Sizable Energy, an innovator in ocean-based long-duration energy storage (LDES), announced it has raised $8 million in new funding to accelerate the commercial deployment of its offshore pumped hydro system. The investment round was led by Playground Global, with participation from Exa Ventures, Verve Ventures, Satgana, EDEN/IAG, and Unruly Capital, which led a previous round.
The company’s ocean-based storage solution is designed to deliver low-cost, grid-scale energy storage by harnessing the power of gravity beneath the sea. After completing rigorous tests at the Maritime Research Institute Netherlands (MARIN) and launching new sea trials off the coast of Reggio Calabria, Italy, Sizable Energy is advancing toward its first megawatt-scale demonstration plant in the Mediterranean Sea.
Global energy experts estimate that the world will require up to 120 terawatt-hours of long-duration energy storage by 2040—ten times current capacity. Traditional onshore pumped hydro remains the dominant form of large-scale storage, but it faces geographic, financial, and environmental constraints. Sizable Energy’s offshore system offers a faster, more modular, and cost-effective alternative, positioning it as a potential leader in next-generation LDES solutions.
Sizable’s patented approach, known as the New Gravity Battery, stores energy by pumping saturated brine—denser than seawater—from the seabed to a surface reservoir. This use of ocean depth as a natural pressure differential allows for efficient, large-scale energy storage. The system operates invisibly from shore, combining readily available materials with existing maritime infrastructure to reduce costs and accelerate deployment.
The company reports that its design delivers the lowest Levelized Cost of Storage (LCOS) among long-duration solutions, outperforming even the most optimistic projections for lithium-ion batteries. Each system can be scaled from a few megawatt-hours to several gigawatt-hours, depending on depth and reservoir configuration.
Following successful MARIN tests, which confirmed operational resilience in challenging marine environments, Sizable Energy’s Italian sea trial will validate the system’s floating components and deployment methods. The data will inform the construction of a full-scale multi-megawatt demonstration plant, with commercial-scale development slated for 2026 in partnership with energy providers, governments, and maritime manufacturers.
Founded by a multidisciplinary team of nuclear, mechanical, and maritime engineers, Sizable Energy combines the proven mechanics of pumped hydro with innovative marine design to create a scalable and sustainable energy storage platform. The company’s long-term goal is to make the power grid more stable, resilient, and cost-effective, which is essential for achieving global decarbonization targets.
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.”
Dr. Manuele Aufiero, CEO and 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, and Board Member, Sizable Energy
