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1、英文资料ENERGYFROMTHESUNThesunhasproducedenergyforbillionsofyears. Solarenergyisthesolarradiationthatreachestheearth.Solarenergycanbeconverteddirectlyorindirectlyintootherformsofenergy,suchasheatandelectricity. Themajordrawbacks(problems,orissuestoovercome)ofsolar
2、energyare:(1)theintermittentandvariablemannerinwhichitarrivesattheearth'ssurfaceand,(2)thelargearearequiredtocollectitatausefulrate.Solarenergyisusedforheatingwaterfordomesticuse,spaceheatingofbuildings,dryingagriculturalproducts,andgeneratingelectricalenergy.
3、Inthe1830s,theBritishastronomerJohnHerschelusedasolarcollectorboxtocookfoodduringanexpeditiontoAfrica.Now,peoplearetryingtousethesun'senergyforlotsofthings.Electricutilitiesaretryingphotovoltaics,aprocessbywhichsolarenergyisconverteddirectlytoelectricity. Elec
4、tricitycanbeproduceddirectlyfromsolarenergyusingphotovoltaicdevicesorindirectlyfromsteamgeneratorsusingsolarthermalcollectorstoheataworkingfluid.Outofthe14knownsolarelectricgeneratingunitsoperatingintheUSattheendof2004,10oftheseareinCalifornia,and4inArizona.No
5、statisticsarebeingcollectedonsolarplantsthatproducelessthan1megawattofelectricity,sotheremaybesmallersolarplantsinanumberofotherstates.PHOTOVOLTAICENERGYPhotovoltaicenergyistheconversionofsunlightintoelectricitythroughaphotovoltaic(PVs)cell,commonlycalledasola
6、rcell. Aphotovoltaiccellisanonmechanicaldeviceusuallymadefromsiliconalloys.Sunlightiscomposedofphotons,orparticlesofsolarenergy. Thesephotonscontainvariousamountsofenergycorrespondingtothedifferentwavelengthsofthesolarspectrum. Whenphotonsstrikeaphotovoltaicce
7、ll,theymaybereflected,passrightthrough,orbeabsorbed. Onlytheabsorbedphotonsprovideenergytogenerateelectricity. Whenenoughsunlight(energy)isabsorbedbythematerial(asemiconductor),electronsaredislodgedfromthematerial'satoms. Specialtreatmentofthematerialsurfacedu
8、ringmanufacturingmakesthefrontsurfaceofthecellmorereceptivetofreeelectrons,sotheelectronsnaturallymigratetothesurface. Whentheelectronsleavetheirposition,holesareformed. Whenmanyel
