Harnessing the Ocean to Store Renewable Energy
▼ Summary
– Pumped-storage hydropower facilities function as massive batteries by storing 8,500 gigawatt-hours of electricity globally, using reservoirs that drain and refill to generate power.
– The technology is crucial for supporting intermittent renewable energy sources like wind and solar but is limited by the scarcity of suitable land-based locations.
– Sizable Energy, co-founded by Manuele Aufiero, is developing an offshore pumped hydro system using two flexible reservoirs connected by a tube and turbines to overcome land limitations.
– The system operates by pumping dense, salty water to an upper reservoir during low-cost electricity periods and releasing it to spin turbines for power generation when needed.
– Sizable aims to mass-produce these systems for deployment by 2026, targeting energy storage at one-tenth the cost of grid-scale batteries and enhancing grid resilience with long-duration storage.
Childhood memories of a unique reservoir in northern Italy sparked an idea that could reshape renewable energy storage. For Manuele Aufiero, family hikes revealed a system where water levels rose and fell with electricity demand, a century-old method called pumped-storage hydropower. These facilities function as massive batteries, storing an impressive 8,500 gigawatt-hours of electricity worldwide. Their ability to provide power for extended periods makes them increasingly vital as wind and solar energy, which are intermittent by nature, become more common. However, a significant limitation exists: suitable land-based locations for such reservoirs are scarce.
Aufiero’s deep appreciation for pumped hydro is matched by his recognition of its constraints. “I’m in love with pumped hydro,” he admitted, “It’s just not enough to keep up with renewables.” This realization drove him to find a solution by relocating the entire concept to the ocean. He co-founded the startup Sizable Energy to bring this vision to life. The company recently secured $8 million in a funding round led by Playground Global, with additional investment from several other venture firms.
The design of Sizable’s offshore power plant resembles an hourglass. It involves two sealed, flexible reservoirs, one floating on the surface and another resting on the seabed, connected by a plastic tube housing turbines. During periods of low-cost electricity, the turbines pump super-salty water from the lower reservoir to the upper one. When the grid requires power, a valve opens. Because the water in the upper reservoir is denser due to its high salt content, it flows downward with force, spinning the turbines to generate electricity as it returns to the lower reservoir.
Aufiero simplifies the concept, explaining they are essentially lifting blocks of salt, but in a dissolved, pumpable form for practicality. The core innovation lies in moving this technology offshore, which enables mass production. Unlike land-based projects that require custom-designed concrete dams for each unique site, the offshore system is standardized. This approach allows for streamlined manufacturing where every component is identical, regardless of the final installation location.
Sizable has already conducted tests using small-scale models in wave tanks and off the Italian coast. The company is now deploying a pilot of the floating components as a step toward a full demonstration plant. Their ambitious timeline aims for several commercial projects worldwide by 2026. At full scale, each turbine is projected to generate 6 to 7 megawatts of electricity, with one turbine for every 100 meters of pipe. Deeper ocean sites offer greater storage potential, and commercial installations would feature multiple reservoirs. The company targets an energy storage cost of approximately €20 per kilowatt-hour, roughly one-tenth the cost of current grid-scale batteries.
This technology is a natural partner for offshore wind farms, as sharing a single electrical connection to the shore can significantly reduce expenses. However, Aufiero notes that Sizable’s reservoirs can connect to any grid near waters with depths of at least 500 meters. He emphasizes the critical need for long duration energy storage, not only for integrating renewables but also for enhancing overall grid resilience. “There is no way we can keep up with that with traditional pumped hydro or batteries,” he stated. “We need something new.”
(Source: TechCrunch)
