Applications of Photovoltaic Technologies Why Solar Cells?


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Applications of Photovoltaic Technologies


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.



Greenhouse Effect

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



Spectrum of light



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.



Solar Radiation

  • Power emitted from Sun =3.8×1023 (kw)

  • Power direct to Earth=1.8×1014 (kW)

  • Solar constant=1353 W/m2



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.



Standard Solar Spectra



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.



Part of periodic table



Compound semiconductors

  • Elemental semiconductors: Si, Ge

  • Compound semiconductors: GaAs, InP

  • Ternary semiconductors: AlGaAs, HgCdTe

  • Quaternary semiconductors: InGaAsP, InGaAlP



Direct and indirect semiconductor



Crystal Structures



Commercial Si solar cells



Metal-insulator-conductor



Photoelectric effect



Absorption of Light

  • Eph < EG Photons with energy Eph less than the band gap energy EG interact 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



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)



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.





Solar Cell-structure




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