American Twin  dual rotor wind turbine
Selsam’s innovative dual-rotor wind turbine is rated at just under 1000 watts, but because of its unique design is actually capable of outputting as much as 2,400 watts. It also requires a shorter, less expensive tower then comparable small-scale wind machines. Just now going into production, the unit is expected to sell for around $1,600US.

A Different Spin on Wind Power

Breakfast with Doug Selsam, inventor of the dual-rotor wind machine.

By Bill Moore

Doug Selsam has been designing wind machines since he was 19-years old, usually exploring off-the-wall ideas like turbine blades filled with helium or hydrogen that will float at the end of tethers, generating power without expensive towers.

So, you'd half-way expect that when it came time for me to interview him, he'd be out for his morning walk to a local restaurant in Fullerton, California to have breakfast, making this also the first telephone interview EV World's ever done over waffles and eggs.

At first, I was just going to write up a synopsis of our conversation, but after listening to the audio with its clatter of plates and chatter of waitresses, I decided to podcast the resulting discussion so you too could sit in on the "virtual" breakfast with us, though you'll have to pick up your own tab on this one.

What makes Selsam's machine unique is the use of multiple turbine blades utilizing the same drive shaft, each offset just enough so that it doesn't interfere with the wind driving adjacent blades. This allows his machine to develop much more power at a lower cost than more conventional designs. The reason has to do with some fundamental mathematics, as he explained to me, while ordering his breakfast.

"The mass of a turbine rotor, a large propeller… as you make that propeller bigger and bigger, larger and larger diameter, that mass climbs as a cubic function. That rotor is not only getting wider, but thicker and a larger wing span as well… basically it's growing in three dimensions. So, the mass that's going up is a function of the volume, which is a cubic function, but the swept area, which is the circle it spins around inside, that swept area is called ‘pi R squared'. It's a squared function.

"In order words, your mass is climbing much faster than your swept area. The larger you make one propeller, the less wind it captures in relation to its mass; the less energy you can capture in relation to how much material you have to use. It's really quite astounding the difference. A large utility-scale turbine will be able to grab about 30 watts per pound of blade material. A small, household turbine gets about 200 watts per pound. That's a six or seven-to-one ratio; and that is not even talking any real steps to minimize the weight of the smaller rotor, so it's probably even a more significant difference than that," he said, as a waitress shouted in the background.

"That's the first difference. It's just the rotor weight; we cut it to a fraction of its original rotor weight. Then smaller rotors spin faster."

Selsam explained that a faster spinning rotor eliminates the need of a gear box to spin the generator fast enough to produce an electric current. His design turns fast enough to eliminate this added component.

"Those are the two advantages: lighter set of rotor weight and higher rpm that can directly drive the generator to get rid of the gear box. We get rid of so much of the cost", he observed. "Basically, all the big cost challenges of wind we get rid of with this design."

The real challenge for Selsam, hasn't been technological, but entrepreneurial: trying to find the right people with whom to do business as he shifted from experimentation to commercialization. He says he is constantly being contacted by people offering various sorts of advice or assistance; he characterized it as an "endless fusillade".

"I think the biggest challenge is to winnow through all the people who say they would like to be involved and target who's actually going to be effective and whose interest isn't going to run out after a few days or few months, even… who's going to stick with it and make it happen.

"The other thing is, like any start-up, it would be nice to have unlimited funds to work with." I'll bet.

For Selsam, perhaps the most daunting challenge is finding the expertise necessary to commercialize his turbine, because most of the "experts" tell him it what he wants to do, can't be done.

"There are very few places to draw from for expertise in this type of thing. You've really got to pick and choose…"

He decided to start with small-scale turbines because he wanted to see his concept become a reality. He said that even though the market for this size turbine is relatively small compared to large, utility scale machines, he didn't want to see his idea fall by the wayside and never materialize like so many other wind power ideas over the decades that never got beyond paper.

"If you've really got a superior wind turbine design, it's probably going to be superior in a small size as well," he stated. "Why not put your money where your mouth is and let the rubber hit the road in the way of small scale…?"

Selsam believes he's done that with his "American Twin" which he claims can develop 1.7kWs of power at the international standard of 11 meters/second wind speed. "We're proving it in the marketplace, not just on paper."

He sees his dual-rotor turbine as part of a "whole family" of wind machines built around the same concept of multiple offset blades mounted on a central drive shaft. He believes that the design can be scales up and here are plans in works for larger machines. He built a 7-blade machine for the California Energy Commission that is sited in a Class 1 wind zone that is producing power as if it were in a Class 5 zone. (Wind zones run from Class 1 to Class 7. The higher the number the stronger and more reliable the wind).

But for now, he's content to offer a wind turbine that produces more power than its competitors at a lower height. He claims that because of the design, he can effectively raise the wind power rating of a site two classes. For example a Class 3 site, which covers much of the central and eastern half of the United States, can produce power equivalent to a Class 5 zone where wind speeds are significantly stronger and more predictable.

To date, his company has sold two units in Southern California. They are on private property so they are not high-profile installations from the public relations or marketing perspective. The cost of the early production unit is $1,600, but he anticipates that this number could come down, especially if he switches from expensive carbon fiber blades to wooden ones, creating what he calls a "bargain basement unit." The machines are being manufactured here in the United States in Southern California.

The California Energy Commission has provided Selsam with much of his R&D funding through several grants. The National Renewable Energy Lab or NREL has promised funding, but federal budget cuts have, he said, forced the agency to not fund any small-scale wind machine proposals, including his. He estimated that when you apply for any grant, there's a one-in-five chance of being selected. He noted that there are lots of state grant programs available, but he needs a skilled grant writer to apply for them and that's someone he's not had a lot of luck finding.

"We do have pending funding from the California Energy Commission now. And I've also got almost unlimited interest from investors, manufacturers, water purifier companies, just all sorts of people… international interest. Right now, we're kind of boot-strapping it because there really isn't enough time to chase down all these leads and meet with all these people…" He added that he's spent so much time over the last several years filling out paperwork that he'd just like to concentrate of building machines.

Maybe it was the fact that he was having breakfast and chatting with me on his cell phone, rather than in his office, but Selsam was refreshingly candid in his responses and I know you'll enjoy listening to our morning talk when you use either the build-in, Flash-based MP3 player below the photo or by downloading the file to your computer hard drive for playback on your favorite MP3 device. The program is about 22 minutes long.

EVWORLD Future In Motion Podcast

Download MP3 File

Times Article Viewed: 12944
Published: 15-Mar-2006


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