A solar power system, a solar power method and a solar thermal hydraulic motor is provided that is simple and cost-effective, that is able to function at low temperatures and low temperature differentials. The solar power system comprises: a plurality of pressure vessels configured to receive working fluid; a solar collector, configured to heat the working fluid in at least one of the pressure vessels to thereby cause the working fluid to expand in the pressure vessel without changing phase; and a mechanical work element, configured to perform work from expansion of the working fluid in the pressure vessels. At least some of the plurality of pressure vessels are selectively couplable to each other to enable transfer residual energy from one pressure vessel after it has been used to perform work to another pressure vessel to assist in performing work.