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Vertical Axis Wind Turbine With Push and Pull
Sterling D. Allan writes "After 10 years of prototyping, wind tunnel testing, patenting, and tweaking, Ron Taylor of Cheyenne (windy) Wyoming is ready to take his vertical axis wind turbine into commercial production. Design creates pull on the back side contributing to 40%+ wind conversion efficiencies. Because it spins at wind speed, it doesn't kill birds, and it runs more quietly. It also doesn't need to be installed as high, and it can withstand significantly higher winds (can generate in winds up to 70 mph, compared to ~54 mph tops for propeller designs). Generating costs estimated at 2.5 cents per kilowatt-hour, putting it in the lead pocket-book-wise not just of wind and solar, but of conventional power as well. Production prototype completion expected in 5-7 months."
I'll be honest, I really have to wonder about the whole windmills-killing-birds business. It always gets dragged up, but does anyone really know how many birds those propellers actually kill? I'm willing to bet it's very low; I also suspect way more birds are killed by flying into vehicles on the highway, or into the sides of highrise buildings (I had one kamikaze into my house last week, and that's not even a high rise).
The whole bird thing sounds like a convenient excuse invented by people who really oppose windmills because of noise or land use issues, but want a fuzzier, more PR-friendly excuse. The kill zone on a windmill is basically going to be the circle described by the rotor tips as they go through the air, so it's not a huge zone (as you get towards the center they're not moving as fast, tangentially) and at any given time it's not as if just flying into that ring would result in death, you'd have to be at a point at the particular moment in time when the blade moved through it. Last time I checked, birds don't hover, so you have two moving objects that would have to compete against some long odds to end up in the same place at the same time. Also, the turbines are noisy as hell -- something which is a legitimate criticism -- and I find it hard to imagine that birds wouldn't be scared off by the sound, air currents, and motion. (Actually they wouldn't make a bad large-scale scarecrow over farmland...)
Call me overly cynical but I find that particular objection dubious.
"Ladies and gentlemen, my killbot features Lotus Notes and a machine gun. It is the finest available."
Thanks for the info. I had never heard of Savonius windmills before -- or at least not heard the name. I've actually seen one before though, but not for any practical purpose: one of those annoying moving-lawn-ornament type things.
In case anyone else is interested in what a Savonius windmill is, there's a page with a little simulation of one here. I think they're selling something (model turbines maybe?) although I didn't really check it out.
I have to wonder though whether one of these is really as efficent as a propeller-type windmill, given that a propeller type one can alter its blade pitch and keep the rotational speed relatively constant in different wind speeds. Is there a way to do that with a Savonius design? It doesn't seem like the airfoils are really anything that you could easily change in flight.
I'm not sure if it's true, but I once heard an interesting factoid about Dutch-style propeller windmills, and how they were among the first mechanical devices to implement a "feedback loop"; you have a tail rotor mounted perpendicular to the main rotor, which drives the mechanism that orients the windmill. If the wind isn't blowing at the mill directly from the front, it causes the small rotor to turn, turning the mill into the wind. When the mill is pointing in the right direction, there's no wind on the small rotor, so it stops. Pretty brilliant, for the 17th or 18th century.
"Ladies and gentlemen, my killbot features Lotus Notes and a machine gun. It is the finest available."
I have to wonder though whether one of these is really as efficent as a propeller-type windmill, given that a propeller type one can alter its blade pitch and keep the rotational speed relatively constant in different wind speeds. Is there a way to do that with a Savonius design? It doesn't seem like the airfoils are really anything that you could easily change in flight.
From my readings, and as a pilot, I can hazard a guess that this is because of the enormous complexity both in manufacturing and in maintenance of having a variable pitch prop. The money that you save (earn) through increased efficiency might be gobbled up the first time you have to higher a technician to climb to the top of a 200m tower and fix a faulty blade. Don't know if this is the only reason, but it's certainly a major one.
I'm not sure if it's true, but I once heard an interesting factoid about Dutch-style propeller windmills, and how they were among the first mechanical devices to implement a "feedback loop"; you have a tail rotor mounted perpendicular to the main rotor, which drives the mechanism that orients the windmill. If the wind isn't blowing at the mill directly from the front, it causes the small rotor to turn, turning the mill into the wind. When the mill is pointing in the right direction, there's no wind on the small rotor, so it stops. Pretty brilliant, for the 17th or 18th century.
