Lessons Learned Monitoring Near and Further From Wind Turbines

Résumé

Without wind to turn them, wind turbines are almost a silent neighbour. Yet, when rotating, we ask if what we hear is the wind, the impact of wind on surroundings, or on the turbines. Hypotheses have been advanced why some people say they are annoyed by wind turbines. These hypotheses leave unresolved questions why the annoyance is not present at all times.A 135-day monitoring program was carried out at a site 537 metres from the nearest wind turbine, with 19 turbines within 3 km. Simultaneous monitoring was conducted over 14-days at a second site 6 km from the nearest wind turbine in the same array.Measurement microphone results at the different sites were compared to a Level 1 ACO Pacific 7146 microphone to ensure consistency.Analysis of microphone recordings near wind turbines showed a correlation between the results and conditions identified as annoying by residents. The correlation was not to maximum sound amplitude.Annoyance was most identified when the difference (LZ10 - LZ90) was ≥ 6 dB and the difference (LA10 - LA90) was ≤ 3 dB.At these times, sound from the wind turbines were prominent, and dominated noise from the wind, or the wind on the surroundings.These conditions were not found to occur at the site distant from wind turbines.Special attention was given to situations when the turbines shut down or started up, as wind speeds do not change appreciably over the transition itself. Similar results were found at other sites near wind turbines.Concluding, the monitoring program identified acoustic conditions consistent with times identified as annoying occurring near wind turbines, that did not exist further from wind turbines. This will be useful as a screening tool to identify when annoyance might occur.