The 65-kW prototype, in operation since 2007, is a proof-of-concept unit and test bed for collecting data that will assist in design and development of a 2.0 MW commercial-scale unit. It is scheduled for operation by Fall 2010.
One school of thought for wind-turbine design says getting rid of the potentially troublesome gearbox makes for more reliable machinery. Although true, the permanent magnet (PM) generators then required become heavier and more expensive. A direct-drive 1.8 MW Enercon, for example, weights 25% more than a gearbox equipped Vestas 1.8 MW. Toronto-based CWind says it has a way around the weight issue in its direct drive design that has a greater generating capacity than many existing turbines.
In the CWind design, a three-bladed rotor turns a large diameter flywheel, the surface of which turns friction wheels, each connected to a generator. Rotor and flywheel operate with the same inertia. The design is reliable because the friction drive limits the torque transmitted through the drive. The company says its turbines will eventually have ratings from 2.0 to a whopping 7.5 MW.
The design is simpler than conventional turbines, says its developer, because scaling up the power train comes by adding more generators. For example, the drive mechanism in the proposed 2 MW design uses eight 250-kW generators. Add 12 more, a larger rotor and drive wheel, and it provides a 5 MW design.
Each generator has an independent load path, so taking advantage of the variable speed lets the turbine deliver higher part-load efficiency at lower wind speeds. Compared with conventional wind turbines, the design is said to be more reliable, has lower maintenance costs, weighs less, and will better absorb wind gusts.
Using conventional industry scaling and cost-of-energy models, a wind farm of these turbines could produce significantly more energy, says the developer, at a lower cost than a similarly sized wind farm of traditional wind turbines.
The developer says design advantages include:
• No gearbox or gearbox bearings to fail, and no oil
to change
• No single point of failure
• Reduced overall cost for manufacturing, operations,
and maintenance
• Energy from gusts is stored as momentum in the
flywheel and recovered when gusts pass.
The red cylinders in the drawing are generators coupled to rubber friction drives that ride on the turbine’s large-diameter flywheel.
• It is impossible to overload the drive train
• Multiple generators operate at the most efficient speed.
Generators come online only with sufficient wind.
Therefore, energy production is higher than a convent-
ional unit even when running below rated power
• Independent load paths allow continuous operation at
partial load while awaiting maintenance
• Distributed load paths allow operating up to 95%
availability during faults because only the fault load
path is isolated
• The design allows maintaining, servicing, and replacing drive-system components using an internal nacelle
crane.
The black tire rolls on the inside the flywheel in the 64-kW prototype. CWind says this unit has proven the key design feature, the friction drive, by showing it would slip when overloaded, thereby protecting the generator components.
WPE
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I know i am way off topic here but I sure would like to find a way to turn a small on my travel trailer while traveling down the road that would some how be powered by the energy I am already using by pulling it. I don’t really want to run a wire from the trucks electrical system to power it. It would be somewhat low output as its primary mission would be to charge the on board batteries. That way I can use the inverter to power a small refrigerator or other items, and not be stressing out the trucks alternator. I also use several different trucks to pull with and it would be that much less wiring to mess upon the trucks. Just throwing this out on several forums to gleen some unique ingenuity ideas.
Unfortunately I’m a bit late to the discussion, but CWind’s friction drive concept has some obvious issues.
Transmitting torque though an elastomeric wheel contact would have somewhat poor efficiency, due to hysteresis effects. It would also not have a good torque limiting function as claimed, since any slippage would result in heating of the elastomeric drive tire carcass, which does not have have much capacity for absorbing heat without failing. Also, an elastomeric drive wheel that overheats due to overload, slippage, or seizure presents a fire hazard.
Since utility-scale wind turbine power electronics (in DFIG AC, medium speed PM DC, and direct-drive PM designs) are by far the most likely point of failure (statistically), eliminating them and using an ultra-reliable synchronous AC generator with a mechanical variable speed drive would be the logical and obvious solution. All you would need is a mechanical variable speed drive with good efficiency, high reliability, and torque capacity suitable for large wind turbine drivetrains.