Solar Cell for Ambient Daylight

Discussion in 'The Projects Forum' started by darenw5, Sep 30, 2008.

  1. darenw5

    Thread Starter Active Member

    Feb 2, 2008
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    For a small self-contained project i'd like to get power from solar cells, but will have only ambient daylight available, not direct sunlight. Not much power will be needed, but of course the more the merrier. This is at an early sketchy stage, so the numbers are flexible, but i'm aiming to get power of about 0.2 to 0.5 W from several square inches receiving general ambient daylight.

    Are some solar cells better than others for this application? Advice on collecting daylight for PV purposes? Any hope of getting PV power in the shade? And dang it, why won't solar cells work at night!? (just kidding about that last question!)
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
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  3. scubasteve_911

    Senior Member

    Dec 27, 2007
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    Daren,

    I was unable to find any hard numbers for you, but I will give you some advice.

    I purchased some decent solar cells on ebay (polycrystalline) that are 25 square inches, which produce 2W each under direct and bright sunlight. This is about 80mW per square inch.

    Besides the obvious problem of indoor lighting being magnitudes less than outdoors in direct sunlight, there is another issue you must consider. You need to look into the quantum efficiency of different types of solar cells, here you will find that energy is being created by light outside of the visible spectrum. Then, you should investigate the various types of lighting used indoors and look into their emission spectra.

    Less 'efficient' lighting will clearly provide light outside of the visible spectrum, which will increase your power gained from the cells. More efficient LED or fluorescent light may give very little power.

    Basically, you need to find out what the typical curves there are for different solar cells and sources of indoor light. Then, compare a typical bright day with a typical indoor light (W/m^2). You will find your answer here if this is feasible. I would think that 0.5W would take a huge array of cells.

    Steve
     
  4. Audioguru

    New Member

    Dec 20, 2007
    9,411
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    A solar garden light has a few square inches of solar cells and charges a battery all day in full sunshine so it can supply 3.5V at only 10mA (only 35mW) to one LED for a few hours at night. If the solar cells don't get fiull sunshine then the garden light doesn't work.
     
  5. darenw5

    Thread Starter Active Member

    Feb 2, 2008
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    hmm, i didn't think much about project lifetime.. magnesium... well, i'd like it last more than 1/2 second!

    Daylight will be bluish - Raleigh scattering - higher energy photons. Finding a good rough number of mW/sqin or any units has been hard (for the amount of time i've spent anyway)

    Those garden lights are great. Been a while since i dissected one. Thanks, those numbers are informative. Looks like it'll be a stretch, needing magic powers not just electronics.

    I will go for more sq. in. of solar cells, and investigate efficiencies for daylight spectra.

    Luckily this is just one speculative hobby project; NASA isn't depending on this for the new moon missions 8P
     
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