|Home | Insulation | Conserving Energy
Heating | Books | Links
Before you invest too much time learning about wind generators and wind energy
systems, it is important to ask a key question: is a wind generator a worthwhile
investment? In other words, do you have enough wind energy in your location
to make it worth the money?
Assessing Your Wind Resource
Wind is the clean, free fuel that powers wind generators. In order for a system to make sense economically, you’ll need a site with sufficient wind. Most systems for homes and farms require an average annual wind speed at ground level of about seven to nine miles per hour, according to the American Wind Energy Association. Although that sounds like a lot of wind, it doesn’t mean that the wind has to blow constantly at seven to nine miles per hour year-round in order for this energy source to make sense.
Not at all.
It means that wind speeds need to aver age seven to nine miles per hour year-round. Remember, however, that wind machines are not mounted at ground level. They’re typically mounted on sturdy poles or towers 80 to 120 feet tall. At these heights, wind also blows at a higher speeds. For example, a wind blowing at 8 miles per hour at ground level could be blowing at about 14 miles per hour at 100 feet above ground. It also blows more smoothly — that is, it is less turbulent. Slight increases in wind speed dramatically increase electrical generation. (For example, increasing wind speed from just 8 to 10 miles per hour will increase electrical output by 100 percent
As a rule, the areas with the best wind resources in North America tend to be along seacoasts, on ridgelines, on the Great Plains, and along the Great Lakes. The northeastern United States and the deserts of the southwest are also excellent wind sites, That said, many other areas also have sufficient wind resources to make a wind system a viable option.
Before even considering installing a wind system, homeowners need to assess their sites very carefully. To assess the suitability of your location, you can begin by taking a look at a wind map. You’ll find several online examples by visiting http://rredc.nrel.gov!wind/pubs/atlas/ or www.awea.org/faq/usresource.html.
These maps show average wind speeds. As you can see, the entire United States appears to be suitable for small wind generators. This map is a bit deceiving, however, for the estimates shown here generally apply to terrain that is well exposed to the wind, for example, hill tops, ridge crests, or plains. So, whatever you do, don’t make a decision based on a map of the entire United States. Local terrain features may cause the wind resource at a specific site to differ considerably from these estimates;’ note the authors of Small Wind Electric Systems. In fact: “The wind resource can vary significantly over an area of just a few miles because of local terrain influences on the wind flow.”
FYI: Even small increases in wind speed can result in huge increases in electrical output.
For a more accurate picture of the wind resource in your area, you should access a map of wind resources in your state. You can obtain a copy on the Internet at <www.awea.org>. Or you can locate a map at the National Wind Technology Center’s web- site at <www.nrel.gov/wind>. in Canada, you may want to contact the Canadian Wind Energy Association,
State maps provide a closer look at potential wind resources by region. Even so, you need to assess the resource at your home before buying a wind generator.
One of the easiest ways to assess local wind resources is to obtain average wind speed data from a nearby airport, again being careful to take into account factors at your site such as the terrain or tree cover that could increase or decrease wind speed.
To obtain data on wind speed at your local airport, you can contact them directly. Or, in the United States, you can contact the National Climatic Data Center. They publish a book titled, Wind Energy Resource Atlas of the United States, that provides a wealth of information. This data is available online at <www.ncdc.noaa.gov>. In Canada, check out the Canadian Wind Atlas at <www.cmc.ec.gc.ca/rpn/modcom/eole/CanadianAtlas.html>. While you are studying the data in your locale, be sure to examine average wind speed by month, so you know how much wind is avail able during different parts of the year. This is especially important if you are planning on installing a wind/PV hybrid system.
When assessing your wind resources using this data, bear in mind that airport wind data are collected by a device called an anemometer, mounted 20 to 33 feet above ground. However, household-sized wind machines are typically mounted higher, usually 80 to 120 feet above ground. Remember also that wind speed increases with height. Wind speed, for example, may be 15 to 25 percent higher at a typical wind turbine height of 80 feet (24 meters) than measurements closer to the ground. As you will soon see, even small increases in wind speed can result in huge increases in electrical output. Finally, as Johnny Weiss at Solar Energy International points out, bear in mind that airports are frequently sited in the least windy places to make takeoff and landing safer.
If your wind resource seems adequate, based on assessments of maps, local airport data, and personal observations, some people, like wind expert Mick Cabrillo of Cabrillo Power and Light, once recommended buying a small, inexpensive wind generator and installing it without further assessment. You could, he noted, then determine how well it worked over a period of a year or so.
Cabrillo argued that, although this may seem like a waste of money, it isn’t, The cost of a tower and a small wind machine is typically only slightly higher than that of an anemometer and a tower. If your site merits a larger investment, you can easily sell the wind machine and use the proceeds to help purchase a larger model, Because state wind maps are so good, Cabrillo no longer offers this advice, Use the state maps and install the system you think will meet your needs.
Relying on the Fickle Wind?
Michael Crenshaw, a wind expert, and writer / editor Claire Henderson, write in an article in the April/May 2005 issue of Mother Earth News, “The idea of relying on the wind as an energy source may strike you as risky, since wind seems to be so variable from day to day. But wind actually acts in fairly predictable ways. Analysis of more than a half-century’s recorded data, from thousands of sites, shows distinct patterns in both wind direction and speed through the season. The windiest months occur in winter, while the calmest winds are during summer:’ (This fact is often used to justify hybrid PV/wind systems, as noted earlier.)
Crenshaw and Henderson go on to say, “Two distinct kinds of wind can be found at most locations:’ They are prevalent winds and energy winds, ”Prevalent winds blow frequently and reliably. Energy winds are storm winds or gusts that piggyback the prevalent winds and vary in velocity and duration:’ In a two-week period, the authors note, there are an average of “seven days of prevalent winds and three days of energy winds:’ Oddly enough, while energy winds blow only 3 of every 14 days, they contain about 70 percent of the potential energy that can be harvested by a wind generator. That because power output increases dramatically at higher wind speeds. For those who are mathematically inclined, the power output of a wind generator increases with the cube of the wind velocity. Here’s an example for everyone to drive home the point. Imagine that wind speed increased from 10 to 12.6 miles per hour, a mere 2,6 miles per hour increment, or 26 percent. That’s hardly noticeable to you or me.
But not to your wind machine.
This modest increase in wind speed will increase power production by 100 percent! That is, it will double power production. Imagine what a 30-to-70- mile-per-hour increase in wind speed during a storm can create!
Storms that create strong winds cause wind generators to produce enormous amounts of electricity. Crenshaw and Henderson note, “While your region of the country might not be ranked as ideally suited for wind power, your individual microclimate paired with energy winds might yield enough energy to justify a wind system’ You’ll need a battery bank or an electrical grid to store the excess electricity for later use.