Posters

Abstract

Nacelle mounted lidars (NML) are meanwhile an established wind measuring technology in the wind energy industry, providing a relatively straightforward possibility to measure the approaching wind in front of a wind turbine. The use of these devices may range from replacing traditional met masts for power performance testing (PPT) to lidar-assisted control. Recently a new IEC norm has been published to ensure standardized measurements using these devices (IEC 61400-50-3:2022). However, varying technologies can be found from different providers on the market motivating the question which type of technology is best for which application. Especially the difference between continuous wave (cw) lidar and pulsed lidar is of interest here. To identify advantages and limitations, we compare two industry-trusted NML representatives for the two technologies: the ZX TM as cw and the Windcube® Nacelle (WCN) as pulsed lidar. Both technologies measure the radial wind speed and apply a wind field reconstruction (WFR) algorithm to retrieve the wind parameters of interest which are (here): the horizontal wind speed and direction as well as the power law shear exponent as a parameter for vertical wind shear. In order to evaluate these technologies and devices from a practical perspective, we installed in total four NML devices on the heavily instrumented Fraunhofer IWES research wind turbine AD8-180 on the Testfeld Bremerhaven with multiple IEC conform reference measurements nearby (mast and vertical profiler). We compared both types of measurement technologies and reconstructed parameters from the devices against each other and against the reference measurements. All measurements were performed during a three-month period starting in December 2021. The installed setup of in total four NML installed side by side and accompanied by extensive reference measurements on the Testfeld Bremerhaven represents a unique setup with extensive possibilities for direct comparisons of the measurement principles. Studies on the evaluation of NML installed on turbines of this size (rotor diameter of 180 m) are rare and the present study stretches the spatial limits of the devices e.g., in terms of maximal ranges. We evaluated not only line-of-sight measurements but also various reconstructed wind field parameters, such as the horizontal wind speed or direction, which can indicate an underperformance or potential yaw misalignment of the wind turbine. Also, the turbine induction and vertical wind shear are evaluated. Depending on the use case and reconstructed parameters, we find significant differences between the two technologies and particular advantages. Compared to pulsed lidar, the cw lidar provides more detailed wind field information, however, it is significantly limited in the number of ranges to be measured. With this study, we provide a comprehensive comparison of the two NML measurement principles, cw and pulsed, based on a unique setup with comprehensive reference measurements at the Testfeld Bremerhaven. The study aims to evaluate the reconstructed wind field parameters and highlights the advantages of each measurement technology. Consequently, the suitability depends on the application and settings, which are taken into consideration within this study.