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Brewing up some wind power

Axial-Flux And Other Diy Wind Turbines

By Rex Ewing

Wind energy is sexy. On rare occasions when I get cajoled into speaking about solar and wind energy, there will unvaryingly be more questions from the audience about wind turbines than solar panels. And why not? Wind captures the imagination in a way that solar cannot, despite the fact that the average renewable-energy enthusiast is a thousand times more likely to invest in solar than wind. Solar panels are quiet, pensive things, eternally absorbed in the sub-atomic-scale goings-on at the PN junction and utterly boring to observe while engaged in the secretive task of harvesting solar energy. Wind machines, in stark contrast, are adrenaline junkies. The blades spin and whir furiously, while the turbines yaw and furl in response to the ever-changing breeze overhead, almost as if they’re daring the wind to kick up the pace as they go about the heady business of turning the energy of the unsettled atmosphere into the electrical energy understood by toasters, hair dryers and table saws.

Little person, big machine. Maya Bartmann stands in front of her father’s 20-foot turbine just before the tower is tilted up.

Problem is, wind turbines can get expensive. My Bergey XL.1—which is presently jousting with a squirrely 17-mph breeze atop a 55-foot tower—retails for over $2,700, and that’s toward the low end of the spectrum for 1,000-watt machines. It’s only natural, then, that so many people should try to save a little money by building their own wind turbines. But is it a wise thing to do?

To answer this question, I made a trek up the canyon to chat with my good friends Dan Bartmann and Dan Fink (hereafter referred to as DanB and DanF) at DanB’s shop. Together Dan and Dan have hand-built more than 200 turbines of varying sizes and outputs, and have proudly mounted them on towers all over the world. Considering that wind-energy devotees travel thousands of miles to attend their workshops, and that their witty, hands-on book, Homebrew Wind Power (Buckville Publications, 2009), is now in its third printing, they seemed like just the guys to talk to.

DanB’s 20-foot machine atop an 80-foot tilt-up tower.

Dan and Dan advocate an axial-flux geometry, in which a magnet-impregnated rotor turns in relation to a fixed stator, like two face-to-face pizza pans set on edge. They are sturdy machines capable of making significant power in low winds. And, as evidenced by DanB’s four-year-old 20-foot-diameter machine (which has survived several 100-plus mph winds), they’re tough as nails.

But first things first. What else is out there? The Internet is rife with plans for making small turbines using low-rpm DC motors, such as those manufactured by Ametek, and Dan and Dan have built their share. “They will make electricity at about 300 rpm, and if you put a three- to five-foot blade on it, it makes a pretty good little 50-watt wind turbine,” says DanB, “but they’re not waterproof and the bearings don’t hold up. I’ve never had one last more than three months without brush or bearing failure, or without the hub coming off the shaft.” Adds DanF: “But they’re cool high-school science projects. Like maybe you could charge up the battery for your father’s popup camper.”

But as a realistic way to lower the power bill? “Forget it. To put a dent in the power bill it takes a lot of swept area. It takes a big machine.”

Okay, scratch that one off the list. What else? “Hugh Piggott’s radial-flux brake-drum windmill worked, but it was very time consuming and expensive to construct,” DanF explains. To which DanB adds, “But it was the first really good plan out there. It involves taking a great big electric motor apart, winding the coils like we do, and gluing them to the outside of the motor’s laminates.” You then take a large brake drum, fix magnets to the inside of it, fit it with a bearing, and voilä: “A 300-pound, 300-watt machine.”

Hugh Piggott, for those new to this business, is a wind-power legend. He lives with his family on an island off the northwest coast of Scotland where the winds are punishing and grid power is nonexistent. Like Dan and Dan, Hugh spends a great deal of his time traveling the world teaching his craft. “Hugh really perfected the furling system we use, and to a large degree designed the modern incarnation of the axial-flux alternator,” DanB confided, with a distinct note of reverence for his friend and mentor. Plans for all of Hugh Piggott’s turbine designs can be found at www.scoraigwind.com.

