NOVELTY - The electric power generation device (1) has two tanks (2,3) for operating fluid. Both tanks have respective heat exchangers (8,9) and respective connections (7,17) connected to a motor unit (5). The device further includes an opening and closing device (4) including an opening and closing valve connected to the tanks so as to connect and separate the inner volumes of the tanks.    USE - Electric power generation device e.g. for use in domestic environments, as well as industrial, livestock breeding, agriculture, or renewable energy generation.    ADVANTAGE - The device is compact and modular in structure which can be used individually or in combination with other devices to provide simple, cheap and reliable electric power generation and continuous electric power supply. The device is suitable for use with fluids of almost any nature, including fluids in phase transition conditions or fluids without transitions, and can exploit thermal sources with low temperature and small temperature differences of e.g. 10 degrees Celsius.    DETAILED DESCRIPTION - The electric power generation device (1) has two tanks (2,3) for operating fluid. Both tanks have respective heat exchangers (8,9) and respective connections (7,17) connected to a motor unit (5). The device further includes an opening and closing device (4) including an opening and closing valve connected to the tanks so as to connect and separate the inner volumes of the tanks. Starting from the initial equilibrium condition of the operating fluid in each tank, the valves of the opening and closing device and one of the connections are closed. The heat exchanger in one tank heats the thermal fluid to a temperature higher than the equilibrium temperature of the operating fluid, increasing the operating fluid temperature and pressure in one tank to values higher than that of operating fluid in the other tank. When the operating fluid temperature or pressure in one tank reaches given value, valve opening in one connection is controlled to allow operating fluid to flow from one tank to the other such that the motor unit drives an electric generator (6). When the pressure difference between tanks reaches or falls below another given value, fluid flow in one heat exchanger is stopped. The valve opening of the opening and closing device is controlled until an operating fluid equilibrium condition is reached. The thermal fluid may be water, refrigerant, gas or air. The operating fluid may be carbon dioxide. An INDEPENDENT CLAIM is also included for an electric power generation method.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic view of an electric power generation device.    Electric power generation device (1)    Tanks (2,3)    Opening and closing device (4)    Motor unit (5)    Electric generator (6)    Connections (7,17)    Heat exchangers (8,9)