Why Turbine Noise Annoys!
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Why Turbine Noise Annoys
• It is established that wind turbine noise annoys more that
most other noise with similar loudness.
• Nothing special about the effect of turbine noise that we
don’t already know
• There’s nothing mysterious
Warnings!
• Most windfarms are not a noise problem – but a
significant number are.
• Audio is much louder than you would hear it 500m or
more away.
– Intended to show character of noise
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Factors that determine noise impact
• Loudness - Noise level in decibels
• Character of the noise
– Frequency distribution and tonality
– How noise varies with time
• Perception
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Loudness - 1
• In low noise rural areas the ETSU-R-97 assessment
depends on lower limits.
– Up to 40dBA during the day and perhaps 10dBA above average
background noise
– 43dBA at night and perhaps 15dBA above average background
noise.
• No other industrial noise source would be allowed at that
level.
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Loudness - 2
• In higher noise areas where limit is background + 5
• Impossible to formulate an accurate baseline.
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Character - Frequency
• Tones – Can nearly always be fixed
– Penalty Applied
• Infrasound
• Low Frequency Noise
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Character - Frequency
Infrasound – 1Hz, 600mm, 6Pa, 104dB
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Character - AM
• Amplitude Modulation seems to be a major factor in the
adverse perception of turbine noise.
• Relentless
• We know very little about it.
• What do we know?
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Character - AM
• 1989 -Jakobsen and Pedersen
–Modulation prominently in range 500Hz to 2kHZ.
• 1997 – Dunbabin
–Blade swish mainly at 500, 1k and 2kHz.
• 1996 ETSU-R-97
–Blade swish 800 to 1000Hz
• 1999 ETSU W391
–Modulation is most apparent in the 1 and 2 kHz octave bands
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Character – AM - Swish
• The AM referred to up to about 2002 was almost all
related to the “swish” heard near the turbine.
• Swish
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Character – AM – Swish - Oerlemans
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Character – AM – Swish - Oerlemans
• In front
• You hear the swish from the down
stroke on the right.
• At Hub height swish disappears.
• At a distance swish disappears.
• And the same happens behind.
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Character – AM – Swish - Oerlemans
• Downstroke Side - You hear the swish coming from the
blades as they go over the top of the trajectory.
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Character – AM – Swish - Propagation
• The feature of Swish is that it does not propagate
downwind but at 45 degrees to downwind and
sometimes as far round as 90 degrees.
• Downwind there is no swish.
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Character – AM – Swish - ETSU W391
• Swish rises and falls at about the same rate
• If anything the rate of rise is slower than the rate of fall.
• Swish again
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Character – AM –Thump
• Thump rises fast and falls slowly
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Character – AM –Swish to Thump
• First Swish
• Then moving into Thump
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Character – AM –Thump - Van den Berg
• observes the difference between “thump” and “swish”.
• Turbines are audible for most of the (day and night) time
as a swishing sound. Thumping is only evident, at times
of high wind shear
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Character – AM –Thump - Van den Berg
• AM is caused by the blades passing through air which
has varying speeds and directions whether this is due to
wind shear, meteorological turbulence or turbulence
created by topography or other turbines
• He considers that excessive wind shear (for example at
night) increases thump.
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Character – AM –Thump - Hayes
• “The presence of high levels of modulation is associated
with wind direction and the inappropriate aerodynamic
conditions seen by the closest three wind turbines to the
dwelling.”
• That is to say these three turbines have turbulent air
striking them.
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Character – AM –Thump - Hayes
• “the source of modulation may be related to wind shear
by which I refer to changes of wind speed and direction
at different heights above ground level.
• Thus the blades at [some] points in the arc may not be
fully pointed into the wind which may result in increased
aerodynamic noise.”
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Conclusion - AM
• Swish does not occur Downwind
• Swish is mid to high frequency (500 to 2000Hz)
• Swish rises slowly and falls fast
• Thump occurs within 45 degrees either side of downwind
• Thump occurs at lower frequencies (125 to 250Hz)
• Thump rises fast and falls slowly.
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Factor 3 - Perception
• EHOs and Consultants well aware that listeners attitude
is important.
• Does the listener perceive they have control of the noise? –
ETSU-R-97 Financial Involvement.
• Noise does not only have to be controlled but the impact
has to be managed.
– What is the relationship between the Exposer and the Exposee?
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Perception - Eveline Maris
• “Exposer and Exposee” from the Dutch researcher.
• Another pair of words
Fair and Unfair
Does the exposee perceive that the exposer is being fair?
Maris established that when the exposer was not fair, annoyance
was higher.
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Perception - Fair and Unfair – Developers
• “Turbine noise will be 10dB below the background noise
at 70 to 190m from the turbine”.
– Still well above background noise at 250m. Clearly heard in
bedroom
• “We want to involve the community in the project. We
want your views”
– We can’t tell you how big the turbines are – its not finalised yet.
– People don’t feel they are being treated fairly
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Perception - Fair and Unfair – Developers
• People perceive that
– Their lives will be blighted by the development
– They gain no benefit
– They pay subsidies in the form of Tax
– They pay more for electricity.
– Developers make all the money
– People don’t feel they are being treated fairly
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Perception - Fair and Unfair – Government
• “Advances in turbine technology have helped to avoid
increased noise from larger turbines”.
Typical 0.5MW turbine in 1996 is 100dBA. Typical 3MW turbine 2010 is 107dBA
• “No evidence to suggest that AM is as a result of
Turbine Size”
Members of NWG – arguably the people with best knowledge of turbine noise in
the UK – told DTI in 2006 “The trend for larger more sophisticated turbines could
lead to an increase in noise from AM”
• People don’t perceive they are being treated fairly
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Perception - Fair and Unfair – Government
• Now:
• Commissions research into how ETSU-R-97 can be
applied in a more consistent and effective manner.
• It is not possible to apply ETSU-R-97 consistently
• Why?
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Perception - Fair and Unfair – Government
• ETSU is inconsistent with other planning guidance in PPS22 and in
Local Plans.
• ETSU is inadequate in that it does not cover some essentials such
as the calculation of turbine noise.
• ETSU is out of date in that wind shear and AM are more significant
issues than they were in 1996 and are not covered.
• What is required is a revision and updating.
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Perception - Fair and Unfair
Investigating a complaint can take years.
• Investigation is complex
• Planning conditions rarely have time scales attached.
• Developers are reluctant to turn turbines off
• People don’t perceive they are being treated fairly
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Conclusions
• ETSU needs to be revised so it can be perceived as
being fair
– Removing lower limits
– Re-examining how margin over background works
• Research into AM as recommended by the NWG in 2006
should be carried out urgently
– Developers cannot predict whether they will have a problem
– Enforceable AM condition not possible
• Method of procurement must be changed.
– Incentives for community projects
• No evidence to suggest this would significantly reduce
investment in renewables
The Future
• The feed-in tariff is bringing a rush of small
developments – 10 to 20kW.
– New developers who produce incompetent reports
– Poor or non-existent manufacturers data
– Lack of a standard (ETSU does not apply)
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A Trip to Rome?
Fourth International Conference on Wind Turbine Noise
12th – 14th April 2011
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