From: John Atkins (jatkins_at_technistar.com)
Date: 04/29/98
Message-ID: <61E97D8651BDD111938D0060B09C92DC046C60@technistar.com> From: John Atkins <jatkins_at_technistar.com> Subject: RE: Concentrating Solar Energy Date: Wed, 29 Apr 1998 08:19:38 -0600
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.com]
Sent: Tuesday, April 28, 1998 8:44 PM
To: domesteading_at_sculptors.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
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Patrick G. Salsbury -
http://www.sculptors.com/~salsbury/
Check out the Reality Sculptors Project:
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