How a geothermal power plant works
Geothermal plants use heat from deep underground. Wells bring hot water and steam to the surface, where it drives a turbine.
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Flash-steam geothermal plant. A production well, separator and reinjection circuit are shown; binary-cycle plants use a different heat-exchanger arrangement. Motion is slowed for inspection. Coloured overlays reveal flow through enclosed equipment; gold pulses show net electrical energy transfer, not individual electrons.
How it works
- Heat in underground rock
- Hot fluid brought to the surface
- Steam or secondary vapour
- Turbine and generator
- Electricity to the grid
Geothermal electricity starts with heat stored in underground rock. Production wells bring hot water or steam to the surface. In the flash-steam arrangement shown here, a pressure reduction causes part of the hot water to become steam. A separator keeps most remaining liquid out of the turbine. Steam expands through the turbine, turning a generator, and then passes to a condenser so the heat-conversion process can continue.
The reservoir fluid determines much of the plant’s design: its temperature, available flow and whether it arrives as liquid or steam. Dissolved minerals and gases also require appropriate fluid handling. Injection wells return suitable fluids underground and support reservoir management. Some sites instead transfer heat through an exchanger to a separate working fluid. The underground heat source and the surface electricity cycle are different design choices, which is why an enhanced geothermal reservoir should not be confused with a new kind of turbine.
Inside the engineering
Follow the machinery, the working fluids and the electrical connection.
Mechanical
Production fluid reaches the separator, which sends steam towards the turbine and separated liquid towards reinjection. A condenser and pumps return condensate; the turbine shaft drives the generator.
Thermal & chemical
Lower pressure allows part of the hot water to flash to steam. Geothermal fluids may contain dissolved minerals and non-condensable gases, requiring management of scaling, corrosion and gas removal. Reinjection supports fluid management; it does not make every reservoir indefinitely sustainable.
Electrical
The generator connects through a transformer and grid equipment. Pumping and cooling consume part of the electrical output. Resource conditions, outages and reservoir management determine availability, rather than sunlight or wind speed.
Main types and variations
The model shows a single-flash steam plant. Dry steam, flash and binary describe surface conversion cycles. Enhanced geothermal and closed-loop systems describe ways to collect underground heat; their surface equipment must still suit the heat delivered.
Dry-steam plant
A steam-dominated reservoir supplies steam through production wells directly to the turbine system. There is no need to create steam by flashing a predominantly liquid resource first. Exhaust steam is condensed, and suitable condensate can be returned underground through injection wells.
What changes in practice
This comparatively direct route depends on a naturally suitable steam resource. A hot-water reservoir cannot simply use the same arrangement without additional conversion equipment.
Single- and double-flash steam
High-temperature water reaches a lower-pressure separator, where some becomes steam for the turbine. In a double-flash plant, the separated liquid passes through another pressure reduction to produce additional steam at a lower pressure. The remaining brine and condensed steam require appropriate reinjection arrangements.
What changes in practice
An extra flash stage can recover more of a suitable resource’s heat, while adding separators, piping and operating complexity to the surface plant.
Binary-cycle plant
Geothermal water transfers heat across a heat exchanger to a separate fluid with a lower boiling temperature. That fluid vaporises, drives the turbine, condenses and recirculates. The geothermal brine stays outside the turbine circuit and is returned underground after giving up some of its heat.
What changes in practice
A separate working fluid enables electricity production from suitable lower-temperature resources and isolates the turbine from the geothermal brine’s dissolved minerals.
Enhanced geothermal systems (EGS)
Where hot rock lacks sufficient natural permeability, controlled stimulation creates or improves connected fractures. Fluid circulates through the hot rock and returns through production wells to a surface plant. The electricity-conversion cycle is selected for the resulting fluid conditions, rather than being dictated by the EGS label.
What changes in practice
EGS describes reservoir development, not a fourth steam cycle. It makes the underground flow paths an engineered part of the project.
Closed-loop geothermal collection
A sealed underground pipe system circulates fluid through hot rock and carries absorbed heat to the surface. The circulating fluid stays inside the pipes rather than flowing through a fracture network. Surface equipment uses the delivered heat for power generation or other suitable heat applications.
What changes in practice
An underground closed loop is different from a binary plant’s closed surface working-fluid circuit. The labels refer to different parts of a geothermal installation.
Worth knowing
- Suitable sites are concentrated in places such as Iceland, Kenya, Indonesia, New Zealand and the western United States.
- Geothermal output is steady, unlike wind and solar.
- Some geothermal fluids release small amounts of gases such as carbon dioxide and hydrogen sulphide.
See real examples
The atlas includes 192 geothermal records worldwide.
Show on the mapRelated answers
Textbook references
The science on this page follows these standard engineering textbooks. See the full bibliography.
- Geothermal Power Plants: Principles, Applications, Case Studies and Environmental ImpactDry-steam, flash and binary plants, reinjection and environmental impact.
Sources
Cutaways reveal enclosed equipment. Layouts, dimensions, materials and animation speeds are illustrative; this is an educational model, not a plant design or a thermodynamic simulation.