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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...



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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

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

 > 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".


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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.


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...

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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.


Morris Dovey
DeSoto Solar
DeSoto, Iowa USA

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