# Geothermal power plants: Techniques

Dry steam, flash or binary: three plants for three reservoirs

Source page: https://www.materialinsights.org/energy/e_geo_power/techniques/

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 plants**^[1](https://doi.org/10.1016/j.geothermics.2013.11.001)^[2](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2026/Jul/IRENA_TEC_RPGC_in_2025_2026.pdf)^[3](https://geysers.com/water)^[4](https://ren21.net/gsr-2025/technologies/geothermal)^[6](https://openknowledge.worldbank.org/entities/publication/22e105c7-550f-531d-8e2c-4011098ecf54) | 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 plants**^[1](https://doi.org/10.1016/j.geothermics.2013.11.001)^[5](https://www.ipcc.ch/site/assets/uploads/2018/02/ipcc_wg3_ar5_annex-iii.pdf#page=7)^[6](https://openknowledge.worldbank.org/entities/publication/22e105c7-550f-531d-8e2c-4011098ecf54)^[7](https://atb.nlr.gov/electricity/2025/geothermal) | 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)**^[1](https://doi.org/10.1016/j.geothermics.2013.11.001)^[7](https://atb.nlr.gov/electricity/2025/geothermal)^[8](https://www.energy.gov/sites/default/files/2014/02/f7/analysis_wang_lifecycle_analysis.pdf) | 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 plants**

Wells tap a reservoir that yields steam directly. The steam is filtered of rock particles, passed through a turbine, condensed and reinjected.^[1](https://doi.org/10.1016/j.geothermics.2013.11.001)^[2](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2026/Jul/IRENA_TEC_RPGC_in_2025_2026.pdf)^[3](https://geysers.com/water)^[4](https://ren21.net/gsr-2025/technologies/geothermal)^[6](https://openknowledge.worldbank.org/entities/publication/22e105c7-550f-531d-8e2c-4011098ecf54)
**Single- and double-flash plants**

Hot 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.^[1](https://doi.org/10.1016/j.geothermics.2013.11.001)^[5](https://www.ipcc.ch/site/assets/uploads/2018/02/ipcc_wg3_ar5_annex-iii.pdf#page=7)^[6](https://openknowledge.worldbank.org/entities/publication/22e105c7-550f-531d-8e2c-4011098ecf54)^[7](https://atb.nlr.gov/electricity/2025/geothermal)
**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.^[1](https://doi.org/10.1016/j.geothermics.2013.11.001)^[7](https://atb.nlr.gov/electricity/2025/geothermal)^[8](https://www.energy.gov/sites/default/files/2014/02/f7/analysis_wang_lifecycle_analysis.pdf)

#### Sources

1. [Efficiency of geothermal power plants: A worldwide review (Zarrouk and Moon, Geothermics 51, 142-153)](https://doi.org/10.1016/j.geothermics.2013.11.001) Elsevier, 2014
2. [Renewable Power Generation Costs in 2025 (Executive summary, Figure S1)](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2026/Jul/IRENA_TEC_RPGC_in_2025_2026.pdf) IRENA, 2026
3. [The Geysers: Water (steam field recharge)](https://geysers.com/water) Calpine (geysers.com), 2024
4. [Renewables 2025 Global Status Report: Geothermal](https://ren21.net/gsr-2025/technologies/geothermal) REN21, 2025
5. [Climate Change 2014: Mitigation, Annex III Technology-specific cost and performance parameters, Table A.III.2](https://www.ipcc.ch/site/assets/uploads/2018/02/ipcc_wg3_ar5_annex-iii.pdf#page=7) IPCC AR5 Working Group III, 2014
6. [Understanding CO2 Emissions from Geothermal Power Generation in Turkey (Live Wire 2021/118)](https://openknowledge.worldbank.org/entities/publication/22e105c7-550f-531d-8e2c-4011098ecf54) World Bank, 2021
7. [Annual Technology Baseline 2025: Geothermal](https://atb.nlr.gov/electricity/2025/geothermal) National Laboratory of the Rockies (formerly NREL), 2025
8. [Life-Cycle Analysis of Geothermal Technologies (Wang, Clark and Sullivan, Argonne National Laboratory, GTP peer review)](https://www.energy.gov/sites/default/files/2014/02/f7/analysis_wang_lifecycle_analysis.pdf) US DOE, 2010

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_geo_power/index.md)
- [Overview](https://www.materialinsights.org/energy/e_geo_power/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_geo_power/correlation/index.md)
- [Efficiency](https://www.materialinsights.org/energy/e_geo_power/efficiency/index.md)
- [Resources and labour](https://www.materialinsights.org/energy/e_geo_power/resources/index.md)
- [Impact on the biosphere](https://www.materialinsights.org/energy/e_geo_power/biosphere/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_geo_power/links/index.md)