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Geothermal Energy

Geothermal energy is heat energy from the depths of the earth. It originates from the earth’s molten interior and from decay of radio-active materials of underground rocks. The heat is brought near the surface due to crustal plate movements, by deep circulation of groundwater and by intrusion of molten magma, originating from a great depth, into the earth’s crust (see Fig. 1). In some places the heat rises to the surface in natural streams of hot steam or water, which have been used since prehistoric times for bathing and cooking.

Figure 1.  A representative geothermal reservoir

Zones of  high heatflow may be located close to the surface where convective circulation plays a significant role. Deep circulation of groundwater along fracture zones brings heat to shallower levels, collecting the heatflow from a broad area and concentrating it into shallow reservoirs. By drilling wells, this heat can be tapped to supply pools, greenhouses and power plants. geothermal activity

The quantity of this heat energy is enormous; it has been estimated that over the course of one year, the equivalent of more than 100 million GWh of heat energy is conducted from the earth’s interior to the surface. Yet, the geothermal energy tends to be relatively diffuse, which makes it difficult to tap. If it were not for the fact that the earth itself concentrates geothermal heat in certain regions – typically regions associated with the boundaries of tectonic plates (see Fig. 2) – then geothermal energy would be essentially useless. Geothermal Plants

Figure 2.  World map showing lithospheric plate boundaries

Geothermal resources are renewable within the limits of equilibrium between offtake of reservoir water and natural or artificial recharge. Within such an equilibrium the energy source is renewable for a long period of time. At other sites the resource lifetime, if not recharged, may be limited to several decades. In any case, if it is not technically a renewable resource, potential global geothermal resources represent a practically inexhaustible energy resource. The issue is not the finite size of the resource, but availability of technologies able to tap the resource economically.

Nature of the Geothermal Energy Resource

On average, the temperature of the earth increases by about 3°C for every 100 meters in depth. This means that at a depth of 2 km, the temperature of the earth is about 70°C, increasing to 100°C at a depth of 3 km, and so on. However, in some places, tectonic activity allows hot or molten rock to approach the earth’s surface, thus creating pockets of higher temperature resources at easily accessible depths. remote power units

The extraction and practical utilization of this heat requires a carrier which will transfer the heat towards the heat-extraction system. This carrier is provided by geothermal fluids forming hot aquifers inside permeable formations. These aquifers or reservoirs are the hydrothermal fields. Hydrothermal sources are distributed widely but unevenly across the earth. High-enthalpy geothermal fields occur within well-defined belts of geologic activity, often manifested as earthquakes, recent volcanism, hot springs, geysers and fumaroles. The geothermal belts are associated with the margins of the earth’s major tectonic or crustal plates and are located mainly in regions of recent volcanic activity or where a thinning of the earth’s crust has taken place.

One of these belts rings the entire Pacific Ocean, including Kamchatka, Japan, the Philippines, Indonesia, the western part of South America running through Argentina, Peru, Ecuador, Central America, and western North America. An extension also penetrates across Asia into the Mediterranean area. Hot crustal material also occurs at mid-ocean ridges (e.g., Iceland and the Azores) and interior continental rifts (e.g., the East African Rift, Kenya and Ethiopia).

Low-enthalpy resources are more abundant and more widely distributed than high-enthalpy resources. They are located in many of the world’s deep sedimentary basins, for example, along the Gulf Coast of the United States, western Canada, in western Siberia, and in areas of central and southern Europe, as well as at the fringes of high-enthalpy resources.

There are four types of geothermal resources: hydrothermal, geopressured, enhanced geothermal systems (formerly Hot Dry Rock), and magma. Although they have different physical characteristics, all forms of the resource are potentially suitable for electric power generation if sufficient heat can be obtained for economical operation.

a.    Hydrothermal Resources

These are the only commercially used resources at the present time. They contain hot water and/or steam trapped in fractured or porous rock at shallow to moderate depths (from approximately 100 to 4,500 m). Hydrothermal resources are categorized as vapor-dominated (steam) or liquid-dominated (hot water) according to the predominant fluid phase. Temperatures of hydrothermal reserves used for electricity generation range from 90°C to over 350°C, but roughly two thirds are estimated to be in the moderate temperature range (150-200°C). The highest quality reserves contain steam with little or no entrained fluids, but only two sizeable, high-quality dry steam reserves have been located to date at Larderello in Italy and The Geysers field in the United States.

Recoverable resources available for power generation far exceed the developments to date. Many countries are believed to have potential in excess of 10,000 MWe which would fulfill a considerable portion of their electricity requirements for many years (e.g., the Philippines, Indonesia and the US).Geothermal Plants

Important low-enthalpy hydrothermal resources are not necessarily associated with young volcanic activity. They are found in sedimentary rocks of high permeability which are isolated from relatively cooler near-surface ground water by impermeable strata. The water in sedimentary basins is heated by regional conductive heat flow. These basins (e.g., the Pannonian Basin) are commonly hundreds of kilometers in diameter at temperatures of 20-100°C. They are exploited in direct thermal uses or with heat pump technology.

b.    Geopressured Resources

Geopressured geothermal resources are hot water aquifers containing dissolved methane trapped under high pressure in sedimentary formations at a depth of approximately 3 to 6 km. Temperatures range from 90 to 200°C, although the reservoirs explored to date seldom exceed 150°C. The extent of geopressured reserves is not yet well known world-wide, and the only major resource area identified to date is in the northern Gulf of Mexico region where large reserves are believed to cover an area of 160,000 km2. This resource is potentially very promising because three types of energy can be extracted from the wells: thermal energy from the heated fluids, hydraulic energy from the high pressures involved, and chemical energy from burning the dissolved methane gas.

c.    Enhanced Geothermal Systems – EGS (formerly Hot Dry Rock resources)

These resources are accessible geologic formations that are abnormally hot but contain little or no water. The EGS potential is 200 GW in the USA and 60 GW in Europe. The basic concept in HDR technology is to form a man-made geothermal reservoir by drilling deep wells (400-5,000 m) into high-temperature, low-permeability rock and then forming a large heat-exchange system by hydraulic or explosive fracturing. Injection and production wells are joined to form a circulating loop through the man-made reservoir, and water is then circulated through the fracture system.

