Geothermal energy is a proven resource for direct heat and power generation. In over 30 countries geothermal resources provide directly used heat capacity of 12,000 MW and electric power generation capacity of over 8,000 MW. It meets a significant portion of the electrical power demand in several developing countries. For example, in the Philippines geothermal provides 27% of that country's total electrical generation, from power plant complexes as large as 700 MW.
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 technology is suitable for rural electrification and mini-grid applications in addition to national grid applications. Direct use of geothermal heat can boost agricultural and aqua-culture production in colder climates and supply heat for industrial processes that can add value to local primary products. Geothermal resources may be especially important and significant in developing nations where no indigeneous fossil fuel resources exist such as oil, coal or natural gas. For example in Tibet, where no readily available fossil fuels exist, the Nagqu geothermal field (Tibet Autonomous Region, PRC) provides a useful energy source for the local population. With the help of the UN, a 1 MWe binary plant was built in 1993.
Costs of geothermal electric power are very dependent on the character of the resource and project size. The unit costs of power currently range from 2.5 to over 10 US cents per kilowatt-hour while steams costs may be as low as US$3.5 per tonne. Major factors affecting cost are the depth and temperature of the resource, well productivity, environmental compliance, project infrastructure and economic factors such as the scale of development, and project financing costs.
I. Geothermal Resources
Geothermal means "Heat from the Earth". The heat that flows from the Earth's hot interior due to crustal plate movements, zones of high heat flow may be located close to the surface where convective circulation plays a signifcant role in bringing the heat close to the surface.
Deep circulation of groundwater along fracture zones will bring heat to shallower levels, collecting the heatflow from a broad area and concentrating it into shallow reservoirs or discharging as hot springs. These reservoirs may contain hot water and/or stream. By drilling into these reservoirs, the hot water and/or steam is piped to the surface where it is used for direct use applications, or the high pressure steam is separated to drive turbines for power generation. The low energy waste water form such power generaiton is then usually re-injected back into the reservoir, or further utilised for direct heat applications. This technology enables it to be utilised to generate electricity and provide domestic and industrial heat. Geothermal energy has proved to be reliable, economic, environmentally friendly and renewable.
In general there are two main categories, the high temperature resources and the moderate/low temperature resources. The high temperature geothermal resources - 220 degrees Celsius and up - are predominantly found in volcanic regions and island chains. The moderate to low temperature resources are found on all continents. The high temperature are almost always used for power production while most of the low temperature resources are used for direct heating purposes or agriculture and aquaculture.
II. Resource Evaluation and Risk Assessment
Geothermal projects typically progress through stages of reconnaissance, exploration and development with various decision points along the way. In the early exploration stage when there are uncertainties of finding a useable heat resource after expending effort on early reconnaissance, surface exploration and/or drilling exploration wells. Carefully implemented regional reconnaissance surveys can, however, lead to a sound prioritisation of target areas by the filtering out of less promising prospects. Good exploration surveys of targeted prospect areas have shown they deliver high success rates for exploration drilling. Examples of such successful programmes include those undertaken in Indonesia, New Zealand and the Philippines where exploration drilling achieved success rates of over 80%.
The range of potential methods for utilising any geothermal resource is very dependent on the temperature of the resource.
Direct Uses of Geothermal Heat
Agriculture and Aquaculture.
With over 8000 MW of installed capacity, geothermal electric power generation is a well-proven technology that has been especially successful in countries and islands that have a high reliance on imported fossil fuels.
Small and Mini-grid Power Generation.
Grid-Based Power Generation.
Unit cost of Steam or Water (US$/tonne)
Some Geothermal Issues….
Power sector reforms open the sector up to private investment and competition, stimulating power utilities to enhance their operating efficiency and improve the quality of service that they provide to their customers. These reforms have opened the way for many private geothermal power projects internationally but have often weakened government owned agencies that have in recent decades taken responsibility for exploration and evaluation of geothermal resources in many countries.
