A new type of wind turbine called SeaTwirl that can store energy is reported to have been successfully tested in Sweden.
The technology consists of a vertical wind turbine used as a flywheel. The device takes advantage of the water as a slide bearing. This makes the unit floating but with the flywheel rotating above the water surface.
The energy absorbed can then be transported into the land and used directly or stored in the device, with the flywheel. The power plant can thus be used as an extra energy reservoir and generates electricity even when there is no wind.