Thousands of bats are killed by spinning wind turbines each year, but researchers in Canada believe they’ve found a way to reduce that death toll by up to 60 per cent without having a serious impact on wind-energy output.

The secret: slowing turbine blades to almost a complete stop during periods of low wind.

“Biologically, this makes sense as bats are more likely to fly when wind speeds are relatively low,” said Robert Barclay, who recently reported on his team’s findings in an article in the Journal of Wildlife Management. “When it’s really windy, which is when the turbines are reaping the most energy, bats don’t like to fly. There is a potential for biology and economics to mesh nicely.”

Barclay co-authored the paper with Erin Baerwald, a PhD student at the University of Calgary, well as with Jason Edworthy and Matt Holder of TransAlta Corporation.

A study published last year found the majority of migratory bats in southern Alberta were killed by barotrauma, a lung injury caused by a sudden drop of air pressure near wind turbine blades. Unlike birds, bats do not have respiratory systems that can withstand such rapid declines in pressure.

TransAlta, Canada’s largest publicly traded provider of renewable energy, initiated a followup study at the same site to determine what could be done.

“Wind power has come of age, so further minimising the impact of wind farms on the surrounding ecology is always important to our industry,” said Jason Edworthy, director of community relations for TransAlta. “Working with the university during the course of this four-year study has given TransAlta the opportunity to test real-world strategies that benefit affected bat populations and make economic sense.”

Until recently, wildlife concerns regarding wind energy focused primarily on bird fatalities. But bat fatalities now outnumber those of birds due, in part, to efforts to mitigate bird deaths by wind turbines.

Most bats killed at wind energy facilities across North America are migratory tree bats, including hoary and silver-haired bats, that are killed during autumn migration. These bats migrate from Canada and the Northern US to the southern US or Mexico.

“Given that more bat fatalities occur in low wind speeds and the relative ease of manipulating operation of turbines, we examined whether reducing the amount that turbine rotors turn in low wind speeds would reduce bat fatalities,” said Baerwald.

Over the one-month experiment, total revenue lost from the 15 turbines was estimated between $3,000 and $4,000.

TransAlta has already applied the low wind mitigation strategy to the 38 turbines identified in the study area.

“The findings from the study area are promising and this new mode of operation is now in place and will be applied to new wind farms,” Edworthy said.

“Although these are promising mitigation techniques, further experiments are needed to assess costs and benefits at other locations,” added Barclay.

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