Other Considerations

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Although swept area, weight, annual energy output, governing mechanisms, shut-down mechanisms and sound levels are the most important factors to consider when buying a wind machine, there are other details that manufacturers provide. We think readers should be familiar with them, but not let them overly influence their judgment.

Cut-In Speed

One factor that is of little relevance is the cut-in speed — the wind speed at which a wind generator starts producing electricity. Most turbines don’t produce appreciable amounts of electricity until wind speeds reach 10 miles per hour. They produce full power at speeds from about 23 to 30 miles per hour.

Some manufacturers recommend installing a turbine with the lowest cut-in speed possible in areas of low wind to make better use of the wind resource. However, because low wind speeds hold very little energy, low speed cut-in isn’t important.

Power Curves

Another useless bit of information provided by wind turbine manufacturers is the power curve like the ones shown in Figure 5.8. Power curves are graphical representation of the power production of a wind turbine (in watts) at different wind speeds.

While power curves make for good visuals, they aren’t always accurate. They’re not always obtained under the most ideal test conditions. Moreover, they are a bit misleading to the uninitiated. That’s because most wind turbines operate at relatively low wind speeds — around 10 to 20 miles per hour — and very rarely operate at the peak of the power curve. As you can see, wind turbines produce much less electricity at lower wind speeds. When considering a wind turbine, what’s important is how much energy it will produce at your site on your tower at your average wind speed — that is, the AEO.

Rated Power

Last but not least is a measurement known as rated power, one we’ve avoided using as much as possible in this book. Rated power is the output in watts at rated wind speed. Much like the output of solar electric modules, rated power of wind turbines was devised to give buyers a way to compare products. Buyers, for instance, typically compare one kilowatt or ten kilowatt turbines as they would compare solar modules.

Rated power is of limited usefulness in large part because there are currently no standards in the wind industry (as there are in the solar industry) for determining rated power. Manufacturers determine rated power in different ways and at different wind speeds — the rated wind speed. This situation will change because the small wind industry is developing a standard technique of measuring performance.

To see why rated power is less than ideal, consider three wind turbines with identical rated power of 1,000 watts or 1 kilowatt: (1) Bergey’s XL.1, (2) Southwest Windpower’s Whisper 200, and (3) Eveready’s Kestrel 1000. At first blush, you might assume that all three wind turbines are identical. After all, they’re one kilowatt turbines. However, Southwest Windpower’s Whisper 200 achieves its 1,000-watt rated output at 26 miles per hour. Bergey’s XL.1 produces its 1,000-watt rated power at 24.6 miles per hour, and Eveready’s Kestrel cranks out 1,000 watts at 23.5 miles per hour.

Although it might seem that the wind turbine that produces 1,000 watts at the lowest wind speed would be the best buy, that’s not necessarily true. There’s much more to consider, including swept area, tower top weight and AEO. As noted learned earlier, in most cases the wind turbine with the largest swept area produces the most electricity, but don’t make that assumption without looking at the annual energy output. At an average wind speed of 8 miles
per hour, the Kestrel 1000 will produce about 900 kilowatt-hours of electricity annually. The Whisper 200 will produce about 720 kilowatt-hours annually and the Bergey will produce approximately 660. (These numbers are based on the manufacturers’ estimates.)

It is also important to note that rated power is one point on the power curve and is the output at a wind speed that is much higher than those typically encountered at most sites. Thus, the rated wind speed only represents a small fraction of the wind resource at a site. We’re interested in output in the typical range of wind speeds at our site, which is well below the rated power. Our advice on rated power: forget it.

Final Factors

When shopping for a wind turbine, be sure to check into the company’s customer service record — how well it supports its dealers and customers. Some companies like Bergey Windpower and
Abundant Renewable Energy have stellar service records. Be sure that the company you buy from offers technical advice should you have trouble and that their technical support staff speaks your native tongue.

Another factor to consider is how long the company has been in business. Doing business with a company that been in business for a while, say ten or more years, is a good idea. A related criterion to take into consideration is how long a wind turbine has been on the market. The longer a wind turbine has been on the market, the better. It has been tried and tested and improved upon.

It’s also important to check on the availability of parts. Parts shipped from foreign countries, such as China, Europe, South Africa or Mexico may take months to arrive, if they’re available at all. Meanwhile, your $30,000 wind energy system sits idle. When shopping, check to see if the importer of the wind turbine you are interested in stocks spare parts.

It’s a good idea to consider the number of moving parts and wear points in a turbine. Some designs, like the Jacobs turbines manufactured by Wind Turbine Industries in Minnesota, contain a lot of moving parts, which results in numerous wear points — up to 300. These machines may require a lot of tinkering at 100 feet.

Be sure to check out the warranty. Warranties typically run five years. The longer the better. In June 2009, Bergey Windpower boosted its warranty to 10 years; others have pledged to follow suit. Also be sure to determine what warranties cover. Is it materials and workmanship or parts only? Does it include shipping? Unfortunately, most warranties do not cover the cost of labor.

We recommend buying from a local dealer/installer, too. That way, you’ll have local support, even if you opt to do the installation yourself. Be sure to ask for references and interview them.

If you buy from an online wholesaler, be aware that most of these companies do not offer technical support, installation advice or assistance. Nor do they offer replacement parts or repair services. If you buy cheap, you are on your own when you need help.

We believe that it is a good idea to stick with name brand wind turbines and avoid newcomers and foreign imports, especially Chinese-made machines, at least at this time. Buying a used or
reconditioned wind turbine may be an economical option, but it’s not a very good idea. The problem with used wind turbines is that you don’t often know what you’re getting.

If you buy a remanufactured wind turbine, you want to be sure that the machine has been fully reconditioned, not just painted and with new blades installed. Make sure that the equipment supplied with the turbine, like the controller or inverter are code compliant. You may also want to obtain an extended warranty. Also be sure you can find a tower for the turbine before you purchase it. Suitable tall towers for the larger small-scale wind machines are hard to find.