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Predicted Sound Levels from the Turitea Wind Farm

Dr Bob Thorne

The Cumulative Effect of Multiple Wind Farms

This Paper presents a Case Study for the assessment of cumulative effect due to multiple wind farms within a locality. The noise predictions are calculated with PEN3D to provide an indication of the potential noise emissions for residents near the proposed Turitea wind farm resulting from cumulative effects of the proposed Turitea wind farm (all turbines), and:

PEN3D is based on an application of sound propagation described in ISO 9613-2 (1996) Acoustics – Attenuation of sound propagation outdoors Part 2: General Method of Calculation[67] and NZS 6808:1998 Acoustics – The Assessment and Measurement of Sound from Wind Turbine Generators[66]. ISO9613 states that the average propagation equation of the standard holds under well developed moderate ground based temperature inversion but this is not necessarily correct. Note 24 to the standard provides-

"The estimates of accuracy in Table 5 are for downwind conditions averaged over independent situations (as specified in clause 5). They should not necessarily be expected to agree with the variation in measurements made at a given site on a given day. The latter can be expected to be considerably larger than the values in Table 5."

PEN3D also implements Pasquill Stability Categories (also known as the CON- CAWE implementation) as described in New Zealand Standard 6801:2008 Acoustics-Measurement of Environmental Sound[73]. The method was previously presented in NZS6801:1999.

All prediction models have limits to their accuracy of prediction[143,144]. This is due to the inherent nature of the calculation algorithms that go into the design of the models, the assumptions made in the implementation of the model, and the availability of good source sound power data. Various researchers have suggested that an uncalibrated model has an accuracy of ±5 dB while a calibrated model has an accuracy of ±2 dB...


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