Presentations

Abstract

How is the wind that a theoretical wind turbine with a 400m rotor diameter would experience, at a real site? And how good are lidars at measuring that? Measuring the wind with lidars is not new. However, until now, for wind resource and wind turbine testing purposes, we usually measured below 250m height. This was mainly because the measurement heights were determined by the state-of-the-art turbine rotor sizes and hub heights. And, possibly because of that too, until rather recently commercially available lidar wind profilers provided measurements only until about that height too. At present we are working on the preparations for a possible expansion of Test Centre Østerild. This would increase its capacity to accommodate wind turbine prototypes with a maximum upper tip height of 450m. As part of these preparations, we have performed a thorough measurement campaign to assess the wind conditions at the site up to that height. In this conference contribution, we will present two results: * Lidar performance at several heights, including 450m. In particular, wind speed measurements and data availability. * Examples of measured wind profiles. Our measurement campaign was designed to allow the wind analyses for different theoretical wind turbine sizes (several hub heights and rotor diameters) and positions. For brevity, we will present here only the results corresponding to a theoretical turbine of hub height 250m and rotor diameter 400m, using two lidars to measure in the height range 50m to 450m at a given location at the site. This location is onshore but close to the coastline, so the measured wind is very similar to offshore conditions, for selected wind directions. Our method is the following: 1. A pre-campaign that consisted of: * A formal calibration of each lidar against a 245m meteorological mast in Østerild. The purpose was to verify the lidars performance and to ensure traceability of the lidar measurements, according to relevant quality and measurement standards (ISO 17025, IEC 61400 50-2). * A simultaneous lidar inter-comparison. This was done to obtain a lidar-to-lidar transfer function. This is essential to the measurement campaign in point 2, which included comparing the measurements of the two lidars. 2. The main campaign, which had a one-year duration. The lidars were moved to two positions close to the test centre, separated by a distance of 1 km. This was meant to exemplify a typical turbine test set up, for the assumed theoretical turbine size, where the lidars’ positions would represent the “wind measurements” and “wind turbine”. 3. A post-campaign, repeating point 1 for quality assurance. In conclusion, in this presentation the workshop participants will gain insights into lidar performance at heights greater than usual and see measurement results from a near-coastal site with high wind speeds.