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Multi-Rotor Wind Power

7rotor.jpgWind is one of the oldest sources of power, with evidence of use dating back to 3200 BCE. But this doesn't mean that there are no more opportunities to innovate. Selsam's new wind turbine system design, partially funded by a grant from the California Energy Commission, is proving able to deliver substantially more power at a given wind speed than equivalent-sized traditional models. The innovation? You can see it in the picture: multiple rotors on a single turbine unit, set an angle.

The tests have been remarkably positive so far. A single seven-rotor unit was able to generate the equivalent of 6000 watts in winds of 32.5 miles per hour, six times the power generation of a single-rotor turbine of the same size (7' diameter) in a footprint not significantly larger than that required by a traditional turbine. This is the largest version they've built so far; an earlier four rotor/4' diameter turbine produced 1 kilowatt, and a 13 rotor/18" diameter system produced 400 watts of power. The angle prevents the rotors from "shadowing" each other in the wind, and the multi-rotor design actually reduces vibration.

The FAQ page addresses some of the expected questions, including where they see the system headed. The string of rotors on a shaft lofted by a helium-filled lifting body notion is intriguing, and indeed Selsam claims that NASA has expressed interest in the design for use on Mars.

Is this the future of wind turbines? Perhaps, but Selsam still has some work to do. Six kilowatts is good, but real-world use will need something substantially larger; just how far will this design scale? Unlike traditional turbine designs, the structure of the Selsam unit appears to provide more perching locations for birds; would bird strikes be a significantly greater issue? Finally, there's the look. As we've noted, wind power advocates often end up fighting a rear-guard action against local conservationist groups opposed to the "visual pollution" of traditional turbines -- systems which many people actually find quite attractive to look upon. The Selsam design, conversely, doesn't (at least in its current form) provide much in the way of visual appeal. Could a revolution in wind power design fail in the market because it's ugly?

Comments (9)

Mark Aalfs:

To achieve the status of revolution, probably a certain level of success is implied. If this strategy does gain any legs, it won't go far without the "form follows function" aphorism. If the concept has cost efficiency in large scale applications, there's no shortage of ways to do it beautifully. Recall the multiple turbine propposals for the new World Trade tower in NY.

Jeff Rusch:

To answer your question: I think that ugly not only will fail, but hurt the cause if they try to put these up in people's backyards, because people will come to associate windpower with ugliness despite a variety of designs.

Make it all white with a single tubular base, without guy wires like the single rotor models, and you're halfway there. Then it will be good in remote locations, but it I'm not ashamed to say it breaks my heart that it's not as pretty. There is something about single-rotor tri-blade wind tubines (windmills!) that is very romantic, the perfect fusion of visual poetry and lifesaving technology. Here's hoping they keep working on the design.

A few days ago I came across this design, which in my view is not ugly at all. You have to see it both in 3D and from above to "get it". The inventors (I've contacted them) are pushing to start things up as fast they can.

I expect to see a variety in designs in windpower ... and also a variety in "licenses", much like in dual-license software, where you only pay royalties if a set of conditions is met.

In fact, I'd like to see an exploration on the issue of "licenses for inventions". SolaRoof is going for "ethical public domain" ... what will be the most effective way to bring change to the world? (I expect to see a whole eco-system of licenses, but ...)


Some sort of camo would be worth trying, and any design that looks less like an old UHF/VHF arial would at least be an improvement. I like the look of the massive wind turbines, they look like clean energy to me. I wouldn't want to see a bunch of them perched on Mt. Everest or in a national forest, but I don't think they detract too much from the Indiana, Illinois, Ohio, &c.. industrial/farmland landscape. As for birds flying into them, perch a couple of hawk decoys and an ultrasonic deterrent on it and I don't think birds will fly anywhere near it. I don't know if birds respond to ultrasonic frequencies, but something similar could solve that problem easily.

Vic Hays:

If the bar were extended into a V or triangular shape the strength and rigidity would be increased immensly with room for more rotors. It would also make for better asthetics than an assymetrical design.

Ray Van Raamsdonk:

So using the wind power formula:
P = 0.5xCpx3.14x1.07x1.07x1.225x14.5x14.5x14.5
Wind speed = 14.5 meters/sec = 32.5 mph
Blade length = 1.0668 meters = 3.5 feet
For P to equal 6000 Watts Cp would have to be 0.89 or greater than the Betz limit of 0.59?
Am I missing something?

Ray Van Raamsdonk:

So using the wind power formula:
P = 0.5xCpx3.14x1.07x1.07x1.225x14.5x14.5x14.5
Wind speed = 14.5 meters/sec = 32.5 mph
Blade length = 1.0668 meters = 3.5 feet
For P to equal 6000 Watts Cp would have to be 0.89 or greater than the Betz limit of 0.59?
Am I missing something?

Arthur Rochester:

There have been reports of turbines being setup in the flight paths of migrating birds and nesting areas for raptors like our beloved Bald Eagle. If the rotors of this design are smaller and more visible, the death toll of passing birds may go down. Instead, the long boom may be the perfect perch.


you are genius.that's a good idea for increasing torque moment in the main shaft.

what about the deformations of the main shaft with long axis? with the rotor weight ?

what about yaw motions ?

please sent the futher progress of your innovations.

thanks friend.


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