Pumped Hydro (PHES)

Pumped hydro energy storage (PHES) stores energy by using excess electricity to pump water from a lower reservoir to a higher one. When electricity demand increases, the stored water is released through turbines to generate power. It is the most widely deployed form of large-scale energy storage, offering high efficiency, long lifespan, and the ability to provide multi-hour to multi-day storage. While highly reliable and mature, PHES is geographically limited by suitable topography and can have significant environmental and permitting challenges.

  • Policy alignment – Strongly supported in many national energy strategies for grid stability and renewable integration.
  • Government funding – Large infrastructure projects often rely on public investment or guarantees.
  • Permitting complexity – Requires extensive environmental and water-use approvals before construction.
  • Energy security – Enhances domestic storage capacity, reducing dependence on imported fuels during peak demand.
  • High capital investment – Dam construction, reservoirs, and turbines require large upfront funding.
  • Long service life – Facilities can operate for 50–100 years with proper maintenance.
  • Economies of scale – Large plants deliver low-cost storage per unit of energy for bulk applications.
  • Revenue flexibility – Can earn from energy arbitrage, capacity payments, and ancillary grid services.
  • Community impact – Can provide jobs and regional development, but may face opposition over land use and resettlement.
  • Recreational benefits – Reservoirs can be used for boating, fishing, and tourism.
  • Public awareness – Well-known and generally trusted as a proven technology.
  • Displacement concerns – Large projects may require relocation of residents or changes to local land use.
  • High round-trip efficiency – Typically 70–85% efficient over long lifespans.
  • Fast response – Can switch from standby to full output in minutes, supporting grid stability.
  • Site constraints – Requires suitable elevation differences and large water volumes.
  • Upgrades and modernization – Turbine and control system improvements can increase capacity and flexibility.
  • Water rights – Operation depends on legal access to sufficient water resources.
  • Environmental regulations – Must comply with habitat protection, fish migration, and ecosystem preservation laws.
  • Construction permitting – Large-scale civil works require detailed planning and safety approvals.
  • Liability provisions – Operators must manage dam safety risks and potential downstream flooding impacts.
  • Low operational emissions – No direct CO₂ emissions during operation.
  • Ecosystem alteration – Reservoirs can disrupt river flow, fish habitats, and surrounding ecosystems.
  • Land use footprint – Large areas may be flooded, impacting wildlife and agricultural land.
  • Water evaporation losses – Open reservoirs lose water through evaporation, especially in hot climates.