Sizable Energy has raised $8m in new funding to accelerate the commercial rollout of its ocean-based long-duration energy storage system. The investment round was led by Playground Global, with participation from Exa Ventures, Verve Ventures, Satgana, EDEN/IAG, and Unruly Capital.
The company recently completed successful testing of its offshore pumped storage technology at the Maritime Research Institute Netherlands (MARIN) and has begun new sea trials near Reggio Calabria, Italy. The system is designed to provide large-scale, low-cost energy storage using gravity and the depth of the ocean.
“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.”
Sizable Energy’s approach adapts the principles of pumped storage to the ocean environment. The company’s patented design stores energy by pumping saturated sea salt brine from the seabed to a surface reservoir, taking advantage of ocean depth to create efficient energy storage.
The system is intended to be modular, scalable, and invisible from shore, capable of being deployed at depths of 500m or more using existing maritime infrastructure. The company says its technology could offer the lowest Levelized Cost of Storage (LCOS) among long-duration energy storage (LDES) options, even when compared with projected cost reductions for lithium-ion batteries.
“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 and board member of Sizable Energy. “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.”
Sizable Energy has tested its system in both laboratory and real-world ocean conditions, demonstrating that it can withstand marine environments and operate reliably. Following the MARIN tests, the company is moving ahead with a megawatt-scale pilot project off the coast of Italy. The Reggio Calabria trial will validate floating components, full-scale assembly, and deployment processes in preparation for a multi-megawatt-hour demonstration plant in the Mediterranean.
Commercial project development is scheduled to begin in 2026, with sites planned in partnership with local manufacturers, governments, and energy providers.
According to industry estimates cited by the company, the world will require up to 120TWh of long-duration energy storage by 2040 – roughly ten times current capacity – highlighting the growing need for scalable, cost-effective storage solutions like Sizable Energy’s ocean-based system.
