It is really simple and cheap to build DIY solar panels for supplemental home heating, and it heats the air directly.
The most interesting is the fact that collector is almost entirely constructed out of empty aluminum cans!
Housing for solar collector is made of wood (plywood 15mm), while its front is 3 mm (0.12 inches) Plexiglas/polycarbonate (you can use tempered glass as well). The back of the case set is made of 20mm rock wool (or styrodur) as insulation.
Solar absorber is made out of beer and soda aluminum cans, painted in matte-black paint resistant to high temperature. The upper part (cover) of cans is specifically designed to provide more efficiency in heat exchange between the cans and the passing air.
details on : http://solar.freeonplate.com/solar_panel_DIY.htm