Black box: This eight-kilowatt wind turbine uses a continuously variable transmission--the small, silver-colored unit on the left below the rotor--to regulate its power. The turbine’s developer, Cedar Park, TX-based Viryd Technologies, claims that its use of mechanical instead of digital power regulation will cut manufacturing costs by 20 percent and boost power output.
Viryd Technologies
A continuously variable transmission could lead to cheaper wind power--if it is rugged enough.
Federal stimulus funds awarded to a wind-energy research consortium led by Illinois Institute of Technology will accelerate testing of small wind turbines that could point the way towards more efficient utility-scale machines. The eight-kilowatt turbines, the product of Cedar Park, TX-based Viryd Technologies, use a mechanical approach--continuously variable transmission (CVT) technology--to convert fluctuating wind speeds into the precise stream of alternating current required by power grids. If it can replace the pricey power electronics that regulate power in most turbines today, the same technology could cut the cost of wind-power generation at any scale.
The question is whether the CVT is tough enough. Viryd parent company Fallbrook Technologies has already commercialized its technology as a smooth-shifting alternative to gears and derailleurs in high-end bicycles and is working on larger vehicle applications. Wind power, however, is a particularly demanding application, according to Jason Cotrell, a senior engineer at the Department of Energy's National Wind Technology Center in Golden, CO. "Wind turbines are subject to very high torque for 80,000 hours of operation, so it's a very challenging environment," Cotrell says. "CVTs tend to be complex, and we haven't yet verified that they're suitably robust."
Most CVTs vary transmission ratios by sliding metal belts up and down a set of precision curved parts--a design that is expensive to implement at high torque. Fallbrook's technology relies on comparatively simple parts, promising lower cost and greater durability, according to CTO Rob Smithson. "It's basically a big ball bearing, which is a global commodity," Smithson says.
The CVT transfers power between a set of rings--an input ring and an output ring--via a set of rolling balls sandwiched between them (seven or eight balls, each slightly smaller than a golf ball, in Viryd's case). Tilting the balls' axis of rotation causes the rings to travel different distances with each rotation of the balls. A pressurized transmission fluid keeps the balls and rings from chewing each other up in the process.
Viryd CEO John Langdon says that its turbine control system manages the balls' tilt to spin the turbine's rotor at the optimum frequency to maximize energy capture for a given wind speed, and to synchronize the AC power output from the turbine's generator with the power grid. As a result, they use substantially less power electronics, and less sophisticated generators. He promises the turbines will be 20 percent less expensive than existing eight-kilowatt turbines, which currently cost about $40,000 installed.
The $8 million project, led by Illinois Institute of Technology's Wanger Institute for Sustainable Energy Research, is one of several to test whether the cheaper turbines can endure. If these prototypes pass muster, Langdon's plan is to install 50 more during the first half of next year for dealers and then to begin marketing the turbine to homeowners and small businesses in the second half of the year. The turbine is rated to generate about 10,000 kilowatt-hours of electricity annually, which is close to the average U.S. homeowner's power budget. Langdon predicts a ready market, thanks to state and federal incentives.
Viryd's eventual goal is to scale up to utility-scale wind farms. Scaling up the CVT technology to deliver on that promise is a matter of increasing the size and number of balls to handle the higher torque coming from the utility-scale machine's larger blades, which can exceed 60 meters in length (15 times longer than the blades on Viryd's eight-kilowatt turbine). A utility-scale turbine could require 12 half-meter-diameter balls, says Langdon.
At least one other startup is chasing the same opportunity--Israel's IQwind. Last month IQwind signed up Spanish engine manufacturer Grupo Guascor to produce its variable-speed transmissions as a retrofit for 750-kilowatt wind turbines.
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As noted in my earlier post, I'm a total novice in wind power. But I got a wry chuckle from, "If it can replace the pricey power electronics that regulate power in most turbines today, the same technology could cut the cost of wind-power generation at any scale."
I spent over four decades in computers and telecom. One of the themes over that span of time was the gradual (and, in fact, continuing) trend of electronics to replace mechanical and electromechanical systems. Moving parts, and even discrete wires, keep getting pushed to the periphery of the system -- only where motion is an essential part of the function. The reason is the exponentially decreasing cost and increasing function of integrated electronics.
For wind turbines, the blade and axle are the essential motions. The idea that electronics takes over at the axle is in keeping with the evolution I am used to seeing. If re-inserting a mechanical transmission is more than a temporary blip, I don't understand as much as I thought I did about technological evolution.
An intriguing question dtutelman. It does seem counter-intuitive to have mechanics taking over from electronics, but power applications are a bit different from the logic and communications roles that we generally associate with digital equipment. Note that AC power is an inherently cyclical analog phenomenon that can only be approximated by digital switching. Of course, the same was once said for sound, and digital has certainly taken over there.
For another such back-to-the-future example of electromechanics challenging power electronics, have a look at my coverage of GE's variable frequency transformers for IEEE Spectrum magazine. See "Power Transmission Without the Power Electronics" at http://www.spectrum.ieee.org/energy/the-grid/power-transmission-without-the-power-electronics
If you are a hammer, everything looks like a nail. Mechanical engineers say "lets put something moving into the system". Electrical engineer says "no, lets use electronics!".
An important factor is cost. If it's cheaper to use a mechanical solution and it works, then there's no reason to go for the electronics. I don't see how power electronics can be completely eliminated, especially with smart grid developments etc.
Of course, I might just be an economist saying "lets look at what it costs guys!"
:)
Check out Voith's "WinDrive". Seems like a more robust solution.
How about using a pair of variable speed hydraulic motors? You know those swash-plate/piston things?
Manufacturing in the United States is in trouble. That's bad news not just for the country's economy but for the future of innovation.
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kjblack
20 Comments
HAWT power generation
Why do companies persist with HAWT power generation units small or large?
Unless they are away from from populated areas they will drive the neighbours, specially at night, mad with the noise generated from the tip speed of the HAWT.
The perfect answer is a good VAWT unit, low in noise and it can be more efficient than a HAWT unit.
I say to companies that are blinkered by manufacturing HAWT units, there is another great option!
Reply
dtutelman
117 Comments
Re: HAWT power generation
Until I saw your post, I had no idea what HAWT and VAWT are. The post did not help. I use Tech Review to educate myself outside my specialty, and appreciate their articles' not assuming the reader knows the specific technologies' culture and jargon. It would be nice if the posts followed that policy as well, but I know the posters have something to say and sometimes forget the readers' needs.
Anyway, it worked to my benefit this time. I had to look it up, and the articles I found had a good, readable rundown of the relative advantages and disadvantages. I agree that VAWT has advantages, particularly in high population areas. But, bottom line, a HAWT will always be more efficient for a given area swept by the turbine. For utility-scale wind farms, in rural areas where blade noise is not an issue, I don't see VAWTs replacing HAWTs.
Obviously, I'm not an expert; I'm a raw beginner. But I've read articles on both sides of the argument, and the efficiency issue does not seem to be in dispute.
Reply
Siphon
152 Comments
Re: HAWT power generation
You're quite right, the VAWT is less efficient. Then again, no one has built a really BIG VAWT (like 5 MW) yet and they could be much more efficient...
Reply