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.
In 60 seconds: how it works
A geothermal plant uses heat from deep underground. Wells bring up hot water and steam, which spin a turbine, and the water is then pumped back down.
- Wells drilled deep into hot rock bring hot water and steam up to the surface.
- In a separator the pressure drops, so part of the hot water turns into steam.
- The steam spins a turbine connected to a generator, which makes electricity.
- The steam is cooled back into water in a condenser.
- The leftover hot water and the condensed water are pumped back underground, so the heat source keeps being refilled.
- A transformer raises the voltage so the electricity can travel to the grid.
Want the engineering detail? Explore the 3D model, then read the engineering notes and the types and variations.
By Power Stations Worldwide · Related reading updated · Preparation and review scope. Educational illustrations; no independent engineering peer review is claimed.
Explore the equipment in 3D
Rotate equipment, follow energy flows and inspect each component. Read the steps below at any time.
Choose a step to read the process. Activate the 3D model or start a guided tour to use the animation controls.
Single-flash geothermal plant with surface condenser and pumped reinjection. One bounded pure-water balance, original enlarged separator/turbine/condenser cutaways and fractured-rock wells. Surface dimensions are nominally 5 m/unit; underground depth is independently compressed and unscaled. Independent cooling supply and ideal complete process-water return are teaching assumptions; binary and dry-steam equipment are not modelled here. 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.
From pressure drop to power—and back underground.
Simple explanation. Hot water carries energy from rock fractures to the surface. Lower pressure lets some water become steam without an extra heater. The separator keeps liquid droplets out of the turbine. Expansion turns a shared shaft and generator; the remaining steam condenses. [G1]
Follow both outlets. Steam becomes condensate after the turbine; separated brine bypasses the turbine. A condensate pump brings the two streams to the same pressure before mixing. A common pump sends the entire ideal process-water return towards the injection well. Reinjection does not guarantee an unlimited supply of heat.
Keep cooling separate. Cooling water is inside condenser tubes; geothermal steam is outside. Heat crosses metal walls. A vacuum pump removes gases that would otherwise raise condenser pressure. Our independent cooling supply and complete pure-water return are teaching assumptions; many real plants use condensate for cooling makeup. [G1]
Selected: Plant overview. Diagram outlines and the 3D highlight share the same selection.
Mechanical details: a separator is not a boiler
A tangential inlet directs the two-phase mixture into the vessel. Droplet-separation internals above a schematic liquid region limit liquid carryover to the steam outlet; a separate lower outlet carries brine. The enlarged cutaway is not a separator-sizing calculation, and its visible liquid level is not the calculated steam mass fraction. Turbine blades rotate; diaphragms, housings, generator stator and shaft bearings stay fixed. Saturated inlet steam becomes wetter during expansion, so moisture erosion matters. [G1]
Well casing and supported pipe expansion loops make the route traceable. Real expansion, corrosion allowance and support loading require site-specific stress and materials work. Surface equipment uses a nominal 5 metres per model unit, with enlarged internals and compressed station spacing; the underground vertical distance is separately compressed and deliberately has no depth scale. Fracture marks show permeable rock, not an open swimming pool.
