Abstract: A solar-collecting apparatus constructed for placement against a structure as against a wall or roof. When installed in a wall or roof it may form a portion of the structure. The apparatus includes an elongate housing having sides and a backing and a transparent glazing covering the housing. A collector assembly in the housing is composed of an outer solar-collector panel and an inner panel which forms with the backing and collector panel, respectively, inner and outer plenums which communicate with each other at one end of the housing. Inlet and outlet ports formed in the housing, adjacent its other end, communicate with the inner and outer plenums, respectively. Forced air admitted into the apparatus through the inlet travels through the inner plenum in one direction and through the outer plenum, alongside the collector panel, in the opposite direction toward the outlet. Baffles placed between the two panels increase heat exchange between the collector panel and air flowing through the outer plenum.