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From: dietz@cs.rochester.edu (Paul Dietz)
Newsgroups: sci.energy,sci.electronics
Subject: Re: solar cells
Message-ID: <1991Jan5.025526.9284@cs.rochester.edu>
Date: 5 Jan 91 02:55:26 GMT
References: <1991Jan3.072059.20842@loop.uucp> <11515@pt.cs.cmu.edu> <1991Jan4.173128.26484@cs.rochester.edu> <1991Jan5.011526.15425@midway.uchicago.edu>
Reply-To: dietz@cs.rochester.edu (Paul Dietz)
Organization: University of Rochester Computer Science Dept
Lines: 35

In article <1991Jan5.011526.15425@midway.uchicago.edu> chi9@quads.uchicago.edu (Lucius Chiaraviglio) writes:
>In article <1991Jan4.173128.26484@cs.rochester.edu> dietz@cs.rochester.edu
>(Paul Dietz) writes:
>>In fact, if sophisticated, expensive single crystal Si, GaAs or high
>>performance tandem cells are ever used on earth on a large scale, they
>>will be used with lens/mirror concentrators at concentration ratios of
>>100 or greater.  This only works in areas with lots of direct sunlight,
>>like the southwest, but that's the sunniest part of the country anyway.
>
>	Uh -- won't the resulting overheating kill the solar cells, or at
>least inactivate them for the duration of exposure to concentrated direct
>sunlight?  My information on this may be out of date, but I thought that even
>a very hot day without concentration of sunlight was enough to lower the
>efficiency of photovoltaic cells.  Also, using concentrators takes away most
>of the advantages that solar cells have in not absolutely requiring unclouded
>sunlight in order to produce a significant amount of electrical energy.

Heating would be a problem (at least for silicon; GaAs cells are more
heat tolerant), so the cells would be mounted in actively cooled
fixtures, probably with some liquid coolant loop.

The ability to use diffuse sunlight is an advantage, but high
concentration is also nice -- silicon solar cells (at least) become
more efficient at high concentration ratios (at constant temperature).
I'm not sure why this is.  Also, concentration schemes should have
a higher overall efficiency than flat plate schemes, since one can
use more sophisticated cells that would be absurdly expensive
with unconcentrated light.  This would become important in the
long run if the area covered by collectors becomes significant.

It is possible to achieve low concentration ratios, even for diffuse
light, by means of involute mirrors or fluorescent concentrators.

	Paul F. Dietz
	dietz@cs.rochester.edu