An improved apparatus and method for absorbing solar energy, the apparatus providing a sealed envelope having a transparent upper panel with a solar energy absorbing panel thermally isolated against convective and conductive heat losses by a partial vacuum in the sealed envelope. The transparent panel has an upwardly extending curvilinear surface which increases its strength characteristics against the pressure differential between the ambient and the partial vacuum inside the envelope. Support structure is also provided in conjunction with the apparatus to place the periphery of the transparent panel under constriction to compensate for tensile stresses imposed thereon by the pressure differential. The inside surface of the transparent panel and the absorber panel are selectively coated with an infrared reflective surface to reflect and reduce losses of infrared radiation emitted by the absorber panel.