It is not only in the North German Plain that you can see them all over the horizon at night: red lights flashing in the sky. These are the wind turbines, which, with their height of usually over 100 m, represent obstacles to aviation and as such have to be lit. But do these lights always have to be active? Isn't it enough for them to be active when an aircraft is approaching?
This idea was already enshrined in the Renewable Energy Sources Act (EEG) in 2018, thereby implementing nationwide what had already been demanded in some cases at state level: The introduction of systems for demand-driven night-time marking (BNK).
The functional principle is quite simple: a virtual cylinder with a radius of 4,000 m and a height of 2,000 feet is placed on each wind turbine (WTG), the so-called effective area. The BNK system monitors this effective area and as soon as an entry is detected, the night marking is activated. Conversely, the lighting remains off when there is no aircraft in the vicinity, so that there is less disturbance for people and nature.
The BNK systems on the market are based on radar or transponder technology in accordance with the requirements of the General Administrative Regulation on the Identification of Aviation Obstacles (AVV). A BNK system can only be used once it has been certified by a type approval body (BMPS). AviaCert GmbH has been designated as a BMPS since June 2020 and has certified several BNK systems since then.
Many steps are necessary to finally deactivate the flashing lights on a WTG as required:
A potential BNK system must undergo a certification or type approval procedure. As part of this procedure, the technical functionality of the system is tested, compliance with all specifications from the AVV, Annex 6, and finally proof is provided in a practical test by driving or flying over the site. As part of the certification/type examination, the BMPS must also define clear specifications for the subsequent site inspections.
When the wind farms are then upgraded at some point, the location of each individual wind turbine is examined in a so-called preliminary aviation assessment to determine whether it is affected by civil or military aviation interests that could prevent the installation of BNK systems. In particular, the interests of air traffic participants who fly in the airspace at night according to visual flight rules must be taken into account. In addition to general aviation, this primarily includes helicopters in rescue services.
As part of the site inspection, the functionality of the BNK system is checked on site for each location. A key aspect here is that the ground coverage of the detection is guaranteed in accordance with the AVV so that, for example, a rescue helicopter taking off is also detected and the lighting is switched on.
In addition to onshore wind farms, wind farms off the coast are also subject to a BNK obligation. In accordance with the AVV, the requirements of the Offshore Aviation Standard (SOLF) must be observed here. Among other things, this stipulates that the BMPS must be involved in every site assessment.
When the EEG was amended in 2018, there was still great confidence that it would soon be possible to introduce BNK systems: the deadline for installation ended in 2020. With the last amendment to the EEG and the AVV in December 2023, the deadline was postponed once again: It is now 01.01.2025. However, as there are now enough systems on the market and the BNK obligation has also been in place long enough, it can be assumed that there will be no further postponements.
So will the night sky over Germany be completely dark again at night from 01.01.2025? No, even if the lighting can be switched off for large periods of the night on many WTGs, there are still WTGs that remain permanently lit. The lighting is also occasionally activated if there are errors in the signal transmission or other problems. As part of a "fail-safe" approach, the lighting is activated automatically in the event of any faults. Overall, however, the light pollution and thus the impact on people and nature should be significantly reduced.