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See also: Geothermal heat pump

See also: Geothermal power

It is increasingly being recognized that the world has to replace fossil fuels with alternate fuels. This recognition is being driven by three premises:

First: Fossil fuels, coal, oil and natural gas, are accelerating in cost as they are consumed in ever-increasing amounts. The February 12, 2008 issue of the Wall Street Journal has two articles to re-enforce this premise. The first article, "China Spurs Coal-Price Surge," by Shai Oster and Ann Davis, informs us that the price of coal out of Newcastle, Australia has increased from $40 USD at the start of 2007to $125 USA at the 2008. The article goes on to inform us that coal will join oil and natural gas in 2015 as sources that are depleting.

The second article, "The Future of World Oil Supply - Filling the Missing Link," by Peter Jackson and Keith Eastwood ,informs us that the world's oil fields will reach peak production around 2025 and then start a rapid decline in production. Second: Oil and gas imports from foreign sources raise concerns over our long-term energy security. We all have witnessed the jump in oil prices caused by wars, strikes and disrupted supplies. Gregory Meyers' article in the same issue of the Wall Street Journal cited Venezuelan President Hugo Chavez' threat to disrupt the supply of oil to the USA because of a dispute with Exxon Mobil Corp. This threat caused a 2% increase in the price of crude oil.

Third: Burning fossil fuels dumps carbon dioxide and other pollutants into the atmosphere. The dumping of the pollutants is considered a fact. The severity of the damage to our atmosphere is still being debated, but most scientists believe that the future consequences will be very damaging to the quality and affordability of the lifestyles of our current and future generations.

Fortunately, renewable energies are accelerating into the forefront to replace fossil fuels, but will the replacement be in time? Germany has adopted wind and solar energies and is leading the world in the replacement of fossil fuels. These alternate fuels are quickly being adopted in many countries to help replace fossil fuels. These countries provide a blueprint for the USA to follow and in replacing its dependence on fossil fuels. The most popular replacements are wind and solar energy. Both of these technologies require us to rethink our energy policies.

There is a third leg available for the replacement of fossils fuels, geothermal energy. This type of energy offers us a potential to replace our coal fired electrical generating plants by 2050. It is available and being utilized today. It is the third leg of the tripod that we need to replace fossil fuels in time to retain our quality of life. What is Geothermal Energy?

Geothermal energy is derived from the heat in the interior of the earth.

Geothermal systems move the heat from the earth into the home in the winter and discharge heat into the ground in the summer. Underground piping serves as a heat source in the winter and a heat sink in the summer. In essence, it is the same heat-exchanging process used by the common refrigerator or air conditioner. Heat from the earth can be used as an energy source in many ways, from large and complex power stations to small and relatively simple pumping stations. Examples of this heat energy can be found almost anywhere. It can be found as far away as remote, deep wells in Indonesia and as close as our own backyard.

In the Western United States and in other places around the world, geothermal energy produces electricity in large power plants. Today, geothermal energy provides about five percent of California's electricity, and 25 percent of El Salvador's. In Idaho and Iceland, geothermal heat is used to warm buildings and other applications. In thousands of homes and buildings across the United States, geothermal heat pumps use the steady temperature just underground to heat and cool buildings, cleanly and inexpensively.

Physics of Geothermal Energy: Just a few meters below the earth's surface the temperature of the soil becomes rather constant. You can depend on this constant temperature throughout the seasons. You can extract this heat in the winter to heat your house or to "bury" your heat in the summer to cool your house. Trench-pipe systems are utilized in areas where ample space is available and well systems are utilized where there is limited space. It is within the trench or well system that "coolant" is circulated to deposit or extract the energy within the earth. As one can extrapolate, the further we reach into the earth the higher the temperature will be. We have a great understanding of the heat transfer parameters for all the zones of the United States. The physical parameters of this technology are beyond the scope of this paper, but past successes in design have demonstrated our ability to harness this energy. In addition, we can gain a great benefit from our oil companies. The technology successes that the oil companies have had in drilling for oil can now be applied to drilling for geothermal energy.

