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Micro Wind Turbines

These topics are covered on this page:
The Truth About Wind Energy Pre-built Micro Turbines Building Your Own

Wind Energy Overview
For most people, on-site wind power is unfortunately not going to be a viable and/or cost-effective source of alternative energy for the home. This is due to issues with the location in which the proposed micro-turbine is to be installed. To produce much electricity, a wind generator must be erected in an area where it is exposed to breezes that are not being obstructed or diverted in some way by nearby objects, including the ground. That is why you'll generally see commercial wind turbines located at a decent elevation and more-or-less out in the open. This is not to say that one can't erect some sort of micro-sized wind turbine in a backyard or above the roof of a house, it's just that the results are likely to be disappointing. There is one application of these tiny wind generators that apparently works well, and that is on a boat. Being on the open water exposes the blades to plenty of wind since there isn't much nearby to interfere. In my own experience, a house-mounted unit right in town with other buildings and trees nearby produced very poorly, the blades spending most of their time standing still, even on a breezy day. My observations indicate that such an installation responds mainly to gusts or sudden wind currents rather than to the main thrust of the wind, which is no doubt being deflected by obstacles.

Pre-built or Kit-built Micro Turbines
Purchasing an inexpensive micro wind turbine is a buyer-beware situation, because sometimes there an inflation of expectations in what the seller says about the device. I purchased one from a fellow on the large Internet auction site who claimed that what I was buying was capable of putting out 125 Watts. Doing some quick calculations using Watt's law (P=IxE or power equals current times voltage), I determined that this should be something like 10 Amps of current at 12VDC, or maybe about 7 Amps, if it was rated in the same manner as two 60W solar panels. Imagine my disappointment when I saw that the "generator" was a little gearhead motor, smaller in size than you'd find on a cordless electric drill. I figured I'd been deceived, but wanted to give the guy the benefit of the doubt since he assured buyers that every unit he sold had been tested for output under "controlled conditions". I figured this meant either a set distance from a large electric fan, or with the shaft being spun by another motor. I also decided he must have determined the wattage rating by multiplying short-circuit current by open-circuit voltage. This is meaningless, of course, since voltage output into a short circuit is almost nothing and current flow through a virtually open circuit is miniscule. I put the shaft into the chuck of an electric drill and verified that there was absolutely no way that what I had purchased could possibly put out the advertised power, even using the incorrect application of Watt's Law. To make a long story short, the most I've ever seen this micro turbine put out in real-world conditions is 1.2 Amps at about 14 Volts, or approximately 17 Watts of power. That was on a day when the wind gusts were so strong that I was afraid the turbine would literally be torn apart. Most of the time, it puts out a few hundred milliamps for very brief periods of time of generally less than 30 seconds.

Homemade Wind Generators
Let me describe the micro wind generator I purchased in more detail, as it's similar in construction to those being sold by others and may give you some ideas for building your own, should you choose to do so. The fellow who built it is a welder and began by welding a short piece of small EMT conduit at right angles to the main frame, a piece of 3/4-inch square steel tubing a foot in length. The small-diameter conduit "down tube" slips into a piece of 1-inch EMT conduit for a pole and becomes the pivot point that the wind generator turns on as the direction of the wind changes. I made an improvement here and slid a large washer over the tube, applying plenty of silicone seal between it and the frame in order to keep water from getting down into the mast, which it would have otherwise done. At the rear of the frame and bolted to it is a piece of white plastic of the type sold at home improvement stores for use in shower enclosures. This measures 9 inches on the bottom and is a foot tall, with a forward edge that tapers back so that the very top is only 1.75 inches wide. The rear edge of the piece is at right angles to the frame and actually extends beyond it by about 3 inches. This is the tail that keeps the front of the generator pointed into the wind.