Ecological and Environmental Impact
Green Energy

Geothermal energy use has a net environmental impact. Geothermal power plants have fewer and more easily controlled emissions than any similar sized fossil fuel power plants (see Fig. 3). Direct heat uses are even cleaner and are practically non-polluting when compared to conventional heating. There are other environmental advantages to geothermal energy, such as power plants using geothermal energy require far less land area than other energy resources (see Table 1). Another advantage, which differentiates geothermal energy from other renewables is its continuous availability 24 hours a day, all year round.


kg CO2  per kilowatt hour

Figure 3.  Relative CO2 emissions for different energy resources

Table 1.  Land uses for different energy technologies

Technology    Land occupied in m2 per GWh per year for 30 years
Coal (including coal mining)    3,642
Solar thermal    3,561
Photovoltaics    3,237
Wind (land with turbines and roads)    1,335
Geothermal    404

Mainstream Technologies

Geothermal energy has been used for centuries for bathing, therapeutic utilizations and water heating. Only in the twentieth century has geothermal energy been harnessed on a large scale for other purposes, such as space heating, industry and electricity generation. The range of potential methods for utilizing any geothermal resource depends mostly on the temperature of the resource.

a.    Direct Heat Use

Lower temperature geothermal resources occur in many world regions. They can provide useful energy for space and water heating, district heating, greenhouse heating, warming of fish ponds in aquaculture, crop drying, etc. (for division of direct heat uses, see Fig. 4). Geothermal fluids are generally pumped through a heat exchanger to heat air or liquid in direct use, although the resources may be used directly if the salt and solid contents are low. In comparison with geothermal electricity production, direct use has several advantages, such as higher energy efficiency (50 – 70%), generally the development time is shorter and less capital investment is involved.geothermal resource

Figure 4.  Direct-Heat Uses

Geothermal heat pump (GHP) technology can use geothermal sources of 20ºC or less. GHP can move heat in either direction; in winter heat is removed from the earth and delivered to the home or building – heating mode, while in summer heat is removed from the home or building and delivered for storage to the earth – air conditioning model.

b.    Geothermal Power Generation Technologies

There are several types of energy-conversion processes for generating electricity from hydrothermal resources. These include dry steam and flash steam systems, which are traditional processes; binary cycle and total flow systems, which are newer processes with significant advantages.

•    Dry Steam Plants

Conventional steam-cycle plants are used to produce energy from vapor-dominated reservoirs. As is shown in Fig. 5, steam is extracted from the wells, cleaned to remove entrained solids and piped directly to a steam turbine. This is a well-developed, commercially available technology, with typical unit sizes in the 35-120 MWe capacity range. Recently, in some places, a new trend of installing modular standard generating units of 20 MWe has been adopted. In Italy, smaller units in the 15 to 20 MWe range have been introduced.

Figure 5.  General Electric Co. dry steam plant at The Geysers, California

•    Flashed Steam Plants

More complex cycles are used to produce energy from liquid-dominated reservoirs which are sufficiently hot (typically above 160°C) to flash a large proportion of the liquid to steam. As shown in Fig. 6,  single-flash systems evaporate hot geothermal fluids to steam by reducing the pressure of the entering liquid and direct it through a turbine. In dual-flash systems, steam is flashed from the remaining hot fluid of the first stage, separated and fed into a dual-inlet turbine or into two separate turbines. In both cases, the condensate may be used for cooling while the brine is re-injected into the reservoir. This technology is economically competitive at many locations and is being developed using turbogenerators with capacities of 10-55 MWe. A modular approach, using standardized units of 20 MWe, is being implemented in the Philippines and Mexico.

Figure 6.  The Mitsubishi flash steam plant in Beowawe, Nevada

•    Binary-Cycle Plants

The operation experience over the years has confirmed the advantages of the binary geothermal plants, not only for the low enthalpy water dominated resources, but also for the high enthalpy resources with high aggressive brine or brine with high non-condensible content. The systems deliver sustainable zero-pollution energy, preventing a long-term depletion (the resource is 100% reinjected).

    Low-Enthalpy Resources (100°C  to 160°C) geothermal electricity
For low-enthalpy resources, binary plants based on the use of organic Rankine cycles (ORC) are utilized to convert the resource heat to electrical power (see Fig. 7). The hot brine or geothermal steam is used as the heat source for a secondary (organic) fluid, which is the working fluid of the Rankine cycle.

Figure 7.  An air-cooled binary plant

In the early 80’s, in order to increase the power output from a given brine resource by increasing the thermal cycle efficiency, a super-critical cycle using isobutane was developed as well as a cascade concept. The super-critical cycle may be slightly more efficient than the cascading cycle, but the cascading system has the advantage of lower operating pressures and lower parasitic loads in the cycle pumps. For example, at a power plant in Southern California, a three-level arrangement was employed and resulted in increased efficiency or power output gain of about 10% over that achievable with a simple ORC. In all of the above arrangements, a modular approach was employed so that high plant availability factors of 98% and above were achievable.Renewable energy

    Moderate Enthalpy Resources (160°C to 190°C)
For moderate enthalpy, two-phase resources with steam quality between 10 and 30%, binary plants are also efficient and cost-effective. Furthermore, when the geothermal fluid has a high non-condensible gas (NCG) content, even higher efficiency can be obtained than with condensing steam turbines.

This binary two-phase configuration is used in the São Miguel power plant in the Azores Islands (Fig. 8). Separated steam containing NCG is introduced in the vaporizer heat exchanger to vaporize the organic fluid. The geothermal condensate at the vaporizer exit is then mixed with the hot separated brine to provide the preheating medium of the organic fluid.

Figure 8.  The ORMAT two-phase binary geothermal power plant
in São Miguel, Azores Islands

Since the onset of silica precipitation is related to its concentration in the brine, dilution of the brine with the condensate effectively lowers the precipitation temperature at which silica crystallizes. This lower temperature added 3.5 MW of heat to the cycle representing 20% of the total heat input. This additional heat is utilized at the same thermal efficiency as the remaining heat due to the nature of the combined steam-brine cycle. Since the cycle efficiency is about 17%, this low temperature heat produces about 600 additional kW.
geothermal company

The second solution to better utilize the resource was the use of a regenerative cycle by the addition of a recuperator heat exchanger between the organic turbine and the air-cooled condenser, since the organic vapor tends to superheat when the vapor is expanded through the turbine. In this case the recuperator reduces the amount of heat that must be added to the cycle from the external source, thereby reducing the amount of brine flow rate required. This results in reduction of about 7% of the total heat input as required to produce the design level  of power output.

    Geothermal Combined Cycle Plants
To best utilize a steam dominated resource a Geothermal Combined Cycle is used where the steam first flows through a back pressure steam turbine and then is condensed in the organic turbine vaporizer (Fig. 9). The condensate and the brine are used to preheat the organic fluid as in the two-phase binary configuration above.

This concept was first used in 1989 in repowering a back pressure steam plant in Iceland, then with 30 MW plant in Hawaii in 1992, followed by a 125 MW plant in the Philippines and a 60 MW plant in New Zealand.

Figure 9.  The ORMAT geothermal combined cycle power plant in Puna, Hawaii

•    Experimental Plants

In an experimental process there are some more systems aiming to utilize the geothermal resource in the efficient manner.

•    Trilateral cycle – out of the binary total flow systems: the most well conceived is the trilateral cycle, which was also partially tested.

•    Absorption and Absorption/Regenerative cycles – of the different cycles proposed, the most advanced system is the Kalina cycle, which was tested on an energy recovery plant. One geothermal plant is being tested recently in Iceland and one is planned in the U.S. A demonstration is yet to be made in a geothermal power plant to prove the practicality of the concentration variations, the high pressure of the system, and other factors.

