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Wind Generators

We originally planned to have perhaps three of the small Air 303 wind modules mounted on the shop roof. We started with one to see how well it worked and were disappointed. The unit was very noisy, broke down multiple times, and did not make its rated output. As noted previously we eventually paid to have the unit modified with the newer 403 components and it has been trouble free for three years now.

We purchased a Whisper 1000 watt model and built a tower for it in 2000. The most logical place for the tower was on a slope beside the runway, a site which mostly precluded a folding, guyed tower. We could have used such a tower though if we installed it farther from the house. But that would have required three times as much (larger) wire, and more disturbance of vegetation. Instead I built a 65 foot free-standing lattice tower. A permanent hoisting mast with an electric winch and a counterweight were included to make the tower easy to raise and lower by myself. A removable stand-off mount allowed the Air module to be moved off the roof, from where the noise and vibration had been occasionally keeping us awake for two years.

The combined output of the two wind generators is about 1200 watts in high winds. More often, we see less than half as much in light winds. But, since that power is potentially available for 24 hours a day it can be substantial. In our application wind accounts for about a third of our total production. Of course there are still times when there is only sun, or only wind. During some of those times the backup generator has to make up any shortfall. And there are occasionally calm, cloudy days when that generator has to do the whole job.

The Whisper 1000

This nine-foot rotor, two-bladed generator (the redesigned model has three blades) http://www.windenergy.com/PRODUCTS/whisperh80.html weighs about 65 pounds. As wind speed increases, the power head hinges to angle out of the wind, thereby regulating rotor speed. The unit generates three phase AC which is converted and regulated by an indoor "EZ Wire Center". This box has adjustable voltage settings and a built-in digital meter. It accommodates one additional input which we used for the other wind generator. That allows the output of each generator to be read separately or combined. When the batteries are full and the wind is still blowing, excess current is diverted to a "dump load", which in this case is a small heater mounted in the workshop. The Whisper came with a detailed instruction manual and installation was uneventful. The governing action works without fuss, its output is on spec, and it’s much quieter than its smaller tower mate. In our experience so far it works as advertised, and we are very happy with it.

The Tower

This drawing shows the basic layout including the hoisting system. The tower itself is a steel tripod. The bottom 21 feet of the legs are 2.5 ID X .185 pipe. The balance of the legs are 2.5 OD X .125 round tube. Most of the horizontal braces are 1.25 X .065 round tube, with some of the longer, lower ones 2 inch and 2.5 inch. Most of the diagonal bracing is 1 X .125 flat stock, with some of the lower ones 1 X .185. This was mostly eyeball engineering, the object being to keep the tower stiff enough to handle the load and light enough to hoist easily. The finished weight (calculated), including the generators and wiring, is 1450 pounds.

The hoisting mast is 5 X 5 X .185 square tubing. The main winch is a 12V, 8000 pound capacity electric model, with a 5/16 inch cable. The backup winch is a manual worm-drive 2000 pound capacity unit with a 1/4 inch cable. The handle has been removed so that it can be run with a rechargeable drill. This winch is only used as convenient way to keep a backup cable tight in case of any problem with the main winch or tackle. There is also a 1500 pound counterweight which has 17 feet of travel up and down the hoisting mast. The counterweight isn’t really necessary, but it serves to lighten the load on the main winch during the initial lift thereby making it easier to lower and then raise the tower powered by a single car battery. All three hoisting cables run up the mast and over sheaves. The mast has two 5/16 inch cables from the top two rear anchors, with two more from the middle to the same anchors. It also has two front guys from the middle which are attached to the same location as the two pivot legs. A manually operated hydraulic ram is attached to the rear leg of the tower so that it can be jacked up about 10 inches until it is well over center in order to lower it.

Five holes were dug for the footings. One trench covered the two hinged legs, one more for the third leg and hoisting mast, and two smaller ones for the hoisting mast rear guy anchors. All of the holes ended up being a little larger than necessary as boulders were dug out, so it took about eight cubic yards of concrete to fill them. The above ground hardware is connected to 4 X 4 X .375 angle stubs sticking up a few inches out of the concrete. These go down about four feet and are welded to a grid of reinforcing bar. Braided copper cable was laid in the excavations prior to concrete pour and these are connected to the tower legs as grounds for lightning protection.

To lower the tower, the two pivot bolts are loosened slightly, and the bolt holding the third leg is removed. The winch cables are slackened, and then the rear leg is jacked until the tower goes over center and its weight goes onto the winch cables. Then the main winch is operated to lower the tower, with the smaller winch run as necessary to keep the backup cable tight. Lowering takes about two minutes.