Great, How Much Will It Cost Us? An MIT study by MIT Professor Jefferson Tester, The Future of Geothermal Energy, a study of the potential for geothermal energy within the United States, found that mining the huge amounts of heat that resides as stored thermal energy in the earth's hard rock crust could supply a substantial portion of the electricity the United States will need in the future, probably at competitive prices and with minimal environmental impact. It was their conclusion that geothermal energy could supply 10% of our electrical needs by the year 2050. This time frame could be accelerated if we, and our government, adopted a more aggressive schedule. A conclusion from the MIT study ,mentioned previously estimates that a project costing $300 million US dollars to $400 million US dollars is needed to fund early generation plants. The same study cites a US government study of geothermal energy which estimates that for every 100,000 nominally sized residential units consumers will save approximately $500 million over a 20 year time span in heating and cooling cost at today's prices. This estimate was from a 1993 US Government report. Installation of a heat pump in a four-bedroom, 3,000 square foot house situated in the middle of the US would cost approximately $26,000.00. Payback at today's energy cost of $0.09 per kilowatt would be in the range of 13 to 14 years. Government incentives and home appreciation are not included in this analysis.

Summary: Geothermal energy is a tested and available renewable energy that can be utilized to replace fossil fuels today. Heat mining has the potential to supply a significant amount of the country's electricity currently being generated by conventional fossil fuel, hydroelectric and nuclear plants. The resolve to replace fossil fuels with geothermal, wind or solar is left to us and to our government. The technologies are available and ready to be deployed.

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Geothermal heat pump

Ground source heating and air conditioning
Ground source heating and air conditioning

A geothermal heat pump system is a heating and/or an air conditioning system that uses the Earth's ability to store heat in the ground and water thermal masses. These systems operate based on the stability of underground temperatures: the ground a few feet below surface has a very stable temperature throughout the year, depending upon location's annual climate. A geothermal heat pump uses that available heat in the winter and puts heat back into the ground in the summer. A geothermal system differs from a conventional furnace or boiler by its ability to transfer heat versus the standard method of producing heat. As energy costs continue to rise and pollution concerns continue to be a hot topic, geothermal systems may hold a solution to both of these concerns.

Geothermal heat pumps are also known as "GeoExchange" systems (a term created by an industry association) and "ground-source heat pumps." The latter term is useful as it clearly distinguishes the technology from air-source heat pumps. Geothermal heat pumps, which can be used in almost any region, should also be distinguished from geothermal heating. Geothermal heating is used in areas where exceptionally high underground temperatures, such as those at hot springs and steam vents, are used to heat indoor spaces without the use of a heat pump.

This article focuses on geothermal heat pumps that use water to exchange heat with the ground, often referred to as "water-source geothermal heat pumps" or "water loop geothermal heat pumps." Another type of geothermal heat pump, the direct exchange geothermal heat pump, is also available and is discussed briefly here and more fully in its own article.


A geothermal heat pump is a heat pump that uses the Earth as either a heat source, when operating in heating mode, or a heat sink, when operating in cooling mode.

Geothermal heat pumps can be characterised as having one or two loops. The heat pump itself, explained more fully in the article on heat pumps, consists of a loop containing refrigerant. The refrigerant is pumped through a vapor-compression refrigeration cycle that moves heat from a cooler area to a warmer one.

In a single loop system, the copper tubing refrigerant loop actually leaves the heat pump appliance cabinet and goes out of the house and under the ground and directly exchanges heat with the ground before returning to the appliance. Hence the name "direct exchange" or DX. Copper loop DX systems are gaining acceptance due to their increased efficiency and lower installation costs but the volume of expensive refrigerant remains high. In a double loop system, the refrigerant loop exchanges heat with a secondary loop made of plastic pipe containing water and anti-freeze (propylene glycol, denatured alcohol or methanol). After leaving the heat exchanger, the plastic pipe goes out of the house and under the ground before returning, so the water is exchanging heat with the ground. This is known as a water-source system. In principle this need not be pressurized, so inexpensive plastic tubing could be used, but in practice the heat-exchange coil in the appliance requires pressurization to flush out air and to obtain the necessary flow.


An installed liquid pump pack
An installed liquid pump pack

Geothermal systems require a length of buried tubing on the property, a liquid pump pack and a water-source heat pump. Expansion tanks and pressure relief valves can be installed. The tubing can be installed horizontally as a loop field or vertically as a series of long U-shapes (see below). The purpose of the tubing is to transfer heat to and from the ground. The size of the loop field depends on the size of the building being conditioned. Typically, one loop (400 to 600 feet) has the capacity of one ton or 12,000 British thermal units per hour (BTU/h) or 3.5 kilowatts. An average house will range from 3 to 5 tons (10 to 18 kW) of capacity. The second component is a liquid pump pack, which sends the water through the tubing and the water-source heat pump. Lastly, the water-source heat pump is the unit that replaces the existing furnace or boiler. This is where the heat from the tubing is transferred for heating the structure. Heat pumps have the ability to capture heat at one temperature reservoir and transfer it to another temperature reservoir. Another example of a heat pump is a refrigerator; heat is removed from the refrigerator's compartments and transferred to the outside.

