THE BIG PICTURE: Geothermal Power Landscape (Infographic)
According to the Global Geothermal Power Tracker (GGPT), a comprehensive dataset of geothermal power facilities, about 14 GW of geothermal power is operational worldwide.
The U.S. has the largest installed capacity at 3,900 MW, followed by Indonesia (2,418 MW), the Philippines (1,952 MW), Türkiye (1,691 MW), New Zealand (1,042 MW), and Kenya (985 MW). Most of the world’s operating geothermal fleet consists of flash power plants, which operate at higher temperatures and directly convert geothermal fluids into steam that drives a turbine.
About 1.6 GW reportedly uses binary cycle technology, which operates at a lower temperature than flash plants, using organic Rankine cycle (ORC) turbine technology, where subsurface fluids heat a secondary fluid to drive a turbine. Interest is also growing in enhanced geothermal systems (EGS), which employ a subsurface circuit of multiple wells and fractures containing a fluid heated by a geothermal resource through direct contact with the resource. Source: Global Geothermal Power Tracker, Global Energy Monitor, May 2024 release
A Burgeoning Technology Landscape for Geothermal Power
According to the International Renewable Energy Agency’s 2023 Global Geothermal Market and Technology Assessment, geothermal energy in electricity generation has grown at a modest rate of around 3.5% annually. Today, it is evolving beyond a focus on the power market, absorbing a broader range of applications within the energy sector, including heating and cooling.
Conventional Technologies
Most of the world’s operating geothermal power plants utilize three primary plant technologies.
Flash Steam Plants. The most prevalent type of geothermal power plant, flash steam plants operate with high-temperature geothermal fluids (typically above 180C). These fluids are brought to the surface under high pressure. When the pressure drops, the fluid “flashes” into steam, which is separated from the liquid and used to drive a turbine. Some plants use a double or triple flash process to maximize energy extraction, flashing the remaining liquid multiple times to generate additional steam.
Dry Steam Plants. Dry steam plants utilize geothermal steam directly from reservoirs to drive turbines and generate electricity. This technology is applicable where geothermal fluids are primarily in the form of steam at high pressures and temperatures, typically above 150C. The steam is extracted from the well and routed to a turbine connected to a generator, producing electricity. The steam is then condensed and re-injected into the reservoir or released (depending on environmental regulations).
Binary Cycle Plants. Binary cycle plants are ideal for lower-temperature geothermal resources (70C to 150C). These plants use geothermal fluid to heat a secondary working fluid, which has a lower boiling point than water. The secondary fluid vaporizes and drives a turbine to generate electricity. Because the geothermal fluid does not come into contact with the turbine, binary plants can operate with a closed-loop system, adding to their efficiency.
Wellhead Generators. Modular wellhead generators, typically under 10 MWe, are installed directly at the wellhead. These small-scale units allow for early power generation while larger plants are being developed, enabling quicker returns on investment. They are particularly beneficial in remote locations or for testing new fields, as they can be deployed rapidly and scaled according to field development needs. POWER profiled an example here: A Modular Power Plant Is Steaming Up Kenya’s Geothermal Efficiency.
Emerging Geothermal Technologies
New technologies are emerging that could allow for the production of geothermal energy from deep-seated resources beyond the ones mentioned above. For a more in-depth look at key players, see POWER’s 2023 explainer here.
Enhanced Geothermal Systems (EGS). EGS technology enhances the permeability of geothermal reservoirs where natural permeability is insufficient. This is achieved by injecting fluids at high pressures to fracture the rock, creating artificial reservoirs that allow for the economic extraction of heat. EGS expands the potential of geothermal energy by making it feasible to extract heat from areas that were previously unsuitable for conventional geothermal development.
Advanced Geothermal Systems (AGS). AGS involves the creation of deep, artificial closed-loop circuits where a working fluid circulates and is heated by surrounding rocks through conductive heat transfer. Unlike conventional systems, AGS does not rely on naturally occurring water-bearing formations with good permeability, making them potentially applicable in a wider range of locations. However, this method requires longer well bores and more sophisticated drilling techniques, which could increase costs.
Supercritical Geothermal Systems. Supercritical geothermal systems target fluids at extremely high temperatures and pressures found deep within volcanic hydrothermal environments. Fluids, which exist in a supercritical state, offer much higher energy content than conventional geothermal fluids. While this technology promises significantly higher power outputs, it faces challenges such as handling corrosive fluids and maintaining equipment integrity under extreme conditions.
—Sonal Patel is a POWER senior editor (@sonalcpatel, @POWERmagazine).