An organic Rankine cycle (ORC) converts waste heat into electricity using a fluid with a low temperature boiling point.

 

Lower boiling point organic fluids are used in organic Rankine cycles (ORCs) to better adapt their operation to lower temperature heat sources. For smaller systems, ORC systems can outperform steam turbines in terms of efficiency (less than a few MWe). In contrast to a water/steam system, the capital and operating and maintenance (O&M) expenses are higher per installed MW. Because ORC technology is more suited to lower temperature sources, it is being aggressively pursued for geothermal power applications.

 

The use of ORC systems as a "bottoming cycle" in concentrated solar power is another possible use for them. In this scenario, high temperatures generate exhaust heat that would otherwise be wasted and is hot enough to run an ORC system for additional power generation. Nonetheless, ORC systems often have very poor efficiency (10–15%), therefore the project economics need to be carefully considered.

 

The efficiencies for ORC’s increase for larger systems where a significant volume of high temperature waste heat is available. As such, ORC Systems are effective in

• Industrial facilities

• Facilities with onsite generators such as CHP that have waste heat