Wind farms need specific guidelines because wind turbines have unique noise generating characteristics and the environments surrounding wind farm sites usually have low ambient noise. …
2 NOISE CRITERIA
The general approach in setting noise criteria for new developments is to require compliance with a base noise level.
This base noise level is typically 5 dB(A) lower than the level considered to reflect the amenity of the receiving environment. Designing new developments at a lower level accounts for the cumulative effect of noise from other similar development and for the increased sensitivity of receivers to a new noise source.
The impact of a given noise is also closely linked to the amount it exceeds the background noise. For example, the same noise in a quiet rural area will generally have a greater adverse impact than in a busy urban area because of the masking effect of high ambient noise environments.
If the noise generated does not exceed the background noise by more than 5 dB(A) the impact will be marginal and acceptable.
A unique characteristic of wind farms is that the noise level from each wind turbine generator (WTG) increases as the wind speed at the site increases. As an offset, the background noise also generally increases under these conditions and can mask the WTG noise.
Comparison with a base noise level alone will therefore not be sufficient to indicate the potential impact of a wind farm: a farm could comply with this base level at lower wind speeds but exceed it when the wind speed rises.
Most international and interstate jurisdictions … set a base noise level for low wind speeds and also ensure that the wind farm noise does not exceed the background noise by more than 5 dB(A) as the wind speed increases.
This general approach recognises the unique noise generating characteristics of wind turbines and the particular ambient noise environments of most sites and is the one used by these guidelines.
Most wind farm sites are within or next to areas where low ambient noise levels are a significant component of that area’s amenity. These might include rural living zones or zones that are not intended to be subject to any other significant ambient noise sources from adjacent premises. …
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The New Zealand Standard NZS 6808 sets the predicted base level (LAeq) at 40 dB(A). This is higher than the approach of these guidelines, but the specified propagation model to be used in accordance with that standard does not account for factors such as ground absorption and topography effects that can substantially reduce the noise level in practice. In addition, the New Zealand Standard requires the criteria to be met at all receivers, regardless of their relative amenity or relationship with the wind farm development.
A comprehensive publication developed by the wind farm industry for the UK Department of Trade and Industry (1996) sets the base level (LA90) at 35 – 40 dB(A). The actual value chosen within this range depends on the number of dwellings affected, the effect on the capacity of the wind farm of meeting the standard, and the duration and level of exposure.
Wind turbines and wind farms have been being developed in Denmark for over 20 years. Denmark has set a base noise level only (and does not consider the influence of background noise). The base noise level (LAeq) is set at 40 dB(A) for a wind speed of V10m = 8 m/s. These guidelines will provide a similar result given the expected influence of background noise. …
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Where the wind farm sites are within or next to areas where more intensive activity is expected, the base noise level may also be increased commensurate with the amenity of that area. It is recommended that the developer discuss such a situation with the EPA and the relevant planning authority.
2.1 Determining wind farm operating criteria
The Environment Protection (Industrial Noise) Policy 1994 limits the noise level from non-domestic noise sources including wind farms to 40 dB(A) or the lowest typical background noise level plus 5 dB(A) (whichever is the greater) in rural areas from 2200 hrs until 0700 hrs the following day.
This limit applies to existing noise sources and does not necessarily reflect the preferred noise criterion for new (planning) development. The general approach for new development applies a night time level of 35 dB(A) to significant development in a rural location.
To prevent adverse impacts from the increased noise of WTGs under high wind conditions, the increasing noise level must also be compared to the corresponding background noise at the relevant receiver.
2.2 Noise criteria – new wind farm development
The predicted equivalent noise level (LAeq,10), adjusted for tonality in accordance with these guidelines, should not exceed:
· 35 dB(A), or
· the background noise (LA90,10) by more than 5 dB(A)
whichever is the greater, at all relevant receivers for each integer wind speed from cut-in to rated power of the WTG. …
2.5 Cumulative development
Separate wind farm developments in close proximity to each other may impact on the same relevant receiver.
Therefore, as for staged development, any additional wind farm that may impact on the same relevant receiver as an existing wind farm should meet the criteria using the background noise levels as they existed before the original wind farm site development. The noise generated by existing WTGs from another wind farm should not be considered as part of the background noise in determining criteria for subsequent development. …
3.1 Background noise
What is background noise?
Background noise is the ‘lull’ in the ambient noise environment.
Intermittent noise events such as from aircraft flying over, dogs barking, mobile farm machinery and the occasional vehicle travelling along a nearby road are all part of the ambient noise environment but would not be considered part of the background noise unless they were present for at least 90% of the time. …
Where, in the opinion of an officer authorised under the Environment Protection Act, the wind farm exhibits tonality as a characteristic, the developer should conduct a tonality test in accordance with a procedure acceptable to the EPA.
An addition of 5 dB(A) should be made to the measured background noise level from a wind farm where tonality is shown to be a characteristic.
Download original document: “Environmental Noise Guidelines: Wind Farms”
This article is the work of the author(s) indicated. Any opinions expressed in it are not necessarily those of National Wind Watch.
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