Sizable Energy, a pioneer in long-duration ocean energy storage, secured $8 million in funding led by Playground Global to accelerate commercial deployment of its offshore pumped hydro system. Following successful tests at MARIN and upcoming sea trials in Reggio Calabria, Italy, the company is advancing its gravity-based technology to deliver low-cost, scalable energy storage.
“Without cost-effective long-duration storage, the grid cannot keep up, regardless of energy source,” said Dr. Manuele Aufiero, CEO and Co-Founder of Sizable Energy. “Our ocean-based system stores gigawatt-scale power affordably, making the grid more stable, resilient, and ready for the future.”
The funding supports expansion of Sizable Energy’s offshore pumped hydro system, which stores energy by pumping dense sea salt brine from the seabed to a surface reservoir, using ocean depth for efficient storage.
Invisible from the shore, the system offers the lowest Levelized Cost of Storage (LCOS) for long-duration energy, is modular and scalable, and uses readily available materials deployable beyond 500 meters deep.
“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,” said Bruce Leak, General Partner at Playground Global. “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.”
Recent MARIN tests confirmed performance in marine environments, and new sea trials in Italy will validate floating components ahead of a multi-MWh demonstration plant in the Mediterranean.
Commercial development is planned for 2026, with partnerships involving local manufacturers, governments, and energy providers.
Additional investors include Exa Ventures, Verve Ventures, Satgana, EDEN/IAG, and Unruly Capital, which led a prior round.