Residents on a river plain at the foot of the Tararua Ranges, New Zealand, experience ongoing noise problems, including sleep deprivation, thought to emanate from a nearby wind farm in the ranges to the east (closest V90 turbine is 3 km away). The problem is worst when wind is from the eastern quadrant. Installation of ‘Hush Glass’ only partly alleviated the problem indoors.
Continuous time series recording of seismic noise using a buried L4 geophone and acoustic surface microphone attached to a wall inside the house, was conducted during March 2009. Use of night hours records minimised extraneous noise, and seismic noise from vegetation was also guarded against by analysis of site wind records.
Early analysis of 196s seismic samples identifies noise bursts lasting 10 seconds or more, every minute or so, associated with easterly wind conditions; with broad spectral power peaks centred on approximately 10 and 28 Hz. Audio playback of the seismic records was identified by the residents as similar to the noise they experienced.
We conclude that seismic energy from the turbines, most likely as Rayleigh waves, is coupled through its concrete foundations into the house, where various vibrational modes are stimulated, thus producing the effects experienced. We note that residents experience these strongest when lying down, i.e. when best aurally coupled to the foundations.
These results provide an initial indication that seismic effects should be assessed in consideration of offset distances from turbines to residences.
Ongoing work will consider such factors as directionality of seismic noise, proximity to the range front fault as possibly accentuating seismic response, either through standing wave or dispersion, and constructive/destructive interference between turbines associated with wind variability as a cause of the intermittent nature of the phenomenon.
Presented at the Third International Meeting on Wind Turbine Noise, Aalborg, Denmark, 17-19 June 2009
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