To gear or not to gear?
Most wind turbines have gearbox transmissions that connect the slowly spinning turbine with the speed-hungry generator. But gearboxes have disadvantages: they’re noisy, complex, and prone to failure. Gearboxes need regular maintenance and lubrication, increasing their total cost of ownership. Some manufacturers have opted for gearless direct-drive turbines, but there’s a trade-off: because the shaft spins slowly, they require much larger permanent-magnet generators, increasing the weight and initial cost of the turbines. A new technology may capture the best of both designs.
Windtech has partnered with Future Force LLC to build a turbine based on the Zero Contact TransmissionTM (ZCT) patented by Future Force. The technology uses a transmission of sorts, but instead of mechanical gears, belts, or chains, the ZCT uses neodymium permanent magnets to make the generator in the turbine spin five times faster than the rotor. Lab tests conducted at the University of St. Thomas (Minnesota) have shown the ZCT to be 98% efficient at transferring energy from its input to its output.
As shown above, the rotor drives the main shaft, which is magnetically coupled (via the ZCT) to five independent generators, each spinning five times faster than the rotor. (The picture only shows four generators, but their documentation says five. There must be one in the middle.) This provides redundancy; the turbine could withstand the failure of one or two generators and still produce some power. The turbine is capable of generating substantial energy at low wind speeds; its peak power occurs when the wind speed is 8.1 m/s (18 mph), where comparable turbines require speeds in excess of 12 m/s (27 mph) to achieve peak output. Its startup speed is a meager 2.2 m/s (5.0 mph). It’s designed for locations with average wind speeds of 4 m/s (8.8 mph), which makes wind power viable in 50% more places.
Windtech is currently testing a prototype of its 100E 10 kW turbine (pictured below) in Glencoe MN. They plan to sell the 100E at a price that’s competitive with other units of similar size, making it more likely that customers will take this turbine out for a spin.
Images: Windtech Inc.