Is there enough wind on my site? What do I need to know? |
Does the wind blow hard and consistently enough at my site to make a small wind turbine system economically worthwhile? 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 that will go a long way towards answering 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 ridge lines, and on the Great Plains; however, many areas
have wind resources
strong enough to power a small wind turbine economically. The wind
resource estimates on this map generally apply to terrain features that
are well exposed to the wind, such as plains, hilltops, and ridge
crests. Local terrain features may cause the wind resource at a specific
site to differ considerably from these estimates.
More detailed
wind resource information, including the Wind Energy Resource Atlas of
United States, published by the U.S. Department of Energy (DOE), can be
found at the National Wind Technology Center, and the DOE Windpowering America.
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 20–33 ft (6–10 m) above ground.
Average wind speed
Average wind speeds increase with height and may be 15%–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.
Summaries of wind data from almost 1000 U.S. airports are also included in the Wind Energy Resource Atlas of the United States (see For More Information).
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.
Direct
monitoring by a wind resource measurement system at a site provides the
clearest picture of the available resource. Wind measurement systems
are available for costs as low as $600 to $1200.
This
expense may or may not be hard to justify depending on the exact nature
of the proposed small wind turbine system. 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, the elevation at the top of the tower where the wind turbine
is going to be installed.
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.
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