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Table 8.8 Nordex N90/2500HS Wind Turbine Sound Power Levels for a 80m hub height
WIND SPEED AT 10m HEIGHT (m/s ) SOUND POWER LEVEL (dB L AEQ )
3 95.0
4 99.0
5 102.5
6 105.5
7 106.5
8 107.0
9 107.0
10 107.0
11 107.0
12 107.0
Table 8.9 Octave Band Sound Power Spectrum (dB L Aeq ) for the Nordex N90/2500HS
Operating in Reference Wind Speed Conditions (v10 = 8 m/s)
OCTAVE BAND CENTRE FREQUENCY, Hz
A-WEIGHTED SOUND POWER LEVEL, dB(A)
63 92.2
125 96.3
250 100.7
500 101.1
1000 99.6
2000 98.5
4000 94.5
8000 87.2
Choice of Wind Farm Operational Noise Propagation Model
8.5.12 Whilst there are several noise propagation models available, here the ISO 9613-2 model 12 has
been used to calculate the noise immission levels at the selected nearest residential
neighbours. This model has been identified as most appropriate for use in predicting far-field
noise radiation from wind turbines in such rural sites.
8.5.13 The model accounts for the attenuation due to geometric spreading, corresponding to the
increasing spreading of sound as it propagates away from the source, atmospheric
absorption, and ground effects. The model offers the ability to account for barrier effects
however, this has not been included for in this assessment due to the relatively flat ground. All
attenuation calculations have been made on an octave band basis and therefore account for
the sound frequency characteristics of the turbines. The ISO 9613-2 algorithm has been
chosen as being the most robust prediction method based on the findings of a joint European
Commission research project into wind farm noise propagation over large distances. The title
of the research project was ‘Development of a Wind Farm Noise Propagation Prediction
Model’ 13 .
8.5.14 Whilst it is impossible to specify exact error bands on noise predictions, the ISO 9613-2 model
was found to be the best available both in flat and complex terrain. This model, like all the
others, tends to over-estimate the noise at nearby dwellings rather than under-estimate it. The
only exception to this finding was the general tendency for the ISO 9613-2 model to over
predict the excess attenuation due to screening by ground features. With this limitation applied
to the ISO 9613-2 model the over-riding conclusion of the work undertaken as part of the EC
research study was that the ISO 9613-2 model tended to predict noise levels which would
generally occur under downwind propagation conditions. The probability of non-exceedence
of the levels predicted by the ISO 9613-2 model was around 85%. The other important
outcome of the research was to clearly demonstrate that under upwind propagation conditions
between a given receiver and the wind farm the noise immission level at that receiver will be
as much as 10 dB(A) to 1 dB(A) lower than the level predicted using the ISO 9613-2 model.
November 2010 Chapter 8 Page 15
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