The German experiment with giant balls that the U.S. is testing to store excess electricity

To store electricity that would otherwise go unused, you first have to generate a significant amount of it - ideally from sustainable sources. In this case, ever-larger wind turbines could be part of the solution, with the biggest yet recently built in Europe. In that context, a team of German researchers has come up with an answer to the energy supply challenge.

Giant spheres on the ocean floor

The Fraunhofer Institute for Energy Economics and Energy System Technology (Fraunhofer IEE) has developed spherical energy storage systems. The concept revolves around a series of hollow spheres resting hundreds of meters beneath the ocean’s surface. Each one features its own independent electrical connection, along with a valve and an integrated turbine. When the “battery” is depleted, renewable electricity from the grid is used to pump water out of the sphere, effectively charging it.

When electricity is needed, the process works in reverse: the valve is opened and water rushes back in under pressure, driving the turbine and sending power back into the grid. According to projections from the scientists involved, these devices could have a lifespan of 50 to 60 years and weigh roughly 400 tons. While further testing is still required, the United States is already experimenting with the concept, with plans for multiple spheres to be deployed off the California coast by 2026 at depths of around 500 meters. Each unit has an energy capacity of about 0.4 megawatt-hours.

Global potential

Where these spheres are deployed will largely determine their future impact. Traditional energy storage facilities often carry a significant environmental footprint, but placing them on the ocean floor offers several advantages. Noting that the expansion potential for conventional pumped-storage systems is “severely limited”, Dr. Bernhard Ernst of Fraunhofer IEE declares: “Therefore, we are transferring their functional principle to the seabed - the natural and ecological restrictions are far lower there. In addition, the acceptance of the citizens is likely to be significantly higher.”

Positioning the spheres deep underwater also creates ample room to optimize key factors like pressure, wall thickness, and overall weight, allowing the system to operate efficiently. Standard submersible motor pumps can be used as well. According to data from Fraunhofer researchers, these spheres could deliver up to 820 million kilowatt-hours of electricity per charge cycle - enough to power more than 200,000 large households annually.

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