An estimated 40 bats die annually per wind turbine at the Blue Sky Green Field wind farm east of Fond du Lac, and WE Energies wants to finds ways to reduce that number without greatly curtailing electricity production.
Multiplied by BSGF’s 88 wind turbines, an estimated 3,250 bats die annually since operations began in 2008, according to 2009 WE Energies commissioned study.
Beginning next month, WE Energies will study how bat fatalities can be reduced by lowering the speed at which the turbine blades began to spin and adding acoustical monitors to detect chirping sounds bat emit.
BSGF has practically no minimal limits on the “cut-in speed” at which the blades begin to operate, according to David Drake, a bat researcher at the University of Wisconsin-Madison.
Bats are most active feeding at low wind speeds but typically not at speeds above 10 mph which scatter their insect prey, he said.
Shutting off or, curtailing the turbines at low wind speeds is probably the most effective way to reduce bat fatalities, said Drake, but that also curtails power production.
In the study, WE Energies proposes to curtail 10 turbines when turbine speed is below 5 meters per second, a condition in which power production is not ideal.
Ten more turbines will be equipped with chirp-detecting acoustical monitors that indicate in real time if bats are present.
“Curtailing turbines at low (wind) speeds when bats aren’t present doesn’t mitigate bat mortality,” said Brian Manthey, a WE Energies spokesman. “The acoustic monitors will help maximize green energy while minimizing bat and bird mortality.”
Wind turbines also cause bird deaths but bats die at two or three times the rate of their feathered counterparts. Fewer birds dies because they migrate at elevations above the turbine rotors 400-foot span, and have body structures that allow them to survive the pressure zone differences caused by spinning rotors, said Drake.
Tree bat species migrate and their populations have been more negatively affected by wind farms than non-migrating cave bats, said Paul White, the Department of Natural Resources mammal ecologist.
The BSGF wind farm is in close proximity to the Midwest’s largest bat hibernation sites, the Neda Mine bat sanctuary near Mayville. A ridge runs along and away from the mine making it an excellent wind farm location, too.
Initially, it was though wind farms would be more hazardous to birds than bats, said White, but research during the past several years as disapproved that. Had the effects on bats been fully realized during BSGF’s permitting process, it may not have been allowed to locate as close as it is now, he said.
White-nose syndrome has killed millions of cave bats in the eastern U.S. and was first detected in Wisconsin last year in Grant County. The white nose threat to bats makes finding even a few cave bats dead at a wind farm places their population even more vulnerable to mortality, White said.
White is looking to the WE Energies study, to be completed by the end of the year, to see if the mitigation measures implemented will save some bat lives.
“It will be reviewed…to see if it works and if it’s feasible to use at wind farms not doing this,” he said.
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