I stumbled on this thread and thought you may be interested in this article from Mother Earth News. This solar heater was constructed for the guys garage. If you get a good amount of sun during the winter, I can see how this would work nicely. But, unfortunately, it would only produce heat during the day.
http://www.motherearthnews.com/Renewable-Energy/2006-12-01/Build-a-Simple-Solar-Heater.aspx
This is an article for a solar heated livestock tank. It would be overkill for chickens, but maybe give you guys some ideas that might lead somewhere.
http://www.motherearthnews.com/do-it-yourself/solar-stock-tank-z10m0gri.aspx
I knew a guy back in Wisconsin that had installed piping on the roof of his garage, used a pressure release valve, and installed radient floor heat tubing in the slab of his garage. I believe the piping was in a shallow box, painted black inside, and had old window panes on it as a lid. The sun heats the piping on the roof (the black box helps that and also keeps the wind from cooling the pipes down) and then the pressure from the expanding hot water forces the hot water down into the slab and the cooling of the water pulls the cold water up to the roof panels. There was no electric pump in the system at all, it was completely convection; however, there may have been some sort of backflow preventer in the system somewhere. I wish I cold remember all the details. I do know it stayed warm enough in the garage to work on his cars and tractors in short sleeves most of the winter. It never went below freezing in his garage either.
Awesome!
