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and, somewhat, to the amount of voltage present. (I'm going to simplify this greatly, so all you electrical engineers out there, please don't drop your teeth!) In other words, the higher the voltage present in a wire-wound field, the more current the field will draw, and therefore the stronger the magnet will be. However, as the rotor speeds up, the flux density of the field increases accordingly.

The nice thing about this arrangement is that the magnets in a wire-wound field generator put very little magnetic drag on the spinning armature when little wind is blowing. But there's plenty of magnetic drag available when the wind is cranking, and the generator is peaking. The power curve of a DC wire-wound field generator nicely follows the power available in increasing wind speeds (the cube law). That's just the way you want it. PM alternators, on the other hand, always have maximum magnetic drag on the current generating stator. This means that performance is at its peak at really only one spot on the entire power curve. All other points on the power curve are a compromise, especially at the low wind speed end of the curve, the part of the curve where the wind system spends most of its life.

In order to overcome this problem, manufacturers using PM alternators have to design more torque into their blades just to get the rotor spinning in low winds. But remember, torque is inversely related to efficiency. So while PM alternators are simpler (no brushes) and cheaper to build than DC generators, the simplicity comes at a price. To be fair, DC generators come at a price, too. They are more expensive than PM alternators.

Brushless alternators offer the best of both worlds. The fields are wire-wound rather than permanent magnets, but there are no brushes to replace. Their power curve is similar to a DC generator. On the down side, brushless are considerably more complicated, and therefore more expensive to repair or replace than either DC generators or PM alternators.

Tower Top Cost is the cost of the complete wind generating device. In most cases, it does not include the cost of any controls, except where noted in "special notes." Different end uses require different types of controllers, and some end uses don't require any controller.

$/Watt refers to the tower top cost divided by the rated output in watts. This figure is included so that you can make direct comparisons with the cost of PV panels.

Available Systems refers to the wind generator's end use. Different end uses will utilize different control systems, which are not interchangeable. Battery Systems is self explanatory. The voltages available for

Wind Speed in Miles per Hour (mph)

-Whisper 1000 ----Windseeker

---Whisper 600 -Rutland

Above: Power curves for small wind generators.

the battery systems are listed. Utility intertie refers to using the utility grid as your storage. Resistance Heating means that the wind system is used for space heating. These controls are the simplest and least expensive end use option. Water Pumping means that a control package is available to pump water with an electrical pump run off the wind generator directly. No batteries! This category designates whether an ac or DC pump is used. Because of the wide variety of controllers available, prices have not been included. Contact the manufacturer with specific needs and for price quotes.

Estimated Monthly Output at Sites with Average Wind Speeds of 10 mph and 12 mph is included so that you have some idea what a wind system will produce at your site. For comparisons, a very efficient home or small cabin would use 75 to 200 kiloWatt-hours (kWh) per month. The "average home in the U.S." (whatever that is) uses 600 kWh/month. An all-electric home would consume 1200-2000 kWh/month, as might a small business or farm. These are manufacturers'

Wind Speed in Miles per Hour (mph)

Jacobs 23-10 Jacobs Long

Above: Power curves for large wind generators.

numbers, not mine. Be aware that "your mileage may vary"! The number in parenthesis is the calculated capacity factor for the system based on estimated monthly output.

Capacity factor refers to the amount of kilowatts that the generator produces over a given period of time compared to its potential if it were running at full output all of the time. Note that different systems boast different capacity factors. Capacity factor for wind generators is a function of the swept area of the rotor and the rated wind speed of the system. Generally, the larger the swept area and/or the lower the rated wind speed, the greater the capacity factor.

Warranty All the manufacturers warrant their products for parts and labor (that is, in house repairs) against defects in materials or workmanship. This means that you must return the defective part to the factory for evaluation and repair or replacement at the discretion of the factory. Standard practice is that you will pay shipping both ways, just as with any other consumer good. Warranties do not cover improper installation, neglect, use of unauthorized components, abuse or "acts of God" (this is why you have homeowners' insurance). Manufacturer liability is for the defective part only, and does not include incidental or consequential damages.

Time in Business is included so that you can see that these manufacturers are not fly-by-nighters. All of these folks have established businesses and have done extensive business in, as well as outside of, the U.S. Footnote: Whisper wind generators have been available for only four years. Prior to that, the company was known as Whirlwind and manufactured a different line of wind systems.

Routine Maintenance refers to what needs to be done to the wind generator to keep it in prime operating condition for a long life. How long? That's hard to say. I recently took down a Jacobs that had seen 60 years of nearly continuous duty. Properly cared for, any one of these systems could match that.

This doesn't mean that you will never have to replace parts or do some major repairs. Blades will need repainting and probably a new leading edge eventually. Bearings wear out and need replacing. Some systems, as noted, need annual greasing or oil changes. Bolts might loosen and need tightening. Adjustments might be needed here or there. It is unrealistic to expect something as complex as a wind generator operating continuously in the harsh environment that it lives in to work flawlessly with no maintenance. If that's your belief, then don't buy a wind generator.