Raising the tower takes about three minutes since the winch runs a little slower hoisting the load. The counterweight descends during the lift, reaching the ground as the tower gets to about the half-way point. Once the tower is near vertical and its weight falls onto the hydraulic jack, a slight tension is kept on the cables as the jack lowers the tower into position. The jack makes it easy to position the tower so the rear leg bolt can be inserted. Then all three bolts are tightened.

Noise

Perception of wind generator noise seems to vary depending on application, so some explanation is in order. Our home is very well insulated, has fixed glazing, and is very quiet inside. Even so, if the doors are open for ventilation, you can hear every bird chirp. But those doors aren’t open in high winds at night when we’re trying to sleep, which is the only time that the noise would be a concern for us. A little noise during high winds does enter in a few other areas though. Some comes in through the chimney which results in some buffeting audible at the fireplace. If the bedroom ventilation grill is open then wind noises are evident there as well, but only if the wind is from that direction. In very high winds there's also a buffeting noise from the wind striking the roof. To sum it up - in moderate winds, it’s almost completely quiet indoors, but at times of high wind there is some background wind noise audible even without the wind generators running.

The generator tower is some 150 feet from the house. The base of the tower is about 10 feet higher than the floor level of the house. The Air unit is about 55 feet above that, and the Whisper is another 10 feet higher. The noise from the Whisper, even at high output, is hardly audible above the background noise of the wind. It’s kind of a whooshing sound, and few people would find it objectionable indoors or out. The Air unit is another story. At low wind speeds it makes a whirring noise. Audible above the sound of the larger generator but not appreciably so. As wind speed gets up to about 20 mph the sound changes to more of a howl. Still not a problem though, indoors or out. As wind speed increases further, the howl gets loud enough to be heard indoors, louder than the background noise and the Whisper noise combined. Once wind speed is about 30 mph, the noise changes to a loud and objectionable "blaat". As the wind speed varies and the blades twist to limit rotor RPM, the blaat noise increases and decreases.

Unless we're short of power, we manually shut off the Air unit at night during high winds, particularly during the warmer weather when the ventilation grills are open. If we had neighbors close by we’d have to shut it down whether we needed the power or not, it’s that noisy. There's a newer model called the AirX which is supposed to be quieter.

Advice, and things I’d do differently next time

If you’re considering wind power, those in the know would advise you to use as tall a tower as possible. You might consider using a smaller generator higher up rather than a larger one closer to the ground. Tilt-up, guyed pole tower kits are cheaper and easier to install than free-standing ones like ours. If ease of maintenance is a concern, consider using a winch, either fixed or attached to a vehicle, rather than "towing" the tower up and down. Choose a generator that is efficient at low wind speeds if that's what you have, and give preference to models with larger rotor diameters.

If I were building another tower like this one I would likely use somewhat smaller diameter but heavier walled tubing for the upper legs. And I’d vary the spacing of the horizontal bracing to allow all the diagonal bracing to be a uniform 45 degree angle. That would minimize the number of components and welding.

Click on this link to see a Page of several thumbnail wind tower photos (click on each thumbnail to see a larger version, use your browser's "back" button to return)

Thanks for all the help

I found the design and building of this tower to be a real challenge. Several people provided helpful insights during the process. Tim O’Flaherty of Nova Scotia, a tireless wind energy advocate and frequent contributor to the Usenet group alt.energy. renewable, directed me to the AWEA discussion group http://www.egroups.com/group/awea_wind_home. From there I corresponded with Michael Klemen of North Dakota. Mike operates several large wind generators, and his web site http://www.ndsu.nodak.edu/ndsu/klemen/ has a detailed data history for each. It also has an organized collection of links to AWEA discussion posts. A very useful resource for anyone considering wind power. Bob Pechie of Connecticut also provided much feedback. He has a site http://www.northeastwindenergy.com/ which includes photos of some impressive towers he has built. And Eugene Maslov, an aircraft engineer from Russia who has some prior experience building wind generators, put in a good deal of time making calculations to proof my guess-and-by-golly tower material choices. Occasionally, after finishing a day’s work welding pieces together, I'd e-mail Eugene the latest photos. By morning there were detailed comments, drawings, and annotated photos awaiting me. Very impressive, especially considering the distance. I would highly recommend him to anyone needing his services. His web site http://www.people.nnov.ru/maslov/index.html#accord201 has photos and details of his very interesting amphibious aircraft designs.

Thanks guys!