Geothermal Energy Production & Utilisation
Key facts
- Direct use applies geothermal heat to a thermal demand.
- Applications range from buildings and district heating to industry, agriculture, aquaculture, bathing and cooling.
- Useful geothermal heat spans a broad range of temperatures.
- Heat exchangers commonly separate geothermal fluids from heating networks.
- Deep geothermal heating can include large heat pumps to raise delivery temperature.
- Proximity to heat demand is central to project viability.
- Heat can be used sequentially through cascading utilisation.
What is direct use of geothermal energy?
Geothermal direct use applies heat from a geothermal resource to a thermal application without first converting that heat into electricity.
In a typical deep geothermal system, hot geothermal fluid is produced through a well. Its heat is transferred to a building, industrial process or heating network, often through a heat exchanger. The cooled geothermal fluid is then commonly reinjected into the subsurface.
This differs from geothermal electricity generation, where heat is converted into electrical power.
It also differs from standalone ground-source or geothermal heat pumps, which use an electrically driven refrigeration cycle to extract and upgrade low-grade heat from the shallow ground.
There is an important overlap, however. A deep geothermal district-heating system may use a large heat pump to raise the temperature supplied to the network. Such a system can still reasonably be considered geothermal direct use because the geothermal resource remains the primary heat source and the heat pump acts as a temperature-boosting component.
Some international statistics include ground-source heat pumps within broader geothermal direct-use totals while others report them separately. ThinkGeoEnergy treats shallow geothermal heat pumps as a distinct technology category for clarity.
What Is Geothermal Energy?
Geothermal Heat Pumps
U.S. Department of Energy, Geothermal Direct Use
What temperatures can be used for geothermal direct heat?
There is no single temperature range that defines geothermal direct use.
Different applications require different temperatures, and the boundaries overlap considerably. Resource temperature, flow rate, heat-exchanger design, network temperature and the use of heat pumps can all change what is technically possible.
As broad guidance:
- Bathing and pools: around 25-50°C (77-122°F)
- Aquaculture: around 20-60°C (68-140°F)
- Greenhouse heating: around 30-90°C (86-194°F)
- Building and district heating: broadly around 40-100°C (104-212°F)
- Food drying and processing: often around 50-150°C (122-302°F)
- Industrial process heat: broadly around 50-150°C (122-302°F) for many low- and medium-temperature processes
- Absorption cooling: often around 80-150°C (176-302°F) as a practical driving-temperature range
District heating and thermal networks
District heating is one of the most established large-scale applications of geothermal direct use.
A geothermal district-heating system typically produces hot water from underground wells and transfers its heat into a distribution network. The network supplies buildings, domestic hot water and other heat users before returning cooler network water for reheating.
Many deep sedimentary systems use a production-reinjection doublet: one well produces geothermal fluid while another returns cooled fluid to the reservoir.
Deep production wells often require downhole pumps to bring geothermal fluid to the surface.
A heat exchanger commonly separates geothermal fluid from the district heating network, helping protect the network from salinity, dissolved minerals and scaling.
Network temperature and hybrid systems
The temperature required by the heating network strongly influences the geothermal system design. Older networks often operate at relatively high supply temperatures. Newer or modernised networks increasingly operate at lower temperatures, which can make a wider range of geothermal resources usable. Where geothermal production temperature is below the network requirement, a large heat pump can raise the temperature. Thermal storage can also help balance geothermal production with changing heat demand. Most district-heating systems also need some form of peak or backup heat capacity. This can come from heat pumps, auxiliary boilers, thermal storage or other heat sources depending on the network. Geothermal therefore often forms the stable base-load component of a wider heat-supply system rather than operating completely alone.Examples of geothermal district heating
Iceland remains one of the world's best-known examples of geothermal heat at urban scale. The Paris Basin in France demonstrates a different model, where deep sedimentary aquifers provide geothermal heat to dense urban areas far from active volcanic regions. Geothermal district heating is also expanding in Germany, China and other markets as cities and utilities seek domestic alternatives to fossil-fuel heating. These examples demonstrate different geological and network conditions rather than one standard model for geothermal district heating.Geothermal Resources
World Bank / ESMAP, Direct Utilization of Geothermal Resources (pdf)
Industrial uses of geothermal heat
Industry requires large quantities of heat for drying, washing, heating, pasteurisation and other processes.
Geothermal resources can provide some of this heat directly.
