A guide rail for directing and retaining one or more slidably removable reflective sheets (106, 306, 406A, 406B, 606A, 606B, 706A, 706B, 1206, 2206) in a solar concentrator, and for maintaining the one or more slidably removable reflective sheets (106, 306, 406A, 406B, 606A, 606B, 706A, 706B, 1206, 2206) in a shape prescribed by the shape of the guide rail, the guide rail comprising a rail body (101, 301, 401, 601 A, 601 B, 701), wherein the rail body (101, 301, 401, 601 A, 601 B, 701) comprises a first L-shaped longitudinal channel (102, 302, 402A, 402B, 602A, 602B, 702A, 702B) formed by first and second walls oriented substantially parallel to one another and joined at a substantially perpendicular angle to a third wall, wherein a fourth wall is joined to the first wall at an end opposite the third wall, and wherein the fourth wall extends toward, but does not touch, an unjoined end of the second wall to form an opening of the L-shaped channel (102, 302, 402A, 402B, 602A, 602B, 702A, 702B) for receiving a longitudinal edge of the one or more slidably removable reflective sheets (106, 306, 406A, 406B, 606A, 606B, 706A, 706B, 1206, 2206).