May 3, 2011
Canadian firm Thin Red Line Aerospace has completed the first structure specifically designed and built for undersea compressed air energy storage (CAES). The structure, also referred to as an “Energy Bag”, is to be anchored to the seabed off the coast of Scotland next month as part of a major renewable energy research project conceived and led by Professor Seamus Garvey of the University of Nottingham and supported by European renewable energy leader E.ON. The project is the first to investigate large scale offshore storage of wind, tidal and wave power as compressed air.
Thin Red Line Aerospace Design Engineer and CEO Maxim de Jong inspects the Energy
Bag during initial test inflation (photo Keith Thomson/Thin Red Line Aerospace)
Renewable energy sources and energy demand are both highly variable, and electrical energy can’t be stored economically on a large scale. Furthermore, storage of generated power is vital if renewable energy is to eliminate mankind’s dependence on fossil fuels. Thin Red Line’s Energy bags are conceived to help address these problems by storing energy in the form of highly compressed air—energy which would be available for use during critical periods of high demand or intermittency of supply. 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.
Energy bags would be anchored at a depth of approximately 600 meters (2000 feet) where the pressure of the ocean takes on the role of high performance pressure vessel. The bag is hereby relegated to a flexible, balloon like structure needing only to restrain the buoyant air bubble contained within—rather than a massive, thick-walled pressure tank of exceptional cost and complexity. At this depth the immense pressure of the ocean ensures high energy storage density, constant pressure regardless of bag volume, and pressure compatibility with existing high efficiency turbine technology. For commercial scale application, Thin Red Line has performed concept development for containment volumes to 6000 cubic meters (212,000 cubic feet).
The prototype energy bag, designed by Thin Red Line’s Maxim de Jong, displaces 40 tons of seawater, and is to be anchored to the seabed by its array of Vectran® fibre tendons capable of restraining a total load of 250 tons—yet the entire systems weighs only 75 kilograms (165 pounds). The design is based on Thin Red Line’s inflatable space architecture currently being investigated in several NASA programs. Thin Red Line is known for their ultra-high performance fabric structures, having notably developed and manufactured the pressure restraining hulls of the Bigelow Aerospace Genesis 1 and 2 satellites launched in 2006 and 2007, the first spacecraft on orbit successfully incorporating large volume, high-stress inflatable architecture.