Engineering details: the same state points drive every reading
Specific enthalpy h is energy per unit mass including flow work (joules per kilogram, J/kg). Specific entropy s is in J/(kg·K), where K means kelvin. The symbol ṁ denotes mass flow in kg/s. All pressures are absolute. The model uses pure-water saturation rows, not actual saline geofluid properties. [G2] [G4]
hafter flash = hin; x = [hin − hf(Psep)] / [hg(Psep) − hf(Psep)]
Psep is separator pressure; x is vapour mass fraction; f and g identify saturated liquid and vapour. Their difference is hfg, latent enthalpy. Ideal flashing is adiabatic (no external heat) and isenthalpic (constant enthalpy), with no shaft work. Well/gathering heat transfer and kinetic/potential changes are neglected. Invalid two-phase states are rejected, not clamped to zero or one. [G1] [G2]
ṁsteam = x ṁproduction; ṁbrine = (1 − x) ṁproduction
ṁproduction hin = ṁsteam hg + ṁbrine hf
The separator balance conserves mass and enthalpy. Steam quality is a mass fraction, not a volume fraction or a fraction of the drawing's height. Inlet benchmark: saturated liquid at 4 MPa, 250.354 °C and 1087.5 kJ/kg. Separator choices are exact 0.5/0.8/1 MPa table rows; the condenser is fixed at 0.010 MPa, 45.806 °C. Internally use hg − hf and sg − sf, avoiding differences between separately rounded latent columns. [G4]
xex,s = (sg,sep − sf,c) / (sg,c − sf,c); hex,s = hf,c + xex,s(hg,c − hf,c)
hex = hg,sep − ηt(hg,sep − hex,s); Pshaft = ṁsteam(hg,sep − hex)
Subscript c means condenser; ex means exhaust; extra s means the ideal constant-entropy reference. ηt is the illustrative turbine isentropic efficiency, 0.80. Exhaust is a wet mixture, not invented superheated steam. The missed ideal work stays in exhaust enthalpy; do not subtract it again as an extra heat loss. [G2]
Q̇condenser = ṁsteam(hex − hf,c); Δhpump = v ΔP / ηpump
Q̇ denotes heat-transfer rate in watts (W). v is the constant-liquid specific-volume approximation in m³/kg; ΔP is pressure rise in pascals (Pa); ηpump = 0.75 is illustrative. The condensate pump raises liquid from condenser to separator pressure. Mix at equal pressure, conserving enthalpy; the common pump raises all returned liquid to the illustrative 4 MPa target. Pump fluid work increases returned enthalpy. Pump motor efficiency 0.95 accounts separately for electrical consumption and motor heat. Volume-addition mixing is an approximation, not a brine equation of state.
Q̇removed = ṁproduction(hin − hreturn); ηnet = Pnet / Q̇removed
return is the pumped reinjection header; net is grid export after all plant auxiliaries and transformer loss. This thermal denominator subtracts retained energy in returned water. It is not the entire incoming enthalpy flux, a reservoir recovery efficiency or a forecast of lifetime generation.
Electrical details: direct three-phase AC export
Illustrative generator efficiency is 0.98 and transformer efficiency 0.995. Electrical auxiliaries include the separately calculated pumps plus 5% of gross output: cooling 3%, gas handling 1%, other loads 1%. These are teaching assumptions, not sourced plant efficiencies. The vacuum-pump concept uses electricity, avoiding an unaccounted motive-steam diversion. Real gas concentrations, abatement duty, cooling weather and tower water losses are not solved.
ns = 120 f / Npoles = 120 × 50 / 2 = 3000 rpm; τ = Pshaft / ω
ns is synchronous speed; f is grid frequency in Hz; Npoles is total poles, not pole pairs; τ is shaft torque in newton-metres (N·m); ω = 2π ns/60 is angular speed in radians per second. Changing flow changes torque/output, not synchronous speed. Three-phase switchgear and a transformer connect directly to the grid; this lesson does not insert an unnecessary AC/DC stage or calculate voltage, current, reactive power, synchronization transients or protection settings. [G3]
Current operating balance
100.000 kg/s in = 17.907 steam + 82.093 brine. Ideal process return = 100.000 kg/s.
| Measurement boundary | Power |
|---|---|
| Production enthalpy flow | 108.750 MW |
| Returned-fluid enthalpy flow | 63.099 MW |
| Thermal power removed from process fluid | 45.651 MWth |
| Turbine shaft power | 9.437 MW |
| Gross generator electricity | 9.249 MWe |
| Condenser heat rejection | 36.701 MWth |
| Pump work into returned liquid | 0.487 MW |
| Electrical pump consumption | 0.512 MWe |
| Cooling auxiliaries | 0.277 MWe |
| Gas-handling auxiliaries | 0.092 MWe |
| Other electrical auxiliaries | 0.092 MWe |
| Generator heat/loss | 0.189 MW |
| Pump motor heat/loss | 0.026 MW |
| Transformer heat/loss | 0.041 MW |
| Net grid export | 8.232 MWe |
Net extracted-thermal efficiency: 18.033%. The actual turbine exhaust quality is 85.677% steam by mass. Cooling-water rate 878.004 kg/s uses an imposed 25→35 °C temperature rise and constant 4180 J/(kg·K) heat capacity, not a cooling-tower or evaporation simulation.
