Slight change in wind turbine speed significantly reduces bat mortality

Nov 01, 2010

While wind energy has shown strong potential as a large-scale, emission-free energy source, bat and bird collisions at wind turbines result in thousands of fatalities annually. Migratory bats, such as the hoary bat, are especially at risk for collision with wind turbines as they fly their routes in the forested ridges of the eastern U.S. This loss not only impacts the immediate area, but is also detrimental to ecosystem health nationwide -- that is, bats help with pest management, pollination and the dispersal of numerous plant seeds.

Since turbine towers and non-spinning do not kill , some scientists have proposed shutting off or reducing the usage of wind turbines during peak periods of migration in the late summer and early fall months when bat activity and fatalities are highest.

In a study to be published online November 1, 2010 in Frontiers in Ecology and the Environment (e-View), a journal of the Ecological Society of America, Edward Arnett from Bat Conservation International in Austin, Texas and colleagues examined the effects of changes in wind turbine speed on bat mortality during the low-wind months of late summer and early fall.

Currently, most wind turbines in the U.S. are programmed to begin rotating and producing power once wind speed has reached approximately 8 to 9 miles per hour (mph)—the wind speed at which turbines begin generating electricity to the power grid is known as the cut-in speed. with a low cut-in speed run more frequently than those set at higher cut-in speeds since they begin rotating at lower wind speeds.

The researchers found that, by raising the cut-in speed to roughly 11 mph, bat fatalities were reduced by at least 44 percent, and by as much as 93 percent, with an annual power loss of less than one percent. That is, programming the turbines to rotate only when the wind reached approximately 11 mph or higher caused the turbines to rotate less frequently and, therefore, killed significantly fewer bats. Because this was performed during months with seasonably low wind speeds already, the overall energy loss was marginal when the researchers calculated the annual power output.

"This is the only proven mitigation option to reduce bat kills at this time," said Arnett. "If we want to pursue the benefits associated with , we need to consider the local ecological impacts that the turbines could cause. We have already seen a rise in bat mortality associated with wind energy development, but our study shows that, by marginally limiting the turbines during the summer and fall months, we can save bats as well as promote advances in alternative energy."

Arnett and colleagues monitored 12 of the 23 turbines at the Casselman Wind Project in Somerset County, Pennsylvania in the Appalachian Mountain region and recorded bat fatalities for 25 summer and fall nights in both 2008 and 2009. The researchers analyzed the fatalities following nights when the turbines were fully operational and when the turbines were set to the less sensitive cut-in speeds of roughly 11 mph and 14.5 mph. In both years, the researchers found at least one fresh bat carcass every night that the turbines were fully operational. Specifically, the researchers reported a mortality rate that was, on average, 3.6 to 5.4 times higher at the fully functioning turbines compared with the turbines set to the altered cut-in speeds.

According to John Hayes, co-author of the study from the University of Florida, "the findings are important step forward in building a comprehensive energy strategy with reduced environmental impacts."

"Rarely do you see such a win-win result in a study," said Arnett. "There is a simple, relatively cost-effective solution here that could save thousands of bats. This is good news for conservation and for wind energy development."

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Provided by Ecological Society of America

5 /5 (6 votes)

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lengould100
not rated yet Nov 01, 2010
In both years, the researchers found at least one fresh bat carcass every night that the turbines were fully operational.


So is this saying that the 12 turbines monitored killed one bat per day in total? And increasing the cut-in speed reduced that by between 44% and 93%? Really, how big is this problem?
Doug_Huffman
not rated yet Nov 01, 2010
Wind usable duty cycle is already barely 30%.
wwqq
5 / 5 (1) Nov 01, 2010
So is this saying that the 12 turbines monitored killed one bat per day in total?


Yes, at least one per day per turbine.

Really, how big is this problem?


Don't know how representative this windfarm is of wind farms in general, but it could be pretty significant.

The US produces an average of 240 GW of coal power. To replace half of this with 1.5 MW wind turbines of the same kind as those 12, with a capacity factor of 30%, would require 250 000 wind turbines. In other words, to produce a quarter of US electricity from wind could kill as many as ~250 000 bats per day, 90 million bats per year, using a naïve extrapolation from this group of 12 wind turbines. That would be a rate 3 times higher than white nose syndrome to date.

This calculation should not be taken more seriously than to point out that there might be a problem here if those 12 wind turbines are at all representative.