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Effectiveness of Changing Wind Turbine Cut-in Speed to Reduce Bat Fatalities at Wind Facilities

“Data previously collected at operating wind energy facilities indicate that a substantial portion of the bat fatalities occurs during relatively low-wind conditions over a relatively short period of time during the summer-fall bat migration period (Arnett et al. 2008). Some curtailment of turbine operations during these conditions and during this period of time has been proposed as a possible means of reducing impacts to bats (Kunz et al. 2007, Arnett et al. 2008). Indeed, recent results from studies in Canada (Baerwald et al. 2009) and in Germany (O. Behr, University of Erlangen, unpublished data) indicate that changing turbine “cut-in speed” (i.e., wind speed at which wind generated electricity enters the power grid) from the normal (usually 3.5–4.0 m/s on modern turbines) to 5.5 m/s resulted in at least a 50% reduction in bat fatalities compared to normally operating turbines. …

“Our study is the first U.S.-based experiment of changing cut-in speed to reduce bat fatalities, and only the third we are aware of anywhere in the world. We demonstrated reductions in average nightly bat fatality ranging from 56 to 92% with minimal annual power loss. Given the magnitude and extent of bat fatalities worldwide, the conservation implications of our findings and those of Baerwald et al. (2009) are critically important. However, additional studies are needed to test changes in turbine cut-in speed among different sizes and types of turbines, wind regimes, and habitat conditions to fully evaluate the general effectiveness of this mitigation strategy.”

Edward B. Arnett and Michael Schirmacher, Bat Conservation International
Manuela M. P. Huso, Oregon State University
John P. Hayes, University of Florida

Annual Report Prepared for the Bats and Wind Energy Cooperative and the Pennsylvania Game Commission

April 2009

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