Ten Times the (Wind) Turbine _ Popular Science - same power, less material and weight!

[JohnWxy]

http://www.popsci.com/category/tags/june-2008/#node-21640


TEn Times the Turbine - full article

Today’s largest wind farms are the size of small towns, made up of turbines 30 stories tall with blades the size of 747 wings. Those behemoths produce a great deal of power, but manufacturing, transporting, and installing them is both expensive and difficult, and back orders are common as the industry grows by more than 40 percent a year. The solution, says inventor Doug Selsam, is to think smaller: Capture more power with less material by putting 2, 10, someday dozens of smaller rotors on the same shaft linked to the same generator.

“The wind-turbine design out there right now is a thousand years old,” Selsam points out, as he lets one of his carved wooden blades speed to a blur in the makeshift wind tunnel he’s made of the alley behind his Fullerton, California, apartment. He brainstormed his multi-rotor approach in the early ’80s, in a fluid-dynamics class at the University of California at Irvine. “The textbook said, this single-rotor turbine design is the most power you can get. I knew then it wasn’t right. More rotors equals more power.”



How the Sky Serpant Works: Aligned at the optimal angle, each rotor receives its own wind, increasing efficiency. Of course, more rotors also means more-complicated physics. The key to increasing efficiency is to make sure each rotor catches its own fresh flow of wind and not just the wake from the one next to it, as previous multi-rotor turbines have done. That requires figuring out the optimal angle for the shaft in relation to the wind and the ideal spacing between the rotors. The payoff is machines that use one tenth the blade material of today’s megaturbines yet produce the same wattage.

Selsam never did graduate from Irvine, but over the next couple decades he kept investigating novel wind designs, and by 1999, after an extended hiatus as a heavy-metal guitarist (he claims that the band Metallica stole its name from his group, Metallix), he turned to wind development full-time. In 2003, he landed a $75,000 grant from the California Energy Commission to develop a 3,000-watt turbine—his seven-rotor design met the challenge—and he has now sold more than 20 of his 2,000-watt dual-rotor turbines to homeowners. He’s built them all in his suburban garage.

[kristopher]

1. I'd like to see detailed production statistics.

I have already seen this, and don't consider it all that novel, frankly. The problem isn't that the conventional turbines are inefficient at extracting available energy, it is that the closer you get to the surface of the planet, the less energy there is available to be extracted. To demonstrate this consider that if a given wind turbine will produce 100watts in a 5 mph wind, the same machine will produce about 800 watts at 10 mph. Going higher produces higher wind speed which produces disproportionately more power than adding rotors at lower altitude and wind speeds.

Anyway, that's the theoretical side of it. I'd like to see the production numbers at different wind speeds. There are offgrid applications where power is required and low wind speeds are all you have (ex: powering a water pump for livestock). So this might very well be a major advance for that specific scenario.

[JohnWxy]

2. YOu think because you saw a picture of oneof these at a low elevation that they are limited to low

elevations. They are not. You can put these at high eleveations too.

By the way, power generated varies with the cube of the wind speed (that's why in your example, doubling the wind speed produces 8 times the power). IT also varies directly with the swept area of the turbine blades.

as I said above, just because you saw a picture of this multiple rotor turbine installed at a fairly low elevation you should not conclude they are limited to low elevation installation. they are not.

[kristopher]

5. No

I believe they are limited to low altitude use because of the design requiring two anchor points - and thus two towers. I used the example instead of the formulaic explanation because to most people the formula means squat, while the example is a good visualization aid.

There have been a variety of multiple blade designs over the years, yet the designers end up pursuing taller towers and larger 3 blade rotors for a reason, it works better than the alternatives. And regarding your mention of increased swept area, that has to be viewed in terms of the cost of adding swept area. Do I get more power and reliability by increasing the radius of one or by adding additional rotors on a long single shaft? How is the apparatus oriented to changing winds? What is the cost of configuring the multiple rotors to be able to change their pitch (and angle of attack) as a response to changing wind speeds?

There may be some site specific applications where it is a very effective answer to a need. But as I said, I'd like to see production statistics. I don't see anything that makes me think this is a particularly significant development in bringing wind power to bear on our energy needs. Cool, yeah. Important? Probably not.

[JohnWxy]

3. By the way these are not meant to replace traditional wind turbines. they are suitable for

sites where the tall wind turbines aren't a good fit. IT's not an either or situation.

[kristopher]

6. That's what I said in my first post on the topic.

[Zachstar]

4. It sounds like a good idea if developed further.

I want smaller towns to have the ability to get off the grid. Because of the space around them they can afford to run small groups of turbines and solar facilities. So I like this research.