Foam insulation for panels

[PaulMel]

I need to rebuild a couple hot water solar panels. The foil backed insulation has corroded. The foil has rotted away in spots. The foam is about one inch. Could the typical insulation with foil on one side used behind vinyl siding on houses work? The panels will probably reach 300F. I know it doesn't reach that behind siding. What have others used to insulate hot water panels? The foil on the inside face of the insulation makes sence to reflect the heat back into the air space and absorber plate.

[georgeodjungle]

i play a lot with solor cooking.

the rmax didn't work to good.

started to smell about 250f.

and buy the time it got to 350F it was a it made a big mess.

maybe some other type or brand that will work for you.

i git the most heat out of fiber glass insulation with the foil painted with black stove paint.

i have a hybrid solor oven that i've had up to 475F.

with no smell but of cooking bread.

hope this helps ya.

[GaryGary]

Hi,

Use Polyisocyanurate insulation.  This is the type that usually comes with alum foil layers on one or both sides.  The stuff we get here is kind of light brown in color and has very fine grain.  Around here, if you ask a lumber yard if they have Polyisocyanurate insulation they say "huh", but if you look closely at the insualtion panels it says right on them that they are Polyisocyanurate. This is what is used in most commercial solar collectors, and should work fine.  As you say foil on the inside is good -- reflects heat back to absorber.  Foil on the outside is also good -- it has a low emissivity, so it does not radiate heat to the outside well (which is good).  For these reflective layers to work, they need to be facing an airspace of at least half an inch -- ie placing the reflective foil right against the absorber will negate any benefit from the foil.

Don't use the polystyrene insulation board (this is the pink or blue or white beaded stuff) -- it will not hold up to the temperatures.

Gary