Demand for new electrical generating capacity in developing countries is at its highest level ever, and with the institution of market economies in many countries, there are new business opportunities in geothermal energy. Presently, about 7,000 megawatts of geothermal electrical power generation is on line in some 20 countries, including (but not limited to) China, Costa Rica, El Salvador, Iceland, Indonesia, Italy, Japan, Kenya, Mexico, New Zealand, Nicaragua, Philippines, Romania, Russia, Thailand, Turkey, and the United States. The largest operating geothermal field is The Geysers in the USA, which produces about 1,300 megawatts. By some estimates, as much as 80,000 megawatts of geothermally generated electrical power are available from volcanic systems in developing countries throughout the world. Indonesia alone estimates its potential at 19,000 megawatts.

In terms of reliability and sustainability of geothermal systems, we know that natural geothermal systems have occurred throughout geologic time, and that a typical lifetime for geothermal activity around magmatic intrusive centers ranges from a minimum of perhaps 5,000 years to more than 1,000,000 years. Geothermal resources are, thus, renewable by any reasonable definition of the word. We further know that the natural rate of recharge of geothermal reservoirs varies from a few to more than 1,000 thermal megawatts. The natural recharge rate represents the minimum rate at which geothermal systems could, in principal, be produced for tens of thousands of years. In commercial development, however, geothermal systems are produced at rates that exceed their natural rates of recharge because to do otherwise would be uneconomic. Thus, geothermal systems have a finite lifetime during which they will produce economic electrical power, although this lifetime may perhaps be supplemented by a further period during which they can be used for direct-heat applications that require lower temperatures.

In operation, geothermal power generation has proven to be very reliable. The Larderello field in Italy has produced power since before World War II, the Wairakei field in New Zealand has been operational since 1958, and The Geysers field in California and produced power since 1960. We can also judge sustainability of geothermal production from an estimate of the thermal resource residing in the rocks of the reservoir, where most of the heat is contained. At The Geysers field in California, the heat content is estimated as being at least equivalent to that obtained by burning 28 billion barrels of oil or 6.2 billion short tons of coal. Large geothermal systems are clearly world-class energy resources.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah