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Thread: Solar cells

  1. #1 Solar cells 
    Forum Masters Degree thyristor's Avatar
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    I know some about solar cells but I've never really understood the theory behind it. Could anybody please explain or give me a good link to a site?


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  3. #2  
    Forum Masters Degree bit4bit's Avatar
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    Basically you have a wafer of silicon, 'doped' to make one half p-type (excess holes), and the other type n-type (excess electrons). When doping occurs a 'junction voltage' immediately forms between the two layers at the junction. (http://en.wikipedia.org/wiki/P-n_junction)

    When light of certain frequencies strike atoms within that region, they become ionised (An electron is broken loose from its orbit due to energy absorbsion), forming a free electron and a hole, which the electric field seprates. The junction then acts as a very high resistance, oppsing any attraction between the free electron and hole, and preventing them from recombining.

    Connecting an external wire from the n-type to p-type material, provides a path of low resistance, allowing the electrons/holes to bypass the internal junction, and recombine, by flowing as current through the wire. There's plenty of good resources about this.


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  4. #3  
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    Exactly!!!

    Too add to that: the electrons are stripped in the first place due to the photon impact from the light. This deals with quantum theory-either it can send the light back in the form of a photon, absorb all energy and convert it to thermal , or it can send electrons out in order to stabilize/equalize itself.

    By being able to see the solar panel at all, we can tell that it is inefficient; if it were to be perfectly efficient, it would be perfect black. It would look like a black void in space, and would not give off any heat, all energy would be turned into electric.

    And; the silicon gets its electrons back from the surrounding matter (I don't think the photon fully replenishes it if at all?)... this begs the question, what if you had a solar panel in a vacuum where light is constantly striking it, converting it to electricity which is then sent out of the chamber. Would it behave any differently?
    Of all the wonders in the universe, none is likely more fascinating and complicated than human nature.

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  5. #4  
    Forum Masters Degree bit4bit's Avatar
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    Photovoltaic cells are not the most efficient source of electricity, nor thermal solar cells, due to the intermittent nature of the sun, and weather. Nuclear fusion is the way to go IMO.

    I thing the only reason a photovoltaic cell would be more efficient in the vacuum of space, would be because it recieves a constant stream of sunlight, uninterrupted by clouds. Even then solar cells are less than 20% eficient. It helps that they work on the same basic princuiples as transistor, because advances in the computer industry mean more advances in PV cells too.
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  6. #5  
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    A while ago I heard that the photons hit the electrons off; then the photon is converted in heat, after which the electrons that were displaced are re-absorbed due to concentration gradients from the surrounding environment. I also heard that the photon is completely absorbed and compensates for the loss of the electrons. Which one is it?


    Dark energy reactors are the way to go
    Of all the wonders in the universe, none is likely more fascinating and complicated than human nature.

    "Two things are infinite: the universe and human stupidity; and I'm not sure about the universe."

    "Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence"

    -Einstein

    http://boinc.berkeley.edu/download.php

    Use your computing strength for science!
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