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coatings for absorbing heat

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Posted by frank on January 21, 2009, 6:43 am
Hello to all, This is my first post to this group and perhaps it is the
wrong group to post to with such an elementary question but I have read
a bit on different coatings for absorbing heat in a solar collector,  Is
there a a big difference in how much heat can be absorbed using
different paints or coatings? is the cost of a good coating worth it?
I'm not up to much on this stuff, perhaps you could point me to where I
could find more info. on this topic. Thanks

Posted by Morris Dovey on January 21, 2009, 1:46 pm
frank wrote:

Yes - I've found that some paints actually serve as insulators that
inhibit heat absorption.

That depends. :-)

Morris Dovey
DeSoto Solar
DeSoto, Iowa USA

Posted by amdx on January 22, 2009, 11:00 pm

  Hi Frank,
All I can do is quote what I read on the Solarheat@yahoogroup
A couple of quotes from the group. (Gary Burk)
 "BBQ Black is a fine absorber, when fresh it claims over 95%." (absorbance)
"A good "Standard Black" has been difficult to come by. Lawrence
Berkeley National Lab has decided to standardize on 2 coats of "BBQ
Black Spray Paint", made by the DAP company, product #760."


Posted by Ecnerwal on February 2, 2009, 10:16 pm

Coatings can make a rather large difference, depending on the
application. The nice ones manage the trick of absorbing heat well, but
radiating it poorly. As far as I know those can only be factory applied,
not a DIY can-of-paint option. There might be a DIY technique for
oxidizing copper to black that has some selective surface effects - I
don't quite recall.

The higher the operating temperature, the more the fancy coating
matters, to a certain extent. Low-temperature air collectors can usually
exploit more square footage of less fancy (and less costly), higher
temperature collectors such as domestic hot water benefit more from
selective surface coatings.

(if this actually posts, I'm finally back, after having been cut off
from the alt groups by lousy news service at Verizon)

Cats, coffee, chocolate...vices to live by

Posted by gary on February 7, 2009, 8:20 pm
 On Feb 2, 3:16pm, Ecnerwal

There is one simple DIY spray on coating that claims to be somewhat
selective (emissivity of 0.52).
Its available in spray cans for easy DIY application.

I just use high temperature black BBQ paint, which absorbs well, and
holds up well inside collectors, but is not selective.

There used to be a metal foil you could buy that was selectively
coated on one side, and had a peel off adhesive on the other side --
you apply it over the absorber.  If anyone knows of a source for this,
please post it.


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