Typical applications include:
- pulp and paper;
- timber drying;
- textiles;
- washing and cleaning;
- selected chemical processes; and
- other low- and medium-temperature industrial heat applications.
IEA, Renewable Energy Essentials: Geothermal
Agriculture and food production
Geothermal heat can support food production both before and after harvest.
Greenhouse and horticultural heating
Greenhouses require substantial amounts of heat in cooler climates and during colder seasons. Geothermal energy can provide stable temperatures for horticulture without relying entirely on fossil-fuel boilers. Geothermal greenhouse development is established in countries including Türkiye, the Netherlands and Iceland, with additional applications in China, Kenya and other geothermal markets. Depending on the resource and greenhouse requirements, geothermal heat may be used directly or combined with heat pumps and other heat sources.Food drying and processing
After harvest, geothermal heat can support processes such as:- fruit and vegetable drying;
- herb and spice drying;
- grain and crop drying;
- milk pasteurisation;
- food preparation; and
- other low- and medium-temperature processing.
World Bank / ESMAP, Direct Utilization of Geothermal Resources (pdf)
Aquaculture
Aquaculture is another recognised direct-use application.
Fish and other aquatic species often require controlled water temperatures. Geothermal heat can help maintain these conditions throughout the year.
Applications include fish farming and other temperature-controlled aquaculture operations.
Geothermal heat can also be useful as part of a cascading system where residual heat from a higher-temperature application is still suitable for aquaculture.
Project design depends on the species, required water temperature, water quality and whether geothermal fluid is used directly or transfers heat through a heat exchanger.
Bathing, spas and balneology
Bathing in naturally heated water is one of the oldest forms of geothermal direct use.
Natural hot springs have played cultural and social roles for centuries in Europe, Asia, the Americas and the Pacific.
Today, geothermal bathing ranges from traditional hot springs and public pools to large spa and wellness destinations.
Examples include geothermal bathing traditions in Iceland and Japan, thermal spas across Central Europe, and hot-spring tourism in Türkiye, New Zealand and other geothermal regions.
The term balneology is sometimes used in connection with thermal and mineral waters and their role in bathing and wellness traditions.
For the ThinkGeoEnergy Knowledge Centre, geothermal bathing is treated as a cultural, recreational, wellness and tourism application. Medical claims should not be inferred simply because water is geothermally heated.
Can geothermal heat provide cooling?
Geothermal heat can also drive cooling systems.
Absorption cooling uses heat as the primary driving energy input for the cooling cycle rather than relying solely on an electrically driven compressor.
This can allow geothermal heat to support cooling for buildings, industry or district energy systems where suitable resource temperatures are available.
Thermally driven geothermal cooling is distinct from geothermal heat pumps.
Heat pumps provide both heating and cooling by transferring heat between a building and the shallow ground. Absorption cooling instead uses geothermal heat from a deeper resource to drive a cooling process.
Geothermal district cooling is still less widespread than geothermal heating, but it represents an additional way of using geothermal heat where resource and demand conditions are suitable.
Cascading geothermal heat
A geothermal resource can sometimes serve several thermal applications in sequence.
Heat can first be directed to the use requiring the highest temperature, then passed to progressively lower-temperature applications.
For example:
Industrial heat or district heating
- greenhouse heating
- aquaculture
- bathing or other low-temperature application
- reinjection
Other geothermal direct-use applications
Geothermal heat can also serve smaller or more specialised applications.
One example is snow melting and pavement de-icing, where geothermal heat is circulated through embedded pipes to keep roads, pavements or other surfaces free of ice and snow.
These applications are particularly relevant in cold-climate geothermal regions and demonstrate that geothermal direct use extends beyond buildings and industrial processes.
What determines whether direct geothermal use works?
A geothermal resource does not automatically become a viable heating project simply because useful heat exists underground.
Several factors need to align.
Resource temperature determines which applications can be supplied directly and where temperature boosting may be required.
Flow rate determines how much thermal energy can be delivered.
Fluid chemistry affects heat exchangers, scaling, corrosion and fluid handling.
Distance to demand is critical because transporting heat requires pipelines and creates thermal losses.
Network temperature determines whether geothermal heat can enter the network directly or requires upgrading.
Infrastructure matters. Existing district heating networks and large industrial heat users can substantially improve project opportunities.
Demand profile affects utilisation. Space-heating demand is seasonal in many climates, while industry may provide steadier year-round demand.
Thermal storage and hybridisation can help balance supply and demand.
Reinjection and reservoir management influence long-term operation.
