Geothermal Power on an upward growth path

Geothermal power generation capacity worldwide rose from 7,972.7 MW in 2000 to 8,933 MW in 2005, with 8,035 MW running. This is about 0.2% of the total world installed power generating
capacity.

The geothermal heat pump (GHP), also known as the Ground-Source Heat Pump (GSHP) or generically as geoexchange, is the fastest growing geothermal application today. GSHP is a highly efficient renewable energy technology that is gaining wide acceptance for both residential and commercial buildings, with 1.4 million installations worldwide by 2005, and growth from 1,854 MWt of capacity in 1995 to 15,284 MWt in 2005.

Ground-Source Heat Pumps are used for space heating and cooling, as well as water heating. The technology relies on the fact that the Earth (beneath the surface) remains at a relatively constant temperature throughout the year, warmer than the air above it during the winter and cooler in the summer. GSHP systems do work that ordinarily requires two appliances, a furnace and an air conditioner and use 25%–50% less electricity than conventional heating or cooling systems.

Geothermal technology is suitable for integrated regional energy systems, rural electrification and mini-grid applications, especially in distributed generation systems, in addition to national grid applications. It is being promoted as a regional resource, combining the exploitation of renewable energy resources together with environmental advantages.

Geothermal energy is contained in the heated rocks and fluid that fill the fractures and pores within the earth’s crust. It can be harvested in two ways, direct use of hot water or steam for space heating or industrial use such as aquaculture, thermal baths and hot springs, and to power electricity generation plants. Direct use is confined to low temperatures, usually below 150o C whereas, power generation employs high temperature resources over 150o C. 80 countries have developed direct use of geothermal energy and 20 exploit geothermal energy for power generation. Direct low-temperature use employs about twice the energy capacity as is used for power generation.

Direct use of geothermal heat has been used for thousands of years. The major direct use applications today are GSHP installations for space heating, presently estimated to exceed 500,000 and are the first in terms of global capacity but third in terms of output. Direct use of geothermal energy achieves 50-70% efficiency, compared with the 5-20% efficiency achieved with the indirect use of generating electricity.

Geothermal power started in 1904 with the Larderello field in Tuscany, which produced the world's first geothermal electricity. Major production at Larderello began in the 1930s and by 1970; power capacity had reached 350 MW. The Geysers in California started in the 1960s is the largest geothermal plant in the world. Individual geothermal power plants can be as small as 100 kW or as large as 100 MW depending on the energy resource and power demand.

The three countries with the largest amount of installed direct heat use capacity are USA (5,366 MW), China (2,814 MW) and Iceland (1,469 MW), accounting for 58% of world capacity, which has reached 16,649 MW.

The global installed capacity of geothermal power generation at in December 2005 was 8,933 MW, of which 8,035 MW was operational. Six countries accounted for 86% of the geothermal generation capacity in the world. The USA is first with 2,564 MW (1,935 MW operational), followed by Philippines (1,931 MW, 1,838 MW operational); four countries (Mexico, Italy,

Indonesia, Japan) had capacity at the end of 2005 in the range of 535-953 MW each. Mexico and Indonesia have grown 26% and 35% respectively between 2000 and 2005. Although on a smaller base, Kenya achieved the highest growth, from 45 MW to 129 MW.

In the last five years geothermal power generation has grown at an annual rate of 2.3% globally,a slower pace than the 3.25 in the previous five years, while direct heat use showed a strong increase. With current technology, the global potential capacity 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 over-exploitation of the Geysers steam field,has been partly compensated by important additions to capacity in several countries: Mexico,

Indonesia, Philippines, Italy, New Zealand, Iceland, Mexico, Costa Rica, El Salvador and Kenya. Newcomers in the electric power sector are Ethiopia (1998), Guatemala (1998), Austria (2001) and Nicaragua.

In 2005 and 2006 the United States showed strong signs of renewed growth for geothermal power generation. Five states now have geothermal power generating facilities; California, Nevada, Utah, Alaska and Hawaii. The Richard Burdett Power Plant (formerly Galena I) in Nevada commenced generating power in 2005 and the first geothermal power plant in Alaska being installed in 2006 at Chena Hot Springs. A fairly extensive list of projects has been
announced for the next ten years, with new installations planned in Arizona, Idaho, New Mexico and Oregon, in addition to the existing five ‘geothermal’ states. 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 require high capital investment for exploration, drilling wells and installation of plant, but have 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.

Construction costs of geothermal plants can vary widely, depending on local conditions and range from a minimum of $1.1 million to $ 3 million per megawatt. The DOE has calculated an average cost of $1.68 million for geothermal plants built in the Northwest of America in the last two years, where the bulk of US plants are situated or planned. However, while this is high in comparison with gas power, which can be as low as $460,000 per megawatt, the operating cost can be lower because there is no cost of fuel.

The leaders in developing geothermal technology and installing new plants are three American companies - Calpine, Unocal and Ormat, and one Japanese company- Marubeni. These companies have been active in establishing joint ventures in the Philippines and Indonesia andmore recently in Central America.