This video

shows a VERY cheap possibility to heat a room to the south of a building.
The apppliance shown seems like a max of 3m2, so it technically collects roughly 300 Watts.
I want to se this on a scale of lets say 10 by 2 m2 attached to the south side of a house. It could collect some 2000 Watts of solar heat at minimum cost. Enough to heat your living room.