An organic Rankine cycle (ORC), is fundamentally the same as a steam Rankine cycle; however, it uses a lower boiling point organic fluid to better match its operation to lower temperature heat sources. ORC systems can achieve better efficiencies than steam turbines for smaller systems (less than a few MW_e).

The Rankine cycle or Rankine Vapor Cycle is the process widely used by power plants such as coal-fired power plants or nuclear reactors. In this mechanism, a fuel is used to produce heat within a boiler, converting water into steam which then expands through a turbine producing useful work.

The superheated vapor passes through a turbine, which allows electricity generation by its expansion. The Rankine cycle is closed by a condenser (using cooling water) that convert saturated vapor at low pressure from the turbine generator into condensate, which is pumped back to the heat exchanger to restart the cycle.