Geothermal Power Plant Types

Hot Dry Rock (HDR) Geothermal Energy.

Mineral-rich geothermal water from the Svartsengi power plant supplies the nearby Blue Lagoon geothermal spa in Iceland.

Geothermal power plants harness heat from the Earth’s interior to generate electricity. The type of power plant depends mainly on the temperature and physical state of the geothermal fluid brought to the surface through production wells. Where natural fluid or permeability is insufficient, an enhanced geothermal system may be created by injecting water underground.

Geothermal power plants convert heat from underground fluids into mechanical energy in a turbine and then into electricity. Depending on the resource and the way the geothermal fluid is used, they can be divided into three main types: dry steam, flash steam and binary cycle.

Dry Steam Geothermal Power Plants

A modern geothermal power plant in Iceland, where geothermal heat is converted into electricity.

Steam from vapour-dominated geothermal reservoirs is brought to the surface through production wells and fed directly to the turbine. The first geothermal power plants were of this type. Unlike flash-steam plants, dry-steam plants do not require a flash separator. After expansion in the turbine, the steam is condensed and the condensate is often reinjected into the geothermal reservoir through injection wells. The thermal efficiency is relatively low compared with conventional high-temperature steam power plants and typically remains below about 20%. Examples of dry steam geothermal power plants can be found at Larderello in Italy (map) and in The Geysers region of California (map).

Flash Steam Geothermal Power Plants

Pipelines transporting geothermal fluid from individual wells to the Svartsengi power plant in Iceland.

Flash-steam plants use high-temperature geothermal water, sometimes mixed with steam, under high pressure. They remain one of the most common types of geothermal power plant. The geothermal fluid passes through a separator or flash tank where a drop in pressure causes part of the hot water to vaporise. The separated steam is then directed to the turbine. The remaining geothermal water, together with the condensate formed after the steam passes through the turbine, is pumped back into the geothermal reservoir. Flash-steam plants typically have relatively low thermal efficiencies, often around 10—15%, depending on resource conditions and plant design.

Binary Cycle Geothermal Power Plants

Active geothermal wells and supply pipelines at the Krafla geothermal power plant in Iceland.

Binary-cycle plants can use relatively low-temperature geothermal resources, typically below about 180 °C. The geothermal fluid passes through a heat exchanger, where it vaporises a secondary working fluid with a lower boiling point, such as isobutane or isopentane. The vapour then drives the turbine. The geothermal fluid never comes into contact with the turbine and, after passing through the heat exchanger, is pumped back into the geothermal reservoir. The secondary working fluid circulates in a closed loop, allowing binary-cycle plants to operate with relatively low emissions. Their thermal efficiency is generally modest because of the lower resource temperatures, but this is offset by the much wider availability of suitable geothermal resources. Examples include geothermal plants at Steamboat Springs in Nevada and the Puna Geothermal Venture plant in the Puna district of Hawaiʻi Island.

The Chena Hot Springs binary-cycle plant in Alaska demonstrated electricity generation from geothermal water at only about 57 °C, one of the lowest resource temperatures used commercially at the time.

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10 pictures

Largest Geothermal Power Plants in the World

The pipeline system of the Hellisheiði geothermal power plant near Reykjavík, Iceland.

Geothermal power plants are commonly located in tectonically active regions where high-temperature geothermal resources occur at accessible depths. Major geothermal developments include Cerro Prieto in Mexico, Hellisheiði in Iceland, Wayang Windu in Indonesia and Wairākei in New Zealand.

Cerro Prieto, Mexico (map)

Cerro Prieto in Baja California, Mexico, is one of the world’s largest liquid-dominated geothermal fields and has been used for commercial electricity generation since 1973. Reservoir temperatures exceed 300 °C in some parts of the field and can reach about 350 °C at depths of several kilometres. The first generating units entered service in 1973, and the complex was gradually expanded over the following decades. Cerro Prieto I eventually reached 180 MW, while Cerro Prieto II and III were each equipped with two 110 MW units. Cerro Prieto IV, commissioned in 2000, added four 25 MW units. The field once had a total installed capacity of 720 MW, but several older units have since been retired or taken out of service. Today, Cerro Prieto remains Mexico’s largest geothermal development and one of the most important geothermal fields in the Americas.

Geothermal well facilities at the Hellisheiði geothermal field in south-western Iceland.

Hellisheiði, Iceland (map)

The Hellisheiði geothermal power plant is located in the Hengill high-temperature geothermal area in south-western Iceland. Commissioned in 2006, it is one of the world’s largest geothermal combined heat and power plants. Six 45 MW high-pressure steam turbines and one 33 MW low-pressure turbine provide a total electrical capacity of 303 MW. The plant also has a thermal capacity of 200 MW and produces about 950 litres of hot water per second for district heating. The hot water produced at Hellisheiði supplies heating to more than half of the Reykjavík capital region.

Wayang Windu, Indonesia (map)

The Wayang Windu geothermal power plant is located about 40 km south of Bandung in West Java, Indonesia. It exploits a high-temperature geothermal field and currently has two generating units with a combined installed capacity of 252 MW. Unit 1, with a capacity of 126.2 MW, was completed in 1999 and began full-capacity operation in 2000. Unit 2, with a capacity of 125.8 MW, was commissioned in 2009. Both units use steam produced from the Wayang Windu geothermal field to generate electricity for the Java-Madura-Bali grid. A third 30 MW unit is currently under development and is expected to begin commercial operation in December 2026. The new unit will use high-efficiency single-flash technology.

Wairakei, New Zealand (map)

A pipeline transporting geothermal fluid within the Wairākei geothermal field in New Zealand.

The Wairākei geothermal power station is located in the Taupō Volcanic Zone in the central North Island of New Zealand. It began generating electricity in 1958 as the world’s second large-scale geothermal power station and the first to use flash steam from a liquid-dominated geothermal resource. The plant was gradually expanded, and in 2005 a binary-cycle unit of about 15 MW was added to recover additional energy from separated geothermal water. The present Wairākei station has an installed capacity of about 132 MW and forms part of a much larger geothermal development that also includes the Poihipi and Te Mihi power stations. The original Wairākei facilities are now being progressively replaced by Te Mihi Stage 2, a new 101 MW binary-cycle plant scheduled to begin operation in 2027.

Other major geothermal developments include The Geysers in California, the Larderello geothermal area in Italy and the Olkaria geothermal field in Kenya. The Geysers comprises 13 operating power plants with a generating capacity of about 725 MW. The geothermal region around Larderello and other parts of Tuscany contains 34 power plants with a combined capacity of about 800 MW, while the Olkaria geothermal field supplies steam to several power plants and wellhead units with a combined output of around 695 MW.

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3 pictures