Noise Monitoring for Renewable Energy
Henk de Haan, dBA Noise Consultants
Many a tome has been penned about sound level monitoring, and many more could be added. Some of my incomplete thoughts on it are offered here.
Under most regulatory regimes, strategies for noise and sound monitoring are determined by the situation and the dominant noise sources at hand, and not by whether the source is renewable or non-renewable. Continuous sources are typically easier to monitor than sources with a highly variable noise emission, such as wind turbines.
Prior to constructing and operating any new development, getting an idea of what the current soundscape entails helps to put future noise levels into perspective and is therefore recommended. I use the word “sound” to indicate that the acoustic signals we hear are not all experienced as noise. Noise is unwanted sound, and the soundscape may include both appreciated sounds (e.g., songbirds, leaf rustle) and unwanted sounds (e.g., an existing non-renewable energy facility or other sources not covered by most noise regulations, such as highways or gravel operations). In that respect, ambient sound level monitoring is not any different for renewable energy compared to other facilities.
The monitoring of ambient sound levels is not required nor encouraged according to regulations in Alberta or British Columbia, but frequently requested by residents close to new developments such as a new wind farm. Apart from satisfying popular demand, the only time you get to measure the unaffected soundscape is before construction starts. Therefore, I believe that ambient sound level monitoring should be actively considered before any development, renewable or otherwise, unless the new development will not generate substantial noise. The cost associated with noise monitoring is minimal compared to the investment in the renewable’s facility itself.
Monitoring of sound levels during construction can help one gain insight into and limit noise levels associated with construction, provided noise limits are enforced; what gets measured for enforcement purposes gets done, while what gets measured for general insight often only gets discussed. Sources such as tonal backup alarms, loud radios, pumps, light tower generators running during the daytime may cause unnecessary grief, while solutions such as broad-band backup alarms are readily available.
Monitoring during operation can provide insight into noise levels, associated with the new facility. Monitoring, however, needs to be part of enforcement of applied noise thresholds. I, therefore, believe that the regulator should conduct noise monitoring as part of their enforcement as well, and not only oblige operators to conduct noise monitoring. Regulatory noise monitoring will increase public confidence. Noise from wind farms is dependent on weather and meteorological conditions, such as atmospheric stability, and with larger turbines this dependency may increase. Predictions made using a relatively simple standard like ISO 9613 are valid for a single weather and operations scenario, and receptor-level noise levels can be expected to deviate frequently from the predicted value. Longer term noise- and weather-monitoring for receptor-level noise levels and their weather dependency can be helpful to increase insight into their dependency and confirm predictions. It can also be helpful to develop a science-based and accepted protocol for such monitoring.
For more continuous sources (e.g., solar power, biomass), where sound noise generation is relatively steady, such extended monitoring is probably not required. Noise from inverters has a continuous character, and dependency is restricted to insolation (i.e., the varying level of electrical generation due to the incident solar intensity). Short-term measurements may, therefore, be sufficient.
Alternatives to noise monitoring could include model calculations, based on verified emissions combined with model calibration. Such an alternative could be useful in situations where receptor-level noise monitoring includes significant difficulties or where compliance can only be predicted with a significant margin.
Henk de Haan is President and Sr. Consultant at dBA Noise Consultants