Geothermal energy is heat associated with the Earth and its subsurface. It can be used directly for heating, provide heating and cooling through geothermal heat pumps, or generate electricity where temperatures and other resource conditions are suitable.
At its most fundamental level, geothermal is heat.
Some of this heat originates deep inside the Earth. Closer to the surface, ground temperatures are also influenced by solar and seasonal effects. The ways we access and use geothermal energy therefore vary considerably, from shallow systems serving individual buildings to wells drilled several kilometres underground for heat and power generation.
Geothermal conditions differ from one place to another. Geology, depth, temperature, groundwater, permeability and local heat flow all influence which resources can be developed and which technologies are appropriate.
This is why geothermal energy should not be thought of as one single technology. It covers a wide range of resources, technologies and applications.
Where does geothermal energy come from?
Much of the Earth's internal heat has been present since the planet formed. Additional heat has been generated through processes inside the Earth, including the radioactive decay of naturally occurring elements.
Heat moves towards the Earth's surface over geological time. Within the Earth's interior, heat can be transported by processes including convection. Through the more rigid crust, heat is transferred mainly by conduction.
This continuous movement of heat creates the temperature conditions that geothermal technologies can use.
Further reading:
What is the geothermal gradient?
The geothermal gradient describes how temperature changes with increasing depth below the Earth's surface.
In many continental settings, the geothermal gradient is roughly 25-30°C per kilometre, although local values can be considerably lower or higher depending on geology, tectonic setting, heat flow, rock properties and groundwater movement.
The figure should therefore be understood as a rule of thumb rather than a universal value. A particular temperature may be reached at relatively shallow depth in one location but require much deeper drilling elsewhere.
This variation is one of the reasons geothermal projects depend heavily on understanding local subsurface conditions.
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Where can geothermal energy be found?
Heat is present beneath the Earth's surface around the world, but that does not mean every geothermal resource can be developed economically.
What matters is whether useful temperatures can be reached at suitable depths and whether the subsurface conditions allow that heat to be extracted effectively.
For conventional geothermal development, favourable combinations of temperature, fluids and permeability are particularly important. Newer engineering approaches can change some of these requirements, expanding the range of geological settings where geothermal energy may be considered.
Geothermal energy in volcanic and tectonically active regions
Some of the world's best-known geothermal areas occur near tectonic plate boundaries, volcanic systems and other areas of high heat flow.
Countries such as Iceland, Indonesia, Italy, Japan, Kenya, New Zealand, the Philippines and the United States have developed geothermal resources in geological settings where high temperatures can occur at relatively accessible depths.
These conditions have supported much of the conventional geothermal power development seen around the world.
But geothermal energy is not limited to volcanic regions.
Geothermal energy beyond volcanic regions
Geothermal resources are also developed in sedimentary basins and other geological settings far from active volcanoes. Depending on temperature and depth, these resources can supply district heating, industrial heat or electricity.
Engineered approaches such as Enhanced Geothermal Systems (EGS) and Closed-Loop Geothermal Systems (CLGS) are also being developed to access heat where the natural conditions required by conventional hydrothermal systems are limited or absent.
Other geothermal resource settings include geopressured formations, mine water and hot fluids produced from existing oil and gas operations. These are resource or development settings rather than separate categories within the main technology overview used in this Knowledge Centre.
Geothermal energy, resources, technologies and applications
These terms describe different parts of geothermal development and should not be used interchangeably.
Geothermal energy is the heat itself.
A geothermal resource is a particular occurrence of that heat that may be accessible and usable. Its characteristics can include temperature, depth, geology, fluids and permeability.
A geothermal technology is the method used to access, transfer or convert that energy. Examples include hydrothermal production systems, EGS, closed-loop systems and geothermal heat pumps.
A geothermal application describes what the energy is ultimately used for, such as heating, cooling or electricity generation.
The distinction becomes particularly useful as geothermal development expands beyond conventional hydrothermal resources and a wider range of technologies is deployed.
How is geothermal energy used?
Geothermal energy has three broad energy applications: heating, cooling and electricity generation.
The temperatures and resource conditions required vary significantly between these applications.
Geothermal heating
Heat can be used directly from geothermal fluids or transferred through heat exchangers for applications such as district heating, buildings and industrial processes.
Direct use can make use of temperatures below those generally required for electricity generation. This gives geothermal heat a much wider potential geographic application than geothermal power alone.
