How does an organic Rankine cycle use lower-temperature geothermal heat?

The organic Rankine cycle (ORC) is a specialized form of binary cycle technology that enables electricity generation from lower-temperature geothermal resources, specifically water temperatures as low as 85–90 °C (185–194 °F).1

In this process, the geothermal heat is not used to boil water directly. Instead, it is transferred via a heat exchanger to a secondary working fluid—typically an organic compound with a lower boiling point than water. This transfer of energy causes the working fluid to vaporize. The resulting vapor is then used to drive a turbine connected to an electrical generator.1

Following the principles of the Rankine cycle, the vapor expands through the turbine to perform work, is subsequently cooled and condensed back into a liquid, and is then pumped back to the heat exchanger to repeat the cycle in a closed loop. By utilizing a fluid that vaporizes at lower temperatures, the ORC effectively captures energy that would otherwise be insufficient for traditional steam-based power generation.12