ORC technology is based on the widely known and proven Rankine Cycle principle. It was named after William John Macquorn Rankine, a Scottish polymath and Glasgow University professor. The Rankine cycle is a cycle that converts heat into energy. The heat is supplied externally to a closed loop.
...so how does it work?
The Organic Rankine Cycle (ORC) is named for its use of an organic (high molecular mass) fluid with a liquid-vapour phase change (boiling point), occurring at a lower temperature than the water-steam phase change in a steam turbine installation.
The relatively low temperature heat is converted into useful energy that, in itself, can be converted into electricity.