Which Bats Steer Clear of Wind Turbine Deterrents—and When?

Flight-path monitoring aims to determine the effectiveness of ultrasonic acoustic deterrents

Technologies that can reduce impacts to bats, birds, and other wildlife not only boost species conservation efforts, but also the efficiency and productivity of wind power projects. DOE supports this environmental win-win with research efforts developing technological innovations that can detect and deter wildlife from approaching wind turbine blades.

Researchers at DOE’s NREL are gaining new insights into one such solution—the use of ultrasonic acoustic deterrents (UADs)—as part of that larger effort.

The intent of UADs is to discourage bats from approaching wind turbines by emitting sounds tuned to the range of hearing for bat species found in the United States and Canada. These devices, which are typically mounted on the nacelle of a standard turbine, may offer wind energy facilities a more cost-effective solution for impact reduction than curtailing operations, or shutting down turbines, when the season and weather conditions indicate that bats may be likely to fly near wind turbines.

Preliminary laboratory and ground-based studies have demonstrated that UADs reduce wind-wildlife impacts for certain bat species. Based on this evidence, operational facilities are already installing UADs to help minimize fatalities. However, additional research is needed to understand variations in the technology’s effectiveness that could be related to ultrasound frequencies, weather effects, and behavioral differences among bat species.

“This is a unique opportunity to study the effectiveness of UADs at the species level,” said Cris Hein, the project’s principal investigator and a senior researcher at NREL. “We need to take a closer look at bat behavioral responses to optimize the effectiveness of UADs for as many species as possible.”

Along with Bat Conservation International, Texas Christian University, Texas State University, Bowman Consulting, Wildlife Imaging Systems, NRG Systems (the designer and manufacturer of the UAD being evaluated), and a leading wind power plant operator, the NREL-led project team developed a new experimental approach to measure UAD effectiveness. Specifically, the team constructed an open-air flight cage that is 60 meters (m) long, 10 m wide, and 4 m high, then covered it with netting. The researchers also developed software that identifies a bat as it flies back and forth in the cage, tracking and recording its movement. The resulting data allow for a quantitative analysis of bat behavioral responses relative to various UAD treatments.

“We learned a lot from the preliminary trials conducted last fall when we built the cage and set up cameras to test the logistics,” said Hein. “Now we have a really good system in place, thanks in no small part to the grad students at Texas State University.”

The project team brings together a range of expertise in physics, biology, and technology, as well as representatives from government, academia, and industry. More flight trials will be conducted at the Texas State campus this summer and fall, which will coincide with times when bat fatalities are highest at wind facilities.

“We think UADs can offer an effective solution, but we also know there is room for improvement,” said Hein. “In the future, we may need a combined approach, including blade-mounted deterrents, a dim ultraviolet light source, or curtailment during times of highest risk to further minimize wildlife impacts.”

By identifying the best wind-wildlife impact-minimization technologies for each wind project, research efforts like this enable the deployment of more efficient, cost-effective, and bat-friendly wind energy projects across the United States. 

Spring 2020 R&D Newsletter

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