How many hours of shadow flicker are permitted?

According to the LAI guidelines (Bund/Länder Working Group on Immission Control), a maximum of 30 hours of astronomically possible shadow flicker per year and a maximum of 30 minutes per day are considered reasonable. The actual (real) figure may be no more than around 8 hours per year. If the value is exceeded, a shutdown module temporarily switches the turbine off.

How is shadow flicker prevented?

Via a shadow-flicker shutdown module: a sensor and an astronomical calendar calculate when the rotor shadow hits a protected window. During those minutes the turbine is automatically stopped until the limit is met again.

Guide · Shadow Flicker

Wind turbine shadow flicker: how disturbing is it really?

In short: Periodic shadow flicker — the moving shadow cast by the rotor blades — is strictly limited by law: no more than 30 hours per year and 30 minutes per day (astronomically possible), and in reality a maximum of around 8 hours per year. If more is reached, the turbine switches off automatically. Permanent nuisance is therefore ruled out.

What is "periodic shadow flicker"?

When the sun is low behind the turbine, the turning rotor casts a moving, periodically flickering shadow — the so-called disco effect. It only occurs when three conditions are met at the same time: sunshine, a suitable sun position (morning/evening, low) and wind (the rotor is turning). On most days of the year at least one condition is missing.

The limits (LAI guidelines)

Criterion	Limit
Astronomical maximum possible	30 hours / year
Per day	30 minutes / day
Real (actual, with weather statistics)	approx. 8 hours / year

The decisive factor is the protected outdoor living area or the living-room window. The values come from the LAI guidelines (Bund/Länder-Arbeitsgemeinschaft Immissionsschutz, the Federal/State Working Group on Immission Control) and are fixed as a condition in the permit notice.

How compliance is ensured

During the procedure, a shadow flicker report calculates the possible shading duration for every affected immission location. If it exceeds the limit, a shadow-flicker shutdown module becomes a condition:

An astronomical calendar knows the critical minutes for each dwelling.
A brightness sensor checks whether the sun is actually shining at all.
Only when both apply is the turbine stopped for those minutes.

The yield loss is minimal (usually well below 1 %), because only a few minutes on a few days are affected. The shadow flicker calculator allows a rough estimate of your own.

Putting it in context: Unlike noise, shadow flicker can be solved technically very cleanly — the shadow can be predicted to the minute and switched off. Anyone who keeps the permitted minimum distance is, as a rule, only briefly affected or not affected at all. More on distance in the guide Distance to dwellings.

Frequently asked questions

Does it also flicker at night or when it is cloudy?

No. Without direct sun there is no shadow flicker. That is why the real burden is much lower than the astronomical maximum — the sensor only switches on during actual sunshine.

Does the shadow on the garden count too?

Protected areas are living rooms and outdoor living areas (terrace, balcony). Pure farmland or traffic areas are not relevant. The report defines the decisive immission locations.

What about the flashing light of the rotor blades?

Reflections are avoided by matt, anti-glare coatings on the rotor blades — this has been standard for years and is also regulated in the procedure.

Shadow flicker from wind turbines – conditions, LAI limits and shutdown module