A solar concentrator has frame members connected together to form a framework, and a flexible sheet attached to the framework such that the flexible sheet takes a loose shape and can flex in response to shaping forces exerted thereon. The sheet has a reflective surface located between the frame members. A shaping force system is operative, when activated, to exert the shaping forces on the sheet, the shaping forces configured to draw the sheet from the loose shape into a desired shape such that solar rays striking the reflective surface are focused on a target, and a solar energy receiver is attached to the framework at a location corresponding to the target. Thin wall tubing filled with pressurized air can provide strong light frame members. When the shaping force system is deactivated, the flexible sheet reverts substantially to the loose shape.