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The science of noise and
vibration and its effects in everyday life is generally very
well understood. But despite what you may read in many
articles this is not the case for wind farm noise.
Wind Farms
are said by the BWEA (www.bwea.com)
to be ‘quiet enough to have a normal conversation with someone
whilst standing directly below a rotating turbine’. This may
well be so. The House of Lords in their Report on Electricity
from Renewables also say:
"thanks to
improvements in technology ...., noise is no longer the issue
it was."
So why should we be concerned
about the noise effects?
Noise assessments of wind farms
is generally carried out using modelling techniques and refers
to the guidelines ETSU-R-97 as a method of establishing
appropriate levels to work to. These guidelines, introduced in
1997, were derived by a government funded working group given
the aim ‘to provide information and advice to developers
and planners on the environmental assessment of noise from
wind turbines’ They have been severely criticized by a
number of qualified acousticians as being ill conceived and of
little credibility due to the assumptions made within them in
including Dick Bowdler, a Fellow of the Institute of
Acoustics. His paper ‘Why ETSU-R-97 is Wrong’ although very
technical in nature clearly highlights the author’s
frustration with the guidelines and their assumptions.
Using these guidelines and
noise modelling techniques that make assumptions on the ground
conditions, wind shear effects, layout of the turbines,
profile of the site and the basic data provided by the
manufacturers about the turbine noise levels is prone to
error. The phrase that comes to mind is ‘All models are wrong,
only some are useful’.
Wind turbines produce
mechanical noise from the drive and gearbox. This is much like
most other industrial machinery noise and can be reduced at
source by careful design as well as being partially attenuated
by the effective use of the nacelle enclosure (the bit that
contains all the working parts behind the turbine hub).
However do not under estimate the size of the machine within
each turbine. These things have to produce 2MW remember so
typically their drive shafts are 600mm diameter, somewhat
bigger than your average car driveshafts. Newer direct drive
turbines eliminate the gearbox and therefore are marketed as
being quieter then the majority of turbines.
Of more concern is the
Amplitude Modulation (or Aerodynamic Modulation) noise that
turbines generate as the blades pass the tower itself.
Typically these events occur at frequencies below 20Hz meaning
that the average human ear may not ‘hear’ the resultant
pressure wave created but may well feel it. This is known as
infrasound. For every article saying that there are no issues
with infrasound from wind farms there is one that points
towards the problems associated with infrasound.
In response
to concerns that wind turbines emit infrasound and cause
associated health problems, Dr Geoff Leventhall, Consultant in
Noise Vibration and Acoustics and author of the Defra Report
on Low Frequency Noise and its Effects, says:
"I can state
quite categorically that there is no significant infrasound
from current designs of wind turbines."
In August 2007 a paper that was
to presented at INTERNOISE (an internationally recognised
noise conference) in Istanbul was summarised before the
conference in a press release that stated “ These results
irrefutably demonstrate that wind turbines in the proximity of
residential areas produce acoustical environments that can
lead to the development of Vibro-Acoustic Disease (VAD) in
nearby home-dwellers” The authors were Professor Mariana Alves
Pereira of the School of Health Sciences at Lusofona
University, Portugal and Nuno Castelo Branco MD, Surgical
Pathologist, President of the Scientific Board for Human
Performance.
So experts are somewhat divided
on this issue.
By its very nature, infrasound
waves have long wavelengths and as the pressure waves produced
can be significant in magnitude at source they have the
ability to travel long distances, reputedly over 2km in some
circumstances.
In 2006 the government (BERR)
commissioned the University of Salford to investigate ‘AM’
effects of wind farms. The resultant survey published in 2007
suggested that around 1 in 5 wind farms have resulted in
complaints about noise, and of these 44% may be complaints due
to ‘AM’, the rest being mechanical noise. The conclusion
reached was that on balance there was little benefit in
conducting more research into ‘AM’ based on the low number of
occurrences across the wind farms evaluated. However the
conclusion was also that ‘AM’ isn’t fully understood as it is
a complex interaction issue. What is clear from many other
postings and articles on websites is that there are many
neighbours of wind farms out there that continue to suffer
‘AM’ and it can have serious consequences on the health and
well being of residents affected in this way.
As a minimum developers should
be asked to produce evidence of ambient infrasound levels as
part of the planning application and then to provide a
guaranteed level of infrasound that would not be exceeded once
operation commences. It is highly unlikely that a developer
would dare to offer to do this due to the possibility of being
faced with a wind farm that does exhibit such issues.
In parts of Europe and indeed in Scotland the minimum distance
from residential areas that wind turbines can be sited is 2km.
This is due in part to the noise risks and effects on health.
In France recently
President
Sarkozy
announced “the end of the
’rush’ that has characterized French policy on wind turbines
up to now and that ultimately means degradation of the
environment. New wind turbines will be installed first in
industrial farm fields and far from emblematic locales.” The
press release goes on to say “This new
policy marks the end of industrial wind turbine installations
in (French) rural and wild areas. This is a relief for the
800 villages and 52 departments represented in the October 6
demonstration. It is also a powerful contribution to the image
of France and shows Europe that an energy policy can reconcile
the fight against global warming and respect for the
countryside and every life.”
Demark has also
stopped further development of onshore wind farms due to noise
and health issues.
A
recent paper “Noise Radiation From Wind Turbines Installed
Near Homes: Effects on Health”, by Barbara J Frey, Feb and
June 2007 stated that ‘a safe buffer zone of at least 2km
should exist between family dwellings and industrial wind
turbines of up to 2MW installed capacity, with greater
separation for a wind turbine greater than 2MW installed
capacity.’
The Swinford turbines are 2 MW
each and come closer than 1km to parts of the village and as
close as 650m from the hill farms so the risks of an
associated noise problem may be greatly enhanced.
Once the turbines are in place,
getting any noise issues sorted may well prove to be
difficult.
There are many useful articles
that illustrate that noise can be a real issue to neighbours
of wind farms. As a starting point try
www.countryguardian.net a site that links to most of the
UK’s wind farm action groups websites.
Here are 3
interesting reports for further reading:
-
Noise Radiation from wind turbines
installed near homes
-
Why ETSU is wrong
-
Salford Report - Aerodynamic Modulation
of Wind Turbine Noise, July 2007
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