Common Systems

Closed loop fields

A closed loop system, the most common, circulates the fluid through the loop fields’ pipes and does not pull in water from a water source. In a closed loop system there is no direct interaction between the fluid and the earth; only heat transfer across the pipe. The length of vertical or horizontal loop required is a function of the ground formation thermal conductivity, ground temperature, and heating and cooling power needed, and also depends on the balance between the amount of heat rejected to and absorbed from the ground during the course of the year. A rough approximation of the initial soil temperature is the average daily temperature for the region. Although copper and other metals can be used, polyethylene seems to be the most common tubing material used currently by installers; often 3/4 inch (19mm) inside diameter tubing.

There are four common types of closed loop systems; vertical, horizontal, slinky, and pond. (Slinky and pond loops depicted below.)

Vertical closed loop field

A vertical closed loop field is composed of pipes that run vertically in the ground. A hole is bored in the ground, typically, 150 to 250 feet deep (45–75 m). Pipe pairs in the hole are joined with a U-shaped cross connector at the bottom of the hole. The borehole is commonly filled with a bentonite grout surrounding the pipe to provide a good thermal connection to the surrounding soil or rock to maximize the heat transfer.

Vertical loop fields are typically used when there is a limited square footage of land available. Bore holes are spaced 5–6 m apart and are generally 15 m (50 ft) deep per kW of cooling. During the cooling season, the local temperature rise in the bore field is influenced most by the moisture travel in the soil. Reliable heat transfer models have been developed through sample bore holes as well as other tests.

Horizontal closed loop field

A horizontal closed loop field is composed of pipes that run horizontally in the ground. A long horizontal trench, deeper than the frost line, is dug and U-shaped coils are placed horizontally inside the same trench. A trench for a horizontal loop field will be similar to one seen under the slinky loop field; however, the width strictly depends on how many loops are installed. Horizontal loop fields are very common and economical if there is adequate land available.

Slinky closed loop field

A slinky closed loop field is also installed in the horizontal orientation; however, the pipes overlay each other. The easiest way of picturing a slinky field is to imagine holding a slinky on the top and bottom with your hands and then move your hands in opposite directions. A slinky loop field is used if there is not adequate room for a true horizontal system, but it still allows for an easy installation. The pump is used to heat the house.

A 3-ton slinky loop prior to being covered with soil. The three slinky loops are running out horizontally with three straight lines returning the end of the slinky coil to the heat pump
A 3-ton slinky loop prior to being covered with soil. The three slinky loops are running out horizontally with three straight lines returning the end of the slinky coil to the heat pump

Closed pond loop

A closed pond loop is not as common, but is becoming increasingly popular. A pond loop is achieved by placing coils of pipe at the bottom of an appropriately sized pond or water source. This system has been promoted by the DNR (Department of Natural Resources), who support geothermal systems and the use of ponds for geothermal systems. A pond loop is extremely similar to a slinky loop, except that it is attached to a frame and located in a body of water versus soil.

Loop field for a 12-ton system (unusually large for most residential applications)
Loop field for a 12-ton system (unusually large for most residential applications)

Open loop systems

In contrast to the closed loop systems, an open loop system pulls water directly from a well, lake, or pond. Water is pumped from one of these sources into the heat pump, where heat is either extracted or added. The water is then pumped back into a second well or source body of water. There are three general types of systems: First water can be pumped from a vertical water well and returned to a nearby pond. Second, water can be pumped from a body of water and returned to the same body of water. Third, water can be pumped from a vertical well and then returned to the same well. While thermal contamination (where the ground temperature is affected by the operation of the system) is possible with any geothermal system, with proper design, planning, and installation any loop configuration can work very well for a very long time. Deep lake water cooling uses a similar process with an open loop for air conditioning and cooling. Open loop systems using ground water are usually much more efficient than closed systems because they will be heat exchanging with water always at ground temperature. Closed loop systems, in comparison, have to make do with the inefficient heat-transfer between the water flowing through the tubing and the ground temperature.

