A generator of electric energy based on a thermoelectric effect includes a layer of thermoelectric material set between two pipes that guide two flows of fluid at temperatures different from one another. Each of the pipes has its wall in heat-conduction contact with respective side of the layer of thermoelectric material. Each pipe has a cavity of passage for the respective flow of fluid occupied by a porous material or divided by diaphragms into a plurality of sub-channels so as to obtain a large heat-exchange surface between each flow of fluid and the wall of the respective pipe and between said wall and the respective side of the layer of thermoelectric material.