Energy - ENGRI 111 ENERGY Click to edit Master subtitle...

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Click to edit Master subtitle style 10/21/09 ENGRI 111 ENERGY
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10/21/09 Issue Fossil fuels produce CO2 CO2 does not let heat escape and produces the “green house” effect Climate changes
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10/21/09 Are we Doing Enough? D.M. Kammen, Scientific American, Sept. 2006
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10/21/09 Photovoltaics Solar cells/photovoltaics Phos – light Alessandro Volta – a pioneer in the study of electricity (1745 – 1827) www.climatechange.gc .ca
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10/21/09 Solar Cells/Photovoltaics Semiconductors devices convert sunlight into electricity Sunlight could potentially supply ~5,000 times world energy needs Cost 20-25 cents/kW-hr
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10/21/09 Photosynthesis photoscience.la.asu.edu/photo syn Solar Energy to Chemical Energy Plants, bacteria
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10/21/09 Absorption Spectra photoscience.la.asu.edu/photo syn
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10/21/09 6CO2 + 6H2O C6H12O6 + 6O2 http://www.sinauer.c om/ Carbohydrates: high-calorie food ~ 1% conversion
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10/21/09 Photovoltaics Nothing more than large-area photodetectors Vast majority are based on Si Si is abundant Si-based photovoltaics can exploit advances in microelectronics
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10/21/09
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10/21/09 + - h ν
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10/21/09 Photovoltaics www.energy.ca.g
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10/21/09 www.fsec.ucf.edu/pvt/pvba panel array
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10/21/09 Issues Top electrode Thickness of top layer in junction Other coatings
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10/21/09 Challenges/Efficiency In the 50’s Si solar cells had an efficiency of ~ 5% By the early 60’s efficiency was 15% Spacecrafts and satellites Fundamental limit of ~30% Silicon cannot absorb all photons
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10/21/09 Sun Spectrum 350 nm 1,100 nm
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10/21/09 www.wikipedia.com Gases in Atmosphere Absorb Radiation
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10/21/09 Si Absorption Spectrum
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10/21/09 Challenges q Silicon cannot absorb all photons q Other losses come from § fast recombination Every photon does not produce an e/h pair § Thermalization Energy more than the Band Gap is lost as heat q Indirect band gap semiconductor Solution: Amorphous silicon
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Hydrogenated Amorphous Si Direct Band Gap More efficient absorption Less material needed
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This note was uploaded on 10/21/2009 for the course ENGRI 1110 at Cornell University (Engineering School).

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Energy - ENGRI 111 ENERGY Click to edit Master subtitle...

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