•    Field Tested Systems

    The total flow steam cycle (bi-phase), although conceptually elegant and theoretically efficient, did not make it to sustained commercial operation in its prior trials, mainly because of clogging in nozzles.

    The direct heat exchanger usage encountered serious problems of fouling and excessive hydrocarbon fluid loss.

    Hybrid systems: this is a complex system combining internal combustion engines with heat recovery from the hot brine and exhaust. The tests have yet to demonstrate the validity of the concept.

Recent Developments

Current uses and commercial status. Electricity from geothermal energy has been generated in Italy for almost 100 years. Until 1974, the total installed capacity for converting geothermal energy into electricity was only about 770 MWe (in Italy, Japan, New Zealand, the United States, and Mexico). Following the second oil shock, the worldwide installed capacity achieved its highest growth of 17.2% per year. The number of geothermal power-producing countries increased from 10 to 17. Recent emphasis has been placed on power production using the liquid hydrothermal resource since power production with dry steam has been commercially viable for several decades. At the end of 2002 a total of over 8,200 MWe was produced from geothermal resources in more than 20 countries. Substantial market penetration has thus far occurred only with hydrothermal technology.

Going into some detail, the seven countries with the largest electric power capacity are: the USA with over 2,000 MWe is first, followed by the Philippines (1,931 MWe); five other countries (Mexico, Italy, Indonesia, Japan and New Zealand) have capacities (in 2003) ranging from 440 – 950 MWe each. These seven countries represent over 91% of the world capacity and about the same percentage of the world output, amounting to about 48,000 GWh.geothermal power generation

The strong decline in the USA in recent years, due to over-exploitation of the giant Geysers field has been partly compensated by important additions to capacity in several countries: Indonesia, Mexico, Italy, New Zealand, Costa Rica, and Russia. Newcomers in the electric power sector recently (2003) are Papua New Guinea (PNG) and Germany.

Direct use, or non-electric application of geothermal energy has enjoyed modest growth. The statistics are a reflection of limited data and it is likely that there are many direct-use applications not reflected in the figures. A lot of data reflect the situation evaluated in 2000. An update of data is currently in progress towards the 2005 World Geothermal Congress and it is expected that it will reveal a decrease in the growth rate for all sectors (GRC Bulletin, July-August 2003). However, Table 12.1 shows that three leading countries, the U.S. (5,366 MWt), China (2,814 MWt) and Iceland (1,800 MWt) cover 58% of the world capacity which reached almost 17,000 MWt. Out of about 60 countries with direct geothermal plants, besides the three mentioned above, Turkey, Italy, Switzerland, Sweden, France, Canada, Germany, Japan and New Zealand have sizeable capacity.
organic Rankine cycle
Heat pump applications. During the last decade number of countries have encouraged individual house owners to install ground-source heat pumps to heat their homes in the winter and (as needed) to cool them in summer. Financial incentive schemes have been set up, commonly funded by the governments and electric utilities, as the GHP reduce the need for peak power and thus replace new electric generating capacity. The U.S. Government Heat Pump Consortium estimates that there were 750,000 GHP units installed in the USA (in 2002), which reduced electric demand by some 1,900 MW. In 2002 the European Union countries installed more than 50,000 GHP units (GHPC, October 2003).

Concerning R&D, several demonstration projects are under development in the framework of Enhanced Geothermal Systems, with participation of the USA, EC, Germany, France, Switzerland, Italy, Japan and Australia. Several HDR projects are under development at Fenton Hill (USA), Soultz-sous-Forêts (France) and at Hunter Valley (Australia).

The Future

The growth rate of the geothermal energy market is not limited by the lack of resources. During the early oil crises, intensive investigations led to the discovery of many geothermal reservoirs for electricity generation, some of which are in operation, while about 11,000 MWe of proven resources is not yet tapped. In the near future, the growth rate will most probably be 3-4% annually, as has been the case during the past few years.
geothermal technology
The report prepared by the U.S. Geothermal Energy Association shows that geothermal resources using today’s technology have the immediate potential to support between 35,450–72,390 MW of electrical generation capacity. Using enhanced technology, currently under development, the geothermal resource could support between 65,580–138,130 MW of electrical generation capacity. Assuming a 90% availability factor, which is well within the range experienced by modern geothermal power plants, this electric capacity could produce as much as 1,090 billion kWh of electricity annually.

Worldwide the report indicates that geothermal power could serve the electricity needs of 865 million people, or about 17% of the world’s population. 39 countries are identified which could be 100% geothermal powered, mostly in Africa, Central and South America and the Pacific.

However, if environmental impacts of energy use are internalized, then the real value of geothermal technology including its superior environmental characteristics and local resource features will be taken into account and the geothermal market will become more profitable. As a result, there will be enhanced geothermal exploration and R&D. The growth rate should then reach 6-7% and more. This outlook should encourage the development of other geothermal resources. The EGS and geopressured technologies may reach maturity around 2010.

remote power units
Lucien Y. Bronicki and Michael Lax
Israeli National Committee / WEC


Bronicki, L., (1998), “Eighteen Years of Field Experience with Innovative Geothermal Power Plants,” World Energy Council, Houston, TX.
Bronicki, L., (2002). “Geothermal Power Stations,” In “Encyclopedia of Physical Science and Technology,” Third Edition, Volume 6, pp. 709-718.
Fridleifsson, I.B. (2000), “Geothermal Energy for the Benefit of the People World-wide,” Web site
Gawell, K., Reed, M., and Wright, P.M. (1999). “Preliminary Report: Geothermal Energy, the Potential for Clean Power from the Earth.” Geothermal Energy Association.
GeothermEx, (1998), “Peer Review of the Hot Dry Rock Project at Fenton Hill, New Mexico.” A Report for the Office of Geothermal Technologies, U.S. Department of Energy.
Grassiani, M., and Krieger, Z., (1999). “Advanced Power Plants for Use with Hot Dry Rock (HDR) and Enhanced Geothermal Technology,” ORMAT, Yavne, Israel.
Huttrer, G.W., (2000). “The Status of World Geothermal Power Generation 1995-2000,” In “Proceedings, World Geothermal Congress,”, pp. 23-27.
Lund, J.W. (2000). “World status of geothermal energy use, overview 1995-1999.” In “Proceedings, World Geothermal Congress, 2000,” pp 4105-4111.
Lund, J.W., and Freeston, D.H. (2000). “World direct uses of geothermal energy 2000.” In “Proceedings, World Geothermal Congress 2000,” pp. 1-21.
Nakićenović, N., Grübler, A., and McDonald A. (1998). “Global Energy Perspectives,” Cambridge University Press, Cambridge..
U.S. DOE, (1998). “Strategic Plan for the Geothermal Energy,” NREL, U.S, Department of Energy, Office of Geothermal Technologies..
Williams, S., and Porter, K. (1989). “Power Plays-Profiles of America’s Independent Renewable Electricity Developers,” Investor Responsibility Research Center, Washington, DC.
World Energy Council. (1994). “New Renewable Energy Resources,” Chapter 4, Kogan Page.
World Energy Council, (2000a). “World Energy Assessment,” United Nations Development Programme, United Nations Department of Economic and Social Affairs.
World Energy Council. (2000b). “Energy for Tomorrow’s World-Acting Now!” World Energy Council Statement.


