Abstract: A power generator including a closed pressure resisting tubular loop having a lower warmed end and an upper cooled end joined by connecting penstock column and a return column, the tubular loop being filled with fluid under pressure, the critical point of which is between the temperatures of the cooled and warmed ends, to cause the fluid to convert to a liquid phase in the upper end for discharge into the penstock column, and cause the liquid to convert into a gas phase in the lower end, for discharge while in its gas phase into the return column so that circulation of fluid as it converts between its liquid and gas phases is continuous, and a hydraulic power unit driven by downwardly moving liquid in the penstock column, reacting to the hydrostatic pressure so generated.