1. The Windmills Project Team: Irene Fiori – U. of Pisa Lara Giordano – INFN Napoli Emanuele Marchetti – U. of Firenze, dept. of earth sciences Federico Paoletti – INFN Pisa Gillian Mayer – AEI Hannover G Mayer – ILIAS WG1 meeting – Perugia – September 19th, 2005

2. 2 Motivation: Measurements of seismic effects of a wind power plant on GEO 600 Prediction for the planned wind power plant at VIRGO In this talk: 1.Determination of the characteristic frequencies 2.GEO microseism 3.Windspeed and seismic wave field analysis

3. 3 Specifications: heightdiameter Nordex N90100 m90 m Nordex S7785 m77 m Enron Wind 1.5s85 m70.5 m Enron Wind 1.585 m65 m All power plants have in common: 3 blades canonical steel tower concrete foundations They differ in height and diameter of the rotor:

4. 4 Map of the site: RIF has been taken directly on the foundations of T4 N GEO 600

5. 5 1. Characteristic frequencies Timeseries at an N90: N90 was off clear oscillation at 1.9 Hz another persisting frequency at 0.29 Hz

6. 6 1. Characteristic frequencies 1. structural resonance 2. structural resonance Nordex N900.29 Hz1.9 Hz Nordex S770.37 Hz2.5 Hz Enron Wind 1.5s0.29 Hz2.2 Hz Enron Wind 1.50.29 Hz2.3 Hz Department of steelworks determined shapes of structural resonances* LowHigh frequency *) P. Schaumann, M. Seidel: Einschwingverhalten von Windenergieanlagen – Berechnungen und Messungen, Hannover, 2000

7. 7 1. Characteristic frequencies Spectra of wind power plants: Nordex S77 running not only resonance peaks, but also peaks which are related to the blade pass frequency (period T  5 s) Enron Wind 1.5 off two main peaks, corresponding to two resonance frequencies

8. 8 1. Characteristic frequencies 0.37 Hz1. struct. resonance approx. 2.5 Hz2. struct. resonance 0.17 Hzblade pass frequency 0.51 Hz3rd harmonic 1.0 Hz6th harmonic 1.5 Hz9th harmonic approx. 2.0 Hz12th harmonic approx. 2.5 Hz15th harmonic frequencycorrespondence A closer look at the spectrum shows which frequencies appear: higher harmonics seem to be present, but are difficult to distinguish peak around 18 Hz is very likely the generator

9. 9 2. GEO microseism Large coherence of STS-2 at low frequencies: Microseism signals are coherent in frequency range of windmills 1st structural res. peak (  0.3 Hz) produced by the windmills? different sources like the North Sea?

10. 10 2. GEO microseism TCC - TFE: + 0.7 s signal reaches TFE first TCC - TFN: + 0.2 s signal reaches TFN first TFE - TFN: - 0.5 s signal reaches TFE first Correlograms for microseism:

11. 11 2. GEO microseism Result: velocity: 650 m/s (depends on day) angle: 43° NE Problem: There‘s no obvious source where these waves could come from expected sources: North Sea/Baltic Sea, Hannover Possible explanation: The measured signal could be a superposition of several (at least two) signals of different sources

12. 12 Map of the site: GEO 600 N

13. 13 3. Field measurements Aquisition times: After the second day we left the stations outside even during nighttime. For station A02 and A03 we lack GPS timing.

14. 14 3. Field measurements Windspeed analysis: seismometer output (RIF) scales with windspeed allows rough correction of data taken at different wind conditions medium and high wind spectra look the same low wind: 0.3 Hz peak persists

15. 15 3. Field measurements Detailed view of RMS in frequency bands: Every frequency is affected by wind except from the highest band another hint that the peak at 18 Hz has an internal source lowest frequency band (red) shows the effect of the adjustment of the rotor at least a windspeed of 1 m/s is needed to make the wind power plant run

16. 16 3. Field measurements Coherence: extremly bad coherence for all stations except from D1 (25 m from RIF) no chance to make correlograms possible explanation: directly on the basement (RIF) large amplification of the signal once the signal reached the ground heavily damped, peaks get broad, coherence is lost. also interference from other windmills D1 - RIF, all three componentsother stations, only vertical component

17. 17 3. Field measurements High resolution view of low frequency coherence between D1 and central STS-2: A dip at 0.29 Hz can clearly be seen. The correlogram shows, that the signal first reaches the STS-2, than D1. low frequency part is microseism as discussed above Low frequencies

18. 18 3. Field measurements Higher frequencies new measurement because of bad coherence: E1 near T3, E2 200 m east of E1 much better coherence now, even at a distance of 200 m some high frequency peaks survive

19. 19 3. Field measurements Comparison: medium wind and no wind conditions, vertical component night-time: low antropic noise light green/blue: spectra at no wind, wind power plants weren‘t running dark green/blue: spectra with medium wind, very likely that all wind power plants were running no significant difference in A1 spectra (near GEO)

20. 20 Conclusions: all windmills have got two structural resonances, persist also when the windmills are not running when running, one can see the blade pass frequency, the 3rd harmonic and higher harmonics of the 3rd low frequency noise produced by the windmills is quickly damped and dominated by the local microseism although the last picture shows that it‘s very unlikely that higher frequencies reach GEO, this cannot yet be excluded. However, if there is an effect it is certainly small.