first recognized the photovoltaiceffect.effect.

18831883 -- first solar cell built, by Charles Fritts, coated semiconductorfirst solar cell built, by Charles Fritts, coated semiconductorselenium with an extremely thin layer of gold to form the junctions.selenium with an extremely thin layer of gold to form the junctions.

19541954 -- Bell Laboratories, experimenting with semiconductors, accidentallyBell Laboratories, experimenting with semiconductors, accidentallyfound that silicon doped with certain impurities was very sensitive to light.found that silicon doped with certain impurities was very sensitive to light.Daryl Chapin, Calvin Fuller and Gerald Pearson, invented the firstDaryl Chapin, Calvin Fuller and Gerald Pearson, invented the firstpractical device for converting sunlight into useful electrical power.practical device for converting sunlight into useful electrical power.Resulted in the production of the first practical solar cells with a sunlightResulted in the production of the first practical solar cells with a sunlightenergy conversion efficiency of around 6%.energy conversion efficiency of around 6%.

19581958 -- First spacecraft to use solar panels was US satellite Vanguard 1First spacecraft to use solar panels was US satellite Vanguard 1

http://en.wikipedia.org/wiki/Solar_cell


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Driven by Space Applications inDriven by Space Applications in

Early DaysEarly Days


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The heart of a photovoltaic system is a solidThe heart of a photovoltaic system is a solid--state device called astate device called a

solar cell.solar cell.

How does it workHow does it work


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Energy Band Formation in SolidEnergy Band Formation in Solid

Each isolated atom has discrete energy level, with two electrons ofopposite spin occupying a state.

When atoms are brought into close contact, these energy levels split.

If there are a large number of atoms, the discrete energy levels form a

continuous band.


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Energy Band Diagram of a Conductor,Energy Band Diagram of a Conductor,

Semiconductor, and InsulatorSemiconductor, and Insulator

a conductor a semiconductor an insulator

Semiconductor is interest because their conductivity can be readily modulated(by impurity doping or electrical potential), offering a pathway to control electronic

circuits.


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SiliconSilicon

Si

Si

Si

Si

Si

-

Si Si Si

Si

SiSi

Si

Si

Si

Shared electrons

Silicon is group IV element with 4 electrons in theirvalence shell.

When silicon atoms are brought together, each atom forms covalent

bond with 4 silicon atoms in a tetrahedron geometry.


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Intrinsic SemiconductorIntrinsic SemiconductorAt 0 K, each electron is in its lowest energy state

so each covalent bond position is filled. If a smallelectric field is applied to the material, no electronswill move because they are bound to their individualatoms.

=>At 0 K, silicon is an insulator.

As temperature increases, the valence electronsgain thermal energy. If a valence electron gains

enough energy (Eg), it may break its covalent bondand move away from its original position. Thiselectron is free to move within the crystal.

ConductorEg 3-5eV, essentially no electron canbe thermally excited at room temperature.


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Extrinsic Semiconductor, nExtrinsic Semiconductor, n--type Dopingtype Doping

Electron

-

Si Si Si

Si

SiSi

Si

Si

As

Extra

Valence band, Ev

Eg= 1.1 eV

Conducting band, Ec

Ed~ 0.05 eV

Doping silicon lattice with group V elements can creates extra electrons

in the conduction band negative charge carriers (n-type), As- donor.

Doping concentration #/cm3 (1016/cm3 ~ 1/million).


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Valence band, Ev

Eg

= 1.1 eV

Conducting band, Ec

Ea ~ 0.05 eV

Electron

-

Si Si Si

Si

SiSi

Si

Si

B

Hole

Doping silicon with group III elements can creates empty holes in theconduction band positive charge carriers (p-type), B-(acceptor).

Extrinsic Semiconductor, pExtrinsic Semiconductor, p--type dopingtype doping


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V

I

R O F

p n

p n

V>0 V


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SolarCells

Light-emitting Diodes

Diode LasersPhotodetectors

Transistors

pp--n Junction (pn Junction (p--n diode)n diode)

A p-n junction is the basic device component for manyfunctional electronic devices listed above.


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How Solar Cells WorkHow Solar Cells Work

Photons in sunlight hit the solar panel and are absorbed by semiconducting materialsto create electron hole pairs.

