On Oct. 6, 2012, Siemens began field testing of its new 154-m (505-ft) rotor for the 6-MW offshore wind turbine in Østerild, Denmark. The direct-drive wind turbine is equipped with the world's longest rotor blades — each blade measures 75 m (246 ft). With a record rotor diameter, each SWT-6.0-154 turbine can produce 25 million kWh of clean electricity in offshore locations, enough to supply 6,000 households. Østerild is a windy site near the coast and offers very favorable conditions for initial testing on shore.

As early as May 2011, Siemens installed the first prototype of its new 6-MW turbine using a 120-m (394-ft) rotor. It has been operating successfully ever since. This next version will use the 154-m rotor and is expected to become the new benchmark in the offshore wind industry.

The gearless-drive technology permits a compact design. Using Siemens' direct-drive technology, the SWT-6.0 is the lightest turbine in its class, having a nacelle weight of only 200 tons. This combination of robust design and low weight reduces offshore infrastructure, installation and maintenance costs.

Siemens developed the SWT-6.0 specifically for demanding conditions in offshore locations. “The new 6-MW turbine is a milestone in wind energy technology,” says Stiesdal. “Compared to our first 30-kW turbine, which we developed 30 years ago, the new STW-6.0-154 will produce over a thousand times more energy per year.”

The rotor blade development is equally impressive. The first blade of the 30-kW turbine was 5 m (1.5 ft) long, approximately the length of a minibus, while the new 75-m rotor blades have a length corresponding to that of an Airbus 380 plane, the world's largest aircraft.

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