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Applications of Photovoltaic Technologies

Applications of Photovoltaic Technologies. Referenced website: http://www.udel.edu/igert/pvcdrom/ http://solarpv.itri.org.tw/memb/main.aspx. Why Solar Cells?. Finite fossil fuel supply Less environmental damage No radiation risk (meltdown) Nearly infinite supply of FREE energy

stewart-velazquez
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Applications of Photovoltaic Technologies

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  1. Applications of Photovoltaic Technologies Referenced website: http://www.udel.edu/igert/pvcdrom/ http://solarpv.itri.org.tw/memb/main.aspx

  2. Why Solar Cells? Finite fossil fuel supply Less environmental damage No radiation risk (meltdown) Nearly infinite supply of FREE energy Sun gives us 32 x1024 joules a year, Cover 0.1% of the Earth’s surface with 10% efficient solar cells with an efficiency of would satisfy our present needs.

  3. Greenhouse Effect Human activities have now reached a scale where they are impacting on the planet's environment and its attractiveness to humans.

  4. Spectrum of light h:Planck’s constant 6.626×10-34 (J-s) ν: frequency (s-1) λ: wavelength (m) c : light speed 3.0× 108(m/s)

  5. Atmospheric Effects Atmospheric effects have several impacts on the solar radiation at the Earth's surface. The major effects for photovoltaic applications are: a reduction in the power of the solar radiation due to absorption, scattering and reflection in the atmosphere; a change in the spectral content of the solar radiation due to greater absorption or scattering of some wavelengths; the introduction of a diffuse or indirect component into the solar radiation; and local variations in the atmosphere (such as water vapor, clouds and pollution) which have additional effects on the incident power, spectrum and directionality. Hu, C. and White, R.M., "Solar Cells: From Basic to Advanced Systems", McGraw-Hill, New York, 1983.

  6. Solar Radiation Power emitted from Sun =3.8×1023 (kw) Power direct to Earth=1.8×1014 (kW) Solar constant=1353 W/m2 T=5762 K

  7. Air Mass (AM) AM0 : The standard spectrum outside the Earth's atmosphere. AM 1: Light incident with the angle of 0 degree. AM 1.5: Light incident with the angle of 48 degree. Intensity Meinel A.B. and Meinel M.P., "Applied Solar Energy", Addison Wesley Publishing Co., 1976 ID : Direct beam intensity (W/m2) IG : Global irradiance(W/m2)

  8. Standard Solar Spectra

  9. Standard Solar Spectra-cont. The AM1.5 Global spectrum is designed for flat plate modules and has an integrated power of 1000 W/m2 (100 mW/cm2). The AM1.5 Direct (+circumsolar) spectrum is defined for solar concentrator work. It includes the direct beam from the sun plus the circumsolar component in a disk 2.5 degrees around the sun. The direct plus circumsolar spectrum has an integrated power density of 900 W/m2.

  10. Part of periodic table

  11. Compound semiconductors • Elemental semiconductors: Si, Ge • Compound semiconductors: GaAs, InP • Ternary semiconductors: AlGaAs, HgCdTe • Quaternary semiconductors: InGaAsP, InGaAlP

  12. Direct and indirect semiconductor phonon E E photon photon Ec Ec Ev P P Ev Direct Semiconductor Indirect Semiconductor High absorption probability Low absorption probability GaAs; InP etc. c-Si

  13. Crystal Structures Amorphous Polycrystalline Crystalline In a crystalline solid atoms making up the crystal are arranged in a periodic fashion Commercial Si solar cells In some solids there is no periodic structure of atoms at all and called amorphoussolids Some solids are composed of small regions of single crystal material, known as polycrystalline.

  14. Commercial Si solar cells SINGLECRYSTAL POLYCRYSTAL AMORPHOUS

  15. Metal-insulator-conductor Eg Empty States (CB) Filled States (VB) metal semiconductor insulator In metal conduction band (CB) and valence band (VB) overlap, in insulator and semiconductor CB and VB are separated by a energy band (Eg). Eg for Si is 1.1242eV (semiconductor) as compared to 5eV for diamond (Insulator)

  16. Photoelectric effect Electron Eg Photon Semiconductor Photon Metal Photon is a particle with energy E = hv Eph( hv)>Eg

  17. Absorption of Light Eph < EG Photons with energy Eph less than the band gap energy EGinteract only weakly with the semiconductor, passing through it as if it were transparent. Eph = EG have just enough energy to create an electron hole pair and are efficiently absorbed. Eph > EG Photons with energy much greater than the band gap are strongly absorbed

  18. N- and P-type Addition of impurities with three valence electrons results in available empty energy state, a hole B, Al, In, Ga(Acceptor impurities) Addition of impurities with five valence electrons results an extra electron available current conduction P, As, Sb (donor impurities

  19. Physics of Photovoltaic Generation If energy of inclined light (Ehp) > Energy band of material (EG). Then, emit electron-hole pair (EHP) to produce the electric current.

  20. Physics of Photovoltaic Generation n-type semiconductor + + + + + + + + + + + + + + + Depletion Zone - - - - - - - - - - - - - - - - - - p-type semiconductor

  21. Solar Cell-structure Busbar Antireflection coating Fingers Emitter Antireflection texturing (grid pattern) Base Rear contact A solar cell is a P-N junction device Light shining on the solar cell produces both a current and a voltage to generate electric power.

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