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Re: [energyresources] Re: PV modules made from scrap silicon

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  • Roger Baker
    ... I think in the past the size of the photovoltaic industry compared to the semiconductor industry was small so that there were comparatively a lot of sliced
    Message 1 of 37 , Apr 9, 2001
      >The computer chip industry makes silicon or SiAs crystals with high
      >precision and low tolerances for flaws. Further, you end up with a chip
      >that is the size of a postage stamp or a small tile. So the total amounts
      >of silicon produced by the computer industry is actually not that large.
      >In order to have large scale PV generation we are talking about a net area
      >on the order of square kilometers of wafers. If PV production becomes
      >large it simply could not rely upon the seconds from the INTELs et. al..
      >So ultimately a PV industry would have to generate its substrates from raw
      >materials.
      >
      >Lawrence B. Crowell


      I think in the past the size of the photovoltaic industry compared to
      the semiconductor industry was small so that there were comparatively
      a lot of sliced wafers that were not up to the very demanding chip
      making specs, and its pretty easy to make efficient PV cells out of
      these -- until the supply of junk wafers is tapped out.

      But there is a whole new range of possibilities for polycrystalline
      and ribbon based silicon cells that are pretty good -- but that don't
      take all the effort of making large silicon boules and slicing them
      up to make the large perfect crystals needed to make conventional
      chips. But in this realm, the techniques have not been perfected
      through research and manufacturing experience to optimize the various
      possible approaches. The best thing about variations on this
      technique is that crystalline silicon is formed at a high temperature
      and thus the doping impurities are locked-in to a rigid, stable
      crystal structure, meaning that such cells are unlikely to degrade
      over time, and could last for centuries if shielded by glass.

      On the other hand the evaporated thin film silicon-germanium
      multi-layer cells like those recently produced by Ovshinsky's Energy
      Conversion Devices are cleverly engineered multi-layer, multi-bandgap
      amorphous cells and these amorphous structures are efficient and
      potentially cheap and thus promising but tend to degrade somewhat
      over time. But this is still a leading approach for making acres of
      cheap cells for covering roofs, etc.

      I think that copper/cadmium indium selenide cells have a weakly
      bonded crystal structure formed at lower temperatures in which dopant
      diffusion over time might well also cause ageing problems. But such
      thin layer cells tend to be cheap to make due to the small amounts of
      exotic materials used.

      I would guess that any cells that have an organic dye sensitizer and
      liquid electrolyte component like the TiO2 cells would be be likely
      to degrade over time.

      Few organic dye molecules are very resistant to prolonged exposure to
      UV, although I think phallocynanine (sic) dyes are. -- Roger
    • Karen Seay
      Hello! Don t know if my reply to the person who asked about long-term effects and dangers of geothermal development in NW N. America got through. Just in case
      Message 37 of 37 , Apr 11, 2001
        Hello!
        Don't know if my reply to the person who asked about long-term effects
        and dangers of geothermal development in NW N. America got through.
        Just in case it did not -
        Close at hand, Yellowstone/Old Faithful predictablilty has been
        recently altered. This may be due to underground nuclear blasts,
        or movements of plates, or other factors.
        Iceland has used geoth without a halt, and with few reported problems,
        for a looooong time.
        I will CC this to the International Geothermal Assoc., and members
        of considerable knowledge and experience may address the question
        by replying back (to me svp).
        Thank you.
        Karen Seay
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