Turbine Performance Analysis in Wake and Wake-Free Conditions Using Nacelle Mounted Lidar at a Wind Farm in Sweden

Abstract: The need for optimizing wind farms’ production and maximizing the profitability of projects necessitates power performance analysis. Nowadays, the use of remote sensing devices for this purpose becomes more and more popular due to many advantages this technology has over traditional met masts. The main objective of this study is to assess the performance of a wind turbine in wake and wake-free conditions through measurements performed with a nacelle mounted lidar. The analysis is based on the data obtained during a Power Curve Measurement campaign performed on an onshore wind farm in Sweden. The power production and power curves are compared for a range of wind direction sectors in order to assess turbine performance in different wake conditions. Surprisingly low power output is observed in wake-free sectors [180°, 240°) and [240°, 300°), whereas production in wake wind directions [300°, 360°) is relatively high. The main reason for this is the wind speed distribution, however the terrain complexity and roughness should also be considered as possible factors. Generally, the wind speed distribution seems to have more influence on the results than the wake conditions. Moreover, the correlation between the met mast and lidar datasets is investigated in the study. The results indicate a good agreement between the wind speed measurement from the two devices, however, a poor correlation is found for turbulence intensity and wind shear exponent. Additionally, the influence of turbulence intensity and wind shear on the power production was analyzed. Generally, the results were in line with the reviewed literature: at low and moderate wind speeds the power production was higher for higher TI values, while the opposite was observed for higher wind speeds, where the higher TI resulted in lower production. As for the wind shear, a pattern is observed for moderate wind speeds, where the higher wind shear resulted in lower power production.