A power plant or power station is a facility that generates useful electricity. It is most commonly classified by fuel or energy source (e.g. coal, natural gas, oil, nuclear, solar, wind, hydro). Power plants can also be classified by prime mover (e.g. steam turbine, gas turbine, reciprocating engine, water turbine) or by thermodynamic cycle (e.g. Brayton cycle, Rankine cycle, combined cycle, Diesel cycle).