John,
I hear you. I have looked into making a passive solar collector for heat. Mine is 8 feet by 12 feet. Doing the math, I could collect nearly 10,000 watts under best conditions. I have the parts, and have it on the list.
If I finish it, it will be used to heat extratopia over the winters. The real problem is that conditions are not perfect in the winter, so the output will not meet its full potential. Still, it will put out some very nice heat a lot of the time. I look at mine as a season extender in that pond.
