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Solar Panel Absorbers

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Posted by Morris Dovey on April 26, 2007, 5:03 pm
 
I've put up a web page (link below) with a graph that may provide a
bit of food for thought for those designing their own solar heating
panels.

Feel free to disregard the crass commercial plug at the bottom of the
page. :-)

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/Absorber.html



Posted by schooner on April 26, 2007, 5:36 pm
 
So how are you targeting the infrared energy with your panels, i.e. what is
special about your design?



Posted by Morris Dovey on April 26, 2007, 6:06 pm
 schooner wrote:

| So how are you targeting the infrared energy with your panels, i.e.
| what is special about your design?

The short answer (which is all I'm comfortable with publishing today)
is "primarily by controlling reflection and re-radiation".

I don't know that there's actually anything "special" about what I'm
doing, other than that it seems to be working really well. I don't
have much doubt that there are a number of ways to skin this cat, and
I'm hoping to motivate others to think independently rather than just
copy what I've done.

The solar energy distribution data, by the way, are available from
NREL.

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/Absorber.html



Posted by Jeff on April 26, 2007, 7:51 pm
 Morris Dovey wrote:


   Then it looks to me like you have your own selective surface and it
is not absorbing more in the IR but rather losing less.

As to the other thread. There are low e glasses that ar IR reflective.
It seems that you are better off with the selectivity inside the
collector rather than at the glazing, to a point. Nothing empirical on
this though...

   On more thing about your energy distribution chart. Note that the
scale is by wavelength rather than frequency. This distorts the length
of the IR tail which should be less than the length of the visible. I
think this may be a more accurate representation:

<URL:
http://www.lbl.gov/Science-Articles/Archive/assets/images/2002/Nov-18-2002/solar_spectrum.jpg  
/>

   Jeff


Posted by Morris Dovey on April 26, 2007, 9:03 pm
 Jeff wrote:
| Morris Dovey wrote:
|
|| schooner wrote:
||
||| So how are you targeting the infrared energy with your panels,
||| i.e. what is special about your design?
||
|| The short answer (which is all I'm comfortable with publishing
|| today) is "primarily by controlling reflection and re-radiation".
|
|    Then it looks to me like you have your own selective surface and
| it is not absorbing more in the IR but rather losing less.
|
| As to the other thread. There are low e glasses that ar IR
| reflective. It seems that you are better off with the selectivity
| inside the collector rather than at the glazing, to a point.
| Nothing empirical on this though...
|
|    On more thing about your energy distribution chart. Note that the
| scale is by wavelength rather than frequency. This distorts the
| length of the IR tail which should be less than the length of the
| visible. I think this may be a more accurate representation:
|
| <URL:
|
http://www.lbl.gov/Science-Articles/Archive/assets/images/2002/Nov-18-
2002/solar_spectrum.jpg
| />

Work with the graph that's most convenient for you. I'm interested in
seeing a distribution with a linear "color" axis because that's more
convenient for me to work with.

Probably a better graph
<msis.jsc.nasa.gov/images/Section05/Image200.gif> than the one I used
can be found on a NASA web page at
http://msis.jsc.nasa.gov/sections/section05.htm  - although the NASA
plot muddies the water somewhat by including absorptions that are
subject to locale-specific variation.

A google image search on 'solar spectral distribution' turned up all
kinds of interesting (and colorful) plots.

For anyone who doesn't remember:

     frequency = c / wavelength; and
     wavelength = c / frequency; where

c is the speed of light in whatever system of units you're working
with.

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/



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