Geothermal power plants use heat carried by underground water or steam to turn a turbine and generate electricity. Depending on the resource, they use natural steam directly, make steam by lowering the pressure of hot water, or transfer heat to a separate fluid that drives the turbine. Geothermal heat can also be delivered directly to buildings and industry without generating electricity first.
What a geothermal power plant needs
A geothermal resource is not simply hot rock. For a conventional hydrothermal power plant, three things must come together: underground heat, fluid to carry that heat, and permeable rock or fractures that allow fluid to move. Wells bring hot water or steam from the reservoir to the surface. The plant then converts the fluid’s thermal energy into mechanical rotation and, finally, electricity.
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The basic electricity-making chain is similar to other thermal power plants: a vapor expands through a turbine, the turbine turns a generator, and the generator produces electricity. What differs is how the plant obtains the vapor. A geothermal plant uses heat from the Earth rather than burning fuel to heat water. The fluid produced from the well may itself be steam, may be hot pressurized water that can be made to boil, or may transfer its heat to another fluid.
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In many systems, cooled geothermal fluid and condensed steam are returned underground through injection wells. Reinjection is a common part of the operating cycle and reservoir management, but it does not by itself prove that a reservoir is fully replenished or guarantee a particular level of output over time.
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How the three main plant types work
The names dry steam, flash steam, and binary cycle describe different ways of getting turbine-driving vapor from a geothermal resource. They are not simply labels for different turbine designs: the key distinction is the form of the produced fluid and whether geothermal fluid enters the turbine.
| Plant type | Produced resource | How the turbine gets vapor | Fluid path after power generation |
|---|---|---|---|
| Dry steam | Predominantly steam | Geothermal steam is piped directly to the turbine. | Steam is commonly condensed into water and reinjected. |
| Flash steam | High-pressure hot water | A pressure drop causes some water to flash into steam; separated steam drives the turbine. | Condensate and remaining brine are commonly reinjected. |
| Binary cycle | Hot water, including lower-temperature resources | Geothermal water heats a separate working fluid, which vaporizes and drives the turbine. | Geothermal fluid stays outside the turbine loop and is returned underground. |
Dry steam: reservoir steam drives the turbine directly
A dry-steam plant is possible where a reservoir produces steam naturally. The steam travels from the well to the turbine and expands through its blades, making the turbine shaft rotate. The shaft turns the generator. Afterward, the steam is commonly cooled and condensed into water, which can be reinjected.
This design has a straightforward conversion path, but it depends on a comparatively uncommon resource: a reservoir sufficiently rich in naturally occurring steam. The first dry-steam geothermal power plant was used in Italy in 1904, according to the U.S. Department of Energy (DOE). The Geysers in northern California is a current example identified by DOE.
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Flash steam: pressure turns some hot water into steam
Flash plants bring high-pressure hot water to the surface. The water enters a separator or tank at lower pressure. Because the pressure has fallen, a portion of the hot liquid rapidly boils, or “flashes,” into steam. That steam is separated and sent through the turbine. The turbine-generator then converts its motion into electricity.
If liquid brine remains after the first separation, a plant may lower the pressure again in a second stage to produce additional steam. Whether a plant uses one or more pressure stages depends on the resource and the design; the process should not be assumed to be identical at every site.
DOE’s introductory explanation describes flash steam for fluids above 182°C (360°F). That is a source-specific guide, not a universal engineering cutoff. The actual choice and design of a plant depend on site conditions, including the fluid’s temperature and characteristics.
Binary cycle: geothermal water heats a separate fluid
A binary plant uses two fluid loops. Hot geothermal water passes through a heat exchanger, where it transfers heat to a secondary working fluid with a lower boiling point than water. The secondary fluid vaporizes and drives the turbine. It is then cooled back into liquid and circulated through its own loop again.
In this arrangement, geothermal water does not contact the turbine. It can be returned underground after giving up heat, while the working fluid remains in a separate circuit. This makes binary technology useful for some lower-temperature resources that would not provide the steam conditions used by dry-steam or flash plants. DOE describes resources below 182°C (360°F) as a category that can support electricity generation with binary technology; that introductory threshold is not a universal dividing line.
Binary systems include different cycle designs. REN21 distinguishes Organic Rankine Cycle systems, which use an organic working fluid, from Kalina Cycle systems, which use a non-organic fluid. The defining principle remains heat transfer between separate fluid loops rather than geothermal steam entering the turbine.
From well to electricity: the operating sequence
- Bring geothermal fluid to the surface. Production wells tap an underground resource with heat, fluid, and pathways for flow through permeable rock or fractures.
