One of the most overlooked benefits from the Sun is it’s ability to heat a dark object. Place a glass or poly-carbonatepanel in front of that dark surface, close off the sides and provide a path for air through natural convection and you have a passive solar furnace.
My pole barn is a giant passive solar furnace. It consists of a very large white garage door with double glazed poly-carbonate panels installed 6” in front of the door. The panels are held together with aluminum quick frame and quick frame connectors. When Sun strikes the glazing the trapped air rises in temperature quickly. When the temperature of this void reaches 95 degrees the interior garage door opens revealing black corrugated tin roof panels. On an average solar day the temperature of the void is well above 140 degrees.
So far I have not had to rely on any powered fans, natural convection has done the job for me. I have experimented with a few solar powered fans but I like the way it takes the chill off naturally. I do have to supplement the heat on very cold days with a propane heater but it lasts all year.
I hope to start experimenting with a closed loop system this year.
If you are interested in building an affordable passive solar furnace using a south facing door click:
