Energy Bag Offers New Storage for Wind Power

Canadian firm Thin Red Line Aerospace is working on the first test deployment of its energy storage system for use with off-shore wind turbines. The Energy Bag provides power storage as "undersea compressed air energy storage" (CAES) to store compressed air deep underwater, and then release it again to drive generators when more power is needed. Storing power for peak load demand or for periods of intermittent wind are an important part of developing a responsive wind generation system that can effectively contribute to the grid at all times.

The process is conceptually straight forward: Wind turbines fill the balloon-like underwater bags with compressed air that later drives electrical generators on demand. While initial application is ideally linked to floating wind turbines, excess electricity from the grid—or from clean energy sources such as tidal and wave power—can also be used to drive compressors to fill the energy bags. The technology is especially suited to countries with relatively deep waters near their coasts.

Instead of engineering a heavy pressure vessel to store large amounts of highly compressed air, the Energy Bag uses a deep water location to serve as the pressure vessel to store the compressed air at extremely high pressures. The prototype Energy Bag itself weighs only 75 kilograms (165 pounds), but is able to displace 40 tons of seawater. It will be located about 600 meters (2000 feet) below the surface, where pressures are 60 to 70 times atmospheric pressure. The power storage in just one bag can be considerable. "At depths of around 600m, there will be enough pressure in one 20m-diameter bag to store around 70MW hours of energy. That’s around the same as 14 hours of energy generation from the largest offshore turbines currently in operation."

The Energy Bag has the potential to be orders of magnitude less expensive than industrial battery storage systems, and even just a fraction of pumped hydro storage systems. Not every location has deepwater locations suitable for this power storage, but several areas in Europe in particular have both good wind potential and deep water close by offshore as potential locations where this could be implemented.