Geothermal power plants: Techniques
Dry steam, flash or binary: three plants for three reservoirs
What this tab covers The methods used to capture this energy: how each works, and how they compare on efficiency, cost, life-cycle emissions, maturity and scale.Three plant types match three kinds of reservoir: dry steam for rare steam-dominated fields, flash for hot water above about 200 °C, and binary for cooler water. All are mature; world capacity was about 15.1 GW at the end of 2024.
Comparison
| Method | Efficiency | Cost | Life-cycle emissions | Maturity | Scale |
|---|---|---|---|---|---|
| Dry steam plants12346 | Highest of the types: up to about 21% (Darajat) | Global geothermal LCOE USD 89/MWh in 2025 (all types) | Operational CO2 depends on reservoir gas; reported global average about 121 g CO2/kWh | mature | The Geysers, California, the best-known example, now injects about 20 million gallons (76,000 m3, calculated) of treated wastewater a day to sustain steam |
| Single- and double-flash plants1567 | Within the 1-21% range; world average about 12% | USD 4,362/kW average overnight capital cost (NREL ATB 2025, identified hydrothermal resources) | Life-cycle median 38 g CO2e/kWh (range 6-79) for geothermal; some Turkish plants 400-1,300 g CO2/kWh in operation | mature | Examples: Cerro Prieto (Mexico), Olkaria (Kenya), Hellisheidi (Iceland) |
| Binary cycle plants (organic Rankine, Kalina)178 | Lowest of the types, down to about 1% on the coolest fluids | USD 9,302/kW average overnight capital cost (NREL ATB 2025, 150-200 °C resources) | Near zero in operation when all fluid is reinjected | mature | Argonne notes that most installed units are binary |
Flash plants cost less per kW because hot fluid yields more power per well; binary plants unlock cooler, more widespread resources at roughly twice the capital cost (NREL ATB 2025). IRENA puts the 2025 global weighted average geothermal LCOE at USD 89/MWh, with installed costs of USD 5,997/kW, well above hydropower (USD 62/MWh); in 2024 country averages ranged from USD 33/MWh in Türkiye to USD 90/MWh in Indonesia (2024, IRENA). Life-cycle emissions are low for most fields but approach coal where reservoirs are rich in CO2.
How each method works
Dry steam plantsWells tap a reservoir that yields steam directly. The steam is filtered of rock particles, passed through a turbine, condensed and reinjected.12346
Single- and double-flash plantsHot pressurised water rises up the well and part of it flashes to steam as pressure drops. A separator sends the steam to the turbine; double-flash plants flash the leftover water again at lower pressure.1567
Binary cycle plants (organic Rankine, Kalina)Hot water stays in a closed loop and heats a second fluid with a low boiling point (an organic fluid such as pentane, or ammonia-water in the Kalina cycle). Its vapour drives the turbine and all geothermal fluid is reinjected.178
Sources
- Efficiency of geothermal power plants: A worldwide review (Zarrouk and Moon, Geothermics 51, 142-153) Elsevier, 2014
- Renewable Power Generation Costs in 2025 (Executive summary, Figure S1) IRENA, 2026
- The Geysers: Water (steam field recharge) Calpine (geysers.com), 2024
- Renewables 2025 Global Status Report: Geothermal REN21, 2025
- Climate Change 2014: Mitigation, Annex III Technology-specific cost and performance parameters, Table A.III.2 IPCC AR5 Working Group III, 2014
- Understanding CO2 Emissions from Geothermal Power Generation in Turkey (Live Wire 2021/118) World Bank, 2021
- Annual Technology Baseline 2025: Geothermal National Laboratory of the Rockies (formerly NREL), 2025
- Life-Cycle Analysis of Geothermal Technologies (Wang, Clark and Sullivan, Argonne National Laboratory, GTP peer review) US DOE, 2010