Blick auf das obere Turmsegment einer Windenergieanlage mit dem neu installieren Mikrofon
Neu installiertes zusätzliches Mikrofon zur Erfassung von Fledermausrufen am Turm einer Windenergieanlage (2022)

The altitude distribution of bats at onshore wind turbines

For several years now, there has been discussion about how the combined effect of a wind turbine’s rotor diameter and tower height affects the risk of bat collisions. A key issue here is the extent to which additional microphones fitted to the wind turbine tower can enhance our understanding through so-called nacelle monitoring (i.e. the acoustic detection of bats in the rotor area). The project has identified the practical scenarios in which it makes sense to install an additional microphone on the wind turbine tower to detect bats.

The analyses have shown that, in order to reduce forecast uncertainty, sampling at nacelle level on as many wind turbines as possible within a wind farm is usually more efficient than carrying out additional tower-level measurements.

From a technical point of view, it makes sense to install an additional tower microphone on wind turbines with a small rotor-free zone. An additional monitoring point on the tower is recommended for wind turbines with a rotor-free zone of less than 30 m, as well as for those with a rotor-free zone of less than 60 m, if there are large roosts of bat species at risk of collision nearby or if land use suggests a high level of bat activity. Monitoring standards are defined for the use of a tower microphone.

In addition, a separate project was carried out to test the reliability of measurements from rainfall sensors. The results showed that two high-quality measuring devices were able to provide plausible data.

Oliver Behr, Sören Greule, Johanna Grimm, Christof Happ, Fränzi Korner-Nievergelt und Florian Stehr. Die Höhenverteilung von Fledermäusen an Windenergieanlagen. BfN-Schriften 741. Bonn 2025

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