Acoustics Standards & Guidance
What is ETSU R97 Wind Farms?
ETSU-R-97 is a key guidance document used in the UK for assessing and controlling noise from wind farms. The full title is “The Assessment and Rating of Noise from Wind Farms,” and it was published in 1997 by the Energy Technology Support Unit (ETSU) for the Department of Trade and Industry (DTI).
It provides specific guidance on how to measure, predict, and assess noise levels generated by wind turbines to ensure that they do not cause undue disturbance to nearby residents.
Key Features of ETSU-R-97:
1. Noise Limits:
ETSU-R-97 sets out acceptable noise limits for wind turbines based on the time of day (daytime and nighttime) and background noise levels at nearby properties.
The document suggests that wind farm noise should not exceed 35-40 dB(A) during the daytime when background noise is low and should not exceed 43 dB(A) at night to avoid sleep disturbance. If background noise levels are higher, the wind turbine noise limits can be set to 5 dB above the prevailing background noise.
2. Daytime vs. Night-time Noise Levels:
Daytime (0700-2300): The noise limit is generally set between 35 and 40 dB(A) or 5 dB above the background noise (whichever is greater). This is based on the expectation that people are awake, and moderate noise levels are acceptable.
Night-time (2300-0700): A fixed limit of 43 dB(A) is recommended to protect residents from sleep disturbance, or a level that is 5 dB above the background noise (whichever is higher).
3. Background Noise Measurements:
The guidance emphasises the importance of taking background noise measurements at noise-sensitive locations, such as residential properties near the proposed wind farm. These measurements should be taken under various wind conditions to establish the natural noise environment before wind turbines are installed.
Noise limits for wind turbines are then set relative to these measured background levels.
4. Use of Noise Prediction Models:
ETSU-R-97 provides a methodology for predicting the noise levels from wind turbines at nearby properties, taking into account factors such as wind speed, distance from the turbines, and topography. Predictions should include the worst-case scenario, such as high wind speeds or turbines operating at maximum output, to ensure noise levels remain within acceptable limits.
5. Noise Mitigation:
If predicted noise levels exceed acceptable limits, the document recommends mitigation measures. These can include:
- Modifying turbine operation, such as reducing turbine speed during high wind conditions.
- Relocating turbines further from noise-sensitive properties.
- Implementing technological solutions, such as improved turbine designs or noise-reduction features.
6. Amplitude Modulation and Other Characteristics:
The guidance addresses the phenomenon of amplitude modulation, which refers to fluctuations in noise levels caused by the blades of the turbine passing the tower (often described as a “swishing” or “thumping” noise). While the document acknowledges the existence of this effect, it does not provide specific limits for it. This has been a point of contention and subsequent research on wind turbine noise.
7. Consultation with Local Authorities:
Local authorities play a key role in ensuring compliance with ETSU-R-97 guidelines, especially during the planning stages of wind farm development. Wind farm developers are expected to submit noise assessments based on ETSU-R-97 methodology as part of the planning application process. If a development does not meet the noise limits set out in the guidance, it may face objections or conditions that require further noise mitigation.
Purpose of ETSU-R-97:
The main purpose of ETSU-R-97 is to provide a standardised method for assessing wind farm noise that balances the need for renewable energy development with the protection of nearby residents from excessive noise. Wind farms can produce both mechanical noise (from the turbines) and aerodynamic noise (from the blades passing through the air), and ETSU-R-97 helps ensure that these sounds are kept within reasonable limits.
Importance and Continued Use:
Despite the criticisms, ETSU-R-97 remains the official guidance for assessing wind farm noise in the UK. Planning authorities and developers rely on it to ensure that wind farms meet acceptable noise levels and that the concerns of local communities are addressed.
It provides a clear framework for developers and regulators, offering an evidence-based approach to predicting and mitigating noise impacts. However, developers often need to supplement ETSU-R-97 assessments with additional noise mitigation techniques or further research to address the concerns raised by modern wind farm developments.