Extracted thermal power = net export + condenser heat + generator heat + pump-motor heat + non-pump auxiliaries + transformer heat. Calculated residual: -2.24e-8 W before display rounding. Pump fluid work is already in return enthalpy; do not count it a second time.
| Point | Absolute MPa | h | State |
|---|---|---|---|
| Resource liquid before ideal well/flash drop | 4.000 | 1087.500 | saturated-liquid · x=0.0000 |
| Flashed mixture entering separator | 0.800 | 1087.500 | wet-steam · x=0.1791 |
| Separated saturated steam → turbine | 0.800 | 2768.300 | saturated-vapor · x=1.0000 |
| Separated liquid → equal-pressure mixing header | 0.800 | 720.860 | saturated-liquid · x=0.0000 |
| Wet turbine exhaust → condenser steam space | 0.010 | 2241.291 | wet-steam · x=0.8568 |
| Condenser liquid → condensate pump | 0.010 | 191.810 | saturated-liquid · x=0.0000 |
| Raised-pressure condensate → mixing header | 0.800 | 192.874 | compressed-liquid |
| Brine + condensate before common reinjection pump | 0.800 | 626.312 | compressed-liquid |
| Pumped combined liquid → reinjection well | 4.000 | 630.989 | compressed-liquid |
Checked example: 100 kg/s at 0.80 MPa
x = (1087.5 − 720.86)/(2768.3 − 720.86) = 0.17907240. Of 100 kg/s, 17.907240 kg/s is steam and 82.092760 kg/s remains brine. The same model gives 9.437 MW shaft power, 9.249 MWe gross, 8.232 MWe net and 36.701 MWth condenser heat. Returned enthalpy is 630.988850 kJ/kg; 45.651 MWth is removed from the fluid. Parameters are illustrative, not a real installation's specifications. [G1] [G2] [G4]
Three common misconceptions
Does the separator heat water until it boils?
No. Reduced pressure creates the mixture. Ideal throttling adds neither external heat nor shaft work; the separator then separates the two phases. [G1] [G2]
Does 18% steam mean the vessel is 18% full of steam?
No. Quality is mass fraction, and steam has a much lower density than liquid. Vessel space, schematic liquid level and visual particle counts are not that mass fraction. [G1] [G4]
Does reinjection make geothermal power last forever?
No. Reinjection supports fluid management, but reservoir heat replenishment, permeability, well spacing and chemistry still matter. Scaling, corrosion and gas handling require site-specific management. This steady-state teaching case cannot predict resource life or emissions.
Compare architectures—separate from this 3D model
Dry steam routes reservoir steam to a turbine without this liquid-flash separator. Binary conversion transfers geothermal heat across an exchanger to a different working fluid, which circulates through its own turbine/condenser loop. These original route summaries are comparisons, not alternative modes of the single-flash model. [G5]
Reservoir steam → turbine/generator → condenser → suitable reinjection
Geothermal water → heat exchanger → reinjection
Separate working fluid: pump → heat exchanger → turbine/generator → condenser → pump
Main book references
- [G1] Ronald DiPippo. Geothermal Power Plants: Principles, Applications, Case Studies and Environmental Impact. 4th ed., Butterworth-Heinemann/Elsevier, 2016; ISBN 9780081008799. Actual publisher excerpts checked: §5.3 Energy Conversion System and §5.4.3 / equation (5.7), Chapter 5 PII B9780081008799000057. These chapter excerpts—not the Topics page's AI-generated definition—support the named mechanisms. Full chapter and unlisted pages were not checked. Publisher metadata gives late-2015 publication dates; the chapter identifies the edition as 2016.
