Abstract: A concentrating solar energy system is disclosed which permits efficient collection without tracking. The system comprises a collector having an elongate, trough-shaped body with an inner reflective surface having a cross-sectional curve of height H, throat opening T, and conforming substantially to the cartesian curve Y = .+-. AX.sup.b, the curve concentrating incident radiation into an included receiving area of maximum dimension R, wherein B is about 0.30 plus or minus 0.15, A is from about 0.5 to 2.5, H/T is between about 0.5 to 2.0 and preferably about 1, and the concentration ratio T/R is at least 3. For photothermal recovery, an absorptive liquid is used circulating in a transparent receiver tube, the liquid being automatically drained to avoid high temperatures when not circulating.