Harvest the Wind
(Page 3 of 7)
June/July 2002
By Michael Hackleman and Claire Anderson
Once you've determined you have a site with average ground-level wind speeds of at least 8 mph (which roughly translate into a speed of 13.9 mph on a 100-foot tower), then you'll need to decide what size wind plant and tower to buy.
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Wind plants have both power (or peak power) and wind-speed ratings (rated power). The peak-power rating is usually more prominent, but is the least effective way to evaluate and compare wind plants. Bergey Windpower Sales Manager Steve Wilke says, "Trying to estimate the energy production of a wind turbine based on its peak-power rating is equivalent to trying to estimate the fuel economy of a car based on its top speed." Currently there are no set guidelines for wind plant ratings: Manufacturers can specify any wind speed to set their rated and peak-power ratings. While the rating might be accurate for a particular wind speed, it will not give you a true picture of how the wind plant will perform at your site, particularly at low wind speeds.
Instead of looking at the prominent peak power rating, you need to study the power production curve (at right) for each wind plant model. The amount of power the wind plant can produce varies greatly depending on the wind speed. The steep slopes on the power curve reflect how small increases in wind speed produce large increases in available energy. They also help illustrate the importance of having good information about the average wind speeds at your site before predicting how much power your wind plant will be able to produce.
COMPONENTS AND COSTS
A complete wind-electric system includes the wind plant and tower, plus a controller, inverter, wiring and battery bank. Wind power expert Paul Gipe recommends buying from a dealer who offers a complete-system package, rather than trying to match components from various manufacturers.
The wind plant captures and transforms wind energy into direct current (DC) electricity. The wind plant must do more than convert the wind's energy into a rotary motion to power the electric generator. It must also automatically and reliably prevent rotor over-speed in high winds or risk damage from centrifugal forces. Finally, it must withstand turbulence, rain, sleet, ice, hail, lightning, corrosion and cold.
Home wind plant costs range from around $1,500 for a 1,000-watt rated wind plant to more than $20,000 for a 10-kw rated turbine. The higher-wattage plants, with their large-diameter, low-rotation-per-minute rotors, are designed to capture energy from low wind speeds. The less expensive models are usually high-speed, small-diameter rotors on lightweight units. Unfortunately, these smaller wind plants, a growing trend in home wind plant design, are proving too noisy for some neighbors in urban and rural areas. Upset neighbors have stopped small-scale wind plant installations or forced their eventual removal.
Paul Gipe has compiled data on the noise effects of several small wind plants. His review is available at www.chelseagreen.com/Wind/articles/noiseswt.htm. Even if you have no close neighbors, don't forget the noise levels of a wind plant with a high-speed rotor may adversely affect your own serenity. (Resist the temptation to mount any wind plant to the rooftop of your home to avoid using a tower. With the roof acting as a resonant chamber, you will be reminded your wind plant is working, day and night, like it or not.)
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