A Canadian startup has developed a small prototype wind turbine that uses friction instead of a gearbox to convert wind energy into electricity. CWind, based in Owen Sound, Ontario, recently began work on a larger two-megawatt prototype. The company claims that its “friction drive” system is more efficient and reliable–and less costly to maintain–than conventional wind turbines, which are prone to expensive gearbox failures.
The blades on most turbines use the wind to turn a drive shaft connected to a gearbox. The gearbox manages the rotation of a second shaft that connects to a large electrical generator. The gearbox is the heaviest piece of equipment in a wind turbine’s “nacelle” (the section at the top of the turbine tower). It’s also a piece that’s among the most vulnerable to failure. Sudden wind gusts put the gearbox under tremendous mechanical stress. Over time this can wear down or break the teeth off its metal gears.
CWind’s design does away with the gearbox completely. Instead, the drive shaft is connected directly to a large metal flywheel. Hugging the outside of the flywheel are eight smaller secondary shafts, each connected to a 250-kilowatt generator and each lined with several specially designed tires that grip the surface of the flywheel. As the flywheel spins, it engages the generators by turning these tire-lined shafts. “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 secondary shafts. The tires are also designed to temporarily slip if a wind gust causes the flywheel to suddenly speed up. This feature eases the impact on the generators. Each secondary shaft can also be disengaged from the flywheel if the wind slows down, in effect reducing friction and allowing shafts that are still connected to keep their generators operating at high capacity. Likewise, connecting more shafts, thus adding more friction when the wind increases, will engage idle generators. “We can operate the generators at optimal speed all the time,” says Nayef, adding that tests on the smaller, 65-kilowatt prototype show efficiency gains over standard wind turbines of up to 5 percent.
CWind founder Paul Merswolke first pursued the design seven years ago after watching a documentary on the London Eye, a 135-meter-tall Ferris wheel on the bank of the River Thames. He saw that simple truck tires were used as “friction rollers” to turn the Ferris wheel and concluded that the same approach could be adapted for wind turbines. Nayef was brought aboard to come up with a preliminary design, and in 2004 CWind approached energy engineering firm MPR Associates in Washington, DC, for help on building a prototype.