One nagging question I had was weather it made sense to use glass over the panel, because I know from training in UV bonding technology that Lexan (AKA polycarbonate) absorbs just about 100% of the sun's UV rays. What good would it do to go to all the trouble to build a solar heater if the transparent covering blocks some of the solar radiation?
The chart at right from Wikipedia shows that even if we loose 100% of the UV we are still going to gain the vast majority of the energy in the sunlight. Fair enough. So, the plan will be to use whatever transparent material we find will fit the heater, and if we lose the UV spectrum it's not a huge loss.