By Tina Casey | CleanTechnica | October 22, 2025
Pumped storage systems predate the renewable energy transition, but they are an ideal match for today’s utility-scale wind and solar farms. For all the improvements in battery-type energy storage systems and new long-duration storage systems, pumped hydro still accounts for about 95% of the bulk-quantity, long-duration energy storage capacity in the US.
Alternative pathways are beginning to emerge. A Texas startup, for example, is repurposing old oil wells for pumped storage. Other solutions involve deploying water pressure in the ocean.
The latest example to cross the CleanTechnica radar comes from the Italian startup Sizable Energy. “Sizable Energy’s patented offshore pumped hydro system stores energy by pumping saturated sea salt brine (heavier than seawater) from the seabed to a surface reservoir, leveraging the depth of the ocean for efficient energy storage,” Sizable explains.
