Halting Swedish wind turbines at still summer nights would save almost all of the tens of thousands of bats killed by the rotating blades every year.
Every turbine kills 10-15 bats annually on average as the creatures are struck when they hunt insects attracted by the spinning unit, according to a study by Sweden’s Energy and Environmental Protection agencies. Halting turbines on summer nights when winds are low would save most of the bats without a significant loss in renewable generation.
“Looking at the number of bats killed at wind power turbines it soon dawns on you that the mortality is so great that it must have a reducing effect on the total population,” said Martin Green, co-author of the study and a bird researcher at the University of Lund.
Nighttime halts could be made a condition by local authorities when renewing or awarding permits. Sweden is preparing to add another 18 terawatt-hours of annual renewable generation, or more than 10 percent of its current electricity demand, before 2030, adding to the nation’s 3,378 existing onshore wind turbines.
Under the study’s proposal, a turbine in southern Sweden would probably stand still for at least 10 nights between July 15 and September 15. As it would be evenings with already low wind speeds, less than 1 percent of total output would be cut, Green said.
Five different species of bats have been found dead below turbines in southern Sweden by the researchers. What they all have in common is that they prefer to hunt at higher altitudes, making them more vulnerable to the rotating blades than peers. None of the species are at risk of extinction, but if nothing is done to limit the deaths, numerous populations are at risk of getting rare, Green said.
A similar study by the University of Exeter in England said hundreds of bat deaths at U.K. onshore windfarms could be avoided if producers turned off turbines at night. Operators that take preventive steps could be rewarded with higher tariffs for their power, the researchers said in the November report.
Environment-related obstacles aren’t new for green energy companies in Sweden. Hydro power producers have battled for decades in court on renewing permits for old stations as they try to meet modern environmental demands and still be profitable.
While the report was commissioned by two government agencies, the authors said it will probably be used more by local authorities when they consider wind power permits rather than a precursor to any law changes.
“Our message is that something can be done about this at a limited cost, as long as the producers want to,” Green said.
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