ETSU-R-97 is a document that has remained unchanged since it was first published nearly two decades ago, despite suffering from heavy critisism over those years. McKenzie and Bullmore propose what an alternative procudure to the assessment and rating of wind farm noise in the UK might be, if ETSU-R-97 were to be superceded.
This paper gives some examples of a potential amplitude modulation (AM) assessment using the three metrics proposed in the IOA AM discussion document. Results are presented, discussing the analysis of noise measurements undertaken at a residential receptor location near a wind turbine site where operational and background noise periods were measured. Some of the issues involved are discussed. The objective of these metrics is a consistent quantification of the modulating character of the wind turbine related component of the noise, which can be implemented in a practical way.
With the increasing number of operational wind farms/turbines, the requirement for noise measurements required to demonstrate compliance with planning conditions is increasing as well. The British ETSU-R-97 noise limits are often set relative to measured or standardised 10 m height wind speeds and therefore the assessment of noise from wind turbines requires simultaneous noise and wind speed/direction measurements. For financial reasons, smaller and single turbine sites are often not equipped with a meteorological mast. If no independent hub height wind measurements are available, wind speed is either taken from nacelle anemometers or derived from power measurements combined with the power curve for the respective wind turbine type. Noise measurements referenced to nacelle anemometer data will be compared with the same measurements but correlated with derived power curve wind speed, and measured wind data from separate met mast or other remote sensing devices. The influence of incorrect filtering of wind data for shadow effects (mast and/or nearby wind turbines) on the noise assessment may be presented, depending on how much time is available. The advantages and disadvantages of the various methods will be discussed.