Investigations into the interaction of wind turbines with terrestrial navigation systems

Flight safety vs. energy turnaround. The energy turnaround in Germany requires the construction of numerous new wind turbines. In addition to the expansion of wind farms off the coast, so-called repowering, in which old, smaller wind turbines are replaced by new, large ones, is also gaining importance. In 2019, only 35 new wind turbines were approved in Germany despite the huge demand. The low number of building permits resulted not only from the consideration of environmental aspects (e.g. bird protection) and acceptance problems among the population (minimum distances from residential areas, infrasound) but above all from the protection requirements for terrestrial navigation systems and aviation radar systems. In particular, the 59 rotating radio beacons operated in Germany often prevent the approval of building applications. The Very High Frequency Omnidirectional Radio Range (VOR) beacons emit radio signals in the frequency range between 108 MHz and 117.95 MHz, from the reception of which the aircraft can derive the directional angle to the transmitter. In the case of the standard VOR (Conventional VOR - CVOR), the directional information is encoded in the differential phase between a 30 Hz frequency-modulated omni-directionally radiated reference signal and a signal radiated at 30 Hz on an antenna circuit. In the Doppler VOR (DVOR), the 30 Hz reference signal is amplitude modulated and the signal radiated on the antenna circuit generates a frequency modulation by the Doppler effect, the phase of which depends on the direction of the receiver in the aircraft relative to the location of the DVOR. In order to protect the rotating beacons from interference of the signal by wind turbines, the German Air Navigation Services (DFS) considers the turbine protection area within a radius of 15 km when new wind turbines are to be approved. For this purpose, it uses a simple assessment tool based on formulas for CVOR and DVOR which superimpose the angular errors due to scattered signals of the individual wind turbines in a highly simplified two-dimensional model. The highly simplifying assumptions made and the insufficient validation of the results have repeatedly led to legal disputes. The aim of the WERAN and WERAN+ projects, funded by the Federal Ministry for Economic Affairs and Energy (BMWi) and implemented under the leadership of PTB, is and was to create a scientific basis for the quantitative assessment of the interference effect.