6 th February 2013, EWEA2013, Vienna

1. FATIGUE DAMAGE EQUIVALENT TURBULENCE: A New Method To Verify Wind Turbine Structural Integrity in Complex Terrain Jointly presented by: Virginia Mangone (Edison) Sannosuke Tanigaki (Wind Energy Corporation) Andrea Vignaroli (Windsim) Matthew Homola (Nordkraft Vind) 6th February 2013, EWEA2013, Vienna

2. The work is jointly proposed by four companies

3. Contents • Company Overview • Motivation • Site Suitability: Current Methodology • Site Suitability: New Methodology • Open Points • Case studies • Concluding remarks

4. Edison Edison is one of Italy’s leading player in the energy field. Its origins date back to 1883, when Edison opened Italy’s first electric energy facility in Milan. Today it is part of EDF group (Eletricité de France) 7.7GW of installed capacity 47hydroelectric power plants 22thermoelectric power plants 32wind farms - 49.8 billion m3 of hydrocarbons reserves 96mineral leases (gas and oil) 3gas storage centers 9 photovoltaic systems 1LNG terminal 1 biomass system 2new pipelines under development 474MWin operation

5. Motivation The IEC 61400-1 3rd Edition is under revision to release Edition 4th Complex Terrains need a more suitable Site Assessment Procedure Complex terrain sites are considered only marginally in the standard likely due to the fact that, when the work started, in the end of the 1980s, there was no need to develop projects in those sites. Currently an increasing number of on-shore wind farms are planned in complex sites, including hills and mountains, and therefore it is necessary to go more deeply in the assessment of those sites.

6. Site Suitability: Current Approach IEC 61400-1 3rd Ed - ch11.9

7. Assessment by reference to wind data The evaluation of the fatigue load counts two separate analyses: • One for the wind speed distribution • One for the turbulence standard deviation • Estimate of Site Wind Speed Distribution • Estimate of 90% quantile of Site Turbulence • (s90q)

8. Points to be highlighted Relevant for Complex Sites • No Sectorwise analysis allowed • Site Complexity taken into account through a correction factor (cCT) to increase the turbulence structure • Other effects (i.e. loadings from up/down flows) not considered • Analysis of the turbulence standard deviation based on the 90% quantile • Log-normal distribution of the turbulence standard deviation assumed Relevant for All Sites • Assessment split in Two Separate Evaluations: one for wind speed distribution and one for turbulence levels • Site specific air density not included • No uncertainty taken into account

9. Site Suitability: NEW Approach Fatigue Damage Equivalent Turbulence

10. BACKGROUND Fatigue Damage Equivalent Turbulence is a constant value of the turbulence which gives the same degree of fatigue damage as a given fluctuating turbulence intensitiy gives.

11. Fatigue Damage Equivalent Turbulence One single evaluation: The basic formula of the Equivalent Turbulence shall be adjusted in order to take into account that the site specific conditions are different from the design ones. If any of the site specific conditions deviates from the design conditions and this deviation produces higher loads, then it shall be consider as a penalty to add in the evaluation of equivalent turbulence: As we are considering complex terrain it must not be forgotten that on those sites the turbulence variance is higher and depends strongly on the wind direction. Therefore the evaluation shall be carried out direction-wise.

12. Correction Factors • Independent from Direction: • Adjustment for Air Density (cad) • Adjustment for Wind Speed Frequency Distribution (cpdf) • it combines in a single analysisbothwindspeed and turbulence • Quality of measurement & Accuracy of flow model (cqm) • it takes into account Uncertainty • Dependent on Direction: • Penalty for Wind shear exponent (cse) /Flow inclination (cfi) Turbulence structure (cct) • effectsthat the terraincomplexityproduces on the wind flow shape • Added Turbulence: Wake from other turbine(s) (swake)

13. Test Cases 1/2 16 different sites on complex terrain tested m-Wöhler exponent from 5 to 12 considered the 90% quantile is not representative of the site specific condition design turbulence distribution (log-normal) (m/s) measured standard deviation (m/s) direction (°) 90% quantile of measured standard deviation 15m/s 15m/s SITE 12 SITE8

14. Test Cases 2/2 SITE 12 • n.WTGs = 4 • WTG Class= IA • n. MAST = 1 • measurement campaign = 4 years • Directional speed up determined by a CFD analysis • worst m-scenario m=12 • Cct=1.15 (all sectors) SITE 8 • n.WTGs = 34 • WTG Class= IIA • n. MAST = 1 • measurement campaign =1.5 years • Directional speed up determined by a CFD analysis • worst m-scenario m=12 • Cct=1.15 (all sectors) more restrictive less restrictive

15. Open Points • Effects that produce Higher Loads: • Correlation between wind turbine loading and excess wind shear exponent/ flow inclination/ turbulence structure over design conditions is not validated • Upflow/Downflow: • the assumption that flow inclination in excess of design value (8degree) could be compensated by the penalty on turbulence is not validated • Outliers: • all measured data of standard deviation are taken into account, which means that a few outliers can influence the results. How the extremes can be evaluated and if they have to be considered for a fatigue analysis is still not established. • Taking into the account all the data is a conservative choice.

16. Conclusion and future work • Current Standard • Fatigue analysis is split in two different evaluations. This criteria leads to too conservative results. • Turbines are designed with the design conditionthattheywillexperienceonly the defined s1 turbulencelevel. In the site assessment, this s1 valueiscompared with the 90% quantile of the site estimates, on the assumptionthatthatvalue of constantturbulence can represent the real situation. However, the 90% quantile isnotalwaysrepresentative of the actual site condition. • New Approach • Defines a single analysis to assess the fatigueload • Based on site statisticsinstead of twotheoreticaldistributions • Itisnotlessrestrictive or more restrictive, itis just more representative of the site conditions • Future Work • FurtherInvestigations on the open points • Full loadcalculations on the test cases to compare the results

17. Thank you for your attention send further questions to: virginia.mangone@edison.it

18. BACK UP

19. Equivalent Turbulence VS 90%quantile of turbulence Flat Terrain. Constant = 1.4m/s IEC assumptions on turbulence: • log-normaldistribution • expected value of σ1 given by the formula: I*(0.75Vhub+3.8) • varianceof σ1 given by the formula: (1.4*I)2 where: I is a site specific non-dimensional coefficient and measures the turbulence intensity 1.4m/s is a constant value andmeasures the turbulence variability. It is assumed as independent from the site and from Vhub. Sites on complex terrain are affected by strong variations in turbulence and the constant value must be increased: i.e. constant=2.0m/s At those sites where “high” variations in turbulence occur, the 90% approach is unable to take fully care of the non-linearity of fatigue damage, especially for high values of m at low wind speeds. Complex Terrain. Constant = 2.0m/s

20. Correction Factors Correction Factors independent from Direction • air density (cad) • windspeeddistribution (cpdf) • quality of measurements (cqm) Correction Factors dependent on Direction • Turbulencestructure(cCT) • Wind Shear /Upflow(cws/cfi) stillpending, more validation work needed

21. Quality of measurements (cqm)

22. Appendix A 1/2

23. Appendix A 2/2