Underwater power plants on the seabed
Feldversuch mit einer Drei-Meter-Kugel im Bodensee.
With the StEnSea project, the Fraunhofer Institute IEE has developed an innovative technology that transfers the principle of pumped-storage power plants to the seabed. Following successful tests in Lake Constance, a test run off the Californian coast at a depth of 500 metres will follow. A milestone for cost-efficient energy storage.
Pumped storage power plants are a proven method of storing energy, but have their limits on land. The StEnSea project transfers this principle to the seabed, where space and conditions are ideal for this technology. The prototype consists of a hollow concrete sphere that stores or generates electricity through water inflow and outflow.
Field test and mode of operation
A three-metre sphere was successfully tested in Lake Constance. Now a 400-tonne concrete sphere with a diameter of nine metres is to be anchored off Long Beach, California. The sphere is pumped empty to store energy and generates electricity by returning water to drive a pump turbine.
The prototype has an output of 0.5 MW and a capacity of 0.4 MWh. The Fraunhofer team plans to scale up the system to spheres with a diameter of 30 metres, which can achieve an output of 30 MW and a capacity of 120 MWh.
Advantages and potential applications
Water depths of 600 to 800 metres are ideal for this storage technology. The pressure and wall thickness allow for cost-efficient constructions. There are possible locations worldwide, for example off Norway, Portugal or the US coast. The technology is also suitable for deep lakes or flooded open-cast mines.
The global storage potential is estimated at 817,000 GWh, which is significantly higher than the capacity of conventional pumped storage power plants. Applications range from arbitrage transactions to the stabilisation of power grids through control reserve.
Cost-effectiveness and scaling
With storage costs of around 4.6 cents per kilowatt hour and a service life of the concrete sphere of up to 60 years, the technology is cost-effective. The efficiency per storage cycle is 75 to 80 per cent. A pilot park with six spheres could achieve 520 storage cycles per year.
Prospects for the energy transition
Bernhard Ernst, project manager at the Fraunhofer IEE, emphasises the importance of the StEnSea technology: “The global energy transition is increasing the need for storage enormously. Our underwater spherical storage systems are a cost-effective solution for short to medium storage periods.”
The StEnSea spherical storage tanks offer a pioneering technology for energy storage. With the test run off the Californian coast, the Fraunhofer team is taking an important step towards scaling up and commercialisation. The technology has the potential to revolutionise energy storage worldwide in the long term.