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Derating Wind Speed
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It's important to understand the different factors that will reduce wind speed at a turbine hub height. Use the following excel spreadsheet (Calculator to Derate Wind Speed) to produce a rough estimate of your wind speed relative to:
  • the wind map you have
  • your proposed tower height, and
  • your best estimate of surface characteristics at your site

Although, this wind speed estimate is not a substitute to the value provided by a wind site assessment it should allow you to make better use of turbine manufacture kilowatt hour power curves and annual energy production curves.

 

 

 

 

 

 

 

Wind speed is "Derated" by applying a wind shear coefficient "α" to the formula:

 

V = (H/Ho)αVo, where:

 

V = the wind speed at your proposed height

Vo = the wind speed from your Map at the referenced height "Ho"

H = the proposed tower height

Ho = the height that the wind speed "Vo" is referenced at (i.e. 60m)

α = the wind shear coefficient

  

Courtesy of NREL