Introduction, continued…
A mistake often made is to assume that sound, when emanating from a source, radiates outwards in a somewhat homogeneous fashion. This is not the case. Dr. Huub Bakker and Mr Bruce Rapley have undertaken a sizeable study of the physical nature of radiating sound and compared this to microphone array studies of the noise from multiple turbines at Makara, near Wellington, New Zealand. They define the term heightened noise zone (HNZ) to describe locations where the noise is louder than expected. This results from the way sound waves interfere with each other, akin to waves created by dropping two pebbles into a pond. As the ripples radiate out they will interact to create a beautifully symmetrical pattern of ripples. In places the ripples will meet crest-to-crest or trough-to-trough creating larger ripples. Where the ripples meet crest-to-trough the ripples become much smaller. These calm areas of water can be seen radiating out as rays from a point midway between where the two pebbles were dropped.
Taking this idea further, Bakker and Rapley reasoned that the same would be true for sound emanating from multiple wind turbines. Theory predicts it. Experiments carried out with an array of eight microphones proves it. Locations only one or two metres apart can have significantly different sound levels, so measuring sound levels using only one microphone or one location can be misleading.
They then looked at how noise from turbines is modulated, including a possible reason for the 'rumble/thump' described by residents. Their use of sonograms to identify and analyse modulation is as beautiful as it is revealing (as the cover of this Review can attest).
The idea of a Heightened Noise Zone stemmed from Bakker and Rapley's work with Dr. David Bennett and Dr. Thorne. Residents near a wind farm at Aokautere, near Palmerston North, New Zealand, had problems with low frequency noise that could be heard "through the pillow" suggesting that the 'noise' was partly vibrational. The noise was only heard—and felt—with the wind blowing from the wind farm and only one of a small number of properties was affected at any one time. Measurements using a seismometer showed otherwise unexplained bursts of vibration when the noise was heard.
The authors suggest two possible reasons for this phenomenon; that seismic waves were being produced by the wind farm in the upwind and downwind directions (Rayleigh waves) or that sound waves were resonating inside the building and shaking it. For either of these possibilities the house appeared to be in a Heightened Noise Zone. (It is noteworthy that a dwelling in the area of Cook Road, near Palmerston North, is said to be uninhabitable because of seismic or vibrational noise from the surrounding wind farm.)
Sound is not the only potential problem with wind farms. Light can create problems of blade flicker (the blade occluding the sun), shadow flicker (shadows falling on the ground or buildings some distance away), and glint (reflection off the blades). The frequencies created by rotating turbine blades are close to those that can trigger photosensitive epileptics but this is only one form of hazard. Various forms of flicker can still be annoying to sensitive individuals, even those who do not suffer from epilepsy. Again, the annoyance factor is dependent to a large degree on the individual. Dr. David McBride examines all these potential hazards, which should be considered by those involved in siting wind farms. Placement cannot be determined by simply mitigating the worst physiological effects, rather it is necessary to also include quality of life measures when assessing the impact on a community.
Greater involvement of the community is called for when siting wind farms. It is easy to overlook the problems of small individual communities when considering the larger issue of wind farm placement. Issues of appropriate sites are dependent to a large degree on geography and, of course, wind history, Nearness to the grid and the ability to access the proposed site also place strong physical constraints on site placement. In this complex series of constraints, it must be easy overlook the importance on the sometimes small number of people who may live close by. Does this mean that the health and well-being, not to mention enjoyment and amenity, of a relatively small number of individuals can be ignored simply so that matters of a physical and engineering nature may take precedence? History now records the growing number of disaffected communities who, after the construction of a wind farm in their locale, are now deeply angered by the intrusion into their neighbourhood. Often such communities cite insufficient consultation during the process and a lack of information about the true nature of the intrusion. Only when the project gets underway or is nearing completion, do the true consequences become apparent.
Frequently such affected communities complain about nuisance noise which is far greater than they were led to believe at the outset of the project. They now find that for some, sleep is now seriously disturbed and the enjoyment of their home is disrupted. Some are essentially forced out of their homes in a search for the peace and tranquility they once enjoyed. Is this good enough?
Why is there such a disparity between the expectation of the developers and the residents and the final reality? Part of the problem is that the physics of sound and the human perception of noise are still not well understood by many involved in the power industry. Human factors should take precedence over physical regulations and readings but are harder to quantify. The variation between individuals is never well accounted for by a statistical mean. While developers may believe that the noise from the turbines will be masked by natural sounds like a stream, the wind in the trees or animals, residents almost universally find these statements to be left wanting. Differences such as these will cause resentment against the developers. This can split communities into the affected and the unaffected, the latter group who, due to no fault of their own, cannot understand the views of those who complain. But for those adversely affected by the wind farm placement, there is no doubt about the intrusion into their lives.
Several chapters in this Review tackle the difficult topic of the difference between theory and practice, assumption and reality. Professor Dickinson raises our awareness of the need for a better understanding of sound, noise and its regulation as it relates to human habitation. If wind farms are to proliferate at their current rate then the impact on communities needs to be addressed urgently. His words echo those of Dr. Thorne and Dr. Shepherd in calling into question physical regulations and standards which bear little meaningful resemblance to the human condition. Dr. Shepherd suggests a way forward without recourse to standards where communities may be actively involved in setting such conditions for industrial activities. While the New Zealand Standard 6808 is still in a state of flux, now is a good time to have that debate.
To understand this issue it is necessary to move away from a model which looks at physiological damage in terms of power or simple energy. A pebble has little energy but may start an avalanche. Effect is not simply a matter of power. It depends on the nature of the stimulus and its effect, not simply on how big the stimulus is. Science has a long road ahead before a deep understanding of the effects of low power stimuli on the human body is achieved. Until such time, this author predicts that many more people will be adversely affected, both physiologically and psychologically, by the poor placement of wind farms. It is the strong suggestion of the author that more research into these very important areas be undertaken with all due speed and that wind turbine placement be more carefully investigated and managed, with a stronger focus on the possible negative effects on the neighbouring communities.
Finally, this present work puts forward a suggested protocol for how the process of monitoring wind turbine sites for the purpose of consent may be managed. The concept of an independent monitoring agent is suggested and a process for more community based management could be instituted. The power companies and wind turbine proponents need to take more consideration of the effects of such industrial activities on the health and mental well-being of individuals and communities. Perhaps the age old question about the needs of the many outweighing the needs of the few should be reassessed.
While the arrival of a new clean, green alternative for generating electricity is promised by wind technology, the realisation of that may be somewhat different. There are numerous obstacles to overcome technically and the effects of such industrial installations on neighbouring communities need to be given more attention. This book is a significant step in putting more serious and relevant information into the public arena so that sensible and productive debate may be had. It is not at all exhaustive, but it is a start.
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