A Canadian startup has developed a small prototype wind turbine thatuses friction instead of a gearbox to convert wind energy intoelectricity. CWind,based in Owen Sound, Ontario, recently began work on a largertwo-megawatt prototype. The company claims that its "friction drive"system is more efficient and reliable--and less costly tomaintain--than conventional wind turbines, which are prone to expensivegearbox failures.



Wheels turning: The blades of CWind's wind turbine moveaninternal flywheel and several shafts that attach to smallgeneratorswithin the nacelle. In the lower image, a rubber wheel rollson theinside wall of a flywheel inside a 65-kilowatt prototype turbine.

The blades on most turbines use the wind to turn a drive shaftconnected to a gearbox. The gearbox manages the rotation of a secondshaft that connects to a large electrical generator. The gearbox is theheaviest piece of equipment in a wind turbine's "nacelle" (the sectionat the top of the turbine tower). It's also a piece that's among themost vulnerable to failure. Sudden wind gusts put the gearbox undertremendous mechanical stress. Over time this can wear down or break theteeth off its metal gears.


CWind's design does away with the gearbox completely. Instead, thedrive shaft is connected directly to a large metal flywheel. Huggingthe outside of the flywheel are eight smaller secondary shafts, eachconnected to a 250-kilowatt generator and each lined with severalspecially designed tires that grip the surface of the flywheel. As theflywheel spins, it engages the generators by turning these tire-linedshafts. "We're using friction. It's not mechanically hard-coupled,"says Na'al Nayef, a CWind engineer and co-inventor of the system.
Nayef says the system uses software to control the eight secondaryshafts. The tires are also designed to temporarily slip if a wind gustcauses the flywheel to suddenly speed up. This feature eases the impacton the generators. Each secondary shaft can also be disengaged from theflywheel if the wind slows down, in effect reducing friction andallowing shafts that are still connected to keep their generatorsoperating at high capacity. Likewise, connecting more shafts, thusadding more friction when the wind increases, will engage idlegenerators. "We can operate the generators at optimal speed all thetime," says Nayef, adding that tests on the smaller, 65-kilowattprototype show efficiency gains over standard wind turbines of up to 5percent.

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