Abstract: The invention describes a new type of engine particularly adapted for the conversion of solar thermal energy at low temperature to mechanical and electrical energy. A relatively cold and a relatively warm chambers are sealed from the outside environment and contain a low boiling point evaporating fluid. A tube dips at its lower open end in the fluid phase of the warm chamber. The upper open end of the tube is branched and opens into the vapor phases of the cold and warm chambers. The level of the fluid in the lower end of the tube rises and falls in response to alternate opening and closing of the communications of the tube with the vapor phases of the warm and cold chambers. The movement of fluid is translated to useful work through a float responding to the fluid levels. A high density fluid may be used in the warm chamber to increase the buoyant force acting upon the float. One modification of the engine functions as a highly efficient fuel-operated steam engine.

Abstract: The low pressure engine operates through a temperature and pressure differential between two chambers containing a low boiling point liquid. The pressure differential causes the liquid to rise in a relatively small interspace between a conduit and a float in the relatively warm chamber. In order to obtain a mechanical advantage the float is temporarily restricted from responding to the buoyant force exerted by the liquid until the liquid in the interspace has reached a predetermined level.

Abstract: The solar-differential temperature motor consists of a relatively warm evaporator chamber inside a transparent enclosure which is designed to absorb and trap solar energy. The evaporator chamber is paired with a relatively cold condensor chamber shielded from direct solar radiation by non-transparent barriers. The cold chamber is cooled by evaporation of water from its surfaces or by immersion in a relatively cold body of water. Insides of warm and cold chambers are sealed from the outside environment and contain a low boiling point fluid. By closing and opening of a communication between the vapor phases of the chambers cyclic difference in vapor pressures between the chambers is obtained. Pressure differences are translated into motion by means of a movable part of the chambers which responds to changes in pressures in the chambers.