Man and Environment

COLORS: another step towards bird protection in wind farms

Detection of a hexacopter flying in a transverse direction in the wind farm over several adjoining antenna beams.
© Fraunhofer FHR

Detection of a hexacopter flying in a transverse direction in the wind farm over several adjoining antenna beams.

Experiments on the Mosel in Coblenz.
© Fraunhofer FHR

Experiments on the Mosel in Coblenz.

Detection of a cormorant in the presence of dynamic clutter caused by the flowage of the river Mosel.
© Fraunhofer FHR

Detection of a cormorant in the presence of dynamic clutter caused by the flowage of the river Mosel.

In times of climate change, growing importance is being attached to renewable energies and, in particular, wind energy. The suitability of a radar sensor as a bridge-builder between the profitable utilization of wind power and statutory bird protection regulations is currently being examined within the framework of the project COLORS.

Background and goals of the study

The study aimed to detect birds in the direct vicinity of wind turbines and analyze their movement in order to carry out a subsequent risk analysis. In cases where birds are in imminent danger, this radar could send a corresponding signal to the control network, whereby operation of the respective turbines can be halted.

The work is carried out in the light of court rulings similar to the decision of the Administrative Court in Minden [VG Minden, 08.08.2016 – 1 L 1155/16]. These provide for subsequent operational restrictions, i.e. the temporary deactivation of individual wind turbines when there is a significant lethal risk to birds of protected species. This case in Minden related to a black stork population which settled in the direct vicinity of wind turbines. The court stated that there was presently »no milder means that could equally guarantee the Black Stork's chance of survival.« The project COLORS takes the first step towards providing these milder means.

Preliminary work

The system parameters necessary to implement a corresponding sensor were determined on the basis of a feasibility study that was carried out in 2014. The results of the study show that a radar operating in the Ku-band with 20 W transmit power is suitable to meet the specified requirements. Aspects relating to the subsequent approval of the system by the Federal Network Agency were also considered. The feasibility study revealed that the antenna must have a high update rate to guarantee wide-area monitoring of the wind farm. Hence, a detailed examination of an electronically steerable antenna concept was carried out in the course of the COLORS study.

Experimental tests

The functionality of the newly developed demonstrator system was tested within the framework of experimental measurements. The first measurements were taken inside a wind farm to investigate the effects of the wind turbines. On this occasion, there was no suitable bird in the wind farm and, for this reason, a hexacopter was used as a calibrated measurement object.

Similar to a bird, the hexacopter exhibited a varying flight path over time. The measurements, which covered a spread of 40°, included wind turbines and open fields. In spite of the reflections caused by the rotors of the wind turbines in the wind farm, it was possible to detect the hexacopter and measure its movement path. Figure 1 illustrates the capacities of the radar demonstrator. It shows a diagonal flight of the hexacopter in the wind farm. The observed movement is characterized by radial acceleration with simultaneous »migration« through the antenna beams. The radar therefore has the ability to measure lateral as well as radial movements. The vertical line in all of the illustrations in Figure 3 shows temporary interference caused by a wind turbine rotor in the direct vicinity of the hexacopter. Due to the periodic movement of the rotors, this interference can be suitably predicted.

Further measurements taken at a dam on the Mosel in Coblenz (comp. Fig.2) featured the measurement of a cormorant which, in terms of its body size, is similar to the stork cited in the court ruling in Minden [VG Minden, 08.08.2016 – 1 L 1155/16]. During the measurement, the bird started its flight at a distance of approximately 500 meters. The increasing speed can be clearly seen in Fig. 4, the Doppler spectrogram of a single spatial direction.

Outlook

Long-term tests, in which the influence of the wind turbines can be determined in different weather conditions, are necessary for the further development of the demonstrator system. Given that the speed and orientation of the wind turbines are determined by environmental influences, it was not possible to investigate all possible scenarios in the first test measurements. Tests, in which the waveform is optimized by means of an additional micro-Doppler analysis of the wing beats, are also planned.