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re: can you focus sunlight onto pv cells
24 jun 2004
n. thornton would have thought:
>a) one only need illuminate one panel to obtain benefit when panels
>are in parallel, as is normal for 12v systems,
agreed. series strings can use attention to layout.
>b) the sun is a disc source rather than point source, so both flat and
>dappled reflectors should be able to deliver sufficiently consistent
>illumination increase over a panel to see a real gain
the disk is tiny, so a "dappled" bright spot may not contribute much to
the output, nor cause a problematic local hot spot with 2 or 3 suns and
cooling. otoh, diffuse sun may contribute half the power, and mirrors
can have several overlapping flat planes, eg in a 3-line approximation
to a linear parabolic reflector. at the last ases conf, roland winston
tested a diffuse reflective box that worked like an integrating sphere
to make more uniform illumination on a pv receiving face.
>c) fixed reflectors can be very cheap
mylar over foil-faced foamboard...
>d) panels can be heatsinked cheaply if necessary for higher
>concentrations by using sheet metal.
wrong. you need numbers here. it seems to me that poly film ducts laid
on top of panels with an inch or two of water inside during the day can
cool effectively and collect useful heat without much loss in pv power,
since the refractive indices of glass, water, and polyethylene are close.
the poly film is slightly cloudy, for a little more optical mixing.
>e) white reflectors can ensure passably even illumination despite
>considerable amounts of dirt, poop etc.
sure. why not mount pvs near a white house wall? (not that white house :-)
nick
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