Geothermal cooling
Geothermal energy can also support cooling.
Ground-source or geothermal heat pump systems can transfer heat from buildings into the ground during warmer periods and draw heat from the ground when heating is required.
Some geothermal resources can also support other cooling technologies, depending on temperature and system design.
Geothermal electricity generation
Higher-temperature geothermal resources can be used to generate electricity.
Wells bring geothermal fluids or heat to the surface, where the energy can be converted into electricity using different power plant technologies. The cooled geothermal fluid is commonly reinjected into the subsurface.
The appropriate generation technology depends on the temperature and characteristics of the geothermal resource.
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What types of geothermal systems are there?
Geothermal energy can be accessed using technologies ranging from shallow ground-source systems to deep wells targeting naturally occurring or engineered geothermal resources.
For the ThinkGeoEnergy Knowledge Centre, the principal technology and resource groupings are shallow geothermal, hydrothermal geothermal systems, Enhanced Geothermal Systems, Closed-Loop Geothermal Systems and superhot geothermal.
These categories are useful for orientation, but they do not form a strict progression by depth, temperature or technological maturity. Some overlap.
Shallow geothermal and geothermal heat pumps
Shallow geothermal systems use the relatively stable temperature of the ground close to the surface as a source or sink for heat.
Geothermal or ground-source heat pumps move heat between buildings and the ground. Unlike deep geothermal systems, they generally do not depend primarily on extracting heat flowing from deep inside the Earth.
They can provide efficient heating and cooling across a wide range of geographic locations.
Hydrothermal geothermal systems
Hydrothermal geothermal systems rely on naturally occurring combinations of heat, fluid and sufficient permeability in the subsurface.
Wells are drilled into geothermal reservoirs to produce hot water or steam. The energy can then be used for heating or electricity generation, depending on temperature and other resource characteristics.
Hydrothermal systems form the basis of most conventional geothermal power generation developed to date.
Enhanced Geothermal Systems (EGS)
Enhanced Geothermal Systems (EGS) are designed to access underground heat where natural permeability or fluid circulation is insufficient for conventional geothermal production.
The subsurface is engineered or stimulated to improve fluid circulation through hot rock. Fluid can then circulate through the created or enhanced fracture network, absorb heat and return to the surface.
EGS can broaden the geographic potential for geothermal development, but its technical and economic viability depends on factors including drilling depth, reservoir performance and the ability to manage stimulation and induced seismicity.
Further reading:
Closed-Loop Geothermal Systems (CLGS)
Closed-Loop Geothermal Systems (CLGS) circulate a working fluid through sealed underground well configurations. Heat passes from the surrounding rock through the well or pipe structure into the circulating fluid without requiring production of geothermal reservoir fluids.
Closed-loop designs are being developed in several configurations and at different depths.
The term Advanced Geothermal Systems (AGS) is also used in the geothermal industry, including in relation to some closed-loop concepts. However, its meaning is not consistent across the sector. ThinkGeoEnergy therefore uses Closed-Loop Geothermal Systems (CLGS) for the specific technology and treats "advanced geothermal" as a broader industry descriptor rather than an exact synonym.
Further reading:
Superhot geothermal
Superhot geothermal targets geothermal resources at very high temperatures with the aim of accessing substantially more energy from individual wells.
It is best understood as a high-temperature geothermal resource regime and development concept, rather than a single extraction technology. Different drilling, reservoir and power-generation approaches may ultimately be used to develop such resources.
Development remains technically challenging because extreme subsurface conditions place high demands on drilling, well construction, materials, measurement equipment and reservoir management.
Is geothermal energy renewable?
Geothermal energy is generally classified as a renewable energy resource because heat continues to flow from the Earth's interior and geothermal fluids can be reinjected into the subsurface.
Renewable, however, does not automatically mean that every geothermal reservoir can be produced indefinitely at any rate.
The long-term performance of an individual geothermal development depends on the resource and how it is managed. Extraction rates, pressure, temperature, natural recharge and reinjection can all affect reservoir behaviour over time.
Sustainable geothermal development therefore depends on matching energy production to the characteristics and response of the resource.
Further reading:
What are the advantages and challenges of geothermal energy?
The characteristics of geothermal energy vary considerably between shallow heating and cooling systems, conventional hydrothermal developments and newer deep geothermal technologies.
Advantages of geothermal energy
- Continuous energy availability: Geothermal heat is available independently of weather conditions or time of day. Geothermal power plants can provide continuous electricity where suitable resources are available.