One of the benefits of an open loop system is that for most configurations and depending on the local environment you are dealing with ground water at a constant temperature of about 50°F/10°C. In closed loop systems the temperature of the water coming in from the loop is often within 10°F/6°C of the temperature of the water entering the loop showing how little heat was exchanged. The constant ground water temperatures significantly improve heat pump efficiency.

Standing Column Well

A standing column well system is less expensive and more efficient than a comparably sized closed loop system. Water is drawn from the bottom of a deep rock well, passed through a heat pump, and returned to the top of the well, where traveling downwards it exchanges heat with the surrounding bedrock. The choice of a standing column well system is often dictated where there is near-surface bedrock and limited surface area is available. A standing column is typically not suitable in locations where the geology is comprised of mostly clay, silt, or sand. If bedrock is deeper than 200 feet from the surface, the cost of casing to seal off the overburden may become prohibitive.

12-ton pond loop system being sunk to the bottom of a pond
12-ton pond loop system being sunk to the bottom of a pond

A multiple standing column well system can support a large structure in an urban or rural application. The standing column well method is also popular in residential and small commercial applications. There are many successful applications of varying sizes and well quantities in the many boroughs of New York City, and is also the most common application in the New England states. This type of Earth-Coupling system has some heat storage benefits, where heat is rejected from the buillding and the temperature of the well is raised, within reason, during the Summer cooling months which can then be harvested for heating in the Winter months, thereby increasing the efficiency of the heat pump system. As with closed loop systems, sizing of the standing column system is critical in reference to the heat loss and gain of the existing building. As the heat exchange is actually with the bedrock, using water as the transfer medium, a large amount of production capacity (water flow from the well) is not required for a standing column system to work. However, if there is adequate water production, then the thermal capacity of the well system can be enhanced by periodic discharge during the peak Summer and Winter months.

Since this is essentially a water pumping system, standing column well design requires critical considerations to obtain peak operating efficiency. Should a standing column well design be misapplied, leaving out critical shut-off valves for example, the result could be an extreme loss in efficiency and thereby cause operational cost to be higher than anticipated. The development and promotion of Standing Column Well technology is generally credited to Carl Orio CGD from Atkinson, New Hampshire.

Common heat pumps

There are also different types of water-source heat pumps. A variety of products are available, for both residential and commercial applications; there are water-to-air heat pumps, water-to-water heat pumps and hybrids between the two. Some manufacturers are now producing a reversible heat pump for chillers also.



Water-to-air heat pump
Water-to-air heat pump

The water-to-air heat pumps are designed to replace a forced air furnace and possibly the central air conditioning system. The term water-to-air signifies that the heat pump is designed for forced air applications and indicates that water is the source of heat. The water-to-air system is a single central unit that is capable of producing heat during the winter and air conditioning during the summer months. There are variations of the water-to-air heat pumps that allow for split systems, high-velocity systems, and ductless systems.


Water-to-water heat pump
Water-to-water heat pump

A water-to-water heat pump is designed for a heating-system that utilizes hot water for heating the building. Systems such as radiant underfloor heating, baseboard radiators and conventional cast iron radiators would use a water-to-water heat pump. The water-to-water heat pump uses the warm water from the loop field to heat the water that is used for conditioning the structure. Just like a boiler, this heat pump is unable to provide air conditioning during the summer months.


A hybrid heat pump is capable of producing forced air heat and hot water simultaneously and individually. These systems are largely being used for houses that have a combination of under-floor and forced air heating. Both the water-to-water and hybrid heat pumps are capable of heating domestic water also. Almost all types of heat pumps are produced commercially and residentially for indoor and outdoor applications.

A heat pump in combination with heat and cold storage

A heat pump in combination with heat and cold storage

Geothermal heat pumps in combination with cold/heat storage

is used extensively for applications as the heating of greenhouses. In summer, the greenhouse is cooled with ground water, pumped from a aquifer, which is the cold source. This heats the water. the water is then stored by the system in a warm source. In winter, the relative warm water is again pumped up, which derives heat. The now cooled water is again stored in the cold source. The combination of cold and heat storage with heat pumps can be very interesting for greenhouses as it may be combined with water/humidity application. This obviously is a great advantage for greenhouses. In the (closed circuit) system, the water used as a storage medium for heat is done in a first aquifer, while the cold water is held in a second aquifer. The heat and cold stored in the water mass is when needed spread as hot or cold air through the use of fans. In the described system, everything can be automated.

