Sizable Energy Secures $8M for Ocean Energy Storage Launch

Sizable Energy Secures $8 Million to Accelerate Ocean-Based Long-Duration Energy Storage Deployment

Sizable Energy, a trailblazer in long-duration ocean energy storage, announced it has raised $8 million in new funding to accelerate the commercial rollout of its innovative offshore pumped hydro system. The round was led by Playground Global, with participation from Exa Ventures, Verve Ventures, Satgana, EDEN/IAG, and Unruly Capital, which led a previous round.

With recent tests completed at the Maritime Research Institute Netherlands (MARIN) and new sea trials underway in Reggio Calabria, Italy, Sizable Energy is advancing toward full-scale deployment of its system designed to provide low-cost, gigawatt-scale energy storage by leveraging the power of ocean gravity.

“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.”

Meeting the Global Need for Long-Duration Energy Storage

As the global energy transition accelerates, one major challenge remains — how to store renewable energy efficiently and affordably for long periods. The world is expected to need up to 120 terawatt-hours of long-duration energy storage (LDES) by 2040, nearly ten times the current global capacity.

Traditional onshore pumped hydro remains the most common form of energy storage, but it faces major constraints. Projects are geographically limited, expensive to build, and often encounter environmental and regulatory hurdles. As a result, new scalable solutions are urgently required to stabilize renewable-heavy power grids and ensure reliable energy supply.

Sizable Energy’s approach — offshore pumped hydro using ocean gravity — offers a breakthrough alternative. Its system moves energy storage offshore, freeing it from land and environmental limitations while providing a modular, fast-to-deploy, and cost-competitive platform for global energy markets.

How It Works: A New Gravity Battery Beneath the Sea

At the core of Sizable Energy’s innovation is its patented offshore pumped hydro system — an elegant blend of physics and marine engineering. The system stores energy by pumping a dense brine solution (heavier than seawater) from a deep-sea reservoir on the ocean floor up to a floating surface tank.

When energy is needed, the brine flows back down through a turbine system, generating electricity. This gravity-based cycle mimics traditional pumped hydro but harnesses the vast natural depth of the ocean to achieve significant storage potential.

Key advantages of Sizable Energy’s system include:

  • Lowest Levelized Cost of Storage (LCOS): Even when compared to the most optimistic projections for lithium-ion battery costs, Sizable’s ocean-based system delivers cheaper long-duration storage.
  • Modular Scalability: The platform can be deployed in modular units ranging from one to hundreds of gigawatt-hours, adaptable to local energy demands and grid needs.
  • Existing Maritime Infrastructure: Components are built from readily available materials and can be manufactured, assembled, and installed using existing offshore and shipyard capabilities.
  • Minimal Visual and Environmental Impact: The system operates invisible from the shore, with no significant alteration to coastal landscapes or ecosystems.

“As a society, we’ve proven that wind and solar can deliver the cheapest electrons,” said Bruce Leak, General Partner at Playground Global and board member of Sizable Energy. “Now we urgently need long-duration storage that can be economically deployed at massive scale. Ocean depth is a practically unlimited resource, and Sizable Energy is leveraging it to deliver energy storage at a fraction of the cost of batteries.”

From Lab to Ocean: Rigorous Testing and Real-World Validation

Sizable Energy’s system has undergone extensive validation through both wave basin laboratory experiments and real-world ocean trials.

In September 2025, the company completed a major series of tests at MARIN, one of the world’s leading maritime research institutes. These trials demonstrated that Sizable’s system can operate reliably in harsh marine conditions, confirming its structural resilience and operational stability — a critical milestone for any ocean-based energy technology.

Building on that success, the company has begun a new sea trial in Reggio Calabria, Italy, where it is deploying full-scale floating components to test assembly procedures, installation logistics, and performance under live ocean conditions. This project will validate the complete operational cycle of the system, preparing the company for a multi-megawatt-hour demonstration plant planned in the Mediterranean Sea.

These pilots will provide vital data on system efficiency, installation economics, and operational durability — paving the way for commercial project development in 2026 across multiple global locations.

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