A solid state temperature gradient cooling system in which thermal energy is, under a first condition, carried from a heat source to a heat storage device (20) and under a second condition is carried from the heat source and storage device (20) to a heat dissipator (2). The change in conditions is responsive to changes in the temperature of the heat dissipator above and below a predetermined value. Bimetallic disc elements (16) are employed, which respond to temperature changes about the predetermined temperature, and snap from a first condition concave/convex surface configuration to a second condition convex/concave configuration. The disc elements (16) are supported about their outer peripheries so that the change in configuration will cause the centre of the disc (16) to move along an axis normal to the disc. This movement is used to respectively open and close a low resistance thermal path (10, 12, 8) between the heat dissipator (2) and a first thermal conducting path (24, 10, 22) defined to transmit thermal energy between the heat source and the heat sink (20).