Two new publications from the ongoing Wind Farm Noise Study mark an important advancement in wind turbine noise assessment methods, guidelines and design that will make wind energy more acceptable to communities around them.
Studies have demonstrated that night-time ‘amplitude modulation’ (AM) from wind turbines is likely to be heard by nearby residents up to five times more often than during daylight hours, depending on wind direction, season and farm distance.
Wind turbines can create shadow flicker and noise, both of which may be annoying to some people. However, the science has established that these effects are minimal and harmless; shadow flicker is predictable and easily avoided while noise varies significantly from day to night. A recent study from Flinders University revealed that long-term monitoring of wind farm noise combined with machine learning algorithms and available knowledge enabled quantification of amplitude modulation (AM), the most prominent occurrence within the noise. AM occurs two to five times more likely at night than during daytime noise.
At night, objects that could potentially hinder vision and avoid wind turbines may be scattered along their blades or tower, protruding out from beneath or behind them, or smashed into the ground beneath them. When left unsecured, such objects can pose risks; one example being a piece of metal falling off an Ohio wind turbine and getting caught beneath its blades – potentially leading to serious injury for workers nearby.
These objects may cause noise problems for residents. Fortunately, researchers are studying these noise issues with the goal of better understanding how wind turbine noise can be detected and mitigated. For instance, scientists have discovered that residents may hear a’swoosh’ sound from turbines five times more often at night than during normal operating hours.
At night, when the sun has set, wind turbines are illuminated with red lights. These signals serve to alert aircraft in the sky of their presence and remain illuminated for extended periods of time.
The lights mounted atop the nacelle of a turbine are designed to illuminate 360 degrees around it, providing visibility from all directions. This ensures that aircraft can safely view them regardless of which way they’re flying.
These lights can be seen for a considerable distance and even by those living close by the wind farm. Some residents complain that these lights disrupt the night sky.
There are various solutions to reduce these issues, such as radar-based systems that only illuminate lights if airplanes approach turbines. The German NWEA has been seeking approval for such a system for some time now.
Another solution is to reduce the number of blinking lights. French company Technostrobe has developed a technology that dims lights two thirds during nighttime operation.
Canadian transportation officials have already given approval for this technology, which is currently in use at a wind farm in Quebec.
The new technology dims the lights at different intervals to prevent birds and bats from being startled by them when it’s dark outside. It can be applied on towers located far away from any airports, like offshore wind farms.
However, installing such a radar-based system could prove expensive. Not only would it need to be maintained and adjusted according to changing weather conditions or other elements, but its performance may not always remain optimal.
Additionally, it may be difficult to convince people of the value of a system if its lights don’t function as promised. For instance, if the radar fails and doesn’t turn on the lights in time to prevent an airplane from colliding with the turbine, nearby residents could become highly annoyed by the light nuisance.
Furthermore, if the obstruction lights must remain activated at all times, they will be highly visible and could negatively influence public perception of the area. This could have serious repercussions for local economies in environmentally sensitive areas where birds are protected by law.
Wind turbines are industrial devices that capture the energy of wind. This energy is converted to electrical power by a generator inside the nacelle (the box housing the blades) of the turbine.
Wind turbines produce two kinds of noise: mechanical noise from the movement of the gearbox, and aerodynamic sound produced by air passing over their blades. The speed and type of blade, as well as wind direction, all influence this sound’s frequency.
Noise levels from wind turbines are not particularly hazardous, but they can be irritating to residents living nearby and reduce their quality of sleep. Therefore, it is essential to limit the distance between residential communities and wind turbines in order to protect human health.
Some studies have discovered that people’s levels of annoyance increase when exposed to low-frequency noise (LFN) from wind turbines, an infrasound. This type of sound has been connected with poorer sleep quality and decreased feelings of wellbeing, among other effects.
To assess the effect of LFN on human vigilance and sleep, this study measured indoor and outdoor wind turbine-generated LF/HF and SDNN for seven households located at various distances from turbines. On average, each household’s indoor LFN exposure varied between 30.7 dB (LAeq) and 43.4 dB (LAeq), depending on the construction material used and how often windows were left open or half-open.
This study revealed that houses constructed with sandstone, concrete and iron and equipped with airtight windows had the lowest indoor LFN exposure levels while those made of brick had the highest. Furthermore, houses with fully open windows had higher LFN levels than those with only partially opened windows.
Annoyance levels were found to be strongly related to a person’s attitude toward wind turbines, with highly annoyed individuals being more likely to hold negative views. These findings are significant as they show that noise annoyance is not only dependent on sound levels but also other aspects such as perception.
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