Hydropower specialist Mike McWilliams has released a new report Global The Global Need for Underground Pumped Storage Hydro. The study examines the accelerating demand for long-duration energy storage (LDES) as Europe and the world move toward Net Zero, and outlines how Zero Terrain Underground Pumped Hydro Storage (UPHS) can address this challenge.
The report notes that global electricity storage capacity today is under 2,000 GWh, while fossil fuel reserves historically provided more than 1 million GWh of backup energy. More than 100,000 GWh of storage will be required by 2060 to ensure reliable and affordable power in a renewable-based system.
While battery storage plays a key role for short-duration balancing, long-duration solutions are essential to integrate variable renewables such as wind and solar. Traditional pumped hydro has supplied over 80% of storage worldwide but is limited to mountainous regions and often faces environmental constraints.
Zero Terrain Underground Pumped Hydro Storage (UPHS) provides a modular alternative. By creating reservoirs in underground caverns, the technology enables gigawatt-scale projects to be built almost anywhere, closer to demand centres and without relying on sensitive landscapes. The fully permitted Paldiski UPHS project in Estonia, designed for 500 MW of capacity and up to 30 hours of storage, demonstrates how the concept can be applied in practice. Beyond stabilising electricity supply, the geological infrastructure can also serve multiple uses, including water reserves, data centres, and secure facilities.
The author, Mike McWilliams, brings more than 45 years of international experience in hydropower planning and development. He advises the Centre for Economics and Business Research (Cebr), the World Bank, and renewable energy developers worldwide, and serves on the Zero Terrain Global Advisory Board.
The report concludes that only gigawatt-scale, modular, and deployable technologies across diverse locations will meet the storage needs of a Net Zero energy system. Zero Terrain Underground Pumped Hydro Storage is highlighted as a technology capable of providing the required long-duration storage and a broad range of essential grid services.
FULL REPORT AND EXECUTIVE SUMMARY
