An undersea compressed air energy storage system for offshore wind farms is currently being trialed at a depth of 100 meters, about 200 meters from the shores of Überlingen, Germany.

The 1:10 scale model utilises the high water pressure in very deep water to store electrical energy with the aid of hollow concrete spheres. Energy is stored by pumping water out of the spheres using an electric pump, replacing it with air. Power is generated when water rushes back into the spheres after flowing through a turbine.

The trial will monitor design, installation, configuration of the drivetrain, various other aspects and simulation of the system as a whole.

The next system will be demonstration-scale, using spheres with a diameter of 30 meters that will need to be placed in at depths of about 600-800 meters upwards.

StEnSea is the brainchild of Professor Horst Schmidt-Böcking (Goethe University Frankfurt) and Dr. Gerhard Luther (Saarland University). The StEnSea prototype model was developed by the Fraunhofer Institute for Wind Energy and Energy System Technology (IWES)

“With a storage capacity of 20 MWh per sphere and standard technology available today, we can envisage a total electricity storage capacity of 893,000 MWh worldwide,” said IWES Head of Division Jochen Bard.

“This would make an important and inexpensive contribution to compensating fluctuations in electricity generation from wind and solar power.”

Mr. Bard says storage capacity with the same volume increases linearly with the depth of the water. At a depth of 700 meters, the storage capacity for a 30 m sphere is approximately 20 megawatt-hours (MWh).

The project has received funding from the German Federal Ministry for Economic Affairs and Energy (BMWi)

It won’t be the first time such a system has been trialed. Hydrostor’s Adiabatic Compressed Air Energy Storage systems been up and running 2.5km off the shore of Lake Ontario in Canada since last year. The company says its solution offers one of the lowest cost energy storage options available on the market today.

Hydrostor recently inked a partnership deal with AECOM to jointly develop and market energy storage projects.