Worldwide Geothermal Power Plants: Status as of June 1980

There are 100 geothermal power units now in operation throughout 12 countries, with a total installed capacity of just over 2110 MW. The average unit thus is rated at 21.1 MW. Newer units may be broadly classified as follows: (a) wellhead units of less than 5 MW; (b) small plants of about 10 MW; (c) medium plants of 30-35 MW; (d) large plants of about 55 MW; and (e) complexes typically consisting of several 55 MW units in a large geothermal field. There is a trend toward turbine units of the double-flow type with a 55 MW rating, used either alone or in a tandem-compound arrangement giving 110 MW in a single power house. This is particularly evident at The Geysers field in California. Double-flash units (separated-steam followed by a surface flash) are suited to high quality reservoirs having high temperature, high steam fractions at the wellhead, and low scaling potential. Single-flash units (separated steam) may be called for where scaling by the spent brine is a potential problem for the liquid disposal system. Binary plants are being used for some very low temperature reservoirs, particularly in the People's Republic of China, albeit in extremely small units. A large-scale pilot plant of the binary type is being planned for the Imperial Valley of California