An apparatus for collecting radiant solar energy to provide solar heating which may be used singly or in multiples as modular units. The apparatus is constructed as a self-contained unit having an insulated base, an energy receiving surface positioned adjacent the insulated base, and a heat exchange fluid conduit for circulating a heat exchange fluid in contact with the energy receiving surface. Other conduits are provided to introduce a heat exchange fluid and to receive or collect the fluid after it has been in contact with the energy receiving surface. The top or cover of the collector module is positioned in spaced relationship adjacent the energy receiving surface. The cover is transparent to solar energy and is provided with a plurality of spaced raised structures having surfaces angularly disposed to transmit radiant solar energy to the energy receiving surface. Side walls provide a self-contained unit and permit mounting of the unit on a surface.