The sounds of high winds

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esidents) noticed the discrepancy between predicted and real noise exposure? There are probably several reasons. One of them is that for a long time wind turbines were not big enough for the effects of atmospheric stability to be clearly noticeable. Since wind turbines have grown taller the effect manifests itself more clearly. Secondly, as the more distant locations have become scarce, more and more turbines are being built closer to where people live, so more people now experience the sound of wind turbines. Thirdly, atmospheric stability over flat land is easier to understand and quantify than in a mountainous or coastal area where the atmosphere is more complex so the effect on wind turbines may be less easily recognizable. Wind turbines as such have not become that much noisier, despite their increase in height and blade span (the sound power depends more on speed than on physical dimensions of the towers). Earlier machines could be quite noisy due to whining or severe thumping, and modern designs are certainly better. The point is they now reach into less familiar parts of the atmosphere. Finally, an important reason to not recognize the unexpected high sound levels certainly is the fact that it impedes commercial interests and national policy. The positive ring of the term 'sustainability' helps investors in wind energy and local authorities (applying national policy) to counterbalance objections concerning possible disadvantages of new projects. As these objections are sometimes strong enough to torpedo projects, investors and authorities don't welcome more negative news. Though the population widely supports sustainable energy, reactions are less positive when a new project adversely affects their lives. This 'contradictory behaviour' is in fact quite understandable: when a new project is planned in an area, residents for the first time have to balance the positive social consequences to the negative local impact: visual impact, flickering shadows, noise and possibly ice throw from turbine blades. The first reaction of wind energy proponents, represented by the Windkoepel (‘Wind dome’), to our research results was to pay a consultant 3
to comment on our report [Van den Berg et al 2002]. This consultant boasted of having advised a large number of wind farm projects, so he clearly understood the position of the wind power industry. In the resulting ‘second opinion’ [Kerkers 2003] no material critique was presented, only procedural arguments were used to declare our results inaccurate and thus irrelevant. The Windkoepel issued a press statement concluding that we had made a lot of fuss, but had not contributed any new insights. 1 They could get back to business. I.2 Digging deeper I too went back to my business, which can be summarized as helping citizen groups to defend their position by objective arguments using known principles of physics. In 2004 an article about my research was published in a scientific journal [Van den Berg 2004a] lending my results the respectability of peer review and triggering an international e-mail influx from interested consultants as well as worried residents, as our first report had done earlier on a national scale. What still puzzled me at that time was how a single turbine could start thumping at night. I thought I understood how the modest blade swish of a single turbine could evolve into louder thumping: the small sound variations due to blade swish from several turbines could add up to louder pulses. But with a single turbine there is nothing to add! Apart from this, in news media in the UK there were complaints that low frequency wind turbine noise had been underestimated and had been making people sick. 2 Some thoughts about this were presented at a conference in Maastricht [Van den Berg 2004b]. I agreed with delegate Jørgen Jakobsen, who presented a paper on low frequency wind turbine noise [Jakobsen 2004], 1 Press statement February 2, 2003 “Onlangs is opschudding ontstaan …..,” (“Recently an upheaval was caused…”), De Windkoepel, Arnhem 2 Catherine Milner: “Wind farms make people sick who live up to a mile away”, online Telegraph, filed January 25, 2004 ( http://news.telegraph.co.uk/news/ main.jhtml?xml=/ news/2004/01/25/ nwind25.xml, consulted December 10, 2005) 4
Page 1 and 2: The sounds of high winds the effect
Page 3 and 4: Promotores: prof dr ir H. Duifhuis
Page 5 and 6: Contents I WIND POWER, SOCIETY, THI
Page 7 and 8: VII THINKING OF SOLUTIONS: measures
Page 10 and 11: I WIND POWER, SOCIETY, THIS BOOK: a
Page 14 and 15: that even though wind turbines did
Page 16 and 17: legitimate problems [Wolsink 1990].
Page 18 and 19: Thinking that this could perhaps be
Page 20 and 21: gas must keep flowing” . 1 I do n
Page 22 and 23: sound and the noise that wind produ
Page 24: combined with the corresponding sec
Page 27 and 28: calculated one and whether sound ch
Page 29 and 30: annoying turbine sound at distances
Page 31 and 32: was 57.9 dB, with a maximum deviati
Page 33 and 34: not correct at night, although the
Page 36 and 37: III BASIC FACTS: wind power and the
Page 38 and 39: 0.1. In a stable atmosphere vertica
Page 40 and 41: With regard to wind power some atte
Page 42 and 43: III.4 Main sources of wind turbine
Page 44 and 45: High frequency: trailing edge (TE)
Page 46: So, what's the sound like...? (....
