# Hydropower dams: Efficiency

Why falling water beats every other natural energy flow

Source page: https://www.materialinsights.org/energy/e_hydro_dams/efficiency/

What this tab covers How much of the energy available is actually captured or extracted, in per cent: theoretical limits, laboratory records, typical new equipment and in-service averages, each with exactly what is being measured.

Hydropower is the most efficient large-scale way of turning a natural energy flow into electricity: modern turbines convert over 90% of the energy of falling water into shaft power at their best operating point. Plants run at about half their rated output over a year, because reservoirs are managed for water supply, flood control and peak demand.

Chart: Efficiency ranges
 Commercial In service

#### Efficiency by measure

| Measure | Range | Type | What is measured |
|---|---|---|---|
| **Hydro turbines (Francis, Kaplan, Pelton), best operating point** | 90 to 92%^[1](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2015/IRENA-ETSAP_Tech_Brief_E06_Hydropower.pdf)^[15](https://doi.org/10.1016/B978-0-443-33771-0.00017-4) | Commercial | Energy of falling water to mechanical shaft power; up to 92% (IRENA-ETSAP), over 90% (2025 review) |
| **Global average capacity factor, projects commissioned 2025** | 43%^[2](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2026/Jul/IRENA_TEC_RPGC_in_2025_2026.pdf) | In service | Annual electricity generated divided by rated output for a full year |

#### Where the energy is lost

| Step | Loss |
|---|---|
| **Turbine hydraulic losses (friction, leakage, turbulence)** | about 8-10% at the best operating point (calculated from 90-92%), more at part load^[1](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2015/IRENA-ETSAP_Tech_Brief_E06_Hydropower.pdf)^[15](https://doi.org/10.1016/B978-0-443-33771-0.00017-4) |

The energy available is the weight of water multiplied by the height it falls (the head). Unlike wind or sunlight, water arrives in a confined, steady stream, so a well-matched turbine can capture almost all of it. Turbine type follows the head: Pelton wheels for high heads, Francis turbines for medium heads and Kaplan propeller turbines for low heads with large flows. The capacity factor of 48% is a choice as much as a limit: many dams are run to cover peak demand or to save water for dry seasons.

#### Sources

1. [Hydropower: Technology Brief E06 (Table 2, turbine efficiency)](https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2015/IRENA-ETSAP_Tech_Brief_E06_Hydropower.pdf) IRENA and IEA-ETSAP, 2015
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. [Hydropower technologies (Waheed et al., in Renewable Energy Technologies, pp. 591-632)](https://doi.org/10.1016/B978-0-443-33771-0.00017-4) Elsevier, 2025

## Other sections

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