Economics depend on drilling and infrastructure costs, heat sales, competing fuels and the scale and reliability of the heat customer.
Direct use works best where a suitable geothermal resource and a substantial heat demand occur reasonably close to one another.
Benefits and challenges of geothermal direct use
Benefits
Direct delivery of useful energy. Heat can be used without first converting it into electricity. Low-carbon heating potential. Geothermal systems can reduce or replace combustion-based heat sources. Actual lifecycle emissions depend on the resource, technology and project. Local energy and energy security. Geothermal heat uses a domestic subsurface resource and can reduce exposure to imported fuels and fuel-price volatility. Continuous availability. Geothermal heat is available independently of wind and sunlight. Cascading opportunities. Heat can potentially serve several applications before reinjection. Long-lived infrastructure. Geothermal wells, networks and surface systems can operate for long periods when resources and infrastructure are appropriately managed.Challenges
High upfront investment. Exploration, drilling and network infrastructure require significant capital before revenue begins. Location dependence. A suitable geothermal resource must be close enough to the heat demand. Heat-network requirements. Many cities and industrial areas do not yet have infrastructure capable of distributing geothermal heat. Seasonal demand. Heating demand can vary substantially over the year. Fluid chemistry. Scaling, corrosion and mineral content can require heat exchangers, treatment or specialised materials. Financing and project structure. Heat projects can be smaller, more local and structured differently from geothermal power projects. Data limitations. Global geothermal heat use remains less consistently tracked than geothermal electricity generation.Geothermal direct use around the world
Direct geothermal heat is used across many countries and applications.
International statistics are not always directly comparable, particularly because some datasets include geothermal heat pumps while others exclude them.
Because reporting conventions and market figures change, country rankings, thermal capacity and annual heat-use totals should always be read together with their methodology and date.
IEA, Direct use of geothermal energy, world, 2012-2024
IEA Geothermal, Data Collection & Information
Frequently asked questions about direct use of geothermal energy
What is direct use of geothermal energy?
Direct use means applying geothermal heat to a thermal demand without first converting that heat into electricity.What temperature is needed for geothermal heating?
There is no universal minimum. Building and district heating can use a broad range of geothermal temperatures, often roughly 40-100°C (104-212°F), while lower-temperature resources can also be used with heat pumps or low-temperature networks.Is geothermal direct use the same as geothermal heat pumps?
No. Direct use generally applies heat from a geothermal resource directly to a thermal demand. Ground-source heat pumps use electricity to extract and upgrade heat from the shallow ground. A deep geothermal heating system can nevertheless use a large heat pump as a booster and still be considered geothermal direct use if geothermal remains the primary heat source.Can geothermal energy supply district heating?
Yes. Geothermal resources can supply district heating where suitable subsurface heat occurs close enough to a network and its customers.Can geothermal heat be used by industry?
Yes. Geothermal heat can support selected industrial processes including drying, washing, timber processing, textiles and other low- and medium-temperature heat applications.Can geothermal heat be used in greenhouses?
Yes. Geothermal heating can provide stable temperatures for greenhouse and horticultural production, including year-round growing in cooler climates.Can geothermal energy provide cooling?
Yes. Geothermal heat can drive thermally powered cooling technologies such as absorption chillers. This differs from cooling provided by ground-source heat pumps.What is cascading geothermal use?
Cascading means using geothermal heat sequentially for applications requiring progressively lower temperatures before the fluid is reinjected.Can geothermal heat be used for snow melting?
Yes. Geothermal heat can be circulated through embedded heating systems for snow melting and pavement de-icing in suitable locations.Why are direct-use geothermal projects often close to heat customers?
Heat is more difficult and expensive to transport over long distances than electricity, so project economics depend strongly on the distance between the resource and the customer.Is geothermal direct heat low-carbon?
Geothermal heat can provide low-carbon heating and reduce fossil-fuel combustion. Actual emissions depend on the resource, pumping requirements, system design and other project characteristics.Sources and further reading
- World Bank / ESMAP Direct Utilization of Geothermal Resources (pdf)
- International Energy Agency - Renewable Energy Essentials: Geothermal
- International Energy Agency - Direct use of geothermal energy, world, 2012–2024
- U.S. Department of Energy - Geothermal Direct Use
- REN21 - Renewables 2025 Global Status Report - Geothermal (pdf)
- World Bank - Opportunities for Direct Uses of Geothermal Energy in Türkiye (pdf)