One guy long ago told me he made a steel box painted it flat black and had a glass top on it. It sat outside and had a pipe going into his window that brought in warm air to heat a room. With some research i found this soda can heat devise. Read the comments and you will see one person made one with dryer flex aluminum duct. Now what would keep a person from making one of these and placing the cans inside on the window seal of the house. Draw in warmish room air and expel even warmer air at the top. Need a window with sun coming into it. Or a mirror outside reflecting the sun at a window. https://tinyhousetalk.com/soda-can-solar-panels/
Looked over a lot of those in the past; some really cool ideas. One used a computer fan connected to a small solar panel to pull the warm air through, and into the room.
My DIL made one of those for her green house, worked really well. My Son actually added a small blower to it. It was a PITA to remove the top and bottom of the cans though.
For years I've thought about snaking some galvanized ductwork back & forth up the sunny (south) side of our house, with the top and bottom ends going through the wall. Heat rising should circulate it pretty well without a fan. If it did need a fan, I could just set one in front of the bottom vent, blowing into the ductwork. So many projects, so little time...
