Building Your Own Wind Generator
Writen by Steve Hicks and reproduced here with his permission
Copyright 1989 Steve Hicks
If work doesn't scare you off and you have a windy site, then building your own wind generator can be a very rewarding experience. Such a project is not for everyone--it will take above-average mechanical skills or an extra amount of determination if you don't yet have those skills.
I have visited a number of do-it-yourself wind machines around the country since 1980 and have developed a profile of the successful builder. Answer yes or no to the following questions and see how you compare to the wind generator homebuilder that succeeds. Do you:
1) Desire to work hard and see the project completed?
2) Own a drill press?
3) Own a welder?
4) Own a metal lathe?
5) Are you willing to read and study wind generator books?
6) Do most of your own car repairs?
7) Have any talent for scrounging used parts?
Of the home craftsmen that have completed a wind generator, I only recall one person that would answer yes to only fourquestions. The average is about five and a half yes answers. If you answer yes to three or less, a wind generator project is probably not for you. If you only have four yes answers, then you should have yes answers to questions one and five. All of the do-it-yourselfers that had six or seven yes answers took on a more difficult project than the one that follows.
If you think you might be interested in building a wind generator, there are three basic things you should do. First check the libraries for wind-related articles and books to learn about estimating the local wind speed, site selection, types of towers and appropriate height and descriptions of successful wind generators. Surprisingly, many home builders do not do these things. The second and third items are to design for simplicity and reliability. A simple first time project is more likely to be completed. It is a lot easier to make changes on a reliable machine that is still standing than a light duty one on the ground that looks like Beetle Bailey after Sarge has beaten him up.
The key to simplicity comes from building a direct-drive machine with the propeller mounted directly to the generator. This means there are no power-robbing gearboxes or belts to deal with, but it will take some time to locate the ideal generator. Although a good 6- or 7-foot-diameter prop will reach 1000 rpm, this is still too slow to be a good match for common car alternators and generators. Most car alternators will not start generating power without their field current switched on--which means more complex controls for the wind machine. Another problem with alternators and car generators is that they usually only have small 5/8-inch or 17-mm-diameter shafts, a little on the light side for a wind machine.
The ideal generator will be a large four-pole one that weighs at least 40 pounds. A few semi type trucks and old city buses used such generators. Even though these generators will be 20-30 years old, they are generally quite serviceable after replacing or repacking the bearings and replacing worn brushes. Sometimes the commutator will need to be turned down on a lathe, a job that isn't expensive. Here are some examples of 12-Volt generator specifications obtained from truck repair manuals in the local library.
Some generators even have their rated output at a specific rpm on the generator tag. The most desirable generators are the ones with the lowest rated rpm since it will lower the wind speed at which the generator starts to put out usable power. For best results the generator should have a rated output no greater than 650 rpm when using a seven-foot prop and no greater than 750 rpm with a higher speed six-foot-diameter prop.
A 6- or 7-foot-diameter prop can easily put out more than 55 Amps in plus-35-mph winds. If the wind gets too strong, even a large 130 pound, 120-Amp generator isn't large enough to keep a good seven- foot prop from over speeding. For high winds you need a governor. A governor can change the pitch of the blades at a certain speed or it can act as a drag brake, much like the simpler Wincharger-type air brake governors. Another type of over speed protection is to have the tail fold parallel with the prop in high winds. Folding the tail manually is also a very good way to shut down the wind plant during periods of high winds.
A home built wind machine in a good site has lots of things going for it: very low cost, a little over a kilowatt-hour a day on the average for a machine with a 6-foot prop where winds average 12 mph, tremendous job satisfaction and a joy to watch--especially on those stormy windy days or nights when solar panels aren't doing anything.
All these benefits sound like a free lunch. Low-cost wind-generated electricity is only achieved by not figuring in your labor. This labor will be many times the amount needed for installing a PV system. If you are going to build your own wind plant, keep it relatively small and simple. If you start with a larger complex machine for high Amps in light winds, you are almost certain to fail. This is similar to telling the Wright brothers in 1903, "Now you can fly, go out, design and build a 747."
My wind system
I live in Livingston, Montana, where the average wind speed is 16 mph and over 20 mph during the winter months. In the winter, the winds are a mixture of strong gusty days and calm ones. It is common for 12 to 48 hour winter periods to average over 40 mph with frequent 60-80 mph gusts. Plus 100 mph winds occur each winter. My residential location and city height restrictions result in tremendous turbulence and lower average speeds with peak gusts only reaching 75 mph.
My machine is a restored 1500-Watt 32-Volt Wincharger that uses a very small tail year round to cope with the turbulent shifting winds. During the summer I drive the generator with either a 10- or 11-foot- diameter Wincharger prop and use the airbrake governor. During the winter months, the prop and governor are replaced with my own design variable pitch governor and a 9 foot diameter rotor. Although this 1500-Watt machine originally came with 12-and sometimes 13-foot-diameter blades, the 9-foot prop will still easily pull 1500 Watts in under 30-mph winds. In higher wind speeds this prop has put out 3 kiloWatts but the generator isn't capable of this amount of sustained power so the governor is adjusted to limit the output to 1700 Watts.
The generator charges a 36-Volt bank of nickel-cadmium batteries which quickly fill up on windy days. Then the excess power is automatically diverted into a large heater. The generator is always fully loaded which maximizes the output and limits the governor wear and tear. On windy nights, all of my 800 Watts of incandescent lights are on in my small 12X15-foot shop.
I will try to provide answers to short specific questions from potential homebuilders if you provide an SASE. My address is:
P.O. Box 394
White Sulphur Springs, MT 59645