Financial and Economic Feasibility
Direct Capital Costs (US$/kW installed capacity)
Risks and Limitations of Geothermal Energy Development
Exploration Risk. There are risks of not finding a useable heat resource after expending effort on early reconnaissance and surface exploration works. Good exploration surveys of targeted prospect areas have proven to deliver high success rates for exploration drilling. Similarly, there is a major cost incurred drilling exploration wells which may not result in useful production. Carefully implemented regional reconnaissance surveys can, however, lead to a sound prioritisation of target areas by the filtering out of less promising prospects. Examples of such successful programmes include those undertaken in Indonesia, New Zealand and the Philippines where success rates of subsequent exploration drilling exceeded 80%.
Size of Development and Reservoir Exhaustion. How a geothermal reservoir will perform over several decades provides another significant risk in geothermal development. A complete understanding of the reservoir can only be obtained by withdrawing fluids from the reservoir over a sustained period. Subsequent assessment of resource size and production capacity is possible to reasonable levels of certainty and forms a critical part of any geothermal development.
Economic and Political Risk. Risk may be encountered in developing countries through changes in economic fortunes, as experienced in Asia in the late 1990's, and from changes in government policy, such as rescinding incentives for the development of rural and renewable energy.
Geothermal Energy Technology (GET)
International Related Links
Earth Energy Links
International Geothermal Association: This site links members in 63 countries, and encourages research and development of geothermal resources through the publication of scientific and technical data. The IGA is based in Italy.
Geothermal Resources Council: This site is designed to provide education on the use and application of geothermal for the generation of electricity. The GRC is based in California.
Geothermal Energy Association: This site promotes the interests of the geothermal industry in the United States and the Association undertakes much of the lobbying activity in that country. The GEA is based in Washington.
U.S. Department of Energy: This site provides information on programs of the U.S. government to promote geothermal energy.
map of geothermal resources in the U.S.: This site shows the location of major geothermal sites in the United States and the potential of the energy source.
Geo-Heat Center: This Center is affiliated with the Oregon Institute of Technology, and this site provides information on both geothermal for generation and earth energy heat pumps.
Earth Energy Society of Canada: The Society was established to promote the use of ground-coupled heat pumps in Canada. Its members include industry manufacturers and installers, as well as electric utilities, engineers, architects and others.
International Ground Source Heat Pump Association: IGSHPA is affiliated with the University of Oklahome, and is the leading organization for research and training in earth energy technology. It is based in Stillwater.
Geothermal Heat Pump Consortium: The Consortium was created to promote the installation of earth energy heat pumps (under the trademark GeoExchange) in the United States. It is based in Washington.
Environmental Protection Agency: The EPA was instrumental in identifying the potential for earth energy heat pumps in the United States. It continues to support research and development.
Space Conditioning: The Next Frontier: A summary of the landmark report produced by the Environmental Protection Agency on the potential for earth energy heat pumps.
International Energy Agency Heat Pump Centre: A number of countries belong to this international centre, which promotes the exchange of technical and scientific information relating to earth energy systems.
Geothermal Energy Technical Site: The U.S. Department of Energy maintains this site to provide technical information on all applications of geothermal energy.
Environmental Protection Agency: This site is designed to acquaint residential consumers in the U.S. with the benefits of earth energy heat pumps.
An Information Survival Kit for the Prospective Geothermal Heat Pump Owner: This site is produced by the Geo-Heat Center in Oregon, and provides an informative guide to residential earth energy systems.
Global Warming Impacts of Earth Energy Systems: Earth energy systems can provide significant reductions of greenhouse gases in residential and commercial buildings. An analysis by NRCan shows that conventional residential heating systems produce from 1.2 to 36 times the equivalent CO2 emissions of ground-source heat pumps. In the commercial/institutional sector, CO2 emission reductions from 15% to 77% were achieved through the use of ground-source heat pumps.
Heating and Cooling with a Heat Pump: NRCan has produced a brochure that explains many of the issues to consider before purchasing an earth energy heat pump. This brochure is available free of charge and can be ordered on-line (third item on the list).
PARRY THOMAS HENRY SEAGRAVE JOHN COBB MALCOLM CAMPBELL DONALD CAMPBELL CRAIG BREEDLOVE KEN WARBY RICHARD NOBLE DON VESCO
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