RE: Concentrating Solar Energy



Yeah. There's two limitations offhand:

1.	Heat. Photovoltaic cells can only take just so much heat. I'd
leave any more than 2x or 3x to the scientists for now! Excess heat will
lessen the life of the panels. 100 suns can probably melt metal - we
used to melt pennies with a big Fresnel in the back yard.

2.	Tracking. You have to accurately position (and move) the panels
to concentrate the light from the Fresnel onto the photovoltaic panel.
The more concentration, the more accuracy required.

You can also do the concentration at the 2x or 3x level with mirrors
hung off each side of the photovoltaic panel, the way solar food ovens
work. This may be easier and cheaper for home, as big Fresnels are
pricey and degrade in the sun. If they were my panels, I'd try to mount
a heat sink on the back side of each, at least for desert/high altitude
sun. 

I know that somebody was making or still is making Fresnel concentrator
panels for home use.

john

	-----Original Message-----
	From:	The Butterfly [SMTP:salsbury at sculptors dot com]
	Sent:	Tuesday, April 28, 1998 8:44 PM
	To:	domesteading at sculptors dot com
	Subject:	Concentrating Solar Energy

	Another interesting bit...
		In that article about the new solar cells, they were
using
	concentrated light to get faster results, so that they could
test their
	efficiencies and so on. The light source they used was "11
suns", or 11x
	the normal solar light level. 
		They talked about some of the large-scale solar power
generating
	stations, and how they used solar concentration to get "100
suns" of energy
	to work with. 

		This got me thinking about scaled-down applications in
off-the-grid
	use. Why not use arrays of mirrors and/or Fresnel lenses to
concentrate
	more solar energy onto your solar cells, or solar water heaters?
Then you
	can get more energy out of the same amount of solar cell
investment, more
	heat out of the same amount of black water pipes, etc. 
		I'm not sure what the operating tolerances of commercial
grade
	solar cells are, but they're certainly more than one "sun". The
above
	example of 100 suns was probably the extreme of the high-end
cells like
	they use for space applications and the aforementioned solar
plants, but
	the article did mention a target range of 10-20 suns for common
usage. 
		You can buy large Fresnel lenses from Edmund Scientific
and other
	scientific supply companies for a reasonable price. My current
Edmund
	catalog has 11" square sheets for $12. They used to sell ones
that were
	2'-3' in diameter, but I don't see one in this catalog. 

		Still, the price is quite cheap for making solar
concentrators, and
	probably give a 2x or greater increase in energy for the solar
cells/water
	heating. 

		Has anyone done any work with this? John Atkins? You
used to play
	with Fresnels, didn't you? 

	-- 
	Pat
		   ___________________Think For
Yourself____________________
		   Patrick G. Salsbury -
http://www.sculptors.com/~salsbury/
	      Check out the Reality Sculptors Project:
http://www.sculptors.com/

---------------------------------------------------------
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