The Organic Rankine Cycle is utilises the same thermal principles as a conventional Rankine Cycle, except instead of water as the working fluid, it utilises an organic molecular fluid, like R245fa refrigerant.
The traditional Rankine cycle boils water (liquid) to create high pressure steam (gas), the steam is then used to rotate a turbine connected to a generator, once the steam has expanded through the turbine and decreased in pressure it’s condensed back into liquid state before being pumped back to the boiler for the cycle to start over again.
The organic Rankine cycle turbine operates on the same principle, but can work effectively with a much lower input temperature. To give an example a large-scale coal or nuclear power station boils water between 300°C and as high as 650°C. An organic Rankine cycle turbine can operate utilising input heat energy between 80°C and 250°C because the boiling point of the working fluid is much lower than water. So high pressure gas can be achieved with much lower input temperature from the heat source (geothermal, waste heat, solar thermal, biomass) meaning a much wider range of input heat sources can be used.