Is Direct Drive the Future? Wind Turbines Without Gears are Lighter, Cheaper, More Reliable

offshore wind turbine photo

Photo: Flickr, CC
Squeezing More Power from the Breeze
These days, the wind industry is all about scaling up, cutting costs, and improving reliability. One way to do that, at least according to Siemens and GE, is to replace the traditional gearboxes and high-speed generators with bigger low-speed generators that don't necessitate a geared transmission (that's why they call it 'direct drive'). Here's why this might be the future of wind turbine design...
offshore wind turbine photo

Photo: Flickr, CC
Siemens's plans hinge on a new design that reduces the weight of the system's generator. In conventional wind turbines, the gearbox increases the speed of the wind-driven rotor several hundred fold, which radically reduces the size of the generator required. Direct-drive generators operate at the same speed as the turbine's blades and must therefore be much bigger--over four meters in diameter for Siemens's three-megawatt turbine. Yet Siemens claims that the turbine's entire nacelle weighs just 73 metric tons--12 tons less than that on its less powerful, gear-driven 2.3-megawatt turbines.

Much of the weight reduction comes from the use of permanent magnets in the generators' rotor--a trick that GE is also using. Conventional turbine generators use electromagnets--copper coils fed with electricity from the generator itself. Henk Polinder, an expert in permanent-magnet generators at Holland's Delft University of Technology, says that a 15-millimeter-thick segment of permanent magnets can generate the same magnetic field as a 10- to 15-centimeter section of copper coils. (source)

So while the current gearbox-systems can do the job reliably, direct drive mechanisms that use about half as many parts should be even more reliable and thus reduce operating costs over the long-term, making electricity from wind farms even more competitive.

This is especially important for offshore wind farms because doing maintenance at sea is a lot more complex and expensive than on the ground.

Production and installation costs should also be lower once production of direct drive turbines scales up; the example above about the 3 MW turbine nacelle weighting 12 tons less than the 2.3 MW nacelle makes a big difference when you have to ship and install hundreds of turbines...

via Technology Review
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