Sizable Energy
Sizable Energy develops offshore pumped-hydro systems for long-duration grid energy storage.
Sizable Energy is a Milan-based company developing gigawatt-scale ocean energy storage. Its system stores electricity by moving saturated brine between seabed and floating reservoirs, using gravity and ocean depth as the storage medium.
The company raised an $8 million round led by Playground Global in October 2025. It is using the capital to advance offshore pumped hydro demonstrations, including tests at MARIN and sea trials connected to a planned Mediterranean demonstration plant.
Sizable Energy addresses the long-duration energy storage market, where power grids need storage that can bridge renewable-energy intermittency over longer periods than conventional short-duration batteries. The company cites a need for up to 120 terawatt-hours of long-duration storage by 2040.
Its market thesis is that onshore pumped hydro remains reliable but is constrained by geography, development timelines, and environmental concerns. Sizable Energy argues that offshore pumped hydro can expand deployment potential by using ocean depth and maritime infrastructure.
Sizable Energy positions its system around the mature mechanics of pumped hydro while moving the storage architecture offshore. Its design uses ocean depth, gravity, saturated brine, and reversible pump-turbines to pursue long-duration storage without consuming land.
The company says the product is modular, scalable, and compatible with existing maritime infrastructure. Its first-party materials also highlight high round-trip efficiency, short deployment cycles, global siting opportunities, and potential coupling with floating wind and solar generation.
Sizable Energy develops offshore pumped-hydro systems for long-duration grid energy storage.