A solar collector has an opaque cover heated by solar energy. Heat flows from the opaque cover by conduction, convection, and infrared emittance across a gap within an at least substantially airtight enclosure to an absorber containing a working fluid. The exterior surface of the opaque cover has high solar energy absorptance and the interior surface has high infrared emittance. The exterior surface preferably has low infrared emittance. In one embodiment, fully wetted surface geometry permits direct and reflected infrared absorption by the absorber. The opaque cover eliminates the weight, cost and other shortcomings of glass. A hollow continuous side wall with rounded corners provides an embodiment that is robust yet economical, that is easy to manufacture and seal, that permits a reduced thickness of the opaque cover and mitigates the destructive potential of severe winds, and that can withstand the compressive forces experienced by an evacuated solar collector.