Underwater revolution for the energy transition
Imagine huge hollow concrete spheres lying at the bottom of lakes or oceans, each the size of a house, manufactured in a CO2-neutral way and waiting to store surplus electricity - and that is precisely the principle behind spherical energy storage systems. They are considered one of the most exciting innovations for the energy transition and could fundamentally change our electricity grid1 Fraunhofer IEE and partners test spherical storage tanks on the seabed 🌐 https://www.iee.fraunhofer.de/de/presse-infothek/Presse-Medien/2024/test-kugelspeicher-auf-meeresgrund-in-kalifornien.html 2 Ball pump accumulator - Wikipedia 🌐 https://de.wikipedia.org/wiki/Kugelpumpspeicher .
How does a spherical energy storage system work?
The principle is ingeniously simple and uses the laws of nature to our advantage:
- Storage: If there is a surplus in the electricity grid - for example when there is strong wind or a lot of sun - this electricity is used to operate a pump that transports the water out of the hollow concrete sphere. This creates a negative pressure inside, almost a vacuum.
- Release: When electricity is required, a valve opens. The surrounding water flows back into the sphere at enormous pressure and drives a turbine, which in turn generates electricity and feeds it into the grid.
The system therefore works like a reverse pumped-storage power plant - but on the seabed or lake bed, not in the mountains3 Storing energy with concrete spheres - ingenieur.de 🌐 https://www.ingenieur.de/technik/fachbereiche/energie/mit-betonkugeln-energie-speichern/ 4 Test of a spherical storage tank on the seabed - GFA News 🌐 https://www.gfa-news.de/news/energiespeicherung-test-eines-kugelspeichers-auf-dem-meeresgrund . A simple principle in itself. As is so often the case, someone just has to do it.
Image source: Fraunhofer IEE
The technology in detail
- Sphere size & depth: Prototypes have a diameter of 3 to 30 metres. The deeper the sphere is (ideally 600 to 800 metres), the higher the water pressure and thus the storage capacity.
- Material: The balls are made of solid concrete, which gives them the necessary stability to withstand the enormous water pressure.
- Pump & turbine: A pump turbine is installed in the upper section of the sphere, which works both as a pump (when charging) and as a turbine (when discharging).
- Connection: An underwater cable connects the sphere to the power grid on land or directly to offshore wind farms.
Advantages over conventional storage systems
- Huge potential: According to the Fraunhofer IEE, spherical storage systems could store up to 817,000 gigawatt hours of energy worldwide - that is many times the current capacity of all German pumped storage plants5 Concrete sphere with turbine: pumped storage power plant on the seabed - energiezukunft.eu 🌐 https://www.energiezukunft.eu/erneuerbare-energien/stromnetze-speicher/pumpspeicherkraftwerk-am-meeresgrund 6 German 9-metre sphere to solve energy transition problem - Focus.de 🌐 https://www.focus.de/earth/analyse/unterwasser-batterien-diese-deutsche-neun-meter-kugel-soll-das-groesste-problem-der-energiewende-loesen_id_260455552.html .
- Low costs: The storage costs are around 4.6 cents per kilowatt hour.
- Longevity: The service life of the concrete sphere is 50 to 60 years, the pump turbine and generator only need to be replaced every 20 years.
- Sustainability: No rare earths are required and the environmental impact is lower than with batteries or land-based pumped storage plants.
Challenges and limits
- Choice of location: Sea or lake beds with sufficient depth and as level a surface as possible are ideal. Suitable locations can be found off Norway, Portugal, Japan or the USA, for example, but also in flooded open-cast mines or deep lakes.
- Efficiency: With an efficiency of 75-80%, the system is slightly below classic pumped storage power plants, but significantly above many battery technologies.
- Construction & maintenance: The production of the giant concrete spheres is energy-intensive, but the technology is constantly being further developed, e.g. with 3D printing processes.
Image source: Fraunhofer IEE
Pilot projects and outlook
The first practical test took place in Lake Constance in 2016: A three-metre sphere was sunk at a depth of 100 metres and successfully operated. The next big step is a pilot project off the coast of California with a nine-metre sphere at a depth of 500 to 600 metres. The aim is to test and further develop the technology on an industrial scale7 Concrete spheres under water as electricity storage? t3n.de 🌐 https://t3n.de/news/betonkugeln-unter-wasser-stromspeicher-batterien-besser-1656524/ 8 Can electricity be stored in concrete? MDR.de 🌐 https://www.mdr.de/nachrichten/thueringen/strom-speicher-beton-redakteur-100.html .
Spherical energy storage as a game changer?
Spherical energy storage tanks are a fascinating example of innovative engineering. They utilise the natural conditions of depth and water pressure to store energy efficiently and sustainably. With their huge potential, they could play a key role in the stability of renewable power grids - and may soon be supplying our everyday lives with clean electricity as "invisible batteries" on the seabed.
All information and technical details have been carefully researched and documented with sources in shortcode format. For further information, we recommend taking a look at the linked original sources and the following documentary on YouTube: Energy storage: New technology for the energy transition | KlimaZeit9 Energy storage: New technology for the energy transition | KlimaZeit 🌐 https://youtu.be/B0LSrUOFXjY
