Geothermal Power in the US

In December 2005 the installed geothermal capacity in the USA was 2,564 MW, of which 1,935 MW was usable. The considerable difference between installed capacity and operating capacity in the USA was due to lack of steam caused by over-exploitation of the Geysers geothermal field in California. On this site, available steam can now only supply 888 MW out of the 1,421 MW installed capacity.

Current geothermal resources using today’s technology are estimated at 6,520 MW and at 22,000 MW with enhanced technology.

Over the last three decades, the US geothermal power-generation industry has grown to be the largest in the world, with over 2,445 MW of installed electrical capacity. Growth during the first two decades (1960-1980) was due to a single utility’s development of one dry-steam resource. After 1983, growth shifted toward independent power producers and development of waterdominated geothermal resources at several locations.

The steady growth of geothermal development in the United States from 1960 to 1979 was led by activities at The Geysers, where the field developments of the partnership of Union Oil Company of California, Magma Energy Company, and Thermal Power Company were greatly expanded toprovide steam to the Pacific Gas and Electric Company (PG&E) electrical-generation system.

This construction made The Geysers field the largest geothermal development in the world. Production from The Geysers peaked in 1988 but pressure declines in the reservoir limited any further expansion of the field. In December 2006, it was announced that the 55 MW Bottle Rock Geothermal Power Plant at The Geysers will reopen after being dormant since 1990. It will operate initially at 20 MW with plans to expand.

Geothermal well drilling has tapered off in the US since the 1980s. In California, four wells were drilled in 1996 (one at The Geysers and three at Salton Sea), nine in 1997 (four at Coso, two at The Geysers and three at Salton Sea) and seven in 1998 (three at Coso, one at The Geysers and three in the Salton Sea). In all, between 1996 and 1998, only 13 production and seven injection wells were drilled in California. The most promising new areas for geothermal
exploration are in Hawaii and the Cascade Mountains of Washington, Oregon, and northern California.

Future developments are planned, with projects being considered in some 55 stages. Not all of these will happen since some are in the pre-planning phase and others are awaiting approval. The opinion in the geothermal industry in the US is up-beat for future expansion.