Abstract: Low cost solar collectors are constructed by stretching a thin elongate, flexible reflective sheet (such as metallized polyethylene terephthalate film) over a frame so as to provide a ridged surface of desired geometric shape. In a preferred embodiment of the invention the frame comprises a plurality of rod-like members, with a supply reel on one end and a take-up reel on the other end. Extra reflective sheet material is stored on the supply reel so that when the sheet material in the concentrator degrades (after prolonged exposure to sun light), the degraded material can be rolled onto the take-up reel and fresh sheet material disposed in its place on the frame.