The data shown in Table 12.1 reflect as far as possible those reported by WEC Member Committees in 2003.

When not available from WEC Member Committees, data were drawn from the Proceedings of the World Geothermal Congress, Kyushu & Tohoku, Japan, 28 May-10 June, 2000, International Geothermal Association, and the Geothermal Resource Council, National statistical source have also provided a small amount of data.

Installed electricity generating capacity in the USA (2002 MW) reflects the level reported by J. Lund at the end of 2002. This level is significantly lower than that published by the DOE/EIA and reported by the US WEC Member Committee (2,898 MW). The difference is attributable to the treatment of downrated capacity.

The direct use of geothermal energy is not only inherently difficult to quantify but in some instances can be subject to constraints on reporting for reasons of confidentiality, etc. The statistics shown for both capacity and output should therefore be treated as, at best, indicative of the situation in a particular country. In many cases the figures had not been updated since the last World Geothermal Congress (2000). As far as possible, direct use includes the capacity and output of geothermal (ground-source) heat pumps.

Annual capacity factors have been calculated on the basis of end-year capacity levels, as average-year data were not available. In general, therefore, the factors shown will tend to be understated. The capacity factors of 1.00 given for direct use of geothermal energy in certain countries reflect the assumptions made in the surveys consulted.

[Table 12.1]
geothermal technology



Argentina is in the forefront of South American utilization of geothermal resources. High-temperature geothermal heat exists in the western region, along the Andes range, and moderate to low-temperature thermal fields have been identified in other parts of the country.

As a 670 kW binary-cycle pilot power plant at Copahue went off-line in 1996, the emphasis in recent years has been on the development of direct use of geothermal power. At present there are 134 direct use projects with an installed capacity of 25.7 MWt.

Australia Geothermal Plants

In recent years the geothermal situation in Australia has changed. The expansion of activity has been caused by the successful demonstration of binary hydrothermal power plants, the commercial success of ground-source heat pumps and also increasing government support of initiatives to reduce greenhouse gas emissions.

Geothermal energy is used directly by the numerous hot water bathing pools throughout the country and a district heating scheme in western Victoria. A hot water spa in the latter region received local government approval in 1999. Ground and water-source heat pumps have increased in popularity throughout the country, with at least 2,000 installations in place (in 2000); an expansion in the market of 50% per annum is expected, including commercial-size hot water systems for drying fruit and vegetables.

Australia has also been found to have a very significant Hot Dry Rocks (HDR) resource, particularly in the center of the country, extending over the north-eastern corner of South Australia and the south-western corner of Queensland. Research aimed at evaluation of HDR began in 1994.

There are only two experimental geothermal  electric power sites in Australia. A 20 kW plant in Mulka (South Australia) operated for three and a half years in the late 1980’s. An eight-fold scale-up of Mulka was commissioned at Birdsville (Queensland) in 1992 (150 kW) and ran until end-1994. after environmental considerations dictated a change in the working fluid, and also after a change of ownership, the plant was put back on line for demonstration in mid-1999.


There has been certain development of Austrian geothermal resources since 1995. The aggregate installed capacity of 58 MWt is utilized for direct applications such as district heating, spa heating, bathing, swimming and the heating of greenhouses.

A 500 kWe binary power plant at Altheim was brought into operation in 2001. Later that year a second 250 kWe binary power plant was installed at Rogner Hotel, Bad Blumau. The annual output is about 4 GWh.

In addition, it has been reported that there are in the order of 19,000 heat pump installations throughout the country, with an estimated total capacity of 228 MW.


It has been demonstrated from research undertaken since 1974 that Canada has a plentiful and widespread geothermal potential. The abundance of hydro-electric resources and inexpensive fossil fuels have, however, proved disincentives to large-scale development. Resources of high-temperature geothermal energy have been established but to date none have been utilized. Rather it has been applications utilizing the low-temperature resources that have come to fruition. A continuing development of the Meager Creek Geothermal Project, located some 170 km north of Vancouver, aims to develop the site potential of some 110 MWe. geothermal activity

Direct utilization of geothermal energy has followed four routes (geothermal heat pumps, aquifer thermal energy storage energy from mine waters and hot spring resorts) and provides an estimated total installed capacity of 378 MWt.


With fast economic growth and increasing environmental concerns, the development of geothermal energy in China increased by 12% per annum during the 1990’s. Studies have identified more than 3,200 geothermal features, of which some 50 fields have been investigated and explored. High-temperature resources are mainly concentrated in southern Tibet and western parts of Yunnan and Sichuan Provinces, whereas low-medium temperature resources are widespread over the vast coastal area of the south-east, North China basin, Songliao basin, Jianghan basin, Weihe basin, etc.

The primary development has been in the growth of geothermal energy used directly. In 1998 it was reported that there were in excess of 1,600 sites being used for installations as diverse as drying, fish farming, irrigation and earthquake monitoring, etc. However, the main emphasis has been in the expansion of installations for space heating, sanatoria and tourism.Geothermal Plants

The development of geothermal power generation has been, by comparison, relatively slow, owing to the large hydro-electric resources in those provinces with high-temperature geothermal resources (Tibet and Yunnan). The largest power complex is located at Yangbajing (Tibet). China’s aggregate capacity is approximately 30 MWe, generating 100 GWh annually.

Costa Rica

The Central American volcanic belt passes through Costa Rica, evidenced by numerous volcanoes and geothermal areas. The fields of Miravalles, Tenorio and Rincón de la Vieja are located in the north-western part of the country and have been studied in detail.

To date, Costa Rica’s geothermal resources have only been utilized for electric power generation. A 55 MWe single flash condensing unit was commissioned in March 1994 at Miravalles, followed soon afterwards by an additional 5 MWe backpressure unit. A second 55 MWe condensing unit came on stream in 1998, and subsequently (in 2000) another 29.5 MWe backpressure unit increased the installed generation capacity of the Miravalles field to 144.5 MWe. A further 18 MWe unit (unit 5) is under construction.

Exploration work on the slopes of the Rincón de la Vieja volcano at the Las Pailes and Borinquen geothermal fields is ongoing.Geothermal Energy

El Salvador

Like Costa Rica, El Salvador lies on the Central American volcanic belt and thus there is a plentiful geothermal resource. The main emphasis has been on using the resource for power generation and although a potential exists for the direct use of geothermal, it has not yet been developed.

Geothermal energy is a plentiful resource in El Salvador, accounting for over 24% of the country’s electricity output. In 2002, power generation from the Ahuachapán and Berlín geothermal facilities was 940 GWh. This power was delivered to a newly deregulated, competitive market, mixed with 1,140 GWh of electricity from hydro projects, 1,805 GWh of electricity from thermo-electric operations, and 430 GWh of power imports from Guatemala (3,175 GWh total).

