How Giant Concrete Spheres on the Seafloor Could Store Renewable Energy

To avoid using large areas of land for building renewable energy storage facilities, the Fraunhofer Institute has been developing a bold yet feasible idea: using hollow concrete spheres submerged in the deep ocean to store energy.

The StEnSea Project: Storing Energy in the Sea

Since 2011, the StEnSea (Stored Energy in the Sea) project has explored how deep-sea pressure can harness energy for short- to medium-term storage. The concept involves sinking massive hollow concrete spheres into the seabed, hundreds of meters below the surface.

When empty, each sphere acts like a fully charged battery. Opening a valve allows seawater to rush in, spinning a turbine connected to a generator that feeds power into the grid. To recharge the system, electricity from the grid powers a pump that pushes the water back out, working against the external water pressure.

Each sphere measures about 9 meters (30 feet) in diameter, weighs 400 tons, and anchors at depths between 600 and 800 meters (1,970–2,625 feet), where conditions optimize its operation.

Next Steps: Full-Scale Prototype in California

Fraunhofer has already tested a smaller version in Lake Constance near the Rhine River in Europe. Now, the institute plans to deploy a full-size, 3D-printed prototype off the coast of Long Beach, California, by the end of 2026. The system will produce 0.5 megawatts of power and store 0.4 megawatt-hours of energy, supplying an average U.S. household for about two weeks.

Researchers aim to determine whether they can scale up the technology to support even larger spheres, with diameters of up to 30 meters (about 100 feet). Fraunhofer researchers estimate that StEnSea has a massive global energy storage potential of 817,000 gigawatt-hours — enough to supply every one of the approximately 75 million homes in Germany, France, and the UK combined for a year.

Estimated Costs and Economic Viability

Estimated storage costs are around $0.051 (or €0.046) per kilowatt-hour, with investment costs of $177 (€158) per kilowatt-hour of capacity. These figures are based on a six-sphere storage park with a total power output of 30 megawatts and 120 megawatt-hours of capacity.

According to the institute, this type of energy storage is especially suitable for grid stabilization services, such as frequency regulation and operating reserves.Grid operators and energy trading companies also use it for energy arbitrage — they buy electricity at low prices and sell it when prices rise.

StEnSea could compete with pumped hydro storage, offering a key advantage: it doesn’t take up any land space.Pumped hydro relies on two reservoirs at different elevations to function, whereas engineers can deploy StEnSea in many locations worldwide, offering immense scalability and flexibility.

The U.S. The Department of Energy invested $4 million in the project and plans to closely monitor the pilot scheduled for 2026 off the California coast.

Explore other unusual ways to generate and store energy — like turning falling rain into electricity or repurposing abandoned mines into massive underground batteries.

Read the original article on: New Atlas

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