The two turbines, which have rotor diameters of 107m, use a synchronous generator and permanent magnets. In July 2008, Siemens installed the first of two new 3.6 MW direct drive turbines to assess whether direct drive technology is competitive with geared machines for large turbines. Most other direct drive designs are based on PMG technology, using high-strength Neodymium magnets.

The exception is Enercon, which has long supplied direct drive generators employing a synchronous generator and having an electrical rotor with windings rather than permanent magnets. Although these developments continue, direct drive turbines have not, as yet, had a sizeable market share. A general trend towards direct drive systems has been evident for some years, although there are considerable challenges in producing technology that is lighter or more cost-effective than the conventional geared drive trains. The motivation for direct drive is to simplify the nacelle systems, increase reliability, increase efficiency and avoid gearbox issues. Other drive train options can be classified as direct drive (gearless) or as hybrid, in other words with some level of gearing (usually one or two stages) and one or more multi-pole generators. A few of the considerable variety of layout and bearing options of the drive train, with gearbox and conventional high speed generator, were discussed in Architecture of a Modern Wind Turbine.

Whilst the rotor configuration of large wind turbines as three composite blades in upwind attitude with full span pitch control has consolidated in the past 10 years, there is increasing variety in current drive train arrangements.

Siemens motor selection