Study finds reduction in turbine bat kills

Wind turbines kill large numbers of bats each year — a public relations quandary for wind energy companies. But the results of a new study show that sacrificing some nocturnal spin time can save the lives of bats, and perhaps boost the industry’s image as well.

The study was conducted by researchers from the Bats and Wind Energy Cooperative at the 34.5 megawatt Casselman Wind Power Project in Pennsylvania. The researchers found that turning turbines off at night during low-wind periods when bats are most active reduced mortality rates – by about 70 percent on average.

A total of 32 bats were found dead around the turbines during the 11-week study, which was conducted last year from July to October during the bats’ migration season. Twenty-one dead bats were found when turbines were fully operational, while 11 were found when turbines were turned off during low-wind phases.

The bat-saving measure came with a cost. The study noted that switching the turbines off when they could otherwise have been generating power would result in an annual loss in productivity of as much as 1 percent at Casselman. Given the wind farm’s generating capacity, that 1 percent could theoretically translate to as much as 1,000 megawatt hours a year.

Using the going rate of $70.00 to $90.00 a megawatt hour of wind energy, that’s a potential $70,000 to $90,000 annual hit to the bottom line.

Andy Linehan, the wind permitting director for Iberdrola Renewables, which is based in Portland, Ore., and owns Casselman, said such fiscal sacrifices may be necessary to get projects through contentious permitting processes, and also to prevent negating the environmental benefits of renewable power. “We want [wind energy] to be a solution to climate change, but not at the sake of killing off massive amounts of wildlife,” he said.

Merlin Tuttle, the founder of Bat Conservation International, said bat kills are increasing as wind farms proliferate. Mr. Tuttle cited a recent study that found 2,000 fatalities during a six-week period at wind power facilities in Pennsylvania and West Virginia. “When magnified across the continent, it’s a very big problem,” he said.

And while turbines are also the cause of many bird deaths, the situation for bats appears to be graver. In studies that tallied bat mortality figures at wind projects across the United States, the number of birds killed per turbine each year ranged from 0.6 to 7.7, according to a report by the National Wind Coordinating Committee. The number of bats killed per turbine ranged from 3.4 to 47.5.

Sometimes the bats die from colliding with the rotor blades – the tips of which can reach speeds of 180 miles an hour – or the turbines can also cause catastrophic damage to a bat’s respiratory system. The sudden drop in air pressure in the area near the blades can cause the bats’ lungs to fill with fluid – similar to when divers surface too quickly and get the bends.

Mr. Tuttle said bats may be drawn to the shine of the metal on the turbines or the sounds they make. Infrared video shot by researchers sheds light on this fatal attraction (the “Contact with Blades” clips are particularly dramatic).

B.C.I., industry and government agencies have joined forces to fund ongoing studies. Other solutions under investigation include bat deterrent devices like “sonar jamming” ultrasonic emitters mounted on wind turbine towers.

By Leora Broydo Vestel

Green Inc.

greeninc.blogs.nytimes.com

18 May 2009

Tags: Wind power, Wind energy

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