Noise Compliance Solutions
With the growing push for full spectrum acoustic monitoring, and advances in technology enabling real time transmission of full spectrum acoustic data via the internet, there are a number of possibilities for improving the measurement of environmental noise, and transparency of compliance with noise pollution guidelines.
This section will include some information about possible solutions being developed as it becomes publicly available. We welcome information from individuals and companies involved in developing solutions.
A wind turbine noise measurement and control system (“NMACS”)
Source: Waubra Foundation, September 2011
Wind Energy Projects (“WEPs”) exist in all states of Australia. At this time (September 2011) some 2000 turbines mostly of capacities of 1.5 to 2.5 MW are in operation. In order to meet its nominated 2020 renewable energy target, the Federal Government is largely reliant on the wind industry adding another 9000 MW of renewable energy capacity by the 2020 date which might be satisfied by around another 4000 turbines.
Projects have mostly been located by the presence of strong winds and the proximity and access of power grids. Locations have not been sensitive to the presence of farmers and other householders. Nor can this be expected to change substantially.
Despite much denial, it is a fact that many neighbours of WEPs are suffering serious health problems that are linked to noise emissions by turbines and that this will be worsened by the increasing use of larger turbines.
The noise forecasts prepared by those consultants favoured by the industry omit infrasound and low frequency noise, as do the planning guidelines and or regulations for WEPs. Complaints by sufferers are largely ignored and relevant bureaucracies have not been keen to find any fault with an industry so favoured by Government. The Waubra Foundation prepared a specification for a low cost and simple system to retrofit to existing wind energy projects, and which should also be mandatory to include in all newly built wind projects, especially in view of the larger (3–4 MW) turbines now being deployed.
Problems measuring low frequency sound levels near wind farms
Proceedings of ACOUSTICS 2011, Paper Number 57, November 2011, Gold Coast, Australia
H.H.C. Bakker & B.I. Rapley
It is current practice to measure sound pressure levels (SPL) from wind farms at a handful of locations in the surrounding countryside. These can be placed near sensitive areas such as residences to provide an indication of the SPL at that point and are used in conjunction with sound level prediction software to infer sound level throughout the affected areas.
The Bakker Rapley paper reports a literature review of human perception of low-frequency sound before describing investigations into sound levels at the Makara wind farm near Wellington, New Zealand where the interference of low frequency sound from the multiple wind turbines form stable SPL patterns. The low frequency emissions from multiple wind turbines were simulated and validated against measurements from microphone arrays. Ten sound frequencies from 1/3 octave immission spectra were chosen from recorded measurements on the site ranging from 55 Hz to 315 Hz. The simulation used the positions of 14 wind turbines closest to a microphone array as point sources of the sounds. Results show that the combined frequencies from a single turbine produced SPL patterns within a 100 m-by-100 m area that varied by 2–5 dB whereas the combined sounds from all 14 turbines varied by 6– 13 dB. Validation of these results was achieved by using three 2-by-4 microphone arrays with 1 m, 2 m and 3 m separation between the microphones. These recorded variations of 6–11 dB in their 15-minute, SPL averages. Additional validation was also shown by direct observation; the sound from the wind turbines was observed to appear and disappear within two to three paces between fixed locations. The conclusion is that measurements of low frequency sound levels can vary considerably over even very short distances and that point measurements may not represent the sound levels throughout their immediate neighbourhood. The locations of increased sound energy are given the name “heightened noise zones”.