"Christian Kaiser" wrote:

...does a Poly-Isocyanurate persist two decades of the temperatures
that the collectors have? The max temperature of that insulation
material is about 300 deg F (150 deg C) - pretty near to the stagnation
temperature, or even below it for good collectors.

When Gary sent me the nice solar pond water heater model he tested in
Montana, I put it together in partial sun with the pump unpowered and
had a meltdown :-) The 2" Styrofoam cover (under a layer of EPDM under
2 layers of polycarbonate) developed multiple 1" hills and 2" valleys.

A 2" double-foil polyiso replacement with foil-taped edges has worked
fine so far. One polyiso ap engineer says it's good to at least 350 F,
when the surface starts to develop cosmetic wrinkles. But I think we
should replace both polycarbonate layers with greenhouse polyethylene
to lower the cost and assembly complexity and stagnation temperature.

I put some polyiso on top of a toaster oven, and it deformed badly...

Nick

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answered in three different ways...

Join PE Drew Gillett and PhD Rich Komp and me for a workshop on Solar House
Heating and Natural Cooling Strategies at the first Pennsylvania Renewable
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http://www.paenergyfest.com/workshop-info.shtml