Electrons (negatively charged) are knocked loose from their atoms, allowing them to

flow through the material to produce electricity.

p n

- +- +- +

- +

- +

hv > Eg


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The Impact of Band Gap on EfficiencyThe Impact of Band Gap on Efficiency

Efficiency,Efficiency, LL = (V= (VococIIscscFF)/PFF)/Pinin VVococ ww EEgg, I, Iscsc ww # of absorbed photons# of absorbed photons

Decrease EDecrease Egg, absorb more of the spectrum, absorb more of the spectrum

But not without sacrificing output voltageBut not without sacrificing output voltage

hv > Eg

-30

-20

-10

0

10

20

30

CurrentD

ensity(mA/cm2)

1.00.80.60.40.20.0

Voltage (volts)

Jsc

VocFF

Dark

Light

Jmp

Vmp

Fill Factor, FF = (VmpImp)/VocIscEfficiency, L = (VocIscFF)/Pin


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Cost vs. Efficiency TradeoffCost vs. Efficiency Tradeoff

Efficiency w X

1/2

Long dHigh XHigh Cost

d

Long dLow XLower Cost

d

X decreases as grain size (and cost) decreases

Large GrainSingle

Crystals

Small Grainand/orPolycrystalline

Solids


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Cost/Efficiency ofPhotovoltaic TechnologyCost/Efficiency ofPhotovoltaic Technology

Costs are modules per peak W; $0.35-$1.5/kW-hr


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89.6% of 2007 Production89.6% of 2007 Production

45.2% Single Crystal Si45.2% Single Crystal Si

42.2% Multi42.2% Multi--crystal SIcrystal SI

Limit efficiency 31%Limit efficiency 31% Single crystal siliconSingle crystal silicon -- 1616--19%19%

efficiencyefficiency MultiMulti--crystal siliconcrystal silicon -- 1414--15%15%

efficiencyefficiency Best efficiency by SunPower Inc 22%Best efficiency by SunPower Inc 22%

Silicon Cell Average Efficiency

First GenerationFirst Generation Single Junction Silicon CellsSingle Junction Silicon Cells


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CdTe 4.7% & CIGS 0.5% of 2007 ProductionCdTe 4.7% & CIGS 0.5% of 2007 Production

New materials and processes to improve efficiencyNew materials and processes to improve efficiencyand reduce cost.and reduce cost.

Thin film cells use about 1% of the expensiveThin film cells use about 1% of the expensive

semiconductors compared to First Generation cells.semiconductors compared to First Generation cells.

CdTeCdTe 88 11% efficiency (18% demonstrated)11% efficiency (18% demonstrated) CIGSCIGS 77--11% efficiency (20% demonstrated)11% efficiency (20% demonstrated)

Second GenerationSecond Generation Thin Film CellsThin Film Cells


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Enhance poor electrical performance while maintaining very lowEnhance poor electrical performance while maintaining very lowproduction costs.production costs.

Current research is targetingCurrent research is targetingconversion efficiencies of 30conversion efficiencies of 30--60%60%while retainingwhile retaininglow cost materials and manufacturing techniques.low cost materials and manufacturing techniques.

MultiMulti--junction cellsjunction cells 30% efficiency (4030% efficiency (40--43% demonstrated)43% demonstrated)

Third GenerationThird Generation MultiMulti--junction Cellsjunction Cells


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SolarHome Systems

Space

Water

PumpingTelecom

Main Application Areas Off-grid


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ResidentialHome

Systems (2-8kW)PV PowerPlants

( > 100 kW)

Commercial Building

Systems (50 kW)

Main Application Areas

Grid Connected


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Future Energy MixFuture Energy Mix


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Renewable Energy ConsumptionRenewable Energy Consumption

in the US Energy Supply, 2007in the US Energy Supply, 2007

http://www.eia.doe.gov/cneaf/solar.renewables/page/trends/highlight1.html


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Top 10 PVCell ProducersTop 10 PVCell Producers

Top 10 produce 53% of worldtotal

Q-Cells, SolarWorld - Germany

Sharp, Kyocera, Sharp, Sanyo Japan

Suntech, Yingli, JA Solar China

Motech - Taiwan


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(in the U.S. in 2002)

1-4

2.3-5.0 6-8

5-7

Production Cost of ElectricityProduction Cost of Electricity

0

5

10

15

20

25

Coal Gas Oil Wind Nuclear Solar

Cost

6-7

25-50


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Future GenerationFuture Generation Printable CellsPrintable Cells

Organic Cell

Nanostructured Cell

Solution Processible Semiconductor


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Organic Photovoltaics Convert Sunlight intoOrganic Photovoltaics Convert Sunlight into

Electrical Power.Electrical Power.

n

Trans-polyacetylene (t-PA)

S

n

Polythiophene (PT)

N

H

n

Polypyrrole (PPY)


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Nanotechnology Solar Cell Design


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Interpenetrating Nanostructured Networks

-

metal electrode

transparent electrode

glass

+- 100 nm

---

metal electrode

transparent electrode

glass

+- 100 nm


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Dye Sensitized SolarCell

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Solar Energy Presentation 0220