Wind turbines that work without a gearbox can make offshore wind power facilities even more reliable. Siemens has now begun selling a three-megawatt turbine with a rotor diameter of 101 meters that requires only half the parts of a conventional geared wind turbine. This simpler design reduces the cost and effort of maintenance and boosts availability. This is particularly advantageous for offshore facilities, as service and maintenance work on the units is very costly. The SWT-3.0-101 wind turbine features a new drive train with a compact, synchronous generator excited by permanent magnets. The generator of the first prototype machine, which was installed in Denmark in 2009, was developed by the experts for large drives at the Siemens Industry Sector. The gearbox normally converts the low speed of the wind rotor into the high speed required for power generation. In the direct drive unit, the synchronous generator converts the motion of the rotor into electrical energy directly. These generators are among the largest permanent-magnet units ever built. Their main advantage is the simple and robust design that requires no excitation power, slip rings or excitation control systems. This means that the generator is already highly efficient in weaker winds.
Another advantage is the small size. With a length of 6.8 meters and a diameter of 4.2 meters, the nacelle can be transported using standard vehicles. It weighs just 73 tons, which is less than the nacelle of the 2.3 megawatt machine from Siemens. Of the five key components of a wind turbine — the rotor, the rotor hub, nacelle, tower and the controller — all but the nacelle were taken from existing products. This minimizes the risk of malfunction or failure associated with the introduction of such innovative products.
Additional test units will be erected during the course of this year, with series production scheduled to begin in 2011. Wind energy is a central part of the Siemens Environmental Portfolio, with which the company generated sales of €23 billion in fiscal 2009.