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Pumped Storage at Sea – A New Form of Energy Efficiency?

image credit: Image courtesy Fraunhofer Institute

Fraunhofer Institute proposes storing energy in spheres on the seabed

Energy storage is increasingly emerging as a complement to renewable energy. The difficulty is that there are limited ways of storing electricity: banks of batteries have a lot of issues. Hydroelectric dams are great, but they can only be build in certain locations. Pumped storage is expensive, but a good solution, unfortunately the complexities of finding the right place to build them is a constraint. See my earlier article here.

The renowned German Fraunhofer Institute based in Kassel is developing an ingenious system to use the concrete spheres on the seabed to store energy, particularly when paired with offshore wind turbines (or possibly tidal turbines in the future). Electricity generated will be used to pump air into the spheres, then when generation is needed, seawater will be let in to turn turbines and deliver power.

The advantage is that you can put these anywhere useful off the coast – you don't have to rely on convenient mountains, as in conventional pumped storage. Ideally they would be adjacent to an offshore wind farm, to store excess electricity.

Fraunhofer call this StEnSea - Storing Energy at Sea. The proposal envisages spheres with a diameter of 30m (or 100 ft) would be located at a depth of 700m (or 382 fathoms), giving a nominal storage capacity of 27MWh. When the actual internal volume and operating efficiency of the system are taken into account, this configuration is expected to yield 18.3MWh storage capacity with a peak power output of 5MW.

A four week test of the technology using a 1:10 scale model was completed in 2016 operating at a depth of 100m (328 ft) in Lake Constance near the Swiss/German border. The economic analysis showed that, when located within an energy park containing over 100 units, at an optimum location the capital cost per sphere would be approximately €8m ($8.8m). The storage cost would be around six or seven euro cents per kWh, making this system more economical than many conventional pumped storage systems on land.

While this is a “blue sky” technology, storage will be needed in many forms in the future and so this should not be dismissed, as from the test it seems to work as designed.

Julian Jackson's picture

Thank Julian for the Post!

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Matt Chester's picture
Matt Chester on Jun 25, 2020 4:17 pm GMT

I admittedly use the talking points that most of the tech needed for the energy transition is already there, it's just about the markets and the policies to get them in place-- but something like this does go to show how much innovative thinking there still is out there! Reminds me of the Commissioner of the U.S. Patent Office who said in 1899 that everything that could be invented already had been :)

Julian Jackson's picture
Julian Jackson on Jun 25, 2020 4:30 pm GMT



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