Manuele Aufiero, co-founder of Sizable Energy, is taking his childhood fascination with pumped hydro to the sea. His Italian startup has raised $8 million in funding led by Playground Global to develop an offshore version of the century-old energy storage method.
Unlike traditional hydropower, which relies on mountain reservoirs, Sizable’s system uses two flexible, sealed reservoirs, one floating at the surface and one anchored to the seabed, connected by turbines. When electricity is cheap, the turbines pump super-salty water upward; when demand spikes, the heavier saltwater flows down, generating power.
By moving the concept offshore, Sizable aims to mass-produce identical systems anywhere with deep waters, drastically lowering costs. Each turbine can generate 6–7 MW, with energy storage costs projected at just $23 per kWh, one-tenth the price of grid-scale batteries.
The startup has already tested prototypes off Italy’s coast and plans commercial deployment by 2026, targeting partnerships with offshore wind farms to share power infrastructure.
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“Long-duration energy storage is essential for renewable integration,” Aufiero said. “We need new ideas, and the ocean is our next frontier.”
