We have a small sun room attached to our house (was used as a greenhouse) approx 4x8 -it has a sloped roof facing south -so DH built a pop can solar heater (warms air as it passes through a maze of black pop cans).
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We have solar panels on the roof powering fans for the pop can heater to keep warm air moving into the room and cooler air moving into the heater. The idea is we can hang laundry to dry year round -regardless of weather. Sounds a little nuts....but works well. We're in the process of going off grid.
I'll post a picture of the inside once DH finishes working in there.....