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1、Copyright 2005 SRI InternationalClean Solar EnergyThe impact of nanoscale science on solar energy production2Sources:http:/www1.eere.energy.gov/solar/pv_systems.html http:/ is Solar Energy?Energy produced by the sun Clean,renewable source of energy Harnessed by solar collection methods such as solar

2、 cells Converted into usable energy such as electricityPhotovoltaic(solar)panelSet of solar panelsSun and electrical power lines3Energy from the Sun is Abundant Solar power systems installed in the areas defined by the dark disks could meet the worlds current total energy demand Source:http:/www.ez2

3、c.de/ml/solar_land_area/420 TWSources:http:/energy.cr.usgs.gov/energy/stats_ctry/Stat1.html http:/www.census.gov/main/www/popclock.htmlCurrent U.S.Energy Demand The US consumes 25%of the worlds energy,but has only 4.5%of its population Solar cells would need to cover an area comparable to the size o

4、f Texas to meet US energy demand today520 TW180,000 TWof sunlighthit the earthevery daySources:http:/energy.cr.usgs.gov/energy/stats_ctry/Stat1.html http:/www.census.gov/main/www/popclock.htmlProjected U.S.Energy Demand in 2050 To meet projected U.S.demand in 2050,solar cells would need to cover app

5、roximately one third of the U.S.6Solar Panel Use Today Large companies like Google,Walmart,and Microsoft use solar energy to partially power some of their facilitiesSolar panels on Microsoft buildingSolar panels being tested on Walmart storeSources:http:/ http:/www.solarwall.de/assets/images/Walmart

6、_SW.jpg7Sources:http:/www.elp.uji.es/juan_home/images/solar_cell/flex1.JPG http:/www.wisconsun.org/images/siemen_cell.jpg,http:/en.wikipedia.org/wiki/Solar_cellSilicon-based solar cellDye-sensitized solar cellPhotovoltaic Solar Cells Generate electricity directly from sunlight 2 Main types:Single-cr

7、ystal silicon(traditional)Widespread Expensive to manufacture Dye-sensitized(“nano”)Newer,less proven Inexpensive to manufacture Flexible8Sources:http:/www.econedlink.org/lessons/EM189/images/cartoon_tv.gif http:/ Cells are Converters of Energy Solar cells are devices that take light energy as input

8、 and convert it into electrical energyLight energySolar cell-converts light energy to electricityElectrical energy(carried through wires)9Source:http:/ Not All Energy is Converted Like chloroplasts in plants,solar cells can only absorb specific wavelengths of light.In both,light that isnt absorbed i

9、s either transmitted through or reflected back.Whether a certain wavelength of lights gets absorbed depends on its energy.Chlorophyll molecules absorb blue and red light,but reflect green light10A Little Background on Light Different colors of light have different wavelengths and different energiesS

10、ource:http:/ of Light by AtomsSources:http:/ electron transition in an isolated atom Absorption occurs only when the energy of the light equals the energy of transition of an electron Light12Molecules have multiple atoms bonded togetherMore energy states in molecules than atomsMore electron“jumps”po

11、ssible-light with a range of frequencies are absorbedSource:Image adapted from http:/ of Light by MoleculesSmallest D DE possible13 Electrons can jump between“bands”Incident light with energy than the“band gap”energy can be used to excite the electronsSource:Image adapted from http:/ of Light by Ion

12、ic Compounds14So What Does this Mean for Solar Cells?In dye-sensitized solar cells Talk about highest occupied molecular orbital(HOMO)and lowest unoccupied molecular orbital(LUMO)Source:Original Images In single-crystal silicon solar cells Talk about“conduction band”(excited states)and“valence band”

13、(ground states)15A Closer Look at Solar Cells How do traditional,silicon-based solar cells and newer,dye-sensitized solar cells work?What are the advantages and disadvantages of each type of cell?Sources:http:/www.norfolksolar.co.uk/img/system.gif http:/ solar cellDye-sensitized solar cell16Source:h

14、ttp:/nanosense.org/activities/cleanenergy/solarcellanimation.htmlHow a Silicon-Based Solar Cell Works A positive“hole”is left in the electrons place This separation of electrons and holes creates a voltage and a current Light with energy greater than the band gap energy of Si is absorbed Energy is g

15、iven to an electron in the crystal lattice The energy excites the electron;it is free to moveClick image to launch animation(requires web access)17Silicon-Based Solar Cell Attributes Expensive Made in high vacuum at high heat High manufacturing costs Need TLC Fragile,rigid,thick Long return on inves

16、tment Takes 4 years to produce energy savings equivalent to cost of productionSource:http:/ a Dye-Sensitized Cell WorksClick image to launch animation(requires web access)Light with high enough energy excites electrons in dye molecules Excited electrons infused into semiconducting TiO2,transported o

17、ut of cell Positive“holes”left in dye molecules Separation of excited electrons and“holes”creates a voltageSource:http:/nanosense.org/activities/cleanenergy/solarcellanimation.html19Source:http:/www.imo.uhasselt.be/polytech/images/zonnecel1.jpgDye-Sensitized Solar Cells Relatively inexpensive Made i

18、n non-vacuum setting mainly at room temperature Relatively simple manufacturing process Need little TLC Thin,lightweight,flexible Short return on investment Takes approx 3 months to produce energy savings equivalent to cost of production20Sources:http:/www.imo.uhasselt.be/polytech/images/zonnecel1.j

19、pg http:/www.norfolksolar.co.uk/img/system.gifDye-Sensitized and Silicon-based Solar Cells Compared Dye-Sensitized Relatively inexpensive Need little TLC Short return on investment Traditional Expensive Need TLC Long return on investment21Sources:http:/en.wikipedia.org/wiki/Solar_energhttp:/ solar c

20、ollector(parabolic)Solar Electric Power Plants Harness solar power to generate electricity Main types:Solar thermal energy Has mirrored surface that reflects sunlight to heat up liquid to make steam to generate electricity Photovoltaic Uses photovoltaic cells that absorb direct sunlight(as discussed

21、 previously)Array of mirrored solar collectors atFPL Energy site in California22Source:http:/www.norfolksolar.co.uk/img/system.gifExample system with water heated by solar collector and used to supplement hot water radiatorSolar Heating Systems Direct heating of fluid;no conversion to electricity Co

22、mponents solar thermal collectors fluid system to move heat(not electricity)reservoir to stock heat for later use Common uses Heat water for home or pool23Sources:http:/p2library.nfesc.navy.mil/issues/emergejan2007/wind_turbine.jpghttp:/ Energy is Solar Energy Wind is driven by solar heating Largest

23、 and fastest growing solar energy conversion systemWind“farm”in CaliforniaWind turbines24Important Summary Questions What are clean and renewable energy sources?What are current and projected global energy demands?How do newer,nanotechnology-influenced solar cells work,and how do they differ from traditional solar cells?