Sizable Energy is commercializing an offshore version of pumped-storage hydropower that places two sealed, flexible reservoirs—one floating on the surface and one fixed on the seabed—connected by a tube housing reversible turbines. Cheap electricity drives the turbines as pumps, moving dense brine to the upper reservoir; when power is needed, the heavier saltwater falls, spinning the turbines to generate electricity. Each 100-metre segment can support a 6–7 MW generator, and deeper water sites offer greater storage capacity. By manufacturing identical modules for deployment in seas at least 500 m deep, the company expects to reach costs of roughly €20 per kilowatt-hour, about one-tenth the cost of grid-scale batteries. The technology pairs naturally with offshore wind farms that can share transmission infrastructure but can also connect to any coastal grid. Sizable has validated small-scale models in wave tanks and off Reggio Calabria, Italy, and is now installing a floating pilot ahead of a full demonstration plant. Commercial projects are targeted for 2026 at multiple global sites. The company has raised $8 million to fund these development milestones.

Total raised

$8M

Funding rounds

1

Latest round

Equity

Latest activity

Oct 2025