Of the 161 MWe of geothermal capacity currently installed in El Salvador (95 MWe at Ahuachapán, and 66 MWe at Berlín), only about 119 MWe are available (63 MWe at Ahuachapán and 56 MWe at Berlín).geothermal technology

Geotérmica Salvadoreña (GESAL) estimates that it can increase effective capacity in the next three years by about 50 MWe with the addition of one new 28 MWe condensing unit at Berlín; reinstallation of the 10 MWe wellhead power plant from Berlín to the Cuyanausul Geothermal Field; and a 12 MWe upgrade of Ahuachapán installations. GESAL is also exploring possibilities to expand operations at other Central American geothermal fields.

Two other prospective geothermal areas are San Vicente in the center of the country and Chinameca in the east; each has an estimated capacity of 50 MWe. Future studies are also planned for Coatepeque, Santa Rosa Lima and Obrajuelo Lempa.

El Salvador passed electricity reform legislation in 1996, creating a free and open power market. A regulatory agency (SIGET) was created to oversee the market, and the country’s state-owned electricity company, CEL, was split into several distribution, transmission and generation companies, some of which were sold to private foreign investors. Geothermal generation assets were spun off from CEL in 1999 into GESAL, which now competes in the open market. Whilst geothermal generation now competes favorably with other energy sources in an open market, its prospects would be affected by projects underway to interconnect all of Central America. The result would be one large market and moreover, with plans to build a gas pipeline from Mexico to El Salvador and/or from Colombia to Panama, the effects would be felt throughout the electricity sector.


Ethiopia is one of those African countries possessing geothermal potential. Considerable resources of both high- and low-enthalpy geothermal have been located in the Ethiopian Rift valley and in the Afar depression. Exploration that began in 1969, has to date, revealed the existence of 24 prospects having about 700 MW potential.

In mid-1998 the 8.5 MWe Aluto-Langano geothermal plant became operational. Aluto-Langano became the first geothermal power plant in Africa to use integrated steam and binary power technology. The plant has recently become inactive, due to resource problems.

In addition to the Aluto-Langano geothermal field, the other areas under exploration are Corbetti in the Lake District and Tendaho in the Central Afar region.


There are only low-enthalpy geothermal resources in metropolitan France; high-enthalpy geothermal resources are found only in France’s overseas departments. The geothermal power plant in Guadeloupe (4.2 MWe) has been operating since 1995.

Although the first geothermal district heating plant was constructed in 1969 in the Paris region, the main development of geothermal energy began following the oil crises of the 1970’s. The resources are found in two major sedimentary basins: the Paris Basin and the Aquitaine Basin in the southwest. Other areas (Alsace and Limagne) have geothermal potential but cannot be so readily utilized. By end-1986 there were 74 plants in operation but by end-1999 this number had fallen to 61, of which 41 are in the Paris region, 15 in the Aquitaine Basin and 5 in other regions. The installed capacity is mainly used for space heating (97%) but also greenhouse heating (2%) and fish and animal farming (1%). In addition, since the 1980’s Frances’ very low-enthalpy resources began to be utilized by the installation of heat pumps. At the present time several thousand plants exist, mainly for collective of individual building heating.

Since the 1980’s the French authorities have begun to support research into the potential of Hot Dry Rocks.


Geothermal resources are prevalent throughout the area of the South Caucasus and are utilized intensively in Georgia. It has been reported that the country’s considerable reserves are being particularly efficiently used in the Tbilisi field. The installed capacity effectively available for direct heat applications has been estimated to be in the region of 350 MWt.


Germany does not possess high-enthalpy steam reservoirs. The geothermal resources are located in the north German sedimentary basin, the Molasse Basin in southern Germany and along the Rhine graben.

Germany’s 2000 Renewable Energy Law (REL) mandates a doubling of renewable power in the country’s electricity market to 10% by 2010. The REL sets specific tariffs for each renewable energy, based upon its real cost. Electricity from geothermal plants would receive ¢8-10/kWh. An outcome of the REL is the first German geothermal power plant (200 kWe), inaugurated in Neustadt-Glewe in 2003.

At end-1999 total installed capacity for direct use of geothermal energy stood at 397 MWt of which 55 MWt represented 27 major centralized plants and 342 MWt small decentralized earth-coupled heat pumps and groundwater heat pumps.

The exact number of small decentralized heat pumps, widespread throughout the country, has not been quantified but is thought to be in excess of 18,000 and likely to grow in future years, possibly to around 40 MWt by the end of 2002.


Guatemala’s Instituto Nacional de Electrificación (INDE) has five geothermal areas for development. All five areas (Zunil, Amatitlán, Tecuamburro, San Marcos and Moyuta) lie in the active volcanic chain in southern Guatemala. INDE has conducted investigative work and development of geothermal power since 1972 and to date 58 MWe has been proved, with a further 398 MWe estimated as potential additional capacity.

The first geothermal power plant in the country was constructed in the Amatitlán area; electricity production from a 5 MWe back-pressure plant began in November 1998. The unit was dismantled. Eventually expansion of the field and construction of a 25 MWe combined cycle plant is envisaged. In addition, the Amatitlán field also supports the direct use of geothermal energy, in the form of using steam for drying concrete blocks and a full dehydration plant.

A second 24 MWe geothermal plant (in the Zunil I field) has been in commercial operation since September 1999. Following INDE’s exploratory drilling work, a contract was signed with Orzunil I for the private installation and operation of the plant. Until 2019 the company will buy steam from INDE and sell power to the national grid. Exploratory drilling the Zunil II field has shown that it possesses 50 MWe potential.


Hungary possesses very considerable geothermal resources and it has been estimated that the country has the largest underground thermal water reserves and geothermal potential (low and medium enthalpy in Central Europe.

To date, there has been no utilization of geothermal energy for the production of electricity. The principal applications of geothermal power used directly are greenhouse heating (62%), space heating (23%), industrial process heat (0.5%), and other uses (13%). It has been reported that geothermal heat pumps represent an additional 3.8 MWt and four spas supply a further 14.2 MWt.

In the mid-1990’s the Hungarian Oil and Gas Company (MOL) began a programme to promote the development of geothermal energy. Three pilot projects have been studied, two of which involve cascaded use of geothermal heat for electricity production and subsequent direct applications.


Geothermal energy resulting from Iceland’s volcanic nature and its location on the Mid-Atlantic Ridge has been utilized on a commercial scale since 1930. The high-temperature resources are sited within the volcanic zone, whilst the low-temperature resources lie mostly in the peripheral area.

Approximately 50% of total primary energy is supplied by geothermal power and the percentage of electrical generation from geothermal resources more than doubled between 1996 and 1999. Iceland’s wealth of hydro-electric resources provided almost all of the balance.

Currently geothermal energy is mainly used for space heating, with about 86% of households being supplied, mostly via large district heating schemes. Reykjavik Energy, operator of the largest of the country’s 26 municipally-owned geothermal district heating schemes, supplies virtually the entire city (approximately 160,000 inhabitants) and four neighboring communities..

