Version 1
: Received: 25 April 2024 / Approved: 26 April 2024 / Online: 26 April 2024 (16:56:39 CEST)
How to cite:
van den Berg, F. (.; Koppen, E.; Boon, J.; Ekelschot-Smink, M. Development of Sound Power of Onshore Wind Turbines including Its Spectral Distribution. Preprints2024, 2024041773. https://doi.org/10.20944/preprints202404.1773.v1
van den Berg, F. (.; Koppen, E.; Boon, J.; Ekelschot-Smink, M. Development of Sound Power of Onshore Wind Turbines including Its Spectral Distribution. Preprints 2024, 2024041773. https://doi.org/10.20944/preprints202404.1773.v1
van den Berg, F. (.; Koppen, E.; Boon, J.; Ekelschot-Smink, M. Development of Sound Power of Onshore Wind Turbines including Its Spectral Distribution. Preprints2024, 2024041773. https://doi.org/10.20944/preprints202404.1773.v1
APA Style
van den Berg, F. (., Koppen, E., Boon, J., & Ekelschot-Smink, M. (2024). Development of Sound Power of Onshore Wind Turbines including Its Spectral Distribution. Preprints. https://doi.org/10.20944/preprints202404.1773.v1
Chicago/Turabian Style
van den Berg, F. (., Jaap Boon and Madelon Ekelschot-Smink. 2024 "Development of Sound Power of Onshore Wind Turbines including Its Spectral Distribution" Preprints. https://doi.org/10.20944/preprints202404.1773.v1
Abstract
The sound power LW of wind turbines (WTs) over the past decades has developed in relation to their electric power P as LW ∝ logP. The spectral distribution of the sound did not change significantly over time. This applies to the average performance of wind turbines, with differences between individual WT types. Because of the expected growth of onshore wind energy, a greater number of people will be living close to wind farms. This sustains the need for sound reduction. Sound reduction measures, such as serrations, reduced tip speed and low noise modes, may counteract the development of higher sound power from ever bigger WTs. To investigate this, the sound production of WT types over the last decades is analysed in relation to their size and electric power and the application of sound reduction measures. The analysis includes the broad band A-weighted and low frequency sound power levels as well as more detailed spectral distributions. Results show that the sound power level of wind turbines above 3 MW on average increases less with size than smaller turbines did. This is due to a lower blade tip speed and the use of sound reducing serrations. The spectral content of wind turbine sound, including the lower frequencies, has not changed significantly.
Environmental and Earth Sciences, Sustainable Science and Technology
Copyright:
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The commenter has declared there is no conflict of interests.
Comment:
September 2024 Leonard M. B. Baart de la Faille Comment on: Development of Sound Power of Onshore Wind Turbines including Its Spectral Distribution Frits (G.P.) van den Berg, Erik Koppen, Jaap Boon, Madelon Ekelschot-Smink doi: 10.20944/preprints202404.1773.v1
All topics in this comment are discussed in: https://www.researchgate.net/publication/384011851 ‘Audiological advisory report on estimated noise and proposed noise limits of the Dutch IJsselwind wind farm’. On appeal to the Council of State. July 2024
== Heading ==1 Aim of the study ‘This study aims to show whether changes in wind turbine technology have affected the existing relation between size and sound power’. The study focuses on available wind turbine specifications based on ISO-61400 measurements. These data however give only a restricted qualification of sound power. The study neglects the effect of larger and higher rotors under the varying micrometeorological circumstances and its consequences for sound production, spectra and generating AM. The study calculates the immission sound power at dwellings with the ISO-9613 method neglecting large deviations in real world, especially for low frequency’s.
== Heading ==2 ISO-61400 data The specs of wind turbines serve in the study as a means to compare sound powers of different wind turbines. These data are however of limited significance when it comes to picture the sound powers in practical circumstances. ISO-61400 gives a standard for sound power measurements in neutral meteorological conditions. In practice the meteorological conditions vary and as a consequence the sound power varies 7 – 10 dB within the defined wind speed class.34 Spectra vary as well. With more turbulence the low frequency’s below 200 Hz will enhance. In very neutral conditions extreme temperature and wind speed gradients will lead to greater wind speed differences along the rotor with local stall and associated low frequency enhancement and increased AM as a result. These processes make comparisons between small and large wind turbines based on ISO-61400 not very meaningful. The data on which the article is based is not available for a second thought. It is in the public health interest the culture of non disclosure to stop. More specific and precise data are needed for research and therefore should be made available by law. This should include one third octave data specified for a wide range of meteorological conditions as well as detailed data on the impact of serrations and (automated) noise modes. At this stage no final conclusions can be drawn about sound power of wind turbines.
