# Hydropower dams: Overview

How a wall across a valley stores months of river flow

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

What this tile covers Reservoirs that store water behind a dam and release it through turbines. Share of use 2.5% share of world energy supply (2024)

Share of world total energy supply captured or extracted by each method, 2024 (latest year where noted). Denominator is the Energy Institute Statistical Review 2025 total of 592.2 EJ (physical energy content method); electricity from wind, solar, hydro and geothermal is counted at output, nuclear at reactor heat. Heat and biomass flows outside EI's total are set against the same 592.2 EJ. Hydroelectricity 16.03 EJ (EI) less about 6% from plants up to 10 MW (UNIDO capacity share, assumed equal for output) = 15.07 EJ of 592.2 EJ (calculated). Large run-of-river plants are included here. Source: [Statistical Review of World Energy 2025 (74th edition)](https://assets.kpmg.com/content/dam/kpmgsites/sg/pdf/2025/08/2025-statistical-review-of-world-energy.pdf), Energy Institute.

#### Key facts

| **Output** | Electricity |
|---|---|
| **Chain** | Solar → gravitational (water stored high) → kinetic → mechanical → electrical |

#### Included from the reference tables

- Storage dams with Francis, Kaplan and Pelton turbines

#### Linked to the material world
[H₂O Water](https://www.materialinsights.org/commodities/water/)

#### Also in Water and ocean
[HyR Run-of-river and small hydro](https://www.materialinsights.org/energy/e_small_hydro/)[WEC Wave energy converters](https://www.materialinsights.org/energy/e_wave_power/)[TdP Tidal and ocean-current power](https://www.materialinsights.org/energy/e_tidal_power/)[OTEC OTEC and salinity power](https://www.materialinsights.org/energy/e_otec/)

Explore paths from here
 More on this tile in the tabs above: efficiency, techniques, resources and labour, impact on the biosphere.

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_hydro_dams/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_hydro_dams/correlation/index.md)
- [Efficiency](https://www.materialinsights.org/energy/e_hydro_dams/efficiency/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)