Page 49 and 50: Figure IV.2: turbines (dots W1….W
Page 51 and 52: L Wj , assumed identical for all k
Page 53 and 54: IV.1. As explained above, the wind
Page 55 and 56: sound level in the measurement inte
Page 57 and 58: Leq,5 min in dB(A) 50 45 40 35 30 A
Page 59 and 60: The same lines as in figure IV.5B,
Page 61 and 62: at hub height, not to a variation i
Page 63 and 64:
IV.10.1 Measured and calculated imm
Page 65 and 66:
wind farm to the measurement locati
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spherical divergence, that is: prop
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Thus, the logarithmic wind profile,
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There are now three factors influen
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direction may change significantly.
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V.2 Measurement results V.2.1 Locat
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P48 microphone. The sound was then
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1/3 octave band Lp in dB 1/3 octave
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1 1 0 1 0 0 1 0 0 0 1 0 0 0 0 A B 8
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same magnitude as close to the turb
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In figure V.5 the equivalent 1/3 oc
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Also plotted in figure V.7 is the v
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V.3 Perception of wind turbine soun
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kHz. For wind turbines we found tha
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V.4 Conclusion Atmospheric stabilit
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VI STRONG WINDS BLOW UPON TALL TURB
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(hub height) wind velocity is 4 m/s
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For the hourly progress of wind vel
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In figure VI.5 the frequency distri
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when V 80 was over 4 m/s. Such a de
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dunes on the North Sea coast, Vliss
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when based on extrapolated wind vel
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The differences between actual and
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hours. This corresponds to an avara
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VII THINKING OF SOLUTIONS: measures
Page 116 and 117:
stability. The turbine thus operate
Page 118 and 119:
sound level was measured close to a
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This type of control can also be ac
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consecutive periods of 15 minutes i
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increase of blade pitch with tilt (
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elatively quiet areas as it control
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VIII RUMBLING WIND: wind induced so
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Finally, in this overview, Boersma
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The friction created by wind shear
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the eddy relative to the screen sur
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(L at,1/3 ~ -26.7·logf), but press
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VIII.3 Comparison with experimental
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the small size of the unscreened mi
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A B reduced pressure level Lred (dB
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microphone, in a 9 cm foam cylinder
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plotted is the calculated screening
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VIII.5 Applications As microphone w
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IX GENERAL CONCLUSIONS The research
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modulation frequencies close to 4 H
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Results from various onshore, relat
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limits, but nighttime immission lev
Page 158 and 159:
X EPILOGUE This is the end of my to
Page 160 and 161:
“….. about 80 per cent of the p
Page 162 and 163:
ACKNOWLEDGMENTS I want to express m
Page 164 and 165:
SUMMARY Ch. III Ch. II Ch. I This s
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and as a result layers of air are l
Page 168 and 169:
500 kW. However, based on the real,
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well known for an unobstructed wind
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SAMENVATTING Bobby vraagt: 'Hoort u
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Vaak wordt aangenomen dat er een va
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gebleken dat de menselijke gevoelig
Page 178 and 179:
Bij een windpark kunnen de fluctuat
Page 180 and 181:
REFERENCES Archer C.L. and Jacobson
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Kerkers A.J. (1999): “Windpark Rh
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Petersen E.L., Mortensen N.G., Land
Page 186 and 187:
Van Ulden, A.P. and Wieringa J. (19
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APPENDICES 179
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dB(G): unit of level after G-weight
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u f : rms longitudinal component of
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downwind turbine with an 80 m tubul
Page 196 and 197:
and total trailing edge immission s
Page 198 and 199:
So for a modern turbine at high spe
Page 200 and 201:
45 wind E (100 gr) 20 Leq (A) Leq,5
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Wiens brood men eet, ….. Een plei
Page 204 and 205:
Vochtproblemen in woningen Venuslaa
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Geluidsbelasting van een windturbin
Page 208 and 209:
Metingen van laagfrequent geluid in
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The sounds of high winds

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