A parabolic cylindrical trough solar concentrator shell is disclosed having a pair of oppositely disposed end support members jointed by spanning structural support members which may be in the form of individual elongated generally triangular polygon members to form the parabolic cylindrical trough. The inwardly directed surface of each polygon member is concave in shape and rendered highly reflective and so disposed such that the composite produces a highly reflective, concave, generally parabolic surface which reflects and focusses radiant energy striking upon it along a line parallel to and above the surface of the trough. A radiant energy receiving and absorbing conduit which carries a fluid heat transfer medium is provided along the focal line. The conduit is structurally supported from the end support members in a manner which allows free rotation of the structure relative to the support. In addition to the composite triangular polygon members, the structure may be fabricated using other shapes or a spanning sheet corrugated for strength covered by a separate reflecting surface.