Reading the winds finds site and size for cost-effective wind-power machines
The development of highly efficient wind machines has eliminated any remaining doubt as to the feasibility of wind power for residential use. The debate now has shifted to the "software" of wind energy.
The most critical factor in determining the cost-effectiveness of a wind system is siting.
A difference in the average wind speed of as little as one or two miles an hour can make the difference between a system that will pay for itself and one that will not.
Professional siting is done in two states. The first step includes observation of wind and geographic characteristics at a site, plus examination of any existing wind data for the area.The second step involves on-site testing of wind speed using specialized equipment.
Most experts on the subject recommend against individuals doing their own siting if the person is serious about spending $8,000 to $10,000 on a residential wind system.
"It's just not possible with the instrumentation today for an amateur to do the proper siting," says Jeff Orchard, a wind-siting analyst for New England Geosystems of New Hampshire.
A three-month siting job with sophisticated equipment that yields continuous readouts can cost an average of $500. The cost can be a strong deterrent to anyone who suspects a site may be incapable of supporting a wind machine.
Yet the initial steps in siting can be done by professional and amateur alike.
A site that is not open and exposed, clear of obstructions, and is not on a hilltop or by the seacoast can generally be eliminated. Zoning laws must be checked to ascertain that there are no local ordinances outlawing the 30- to 60 -foot tower upon which the wind machine will ultimately rest.
Although wind speed can vary tremendously over short distances, for the sake of comparison the data from local airports and existing wind maps which note wind characteristics over large geographic areas can be employed.
If the wind at a site averages more than 12 miles an hour, the site may warrant further testing. This is the point at which the amateur and professional diverge. For the homeowner who wishes to do his own testing, several states, including Wisconsin, Washington, and Oregon, now offer anemometer-loan programs at a small cost.
An anemometer is a gauge with three horizontally mounted cups that catch the wind and measure its speed.
Usually it is mounted on a tower and attached to a recording device, such as an odometer, which collects the data from which the average wind speed can be calculated. In states where no anemometer-loan program exists, wind-system dealers will often rent the anemometer/odometer combination, or it can be bought for roughly $180.
However, wind engineers now regard average wind speed as an inadequate statistic on which to base a decision to buy an expensive wind machine.
The power in wind varies with the cube of the wind speed. In other words, if the wind speed rises from 10 m.p.h. to 15 m.p.h., the increase in power is not 50 percent, but more than 300 percent. Seen another way, with all other factors being equal, a wind that blows at 10 m.p.h. half the time and 15 m.p.h. half the time, is more powerful than wind that blows at 12 1/2 m.p.h. constantly.
For this reason professional wind analysts now measure the energy "density" in wind; that is, the amount of time the wind blows at each different velocity. This is accomplished by attaching an electronic data logger to the anemometer to produce continuous readouts.
Finally, these experts insist that, whatever the method used to test a site, no decision to install a wind machine for economic reasons should be made without first considering local utility rates.
Few 500- to 1,500-watt residential wind machines can achieve cost-effectiveness in areas of low or moderate electric rates, no matter how hard the wind blows.
The reason is twofold. Obviously, greater savings can be derived from generating your own electricity in areas where high rates are the norm. But there also is a new law that requires power companies to buy back -- at half price -- the excess power a wind machine generates.
With the average life of a wind machine placed at 20 years, most wind-system dealers will advise in favor of installing a machine if calculations show that it will pay for itself in 10 years.
The proliferation of dealers and systems can present the homeowner who is considering a wind machine with a jumble of confusing choices, industry analysts admit.
"Every company has its own methodology," says Ross Bisplinghoff, wind program manager for the Northeast Solar Energy System in Boston, who warns that the field is so new that there are few guarantees to protect the unwary consumer.