Abstract: An expansion motor that converts energy input from a source of pressurized gas, such as steam, into work on reciprocating pistons. The expansion motor can be driven by compressed gas, exhaust from another motor, or steam produced in a heat transfer device heated by exhaust from an industrial process. By expanding the pressurized gas, the expansion motor can extract energy from gas having a relatively low pressure and flow rate. The expansion motor can include a lubrication system whereby lubricating oil flows through internal bores in a rotating shaft in order to lubricate bearings joining the pistons to the shaft. A power generating method that uses a wind power or tidal power to compress air to drive the expansion motor, and a power generating method that uses heat from incineration of biomass material or municipal solid waste to produce steam in an evaporator coil to drive the expansion motor, are also claimed. Potable water can also be produced by the claimed methods.