In a groundbreaking advance for renewable energy, researchers from Norway and Germany have developed a pioneering underwater energy storage system that turns ocean pressure into a powerful asset.
This innovative solution promises a sustainable, scalable alternative to conventional batteries, especially for coastal and island communities that rely heavily on intermittent wind and solar power.
What Is Deep-Sea Energy Storage?
The concept, known as StEnSea (Stored Energy in the Sea), involves placing vast hollow concrete spheres on the seabed, typically at depths of 600 to 800 metres. These depths create immense water pressure. When there is surplus energy, such as during periods of high wind generation, electricity is used to pump water out of the spheres against this pressure. To release the stored energy, water is allowed to flow back in, turning turbines and generating electricity on demand.
This system mimics the principles of pumped-hydro storage but innovatively adapts them to the ocean floor.
Who’s Behind This Innovation?
This initiative is a collaborative effort involving world-class European research institutions and private industry:
Germany
- Fraunhofer IEE (Institute for Energy Economics and Energy System Technology): Originators of the StEnSea concept. They led early research and continue to oversee large-scale testing and international deployment.
- University of Stuttgart: Provided engineering design, simulation, and system modelling.
- Hochtief Solutions AG: Built the first working prototype, a 3-metre-diameter sphere tested in Lake Constance.
- Pleuger Industries: Specialises in subsea pump-turbine technology used in the system.
- Sperra: A start-up focused on 3D concrete printing, essential for fabricating subsea spheres.
Norway
- University of Bergen (UiB): Offers deep-sea engineering and oceanographic expertise through the Geophysical Institute and the Centre for Deep-Sea Innovation.
- NORCE, Western Norway University of Applied Sciences (HVL), and the Institute of Marine Research: All contribute via the SFI Smart Ocean research centre, supporting marine-based energy systems.
- Runde Environmental Centre: Provides test facilities with ideal seabed conditions at 700 metres depth.
Technical Performance at a Glance
|
Feature
|
Specification
|
|---|---|
| Ideal Operating Depth | 600 – 800 m |
| Pressure at Depth | 60 – 80 bar |
| Full-Scale Sphere Diameter | 28.6 m |
| Energy Storage Capacity | 18 – 31 MWh per unit |
| Power Output | 5 MW per sphere |
| Round-Trip Efficiency | 72 – 75% |
The project’s first prototype in Lake Constance (2016) validated the system at 100 metres depth. The next milestone: a 9-metre sphere (0.5 MW / 0.4 MWh capacity) to be deployed off the coast of California by 2026, supported by funding from both Germany’s BMWK and the US Department of Energy.
Why It Matters for the Future
The need for long-duration, sustainable energy storage is greater than ever. Unlike lithium-ion batteries, which degrade over time and rely on finite raw materials, StEnSea spheres are:
- Environmentally friendly: Concrete structures pose minimal ecological disruption.
- Cost-efficient and durable: With no chemical degradation and minimal maintenance needs.
- Scalable: Units can be modularly installed across global coastlines.
GIS-based studies by Fraunhofer IEE have shown vast potential for deployment along the coasts of Norway, Japan, Portugal, and the USA, where seabed conditions and pressure depth are optimal.
Key Challenges
GIS-based studies by Fraunhofer IEE have shown vast potential for deployment along the coasts of Norway, Japan, Portugal, and the USA, where seabed conditions and pressure depth are optimal.
- Infrastructure: Requires specialised ROVs (e.g. UiB’s Ægir 6000) for subsea construction and maintenance.
- Regulation: Needs robust marine permitting and environmental oversight.
- Capital cost: Upfront investment is significant, although long-term returns are promising.
A Game-Changer for Coastal Communities
For island nations and coastal regions striving for energy independence, deep-sea pumped-hydro could offer a game-changing solution. It complements renewables by storing excess energy during peaks and releasing it during lulls, ensuring grid stability and energy security.
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