Wind Farms – Noise Challenges
18 December, 2018 | Blog
The noise impact of wind farms has been relatively understood for some time now. Today, the studies are clear: wind turbines produce potentially harmful noise if they are too close to sensitive environments.
Figure 1: Noise level generated by a typical wind turbine based on distance
However, we can predict the noise impact of wind turbines using specialized software, which optimizes the potential of a wind project while minimizing its environmental impact. Unfortunately, there can still be challenges that make it more complicated to decide what steps to take; that’s why we are focusing on the noise challenges of wind projects.
Regulation versus social licence
Sadly, in Canada, the noise impact of wind farms is a provincial and municipal challenge, as there are no federal regulations on this topic. Municipal nuisance regulations can be legally valid when the relevant province does not have a wind noise regulation. The lack of clear legal framework can sometimes make it difficult to assess the impacts of a wind project. That said, provinces without specific regulations sometimes require noise impact analyses that are based on the regulation from a neighbouring province or on guidelines designed to address a legislative gap.
Current Canadian provincial regulations have set the maximum acceptable noise level in rural areas to 40 dBA. But is this enough? The World Health Organization maintains that this noise level is not harmful to your health. However, several European countries are asking that noise levels be lowered to 35 dBA. So who is right? Health Canada carried out a study correlating the disturbance level of a wind project based on the noise amplitude at the homes being studied. The study revealed that noise annoyance increases significantly when an average noise level of 35 dBA is reached. Additionally, responsible authorities usually request an analysis of the number of homes that are exposed to more than 35 dBA to determine the number of people potentially annoyed by the wind project, despite compliance with standards.
So, what noise criteria should we base wind projects on? The answer lies in combining regulations and analyzing the density of sensitive environments that surround the wind project that is being studied to truly understand associated risks.
Simulation versus reality
Another bone of contention encountered in a noise study for a wind project is how the results of sound propagation simulations are interpreted compared to the actual noise receptors will experience.
Those responsible for studying the environmental impacts of wind projects require that certain protocols be respected and want recognized calculation methods (ISO 9613, CONCAWE, NORD2000, etc.) to be used. Although standardized, these methods sometimes induce conservative or unrealistic results. Standardized simulations therefore risk painting an unrealistic picture of the project impact if the calculations are not interpreted by someone who is capable of identifying the limitations of the enforced protocols.
Figure 2: Noise propagation – Wind farm
A typical example of an unrealistic representation is the difference between a carrier wind and a prevailing wind: the procedure requires simulating the noise from a turbine under favourable conditions for noise propagation (wind toward receptors). But in fact, is this even likely? If the prevailing winds are blowing in the opposite direction of the home, shouldn’t they be ignored? The noise from a wind turbine can vary by over 10 dBA, based on wind direction. So it would be possible to place a wind turbine in a more beneficial area (despite the presence of a home), if the study reflects wind amplitude and direction. It is essential to analyze local climate conditions to maximize the energy potential while respecting targeted noise objectives. The analysis is potentially more demanding, but the long-term benefits largely outweigh the alternative of blindly applying required protocols.
A second unrealistic scenario encountered when abiding by procedures is when a home is surrounded by many wind turbines. Carrier wind simulations are requested to simulate the noise generated by each wind turbine. But what happens when wind turbines are located in opposite directions to specific homes? Protocol requires simulations of different wind directions that can generate noise. This is physically impossible, as the winds can only come from one direction.
Figure 3: Source: https://www.homebuilding.co.uk/renewable-technology-guide/
To understand the true acoustic impact that a wind farm configuration can have, a simulation based on actual wind conditions must be performed to understand the noise impact of a wind project. Once again, the analysis is more exhaustive, but the economic benefits observed over the life of the project will more than compensate for the preliminary analysis.
Controlling noise emissions from wind turbines in an urban setting
Many technological innovations are now available or are being developed to minimize the acoustic impact of wind turbines. If ever a wind project is subject to operating restrictions (e.g., slowing some wind turbines to reduce their noise), there are solutions, under certain weather conditions, to control noise emissions created by turbines while increasing their power generation.
First, wind turbines can be damaged (lightning) or wear over time. An acoustic camera can be used to determine whether certain wind turbine components generate more noise today than when they were first started up. Acoustic cameras use a microphone matrix to locate the noise origin.
Figure 4: Noise imagery – dominant wind turbine noise sources
This technique helps determine whether the noise problem can simply be resolved through maintenance without even having to access the nacelle.
Many companies have optimized the shape of wind turbine blades to maximize the power potential while minimizing noise impacts: a Canadian company succeeded in increasing blade efficiency by 20% while reducing the noise level by 2 dBA. Some of these types of solutions are also available as additions to standard blades.
Finally, there are real-time servo systems to maximize wind turbine production while complying with regulatory acoustic criteria. This system listens to the noise that is generated by wind turbines and slows them to maintain acceptable noise levels for protected homes.
As you can see, noise challenges from wind farms that are located near inhabited areas can sometimes become complex. It is important to take the time necessary to analyze the project in order to ensure that its impacts are properly understood. This helps prevent unpleasant surprises or bad decisions, like selecting a wind farm configuration that is not optimal, since the location’s actual constraints were not properly understood. BBA experts can help you through every step of a wind project (construction, operation and optimization) to ensure its maximum performance.
This content is for general information purposes only. All rights reserved ©BBA