Assessing Wind Resources

The document outlines a 'funnel' process for wind resource assessment, moving from general wind maps to site-specific measurements. It emphasizes that wind energy production is approximately proportional to the square of wind speed, meaning small estimation errors can lead to significant financial losses. The guide details the use of wind power classes, the impact of wind shear on tower height selection, and the importance of analyzing year-to-year wind variability to satisfy lender requirements. It also provides specific siting advice regarding wind roses, turbine wake effects, and the use of set-backs or easements to protect wind access.

• Wind energy production is highly sensitive to wind speed; an overestimation of wind speed by 10 percent results in an overestimation of energy production by 21 percent.
• The wind resource assessment process is described as a 'funnel' that starts with rough estimates from wind maps and progresses to refined, site-specific wind speed estimates used for cash flow analysis and loan applications.
• In the US Midwest, wind resources generally decrease from west to east, with the highest potential (Wind Class 4) in the northwest and western parts of the region, and the lowest (Class 2) in the eastern part.
• Wind shear—the change in wind speed at different heights—can be used to justify taller towers; for example, increasing tower height from 100 to 130 feet can increase energy production by 6.6% to 12.2% depending on the power law coefficient.
• For projects in Minnesota, a 1/5 or 1/4 coefficient for wind shear calculations may be more appropriate than the commonly used 1/7 power law rule-of-thumb.
• Lenders typically require an assessment of the 'downside' of annual wind performance, such as the wind speed likely to be exceeded 90 percent of the time, to ensure loan coverage during poor wind years.
• To avoid unacceptable energy losses due to 'wake effects,' wind turbines should be spaced 8–10 rotor diameters apart in dominant wind directions and 3–5 diameters in directions where winds are weak.
• To protect wind access from future developments on adjacent properties, developers should implement set-backs or acquire wind easements, with a buffer of approximately 1,600 feet suggested for some cases.
• The cost and duration of on-site measurement programs should scale with the investment size: multi-million dollar projects may require two years of measurements with multilevel towers, while small projects under $1 million may only need six months of data from a tilt-up tower.

APA

Tennis, M. W., Clemmer, S., & Howland, J. (n.d.). Assessing Wind Resources. Union of Concerned Scientists. https://www.ucs.org/sites/default/files/2019-09/wind_resource_assessment.pdf

Chicago

Tennis, Michael W., Steven Clemmer, and Jonathan Howland. Assessing Wind Resources. Union of Concerned Scientists, n.d. https://www.ucs.org/sites/default/files/2019-09/wind_resource_assessment.pdf.

Wikipedia

{{cite report |last1=Tennis |first1=Michael W. |last2=Clemmer |first2=Steven |last3=Howland |first3=Jonathan |title=Assessing Wind Resources |publisher=Union of Concerned Scientists |url=https://www.ucs.org/sites/default/files/2019-09/wind_resource_assessment.pdf |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{tennisndassessing, author = {Tennis, Michael W. and Clemmer, Steven and Howland, Jonathan}, title = {{Assessing Wind Resources}}, institution = {Union of Concerned Scientists}, url = {https://www.ucs.org/sites/default/files/2019-09/wind_resource_assessment.pdf}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }