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re: limits of photovoltaic panel concentration?
10 dec 2005
=?iso-8859-1?q?roland_m=f6sl?= wrote:
>let's assume to concentrate 2 times the solar energy.
>
>this means 2000 instead of 1000 w per squaremeter.
>
>both side of the photovoltaic can put away heat
>with nearly no wind with about 7 w per squaremeter.
each side of an outdoor surface might move 2 btu/h-f-ft^2
in still air, ie 11 w/m^2c, or more, with radiation.
>the normal panel becomes 70 degree celsius more
>hot than the air temperature.
if 85% of 750 w/m^2 c am2 sun becomes heat in a t (c) panel in 20 c air,
and it loses heat by convection and radiation...?
>the concentrator panel becomes 140 degree celsius more hot
... 160 c on a 20 c day? maybe cooler, with radiation loss...
>70 degree celsius means at cristallin silicon with 0,48% less
>output per degree more 33,6% less efficiency.
...70x0.0048 = 0.336, and 1-0.336 = 0.664, so it looks like this cell
would produce 66.4% of the electrical energy it would produce at 20 c.
>so the 1:2 concentrator does not produce the double energy.
>because of the worse efficiency at higher temperatures,
>it is only 32,8% more.
... 140x0.0048 = 0.672, but 2(1-0.672) = 0.656, so the 2:1 pv might
produce less electrical power than the 1:1, using these calcs...
but if it's cooled to 60 c with a thin polyethylene film water bag on top
that absorbs 6% of the solar power, it might make 2x0.94(1-40x0.0048) = 1.52
times more power than a 1:1 pv at 20 c, or 1.52/0.664 = 2.3x more power
than a 1:1 pv at 90 c, and also make hot water for showers.
nick
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