Turn, Turn, Turn!
All Wind Turbine Noise Impact Assessments Are Not Created Equal
When it comes to green power alternatives, wind power is a popular and growing option. It’s easy to see why: it is clean, affordable, and endlessly renewable. In fact, electricity from wind energy is one of the fastest growing methods of electrical generation in the world. And Canada is now the fifth-largest market in the world for the installation of new wind turbines.
Why We Need Wind Turbine Noise Studies
But despite the positives, wind turbines have generated some public concerns. For people living near wind turbines, it can be noisy if improperly designed or tuned. This created a need to properly assess the risk of excessive noise levels at the neighbouring dwellings before a project can be built.
Today a noise impact study is required before you can move through the design and permit stage of building a wind turbine. It is meant to assess possible noise impacts before the project is in operation rather than after. While there are methods of verifying the noise levels from wind farms and wind turbines post-construction, it can be more costly to correct and generally easier to resolve pre-construction. There was a time when wind turbine operators in Canada faced issues getting the noise levels of its equipment tested. Only a handful of companies in the U.S. and Europe were accredited to complete wind turbine sound power measurements until our team at Aercoustics became the first Canadian organization to certify noise levels of wind turbines.
Key Considerations When Conducting a Wind Turbine Noise Study
Who you get to conduct this noise impact study and how they go about it, can make or break your project. There have been stories within the industry involving project developers who were provided with suspect noise modelling for their application, only to find out after the lengthy permit process that it was not done correctly and major changes need to be made to secure approval.
It is important when reviewing, evaluating or conducting such studies that the appropriate methodology, calculations and site considerations be employed. There are many factors to be considered in a noise impact assessment including the topography, if the ground is absorptive or reflective, the layout of the turbines and more. All of them need to be part of the review.
An acoustical engineer will know all of the important test factors. Wind turbines are unique and noise studies have some subtleties that can lead to incorrect predictions on the noise impact.
Here are some critical things to consider:
1) Sound spreads differently close to the ground compared to when it is elevated
For the most part, the industry in North America uses the ISO 9613-2 standard for outdoor sound propagation. The scope of this standard was last updated in 1996, before the advent of large-scale wind turbines. Broadly speaking, the standard was designed to predict sound propagation for noise sources close to the ground – which doesn’t directly consider aspects that may affect noise sources that are elevated such as wind turbines. As the height increases, there are different atmospheric interactions and can result in different sound levels. To account for this, there are some parameters that an experienced acoustical engineer needs to incorporate in the modelling. If not, the standard will give a result which will be quieter than reality and yield false results. The difference can be off by 3-5 dB, which doesn’t sound large but it can mean the difference between a compliant and non-compliant project on paper.
2) Wind farm noise sources are further than you might think
Typically when doing noise modelling, a search radius needs to be inputted into a program or algorithm. The default is to measure the predicted noise level one or two kilometres away from a nearby house. However, major wind farm noise sources can be as far as five kilometres from the spot you are doing your calculations. Using the default search radius means only measuring the noise from the closest turbines and arguably miss the next 10 leading to an under prediction of the noise level.
3) Consider the worst-case scenario
Noise behaves differently in different atmospheric conditions and wind turbines are not like other industrial noise sources. For example, a manufacturing facility produce noises when the machines are running but no sound when the operations are shutdown. Wind turbines make different sounds depending on the wind speed and weather. The sound level generated by the facility at a given dwelling will vary based on the wind speed, wind direction, humidity and temperature profile. The impact to a person would also depend on the existing ambient noise. On a very windy day, the turbine will be much louder so this needs to be taken into consideration. Assess a reasonably worst-case condition so that you are certain a turbine meets the requirements in good conditions or bad.
Find a Partner Experienced in Wind Turbine Noise Modelling
There are many reputable engineering firms that can complete a noise impact assessment but not all of them have expertise with wind farms and wind turbine noise modelling. Wind farms are unique installations and present different challenges when it comes to noise. From elevation to weather impacts to distance travelled, the errors can easily stack up if you are using a more standard model.
Depending on where your project is located, it can take several months to get an approval for a wind turbine. If the wind turbine noise studies are done incorrectly, you might not find out until you’re close to the end of the permitting process. When you’re that far down the road, you may be forced to make concessions and modify the turbine and design in order to get the permit and move on. Don’t risk your credibility with the regulator and don’t risk losing valuable time and money. Make sure your first noise impact assessment report is performed properly and reports the correct numbers.
