On Sun, 21 May 2006, Martin K wrote:

> Thanks for the information about the catenary.
> After doing some research I found that I may be more interested in a
> cusp design.
> What I'm trying to do is build a solar water heater from scrap materals.
> After looking at the cost of material for a flat plate design (copper
> sheet, tubing) I am considering a parabolic cusp reflector which appears
> to be just two parabolas intersecting (think of a w shape - or a lower
> case omega)
> I have kevlar and glass tubes to build it from. If I had to buy the
> materials it would be much more expensive. I think the parabola design
> can be more efficient as well.
> If anyone has any thoughts (usually not lacking here), I'd be glad to
> hear them.

Polished aluminium reflector should work. Zinc plated mild steel sheet 
makes a good absorber (not reflector !). Aluminium paint over almost 
anything may be a good reflector. Black PVC tubing can make a good 
collector. Use the matte kind (not shiny).

Peter
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