Belgian Offshore Storage Solution
The idea is not new: build a circular dike in the sea and pump water out of it with energy from wind turbines for storage purposes if there is no actual demand for energy, like during the night. Let water flow back in again, propelling turbines to generate energy on the moment that you need it.
In 1981 the Dutch engineer Lievense presented the plan for this type of storage, but that was 1981 (when we heard him present his plans at our university) and now is 2015, where the energy problem has become acute. Decision for a go ahead: this summer.
Discharge capacity: 500 MW for four hours
Max. difference water levels: 30 meter
[source] Original Plan Lievense