Direct Exchange

While this article focuses on water-source systems in which the refrigerant exchanges its heat with a water loop that is placed in the ground, a direct exchange system (often known as DX geothermal) is one in which the refrigerant circulates through a copper pipe placed directly in the ground. This eliminates the need for a heat exchanger between the refrigerant loop and the water loop, as well as eliminating the water pump. These simpler systems are able to reach higher efficiencies while also requiring a shorter and smaller pipe to be placed in the ground, reducing installation cost. DX systems are a relatively newer technology than water-source. DX systems, like water-source systems, can also be used to heat water in the house for use in radiant heating applications and for domestic hot water, as well as for cooling applications. Though corrosion or cracking of the copper loop has sometimes been a concern, these can be eliminated through proper installation. Since copper is a naturally-occurring metal that survives in the ground for thousands of years in most soil conditions, the copper loops usually have a very long lifetime.

Benefits of Geothermal Heat Pumps

Geothermal systems are able to transfer heat to and from the ground with minimal use of electricity. When comparing a geothermal system to an ordinary system, a homeowner can save anywhere from 30% to 70% annually on utilities. Even with the high initial costs of purchasing a geothermal system the payback period is relatively short, typically between three and five years. Geothermal systems are recognized as one of the most efficient heating and cooling systems on the market.

The U.S. Environmental Protection Agency (EPA) has called geothermal the most energy-efficient, environmentally clean, and cost-effective space conditioning systems available. The life span of the system is longer than conventional heating and cooling systems. Most loop fields are warranted for 25 to 50 years and are expected to last at least 50 to 200 years. Geothermal systems use electricity for heating the house. The fluids used in loop fields are designed to be biodegradable, non-toxic, non-corrosive and have properties that will minimize pumping power needed.

Some electric companies will offer special rates to customers who install geothermal systems for heating/cooling their building. This is due to the fact that electrical plants have the largest loads during summer months and much of their capacity sits idle during winter months. This allows the electric company to use more of their facility during the winter months and sell more electricity. It also allows them to reduce peak usage during the summer (due to the increased efficiency of heat pumps), thereby avoiding costly construction of new power plants. For the same reasons, other utility companies have started to pay for the installation of geothermal heat pumps at customer residences. They lease the systems to their customers for a monthly fee, at a net overall savings to the customer. It is important to recognize that this may be ultimately less sustainable resulting in more overall energy being used by the house.

Geothermal heat pumps are especially well matched to underfloor heating systems which do not require extremely high temperatures (as compared with wall-mounted radiators). Thus they are ideal for open plan offices. Using large surfaces such as floors, as opposed to radiators, distributes the heat more uniformly and allows for a lower temperature heat transfer fluid.

Undisturbed earth below the frost line remains at a relatively constant temperature year round. This temperature equates roughly to the average annual air-temperature of the chosen location, so is usually 7-21 degrees Celsius (45-70 degrees Fahrenheit) depending on location. Because this temperature remains more constant than the air, geothermal heat pumps perform with far greater efficiency and in a far larger range of extreme temperatures than conventional air conditioners and furnaces, and even air-source heat pumps.

A particular advantage is that they can use electricity to heat spaces and water much more efficiently than an electric heater.

Geothermal heat pump technology is a Natural Building technique. It is also a practical heating and cooling solution that can pay for itself within a few years of installation.

Today there are more than 1,000,000 geothermal heat pump installations in the United States.

The current use of geothermal heat pump technology has resulted in the following emissions reductions:

The current use of geothermal heat pump technology has resulted in the following emissions reductions:

  • Elimination of more than 5.8 million metric tons of CO2 annually
  • Elimination of more than 1.6 million metric tons of carbon equivalent annually

These 1,000,000 installations have also resulted in the following energy consumption reductions:

  • Annual savings of nearly 8,000 GWh
  • Annual savings of nearly 40 trillion Btus of fossil fuels
  • Reduced electricity demand by more than 2.6 GW

The impact of the current use of geothermal heat pumps is equivalent to:

  • Taking close to 1,295,000 cars off the road
  • Planting more than 385 million trees
  • Reducing U.S. reliance on imported fuels by 21.5 million barrels (3,420,000 m?) of crude oil per year.

