On Thu, Sep 07, 2006 at 02:18:13PM +1100, Evan Beaver wrote:
> Wind speed occurs in line with a Rayleigh distribution of shape factor about
> 2, for those who are interested. This means that peak wind, and therefore
> peak noise, occur only .001 of the time at best. This is not very often. In
> general the turbines will spin fairly quietly in a 5-10k breeze. Most
> descriptions of the noise produced by turbines describe it as being similar
> to living near a road or even the ocean. it is 'pink' noise and can actually
> be quite soothing to some people.
OK I had another look at the Bald Hills EES - combine the wind rose
(p17, Appendix 5) and the sound power output graph (p10 Appendix 11)
and it looks to me about 40% of the time the turbines would be very close
(within 2db) to peak noise power. Rather different to 0.1%.
The turbine noise spectra may roughly be 1/f (like many things)
but it isn't just pink noise. If you want endless detail you can find
a PhD Thesis here which discusses the character of the noise:
http://dissertations.ub.rug.nl/FILES/faculties/science/2006/g.p.van.den.berg/
and it particular how amplitude modulations can make it annoying to
people as faraway as 1km.
An interesting aspect is that wind turbines generate infrasound which
some bird hear much better than us. So a pigeon might be able to hear
a wind turbine from several kilometres away - not that this implies any
environmental impact as a consequence.
I'm boring everyone with this, not because I'm anti-wind farms - I
don't think noise or bird collisions are a show-stopper for wind farms
generally, although they may be at particular sites - I feel strongly we
as a society should be making informed decision with the environmental
impacts of choices presented as accurately as possible using the best
scientific data we have.
Andrew
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