== Heading ==3 Turbine dimensions Comparing turbines with different hub height and/or rotor diameter on the basis of ISO-61400 data is corrupted by the fact that influence of the micro-meteorological differences over the rotor blades is strongly influenced by these dimensions. This means that the effect of variations in the meteorological stability or wind shear have different effects on sound power and spectra for different turbine dimensions. This also holds for AM. The conclusions of the article about wind turbine dimensions therefore have no scientific bases.
== Heading ==4 Immission calculations The study calculates immission sound power and spectra with the ISO-9613 sound propagation model. However this method is designed and validated for industrial objects of maximum height of 30 meters, with low wind speed and up to 1000 meters. There is overwhelming data indicating the low quality of this calculations. It is very odd to use a calculation model for wind turbines which neglects the influence of wind itself. Even the normal variation within de neutral stability class can lead to large fluctuations in low frequency sound propagation without ISO-9613 to notice. Based on consultancy calculations using this model the Dutch government concludes that low frequency’s play no substantial role in wind turbine noise. The present study states: ‘the 63 and 125 Hz 1/1-octave bands which include the 50-160 Hz 1/3-octave bands, but not the lower 1/3-octave bands (10-40 Hz). However, the levels in the range 10-40 Hz are so low they can be considered negligible, based on the spectral distribution in the present study.’ Measurements conducted on Dutch and German wind farms show however this consideration doesn’t hold in practice. The 31 Hz one third octave band, and in general the low frequencies, are very important with respect to annoyance. The conclusions in the article about immission levels of wind turbine sound are all based on an invalid estimation of the sound propagation. Sound propagation depends to a great deal of the hub height of wind turbines.
== Heading ==5 Serrations In discussing the effect of serrations the study focus mainly on the balance between the broadband and the low frequency sound power. Calculated this way there is hardly any effect upon this balance. With serrations the broadband power can increase 2,4 dB to meet the same noise limits and because of the unchanged balance also the low frequency’s increase with the same portion. This is not mentioned in the study although it can result in a relatively strong increase of annoyance because hearing is very sensitive for small level increments at low frequency’s. The study stresses the advantage of serrations in reducing maximum sound power, but neglects the associated increase of low frequency annoyance.
== Heading ==6 Conclusions The study concludes: ‘The results show that the size of wind turbines of 3 MW and above has a small effect on their sound emission.’ In fact sound emission is much more complicated then the very limited data from manufacturers and depends strongly on wind turbine height and rotor diameter. ‘To mitigate sound emission, trailing edge serrations have proven to be effective.’ In fact serrations give room to increase the maximum broadband level resulting in a relative increase of low frequency annoyance. ‘To reduce sound emission at specific times or in specific conditions a low noise mode can be applied to a wind turbine. On average this has an effect on sound level, but not on its spectral distribution. This conclusion cannot be drawn from the presented data. Much more data is needed and the effect on AM has to be established as well.'
This comment is meant to be a firm statement: the general outcome doesn’t hold and the complexity of wind turbine sound propagation must be appreciated.
Commenter:
The commenter has declared there is no conflict of interests.
Leonard M. B. Baart de la Faille
Comment on:
Development of Sound Power of Onshore Wind
Turbines including Its Spectral Distribution
Frits (G.P.) van den Berg, Erik Koppen, Jaap Boon, Madelon Ekelschot-Smink
doi: 10.20944/preprints202404.1773.v1
All topics in this comment are discussed in:
https://www.researchgate.net/publication/384011851 ‘Audiological advisory report on estimated noise and proposed noise limits of the Dutch IJsselwind
wind farm’. On appeal to the Council of State. July 2024
== Heading ==1 Aim of the study
‘This study aims to show whether changes in wind turbine technology have affected the existing
relation between size and sound power’. The study focuses on available wind turbine specifications
based on ISO-61400 measurements.
These data however give only a restricted qualification of sound power.
The study neglects the effect of larger and higher rotors under the varying micrometeorological
circumstances and its consequences for sound production, spectra and
generating AM.
