small wind

Small Wind Toolbox

Evaluating the Site

How's Your Wind Density?
If you think your site is windy enough to power a small wind turbine, odds are you're right -- half the land mass in the United States has sufficient wind to make a small turbine viable. It's crucial, however, that the wind on your property is sustained for long periods at a time

The Department of Energy measures wind power on a scale of 1 (weakest) to 7. If winds on your site are at least class 2 (annual wind speeds averaging 9.8-11.5 mph), it may be suitable for wind generation, subject to other conditions also discussed on this site.

Do You Have the Clearance?
A good small wind turbine site is typically at least one acre in size. Turbines should be mounted at least 30 feet above any physical wind barriers (i.e., trees, buildings, bluffs, etc.) within a 500 foot radius to avoid turbulence that can significantly impede production and cause damage to turbines. Winds are faster at higher elevations, and there is exponentially more extractable energy in faster winds (energy in the wind is proportional to the cube of the wind’s speed). This means even a small boost in height can greatly enhance a turbine’s output.

Most small wind turbine manufacturers recommend mounting turbines at least 65 feet high, but particular site conditions should be the primary factor when determining tower height. Towers from 80 to 140 feet tall may be optimal.

Zoning restrictions on your site may limit the allowable tower height, requiring you to seek a conditional use permit or variance from your city or county planning department. Local authorities have the discretion to issue zoning waivers for small turbines where appropriate.

Additional Resources

• Wind Energy Resource Atlas of the United States http://rredc.nrel.gov/wind/pubs/atlas/
• Basic Principles of Resource Evaluation
  www.awea.org/faq/basicwr.html
• Basic Principles of Wind Turbine Power Production www.awea.org/faq/basicpp.html
• Basic Principles of Wind Turbine Aerodynamics www.awea.org/faq/basicop.html
• Understanding the Difference Between Energy and Power www.awea.org/faq/basicen.html 
• Calculating Power Potential from a Given Wind Speed www.awea.org/faq/windpower.html
• The Choose Renewables Resource Estimator Tool www.chooserenewables.com/estimator_start.php
• National Renewable Energy Laboratory’s Energy Atlas of the Western U.S. www.energyatlas.org

Always remember that wind maps give only broad estimates -- the wind speed on any particular site is largely determined by terrain. Consult a turbine dealer or other professional site assessor to research your wind resource more thoroughly.

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