1. Fabrizio Magni magni.fabrizio@gmail.com Mattia Boccolini mattia.boccolini@garradhassan.com Christof Stork christof.stork@garradhassan.com Study of extreme wind speed for italian wind farm sites EWEC 2007, Milan, 8 May 2007 - Boccolini, Magni, Stork

2. Study of extreme wind speed for italian wind farm sites To assess the validity of three different codes to estimate extreme wind speed; Targets: To identify factors that improve extreme wind speed predictions; To compare directional roughness length and extreme wind speed values; To compare the whole data set and the data subset analysis results Slide : 02 EWEC 2007, Milan, 8 May 2007 - Boccolini, Magni, Stork -

3. Study of extreme wind speed for italian wind farm sites Analysis of anemometer data; Wind shear evaluation: Roughness length calculation; Time average calculation; Slide : 03 EWEC 2007, Milan, 8 May 2007 - Boccolini, Magni, Stork -

4. Study of extreme wind speed for italian wind farm sites Wind shear evaluation: Difference between global and sector results Some errors in extreme wind speed evaluation Slide : 04 EWEC 2007, Milan, 8 May 2007 - Boccolini, Magni, Stork -

5. Study of extreme wind speed for italian wind farm sites Standard Gumbel (SG); Extreme wind speeds evaluation: Modified Gumbel (MG); Improved Independent Storm (IMIS); Gumbel-Bergstr ö m (GB); Codes Methods Eurocode 1 (EC1) Testo Unitario (TU) Old Italian Code (DM’96) Slide : 05 EWEC 2007, Milan, 8 May 2007 - Boccolini, Magni, Stork - [m] Too short observation period

6. Study of extreme wind speed for italian wind farm sites Aspects involved in result accuracy: Slide : 06 EWEC 2007, Milan, 8 May 2007 - Boccolini, Magni, Stork - ; Amplitude of data sets; Accuracy of Roughness length evaluation Extreme wind speed evaluation techniques; Number, height and precision of anemometers;

7. Study of extreme wind speed for italian wind farm sites Slide : 07 EWEC 2007, Milan, 8 May 2007 - Boccolini, Magni, Stork - Extreme wind speed evaluation techniques: Percentage difference between code predictions and data results [Err %]

8. Study of extreme wind speed for italian wind farm sites Amplitude of data sets: Slide : 08 EWEC 2007, Milan, 8 May 2007 - Boccolini, Magni, Stork - Involved data SG, MG : 1 value/year IMIS : ≈ 100 values/year GB : All data recorded Less accuracy Errors sensitivity Good accuracy Extreme wind speed in Campania using data subset

9. Study of extreme wind speed for italian wind farm sites Number, height and precision of anemometers: Few anemometers, too close to each other and to the ground Slide : 09 EWEC 2007, Milan, 8 May 2007 - Boccolini, Magni, Stork - Large errors in wind shear evaluation z V Campania Data set: Roughness lenght evaluation

10. Study of extreme wind speed for italian wind farm sites Accuracy of Roughness length evaluation: Slide : 10 EWEC 2007, Milan, 8 May 2007 - Boccolini, Magni, Stork - Accurate evaluation of extreme wind speed

11. Study of extreme wind speed for italian wind farm sites Wind speed amplification coefficient: Slide : 11 EWEC 2007, Milan, 8 May 2007 - Boccolini, Magni, Stork - Exact roughness length Measured roughness length It is important: to measure roughness length carefully to choose accurate time averaging value

12. Study of extreme wind speed for italian wind farm sites Slide : 03Slide : 12 EWEC 2007, Milan, 8 May 2007 - Boccolini, Magni, Stork - Return Period dependence: T R dependence formula (EC1, TU, DM’96); T R dependence formula (SG, MG, IMIS, GB);  TRTR ACCURACY OF THE EXTRAPOLATION

13. Study of extreme wind speed for italian wind farm sites Slide : 03Slide : 13 EWEC 2007, Milan, 8 May 2007 - Boccolini, Magni, Stork - Concluding remarks: More extensive study in terms of number and spread of masts as well as longer observation periods should be performed to draw robust conclusions