Solar Spectrum
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(2) Solar Spectrum. -Black body radiation. Light bulb 3000°K. Red->Yellow->White. Surface of Sun 6000°K. 2.
(3) Solar Spectrum. -Black body radiation. Light bulb 3000°K. Red->Yellow->White. Surface of Sun 6000°K. 3.
(4) Solar Spectrum. -Black body radiation. Light bulb 3000°K. Red->Yellow->White. Surface of Sun 6000°K. 4.
(5) Solar Spectrum. -Atmospheric Absorption and Scattering. Light bulb 3000°K. Red->Yellow->White. Surface of Sun 6000°K. 5.
(6) Solar Spectrum. -Atmospheric Absorption and Scattering. Light bulb 3000°K. Red->Yellow->White. Surface of Sun 6000°K. 6.
(7) Solar Spectrum. -Atmospheric Absorption and Scattering. Air Mass through which solar radiation passes. 7.
(8) Solar Spectrum. -Atmospheric Absorption and Scattering. Air Mass through which solar radiation passes. 8.
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(11) 11.
(12) 30% lost to Rayleigh Scattering λ-4 (blue sky/orange sunset). Scattering by aerosols (Smoke, Dust and Haze S.K. Friedlander). Absorption: Ozone all below 0.3 µm, CO2, O2, H2O. 12.
(13) 10% added to AM1 for clear skies by diffuse component. Increases with cloud cover. ½ lost to clouds is recovered in diffuse radiation. 13.
(14) 14.
(15) 15.
(16) Appendix A1. Direct and Diffuse Radiation. Global Radiation = Direct + Diffuse Radiation. AM1.5 Global AM1.5G irradiance for equator facing 37° tilted surface on earth (app. A1). Integral over all wavelengths is 970 W/m2 (or 1000 W/m2 for normalized spectrum) . is a standard to rate PV Close to maximum power received at the earths surface.. 16.
(17) Standard Spectrum is compared to Actual Spectrum for a site. Solar Insolation Levels. March. September. June. December. 17.
(18) Cape Town/Melbourne/Chattanooga. Gibraltar/Beirut/Shanghai. 18.
(19) Appendix B. 19.
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(21) 21.
(22) Need:. -Global radiation on a horizontal surface. -Horizontal direct and diffuse components of global value. -Estimate for tilted plane value. Equations given in Chapter on Sunlight. Peak sun hours reduces a days variation to a fixed number of peak hours for calculations. SSH = Sunshine Hours. Total number of hours above 210 W/m2 for a month. Equations in Chapter 1 to convert SSH to a useful form.. 22.
(23) Estimates of Diffuse Component. Clearness Index KT = diffuse/total. This is calculaed following the algorithm given in the chapter. Use number of sunny and cloudy days to calculate diffuse and direct insolation. Described in the book. 23.
(24) Tilted Surfaces. PV is mounted at a fixed tilt angle. 24.
(25) Sunny versus Cloudy. 25.
(26) 26.
(27) Calculation for . Optimal Tilt Angle. Given in the Chapter. 27.
(28) 1. 28. cosθ.
(29) P-N Junctions and Commercial Photovoltaic Devices. Chapter 2. 29.
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(31) 31.
(32) Czochralski Process. 32.
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(35) 35.
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(38) 38.
(39) Hot Wall CVD. 39.
(40) Plasma CVD. 40.
(41) 41.
(42) 42.
(43) Market Share. CIS= Copper Indium Gallium Selenide. a-Si= Amorphous Silicon. Ribbon= Multicrystalline Silicon from. Molten Bath. CdTe= Cadium Telluride/Cadmium Sulfide. Mono = Monocrystalline Silicaon. Multi= Muticrystalline Silicon. 43.
(44) http://www.asdn.net/asdn/physics/p-n-junctions.shtml. Depleted of . Free Carriers. 44. Negative ion cores. Positive ion cores.
(45) Carrier Generation. Carrier Recombination. Carrier Diffusion. Carrier Drift in Depletion Region. due to inherent field. 45. On average a minority carrier. Travels the diffusion length. Before recombining. This is the diffusion current. Carriers in the depletion region. Are carried by the electric field. This is the drift current. In equilibrium drift = diffusion. Net current = 0.
(46) 46.
(47) I–V characteristics of a p–n junction diode (not to scale—the current in the reverse region is magnified compared to the forward region, resulting in the apparent slope discontinuity at the origin; the actual I–V curve is smooth across the origin).. http://en.wikipedia.org/wiki/Diode. 47.
(48) I–V characteristics of a p–n junction diode (not to scale—the current in the reverse region is magnified compared to the forward region, resulting in the apparent slope discontinuity at the origin; the actual I–V curve is smooth across the origin).. http://en.wikipedia.org/wiki/Diode. 48.
