The Pelastar floating commercial wind turbine is mounted on a buoyant base that is anchored to the bottom but kept submerged below the surface, minimizing the effect of rough water. The design allows use of wind turbines farther offshore in much deeper water. Courtesy MAREC
GVSU’s Michigan Alternative and Renewable Energy Center in Muskegon recently hosted a presentation on a new design for floating commercial wind turbines that could possibly avoid one of the main criticisms of offshore turbines.
The design is for wind turbines situated in much deeper water, at a greater distance from shore than the commercial wind farms proposed in the last few years in Lake Michigan, “which should soften the impact of the visual concerns that people have,” said MAREC director Arn Boezaart.
A representative of Glosten Associates Inc., naval architects and engineers out of Seattle, made a presentation last month at MAREC on the PelaStar floating wind turbine system, which was developed beginning in 2006 by Glosten naval architects.
Boezaart said the traditional way of locating wind turbines offshore is to have them actually standing on the bottom, called “monopole” construction. Water depth, however, is a major limitation.
Glosten’s PelaStar design, however, begins with a large, floating platform, like a giant steel box, upon which the wind turbine is built at dockside. The completed turbine on its floating base is then towed out to sea, to where it will be located. The floating base is then semi-flooded, allowing it to sink below the surface, while very large cables are used to anchor it to the bottom. Once securely anchored, air is pumped back into the platform, making it fully buoyant again, but still below the surface of the water, where the base is not affected by rough water.
“Engineers call that a tension leg platform,” noted Boezaart, adding that such a setup is very stable.
If the wind turbine is in need of repairs, its base can be released from the cables and towed back to dockside where the work would be much safer and less expensive to perform, according to Boezaart.
According to Bruce Goodman, a Varnum Law attorney focused on alternative energy issues, the first demonstration of a six-megawatt PelaStar system is being backed by a consortium of British and American companies and will be in operation in late 2015 off the coast of Cornwall, England. He wrote in his Michigan Energy News newsletter that the floating platform must be in at least 50 meters of water depth, and can be used in depths of up to 500 meters.
Boezaaart said shallower waters near coastlines are generally subjected to a greater degree of regulation, which discourages wind farm projects, and such projects are also generally opposed by local residents who can see the turbines from homes on the shoreline.
The Bureau of Ocean Energy Management is a federal agency that granted the first U.S. commercial license for an offshore wind farm, the Cape Wind Project, on Oct. 6, 2010, after years of extensive environmental review and consultations. It will be in 46 square miles of federal waters off Massachusetts, and consist of 130 wind turbine generators, each rated at 3.6 megawatts, for a total capacity of 468 megawatts.
Others are planned; however, there are no announced plans yet for any commercial wind farms in Lake Michigan.