Abstract: A modular, air-to-air solar energy collector for adding heat to a circulating flow of air includes a frame-like enclosure and a solar radiation absorbing plate disposed within the frame-like enclosure. The enclosure includes a light-transmissive outer panel, a back panel, an air inlet adjacent a first end and an air outlet adjacent at the same end. A first air flow passageway is defined by the light-transmissive outer panel and the outwardly facing surface of the solar radiation absorbing plate and a second air flow passageway is defined by the inwardly facing surface of the solar radiation absorbing plate and the back panel. A connecting flow aperture at one end of the solar radiation absorbing plate provides flow communication between the first air flow passageway and the second air flow passageway such that entering air passes across the outwardly facing surface of the absorbing plate and is then routed through the connecting flow aperture to the second air flow passageway.