Abstract: A body of water is confined in a closed vessel and heated to above 100.degree.C. This water is then drawn in a liquid state from this vessel and passed through a first expander where it is separated into steam and condensate. The steam from this first expander is used to drive the first stage of a load and the condensate is passed to another expander where it is again transformed into steam and condensate, the steam being used to drive the second stage of the load. Several such expanders are provided and the condensate from the last expander is fed to a low-pressure storage vessel. The high-pressure vessel is filled almost to the top with water during periods of low power consumption and the water is drawn off during peak-power periods. Superheaters may be provided in the outlet conduits of the expanders and the water at above 100.degree.C may be fed directly into the lower-pressure expanders to maintain their operating efficiency.