Health effects of wind turbine noise: fact or fiction?

Noise is a major issue for public health. According to the World Health Organisation (WHO), it represents the second highest environmental risk factor in Europe in terms of morbidity, behind air pollution.

In western Europe, over a million healthy years of life are lost every year due to transportation noise, the effects of which have been established with sufficient evidence concerning sleep disturbance, annoyance, cardiovascular disease and cognitive impairment in children.

While the health impact of transportation noise has been extensively studied, this is not necessarily the case for other sources of environmental noise. One example is wind farms, which have grown significantly in France and many other countries. Alongside their aesthetic impact on the landscape, the noise pollution from wind turbines is one of the most common arguments put forward by opponents of these installations.

However, the information available in the public sphere, particularly online, around the actual impact of this kind of noise and its effects often does not correspond to facts established and reviewed by the scientific community. Let’s look into what we currently know on this issue.

Wind turbine noise: a specific type of noise

Compared to many other sources of environmental noise, of human or natural origin, the sound levels induced by a wind farm are very moderate. Measured outside a local resident’s home, they rarely exceed 40 dBA, which is equivalent to the noise level in a calm office.

By comparison, the sound level of road traffic noise at the façade of a local resident’s building can exceed 70 dBA (the threshold sound level for a road-traffic noise black spot in the daytime).

Nevertheless, despite these very moderate levels, local residents sometimes report annoyance from wind turbine noise. There could be multiple reasons for this.

First of all, let’s remember that the decibel scale is logarithmic, which means that adding 3 more decibels is equivalent to doubling the sound energy, and 10 more decibels multiplying it by 10. However, while annoyance due to noise increases with the level of noise exposure, there are usually no simple laws governing its evolution. It depends on each source of noise and its characteristics (permanent noise, impulse noise, low/high frequency noise, etc.).

In the case of wind turbine noise, wind farms are located in mainly rural environments. Therefore, the relatively low background noise in these areas may facilitate the perception of the noise emitted.

The annoyance could also be due in part to the specific characteristics of the sound signal generated by wind turbines. The noise is continuous, and can sometimes have pronounced tone (mechanical noise from the machinery, degraded surface of the blades). However, these are generally a symptom of a wind turbine’s malfunction, which can be corrected.

When the wind turbine blades are operating, “amplitude modulation” of the sound can also occur and cause annoyance. This modulation results in fluctuations in the sound level over time (with a period of about one second). The reasons for this phenomenon are not yet clear but many possible explanations are being investigated.

For example, it could come from aerodynamic stall at the blades, specific weather conditions affecting sound propagation, specific sound directivity of noise generated by the moving blades, or interactions between the noise from the blades and the ground.

Lastly, wind turbine noise also includes low-frequency components (20-200 Hz, audible) and infrasound (frequency below 20 Hz, generally considered inaudible), which propagate further than higher-frequency noise. Although predominant in the wind turbine sound spectrum, the infrasound generated by a wind farm remains far below the known thresholds of human perception.

The existence of these various phenomena has been clearly confirmed. Now, scientists are examining how to model and integrate them in current noise prediction methods.

To improve our knowledge of physical phenomena and better control the noise emitted by wind turbines, the PIBE research project was initiated. It has three main objectives: characterising and modelling sound amplitude modulations, estimating the variability of sound levels (mainly by evaluating the influence of local micrometeorology on sound emissions from the blades and sound propagation) and designing devices that minimise noise produced by the blades.

A limited number of people exposed to wind turbine noise

To assess the public health challenges represented by exposure to wind turbine noise, two aspects must be considered: the number of people affected and the severity of the effects of wind turbine noise on health, if they are demonstrated.

A recent study on the metropolitan French population’s exposure to wind turbine noise indicated that over 80% of people exposed to this noise is exposed at levels lower than 40 dBA.

In 2017, the reference year for this study, the proportion of the metropolitan French population exposed to wind turbine noise above this level varied between 0.08% (night-time conditions) and 0.18% (daytime conditions), depending on the propagation conditions.

In comparison, for the same year, the proportion of the metropolitan French population exposed to noise over 40 dBA in night-time conditions was 15% for road-traffic noise, 7% for railway noise and 0.7% for aircraft noise.

No evidence of health effects

Recent articles summarising current knowledge indicate a lack of evidence for health effects of wind turbine noise, except for annoyance.

