A collector system (12) is disclosed that comprises a row of linearly conjoined collector structures (13). The collector system is arranged to be located at a level above a field of reflectors (10) and to receive solar radiation reflected from the reflectors within the field. The collector structure (13) comprises an inverted trough (16) and, located within the trough, a plurality of longitudinally extending absorber tubes (30) that, in use, are arranged to carry a heat exchange fluid. The absorber tubes (30) are supported side-by-side within the trough and each absorber tube has a diameter that is small relative to the aperture of the trough. The ratio of the diameter of each absorber tube to the trough aperture dimension is of the order of 0.01:1.00 to 0.10:1.00 and, thus, the plurality of absorber tubes functions, in the limit, effectively to simulate a flat plate absorber.