Solar I, completed in 1939, was the first house in America to be heated by the sun's energy. It was an experimental lab, a single story house-like structure containing two rooms, designed by Professor Hoyt C. Hottel on the present site of building 36 [see MIT map].

Solar I used solar radiation as a heat source for the winter. Projects were conducted on summer air conditioning and power generation. To heat the building, a sun heat trap tilted at a 30 degree angle was placed on the roof under three layers of glass.

The bottom of the box was fitted with a sheet of copper painted black, under which tubes ran. Water circulated through these tubes and then ran down into a metal tank located in the basement.