Whilst 77% of the direct use of geothermal heat is used for space heating, 8% is used for industrial process heat, 6% for swimming pools, 4% for greenhouses, 3% for fish farming and 2% for snow melting. Total installed capacity for direct use was 1,800 MWt at end-2002; an annual output of 24,700 TJ.

In recent years there has been an expansion in Iceland’s energy-intensive industrial sector. To meet an increased demand for power, the capacity of geothermal plants has grown rapidly from 50 MWe and currently stands at over 200 MWe. Geothermal electricity generation was 1,433 GWh in 2002.


The islands of Indonesia possess enormous geothermal resources: geological surveys have identified as many as 244 prospects, of which 70 are specified as high-temperature reservoirs with an estimated total resource potential of nearly 20,000 MWe. Of this potential about 49% is in Sumatra, 29% in Java-Bali, 8% in Sulawesi and 14% in other islands.

A very small amount of geothermal energy is used directly for bathing and swimming, all instances being in West Java.

The financial crisis that hit Indonesia towards the end of 1997 and the resultant adverse affect that it had on the power sector demand and growth resulted in delaying the development of geothermal energy. By December 2002, the country will have increased its geothermal electric power generation capacity to 807 MWe. This figure includes currently operating facilities with a capacity of 330 MW at Gunung Salak, 140 MW at Kamojang, 145 MW at Darajat, 110 MW at Wayang Windu, 2 MW at Sibayak, 20 MW at Lahendang and an additional 60 MW at Dieng.

In the future the Government plans to significantly alter the fuel mix of electricity generation by increasing the use of coal, geothermal energy and hydro power and thus reducing the use of oil and gas.


Italy is one of the world’s leading countries in terms of geothermal resources. The high-temperature steam-dominated reservoirs lie in a belt funning through the western part of the country from Tuscany to Campania (near Naples). Commercial power generation from geothermal resources began in Italy in 1913 with a 250 kW unit. Subsequently the main emphasis has been on the production of power rather than on direct use of the heat.

Following the limited development of resources during the first half of the 20th century, it was the second half that saw rapid growth. By end-1999, total Italian installed geothermal capacity stood at 621 MWe. The growth continued in recent years and by the end of 2002 Italy had 862 MWe of geothermal power plants installed.

In addition to the Italian country report presented at the World Geothermal Congress 2000, a detailed analysis of direct uses was also presented. The analysis found that several large geothermal fish farms (approximately 110 MWt), larger hotels and balneological spa uses (in the Abano district and on the island of Ischia) had been excluded from the country report.

Italian direct uses (excluding balneological/swimming pool use) can be conservatively estimated at about 680 MWt with a production of approximately 9,000 TJ/year.


Japan has a long history of geothermal utilization, both direct and for power generation. The first experimental power generation took place in 1925, with the first full-scale commercial plant (23.5 MWe) coming on-line at Matsukawa, in the north of the main island of Honshu, in 1966. Following each of the two oil crises, development of Japan’s geothermal resources was accelerated and by end-1984, 314.6 MWe capacity had been commissioned. Growth continued and unit size decreased as technological improvements occurred. By end-1999, installed capacity stood at 546.9 MWe (consisting of 19 units at 17 locations). The existing plants are all located in the Tohoku region of northern Honshu and on the southern island of Kyushu.

The country’s power generation potential from geothermal is estimated to be in the range of 2,500 MWe. The planned government deregulation of the electricity sector, bringing about lower medium and long-term electricity costs, is expected to result in geothermally-generated power becoming uncompetitive.

Direct use of geothermal got water has a long tradition in Japan, where enjoyment of natural baths is a national recreation. There is widespread usage of geothermal heat for purposes other than bathing (which accounts for 11% of capacity): space heating (including hot water supply) 51%; greenhouse heating 13%; snow melting 12%; fish breeding 9%; air conditioning (cooling) 2% and industrial process heat and other 1% each. The quantification of direct use capacity is particularly difficult in Japan. It is thought to be considerably larger than the reported figures.

Hot spring water above 15ºC is widely available, thus there is little demand for heat pumps.

From the beginning of 1980 the New Energy and Industrial Technology Development Organization (NEDO) has initiated 52 surveys to evaluate those areas with the most promising geothermal potential for power generation. In the context of Japan’s “New Sunshine Project”, NEDO is promoting technical developments in the surveying, drilling and exploitation of geothermal resources. Research is also being carried out into deep-seated resources and a hot dry rock generation system. In addition to various other governmental research organizations, private sector research bodies are also involved.


Kenya possesses substantial geothermal resources at Olkaria near Lake Naivasha (about 80 km north-west of Nairobi) and at other locations in the Rift Valley.

The first geothermal unit came into operation at Olkaria in July 1971, with an initial installed net capacity of 15 MWe. Two more 15 MWe units were added, so that by end-1999 the 45 MWe.  The geothermal power output was increased by 12 MWe in 2000 when the first two stages of Kenya’s first private geothermal plant were completed by ORMAT at Olkaria III. The additional stage of Olkaria III (38 MWe) is under development. The 64 MW Olkaria II power plant was commissioned in November 2003, bringing the country’s installed capacity to 121 MWe.

173 MWe of geothermal capacity is planned to be in operation by 2005 and a total of 576 MWe by 2017. In order to attract sufficient investment funds to achieve this goal, the restructuring of the power industry must continue. It is expected that in the future the power industry will be a partnership of the private and public sectors.

A minimum amount of geothermal energy is used for direct heat. For the time being flowers are being grown on an experimental basis, but it is intended that this should become a commercially viable operation.


Reflecting the country’s location in a tectonically active region, Mexico’s geothermal manifestations are particularly prevalent in the central volcanic belt, as well as in the states of Durango, Chihuahua, Baja California and Baja California Sur. Development has, in the main, been concentrated on electric power production although there is some utilization of geothermal power for direct purposes.

In 2003 Mexico celebrated its 30th anniversary of uninterrupted geothermal electric operation. During the last 30 years, it has scored a number of achievements in developing the country’s geothermal potential, including bringing online the Los Azufres (1982), Los Humeros (1990) and Las Tres Vírgenes (2001) geothermal fields. Mexico’s geothermal-electric capacity grew from 37.5 MWe to 853 MWe during the period – a figure that jumped to 953 MWe when the 100 MWe Los Azufres II was commissioned in the summer of 2003.

Geothermal heat used directly is predominantly utilized for bathing and swimming. Of the reported 164.19 MWt installed capacity (end-1999), virtually 100% was located in resorts throughout the volcanic zone. Minimal amounts of direct heat are utilized for space heating, greenhouse heating, agricultural drying, timber drying and mushroom breeding.

New Zealand

New Zealand is exceptionally rich in geothermal fields, as well as a large number of other geothermal features. Substantial capacity exists for both the generation of geothermally-produced power and also for geothermal energy used directly.

