New Renewable Power Storage Method
Tests have been completed in the German Bodensee with a 20 ton, 3 meter concrete hollow sphere, sunk to the bottom of the lake. When water flows into the sphere, electricity can be generated. Alternatively, wind power can be used to empty the sphere again and as such (virtually) load the battery again. Future dimensions are thought to be 20 meter or lager (4,200 m3 volume).
In March 2017 the research project StEnSea (Storing Energy at Sea) announced their successful completion of a four-week test of a pumped storage underwater reservoir. In this configuration a hollow sphere submerged in deep water acts as the lower reservoir while the upper reservoir is the enclosing body of water. When a reversible turbine integrated into the sphere uses surplus electricity to pump water out of the sphere the force of the pump must act on the entire column of water above the sphere, so the deeper the sphere is located, the more potential energy it can store and convert back to electricity by letting water back in via the turbine. As such the energy storage capacity of the submerged reservoir is not governed by the gravitational energy in the traditional sense, but rather by the vertical pressure variation.
Estimated storage cost at large scale operation: 1.6-2.0 eurocent/kWh.
Storage capacity hollow sphere with 30m diameter with a volume of 12,000 m³ and water depth of 700 meter: 20,000 kWh.
Norway would be a suitable location as it has trenches off the coast with water depths of up to 725m. More depth means higher pressure and more power storage capacity per m3 storage volume.
[spiegel.de] – Riesige Betonkugel speichert Energie
[wikipedia.org] – Pumped-storage hydroelectricity
[energiesystemtechnik.iwes.fraunhofer.de] – StEnSea, Storing Energy at Sea
[revolution-green.com] – STENSEA – Stored energy in the Sea
[chalmers.se] – Subsea Pumped Hydro Storage