Draft National Wind Farm Development Guidelines - July 2010

Regression analysis should be carried out for each category (e.g. wind direction, time of
day, etc) according to Section 6.3.4 of AS4959–2010. Where the different regression curves
are within 1-3dB of the regression curve for all data at each integer wind speed, significant
variation in background noise level with wind direction is not considered likely and the
noise limits should be determined using all the data. Note: To avoid excessive analysis, the
aim should be to determine the worst-case criteria where this is due to a systematic
variation on the distribution of background sound level vs. wind speed due the factors
mentioned above.
Where the variation is greater than 3dB, some variation in background noise level with the
selected category is likely and that category should be analysed separately. The same
analysis process described above should also be used to establish noise level limits for
stakeholder properties with agreed alternative noise level limits. The minimum noise level
limit should be corrected as per the agreement with the stakeholder, within the upper
bounds discussed in Section B.4.1 Establish noise criteria (page 45).
Application of noise level limits in the case of cumulative development is discussed in
Section B.5.
Undertake a tonality assessment
Tonality should be assessed as part of the noise impact assessment, based on tonality tests
included in IEC 61400-11: 2006, or other tonality assessment approved by the relevant
authority.
Undertake noise emission predictions (detailed)
As suggested by the flow chart in Appendix A of AS4959–2010, further wind farm noise
emission predictions should be carried out once noise level limits have been established at
all relevant receivers.
• Updating preliminary noise emission predictions
The wind farm layout is likely to have changed significantly since the time of the
preliminary predictions, and the detailed noise emission predictions can be used to
optimise the noise received noise levels and to reflect the final layout
• Detailed noise emission predictions
Detailed prediction methods should be implemented according to Section 5.3 of
AS4959–2010. Predictions should be carried out for each nominal wind speed at
intervals of 1m/s between the cut-in wind speed and the rated wind speed.
The modelling assumptions should reflect typical (but not extreme) ‘worst case’
meteorological conditions for sound propagation towards the receiver. The relevant
authority should be consulted to identify any specific requirements for modelling
assumptions. All modelling assumptions should be clearly stated.
Where ISO 9613-2 is used, 7 the parameters provided in Table B-3 are likely to provide a
generally realistic and conservative assessment of noise emission. It is acceptable to
use alternative parameter values. For example, reasonable worst case temperature
and humidity levels may be determined from review of annual meteorological data
from the Bureau of Meteorology. However, a clear explanation for the reasons for
changes in parameters should be provided.
The use of a single value to represent air absorption across the entire frequency
spectrum is not considered suitable for detailed noise emission prediction unless
7 International Standards Organisation (1996) Acoustics – Attenuation of sound during propagation
outdoors Part 2: General method of calculation. ISO 9613-2:1996, Geneva, Switzerland.
Page 52 Draft National Wind Farm Development Guidelines – 2 July 2010