Rigorous testing has confirmed that the offshore pumped-hydro system operates reliably in harsh ocean conditions, paving the way for a pilot project in the Mediterranean Sea.
Italy-based Sizable Energy, a developer of long-duration ocean energy storage, has raised $8 million in a round led by Playground Global, with participation from Verve Ventures and Unruly Capital.
Sizable Energy is building gigawatt-scale storage using an offshore pumped-hydro approach. Founded by engineers across nuclear, mechanical, energy, and maritime disciplines, the company aims to deliver long-duration energy storage (LDES) for a more reliable and cost-effective grid. Its patented system applies proven pumped-hydro principles to a marine architecture designed for modularity and scale, storing energy by pumping saturated sea-salt brine from the seabed to a surface reservoir and leveraging ocean depth for efficiency.
With the International Energy Agency estimating a need for up to 120 TWh of LDES by 2040, about ten times today’s capacity, Sizable targets and constraints are facing onshore pumped hydro (slow builds, geographic limits, environmental concerns) with an offshore solution that is modular, cost-effective, and designed for rapid deployment.
Invisible from shore, the system targets a low levelized cost of storage, scales from single-digit to hundreds of GWh, and uses readily available materials that can be manufactured and installed at depths of 500+ meters using existing maritime infrastructure.
The company has validated its core technology in wave-basin laboratories and open-ocean trials. Recent testing at MARIN indicated reliable operation in harsh ocean conditions, a key milestone ahead of a megawatt-scale pilot. A new sea trial off Reggio Calabria, Italy, will validate major floating components and the full assembly and deployment process, paving the way for a multi-MWh demonstration plant in the Mediterranean.
The new funding will accelerate the development and deployment of Sizable Energy’s offshore pumped-hydro system to deliver economical, reliable LDES.