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Offshore wind turbine goes really, really big

Siemens' 6-megawatt turbine uses permanent magnet for direct-drive generator and lightweight materials to ease operation in harsh ocean environment. And how about that 500-foot sweep?

A prototype of Siemens six-megawatt wind turbine with a direct-drive generator designed for offshore wind farms. Blades will be as long 75 meters but use lightweight materials.

When it comes to capturing energy from powerful offshore winds, bigger is better.

Siemens today introduced a larger version of its 6-megawatt wind turbine with a permanent magnet-driven generator set for installation offshore in Europe. The diameter of the circle created by spinning rotor blades will be either 120 meters or 154 meters (that is, almost 400 feet or 505 feet) across.

Land-based turbines typically have a capacity of up to 2 megawatts, but larger turbines are being designed to capture stronger, steadier offshore winds. Siemens projects that up to 50 of its SWT-6.0 turbines will be installed in Denmark, Germany, the Netherlands, and the U.K. next year and in 2013.

Even though offshore winds generally offer a better wind resource, installing and operating turbines in harsh ocean environments is very challenging.

To ease the maintenance of its offshore turbines, Siemens is using a direct drive generator, rather than a traditional gear box, because it cuts the number of parts in half. The turbine also uses lighter materials, which reduce the cost of installation and maintenance.

The rotor of most wind turbines today is connected to a gearbox and a generator to produce a flow of current. A direct-drive turbine has a permanent magnet attached to the spinning rotor which connects directly to a generator.

Direct-drive technology is being more widely used in the wind industry because of reliability but one of the potential constraints on its adoption is the availability and cost of permanent magnets which are made of rare earth metals.

Having fewer moving parts has advantages for the people who need to helicopter in and service these turbines: the nacelle, or housing behind the rotor and blades, is "particularly spacious" and gives technicians easy access to important components, Siemens said.