Abstract

Long-range Doppler wind lidars are applied more and more for high resolution areal measurements in and around wind farms. Proper alignment, or at least knowledge on how the systems are aligned, is of great relevance here. The paper describes in detail two methods that allow a very accurate alignment of a long-range scanning lidar without the use of extra equipment or sensors. The well-known so-called Hard Targeting allows a very precise positioning and north alignment of the lidar using the known positions of the surrounding obstacles, e.g. wind turbine towers. Considering multiple hard targets instead of only one with a given position in an optimization algorithm allows to increase the position information of the lidar device and minimizes the consequences of using erroneous input data. The method, referred to as Sea Surface Leveling, determines the leveling of the device during offshore campaigns in terms of roll and pitch angle based on distance measurements to the water surface. This is particularly well suited during the installation of the systems to minimize alignment error from the start, but it can also be used remotely during the measurement campaign for verification purposes. We applied and validated these methods to data of an offshore measurement campaign, where a commercial long-range scanning lidar was installed on the transition piece platform of a wind turbine. In addition, we present a model that estimates the quasi-static inclination of the device due to the thrust loading of the wind turbine at different operating conditions. The results show reliable outcomes with a very high accuracy in the range of 0.02° in determining the leveling. The importance of the exact alignment as well as the possible applications are discussed in this paper. In conclusion, these methods are useful tools that can be applied without extra effort and contribute significantly to the quality of successful measurement campaigns.

Highlights

  • Scanning long-range Doppler wind lidar devices play an increasingly important role in the assessment of wind conditions (Krishnamurthy et al, 2016)

  • In the following the results of the Hard Targeting (HT), the Sea Surface Leveling (SSL) and the Platform Tilt Model (PTM) are presented for the reference case

  • Since the lidar was installed on the platform southwest of the tower of wind turbine GT58, we could not see a large part of the 305 wind farm GTI from the lidar

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Summary

Introduction

Scanning long-range Doppler wind lidar devices play an increasingly important role in the assessment of wind conditions (Krishnamurthy et al, 2016). Due to their ability to measure the wind speed over long distances and over an entire area 20 with high temporal and spatial resolution, it is possible to obtain knowledge about wind fields. This can be utilized for wind resource assessment offshore from the coast (Koch et al, 2012; Shimada et al, 2020) or existing offshore platforms and wind energy research on e.g. wind turbine wakes (Krishnamurthy et al, 2017), wind farm cluster wakes (Schneemann et al, 2020a), meteorological phenomena like low level jets (Pichugina et al, 2016) or global wind farm blockage (Schneemann et al, 2020b) and minute-scale wind power forecasts to improve grid stability and energy trading (Theuer et al, 2020).

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