Wind turbines and air traffic control

Deutsche Flugsicherung GmbH, the air navigation and service provider in Germany, operates around 60 air navigation systems (VHF monodirectional radio ranges) on the ground. Similar to lighthouses for ships, they guide aircraft and thus ensure safety in the sky. Wind turbines may scatter and reflect the VHF radio signal emitted by air navigation systems, thereby generating a bearing angle error. Due to this bearing angle error, the signal of the navigation system is slightly distorted when it reaches an aircraft. According to a survey conducted by the Fachagentur Windenergie, German wind energy association in the second quarter of 2019, it was impossible to implement more than 1000 wind turbines with a total output of 4800 megawatts because the planned location would have been too close to a non-directional radio beacon and would have potentially influenced its signal.

In order to realistically assess the interference effect, PTB – in cooperation with Deutsche Flugsicherung GmbH and the Bundesaufsichtsamt für Flugsicherung (German Federal Office for Air Traffic Control) – has both reviewed the scientific basis of the assessment procedure used to date and developed a new forecasting method. DVOR (Doppler Very High Frequency Omnidirectional Radio Range) navigation beacons, of which there are almost 40 in Germany, were focused on. To test the entire electromagnetic field around VORs and wind turbines, drones with precision navigation were developed whose eight rotors enable stationary hovering flight in order to carry out on-site measurements at altitudes of up to several hundred meters. By means of high-frequency measurements and integrated antennas, it was possible to record how the DVOR radio signals propagate, how they are reflected and scattered by wind turbines and how the reflected signals overlap with the direct signals of the DVOR. Presuppositions and real measured data from individual wind turbines were then compared with a comprehensive full-wave simulation carried out on the mainframe computer of Leibniz University Hannover. Here, it was possible to simulate the bearing angle error caused by wind turbines also for large-scale scenarios with numerous wind turbines.

This has provided an easy-to-use method for predicting the angle error, which no longer adds up the individual errors, but superimposes the individual waves and then determines the resulting bearing angle error. The last step still to be taken consists in transferring this state-of-theart method into practice. The results were obtained within the scope of the WERAN and WERAN plus projects, which were funded by the Federal Ministry for Economic Affairs and Energy. In addition to PTB, Leibniz University Hannover, FCS Flight Calibration Services GmbH, Jade Hochschule Wilhelmshaven, the Institute of Computational Mathematics of TU Braunschweig and steep GmbH were involved in these projects.