Bat Survey for Wind Turbines
The bat survey (Fledermausgutachten) records the activity of collision-prone bat species in the rotor zone and assesses the mortality risk. It is a mandatory component of every BImSchG permitting procedure and typically results in the condition of a bat-friendly curtailment algorithm during critical summer nights.
What is surveyed?
- Nacelle monitoring: Ultrasound detector at nacelle height (80–160 m), recording calls of passing bats throughout the entire season
- Ground-level survey: Detector plus field visits, recording the species community at the site
- Roost search in the project area (cavity trees, buildings) — particularly relevant at forest sites
- Derivation of the curtailment algorithm: At which wind speed / temperature / time of year must the turbine be shut down at night?
Key collision-prone species
| Species | Significance | Notes |
|---|---|---|
| Common noctule | High-flying | Most frequent collision find at wind turbines nationwide |
| Leisler's bat | High-flying, long-distance migrant | Annex IV Habitats Directive |
| Nathusius' pipistrelle | Migratory species | Collision peak in late summer/autumn |
| Common pipistrelle | Most abundant species in DE | Collision risk especially near roosts |
| Soprano pipistrelle | Cryptic sister species | Not always acoustically distinguishable from common pipistrelle |
Standard curtailment algorithm
Based on the recorded activity, a smart curtailment algorithm is derived (Brinkmann/Niermann/Behr). The turbine is preventively shut down during critical phases:
- Season: typically 1 April to 31 October
- Time of day: sunset to sunrise
- Wind: curtailment at < 5.5–6.5 m/s at nacelle height
- Temperature: curtailment at > 10 °C
- Precipitation: restart permitted during rain
Curtailment algorithm for bat protection — three conditions must be met simultaneously (AND logic)
What does it cost?
Guideline cost €10,000–30,000 for nacelle monitoring over one season. Key factors:
- Number of turbines (nacelle monitoring per turbine or by sample)
- Additional ground-level survey (forest sites, building-adjacent sites)
- 2-year post-commissioning monitoring — often a permit condition, additional €15,000–25,000
Who prepares it?
Specialist chiropterologists — usually the same consultancies that also carry out the bird surveys, but with a dedicated bat expert. Key criterion: calibrated detector technology (Avisoft, Petersson, Batlogger) and experience with the local species community.
Request a bat survey
We connect you with a chiropterology-experienced consultancy — including nacelle monitoring and a curtailment concept for the permit condition.
Get in touchFrequently asked questions
What is the difference from a ground-level survey?
Nacelle monitoring records activity at rotor-blade height — exactly where the mortality risk arises. The ground-level survey describes the species community at the site but is only indirectly indicative of risk in the rotor zone. Authorities typically require both.
Can the curtailment algorithm be adopted from a similar site?
No. Every site has its own activity profile, which can only be determined through site-specific measurement. Only after 2 years of operational monitoring can the algorithm potentially be relaxed.
What about anti-bat acoustic devices (ultrasound deterrents)?
Anti-bat devices are an alternative technology (acoustic deterrence) but are not yet certified in Germany. Currently, the smart curtailment algorithm is the standard solution.
How much yield does curtailment cost during repowering?
For repowering, typically 1–4% per year — modern turbines have optimised algorithms with precise thresholds. Where economic viability is tight, factor the yield loss into the LCOE calculation.