The study calculates the immission sound power at dwellings with the ISO-9613 method
neglecting large deviations in real world, especially for low frequency’s.
== Heading ==2 ISO-61400 data
The specs of wind turbines serve in the study as a means to compare sound powers of different wind
turbines. These data are however of limited significance when it comes to picture the sound powers
in practical circumstances. ISO-61400 gives a standard for sound power measurements in neutral
meteorological conditions. In practice the meteorological conditions vary and as a consequence the
sound power varies 7 – 10 dB within the defined wind speed class.34
Spectra vary as well. With more turbulence the low frequency’s below 200 Hz will enhance. In very
neutral conditions extreme temperature and wind speed gradients will lead to greater wind speed
differences along the rotor with local stall and associated low frequency enhancement and increased
AM as a result. These processes make comparisons between small and large wind turbines based on
ISO-61400 not very meaningful.
The data on which the article is based is not available for a second thought. It is in the public health
interest the culture of non disclosure to stop. More specific and precise data are needed for research
and therefore should be made available by law. This should include one third octave data specified
for a wide range of meteorological conditions as well as detailed data on the impact of serrations
and (automated) noise modes.
At this stage no final conclusions can be drawn about sound power of wind turbines.
== Heading ==3 Turbine dimensions
Comparing turbines with different hub height and/or rotor diameter on the basis of ISO-61400 data
is corrupted by the fact that influence of the micro-meteorological differences over the rotor blades
is strongly influenced by these dimensions. This means that the effect of variations in the
meteorological stability or wind shear have different effects on sound power and spectra for
different turbine dimensions. This also holds for AM.
The conclusions of the article about wind turbine dimensions therefore have no scientific bases.
== Heading ==4 Immission calculations
The study calculates immission sound power and spectra with the ISO-9613 sound propagation
model. However this method is designed and validated for industrial objects of maximum height of
30 meters, with low wind speed and up to 1000 meters. There is overwhelming data indicating the
low quality of this calculations. It is very odd to use a calculation model for wind turbines which
neglects the influence of wind itself. Even the normal variation within de neutral stability class can
lead to large fluctuations in low frequency sound propagation without ISO-9613 to notice.
Based on consultancy calculations using this model the Dutch government concludes that low
frequency’s play no substantial role in wind turbine noise.
The present study states:
‘the 63 and 125 Hz 1/1-octave bands which include the 50-160 Hz 1/3-octave bands, but not the
lower 1/3-octave bands (10-40 Hz). However, the levels in the range 10-40 Hz are so low they can
be considered negligible, based on the spectral distribution in the present study.’
Measurements conducted on Dutch and German wind farms show however this consideration
doesn’t hold in practice. The 31 Hz one third octave band, and in general the low frequencies, are
very important with respect to annoyance.
The conclusions in the article about immission levels of wind turbine sound are all based on an
invalid estimation of the sound propagation. Sound propagation depends to a great deal of the hub
height of wind turbines.
== Heading ==5 Serrations
In discussing the effect of serrations the study focus mainly on the balance between the broadband
and the low frequency sound power. Calculated this way there is hardly any effect upon this
balance. With serrations the broadband power can increase 2,4 dB to meet the same noise limits and
because of the unchanged balance also the low frequency’s increase with the same portion. This is
not mentioned in the study although it can result in a relatively strong increase of annoyance
because hearing is very sensitive for small level increments at low frequency’s.
The study stresses the advantage of serrations in reducing maximum sound power, but neglects the
associated increase of low frequency annoyance.
== Heading ==6 Conclusions
The study concludes:
‘The results show that the size of wind turbines of 3 MW and above has a small effect on
their sound emission.’
In fact sound emission is much more complicated then the very limited data from
manufacturers and depends strongly on wind turbine height and rotor diameter.
‘To mitigate sound emission, trailing edge serrations have proven to be effective.’
In fact serrations give room to increase the maximum broadband level resulting in a
relative increase of low frequency annoyance.
‘To reduce sound emission at specific times or in specific conditions a low noise mode can
be applied to a wind turbine. On average this has an effect on sound level, but not on its
spectral distribution.
This conclusion cannot be drawn from the presented data. Much more data is needed
and the effect on AM has to be established as well.'
This comment is meant to be a firm statement: the general outcome doesn’t hold and the complexity
of wind turbine sound propagation must be appreciated.