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Re: Vs: How to produce cheap mirrors? - Page 2

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Posted by TimLa on March 30, 2005, 5:32 am
 
I recall a popular science article many, many years ago that had a solar
reflector made with this exact concept.  I think they had an array of small
aluminum hoops... maybe I can find it...

-T

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Posted by Morris Dovey on March 30, 2005, 8:04 am
 
Brian Sanderson wrote:


Looked around my shop today (It's actually in a hanger) but
couldn't spot any of these "plugs"...

But your description of a catenary reflector surface got me
thinking about possible non-parabolic concentrator surfaces. I
went Googling; but discovered the futility of searching for
non-anything (I knew better but wanted to be able to say I'd made
a serious effort before asking.)

I'd like to ask you - and the rest of the group for info and/or
links to any "interesting" collector surfaces anyone might have
encountered or dreamed up. I'd be *especially* interested in
those for which there is a mathematical description.

Are there any concentrator shapes which are to /any/ degree
"self-tracking" (use different areas of surface at different
times of day and/or different times of year without significant
loss of efficiency)?

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

Posted by Duane C. Johnson on March 30, 2005, 11:35 am
 Hi Morris;


The surface of the vacuum formed stretchable Mylar membrane
is a spherical surface.

The SAIC heliostat and dish reflectors you are referring to
are not exactly stretched membranes. They were made with
stainless steel foil that was pre formed to a parabolic shape.
The vacuum is used to maintain the shape. Yes, changes in
pressure can slightly modify the preset shape for final
focusing.
http://www.algor.com/news_pub/cust_app/saic/saic.asp
http://www.dlr.de/tt/institut/abteilungen/system/publications/energex2000-s.PDF

 > I went Googling; but discovered the futility of searching for

 >
  loss of efficiency)?

You are asking about Compound Parabolic Concentrator, CPC,
pioneered by Roland Winston and Rabl. These are in the class
of concentrators called "Non Imaging Optics".

Duane

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Posted by Ecnerwal on March 30, 2005, 2:03 pm
 

Well, there's non-imaging optics stuff from U Chicago (and probably
others), some of which have been built. They are interesting, but a bit
tricky for normal people to play with. They (or at least some of them)
are designed to have high acceptance angles, which I take to mean good
performance significantly off-axis.

http://hep.uchicago.edu/solar/NIoptics.html

There's a 1970s or 1980s era trough - W-something, if my sieve of a
brain recalls that fragment correctly - anyone else recall this? It was
a design where the trough reflector shape allowed it to sit still but
accept more sun than a typical non-tracking trough (it had a possibly
glorified or perhaps non-glorified flat plate in the bottom, as I
recall). Not a parabolic type trough. I can't recall the name and can't
seem to find any non-parabolic trough articles on the web. May not have
been very successful in practice...

--
Cats, Coffee, Chocolate...vices to live by

Posted by Morris Dovey on March 30, 2005, 5:01 pm
 A Google search on "non-imaging optics" was most satisfying!

Because my primary interest has been in low-cost solar heating of
structures I haven't paid much attention to
high-temperature/concentrating solutions. The provided links and
better search criteria will definitely help me get up to speed.

Thanks!

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

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