Undersea Ocean Renewable Energy Storage

Ocean Energy Storage

by Allison Kerley

Slocum et al. (2013) propose a new design for an energy storage and generation unit composed of underwater concrete spheres and offshore wind turbines. The proposed design utilizes pumped storage hydraulics (PSH). During times of low energy demand from the grid, the cylinder would contain water at equal pressure with the surrounding ocean. In the proposed design, the floating wind turbines generate energy and the excess energy is used to pump water out of the storage sphere, creating a vacuum. When energy is needed from the sphere, the turbine would open, allowing water to pass through into the sphere. The proposed sphere design would have an inside diameter of 25 m, and would retain a 1/20th-atm environment when fully discharged. The proposed design could be used without alteration in depths between 200 and 700 m, and would continue to be economically feasible to a depth of approximately 1500 m. The authors tested a small-scale dry version of the proposed design, with the test sphere having an inner chamber diameter of 75 cm, with a ten meter height difference from the top of the pump and wind turbine to the top of the sphere. The test unit was found to have a low round-trip efficiency of 11%, which the authors attribute to their inability to use the most efficient pump and turbine technology due to the small size of their test model. They calculated that in a full scale model, the lowest round-trip efficiency would be 70%. Continue reading