- Prepare the heat or vapor for the chosen cycle. A dry-steam plant routes natural steam to the turbine; a flash plant separates steam created as hot water enters lower pressure; a binary plant transfers heat to a second fluid in a heat exchanger.
- Turn the turbine. Expanding vapor pushes the turbine blades and rotates the connected shaft.
- Generate electricity. The rotating shaft drives a generator, converting mechanical motion into electrical energy.
- Cool and manage the fluids. Steam may be condensed, and cooled geothermal water or remaining brine is commonly reinjected. In a binary plant, the secondary working fluid is also cooled and recirculated in its separate loop.
The turbine-generator is only one part of the system. Wells and surface equipment must deliver and handle the resource, and plant operators must manage the fluids and heat transfer. The geology therefore shapes both whether a project can work and which conversion process makes sense.
How geothermal heat is used without generating electricity
Geothermal heat does not have to pass through a turbine. DOE defines direct use as “the use of geothermal energy for heating or other applications without first converting it to electricity.” In a direct-use system, a well supplies hot water for a nearby heating or industrial application. DOE describes direct-use well temperatures of 80–300°F.
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Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallUses include building and space heating, as well as processes that need heat rather than electrical power. Examples identified by DOE include fish farming, greenhouses, food processing and agricultural drying, beer brewing, and drying pulp, paper, lumber, and other materials. Depending on the system, cooled fluid may be reinjected or disposed of at the surface.
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District heating serves multiple buildings
A district-heating system distributes geothermal heat through a network to more than one building. The network is the delivery method: it carries heat from a geothermal source to users. It is distinct from a geothermal power station, whose primary conversion process uses vapor to turn a turbine and generate electricity.
A project may sometimes use heat that remains after electricity generation, but this is not a feature that should be assumed for every geothermal power plant. Whether heat can be delivered usefully depends on the project and its heat users; the available descriptions do not establish that all plants supply buildings or industry.
Geothermal heat pumps are a different technology
Geothermal heat pumps use the relatively stable temperature of shallow ground to help heat and cool buildings. They do not operate like deep-well utility power plants: they are not the same equipment as a plant that produces hot fluid for a turbine-generator. The shared word “geothermal” refers to heat from the ground, not to identical systems or resource depths.
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Geothermal generation is a modest share of electricity worldwide, while direct-use heat is a separate and substantial measure of geothermal energy use. The figures below describe different products and geographies, so they should not be combined as though they were the same output category.
| Measure | Reported value | Qualification |
|---|---|---|
| Global geothermal electricity generation | 99 TWh in 2024 | REN21’s 2025 estimate; 1.7% higher than 2023 and approximately 1% of renewable electricity generation. |
| Global direct-use geothermal thermal supply | 245 TWh (882 PJ) in 2024 | REN21’s 2025 estimate; 19.5% higher than 2023, driven largely by policy-led expansion in China. |
| U.S. utility-scale geothermal generation | About 16 billion kWh, or 0.4% of U.S. utility-scale generation, in 2025 | U.S. Energy Information Administration (EIA) preliminary data published in 2026, based on February 2026 Electric Power Monthly tables. Plants operated in seven states; California provided 68.6% and Nevada 24.7% of U.S. geothermal generation. |
| Geothermal electricity across 25 countries | About 92 billion kWh in 2022 | EIA figure on a page accessed in 2026. Indonesia led at about 17 billion kWh and Kenya generated about 5 billion kWh; this is an older, named-year comparison, not a replacement for the 2024 global estimate. |
The 2025 U.S. figure is preliminary, and REN21’s global totals are estimates. Keeping the year and scope with each number matters: a U.S. utility-scale electricity statistic is not directly comparable to a global total that includes direct-use heat.
What the plant type does—and does not—tell you
The conversion cycle indicates how a plant handles its produced fluid, but it is not a complete performance or environmental assessment. A binary plant keeps geothermal fluid out of the turbine loop; EIA describes binary-cycle plants as closed systems with no air emissions. That specific description should not be generalized into a claim that every geothermal plant emits nothing.
Likewise, reinjection is common, but it does not guarantee sustainable output or establish that a reservoir is completely renewed. The introductory temperature ranges used to explain flash and binary systems are not substitutes for a site-specific resource assessment. The available source descriptions do not establish universal plant efficiency, capacity factors, project costs, lifecycle emissions, or detailed environmental impacts.
For a reader distinguishing systems, the most useful questions are: what fluid comes out of the production well, how does the plant create turbine-driving vapor, does geothermal fluid enter the turbine loop, and where does the cooled fluid go? For direct-use heat, instead consider the temperature needed by the user, the distance between the resource and buildings or industrial demand, the scale of demand, and whether a distribution network is available. Those factors describe the system’s purpose and layout without implying a project cost or output that has not been established.
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