Solar Energy IIChapter 4 SummarySlide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Renewable Energy ConsumptionThe Solar SpectrumHow much energy is available?Input flux (average properties)Making sense of the dataAnother View ofComparable numbersiClicker QuestionSlide 21Energy BalanceAverage InsolationInsolation variationSlide 25Slide 26Average daily radiation receivedHigher Resolution Insolation MapTilted SurfacesWhich is best?Orientation ComparisonNumerical Comparison: Winter at 40º latitudeTotal available solar energySo why don’t we go solar?Making sense of the big numbersAlternatives for using solar energyMethods of Harvesting SunlightPhotovoltaic (PV) SchemeProvide a circuit for the electron flowSlide 40Slide 41PV typesHow good can it get?Silicon Photovoltaic BudgetPV Cells as “Batteries”Typical I-V curvesSlide 47Slide 48How much does it cost?Solar EconomicsSolar’s Dirty SecretThe Powell Solar Array at UCSDPowell PV Project DisplaySlide 54Slide 55Slide 56Slide 57Slide 58Powell Array ParticularsUCSD 1 MW initiative: Gilman = 200 kWThe Biggest of the BigSolar Economics, revisitedSlide 63Slide 64Notable quotesSlide 66Slide 67Review Four Basic Solar Energy SchemesPhotovoltaic ReminderPhotovoltaic power schemeTypical InstallationPutting photovoltaics on your roofWhen the sun doesn’t shine…Photovoltaic TransportationPhotovoltaic transportationFuture ProjectionsBut not all is rosy in PV-land…Solar Thermal GenerationConcentration SchemesThe steering problemPower TowersWho needs a parabolaBarstow SchemeSolar thermal economicsFlat-Plate Collector SystemsFlat-Plate CollectorControlling the heat flowWhat does the glass do, exactly?An example water-heater systemSlide 90Slide 91Flat plate efficienciesHow much would a household need?Some Amusing Societal FactsPassive Solar HeatingSouth-Facing WindowThe Trombe WallHow much heat is available?1Solar Energy IILecture #9HNRS 228Energy and the Environment2Chapter 4 Summary•Energy from the Sun–Spoke way too much about this in our last meeting•Today’s focus–Photovoltaic systemsMaking electricity directly–Solar Thermal SystemsElectric power generation indirectly–Passive solar systems3iClicker QuestionThe release of energy from the Sun is accompanied by a very slight A increase in the Sun's gravitational attraction on the planets B increase in the Sun's rotation rate C decrease in the mass of the Sun Dall of the above are trueE none of the above are true4iClicker QuestionThe release of energy from the Sun is accompanied by a very slight A increase in the Sun's gravitational attraction on the planets B increase in the Sun's rotation rate C decrease in the mass of the Sun Dall of the above are trueE none of the above are true5iClicker QuestionMost of the Sun's energy is produced in A supergranules B the convection zone C the photosphere D the chromosphereE the core6iClicker QuestionMost of the Sun's energy is produced in A supergranules B the convection zone C the photosphere D the chromosphereE the core7iClicker QuestionEnergy generation in the Sun results from •A fission of uranium•B fission of hydrogen•C gravitational contraction •D the Sun isn't generating energy•E fusion of hydrogen8iClicker QuestionEnergy generation in the Sun results from •A fission of uranium•B fission of hydrogen•C gravitational contraction •D the Sun isn't generating energy•E fusion of hydrogen9iClicker QuestionThe highest temperatures found in the Sun’s atmosphere is located in the •A chromosphere •B corona •C photosphere •D core•E cytosphere10iClicker QuestionThe highest temperatures found in the Sun’s atmosphere is located in the •A chromosphere •B corona •C photosphere •D core•E cytosphere11iClicker QuestionSunspot cycles are, on the average, what length?•A 22 years•B 11 years•C 5.5 years•D 1 year•E 3 years12iClicker QuestionSunspot cycles are, on the average, what length?•A 22 years•B 11 years•C 5.5 years•D 1 year•E 3 years13Renewable Energy ConsumptionEnergy SourceQBtu (1994)Percent (1994)QBtu (2003)Percent (2003)Hydroelectric3.037 3.43 2.779 2.83Geothermal0.357 0.40 0.314 0.32Biomass 2.852 3.22 2.884 2.94Solar Energy0.069 0.077 0.063 0.06Wind 0.036 0.040 0.108 0.11Total 6.351 7.18 6.15 6.314The Solar SpectrumO2H2OH2OH2O,CO2H2O, CO2Atmospheric absorptionabove the atmosphereat ground level15How much energy is available?•Above the atmosphere, we get 1368 W/m2 of radiated power from the sun, across all wavelengths–This number varies by ±3% as our distance to the sun increases or decreases (elliptical orbit)–The book uses 2 calories per minute per cm2•At the ground, this number is smaller due to scattering and absorption in the atmosphere–about 63%, or ~850 W/m2 with no clouds, perpendicular surface–probably higher in dry desert air16Input flux (average properties)17Making sense of the data•Derived from the previous figure–52% of the incoming light hits clouds, 48% does not25% + 10% + 17%–in cloudless conditions, half (24/48) is direct, 63% (30/48) reaches the ground–in cloudy conditions, 17/52 = 33% reaches the groundabout half of the light of a cloudless day–averaging all conditions, about half of the sunlight incident on the earth reaches the ground–the analysis is simplifiedassumes atmospheric scattering/absorption is not relevant when cloudy18Another View of19Comparable numbers•Both versions indicate about half the light reaching (being absorbed by) the ground–47% vs. 51%•Both versions have about 1/3 reflected back to space–34% vs. 30%•Both versions have about 1/5 absorbed in the atmosphere/clouds–19% vs. 19%20iClicker Question•Roughly what percentage of light from the Sun reaches the ground?–A 10%–B 20%–C 30%–D 40%–E 50%21iClicker Question•Roughly what percentage of light from the Sun reaches the ground?–A 10%–B 20%–C 30%–D 40%–E 50%22Energy Balance•Note that every bit of the energy received by the sun is reflected or radiated back to space•If this were not true, earth’s temperature would change until the radiation out balanced the radiation in•In this way, we can compute surface temperatures of other planets (and they compare well with measurements)23Average Insolation•The amount of light received by a horizontal surface (in W/m2) averaged over the year (day & night) is called the insolation•We can make a guess based on the facts that on average:–half the