[dendronepthya]

A quick note on acrylic. I read the description of the UV resistant acrylic and the thing that concerned me was the language used. It sounded more like a marketing pitch "guaranteeing" a certain result without any description of the mechanism for getting that result. From what I understand, the very nature of the acrylic polymer makes it vulnerable to UV degradation. The bonds basically come apart, and that's why you see the acrylic get yellow and brittle. My question would be whether the acrylic manufacturers actually fixed this on a chemical engineering level or are they just adding some sort of UV stabilizer (like a sun block). From what it sounds like, it is the latter which would still give me serious concerns about using the material for a greenhouse system. There are plastics out there that are UV resistant by nature such as polycarbonate and polyethylene, but I don't know if they can be made as clear as acrylic.

Treeman,
Take some pics of the Geothermal radiator when you get a chance. I'm interested to see it when it's all done.