LAI Guidelines for Wind Turbines
The LAI (Bund/Länder-Arbeitsgemeinschaft Immissionsschutz) published uniform guidelines in 2002 for assessing periodic shadow flicker from wind turbines. These have been adopted in nearly all federal states as a binding assessment basis — the so-called 30/30/8 rule.
The Three Thresholds (Core of the Guidelines)
| Threshold | Value | What does it mean? |
|---|---|---|
| Astronomical (worst-case) | ≤ 30 h per year | Assumption: sun always shines, turbine always rotates, wind from unfavorable direction |
| Daily value | ≤ 30 min per day | Maximum shadow duration on a single day |
| Real-meteorological | ≤ 8 h per year | Actual shadow duration accounting for clouds, wind, and standstill |
The three LAI thresholds for shadow flicker — astronomical, daily, and real-meteorological
In practice, the astronomical 30 h value is usually decisive — if met, the real value is automatically well below the threshold.
How Is It Calculated?
- Geometric modeling of the turbine (rotor diameter, hub height, site coordinates)
- Sun position calculation year-round (astronomy algorithm, second-precise)
- Shadow projection onto the immission point (residential building, mapped with protection status)
- Accumulation per day and total — comparison against the three thresholds
- Cartographic display as iso-line maps
Shadow Flicker Shutdown Module
If calculations show that thresholds would be exceeded at an immission point, a shadow flicker shutdown module is prescribed:
- Astro-clock pre-programmed with site coordinates and immission point locations
- Brightness sensor detects whether the sun is actually shining (no sun = no shadow)
- Optional: wind direction sensor to shut down only when the rotor faces the critical direction
- Module shuts down the turbine preventively once the daily or annual budget at the immission point is reached
- Yield loss typically < 1% per year
Other Content of the LAI Guidelines
- Reflection ("disco effect"): practically eliminated by matte rotor blade coating. Addressed in the guidelines but rarely relevant in practice.
- Concept of immission points: calculations are performed at habitable rooms (bedroom, living room), not at the exterior wall.
- Pre-existing load: for multiple turbines, shadow effects are accumulated per immission point.
Revision of the LAI Guidelines — Status 2026
The LAI has announced a revision of the guidelines. Triggers include the EEG 2024 reforms that make larger turbine heights common, and lawsuits challenging detail aspects of the existing version. A new version is expected in 2026/27. Until then, the 2002 version applies unchanged.
Shadow flicker report for your site?
We connect you with an engineering firm that calculates according to LAI using certified software (WindPRO, WindFarmer) — including the shutdown module concept.
Contact usFrequently Asked Questions
Are the LAI guidelines legally binding?
They are an administrative regulation, not statutory law, but consistently applied by permitting authorities and recognized by courts. Any deviation requires special justification.
Who checks compliance with the 30/30/8 rule after commissioning?
The permitting authority, in complaint cases via spot measurements at the immission point or readout logs from the shadow flicker shutdown module.
What about federal states that haven't adopted the LAI guidelines?
Very few states deviate — and even there the LAI values are the de facto standard because no competing regulation exists. Bavarian practice is identical to other states.
Does the 30/30/8 rule apply to offshore turbines?
No — offshore turbines have no relevant shadow flicker impact on residential buildings. The LAI guidelines apply exclusively to onshore turbines.