Sizable Energy, a clean-tech energy-storage developer specializing in offshore pumped hydro energy storage, raised $8 million, led by Playground Global, with participation from Exa Ventures, Verve Ventures, Satgana, EDEN/IAG, and Unruly Capital, which led a previous round.
The newly raised capital will accelerate the development and deployment of this offshore technology. The company has begun preparations for its subsequent sea trial off the coast of Reggio Calabria, Italy.
The company is targeting the long-duration energy storage sector through its offshore pumped hydro storage technology. While conventional onshore pumped hydro systems are well-established, they often face challenges such as lengthy development timelines, high scalability costs, and geographical or environmental constraints.
Sizable Energy’s approach differs by utilizing an offshore system, which is claimed to be modular, cost-effective, and ready to deploy. The system stores energy by pumping saturated sea salt brine (heavier than seawater) between two reservoirs, one positioned on the seabed and another floating on the ocean surface.
The system features a connecting pipe and reversible pump-turbines that move the brine between the two reservoirs, facilitating energy storage and release. The technology leverages materials that can be manufactured, assembled, and deployed at ocean depths of 500 meters or more, utilizing existing maritime infrastructure.
This pilot project aims to validate all major floating components and demonstrate full-scale assembly and deployment procedures for a multi-MWh demonstration plant in the Mediterranean Sea. Sizable Energy plans to initiate commercial project development by 2026.
“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,” said Bruce Leak, general partner at Playground Global and board member of Sizable Energy.
According to Mercom’s 1H and Q2 2025 Funding and M&A for Energy Storage report, VC funding in the sector totaled $1.7 billion across 36 deals, down 29% compared to the previous year. Energy Storage Downstream companies received the most VC funding in 1H 2025. Other top-funded categories included Materials and Components, Energy Storage Systems, Sodium-based batteries, and Thermal Energy Storage companies.
