Swaying without tilting in wind and deep water

Wind energy will have to play a pivotal role in any successful strategy to mitigate global climate change. For the past decade it has been the fastest growing source of electricity in the world. Until recently most wind energy systems have been developed on land. Beginning in 1990 wind turbines began to migrate offshore where the winds are generally stronger and steadier.

Technology has limited the development of offshore wind projects to shallow water sites (up to 50 feet). In the United States offshore shallow water sites free of conflicts with other uses are far and few between. Deeper water sites are plentiful but pose formidable engineering challenges.

Pioneering wind engineer William Heronemus anticipated these opportunities and challenges while teaching at the University of Massachusetts. He was the first to identify the potential of offshore wind off the coast of New England. In the 1970's he designed floating platforms capable of supporting multiple wind turbines.

The notion of offshore wind was, as you can imagine, originally dismissed. Floating wind turbines were considered outrageous if not just completely ignored.

The concept of floating wind turbines is now being taken very seriously -- especially given the rising cost of steel and other materials. Sway Systems is one company that has accepted this design challenge head-on. There are and will be others. (GW)

Deep-Water Wind: In the Wind, Out of Sight

By Philip Proefrock
ecogeek
February 25, 2008

A lot of EcoGeeks think that there is a beauty to wind turbines, even beyond their ability to provide emissions-free energy. But to others, wind turbines are an eyesore. A Norwegian company called Sway is developing a deepwater system that will allow turbines to be situated farther out to sea where winds can be steadier and stronger, and where the turbines are hidden from all save a few passing ships. "The SWAY® system is a floating foundation capable of supporting a 5MW wind turbine in water depths from 80m to more than 300m in some of the world's roughest offshore locations." This could allow wind farms to be farther off shore where they would be out of sight.

Off-shore wind turbines have needed to be situated in relatively shallow waters to be able to have sufficient footings to anchor and support them. This new deep-water turbine uses a floating tower to support the turbine, and is anchored to the sea bed with a single tension rod. Because the turbine body floats itself, the rod only needs to help the structure resist the forces of wind and waves, but does not need to support the entire structure.

The SWAY concept, which is covered by several patents, is based on a floating elongated pole extending far below the water surface with ballast at the bottom part. Since the center of gravity in this manner is placed far below the center of buoyancy the tower has sufficient stability to resist the large loads and weight from the wind turbine placed on top of the tower.

The more compelling part of the Sway system is that it keeps the tower upright against the wind forces that would otherwise overturn it. (The wind pressure on the rotor for a 5MW turbine is approximately 60 tons.) The Sway tower maintains a nearly vertical configuration, and only tilts less than 1 degree from its equilibrium position in storm conditions so as not to lose power.

There is some added cost in situating these turbines further from shore and from the end energy users. But the tradeoff with political acceptability and availability of wind may make these turbines more than useful for providing wind power. Sway wind-power towers could also be used near off-shore oil and gas rigs, and provide clean power for their operation, instead of the diesel generators these platforms utilize presently.