Abstract: A lens is used to concentrate solar rays to heat an expansible fluid. Energy is extracted from the fluid to drive an electric current generator. The heated fluid may first pass through a heat sink to provide a more continuous flow of heated fluid to the current generating system. The lens itself may be biconvex and comprise two or more plates. If desired, the volume between the plates may be filled with a fluid, preferably having the same index of refraction as the material of the plates. Suitable apparatus may be provided to control the aximuth and bearing of the lens so that it is always situated as nearly as possible between the sun and the fluid container.