Sizable Energy, a company developing offshore pumped-hydro energy storage systems, announced it has raised $8 million in funding, led by Playground Global, in support of its mission to commercialize a gravity-based long-duration energy storage (LDES) solution.
The funding follows successful validation of the system in a wave basin at the Maritime Research Institute Netherlands (MARIN), and the company has begun deployment of a sea trial off the coast of Reggio Calabria, Italy. These milestones mark important steps toward a megawatt-scale demonstration plant and ultimately commercial deployment in 2026 across multiple global sites.
Sizable Energy’s patented offshore pumped-hydro system stores energy by pumping saturated sea-salt brine (denser than seawater) from the seabed into a surface reservoir, leveraging ocean depth to deliver modular, scalable storage from gigawatt-hour to hundreds of gigawatt-hour capacity. The company says this architecture offers the lowest levelised cost of storage (LCOS) even compared to optimistic future projections for lithium-ion batteries and can be deployed without major land-use constraints.
According to the company, the world may require up to 120 terawatt-hours of long-duration storage by 2040 — about ten times current capacity — and traditional on-shore pumped hydro systems are constrained by geography, environmental concerns and lengthy build times. The offshore solution is pitched as a faster, more flexible path to energy-storage scale-up.
KEY QUOTES:
“Without cost-effective long-duration storage, the grid cannot keep up, regardless of energy source. Our ocean-based system stores gigawatt-scale power affordably, making the grid more stable, resilient, and ready for the future. Our ocean-based system stores gigawatt-scale power affordably, making the grid more stable, resilient, and ready for the future.”
Dr. Manuele Aufiero, CEO & Co-Founder, Sizable Energy
“As a society, we’ve proven that wind and solar can deliver the cheapest electrons. Now we urgently need a long duration energy storage solution that can be economically deployed at massive scale. Ocean depth is a practically unlimited resource, and Sizable Energy is leveraging it to deliver long-duration energy storage at a fraction of the cost of batteries. Their gravity-based approach is the clear path to enabling energy abundance.”
Bruce Leak, General Partner, Playground Global & Board Member, Sizable Energy
