A power generation system includes a first vessel having a generally constant volume and a second vessel having a variable volume. Thermal energy is supplied to an ideal gas within the first vessel in order to raise its temperature and pressure. The thermally compressed gas is then released into, and expands the volume of, the second vessel. The expanding volume of the second vessel expands raises a mass and/or strains an elastic member, thus storing gravitational and/or elastic potential energy. This stored potential energy can be released on demand by evacuating the second vessel, typically into a third vessel, and used to power a generator. Preferably, the potential energy is used to coupled to the generator using a planetary gear drive, such that a relatively small number of input rotations yields a relatively large number of output rotations.