The first geothermal power plant came into operation at Wairakei, north of Lake Taupo (North Island) in November 1958, with an initial capacity of 69 MWe. The second stage of development, which added a further 123 MWe of capacity, began operation in October 1963. Wairakei was the second geothermal power station to be built in the world and the first to tap a hot pressurized water resource. Owing to an initial very rapid run-down in field pressure, the maximum output achieved from the station was 173 MWe. In 1983 all high-pressure turbine/generator units were decommissioned, owing to the decline in high-pressure steam output from the field. The current installed capacity of Wairakei is 162 MWe with an additional 15 MWe binary power planned to be in service by 2005.

Between 1966 and 1990 three more power plants were commissioned within the central North Island’s Taupo Volcanic Zone (TVC), in the localities of Reporoa and Kawerau. Their combined capacity (one back pressure unit, 3 binary units and 4 combined cycle units) amounted to 130 MWe.

Between 1996 and 1999 four plants were commissioned: the 55 MWe McLachlan plant (Taupo locality), a 25 MWe combined-cycle plant at Rotokawa (Taupo locality), the 12 MWe Ngawha binary plant (Northland locality, about 245 km north of Auckland) and a 55 MWe combined-cycle at Mokai (Taupo locality). The Rotokawa Extension plant, adding another 6.5 MWe to the existing plant, was completed in 2002 bringing the geothermal installed capacity to almost 448 MWe.

Potential generation capacity from the geothermal resources of the TVC has been conservatively estimated at 2,000 MWe.

At end-1999 installed capacity for direct heat uses stood at 307.9 MWt. The main user of direct heat is Kawerau. A 210 MWt plant generates clean process steam for various procedures within a pulp and paper mill operation. Geothermal steam at other locations is also used for agricultural drying (10% of direct-heat capacity), bathing and swimming (9%), space heating (7%) and fish and animal farming (6%).


Nicaragua is the Central American country with the greatest geothermal potential, on the order of several thousand megawatts (MW). Reserves that can be estimated with a higher degree of confidence total about 1,100 MW. Medium- and high-temperature resources are associated with volcanoes of the Nicaraguan Depression, which parallels the Pacific Coast. The current installed geothermal capacity of the country is 77 MW – all at the Momotombo Geothermal Field.

Geothermal exploration began in the country at the end of the 1960’s, focusing on the Momotombo and San Jacinto-Tizate geothermal fields. Studies increased after 1973, at a time when the oil crisis had a large impact on Nicaragua’s economy. Geothermal electricity production started at Momotombo in 1983.

Exploitation of geothermal power in the Momotombo area, located at the foot of the volcano of the same name, began when the first 35 MWe single-flash unit was commissioned in 1983. A second 35 MWe unit was added in 1989. Gross output of electricity reached a peak of 468 GWh in 1992 but subsequently fell away to a low of 121 GWh in 1998 owing to overexploitation of the field and lack of re-injection.

In 1999, ORMAT International, Inc. (Sparks, NV) won a 15-year contract to exploit the geothermal resource and improve electricity output at the Momotombo Geothermal Field. Since then, the company has drilled four deep wells (OM-51 to OM-54), and of these, only OM-53 was a good producer (9 to 11 MW). Mineral scales have been cleaned out of eight production and four injection wells using mechanical methods. In addition, chemical-scale inhibition systems have been installed in five wells. About 80% of waste geothermal fluids are being injected back to the reservoir at this time, and a new reservoir management plan has been implemented. Since May 2002, these efforts have increased and stabilized the electrical output of the flash plant at about 29 MWe. In November 2002, a 7.5 MWe ORMAT binary energy converter came online, raising generation capacity at Momotombo to about 35 MWe. The field now has 12 production wells, and four injection wells.

A Geothermal Master Plan for Nicaragua was completed in November 2001. It assessed the geothermal resource potential of identified fields and prospects in the country. At present, concessions for geothermal exploration and/or exploitation are in place for Momotombo, San Jacinto-Tizate and Casita-San Cristóbal. Apart from these, the three most promising geothermal prospects are:

El Hoyo-Monte Galán. Located west of Momotombo, this field has an estimated capacity of 200 MW for 30 years.

Managua-Chiltepe. This area is located about 15 km NW of Managua, Nicaragua’s capital, and has an estimated capacity of up to 150 MW for 30 years.

Masaya-Granada-Nandaime. This area, which includes several volcanoes and geothermal prospect areas, is near the northwestern shore of Lake Nicaragua. it may produce 200 MWe for 30 years.

To date all geothermal energy has been used for power generation but the Government, with support from the European Union and the UN Economic Commission for Latin America and the Caribbean, will conduct a geothermal rural electrification and direct application pilot project in the areas of the Cosigüina Volcano and Ometepe Island. Low-enthalpy fluids will be investigated for use in grain-drying, fish farming and heating greenhouses.

Papua New Guinea

Although there are numerous volcanic islands scattered along the western Pacific Rim, the first geothermal commercial development only occurred recently on the island of Lihir, off the northeast coast of Papua New Guinea. In 2003, Lihir Gold Ltd. commissioned a 6 MWe geothermal power plant, the first in the country, servicing the nearby gold mine (10% of its power needs). Lihir is among 40 identified geothermal resources in PNG; 38 are unexplored.


The Philippines archipelago is exceptionally well-endowed with geothermal resources. Today the country is the world’s second largest user of geothermal energy for power generation.

The geothermal plants in the Philippines are generating about one-fifth of the national electricity supply from six fields, in which there are 11 areas in production. The fields, spread throughout the islands, are at Mak-Ban (Luzon), Tiwi (Luzon), Tongonan (Leyte), Palinpinon (Negros), Bac-Man (Luzon) and Mindanao (Mindanao). Operations began in 1979 with 278 MWe and grew steadily until the mid-1980’s, when installed capacity reached 894 MWe. Further capacity was not added until 1993, after which is grew rapidly again to reach 1,909 MWe by 2000.

Three new geothermal areas at Mt. Labo (Luzon), Northern Negros (Negros) and Cabalian (Leyte) are presently in an advanced development stage.

Within the terms of the Philippine Energy Plan, the Government is planning, by 2008, to increase geothermal capacity by 526 MWe. Output would increase to 13,865 GWh but the geothermal contribution would fall to 18.5% (from a current 23%) owing to the use of natural gas for power generation.


The limited geothermal resources in mainland Portugal have been developed for direct use, whereas geothermal occurrences in the Azores islands are utilized for the production of electricity as well as being used directly.

There are about 50 natural low-enthalpy occurrences spread throughout the mainland.

Twelve areas with potential for developing geothermal electricity generation have been identified on the islands of Faial, Pico, Graciosa, Terceira and São Miguel in the Azores. At the present time the installed geothermal power capacity of São Miguel binary dual-phase power plant is 16 MWe.

As the estimated potential of the Ribeira Grande field is in the range of 80 MWe, it is envisaged that an additional 24-30 MWe capacity could be constructed by 2010, thereby meeting 40-45% of the electrical demand of the island.

São Miguel also has an installed “direct use” capacity of 1.5 MWt (end-1999) using geothermal energy for direct heat. Six small greenhouses use the 90ºC waste water from a nearby geothermal power plant in order to grow experimental crops.


