Abstract: A solar energy collector 16 for utilizing the energy of the sun to heat a working fluid. The collector comprises a core conduit 30 having a working fluid inlet end 32 and a closure 38 fitted across the other end. A single return conduit 42 is spirally wound upon the exterior surface of the core conduit, wherein the windings are in close lateral juxtaposition but with the return conduit and the core conduit both exposed to direct impingement of solar rays. A transparent tube 48 coaxially surrounds the core conduit 30. Annular members 52 and 54 are positioned at each end of the transparent tube 48 to maintain the spatial relationship of the members and form an annular air insulation zone around the core conduit 30 and return conduit 42.