Costs and savings

The initial cost of installing a geothermal heat pump system can be two to three times that of a conventional heating system in most residential applications, new construction or existing. In retrofits, the cost of installation is affected by the size of living area, the home's age, insulation characteristics, the geology of the area, and location of the home/property. For new construction, proper duct system design and mechanical air exchange should be considered in initial system cost. These systems can save the average family from US$400-1400/year, reducing the average heating/cooling costs by 35-70% per household.


Information from Wikipedia is available under the terms of the GNU Free Documentation License

Geothermal power

Geothermal power (from the Greek words geo, meaning earth, and thermal, meaning heat) is energy generated by heat stored beneath the Earth's surface or the collection of absorbed heat derived from underground in the atmosphere and oceans. Prince Piero Ginori Conti tested the first geothermal generator on 4 July 1904, at the Larderello dry steam field in Italy. The largest group of geothermal power plants in the world is located in The Geysers, a geothermal field in California. As of 2007, geothermal power supplies less than 1% of the world's energy.

The Nesjavellir Geothermal Power Plant in Iceland
The Nesjavellir Geothermal Power Plant in Iceland


Geothermal energy offers a number of advantages over traditional fossil fuel based sources, primarily that the heat source requires no purchase of fuel. From an environmental standpoint, emissions of undesirable substances are small. It is also nearly sustainable because the heat extraction is small compared to the size of the heat reservoir, which may also receive some heat replenishment from greater depths. In addition, geothermal power plants are unaffected by changing weather conditions. Geothermal power plants work continuously, day and night, making them base load power plants. From an economic view, geothermal energy is extremely price competitive in some areas and reduces reliance on fossil fuels and their inherent price unpredictability. It also offers a degree of scalability: a large geothermal plant can power entire cities while smaller power plants can supply more remote sites such as rural villages.

Krafla Geothermal Station in northeast Iceland
Krafla Geothermal Station in northeast Iceland


From an engineering perspective, the geothermal fluid is corrosive, and worse, is at a relatively low temperature (compared to steam from boilers), which by the laws of thermodynamics limits the efficiency of heat engines in extracting useful energy as in the generation of electricity. Much of the heat energy is lost, unless there is also a local use for low-temperature heat, such as greenhouses or timber mills or district heating, etc.

There are several environmental concerns behind geothermal energy. Construction of the power plants can adversely affect land stability in the surrounding region. This is mainly a concern with Enhanced Geothermal Systems, where water is injected into hot dry rock where no water was before. Dry steam and flash steam power plants also emit low levels of carbon dioxide, nitric oxide, and sulfur, although at roughly 5% of the levels emitted by fossil fuel power plants. However, geothermal plants can be built with emissions-controlling systems that can inject these substances back into the earth, thereby reducing carbon emissions to less than 0.1% of those from fossil fuel power plants. Hot water from geothermal sources will contain trace amounts of dangerous elements such as mercury, arsenic, antimony, etc. which if disposed of into rivers can render their water unsafe to drink.

Although geothermal sites are capable of providing heat for many decades, eventually specific locations may cool down. It is likely that in these locations, the system was designed too large for the site, since there is only so much energy that can be stored and replenished in a given volume of earth. Some interpret this as meaning a specific geothermal location can undergo depletion, and question whether geothermal energy is truly renewable. For example, the world's second-oldest geothermal generator at Wairakei has reduced production. If left alone, however, these places will recover some of their lost heat, as the mantle has vast heat reserves. An assessment of the total potential for electricity production from the high-temperature geothermal fields in Iceland gives a value of about 1500 TWh (total) or 15 TWh per year over a 100 year period. The electricity production capacity from geothermal fields is now only 1.3 TWh per year.


If heat recovered by ground source heat pumps is included, the non-electric generating capacity of geothermal energy is estimated at more than 100 GW (gigawatts of thermal power) and is used commercially in over 70 countries. During 2005, contracts were placed for an additional 0.5 GW of capacity in the United States, while there were also plants under construction in 11 other countries.

Estimates of exploitable worldwide geothermal energy resources vary considerably. According to a 1999 study, it was thought that this might amount to between 65 and 138 GW of electrical generation capacity 'using enhanced technology'.

A 2006 report by MIT, that took into account the use of Enhanced Geothermal Systems (EGS), concluded that it would be affordable to generate 100 GWe (gigawatts of electricity) or more by 2050 in the United States alone, for a maximum investment of 1 billion US dollars in research and development over 15 years.

The MIT report calculated the world's total EGS resources to be over 13,000 ZJ. Of these, over 200 ZJ would be extractable, with the potential to increase this to over 2,000 ZJ with technology improvements - sufficient to provide all the world's present energy needs for several millennia.