Geothermal resources have been identified in several areas of the Federation: the Northern Caucasus (Alpine and Platform provinces), Western Siberia, Lake Baikal and, most significantly, in Kamchatka and the Kuril Islands. It has been estimated that the high-temperature resources defined to date in the Kamchatka Peninsula could ultimately support generation of 2,000 MWe or more. However, at the present time Russia’s energy sector is based on fossil fuels and the exploitation of hydroelectric and nuclear power, and therefore the contribution from geothermal energy is tiny. Over the past 30 years there has been some development of high-temperature resources for power generation, but the main thrust of Russian geothermal utilization has been, and continues to be, for direct purposes.

Investigations into using geothermal energy for power generation in Kamchatka began in 1957, and in 1966 a 4 MWe single-flash plant was commissioned at Pauzhetka. It was enlarged to 11 MWe in 1980; in 1999 a 12 MWe geothermal power plant was put into operation at Verkhne Mutnovsky, followed in 2002 by the inauguration of the 50 MW Mutnovsky geothermal power plant.

At end-1999 installed capacity for direct use amounted to more than 300 MWt. The heat is used mainly for space and district heating but also for a range of agricultural purposes (greenhouses, soil heating, fish and animal farming, cattle-breeding), for various industrial processes (manufacturing, wool washing, paper production, wood drying, oil extraction) and for spas and recreational bathing.

Although there is much scope for the installation of heat pumps in Russia, their use is presently at an early stage of development.


The only reported use of the geothermal energy resource in Sweden is from heat pumps. It has been estimated that by 1998 in the region of 55,000 had been installed, with an aggregate capacity of 377 MWt.


Switzerland’s installed capacity for utilizing geothermal energy has grown rapidly in recent years and the country now ranks among the world leaders in direct-use applications (there is no geothermal-based electricity). There are two main components to Switzerland’s geothermal energy: the utilization of shallow resources by the use of horizontal coils, borehole heat exchangers (BHE), foundation piles and groundwater wells, and the utilization of deep resources by the use of deep BHE’s, aquifers by singlet or doublet systems, and tunnel waters. In virtually all instances heat pumps are the key components.

At end-1999 there were in the region of 21,000 ground-source heat pumps installed throughout the country, representing about 500 MWt. The remaining approximately 50 MWt of capacity was utilized for bathing and swimming (17 locations, 25 MWt), space heating (20 MWt) air conditioning (5 locations, 2.2 MWt) and snow melting (0.1 MWt).

Following successful drilling to tap deep aquifers for a district heating network at Riehen (on the border with Germany and operational since 1995), the network was extended and this became the first example of cross-border geothermal utilization.

There remains substantial room for growth in Switzerland’s geothermal sector. The manual growth rate for heat pumps is estimated at 15% and the Government is actively supporting research and development into geothermal energy.


Investigations of geothermal features n Thailand began in 1946 and in the intervening period more than 90 hot springs located throughout the country have been mapped. However, it was not until 1979 that systematic studies of the resources began.

A small (0.3 MWe) binary-cycle power plant was installed at Fang, in the far north near the border with Myanmar. Since commissioning in December 1989, this sole Thai geothermal plant has operated successfully, with an 85-90% availability factor. In addition, the Electricity Generating Authority of Thailand (EGAT) is using the 80ºC exhaust from the power plant to demonstrate direct heat uses to the local population. the exhaust is being used for air conditioning, cold storage and crop drying. A further example of utilizing the heat directly is a public bathing pond and sauna that have been constructed by the Mae Fang National Park.

Geothermal systems at San Kampaeng, Pai and nine other locations are reported to be under further investigation, but to date Thailand’s national programme on geothermal energy has still not been firmly established and no other developments have occurred.


A significant factor in Turkey’s high geothermal potential is the fact the at the country lies in the Alpine-Himalayan oregenic belt. Geothermal exploration began during the 1960’s, since when about 170 fields have been identified. Although some of this number are high-enthalpy fields, 95% are low-medium enthalpy resources and thus more suited to direct-use applications.

At end-1999, geothermal installed capacity for direct uses totaled 820 MWt, of which 392 MWt provided the space heating and thermal facilities of 51,600 residence-equivalents, 101 MWt provided heating for 45.4 ha of greenhouses and 372 MWt was utilized for bathing and swimming (194 spas). The engineering design to supply a further 150,000 houses with geothermal heat has already been completed. Projections for 2010 indicate that 500,000 residence-equivalents (3,500 MWt) will be so equipped and by 2020, 1.25 million residence-equivalents (8,300 MWt). Installed capacity for spas and other uses is projected to reach 895 MWt by 2010 and 2,300 MWt by 2020.

Following research undertaken in 1968 into using geothermal resources for the production of electricity, a 0.5 MWe pilot plant was installed in 1974 in the Kizildere field (near Denizli in south-western Turkey). In 1984 the 20.4 MWe single-flash Kizildere geothermal power plant came into operation. In addition to electricity generation, the plant has an integrated liquid CO2 and dry ice production factory that utilizes the geothermal fluids.

To date, at least four other geothermal fields with electric power generating potential have been discovered and studied to varying degrees.

United States of America

The USA possesses a huge geothermal resource, located largely in the western half of the country. Research has shown that geothermal energy has been used in North America for many thousands of years but the first documented commercial use was in 1830 in Arkansas. In 1922 an experimental plant began generating electricity in California but, proving to be uneconomic, it soon fell into disuse. Another 38 years were to pass before the first large-scale power plant began operations at The Geysers, north of San Francisco, California. The USA is the world’s largest producer of electricity generated from geothermal energy.

Only California, Nevada, Hawaii and Utah utilize geothermal energy for power generation; investigative studies undertaken in Oregon during the early 1990’s proved to be unsuccessful. However, the 1990’s saw dramatic change in the geothermal power industry: plants came on line, plants were retired, there were changes of ownership (resulting, in some cases, in operational efficiencies) etc. By end-2002 total effective capacity stood at 2,002 MWe, remaining the world leader in geothermal power production.

Generation from geothermal energy of 16,813 GWh in 1999 represented 0.5% of total US electricity production. At The Geysers, a major area of development in California, a project for injecting recycled wastewater into the reservoir has become the world’s first wastewater-to-electricity system.

Geothermal heat suitable for direct utilization is far more widespread through the US, ranging from New York State in the east to Alaska in the West. At end-1999 a total 566 MWt installed capacity was used for fish and animal farming (129 MWt), greenhouse heating (119 MWt), bathing and swimming (107 MWt), district heating (99 MWt), space heating (83 MWt), agricultural drying (20 MWt), industrial process heat (7 MWt), and snow melting (2 MWt). In addition, it is estimated that 45,000 heat pumps have lately been installed annually, resulting in a total capacity of some 5,366 MWt at end-2002. Apart from a decline in industrial process heat, direct uses of geothermal energy continue to expand. The heat pump market is expected to continue to grow strongly, to reach an estimated 1.5 million units in service by 2010.


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