Ocean energy storage innovator Sizable Energy has raised $8 million in funding to accelerate the development and deployment of its offshore long-duration energy storage (LDES) systems.
The round was led by Playground Global, with participation from Verve Ventures and Unruly Capital.
Turning the Ocean Into a Giant Battery
Founded by engineers from the nuclear, mechanical, energy, and maritime sectors, Sizable Energy is reimagining pumped-hydro storage for the ocean. Its patented system stores energy by pumping dense, saturated sea-salt brine from the seabed to a surface reservoir, using natural ocean depth to generate gigawatt-scale storage capacity.
The approach adapts proven hydropower principles to the offshore environment — offering modular, scalable, and cost-effective storage that sidesteps the geographic and environmental constraints of onshore installations.
“We’re bringing the world’s most trusted energy storage technology offshore,” said a Sizable Energy spokesperson. “Our system delivers reliable, large-scale energy storage without consuming land, disturbing habitats, or depending on rare materials.”
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Meeting Global Demand for Long-Duration Storage
The International Energy Agency projects global LDES demand to reach 120 TWh by 2040, nearly ten times current capacity. While onshore pumped hydro remains the gold standard, it faces slow permitting, land limitations, and high upfront costs.
Sizable Energy’s offshore system overcomes those barriers. It can be deployed at depths beyond 500 meters, built using standardized materials and existing maritime infrastructure, and remains invisible from shore. Each installation can scale from a few to hundreds of gigawatt-hours, targeting a low levelized cost of storage (LCOS).
Proven in Harsh Ocean Conditions
The company’s technology has undergone extensive wave-basin and open-ocean testing. Recent trials at MARIN (the Maritime Research Institute Netherlands) confirmed the system’s ability to operate reliably under extreme offshore conditions — a major milestone ahead of a megawatt-scale pilot.
An upcoming sea trial off the coast of Reggio Calabria, Italy, will test the floating assembly, deployment process, and operational performance. The results will inform the design of Sizable’s planned multi-MWh demonstration plant in the Mediterranean Sea.
Funding the Next Phase
The $8 million infusion will fund engineering development, pilot deployment, and global partnerships as Sizable Energy scales toward commercial readiness.
“Sizable’s approach combines physics-proven energy storage with the scalability of offshore engineering,” said a representative from Playground Global. “It’s a powerful step toward a resilient, decarbonized energy grid.”
About Sizable Energy
Sizable Energy is developing offshore long-duration energy storage (LDES) based on its patented pumped-brine system. By leveraging ocean depth and the gravitational potential of dense sea-salt brine, its modular technology provides secure, sustainable, and cost-effective energy storage at gigawatt scale. Headquartered in Italy, Sizable Energy aims to make offshore pumped hydro a cornerstone of the global clean energy transition.
