Presentations

Abstract

The evaluation of extreme wind velocities is critical for assessing the suitability of wind turbines in repowering projects. In many cases, the increase in hub heights and rotor diameters leads to higher sensitivity to extreme-wind loading compared to the replaced turbines, making the accurate determination of IEC extreme-wind parameters a key design driver. In common engineering practice, IEC extreme-wind parameters are computed at the measurement location (reference anemometer) and then extrapolated to the geographic position of the repowered layout by scaling them proportionally to the expected mean-wind speed differences—assuming that mean-wind speed-up factors are representative of extreme-wind speed-up factors. However, the IEC standard (IEC 61400-15-1) specifies that extrapolation should be based on “appropriate speed-up factors that are representative of extreme wind speeds”. In repowering or revamping scenarios, the availability of long-term wind measures from the nacelle anemometers on the existing turbines—typically covering a sufficiently large sample of independent storm events—provides an opportunity to derive a spatial mapping of extreme-wind behavior across the entire area of interest. This enables the estimation of extreme-wind speed-up factors directly from operational data, rather than relying on mean-wind proxies. We tested this approach at sites where SCADA and met-mast measurements were available concurrently. First, we assessed the accuracy of nacelle anemometry relative to mast measurements, specifically in the high-wind regime. We then derived extreme-wind speed-up factors by analysing multiple turbine pairs by testing several interpolation approaches, including directional and high velocities filtering, orthogonal TLS or non-linear interpolation, and speed-up factor for grouped storm events. Results from case studies are presented, including a comparison against the conventional assumption of using mean-wind speed-up factors. The findings highlight the implications for Vref and Vgust determination in repowering and provide insights into IEC-compliant horizontal extrapolation of extreme winds.