- [G2] US Department of Energy. DOE Fundamentals Handbook: Thermodynamics, Heat Transfer, and Fluid Flow. Vol. 1, DOE-HDBK-1012/1-92, June 1992, Rev. 0. Actual handbook, checked printed p. 29, pp. 48–49 and 79–80: throttling, mixture quality and turbine energy/efficiency relationships. The website's example is an original derivation.
- [G3] H. H. Woodson and J. R. Melcher. Electromechanical Dynamics. Part I, Wiley, 1968. Actual MIT-hosted Chapter 4, checked §4.1.8 / equation (4.1.95), synchronous speed and pole pairs.
Supplementary technical sources
- [G4] A. H. Harvey. Thermodynamic Properties of Water: Tabulation from the IAPWS Formulation 1995. NISTIR 5078, 1998. Actual Table 2, checked printed pp. 11–13 and exact 0.010/0.50/0.80/1.00/4.0 MPa rows. No brine chemistry correction or general steam-property solver is claimed.
- [G5] US EIA. Geothermal power plants: checked flash, dry-steam and binary paths. Illustrations here are original.
Named passages checked 3 October 2026. Software, geometry and educational reviews are recorded separately; no independent engineering peer review, installation approval, piping/vessel design, reservoir forecast or validated time-domain simulation is claimed.
Download the original editable Blender scene. Reproduction, assumptions and tests live in the project's Geothermal engineering and reference reports.
Inside the engineering
Follow the machinery, the working fluids and the electrical connection.
Mechanical
A supported gathering loop feeds tangential separator entry. Steam passes droplet-control internals to the turbine; separated brine bypasses it. A coaxial turbine–generator train has fixed housings, stators and bearings. Condensate reaches separator pressure before mixing; a common pump then raises the complete return for reinjection.
Thermal & chemical
Pressure reduction causes flashing without an extra heater. Steam condenses outside physically separate cooling-water tubes; the cooling tower recirculates its own supply. An electric vacuum-pump concept removes non-condensable gases, but gas mass/chemistry and cooling makeup/blowdown are excluded from the pure-water model. Scaling, corrosion and reservoir heat depletion require site-specific management; reinjection is not unlimited reservoir life.
Electrical
One illustrative two-total-pole, 50 Hz synchronous generator runs at 3000 rpm when active, displayed 100:1 slower. Three-phase switchgear and transformer feed the grid directly. One model separates turbine work, generator loss, pump work/motor loss, cooling/gas/other electrical auxiliaries, transformer loss, net export and condenser heat; zero flow is isolated off, not a shutdown simulation.
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.
- Suitable resources can supply power independently of sunlight and wind, but well conditions, reservoir management, chemistry and outages still constrain output.
- Geothermal fluids may contain carbon dioxide and hydrogen sulphide; concentrations and treatment requirements are site-specific, not calculated by this lesson.
See real examples
The atlas includes 192 geothermal records worldwide.
Show on the mapRelated answers
Textbook references
Suggested technical background for this topic. These books are further reading, not proof that every explanation was checked against every edition. See the full bibliography and review scope.
- Geothermal Power Plants: Principles, Applications, Case Studies and Environmental ImpactDry-steam, flash and binary plants, reinjection and environmental impact.
Sources
- DiPippo 4th ed.: actual single-flash energy-conversion excerpt (§5.3) ↗
- DiPippo 4th ed.: actual separation excerpt (§5.4.3 / eq. 5.7) ↗
- DOE thermodynamics handbook: actual throttling, quality and turbine passages ↗
- NISTIR 5078: actual saturation properties (Table 2) ↗
- Woodson/Melcher: actual MIT-hosted machine chapter (§4.1.8) ↗
- EIA: Geothermal power plants ↗
- US DOE: Geothermal produced fluids and treatment ↗
Cutaways reveal enclosed equipment. Layouts, dimensions, materials and animation speeds are illustrative; this is an educational model, not a plant design. The pure-water steady-state balance is not a reservoir forecast, transient, gas-chemistry, piping-stress or safety simulation.