Never heard that before, but it sounds pretty cool and feasible. It makes sense if you consider that bearings would have been pretty difficult back then, and thus you might not be able to rely on a little tail flap a la weather vane for orienting the mill.
www.eissq.com/BandP.html Ball and Plate System. Amuse your friends. Crush your enemies.
The energy you can take from the wind is proportional to the area of the device, and the cube of the wind speed. Three-bladed wind turbines are tall and big because wind is faster higher up, and so they can sweep a huge area. A three blade arrangement is aerodynamically optimal, getting closest to the Betz limit of about 59% (not 20-30% or whatever the web page said).
Also, bird death is about 1 per turbine per year for current technology. This is about 9 orders of magnitude less than bird death from buildings/vehicles/airplanes etc., and that's not considering the enviornmental consequences on bird life of NOT using renewable sources...
Dumpy little vertical axis machines may have limited uses in isolated installation, and for revolving advertising, but they are not practical for large scale generation. The rotor of a modern 5MW wind turbine is about the same size as an athletics track. Imagine how big this vertical axis machine would have to be to match the wind capture of this. If the alternative is to have many small devices, there would be a very large number indeed: this carries costs of electrical interconnection, massive maintenance overhead from trillions of puny alternators and gearboxes, all of which was probably ignored in arriving at the 2.5 cents per kWh.
The only way to make money with this turbine is to be the poor guy's patent attourney.
There have been wild claims for savonious rotors for many years. One, in Mother Earth News back around 1976 or thereabouts claimed 6 kw output for a machine made of two split oil drums, around 3 feet in diameter and 6 feet tall -- that's 18 square feet of frontal area. Power goes with the dimension squared (for circular frontal area) and speed cubed, so, double the dimension (radius, diameter), you see 4 * the area and thus 4 * the power available. Double the speed and you see 8 * the power available, all given some constant (never happens) coefficient of conversion.
Roughly, power = 1/2 * rho * v^3 * a * k * c
where rho is mass density of air, v is windspeed, a is area, and k converts all units to power units. If you use square feet and feet per second as units, and 0.00238 slugs/ft^3, then you need to know that 550 ft-lbs/second will convert to horsepower. "c" is the conversion coefficient, typically around 0.25 for a good bladed rotor, probably closer to 0.1 for a savonious. I have built and seen rotors that did better than 0.3. Factor in loss due to generator power conversion, transmission line losses, etc, and things go downhill from there.
In general, there is a Betz limit that says, mathematically, that the most you can ever harness from a fluid flow such as wind is 59%, though there are suspected ways around that. When these people deride "tip speed ratio" they are giving up the fact that, when you can travel faster than the wind, as does the outer regions of a bladed turbine, you have the opportunity to generate more power due to the lift-to-drag ratio of high aspect ratio blades (wings) providing lots more torque than you would get by mulling along at around the same speed as the wind. Take a look at those multibladed farm water pumpers. They have a tip speed ratio rarely greater than one, and their conversion efficiency is fairly low. They're good for high starting torque to lift water. In electrical generation, you don't worry about starting torque because generators don't "kick in" till you're flying fairly fast. There is one aspect to the claims in the granted patent: he adds external "airfoils" to direct more wind into the central sevonious rotor, speaking of which, it's hard to tell from the pictures, but he may miss one nice point about generalized savonious rotors: the gap in the middle. If he closed that, he loses a lot due to the "airfoil" effect of the retreating (driving) blade directing some of the airflow through the gap into the advancing (dragging) blade (cup if you like).
In some sense, what he claims in his patent is well known in prior art. It's a lot like those dumbass patents the USPTO is granting these days for stuff like "one click", or "shopping carts" -- those folks in the USPTO never go outside and smell the roses. The patent presently granted can be stomped all over with photos from even ths us department of energy archives.
Dumb stuff like this comes along all the time. I don't think this is the work of a charlatan; rather, it really appears to be the work of an honest, but not well educated fellow. Clever, but not original or novel (novel to him, not to the rest of the world). Too bad every time someone comes along with a perpetual motion machine or something close (really cheap energy), they have to slam everything else that's already out there.
An earlier poster here commented on the apparent low quality of the website that printed the press release. Too bad about that. I'm reminded of the somewhat childish but good hearted efforts, long before the web, in the late 70's following the huge gas pump crisis in the U.S. Everybody and his uncle started printing journals, whatever, including The Mother Earth News. Some of it was good, some of it was rubbish, but we all had a ton of fun doing it. Looks like what goes around comes around. Again.
Jack Park
I think it's more likely that "Sterling Alan" is paying /. to post stories that he writes.