https://www.pv-magazine.com/2025/03/14/unlimited-energy-storage-in-europe/
Most studies of European 100% renewable energy overlook pumped-hydro energy storage (PHES), for the following, incorrect, reasons: there are few PHES sites; more dams on rivers are required; large areas of land are flooded; large amounts of water are required; there is a heavy environmental cost; and the capital cost of PHES is high. All these perceptions are wrong.
The global pumped hydro atlas lists 820,000 sites in the size range of 2-5000 GWh with a combined storage of 86 million Gigawatt-hours. This is equivalent to 2 trillion electric vehicle batteries.
Europe has over 6000 premium PHES sites with a combined storage of about 1100 terawatt hours, which is about 40 times more storage than required for a fully electrified and decarbonized Europe. There are also many lower-quality sites (classes A-E).