New challenges in assessing bat activity at wind turbines
Modern wind turbines with large diameters and large hub heights require monitoring of bat activity not only from nacelle level, but also at height of lower blade tip. That way bats can be accessed climbing the mast and being in danger of getting killed before reaching the detection area of a nacelle based microphone. We invented In cooperation a new solution with one of the largest mast manufactures in Germany. The so-called mast-microphone can be installed through a whole in the turbine mast. That way bat corder and equipment is safe inside the turbine mast, easily accessible, while the mic samples data from outside. The microphone features a small speaker for generating a daily test signal, just as in the normal disc-microphone.
The mast mic consists of a plastic cylinder (28 mm to 60 mm) and can be adjusted in its position using a threaded rod (see picture). Its maximal adjustment is ca. 30 cm. It is fixed to the mast inner wall using an aluminium plate.For installation a 30 mm hole must be either drilled or already available at the mast. It can be inclined 10° downwards to disable rain water running into the hole.
We recommend that you plan the installation with the turbine manufacture as early as possible. The hole usually can be planned when the mast is build and thus no drilling is necessary.
To further secure the microphone against weather influences we recommend an installation out of the main weather direction. This also minimizes problems due to the fine spray the wing tips may produce agt higher speeds.
Depending on the actual legal requirements the microphone may get installed in lower air spaces. To reduce recording activity close to the ground the threshold of the batcorder may be adjusted directly or afterwards when analyzing the recordings.