[jhallenworld]

Young me went to a solar exhibition at Brookhaven National Labs around 1978 or so. They had an electric car (maybe the Electrovette?), photo electric panels and outside someone showing how to make a forced air solar heater. It was an insulated box with a glass or plexiglass window to allow light in. Inside was an array of cut up soda cans, all painted black. A port for air inlet and a port for outlet and voila.

[I'm pretty sure this was in BNL's old graphite research reactor building, which was open for tourists. I've since learned that this was an air-cooled reactor like the one in the famous UK Windscale accident, and that it has now been completely disassembled.]

Solar was big then- I remember a talk about it at the local library also. People were making parabolic solar hot-dog cookers.