Abstract: Solar-to-thermal energy converter comprising an insulated frame, a solar energy absorber mounted in the frame, a fluid flow heat exchange means thermally coupled to the absorber to carry away as thermal energy the absorbed solar energy, and a window transmissive to solar energy mounted in the frame above the absorber, featuring a temperature actuated heat loss enhancer comprising a fluid flow heat pickup means thermally coupled to the absorber, an exterior heat rejector element, a fluid flow heat rejector means thermally coupled to the heat rejector element, and a thermally actuated valve connected between said fluid flow pickup and rejector means to form a fluid flow circuit separate from the fluid flow heat exchange means and powered by the heat-produced differential buoyancy forces of the fluid therein when the valve is open.

Abstract: In a solar-to-thermal energy converter comprising an insulated frame, a solar energy absorber mounted in the frame, fluid flow heat exchanger means thermally coupled to the absorber to carry away as thermal energy the absorbed solar energy, and a window transmissive to solar energy mounted in the frame and spaced from the absorber, that improvement consisting of a heat loss suppressor comprising a multiplicity of walls extending between the window and the absorber, adjacent walls being at least in part non-parallel to each other to define a first set of elongated channels generally diverging and opening toward the window interleaved with a second set of elongated channels generally diverging and opening toward the absorber, the walls being of materal transmissive to solar energy and absorptive of thermal energy, the channels being narrow enough to reduce conversion heat loss and deep enough to reduce radiation heat loss.