(49) Electron-hole pair. -Generation. -Recombination. Carrier lifetime (1 µs). Carrier diffusion length (100-300 µm). 49.
(50) 50.
(51) N=photon flux. α=abs. coef.. x=surface depth. G=generation rate. e-h pairs. 51.
(52) N=photon flux. α=abs. coef.. x=surface depth. G=generation rate. e-h pairs. 52.
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(54) 54.
(55) I0 is dark saturation current. q electron charge. V applied voltage. k Boltzmann Constant. T absolute temperature. 55.
(56) N=photon flux. α=abs. coef.. x=surface depth. G=generation rate. e-h pairs. At x = 0 G =αN. Function is G/Gx=0 = exp(-αx). Electrons absorb the band gap energy. 56.
(57) Silicon Solar Cell. Diode Equation. Photovoltaic Equation. 57.
(58) Efficiency of Light Conversion to e-h pair. 58.
(59) Short Circuit Current, V = 0. 59.
(60) Inefficiency of the e-h pair formation and collection process . 60.
(61) Open Circuit Voltage. Voc drops in T because I0 increases. 61. http://pvcdrom.pveducation.org/CELLOPER/TEMP.HTM.
(62) Maximum Power. 62.
(63) Fill Factor. Effect of Shunt Resistance on fill factor. http://www.pv.unsw.edu.au/information-for/online-students/online-courses/ photovoltaics-devices-applications/syllabus-details 63.
(64) Fill Factor. Effect of Shunt Resistance on fill factor. http://www.pv.unsw.edu.au/information-for/online-students/online-courses/ photovoltaics-devices-applications/syllabus-details 64.
(65) 65.
(66) Spectral Response. Quantum Efficiency = number of e-h pairs made per photon. Band gap determines when this is greater than 0. Need band gap between 1.0 and 1.6 eV to match solar spectrum. 66 1.5 eV. Si 1.1 eV Cd.
(67) Issues effecting quantum efficiency. Absorption spectrum. Band Gap. Spectral Responsivity = Amps per Watt of Incident Light. Short wavelengths => loss to heat. Long wavelengths => weak absorption/finite diffusion length. 67.
(68) 68.
(69) Chapter 4 Cell Properties. Lab Efficiency ~ 24%. Commercial Efficiency ~ 14%. Lab processes are not commercially viable. 69. C is Cost of Generated Electricity. ACC Capital Cost. O&M is Operating and Maintenance Cost. t is year. E is energy produced in a year. r is discount rate interest rate/(i.r. + 1).
(70) C is Cost of Generated Electricity. ACC Capital Cost. O&M is Operating and Maintenance Cost. t is year. E is energy produced in a year. r is discount rate interest rate/(i.r. + 1). Increased Efficiency increases E and lowers C.. Can also reduce ACC, Installation Costs, Operating Costs. To improve C. For current single crystal or polycrystalline silicon technology . Wafer costs account for ½ of the module cost.. ½ is marketing, shipping, assembly etc.. We can adresss technically only the efficiency E. 70.
(71) Solar Cell Module Efficiency. Optical Losses Due to Reflection. 71. 1) Minimize surface contact area. (increases series resistance). 2) Antireflection coatings. ¼ wave plate. transparent coating of thickness. d1 and refractive index n1. d1 = λ0/(4n1). n1 = sqrt(n0n2). 2) Surface Texturing. Encourage light to bounce. back into the cell.. 3) Absorption in rear cell contact. . Desire reflection but at. Random angle for internal . reflection.
(72) d1 = λ0/(4n1). n1 = sqrt(n0n2). 72.
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(74) Dobrzanski, Drygala, Surface Texturing in Materials and Manufacturing Engineering, J. Ach. In Mat. And Manuf. Eng. 31 77-82 (2008).. 74.
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(76) Reduce recombination at contacts by heavily doping near contacts. 76.
(77) Blue. Recombination Losses. Red. 77.
(78) Recombination Losses. 78.
(79) Recombination Losses. 79.
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(83) Bulk & Sheet Resistivity. Sheet Resistivity. 83.
(84) Eglash, Competition improves silicon-based solar cells, Photovoltaics December, 38-41 (2009).. 84.
(85) SunPower San Jose, CA. 20% eficiency from Czochralski silicon. 85.
(86) Eglash, Competition improves silicon-based solar cells, Photovoltaics December, 38-41 (2009).. 86.
(87) Suntech, Wuxi, China. multi crystalline cast silicon. Efficiency 16.5%. Cost $1.50 per watt . 87.
(88) Eglash, Competition improves silicon-based solar cells, Photovoltaics December, 38-41 (2009).. 88.
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