Sound Protection Report for Wind Turbines

The sound protection report (Schallschutzgutachten) is one of the central mandatory reports in the BImSchG permitting procedure for wind turbines. It assesses whether the noise generated by the turbines complies with the immission thresholds of the TA Laerm at the nearest residential buildings — and identifies what mitigation measures are required if not.

When is a sound protection report required?

• Always in the BImSchG procedure — both in the simplified and the formal process
• Also for repowering (new turbine = new procedure = new report)
• For turbine replacement or capacity upgrades to existing turbines
• On request of the permitting authority in response to neighbour complaints at existing sites

What must be included? — Mandatory contents

1. Source data of the turbines: sound power level L_WA in dB(A) from the manufacturer's measurement report (FGW TR 1 or IEC 61400-11), incl. ±2σ safety margin
2. Immission points: list of all sensitive receptors (IO) within the impact zone with protection category per TA Laerm (general residential area, mixed-use, village, commercial area)
3. Calculation per DIN ISO 9613-2 (point-source model, octave-band spectrum, alternatively LAI point-source model with flat-rate surcharge)
4. Consideration of reflection, ground, weather (worst-case assumptions)
5. Level summation for multiple WTGs + pre-existing noise from other installations
6. Assessment against TA Laerm thresholds day/night (see table below)
7. Mitigation and optimisation measures if thresholds are exceeded: night-time reduced mode, noise-reduced mode, turbine type change

TA Laerm thresholds (excerpt)

The decisive value for WTGs is usually the night-time threshold for the nearest general residential area (40 dB(A)) — it triggers a noise-reduced night mode in many cases.

What happens if thresholds are exceeded?

The report must propose mitigation measures that ensure compliance:

• Noise-reduced night operation (most common solution): speed and/or pitch reduction at night, yield loss typically 1–4% p.a.
• Turbine type / manufacturer mode optimisation: some manufacturers offer certified quiet modes with defined L_WA values
• Layout adjustment: repositioning critical turbines further from the receptor
• Noise protection at the receiver (sound-insulating windows) — rather exceptional, rarely used in practice

What does a sound protection report cost?

Guideline value EUR 5,000 – 25,000 for a wind farm with 3–6 turbines. Key factors:

• Number of turbines + number of immission points
• Pre-existing and additional loads (other WTGs, industry, traffic) — higher complexity
• Need for a mitigation concept (night-shutdown logic)
• Special low-frequency / infrasound report (rare, but if required + EUR 5,000–15,000)

Who prepares the report?

Sound protection reports may only be prepared by measurement bodies accredited under § 29b BImSchG or qualified acoustics engineering firms. Established providers in the onshore WTG sector include TUeV Sued, Deutsche WindGuard, ITAP, Woelfel, KOETTER Consulting Engineers, Mueller-BBM, as well as numerous regional specialists.

Sound protection report WTG — mandatory contents, TA Laerm thresholds, costs and repowering relevance

Frequently asked questions

What is the difference between acoustic emission prognosis and sound protection report?

The acoustic emission prognosis is the actual noise level calculation (source data + propagation model + comparison with TA Laerm). The sound protection report is usually the extended document that additionally proposes concrete measures and describes the mitigation concept. In practice, the terms are often used interchangeably.

How reliable are the prognoses?

Very reliable — the point-source model per DIN ISO 9613-2 has been proven in permitting practice for decades and is designed conservatively. Real-world measurements typically come in 0.5–2 dB below the prognosis. Authorities accept the model without dispute.

Do we need to measure after commissioning?

Often yes — the permit almost always includes the condition of an acceptance measurement after commissioning (typically within 6 months). The measurement is performed per FGW TR 1 / IEC 61400-11 and verifies the turbine's sound power level against the value used in the report.

What about infrasound and low-frequency noise?

The sound protection report assesses the audible frequency range (16 Hz – 16 kHz) per TA Laerm. Infrasound (< 20 Hz) is not addressed in standard reports — the TA Laerm does not provide thresholds for it. Low-frequency components between 8 and 100 Hz can be assessed additionally in special reports per DIN 45680, which are rarely required in practice.