In order to assess the risk of bats dying at wind turbines, the acoustic activity of bats within the operating range of the rotor blades is recorded. Ultrasonic detectors are attached to the nacelles of the mast top, but scientists have concluded that the effectiveness of this acoustic monitoring is insufficient to reliably predict mortality risk, especially for bats at large turbines.
In a recent analysis, a team of scientists led by the Leibniz Institute for Zoo and Wildlife Research concluded that the effectiveness of this acoustic monitoring is insufficient. They therefore recommend installing supplementary ultrasonic detectors at other locations on the wind turbines and developing additional techniques such as radar and thermal imaging cameras for monitoring.
The results of their analysis are published in the scientific journal Mammal Review.
Wind is a form of renewable energy source which is widely used for energy generation. One downside of wind energy is that many bats die when colliding with rotor blades of wind turbines. This is an urgent problem for conservation because all bat species are protected by law because of their rarity.
To find out when the operation of wind turbines poses a threat to bats and when it does not, the temperature and wind conditions at which bats are particularly active at turbines are determined. For this purpose, the echolocation calls of bats are recorded when they fly into the risk zone near the rotor blades. From this, threshold values for wind speed and temperature can be derived for a bat-safe operation of wind turbines. Wind turbines then only produce electricity when none or only a few bats are active.
The sonar beam of bats also means that echolocation calls do not spread evenly in all directions, but preferentially towards the front in the direction of flying. If bats do not fly directly towards the microphone, the calculated detection range decreases further. In addition, ultrasonic detectors are usually mounted on the underside of the nacelles and the microphone therefore points downwards. Bat calls above the nacelle are therefore not registered. The focus is on the lower half of the danger zone, although bats can also be found in the upper half.
In order to improve the cover of the risk zone of the rotor blades, the scientists recommend additional detectors at other locations, e.g. above as well as on the lee side of the nacelle. In order to also detect bats circling up the mast of the turbine, it may also be advisable to install ultrasonic detectors directly on the mast. This would also register animals flying at lower levels above ground or collecting insects from the mast surface. Complementary sensor technology such as radar systems or thermal imaging cameras could provide additional information.
Based on the recordings, consultants and researchers can determine the bat species and assess under which conditions (temperature, time of day, wind strength) they are most active. With this information, conditions can be described that restrict the operation of wind turbines during times of particularly high bat activity, thus reducing the risk of killing.
Image credit: David Clarke via Flickr
