Assessing Your Wind Resource

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Once you have executed a strategy to make your home or business — and its occupants — more energy efficient and have recalculated energy consumption, it is time to determine how much wind is available to you and when it is available. From this information, you can select a wind turbine that will produce enough electricity to meet your needs.

An assessment of available wind resources can be made using one or a combination of techniques. Professional small wind site assessors, however, rely principally on state wind maps and online sources.

State Wind Maps

One of the best and easiest ways to assess the wind resources in a region is to consult a state wind map. State wind maps list average annual wind speed in meters per second and miles per hour. Unfortunately, wind speed estimates on the map are reported at 165 and 195 feet (50 or 60 meters) above the surface of the ground.

Most states have good wind maps. You can locate your state’s wind map at the Wind Powering America website of the DOE at eere.energy.gov/windandhydro/windpoweringamerica/index.asp. It’s probably faster to search for “Wind Powering America” than to type out this URL. Another great source is www.awstruewind.com. AWS Truewind prepared most of the Wind Powering America maps. The Canadian Wind Atlas can be obtained by visiting cmc.ec.gc.ca/science/rpn/modcom/eole/CanadianAtlas.html.

While wind maps are an excellent source of information for your area, they do have some limitations. One of them is resolution. In some areas, like the plains of western Kansas, wind maps show uniform wind speeds over large areas. If you live in one of those areas, the map will give you a pretty accurate idea of average wind speed. However, wind speeds over more complex topography can vary considerably over short distances. The resolution of the maps isn’t good enough to pinpoint an exact location. Dan’s home in the foothills of the Rocky Mountains is a good example. The
state wind map shows three different classes of winds in his area. Which one applies depends on the specific location. A neighbor a tenth of a mile away in a valley may have very little wind, while a neighbor perched on top of a mountain will have a great deal of wind. In general, the more complex the terrain, the less accurate the wind maps are.

When assessing wind resources, remember that hills, cliffs, forests and buildings can reduce wind speed. However, some types of hills and cliffs can magnify winds, as shown in Figure 4.4. It depends on where you’re located. In most cases, though, wind maps are adequate for siting a small wind turbine. That said, it’s always a good idea to assess the topography, vegetative cover, and ground clutter when estimating average annual wind speed. If you live in an open field on top of a knoll, your wind resource may be significantly higher than a neighbor who lives a mile away in a tree-covered vall

Online Databanks

While state wind maps are an excellent source of information, a few states have not invested in the best mapping technology. Because of this, some professional small wind site assessors perform small wind site analyses using a very extensive online database developed by NASA. The website, Surface Meteorology and Solar Energy, is at eosweb.larc.nasa.gov/sse.

This site provides a wealth of data on wind energy, including tables that show both the monthly and annual average wind direction and average wind speed at sites throughout the world. The site is pretty user friendly, but you will need to start by setting up a free account.



Fig. 4.4: Effect of Topography on Wind Speed. Hills can dramatically increase wind speed. Placement of a tower on the top of the hill could result in a significant increase in the power output of a turbine. Placement of a turbine at the base of a hill could result in much lower output.

Like wind maps, NASA data provides good information, but you should still assess your site very carefully, especially in complex topography. If your site is in a valley or surrounded by trees or buildings, the wind speed at the hub height may be significantly lower than the satellite data suggests.

When in doubt, hire a professional wind site assessor to analyze your site and make recommendations for tower/turbine placement and minimum acceptable tower height. A list of certified wind site assessors is posted online at the Midwest Renewable Energy Association’s website, the-mrea.org. They’re the national certifying body for wind site assessors. You can also ask a professional installer to render an opinion, although not all installers are as knowledgeable about wind and wind site assessment as certified wind site



assessors. Some installers may be more interested in selling and installing a turbine and tower than in giving you an objective wind site assessment.