Re: Solar thermal panels to heat garage floor
Patio door glass comes in standard tempered sizes of 28x76" or 34x76" These can be had free or almost free from almost any glass shop. A single glazing of tempered patio door glass would allow you to build modules of almost any size. I agree that premade absorber plates would be the easiest, but a simple manifold or loop of copper tubing, placed on top of a piece of scrap steel, on top of 2" of thermax insulation enclosed in a wooden box covered with a number of patio door glazing units would be a pretty easy DIY project. A simple Grunfos pump and a simple aqua stat, T&P valve, air bleed valve and away you go.
I built a domestic hot water system much like that, but with no glycol,, cost ~300 when all was said and done,,, had the copper and the steel however.
As for over heating in the summer,,, make some simple summer shades. If it doesn't get sun,, it won't get warm. You can also consider the over hang of the roof to shade it in the summer, as well as plantings etc.
Please note, being a moderator does not add any weight to my opinions 300 watts Siemens/BP panels,plus a Sun 90,, making ~400. ~30 amps into Rogue MPT-3024, 450 ah of Trojan T-105, Morningstar ts300 inverter, a Tri-Metric meter.a collection of antique generators, plus 2 Honda eu-1000i's (also a BS2512 IX controller) and assorted other stuff!