Noise is a critical issue for wind farm development. Turbine setback distances from residences are a central design consideration and as such noise assessment is a multi stage process.
In the feasibility stage, you should have undertaken a preliminary noise assessment. This involves basic calculations with a few worst case assumptions, in order to ensure your wind farm design is 'on track' with noise regulations. This preliminary assessment is generally not detailed enough to submit in a planning application. In the detailed assessment stage, you'll need to hire noise experts to undergo a full investigation of the noise levels expected at residences.
A detailed noise assessment builds on the preliminary noise assessment by adding more site-specific data, gathering actual background data at the site, and performing more complex calculations. The noise assessment report written for Hepburn Wind is attached to this article in the 'More information' section.
Main topics covered in this article include:
Wind turbine noise
Wind turbine noise is discussed in the article Preliminary noise assessment. All of the same noise regulations and limits described in that article will apply for the detailed noise assessment. The difference between a preliminary noise assessment and a detailed noise assessment is the level of detail used in the calculations.
Detailed noise assessment method
The preliminary noise assessment is based on a model within the New Zealand Standard that calculates the noise propagation at an average frequency (ie. 500 Hz). The model is based on hemispherical spreading of the sound from the source and only takes into account attenuation due to atmospheric absorption.
Detailed noise assessment includes assumptions about:
- Weather conditions
- Screening effects (due to the topography)
- Acoustic absorption and reflection due to vegetation and ground cover
- Source strength variation
- Ground attenuation effects
- Barriers and reflections
Scoping the job for a consultant
When engaging a consultant to write a noise assessment report it is best to follow the tips and tricks in the article Engaging specialists for environmental & technical studies. Good practice involves writing a detailed scope and getting multiple quotes for the job.
The scope should generally include:
- A detailed description of your wind farm including turbine types and the locations of residences (See suggested inputs below)
- The reason you are having the report written (e.g. to satisfy planning conditions)
- Who will need to read the report
- What you expect too see in the report (See "what to expect" below).
Information a consultant will need
The inputs to a noise assessment report are typically:
- GPS coordinates of all wind turbines
- GPS coordinates of all residences being considered in the assessment and whether or not they are a participant (co-op member or landowner etc) in the project
- A digital topographical map with height contours at intervals of not less than 10 m
- The type of wind turbines to be used
What to expect in the consultant report
A good consultant report will be a stand-alone document with plenty of description such that it can be interpreted by somebody who is not a professional in the field. This may also involve a glossary explaining noise-specific terminology. It will also list in appendices all of the input data including locations of residences and turbines.
A few things to look for are:
- A description of all inputs and assumptions
- An outline of the applicable noise regulations, guidelines and limits
- The methodology used to measure wind speed at site
- The methodology used to select locations for background noise measurement
- The methodology used to measure background noise at those locations
- The calculations and results for predicted noise levels at all residences
- Final statements concluding whether predicted noise levels at residences comply with regulations