Some manufacturers recommend only a visual inspection as their maintenance. Bergey Windpower Company, for example, suggests that after you install one of their units, once a year you need to go out to the base of the tower and look up to see if it is still running. That's it for another year! There is no question that Bergey builds the most maintenance-free wind generators available in the industry. However, I am a little more conservative than they are. Many of the catastrophic failures that I have seen over the years with various systems were due to something as seemingly inconsequential as a bolt loosening. I believe that the prudent wind generator owner should thoroughly inspect his/her system twice a year at a minimum; once on a nice fall day before winter hits and again on a warm spring day before thunderstorm season. As they say, prevention is the best cure! Preventative maintenance becomes more important as your investment in the system increases.

Most of the great strides in reduced maintenance have come not from new designs, but from new materials. The designs for today's wind generators have been around for a long time. For example, the side-facing governing mechanism was patented in 1898 and used on waterpumpers. The tilt-up style of governing was patented in 1931. The blade-activated governor was patented in 1951, however, such things as graphite impregnated nylon used in some bushings or the aliphatic resin tapes that are used for leading edge protection were just being developed ten years ago. Continuous upgrading by incorporating modern materials in wind system components has helped greatly in the maintenance arena. The manufacturer who cuts corners by using cheap materials is the one who is courting trouble with his customers.

Power Curves

The power curves for the wind systems reviewed here have been put together so you can easily compare one system to another. The curves compare the power output of the various systems as a function of wind speed. Be aware that this is an "apples and oranges" comparison. To use the PV analogy, it is better to compare all panels of a given wattage than to put all panels made on the same chart. The problem with wind generators is that there are not that many models available to choose from. Because some equipment outputs are close, some reasonable comparisons can be made.

Noise

Questions often arise about how much noise a particular wind generator makes. For the most part, a well designed wind generator is relatively quiet. By the time the wind generator is cranking enough to cause some noise, trees are rustling and buildings are rattling as well.

Wind generator noise can come from two sources: mechanical noise and blade noise. Mechanical noise would emanate from something such as a gearbox. Most of the systems reviewed are direct drive, meaning the blade is coupled directly to the generating device. Only the 10 kW Jacobs utilizes a gearbox.

Blade noises can be caused by two things: rpm and/or the airfoil. Rpm should be obvious. The faster something spins, the more noise it is likely to make. The shape of the airfoil can also have an effect of the amount of noise the blades make. As a rule, true airfoils are quieter than single-surface airfoils.

Installation

The installation of a wind generator on a tower can be accomplished with either a gin pole or a crane. A gin pole is like a boom that is mounted on top of your tower. Using cables and rigging, either the entire wind generator or its component parts are hoisted to the top of the tower, where they are installed. This is relatively easy to do with the smaller systems. However, only an experienced crew should attempt this with something as large as a 10 kW system. These wind generators are probably better installed with the help of a crane.

An alternative is to install a tilt-up tower. Tilt-up towers tilt down to ground level, where the wind generator can be easily installed and serviced. Tilt-up towers are generally more expensive than either freestanding or guyed towers.

My Choice?

"So, Mick, what do you recommend?" is the most frequently asked question that I get. The answer: it all depends on your situation.

I can honestly say that, properly specified and installed, any one of these machines will do a fine job of producing electricity for many years. They all have their own personalities and idiosyncrasies, just like the cars we drive. And, just like the cars we drive, they come in a variety of shapes and prices. Finally, just like the cars we choose, they will all get us from point A to point B. However, not all cars, nor all wind generators, are created equal. Quality comes at a price.

I hope you now have all of the tools you need to make an educated choice. But make sure that you digest the facts and figures, as well as your needs and pocketbook, so that you may choose well.

Access

Author: Mick Sagrillo ruminates on wind generators at Lake Michigan Wind & Sun, E3971 Bluebird Rd., Forestville, WI 54213 • 414-837-2267 Wind Generator Manufacturers

The manufacturers can be contacted for prices or more information. Or you can contact your favorite wind generator dealer.

Bergey Windpower Co., 2001 Priestly Ave., Norman, OK 73069 • 405-364-4212 • FAX 405-364-2078 Manufactures the BWC 1500 and the BWC Excel.

Lake Michigan Wind & Sun, E3971 Bluebird Rd., Forestville, WI 54213 • 414-837-2267 • FAX 414-837-7523 Remanufactures the Jacobs "short case" and Jacobs "long case."

Trillium Windmills, Inc., R.R. #2, Orillia, Ontario, L3V 6H2, Canada • 705-326-6513 • FAX 705-325-9104 North American distributor for the Rutland Windchargers (which are manufactured by Marlec Engineering Co., Ltd. of England) Southwest Windpower, 1855 Kaibab Lane #5, Flagstaff, AZ 86001 • 602-779-9463 • FAX 602-779-1485 Manufactures the Windseeker

Wind Turbine Industries, Corp., 16801 Industrial Circle SE, Prior Lake, MN 55372 • 612-447-6064 • FAX 612-447-6050 Manufactures the Jacobs 23-10

World Power Technologies, 19 Lake Ave. N, Duluth, MN 55802 • 218-722-1492 • FAX 218-722-0791 Manufactures the Whisper 600, Whisper 1000, and Whisper 3000 |ti

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