Small Wind Guidebook/Is There Enough Wind on My Site
Is There Enough Wind on My Site?
Is the wind resource at your site good enough to justify your investment in a small wind turbine system? That is a key question and not always easily answered. The wind resource can vary significantly over an area of just a few miles because of local terrain influences on the wind flow. Yet, there are steps you can take to answer the above question.
As a first step, wind resource maps can be used to estimate the wind resource in your region. The highest average wind speeds in the United States are generally found along seacoasts, on ridgelines, and on the Great Plains; however, many areas have wind resources strong enough to make a small wind turbine project economically feasible.
Another way to indirectly quantify the wind resource is to obtain average wind speed information from a nearby airport. However, caution should be used because local terrain influences and other factors may cause the wind speed recorded at an airport to be different from your particular location. Airport wind data are generally measured at heights about 20 to 33 ft (6 to 10 m) above ground.
Average wind speeds increase with height and may be 15% to 25% greater at a typical wind turbine hub height of 80 ft (24 m) than those measured at airport anemometer heights. The National Climatic Data Center collects data from airports in the United States and makes wind data summaries available for purchase.
Another useful indirect measurement of the wind resource is the observation of an area’s vegetation. Trees, especially conifers or evergreens, can be permanently deformed by strong winds. This deformity, known as “flagging,” has been used to estimate the average wind speed for an area.
Small wind site assessors can help you determine whether you have a good wind resource on your site. State or utility incentive programs may be able to refer you to site assessors with training in assessing the wind resource at very specific sites. Computer programs that estimate the wind resource at a particular site given specific obstacles are also available. Site assessors and computer programs can help to refine the estimates provided on wind resource maps.
Direct monitoring by a wind resource measurement system at a site provides the best picture of the available resource but it has a cost. Wind measurement systems are available; whether this expense is justified depends on the nature of the proposed small wind turbine system and its costs. The measurement equipment must be set high enough to avoid turbulence created by trees, buildings, and other obstructions. The most useful readings are those taken at hub height.
Finally, if there is a small wind turbine system in your area, you may be able to obtain information on the annual output of the system and also wind speed data if available.