Mounted at the front of the frame and parallel with it is the gearhead motor described earlier. About 2.75 inches long, it is held to the top edge of the frame by two pieces of strapping going over it and bolted through the sides of the square steel. An ample amount of clear silicone seal was used to glue the motor to the straps, as the body is stepped and the rear portion is not in contact with the frame. The motor has what is known as a gearhead on the front which reduces the rotation of the shaft by a ratio of about 27:1. In generator use, it means that the blades can turn the shaft of the motor itself at an appropriately high number of RPMs while spinning at a much slower rate of speed themselves. I don't know what the motor's nominal voltage rating is as I can't see the label, but I'm guessing it is between 20 and 50 Volts. Mounted to the gearhead shaft with two setscrews is a homemade aluminum cylindrical adapter that fits over the shaft and adapts it to accept a 1/4 inch bolt for securing the blade hub. This circular hub, about 4.5 inches in diameter, is made of thin steel with a mounting hole drilled in its center. Another 8 bolt holes allow four blades to be mounted around its circumference. Each of these has been cut from a piece of thinwall PVC pipe and is about 16 inches in length. Covering the gearhead motor assembly is a piece of corrugated PVC hose of the type used to connect to a sump pump. It has been split at the bottom in order to fit over the assembly and is glued in place with silicone seal. Short black and red wires are soldered to the terminals at the back of the motor with a blocking diode inserted part way down the red one. A piece of tubing was shrunk over the diode and both leads. The builder drilled a vertical hole through the frame right above the pivot so that wiring might be run down through the mast, which I have done in my installation. I sealed around the wires with silicone in order to keep moisture out of the conduit.

I may someday try to build my own micro wind generator, although my experience with wind to date has been a bad one. Folks do succssfully build their own and sometimes post the information on the Internet. Generally speaking, the blades they use are fairly large and are connected to a motor/generator/alternator of much greater capacity than a few Amps. DC permanent magnet motors seem to be preferred for electrical generation, with certain Ametek models being very much in favor. These were used to drive reels of tape in early mainframe computers and often showed up inexpensively on the surplus market. That is no longer the case now that new uses for them have been discovered by hobbyists. Another item that is in demand for use in electrical generation is a used treadmill motor of the permanent magnet variety, which most are. Both these and the Ameteks have a high voltage rating, meaning that they don't have to rotate at an exceedingly fast rate in order to produce just the 16 Volts or so necessary to charge a 12-Volt storage battery. That is the key to electrical generation from wind or pedal power, as it's difficult to directly spin the shaft of a low-voltage motor fast enough to produce the necessary voltage. One way around this is to use a lower voltage motor with a gear drive to increase the rotational speed of the shaft. This is the method used in the micro wind turbine I bought. The disadvantage to doing this is that the meshing gears create a whine that may be annoying. Plus, it means additional parts to wear out with time. I have not tried it myself, but the thought occurs to me that a discarded 18 or 19.2 Volt cordless drill might be useful as the generator portion of a home-built wind turbine. This would be much less expensive, though less durable, than other motors and the internal gearing would allow for a relatively low blade speed. It would be exceedingly noisy, however.

One problem I encountered in my installation, which I haven't read much about elsewhere, is RFI, or radio-frequency interference from the sparking at the brushes of the motor/generator. When the blades were spinning, static could be heard in radios and the DTV signal to the television became interrupted. Elimination of this nuisance necessitated connecting a combination capacitive and inductive interference filter to the wind generator's wiring, just beyond the point where it left the bottom of the mast. I also ran the several feet of cable between the end of the conduit and the filter/terminal box through a grounded braid in order to shield it.

In doing some Internet research on the topic of wind power, I came across several alternatives to the traditional blade configuration of the micro wind generators. One design employed an aluminum vertical turbine of the sort used on the roof of a building to remove hot air from the attic area to the outside. A kit was available for constructing a multi-pole generator inside, which I thought was a novel and worthwhile idea. A vertical turbine like this will react to wind currents from any direction. Another design someone came up with was to put strips of aluminum between the spokes of a bicycle wheel to make blades, of sorts. They had a video of the wheel spinning in a breeze, but I don't think they had tried harnessing the energy from it. That would probably involve some sort of friction drive against the tire or a large rubber belt around the rim. Like a traditional blade assembly, this design would require a tail be mounted opposite as well as a pivot point in order to keep it headed into the wind.

Before embarking on any project to install a micro wind generator, spend the time to thoroughly research the subject and the particular siting situation you have. Even micro wind turbines can produce noise and, when mounted to a building, this noise is conducted through the pole and into the structure where it becomes a low-pitched humming vibration. Keep potential objections from neighbors and city or town officials in mind, especially if it will be left up 24/7. It's also important to think of safety issues, such as what would happen if a sudden storm were to come up and send pieces of the blades flying through the air where they might damage property or worse. Potential liability may outweigh any benefit to having the electricity from wind power. My own circumstances determined that the small amount of electricity produced by the micro wind turbine was not worth the drawbacks associated with having it mounted outside all the time. The output from our solar panel being sufficient, "twirlybird" spends most of the time indoors, waiting for a windy day when its energy might be needed.

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