A Canadian company has come up with a novel design for large wind turbines.
The three bladed rotor attached to the main shaft is attached to a flywheel driving the friction wheels which operate multiple generators. The rotor and flywheel operate with the same inertia. The design is reliable because it inherently limits the torque transmitted through the drive and incorporates the following key advantages:
- No gearbox – no oil, gearbox bearings or gears to fail
- No single point of failure
- Reduced costs overall for manufacture, operations and maintenance
- Not reliant on conventional turbine supply chain for bearings, gears, generators or gearboxes
- Friction drive system built to absorb sudden wind gusts – energy is stored as momentum and recovered when gust passes
- It is impossible to overload drive train
- Multiple Generator Drive, each operate at the most efficient point – each generator only operates when there is sufficient wind, ...therefore energy yield is higher even when running below rated power
- Independent load paths giving continuous operation at part load while waiting for maintenance or replacement of component parts
- Distributed load paths allow operation up to 95% availability during faults as only the fault load path is isolated
- Distributed power system , low torques
- Ability to maintain, service and replace all drive system component parts using only the internal nacelle crane
- Full power conversion – grid friendly and variable speed
- Scalable to 7.5 MW
http://www.cwind.ca/html/fd.html- - - - - - - - - - - - - - - - - - - - - - - - -
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.
http://www.technologyreview.com/energy/24050/?mod=related According to their website, CWind wants to manufacture their wind turbines in Ohio. I hope they do.
Siemens has been testing gearless wind turbines since 2003 and has announced their SWT2.3-113 wind turbine which boasts a 50% reduction in moving parts compared with "standard" wind turbines and uses an innovative design that wrings the most power out of low and medium wind speeds.
GE says they will have a gearless wind turbine on the market by the end of 2012
The multiple wheels and bearings in a wind turbine gearbox suffer tremendous stress because of wind turbulence, and a small defect in any one component can bring the turbine to a halt. This makes the gearbox the most high-maintenance part of a turbine. Gearboxes in offshore turbines, which face higher wind speeds, are even more vulnerable than those in onshore turbines. Butterfield is leading a gearbox-reliability study with turbine makers to identify design weaknesses that could be avoided.
ScanWind's turbine design gets rid of the gearbox completely. Instead, the rotor shaft is attached directly to the generator, which spins at the same speed as the blades.
In a turbine generator, magnets spin around a coil to produce current--the faster the magnets spin, the more current is induced in the coil. To make up for a direct drive generator's slower spinning rate, the radius of rotation is increased, effectively increasing the speed with which the magnets move around the coil.
...snip...
GE, meanwhile, expects to have a market-ready product by late 2012. It is targeting the European market initially because nearly all of the 1,473 megawatts of offshore wind power currently available come from installations along European coasts. According to industry analysts, this capacity must reach 30,000 megawatts by 2020 if the European Union is to meet its renewable-energy targets.
http://www.technologyreview.com/energy/23517/?mod=related Elsewhere in the article it says that GE bought ScanWind.
These new wind turbines do away with the gearbox and the oil that it needs, which reduces maintenance costs as well as increases reliability. This makes them perfect for offshore wind farms. Gearless wind turbines should be the de facto standard in decades to come due to reduced maintenance and repair costs alone.