Hydropower dams: Efficiency
Why falling water beats every other natural energy flow
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 serviceEfficiency by measure
| Measure | Range | Type | What is measured |
|---|---|---|---|
| Hydro turbines (Francis, Kaplan, Pelton), best operating point | 90 to 92%115 | 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 | 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 load115 |
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
- Hydropower: Technology Brief E06 (Table 2, turbine efficiency) IRENA and IEA-ETSAP, 2015
- Renewable Power Generation Costs in 2025 (Executive summary, Figure S1) IRENA, 2026
- Hydropower technologies (Waheed et al., in Renewable Energy Technologies, pp. 591-632) Elsevier, 2025