In the search for alternatives to fossil fuels, wind power is high on most people’s lists. But for all their non-climate changing goodness, wind farms pose an environmental problem of their own: Large concentrations of wind turbines can mean significant local mortality for birds and for bats, which are struck by the turning blades.

For environmentalists and turbine manufacturers, finding a way to overcome this mortality is, naturally enough, important. It’s all very well reducing carbon emissions, but a ground full of bat and bird carcasses hardly screams environmental friendliness.

But there is evidence that mortality rates can be reduced relatively simply: for example, by not siting wind farms in areas of high concentrations of bats or on migratory bird pathways, or by using more modern turbines with larger, slower-turning blades.

It may seem obvious, but the frequency with which turbine blades turn is the single biggest factor in bat and bird mortality, and the ease with which a slight change in that factor can cause a significant decrease in bat mortality, at least, is underlined by a new study published Monday in the journal Frontiers in Ecology and the Environment.

In the study, Ed Arnett of Bat Conservation International 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. They 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.

In both years, the researchers found at least one fresh bat carcass every night that the turbines were fully operational.

That changed, however, when the turbines’ “cut-in speed” was slightly altered.

The cut-in speed is the wind speed at which turbines are programmed to begin rotating and producing power. Currently, most turbines in the US cut in at wind speeds of approximately 8 to 9 miles per hour.

Arnett and colleagues found that a higher cut-in speed means less frequent turbine rotations and thus fewer bat deaths. Specifically, 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.

Says Arnett:

“This is the only proven mitigation option to reduce bat kills at this time. If we want to pursue the benefits associated with wind energy, 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 [...] Rarely do you see such a win-win result in a study. 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.”

Photo: Harvey McDaniel