The deterrent. (A) Bottom view, schematic depiction: The elements are connected to plastic struts and fastened to the drone's landing gear. Light and sound beams are illustrated for demonstration and are not indicative of actual transmission range. (B) Front view of the deterrent. (Image: zslpublications.onlinelibrary.wiley.com)

According to Tel Aviv University and University of Haifa researchers, wind turbines around the world kill millions of bats and other animals annually who fly into their blades.

The solution is a drone-mounted technology that transmits a combination of ultrasonic signals and light. This deters the bats, forcing them to fly at a higher altitude — allowing the turbines to operate continuously.

Wind turbines are, of course, an excellent source of renewable energy, but their method of operation leaves myriad biological challenges, said University of Haifa’s Professor Yuval Werber, study lead. Previously, the only way to thwart bat deaths was to cease turbine activity whenever they’re active. That, obviously, reduces turbine efficiency.

The drone, though, is in constant motion and transmits a combination of visual and acoustic signals designed to warn bats of danger, he added. The trick is that, when signals are stationary and constant, animals tend to ignore them.

The study was conducted in the bat hotbed of Hula Valley, Israel. The team operated the drone at a height of 100 meters (.06 miles), the height of the center of the average wind turbine, and back and forth along a path of about 100 meters. Radar and LiDAR devices were used to track the bats’ activity, and acoustic recordings of in-flight bats — using receivers placed at three different heights: 1 meter, 150 meters (.09 miles), and 300 meters (.19 miles) — on elevated receivers via blimp, were implemented.

Werber noted that the study was the world’s first to combine the technologies — radar, LiDAR, and high-altitude acoustic recorders – to track bats.

The researchers then compared the bats’ normal activity with their activity in the presence of the deterrent-carrying drone, and the results showed that the device served its purpose: The drone’s presence decreased bat activity underneath it by about 40 percent at a distance of about 400 meters (0.25 miles). However, their activity increased above the drone’s altitude of 100 meters, up to 800 meters (0.5 miles).

Werber said that the results show the device is effective in repelling bats from its environment — the creatures sense the emitted sights and sounds and avoid the blades, as planned.

A bat, who would certainly benefit from this new technology. (Image: Jens Rydell)

Here is a Tech Briefs interview with Werber, edited for clarity and length.

Tech Briefs: What inspired your research?

Werber: Wind turbines are considered one of the main man-related factors responsible for bat fatalities. The gravity of the situation concerning the wind-power industry and bats inspired us. We chose to try and take advantage of Israeli development of this industry and the ministry of energy’s interest in the subject to try and find a solution for this problem.

Tech Briefs: Why just bats? What about other flying creatures?

Werber: Bats were drastically overlooked by the industry until not very long ago. While it was soon noticed that turbines are lethal to birds, it took much longer for the effect on bats to become apparent. This caused the industry to develop in bat-sensitive regions and adopt policies and protocols that are harmful for bats.

Bats are ecologically sensitive — they reproduce slowly and rely on senses that are susceptible to the negative effects of wind turbines. Our solution can potentially prove useful to other flying animals with some adjustments, but it is currently aimed at alleviating the stress of bat populations, which are being seriously harmed.

Tech Briefs: What were the biggest technical challenges you faced?

Werber: The main technical challenge was getting the deterring signal to a relevant height without using the structure of the turbine. A second major challenge was finding a way to stop the phenomenon of habituation, when animals get used to repetitive stimuli and stop being deterred. The use of drones came a long way in helping assess and overcome both of these major challenges.

Tech Briefs: Can you explain in simple terms how the technology works?

Werber: The deterrent uses movement, sound, and light, which together produce an intricate, pulsating disturbance in the airspace. The light-emitting element is made of four full-spectrum square COB-LED panels (50 W each, 400-780 nm, 6200-6800 K), connected to an on-board controller that activates them intermittently, creating a bright white, flashing, dynamic stimulus, visible to a human eye up to about 200 meters away.

The sound-emitting element is made of four piezoelectric speakers that broadcast linear chirps sweeping between 15-80 kHz, at about 100 dB SPL re 1m (at all frequencies), connected to a separate controller. The speakers produced identical chirps with a short phase delay to increase randomization.

The wide spectrum of both audio and visual stimuli aimed to account for a wide perceptive range across bat taxa, aiming to stimulate as many species as possible over a roughly spherical volume of transmission up to a few hundred meters away from the deterrent. The movement of the drone, along with the randomization of the auditory and visual signals, reduced repetitiveness to a minimum.

Tech Briefs: What’s the next step with regards to your research/testing?

Werber: The first would be to test the device around wind turbines and assess the effect in realistic circumstances. Based on these we would next test possibilities of autonomous operation toward automatic implementation of the device.

Tech Briefs: Do you have any advice for engineers aiming to bring their ideas to market?

Werber: If you are working on wildlife-related ideas, you should thoroughly get to know your animal and study it in depth. You might find both wanted and unwanted surprises.

Tech Briefs: Anything else you’d like to add?

Werber: Radar was a major tool in the process of studying the effect in this experiment. Radar ecology is a fast-developing field, in which scientists study aerial wildlife using radar technologies. Radar ecology will play a major role in future human development, as we go higher with energy production, transportation, etc.