Geothermal power generation growth is continuing, but at a lower pace than in the previous decade, while direct heat use shows a strong increase. With current technology, the global potential for geothermal generation is estimated at 72,500 MW and at 138,100 MW with enhanced technology.
A strong decline in the USA in recent years, due to overexploitation of the Geysers steam field, has been partly compensated by important additions to capacity in several countries: Indonesia, Philippines, Italy, New Zealand, Iceland, Mexico, Costa Rica, El Salvador. Newcomers in the electric power sector are Ethiopia (1998), Guatemala (1998), Austria (2001) and Nicaragua.
Japan, Philippines and Nicaragua have all announced ambitious plans for further development of geothermal power.
There are three basic technologies for generating electricity from geothermal energy. Dry steam power plants using dry steam systems were the first type of geothermal power generation plants to be built. They use the steam from the geothermal reservoir as it comes from wells and route it directly through turbine/generator units to produce electricity.
Flash steam plants are the most common type of geothermal power generation plants in operation today. They use water at temperatures greater than 182° C that is pumped under high pressure to the generation equipment at the surface. Upon reaching the generation equipment, the pressure is suddenly reduced, allowing some of the hot water to convert or “flash” into steam. This steam is then used to power the turbine/generator units to produce electricity.
Binary cycle geothermal power generation plants differ from dry steam and flash steam systems in that the water or steam from the geothermal reservoir never comes in contact with the turbine/generator units but is used to heat another “working fluid” which is vaporised and used to turn the turbine/generator units.
Geothermal power projects are characterised by high capital investment for exploration, drilling wells and installation of plant, but low operating costs because of the low marginal cost of fuel. Return on investment is not achieved as quickly as with cheaper fossil fuel power plant, but longer term economic benefits accrue from the use of this indigenous fuel source.