The Organic Rankine Cycle (ORC) is a favourable process for power production from 
low to medium temperature heat sources. The working principle of an ORC is similar 
to the most widely used process for power generation, the Clausius Rankine Cycle. 
The main difference is the use of organic substances, like silicone oils, 
fluorocarbons or hydrocarbons instead of water / steam as working fluid. The boiling 
pressure of these substances at low temperatures is higher compared with water.
Due to this favourable features the ORC is at the moment the state-of-the-art 
solution for electricity production from solid biomass in a power range of 400 – 
1500 kW. The manufacturer Turboden (Italy) has already sold more than 60 ORCs mostly 
used for combined heat and power production. The temperature of the heat source is 
around 300 °C, the working fluid is a silicone oil. 
The temperature of geothermal or waste heat is much lower, mostly in a range up to 
150 °C. For this purposes mostly hydrocarbons or fluorocarbons are used as working 
fluids. For this purposes fewer projects have been realized.
The purpose of the presentation is to introduce the principles of the Organic 
Rankine Cycle, to discuss process variations, possible applications and the state of 
the art. Second part of the presentation will be devoted towards the development of 
an ORC-cycle within an EU-funded project at the TU Munich.

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