A solar collector of the direct flow type comprises a solar absorbing tube 3 containing elongate tube 11, and a working fluid. The elongate tube 11 contains a concentrically positioned inner pipe 12 thereby forming two concentric internal flow passage ways 13, 14 for the flow of a fluid to be heated. The elongate tube 11 extends out of one end of the solar absorbing tube 3 and into an end fitting 15 wherein an annular outer passageway 13 of the elongate tube 11 communicates with a cold fluid inlet conduit 16 within the end fitting 15 and the inner passageway 14 of the elongate tube 11 communicates with a hot water outlet conduit 17 within the end fitting 15. A central dividing wall 19 divides the fitting 18 into the cold fluid inlet conduit 16 and the hot fluid outlet conduit 17. The dividing wall 19 is a separate insert component which is mounted in the passageway. Fluid can flow between the tubular passages 18 of adjacent solar tubes 3. The open ends of the passages 18 comprise recesses to provide a circumferential seat 20 for an o-ring 21 or similar sealing means to provide a fluid-tight seal when adjacent end fittings 15 are mounted together.