- Heating and cooling: Geothermal energy can provide heat directly and support cooling, allowing it to serve energy needs beyond electricity generation.
- Local energy resource: Geothermal developments use domestic subsurface heat rather than continuously imported fuel.
- Low lifecycle emissions: Most geothermal technologies have relatively low lifecycle greenhouse-gas emissions compared with fossil-fuel generation. Actual emissions vary by technology and reservoir chemistry, particularly where naturally occurring gases are present in geothermal fluids.
- Small surface footprint: Geothermal developments can produce substantial amounts of energy from comparatively compact surface sites, although land requirements vary by technology and project design.
Challenges of geothermal energy
- Location and subsurface uncertainty: The quality and accessibility of geothermal resources depend on local geological conditions. Exploration therefore plays an important role in conventional geothermal development.
- High upfront costs: Drilling and subsurface development require substantial capital before a project begins generating revenue.
- Drilling depth and technical complexity: Deeper and hotter resources can require more demanding drilling, materials and well designs.
- Reservoir management: Long-term operation requires appropriate management of fluid production, pressure, temperature and reinjection.
- Induced seismicity: Some geothermal development methods involving subsurface stimulation or fluid injection can cause induced seismicity. This issue is particularlyrelevant to certain EGS projects and should not be applied equally to all geothermal technologies.
- Water and fluid management: Depending on the technology and resource, projects may need to manage geothermal fluids, water requirements, mineral scaling, corrosion or naturally occurring gases.
The relevance of each of these factors depends on the resource, technology, application and project location.
Geothermal energy around the world
Geothermal energy is used in many different geological and climatic settings.
Some countries have developed high-temperature resources primarily for electricity generation. Others use geothermal energy extensively for district heating, buildings, agriculture, industry, bathing and other direct applications.
Shallow geothermal and heat pumps broaden this geographic reach further because they do not require the high-temperature resources associated with conventional geothermal power generation.
Rather than maintaining changing global statistics in this guide, ThinkGeoEnergy connects current market and power-generation data directly to its geothermal intelligence and power-plant database.
Explore geothermal energy
This guide provides the starting point for the ThinkGeoEnergy Geothermal Knowledge Centre. The following guides examine individual resources, technologies and applications in greater detail.
Frequently asked questions about geothermal energy
What is geothermal energy in simple terms?
Geothermal energy is heat associated with the Earth and its subsurface. It can be used for heating and cooling or, where temperatures are high enough, to generate electricity.
What is the geothermal gradient?
The geothermal gradient is the rate at which temperature increases with depth. In many continental settings, roughly 25–30°C per kilometre is a useful rule of thumb, but actual gradients vary widely with local geology and heat flow.
Is geothermal energy available everywhere?
Heat is present beneath the Earth's surface everywhere, but useful geothermal resources are not equally accessible. Temperature, depth, geology, fluids, permeability, drilling requirements and economics determine what can be developed.
Do you need to live near a volcano to use geothermal energy?
No. Volcanic and tectonically active regions can provide favourable high-temperature resources, but geothermal heating, shallow geothermal, sedimentary-basin resources and newer technologies can be developed in many non-volcanic regions.
What is the difference between geothermal heating and geothermal power?
Geothermal heating uses heat directly, while geothermal power converts geothermal heat into electricity. Heating can generally use lower-temperature resources than electricity generation.
What is the difference between a geothermal heat pump and a geothermal power plant?
A geothermal heat pump transfers heat between a building and the shallow ground for heating and cooling. A geothermal power plant accesses much hotter resources, usually at greater depth, and converts their thermal energy into electricity.
Is geothermal energy renewable?
Geothermal is generally classified as renewable, but sustainable operation of an individual geothermal resource depends on how it is developed and managed over time.
Is geothermal energy low-carbon?
Geothermal energy generally has low lifecycle greenhouse-gas emissions compared with fossil-fuel energy, but emissions vary by technology and resource. Some hydrothermal reservoirs contain naturally occurring gases that can increase emissions.
Does geothermal energy cause earthquakes?
Most geothermal applications do not involve significant induced seismicity. Some projects involving fluid injection or subsurface stimulation, particularly certain EGS developments, can cause induced seismic events and require careful monitoring and management.
Author: Alexander Richter, ThinkGeoEnergy
Last reviewed: 12 August 2026