The invention concerns a stationary power plant, in particular a gas power plant, to generate electricity; having an internal combustion engine, comprising a fuel medium inlet and an exhaust gas outlet, whereas an exhaust-gas flow of the internal combustion engine is discharged via the exhaust gas outlet; having an electrical generator, which is driven by the internal combustion engine to generate electricity, and which is coupled or can be coupled to an electrical grid, in order to feed the generated electricity into said grid; having a fuel medium supply, which is connected to the fuel medium inlet; wherein a steam circuit, in which a working medium is circulated by means of a feed pump, is provided, comprising a heat exchanger arranged in the exhaust gas flow, by means of which waste heat of the exhaust gas flow is transferred to the working medium for partially or completely evaporating the working medium, further comprising a condenser, in which the working medium partially or completely condenses. The invention is characterized in that a reciprocating piston expander is provided in the steam circuit, in which the working medium expands to produce mechanical work, and the reciprocating piston expander is connected mechanically to the internal combustion engine and/or the electrical generator by means of a releasable clutch.