We then discussed the concept of vertical-axis turbines, machines that spin on an axis perpendicular to the ground and, realistically speaking, are hardly worth a minute of your time. Commercially, this concept is exemplified by the sleek and shiny Darius machines, though in the handyman’s backyard the result is invariably less elegant. Whatever it looks like, however, there are two inescapable problems with the vertical axis design. One, they’re installed near the ground where there’s lots of turbulence and very little useful wind, and two, they have as much mass turning into the wind as away from it. This adds up to something like a four-fold loss in efficiency, making these machines poor competitors against the far more common horizontal-axis turbines.

The completed alternator for a 12-foot machine with the tail boom attached.

Which takes us back to the axial-flux design and why Dan and Dan are so sold on it. “The axial-flux is cool because it’s a pretty well sorted out design that’s been around for 120 years and is easy to build,” DanB tells me. “You can build an alternator with fairly primitive tools that’s going to work well. And that’s really tough to do any other way.”

Why, after more than a century, does the axial-flux design emerge as the winner in the DIY category? “Because,” DanB points out, “the super-powerful neodymium magnets we’re using only became affordable in the last 15 years.” The stronger the magnets fixed to the rotor, the stronger the induced electromagnetic field and the more amperage the alternator’s windings can produce. When it comes to these magnets, however, super-powerful is almost an understatement. They will cause a lot of pain to any body part that carelessly gets in the way when they’re feeling…attractive.

If you cruise the Internet, you will run across any number of hucksters claiming that, by buying their plans and building their wind-turbines, you can lower or eliminate your power bill. These claims are utterly absurd. Like most people with wind turbines (myself included), Dan and Dan live off the grid. And practically speaking, off gridders are the only folks for whom DIY wind turbines are worth the time and effort. This exclusiveness has not so much to do with the turbine itself as it does with the sum of the other components necessary to make the turbine useful: you will need a tower tall enough to hold the turbine up at least 20 feet above the tallest obstruction within 300 feet. (Sorry, but rooftop mounts are a bad joke.) In addition, you will need at least a couple hundred feet of heavy copper wire, rectifiers or a charge controller to convert the alternator’s AC to battery-compatible DC, a dump load to soak up excess power, and several heavy-duty batteries to store the turbine’s output. As if all this weren’t enough, you’ll also need an inverter to change the batteries’ low-voltage DC into high-voltage appliance-friendly AC. To do all this right you should be prepared to spend several thousand dollars in addition to what you’ll have wrapped up in the turbine. If you live off the grid in a windy enough site, or you have a grid-tied PV system with batteries, then a high-quality DIY wind turbine might make sense. But if your power is supplied exclusively through the grid—hence, no batteries—you’ll be much better off buying a commercial turbine with direct grid-tie capabilities.

Stator windings ready to be set in resin.

To build, say, a 12-foot-diameter axial-flux machine, plan on about 60 hours of labor and an outlay of $1,000 to $1,600, depending on how much of the metal fabrication you do yourself. For your time and money you will get a serious machine that will produce up to 1,500 watts in 25-mph winds, and outperform my expensive Bergey XL.1 by two-to-one in lighter winds. Will it supply all or most of your electricity? If you live on a hilltop in Terra Del Fuego, maybe, or in a small cabin with minimal loads. Otherwise, no. But if you’re off grid relying entirely on solar electricity, you will find that wind has a few tricks that solar cannot duplicate, like the ability to make electricity at night and during stormy weather.

Dan Bartmann and Dan Fink can be reached through www.otherpower.com, where plans, books, parts, kits and seminars are also offered. Or you can stick some blades on a DC motor and charge up the auxiliary battery in your boat or RV. Either way, it’s bound to be a learning experience.

Rex Ewing is the author of Power With Nature and Crafting Log Homes Solar Style, and the newly released 2nd edition of Got Sun? Go Solar, a best-selling book that explains renewable energy options for grid-tied homes. Rex lives off the grid with his wife, LaVonne, in a hand-hewn log home in the Colorado foothills. His books can be purchased at the Countryside Bookstore.

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