The key characteristic of an EGS (also called a Hot Dry Rock system), is that it reaches at least 10 km down into hard rock. At a typical site two holes would be bored and the deep rock between them fractured. Water would be pumped down one and steam would come up the other. The MIT report estimated that there was enough energy in hard rocks 10 km below the United States to supply all the world's current needs for 30,000 years.

Drilling at this depth is now possible in the petroleum industry, albeit it is expensive. (Exxon announced an 11 km hole at the Chayvo field, Sakhalin. Lloyds List 1/5/07 p 6) Wells drilled to depths greater than 4000 metres generally incur drilling costs in the tens of millions of dollars. The technological challenges are to drill wide bores at low cost and to break rock over larger volumes. Apart from the energy used to make the bores, the process releases no greenhouse gases.

Other important countries considered high in potential for development are the People's Republic of China, Hungary, Mexico, Iceland, and New Zealand. There are a number of potential sites being developed or evaluated in South Australia that are several kilometres in depth.

History of development

Geothermal steam and hot springs have been used for centuries for bathing and heating, but it wasn't until the 20th century that geothermal power started being used to make electricity.

Prince Piero Ginori Conti tested the first geothermal power generator on 4 July 1904, at the Larderello dry steam field in Italy. It was a small generator that lit four light bulbs. Later, in 1911, the world's first geothermal power plant was built there. It was the world's only industrial producer of geothermal electricity until 1958, when New Zealand built a plant of its own.

The first Geothermal power plant in the United States was made in 1922 by John D. Grant at The Geysers Resort Hotel. After drilling for more steam, he was able to generate enough electricity to light the entire resort. Eventually the power plant fell into disuse, as it was not competitive with other methods of energy production.

In 1960, Pacific Gas and Electric began operation of the first successful geothermal power plant in the United States at The Geysers. The original turbine installed lasted for more than 30 years and produced 11 MW net power. The Geysers are currently owned by the Calpine corporation and the Northern California Power agency; and it currently produces over 750 MW of power.

Development around the world

Geothermal power is generated in over 20 countries around the world including Iceland, the United States, Italy, Germany, Turkey, France, The Netherlands, Lithuania, New Zealand, Mexico, Nicaragua, Costa Rica, Russia, the Philippines, Indonesia, the People's Republic of China, Japan and Saint Kitts and Nevis. Chevron Corporation is the world's largest producer of geothermal energy. Canada's government (which officially notes some 30,000 earth-heat installations for providing space heating to Canadian residential and commercial buildings) reports a test geothermal-electrical site in the Meager Mountain-Pebble Creek area of British Columbia, where a 100 MW facility could be developed.


Geothermal power is very cost-effective in the Rift area of Africa. Kenya was the first African country to build geothermal energy sources. Kenya's KenGen has built two plants, Olkaria I (45 MW) and Olkaria II (65 MW), with a third private plant Olkaria III (48 MW). Plans are to increase production capacity by another 576 MW by 2017, covering 25% of Kenya's electricity needs, and correspondingly reducing dependency on imported oil. In Ethiopia there is another plant for geothermal power (in 2008 some experts from Iceland calculated that Ethiopia has at least 1000 MW of that energy). Hot spots have been found across the continent, especially in the Great Rift Valley.


Main article: Geothermal energy exploration in Central Australia


Chile currently has no geothermal power plants but has a geothermal capacity of 16,000 MW for at least 50 years. The thermal spring areas are located in quaternary volcanic zones in the Andes such as El Tatio, Liquiñe and Cordón Caulle.


Main article: Geothermal power in Iceland

Iceland is situated in an area with a high concentration of volcanoes, making it an ideal location for generating geothermal energy. 19.1% of Iceland's electrical energy is generated from geothermal sources. In addition, geothermal heating is used to heat 87% of homes in Iceland. Icelanders plan to be 100% non-fossil fuel in the near future.


Mexico has the third greatest geothermal energy production with an installed capacity of 959.50 MW by December 2007. This represents 3.24% of the total electricity generated in the country.

New Zealand

Main article: Geothermal power in New Zealand

New Zealand has operated geothermal power stations since the 1950s. First developments were at Wairakei and Kawerau (direct heat and power). Other stations include Ohaaki, Rotokawa, Poihipi, Nagwha and Mokai.

North Dominica

North Dominica recently installed a geothermal power plant near the city of Opravy.


