According to an article by Martin Lamonica in the February 15, 2013 issue of Technology Review, Belgium has plans to develop a manmade “atoll”  in the North Sea to store wind energy.  The idea is to place the small island offshore, near a wind farm.  When excess energy is produced at off-peak periods the island will store the energy; releasing it later during peak usage times.

“The idea of using an “energy atoll” may seen outlandish on the surface, but it’s really not, says Haresh Kamath, program manager for energy storage at the Electric Power Research Institute (EPRI). This approach, first proposed by a Dutch company, uses cheap materials—water and dirt. On the other hand, the engineering challenges of building in the ocean and technical issues, such as using salt water with a generator, are significant.”