Abstract: An apparatus for producing mechanical energy utilizing the sun's rays is disclosed. The apparatus includes a continuously rotating structure having a plurality of thermally actuated pump units, consisting of a temperature sensitive cell and a piston assembly, mounted thereon. A focusing means concentrates solar rays on a number of the cells causing the expansion of material contained in each cell, resulting in the extension of a piston rod, the compression of a cylinder within the piston assembly and the transfer of fluid contained therein to a high pressure accumulator for operating hydraulic motors or the like. When rotated from under the focusing means, the cell cools resulting in a decrease in volume of the expansible material and a retraction of the piston rod causing fluid to enter the piston assembly from a reservoir.