Demand-Driven Night Marking (BNK) for Wind Turbines
Demand-driven night marking (BNK) is an anti-blink regulation: the red night lighting of a turbine only activates when an aircraft is nearby — instead of blinking continuously. This reduces nighttime light pollution by over 95 %.
Legal Basis
- § 9 para. 8 EEG: subsidy sanction if BNK is not installed
- Air Traffic Regulation (LuftVO): technical requirements for obstacle marking
- General Administrative Regulation on Marking of Aviation Obstacles (AVV-Kennzeichnung): detail regulations, last revised 2020
- Mandatory for turbines with total height > 100 m (= practically all modern onshore WTGs)
How It Works — Three Technology Lines
| Technology | How does it work? | Advantages | Providers |
|---|---|---|---|
| Primary radar | Ground/mast-mounted radar detects approaching aircraft within radius | Detects all aircraft, even without transponder | Lanthan Safe Sky, Dark Sky, Reetec |
| Transponder-based | Evaluates ADS-B signals of commercial aircraft | Lower hardware costs, no radar permit needed | Quantec Networks, ENERTRAG |
| Secondary radar / Hybrid | Combines primary and secondary radar data | Maximum detection performance | AvioSafe, Air Avionics |
BNK systems compared — primary radar vs. transponder vs. passive/camera (mandatory since 2024 for WTGs > 100 m)
Retrofit Costs
Per turbine (existing fleet retrofit) typically EUR 25,000–40,000, depending on:
- Technology choice (radar significantly more expensive than ADS-B evaluation)
- Park size (radar rarely worthwhile for 1 turbine, economical from 3–5 turbines onward)
- Shared solution with neighbouring parks (shared radar reduces cost per turbine significantly)
- Permit process for the BNK system itself (own procedure at the Federal Network Agency and aviation authority)
Additionally, running costs of approx. EUR 1,000–3,000 per turbine per year for maintenance, software updates and ADS-B signal licence.
Existing Fleet Retrofit — Status
The original deadline of 31.12.2022 was extended multiple times due to supply shortages. Current status: mandatory retrofit by 31.12.2024, with exceptions for turbines where a shared BNK system with neighbouring parks is in preparation.
Typical Light Signals
- Daytime (good visibility): usually no lighting needed, or white daytime lights (for turbines > 150 m)
- Night without aircraft: lights off (= the BNK effect)
- Night with aircraft in detection radius: red lighting active (typically 4–8 minutes, then re-check)
- Poor visibility conditions: BNK system switches to permanent lighting as safety standard
Who Handles the Planning?
BNK providers (Lanthan, AvioSafe etc.) typically handle complete planning + the permit procedure at the Federal Network Agency + aviation supervisory authority. Independent engineering firm planning is possible but rarely economical.
BNK retrofit for your wind farm?
We connect you with a certified BNK provider — optionally including a comparison of multiple technology options and shared radar solutions with neighbouring parks.
Get in touchFrequently Asked Questions
Does BNK work for very small aircraft or drones?
ADS-B-based systems only detect aircraft with an active transponder (all commercial aircraft, many private pilots). Radar systems detect all objects above a certain minimum size. Drones are technically difficult to detect — with dense drone traffic (rare) radar is superior.
What about turbines built before 2017?
They must also retrofit — the deadline applies to the entire existing fleet. Exception: turbines to be replaced by repowering within the next 5 years can apply for a justified deferral.
Can multiple parks share one BNK system?
Yes — this is in fact the most economical approach. A primary radar can cover a radius of up to 10–15 km. Common practice in northern German park clusters; costs per turbine drop to EUR 10,000–15,000.
What is the state of BNK research?
The AVV-Kennzeichnung is continuously updated. Currently under discussion: extension to demand-driven daytime marking (daytime BNK) and automatic visibility detection for reduced daytime flashes.