Most of the available studies found a significantly positive association between the noise levels emitted by wind turbines and the percentage of highly annoyed people. Furthermore, at equivalent sound levels, the noise produced by wind turbines may be perceived as more annoying than that emitted by other sources (particularly transportation), due to certain aforementioned acoustic characteristics of the sound signal, including the possible existence of amplitude modulation of the signal.

However, the acoustic properties of the noise emitted by wind turbines cannot explain all the annoyance alone. It may also depend on other non-acoustic factors, like the wind farm’s visibility, the attitude of people exposed to it, and specific interests between a local resident and the farm (financial interest for example).

Very few studies have examined the effects of wind turbine noise on sleep disturbance, cardiovascular diseases, metabolic and endocrine systems, cognition and mental health. The WHO highlights that the evidence for health effects of wind turbine noise is either non-existent or of low quality.

Low-frequency noise or infrasound emissions from wind turbines are often cited as a potential source of risk to human or animal health.

However, a 2017 review report,from the French Agency for Food, Environmental and Occupational Health & Safety (Anses) as well as more recent international research have concluded that there is no sufficient scientific evidence supporting the existence of health effects related to these emissions and that there is a lack of studies in this area.

This report does recognise that local residents may report true situations of ill-being, but their connection to wind turbine noise is complex and often difficult to establish.

While certain theories discussed by opponents (“wind turbine syndrome” and “vibroacoustic disease”) were deemed to be lacking in credibility by the Anses review report, other mechanisms of effects are yet to be explored, such as those that could affect the cochleovestibular system and cause physiopathological effects. This sensory system, located in the inner ear, plays a role in our sense of movement and equilibrium. We know that it is particularly sensitive to low-frequency sound and infrasound.

However, while certain cellular effects have been observed in laboratory animals via pure intense sounds (though not necessarily equivalent to very low-frequency sound in humans), their existence remains to be demonstrated in humans, and for similar sound exposure as wind turbines (complex sounds, of lesser intensity, but prolonged in duration).

Such effects could explain the reported annoyance, which is sometimes higher than would be predicted by estimations and measurements of the acoustic field, or established knowledge concerning sensitiveness to infrasound or low-frequency sounds.

Understanding the health effects of wind turbine noise, especially infrasound

To address the current lack of knowledge, the WHO and Anses in France have recommended epidemiological studies on a significant number of individuals, using objective measurements of participants’ health status, and measuring exposure to wind turbine noise in an objective and standardised way for a wide range of sound levels and frequencies (including low-frequency noise and infrasound).

The French research project “RIBEoIH” Research on the Impacts of Wind Turbine Noise on Humans: Sound, Perception, Health) was set up to respond to this need. Currently underway, it has multiple objectives:

• To evaluate the health effects of audible noise, low-frequency noise and infrasound emitted by wind turbines, and better understand the annoyance reported by local residents;

• To identify the auditory mechanisms associated with the perception of infrasound and low-frequency noise emitted by wind turbines;

• To better understand the effects of infrasound on the inner ear and central nervous system of humans.

To achieve this, the project is divided into two complementary parts: an epidemiological study performed on 1,200 people living in proximity to wind farms in France, and a psychoacoustic and physiological study.

The second study will involve taking psychoacoustic and physiological measurements in a controlled laboratory environment, with the help of wind turbine sounds measured or synthesised by a physical model for various wind turbine operating conditions. This will make it possible to determine the parameters with a significant role in the effects of noise emitted by wind turbines on auditory sensation and annoyance.

Evaluating the consequences of wind turbine noise on sleep

Another project, called “EOLSOMnie” is aimed at better understanding the effects of wind turbine noise on sleep. This is a specific sleep study on a sub-sample of around a hundred participants in the epidemiological study for the RIBEolH project.

The aim is to evaluate the effects of audible noise emitted by wind turbines on individual sleep parameters and to determine if low-frequency noise and infrasound produced by wind turbines modify sleep physiology.

The results of these two projects will provide scientific basis to future works that could investigate recommendations for noise thresholds to be applied in the development of wind turbines, for which information is currently lacking.

A better understanding of the impacts of noise emitted by wind turbines will help better control them and provide more support for developing wind energy in respect of everyone. It is an important step to be able to develop this renewable energy in the best possible conditions, as part of the essential energy transition underway.