Presentations

Abstract

Increasing offshore wind turbine hub heights poses some challenges for continued use of Floating LiDAR Systems (FLS). Hub heights and tip heights of around 150 m and 250 m respectively are already a reality [1,2], and although FLS units can measure wind speeds at these heights, LiDAR and FLS unit performance assurance is usually only performed by comparison with reference masts up to 100 m height. The Offshore Wind Accelerator (OWA) project "Floating LiDARs for Ever Increasing Hub Heights" addressed these challenges. The key findings of the project will be described, including collecting information on known limitations of FLS system capability at increasing heights, developing a methodology and worked example for a two stage (tall onshore mast > LiDAR; LiDAR > FLS) FLS calibration and uncertainty assessment, and an error modelling exercise. This exercise, for the first time, combined a variable representation of aerosol distribution with height with existing models [3,4] for LiDAR error which embody shear, and LiDAR weight function. This novel formulation will be provided and results described, including examples of modelling input profiles of wind shear, LiDAR weight function and aerosol distribution, and wind speed measurement error using this novel model for two LiDAR types (continuous wave and pulsed). Amongst the significant conclusions are that one of the most common LiDAR types shows appreciable error at increasing heights that is significantly impacted by aerosol concentration, and that much more needs to be known about aerosol concentration profiles. The error modelling performed has made it clear that there is significant uncertainty on the effectiveness of continuous wave lidars at higher heights that are of relevance today. [1]https://www.ge.com/renewableenergy/wind-energy/offshore-wind/haliade-x-offshore-turbine [https://www.ge.com/renewableenergy/wind-energy/offshore-wind/haliade-x-offshore-turbine] [2]https://www.vestas.com/en/products/offshore/V236-15MW [https://www.vestas.com/en/products/offshore/V236-15MW] [3] Mikkelsen, T. (2009). "On mean wind and turbulence profile measurements from ground-based wind lidars: limitations in time and space resolution with continuous wave and pulsed lidar systems". In European Wind Energy Conference and Exhibition 2009, EWEC 2009 (Vol. 6, pp. 4123-4132). [4] Rozenn Wagner, Torben Mikkelsen, Michael Courtney. "Investigation of turbulence measurements with a continuous wave, conically scanning LiDAR". Risø-R-1682(EN). March 2009.