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Power curve measurement of a floating offshore wind turbine with a nacelle-based lidar

Understanding the power performance of floating offshore wind turbines is essential for the economics of floating wind, which requires reliable wind speed measurements. This work investigates the use of nacelle-based lidar technology for power curve measurement of a floating offshore wind turbine. In a five-month long measurement campaign, a nacelle-based lidar was installed on top of a 2MW floating offshore wind turbine. It was used to reconstruct the wind field including a carrier-to-noise ratio threshold filter, an availability filter and a hard target filter for the one hertz line of sight measurements. The quality of lidar wind speed estimations were compared to nacelle-based sonic anemometer measurements in terms of their linear correlation and root mean squared error of ten minute averages. The correlation of rotor averaged wind speed estimation of lidar and sonic wind speed measurements showed a 0.97 coefficient of determination. Variability of correlation is investigated in terms of nacelle excitations to identify the uncertainty related to the use of nacelle lidars for floating wind applications. Findings show that the quality of correlation decreased with higher nacelle excitations, which are caused by both wind and waves. Consequently, wind speed estimations were used for power curve measurement to investigate the qualification of using a nacelle-based lidar for such an application. Although lidar measurements showed higher scatter, they provided a reasonable wind speed estimate and a similar power curve to sonic measurements.