Altering turbine speed reduces bat mortality at wind-energy facilities

  • Published source details Arnett E.B., Huso M.M.P., Schirmacher M.R. & Hayes J.P. (2010) Altering turbine speed reduces bat mortality at wind-energy facilities. Frontiers in Ecology and the Environment, 9, 209-214.


This study is summarised as evidence for the following.

Action Category

Increase the wind speed at which turbines become operational (‘cut-in speed’)

Action Link
Bat Conservation
  1. Increase the wind speed at which turbines become operational (‘cut-in speed’)

    A replicated, randomized, controlled study in 2008–2009 at a wind farm in a forested area of Pennsylvania, USA (Arnett et al 2010) found that increasing the wind speed at which turbines become operational (‘cut-in speed’) resulted in fewer bat fatalities than at conventional turbines. Average bat fatality estimates were lower at turbines with cut-in speeds increased to 5 m/s (0.3–0.7 bats/turbine) and 6.5 m/s (0.5–0.6 bats/turbine) than at turbines with conventional cut-in speeds (3.5 m/s: 2.0–2.3 bats/turbine). Fatality estimates did not differ significantly between the two treatments. In July–October 2008 and 2009, two treatments (cut-in speed increased to 5 or 6 m/s) and one control (cut-in speed of 3.5 m/s) were each randomly assigned to three groups of four turbines for 25 nights/treatment. All 12 turbines were prevented from turning (‘feathered’) below cut-in wind speeds. Daily carcass searches were conducted along transects in plots (126 x 120 m) centred on each of the 12 turbines. Carcass counts were corrected to account for unsearchable areas within plots. If applied to the entire wind farm (23 turbines), annual power output losses were projected to be 0.3% with cut-in speeds increased to 5 m/s, and 1% with cut-in speeds increased to 6.5 m/s.

    (Summarised by: Anna Berthinussen)

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