# Pumped hydro storage: Science and technology Why water never wears out, and plants last a century Source page: https://www.materialinsights.org/energy/e_pumped_hydro/sg-sci/ What this tab covers The physics and chemistry: how the energy is stored, which materials it needs (scarcity, toxicity, recyclability) and what makes it age. Pumped hydro stores electricity as the height of water held between two reservoirs. It uses common materials and lasts longer than any other grid store, which makes it the default long-duration option where geography allows. #### Mechanism Favourable When power is cheap, reversible pump-turbines lift water from a lower reservoir to an upper one; when power is needed the water falls back through the same machines, which then act as generators. The energy held is proportional to the volume of water and the height difference (the head), so high-head sites store more per cubic metre. Variants include classic river-linked schemes, closed-loop (off-river) schemes that recirculate the same water, and conversions of disused mines. Pumped hydro made up more than 90 percent of the world's energy storage in 2024.^[1](https://www.hydropower.org/publications/2025-world-hydropower-outlook) Share of global energy storage over 90% (2024)^[1](https://www.hydropower.org/publications/2025-world-hydropower-outlook) Example rated head (Tiantai, China) 724 m, two 425 MW units^[1](https://www.hydropower.org/publications/2025-world-hydropower-outlook) #### Material scarcity and toxicity Favourable The plant is mostly concrete, rock fill, steel penstocks and conventional electrical machines, so it depends on no critical or conflict minerals and holds no toxic or flammable storage medium. The binding scarcity is geographic: suitable sites with height, water and acceptable environmental impact. In the US, about 80 sites have been identified, mostly closed-loop.^[1](https://www.hydropower.org/publications/2025-world-hydropower-outlook) US identified PSH sites about 80, mostly closed-loop^[1](https://www.hydropower.org/publications/2025-world-hydropower-outlook) #### Degradation and ageing Favourable Water does not wear out, so there is no capacity fade in the battery sense. Ageing is mechanical: turbine runners, seals, generators and control systems need overhaul over decades, while dams, tunnels and caverns can last more than a century. PNNL describes operating lives of commonly more than 50 years and notes the oldest US plant is 95 years old. Upgrades are common; Duke Energy's Bad Creek plant gained 320 MW in a refurbishment.^[1](https://www.hydropower.org/publications/2025-world-hydropower-outlook)^[5](https://www.pnnl.gov/main/publications/external/technical_reports/PNNL-34458.pdf) Operating life commonly 50+ years (PNNL); over 100 years possible (IHA)^[1](https://www.hydropower.org/publications/2025-world-hydropower-outlook)^[5](https://www.pnnl.gov/main/publications/external/technical_reports/PNNL-34458.pdf) Oldest US plant 95 years^[5](https://www.pnnl.gov/main/publications/external/technical_reports/PNNL-34458.pdf) Bad Creek uprate +320 MW on a 1,680 MW plant^[1](https://www.hydropower.org/publications/2025-world-hydropower-outlook) #### Sources 1. [2025 World Hydropower Outlook](https://www.hydropower.org/publications/2025-world-hydropower-outlook) International Hydropower Association, 2025 2. [Emerging Technologies Review: Pumped Storage Hydropower (PNNL-34458)](https://www.pnnl.gov/main/publications/external/technical_reports/PNNL-34458.pdf) Pacific Northwest National Laboratory, 2023 ## Other sections - [Summary](https://www.materialinsights.org/energy/e_pumped_hydro/index.md) - [Overview](https://www.materialinsights.org/energy/e_pumped_hydro/overview/index.md) - [Correlation](https://www.materialinsights.org/energy/e_pumped_hydro/correlation/index.md) - [Engineering and performance](https://www.materialinsights.org/energy/e_pumped_hydro/sg-eng/index.md) - [Economics](https://www.materialinsights.org/energy/e_pumped_hydro/sg-econ/index.md) - [Impact and additionality](https://www.materialinsights.org/energy/e_pumped_hydro/sg-impact/index.md) - [What to track](https://www.materialinsights.org/energy/e_pumped_hydro/tracking/index.md) - [Relationships](https://www.materialinsights.org/energy/e_pumped_hydro/links/index.md)