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Discussion in 'Photovoltaics' started by Flagpole, Jan 9, 2005.

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  1. Flagpole

    Flagpole Guest

    hi

    If solar cells currently absorb 20% - 30% of the suns energy, what spectrum
    does this fall under? does the limitation of the spectrum captured the
    reason for such low efficiency?

    thanks for help
     
  2. More like 10%-15%, unless you count the heat...
    Solar photo-voltaic cells work because the incoming photon knocks loose
    an electron. One definition of electric current is flowing electrons,
    thus the photon causes current to flow.

    This only works if the incoming photon has enough energy to knock the
    electron loose. So only the higher energy light is converted to
    electricity, the lower energy light just results in heat. (ultraviolet
    end of the spectrum is higher energy than the infrared end.)

    You only get one electron per photon, so if a photon has more energy
    than needed, the rest of the energy results in, you guessed it, heat.

    Research continues into materials with a lower bandgap energy (so lower
    energy light can knock out electrons) and also higher bandgap energy, as
    well as making multi-layer cells so that different photons can knock
    loose electrons from different layers.

    All alternatives are fantastically expensive compared to the old standby
    -- silicon. Thus silicon remains the material of choice for commercial
    solar PV cells / modules / panels.

    sdb
     
  3. That is approximately true, but the energy of the impinging photon has to
    approximate the energy of the bandgap.
    Commonly available solar cells are tuned for green light.
    In fact, many multicrystalline cells are coated with an interference layer
    that presents a blue color.
    These cells are almost completely insensitive to that particular color,
    since the blue color represents reflected light.
    This interference layer is so chosen because it actually increases the
    transmission of green light into the cell.
    It also protects the cell from blue light, which causes slow degradation of
    multicrystalline cells.
     
  4. George  Ghio

    George Ghio Guest


    Approx. 300 t0 1250 nm at the earths surface

    does the limitation of the spectrum captured the
     
  5. message

    Thank you for your expert reply.
     
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