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 organic Rankine cycle is is similar to the Rankine steam cycle, but uses an organic fluid such as refrigerants and hydrocarbons instead of water as the working fluid. The ordinary Rankine cycle uses thermal power to convert water to steam, which expands through a turbine in order to generate electricity.

A heat pump upgrades lower temperature heat source and lifts it to a higher temperature, whereas the Organic Rankine Cycle (ORC) converts waste heat to power (mechanical or electrical). Waste heat sources occur in commercial and industrial operations, and mobile and stationary internal combustion engines.