The organic Rankine cycle is an alternate form of the Rankine cycle, most often used when the high temperatures required to produce steam are not available. The ordinary Rankine cycle uses thermal power to convert water to steam, which expands through a turbine in order to generate electricity. However instead of using water, which has a relatively high boiling point, the organic Rankine cycle makes use of an organic fluid that has a much lower boiling point than water. An ideal fluid for this should have a low boiling point so it will vaporize faster, along with a low freezing point so it will never become solid throughout the cycle. Compounds of butane or pentane satisfy these requirements and are commonly used.
These systems are used when high temperatures are not available. Examples include systems making use of waste heat in a cogeneration system, low temperature geothermal electricity generation, or solar ponds.
Aside from the working fluid their working principle is no different from a normal Rankine cycle. Visit this page for more information.