Underwater Energy Storage Could Capture Excess Renewables

3 min Read

A significant amount of energy from wind and solar goes to waste due to insufficient storage options. Pumped storage power plants often face local resistance as solutions. The Fraunhofer Institute for Energy Economics and Energy System Technology (IEE) has now developed a new approach: spherical energy storage systems on the seabed.

First, the good news: The share of renewable energies in Germany’s electricity generation reached a new record of 62.7 percent in 2024, according to the German Environment Agency. On some days, there is so much wind and sunshine that the energy goes to waste, as the power grid would otherwise be overloaded.

On peak days like these, energy suppliers in Germany are sometimes forced to export expensive electricity to Austria, where there are sufficient pumped storage and other storage power plants available. Domestic battery storage systems and hydrogen as a potential large-scale energy carrier, however, are not yet advanced enough.

Pumped Storage Not Uncontroversial

Pumped storage facilities currently account for the majority of storage capacities in Germany, with 30 power plants and a net total capacity of nearly 6,500 megawatts, according to Speicherbranche.de. The largest of these, with a net capacity exceeding 900 megawatts, are located in Thuringia, Saxony, and Baden-Württemberg.

Since 1958, Bavaria’s largest pumped storage power plant has stood in Happurg, north of Nuremberg. The facility, which was shut down for years due to a leak, is now set to be reactivated by the energy conglomerate Uniper at a construction cost of approximately 250 million euros. However, residents and environmentalists are already warning against excessive interference with nature and are rallying against the project.

Therefore, the new approach developed by the Fraunhofer Institute for Energy Economics and Energy System Technology IEE, in collaboration with partners, and currently being tested off the coast of California, might offer a more elegant solution to the problem of storing renewable energies in sufficient quantities.

Pumped storage spheres could overcome resistance

The “StEnSea” project involves pumped storage spheres made of concrete using additive manufacturing (3D printing). These spheres fill with water from the surrounding pressure at the seabed, which is then pumped out using excess energy. When power is needed again, seawater is allowed to flow back into the spheres, generating energy through turbines. Researchers from the Fraunhofer IEE, along with partners, have already successfully tested the technology developed by Prof. Dr. Horst Schmidt-Böcking and Dr. Gerhard Luther in 2011 in a field trial in Lake Constance. Spheres with a diameter of three meters were used in this trial. The concrete spheres deployed off the US coast at depths of 500 to 600 meters and anchored to the seabed have a diameter of nine meters and weigh 400 tons each, according to the Fraunhofer IEE. The advantage of the seabed off California is that it drops off quite steeply.

Germany’s coasts too shallow

The German North Sea coast, with depths of 15 to 30 meters, is unsuitable. According to the Fraunhofer Institute for Energy Economics and Energy System Technology (IEE), ideal water depths are between 600 and 800 meters. The institute names the coasts off Norway, Portugal, west and east of the USA, Brazil, and Japan as possible locations.

The StEnSEA project off the famous Long Beach near Los Angeles involves the startup Sperra, which provides the 3D concrete printing, and Pfleuger Industries, a German-owned company headquartered in Miami that is one of the leading manufacturers of underwater pumps.

The researchers at the Fraunhofer Institute estimate a global potential of 817,000 gigawatt hours for their technology. At the ten best European locations alone, this should amount to 166,000 gigawatt hours, which is many times the capacity of Germany’s onshore storage power plants.

Source of title image: Unsplash / American Jael

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“At the ten best European locations alone, this should amount to 166,000 gigawatt hours, which is many times the capacity of Germany’s onshore storage power plants.”