The inaudible noise of wind turbines

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Juniper Cobb
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December 02, 2005, Tahiti Federal Institute for Geosciences and

1 The inaudible noise of wind turbines Lars Ceranna, Gernot Hartmann, and Manfred Henger Presented at the Infrasound Workshop November 28 December 02, 2005, Tahiti Federal Institute for Geosciences and Natural Resources (BGR), Section B3.11 Stilleweg 2, Hannover, Germany page 01

Regional distribution of wind turbines in Germany

1882 MW 3782 WT 3563 MW 454 WT 320 MW 205 WT 182 MW

Rheinland-Pfalz Sachsen Thürigen Brandenburg

2 Regional distribution of wind turbines in Germany 1955 WT 1589 MW 596 WT 542 MW 34 WT 28 MW 2605 WT 1882 MW 3782 WT 3563 MW 454 WT 320 MW 205 WT 182 MW 973 WT 818 MW 1197 WT 1404 MW 329 WT 322 MW 206 WT 162 MW 1325 WT 1442 MW 622 WT 575 MW Baden-Würtemberg Bayern Saarland Hessen Rheinland-Pfalz Sachsen Thürigen Brandenburg Mecklenburg-Vorpommern Niedersachen Nordrhein-Westfalen Sachsen-Anhalt Schleswig-Holstein # wind turbines / 100 km 2 source: Ender, page 02

3 Content The Influence of Wind turbines on Infrasound recordings: IGADE The German Infrasound Station IGADE Data Examples, routine Analysis Noise Measurements at a single Wind Turbine Theoretical Estimation of the Sound Pressure Level Comparison with Measurements Scenarios, large Wind Farms, 5 MW Wind Turbines Conclusions page 03

4 The German infrasound station IGADE page 04

5 Milestones of the establishment of IGADE Site Inspection 30 April 2003 Installation of IGAH1 September / October 2003 IGADE Extension to 4 element array September January km, 220 Growing number of Wind turbines close to the array April / May 2005 page 05

6 The spectral fingerprint of wind turbines: IGAH1 page 06

7 The spectral fingerprint of wind turbines: IGADE 07-May :10 12:30 (UTC) 14-Sep :40 20:00 (UTC) 3 blades, f=1 Hz, 20 rpm 3 blades, f=1.35 Hz, 27 rpm page 07

8 The fingerprint of wind turbines in the routine analysis PMCC analysis February November 2005, [ ] Hz page 08

9 Content The Influence of Wind turbines on Infrasound recordings: IGADE The German Infrasound Station IGADE Data Examples, routine Analysis Noise Measurements at a single Wind Turbine Theoretical Estimation of the Sound Pressure Level Comparison with Measurements Scenarios, large Wind Farms, 5 MW Wind Turbines Conclusions page 09

10 A single wind turbine in northern Germany VESTAS V kw h=65 m, r=24 m rpm=[20 26] page 10

11 Configuration of the Hufe field experiment : 07-Jul Jul-2004, HUF01, HUF02, HUF03, HUF : 19-Jul Jul-2004, HUF01, HUF05, HUF06, HUF07 8 : 29-Jul Aug-2004, HUF08, HUF09, HUF10, HUF11 page 11

12 Measuring along the track and in the wood Huf07 Huf06 Huf05 Huf04 Huf03 Huf08-Huf11 Huf02 Huf01 page 12

13 Station Huf01 page 13

14 Measured signals, Huf03, d=200 m frequency domain page 14

15 Measured signals, Huf03, d=200 m time domain, 0.5 Hz high pass filtered page 14

16 Measured signals, Huf03, d=200 m frequency domain page 14

17 Time-frequency analysis, Huf03, d=200 m page 15

18 Content The Influence of Wind turbines on Infrasound recordings: IGADE The German Infrasound Station IGADE Data Examples, routine Analysis Noise Measurements at a single Wind Turbine Theoretical Estimation of the Sound Pressure Level Comparison with Measurements Scenarios, large Wind Farms, 5 MW Wind Turbines Conclusions page 16

19 Theoretical SPL-estimation Hubbard & Shepherd (1991, JASA) k n 2 im ( / 2 ) T nb m Q P n e J x ( k nr e sin ) a m cos a m 4 d m k nr e P n RMS sound pressure of the n-th harmonic n sound pressure harmonic number k n nb /c B number of blades rotor speed c 0 sound speed R e effective blade radius d distance from the rotor m blade loading harmonic index (m=,-1,0,1,..) J x Bessel function of first kind and of order x=nb-m azimuth to listener altitude angle to listener a Q m complex Fourier coefficients of thrust forces a T m complex Fourier coefficients of torque forces page 17

20 Comparison between measured and estimated SPL SPL as a function of distance SPL as a function of azimuth account for surface effects (e.g. reflections) by adding 3 db to the estimated curves page 18

21 Estimating the SPL generated by wind turbines Blade diameter page 19 Tower height Power Blade diameter Tower height Energy production per year

22 Estimating the SPL generated by (a) large wind turbine(s) page 20

23 Estimating the SPL generated by (a) large wind turbine(s) page 20

24 Estimating the SPL generated by Wind Turbines/Farms at ~2 Hz single wind turbine 11-element wind farm noise level page 21

25 Content The Influence of Wind turbines on Infrasound recordings: IGADE The German Infrasound Station IGADE Data Examples, routine Analysis Noise Measurements at a single Wind Turbine Theoretical Estimation of the Sound Pressure Level Comparison with Measurements Scenarios, large Wind Farms, 5 MW Wind Turbines Conclusions page 22

26 Conclusions number of wind turbines and their size is constantly growing wind turbines and wind farms generate strong infrasonic noise which is characterized by their blade passing harmonics (monochromatic signals) generated noise of wind turbines can theoretically be estimated geometrical spreading ~ R -1 SPL ~ rpm 4 recordings from field measurements near a single wind turbine show that the theoretical model is also valid for frequencies below a few Hz minimum distance between an infrasound array and a wind farm can be estimated to avoid reduction of the array s detection capability (e.g. 600MW wind turbine: d>15 km, 11-element wind farm: d>30 km) page 23

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