30 March 2020

Determining the impact of wind turbines on flight navigation systems

Researchers are developing a forecasting tool that calculates the impact of wind turbines on aviation navigation aids.

What impact do wind turbines (WTGs) have on aviation navigation systems? How great is their disruptive effect really? And how can this be measured precisely? The Physikalisch-Technische Bundesanstalt (PTB) has now succeeded for the first time worldwide in answering these questions with metrological accuracy. The findings enable the development of a forecasting tool that can provide clear, scientifically and legally sound predictions for the disruptive effects of planned wind farms in the future.

Deutsche Flugsicherung (DFS) operates around 60 navigation systems, so-called omnidirectional radio range beacons. These flat ground stations with antennas permanently transmit VHF radio signals. Similar to lighthouses, they point aircraft in the right direction and ensure safety in the airspace. WTGs can influence the interference-free transmission of VHF waves and thus the directional accuracy. This is because the radio waves can scatter and be reflected on the surfaces of the WTGs and thereby create a so-called angular error. This means that the signal from the navigation system is slightly distorted when it arrives at the aircraft.

Faster and more accurate decisions on building permit applications

According to a survey by the Fachagentur Windenergie in the 2nd quarter of 2019, more than 1000 WTGs with a total output of 4800 megawatts cannot be built at present because they are planned too close to a navigation system and could therefore possibly interfere with the omnidirectional radio range beacon. In case of possible interference, the installation of the WTG is not approved. The expansion of wind power is faltering because not enough projects are receiving approval. The newly developed forecasting method of the PTB would make it possible to reach decisions on building permit applications faster and more accurately in future.

In the „WERAN“ project funded by the German Federal Ministry for Economic Affairs and Energy (BMWi), the PTB and its project partners have investigated the scientific principles underlying the evaluation procedures used so far. In the currently ongoing follow-up project "WERAN plus", the researchers are now developing a new forecasting method in order to be able to provide a realistic assessment of the possible interference effect of WTGs on omnidirectional radio range beacons in advance. The focus here is on so-called DVOR navigation systems (Doppler Very High Frequency Omnidirectional Radio Range).

Drones with precise navigation

The scientists have developed drones with precision navigation whose eight rotors enable a steady-state hover flight (octocopter). This enables them to carry out on-site measurements at heights of up to several hundred metres. Using specially developed high-frequency measurement technology and integrated antennas, the researchers were able to precisely determine how the DVOR radio signals disperse, are reflected and scattered at the WTGs. They were also able to determine how the reflected signals overlap with the direct signals of the DVOR.

At the same time, the project partners at Leibniz Universität Hannover have developed simulation methods that can be used to calculate the magnitude of the angular error caused by WTGs on the mainframe computer. The researchers compared the results of these simulations with the detailed measured data from the octocopter flights. The scientists have also developed an improved forecasting tool. All this work is carried out in close cooperation with the DFS.

The good correlation between on-site measurements at wind farms, the simulations and the results of the improved forecasting tool represents a new state of the art. This is now to be put into practice. In December 2019, the PTB presented the results to the relevant specialist circles at scientific conferences and user meetings. In the first half of 2020, PTB will present its improved method to the public. This allows the results obtained in research projects to be applied straight away.

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