Examples of Combined Heat and Power Plants Using Geothermal Energy

Abstract

Examples of combined heat and power plants (CHP) using both high temperature (above 200oC) and low temperature (around 100oC) geothermal resources are described. These installations, some of which have been in operation for over 30 years, make more efficient use of the geothermal resources by cascading the geothermal fluid to successively lower temperature applications, thereby improving the economics of the entire system dramatically. The cascaded use, after being used for power generation, can include space or district heating, greenhouse heating, and aquaculture pond and swimming pool heating. The high temperature geothermal power plants normally use flash steam technology, whereas the low temperature operation use binary or Organic Rankine Cycle (ORC) power units. High temperature power generation with geothermal energy is usually economic as stand-alone plants, but low-temperature power generation is often not economic, with net plant efficiencies normally below 10% due to the low source temperature and relatively high parasitic loads from pumps. Examples of high temperature CHP installation described in this paper include the Sudurnes Regional Heating Corporation plant at Svatsengi, Iceland, and the Nesjavellir Geothermal plant near Reykjavik, Iceland. Low temperature installations described in this paper include ones at Bad Blumau and Altheim, Austria, Neustadt-Glewe, Germany, and at Egat, Thailand.