Abstract: The invention relates to a process for transforming heat having a low temperature into motive power, wherein heat which is carried by a first fluid is used for heating a condensable second fluid which participates in a thermodynamic cycle and wherein the second fluid is expanded thereby producing motive power or thermic energy having a higher potential. The apparatus for putting into practice this process comprises a superheater, in which the first fluid carrying the heat to be transformed and the second fluid circulate, an expansion device for the second fluid which produces motive power, a heat exchanger in which the expanded second fluid and a compressed second fluid circulate, a condenser for transforming the expanded second fluid into a liquid, a compressor for feeding the liquid second fluid to the superheater via the heat exchanger, and a gaseous fluid circulating through the condensor which mixes via ports and a convergent nozzle in the superheater with the first fluid.

Abstract: The invention has for its object a solar boiler comprising a surface exposed to radiations, having a plurality of cavities or cells acting as black bodies. Each of the cavities is formed by a blind tube protruding in a space in which a heat conveying fluid is allowed to circulate. The invention may be applied e.g. for producing hot water or steam.