Denmark has two geothermal power plants, one in Thisted started in 1988, and one in Copenhagen started in 2005.


Portugal has a geothermal power plant on São Miguel Island, in the Azores islands.


The Geothermal Education Office and a 1980 article entitled "The Philippines geothermal success story" by Rudolph J. Birsic published in the journal Geothermal Energy (vol. 8, Aug.-Sept. 1980, p. 35-44) note the remarkable geothermal resources of the Philippines. During the World Geothermal Congress 2000 held in Beppu, Oita Prefecture of Japan (May-June 2000), it was reported that the Philippines is the largest consumer of electricity from geothermal sources and highlighted the potential role of geothermal energy in providing energy needs for developing countries.

Geothermal power plant in Valencia, Negros Oriental, Philippines
Geothermal power plant in Valencia, Negros Oriental, Philippines

According to the International Geothermal Association (IGA), worldwide, the Philippines ranks second to the United States in producing geothermal energy. As of the end of 2003, the US has a capacity of 2020 megawatts of geothermal power, while the Philippines can generate 1930 megawatts. (Mexico is third with 953 MW according to IGA). Early statistics from the Institute for Green Resources and Environment stated that Philippine geothermal energy provides 16% of the country's electricity. By 2005, geothermal energy accounted for 17.5% of the country's electricity production. More recent statistics from the IGA show that combined energy from geothermal power plants in the islands of Luzon, Leyte, Negros and Mindanao account for approximately 27% of the country's electricity generation. Leyte is one of the islands in the Philippines where the first geothermal power plant started operations in July 1977.


There is a geothermal plant on the north slope of Mutnovsky volcano in Kamchatka, presumably supplying power to Petropavlovsk-Kamchatsky.

Saint Kitts and Nevis

The island of Nevis, long known for its numerous hot springs, commenced drilling for the construction of a geothermal powerplant at Spring Hill, Nevis, in January 2008. When completed (estimated 2010), the plant will supply 50 megawatts of electricity, enough to fulfill all of Nevis' demand (approximately 10 megawatts), and also enough to export to neighbouring Saint Kitts as well as other nearby islands via submarine electrical transmission cables. The project, being undertaken by West Indies Power, will make Saint Kitts and Nevis the first country in the Caribbean to utilize large-scale Geothermal energy, and, when complete, will make Saint Kitts and Nevis one of the least dependent nations in the world on fossil-fuels.

United Kingdom

Main article: Geothermal power in the United Kingdom


Main article: Geothermal power in Turkey

Turkey currently has the 5th highest direct utilization and capacity of geothermal energy in the world.

United States

Main article: Geothermal energy in the United States

The United States of America is the country with the greatest geothermal energy production.

The West Ford Flat power plant is one of 21 power plants at The Geysers
The West Ford Flat power plant is one of 21 power plants at The Geysers

The largest dry steam field in the world is The Geysers, 72 miles (116 km) north of San Francisco. The Geysers began in 1960, has 1360 MW of installed capacity and produces over 750 MW net. Calpine Corporation now owns 19 of the 21 plants in The Geysers and is currently the United States' largest producer of renewable geothermal energy. The other two plants are owned jointly by the Northern California Power Agency and the City of Santa Clara's municipal Electric Utility (now called Silicon Valley Power). Since the activities of one geothermal plant affects those nearby, the consolidation plant ownership at The Geysers has been beneficial because the plants operate cooperatively instead of in their own short-term interest. The Geysers is now recharged by injecting treated sewage effluent from the City of Santa Rosa and the Lake County sewage treatment plant. This sewage effluent used to be dumped into rivers and streams and is now piped to the geothermal field where it replenishes the steam produced for power generation.

Another major geothermal area is located in south central California, on the southeast side of the Salton Sea, near the cities of Niland and Calipatria, California. As of 2001, there were 15 geothermal plants producing electricity in the area. CalEnergy owns about half of them and the rest are owned by various companies. Combined the plants have a capacity of about 570 megawatts.

The Basin and Range geologic province in Nevada, southeastern Oregon, southwestern Idaho, Arizona and western Utah is now an area of rapid geothermal development. Several small power plants were built during the late 1980s during times of high power prices. Rising energy costs have spurred new development. Plants in Nevada at Steamboat near Reno, Brady/Desert Peak, Dixie Valley, Soda Lake, Stillwater and Beowawe now produce about 235 MW.


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