Turbine performance measurement using nacelle mounted lidars in complex terrain – techniques for reducing uncertainty
Creators: name: Slinger
Publisher: name: Zenodo
Year: 2019
Subjects: Wind lidars, complex terrain, wind energy, induction zones

description: A WESC 2019 talk presented in the "Demystifying Complex Terrain" Mini Symposium (session number 1.4a). With many of the available wind sites in simple terrain already exploited, developers are increasingly exploring more complex sites. Whilst turbine performance measurement using nacelle mounted lidars has become established for simple sites, complex sites introduce several challenges for the use of such lidars. These include terrain-induced complex windflows and lidar probe beam position, relative to the ground, as the terrain varies in different sectors around the turbine(s) under test. The former can violate some of the assumptions used in the lidar wind field construction algorithms, introducing measurement uncertainty unless care is taken. Site calibration is important for complex sites, yet the procedures developed and described in the IEC standards<sup>1</sup> are not appropriate for turbine-mounted lidars, so alternative approaches must be found. This symposium presentation will discuss several approaches that can improve the measurements process for turbine mounted lidars in complex terrain. These will include: 1. the use of computational fluid dynamics (CFD) as both an alternative to traditional site calibration and a simple way of incorporating probe height variation due to terrain variation. 2. the development of lidar based wind flow complexity measurement techniques to allow quality filtering of wind yaw misalignment (WYM) and power curve (PC) tests. Wind flow complexity measurement can be used to determine terrain and forestry induced flow effects, as well as for wake detection. 3. lidar measurements made deep in the induction zone of the test turbine. This approach can minimise the effects of terrain, as the wind evolves as it propagates from the lidar measurement range to the rotor. Lidar measurements made in the induction zone can be used directly for the determination of relative power curves. Additionally, newer techniques based on either analytic wind zone induction models<sup>2</sup>, or empirical measurements to characterise the effects of the induction zone, now exist. These allow lidar measurements in the induction zone to be related (back-propagated) to the free flow wind-speeds upwind of the turbine and hence can be used for absolute power curve measurements<sup>3</sup>. The above approaches will be illustrated using results from a sophisticated measurement campaign performed on a recently commissioned windfarm in Western Scotland, consisting of 30 2.05 MW turbines. Terrain and the presence of forestry dictate that it is a complex site. 12 of the turbines were selected and concurrently instrumented with a newly developed nacelle mounted circular scan multirange CW lidar. A ground lidar was also deployed on the site. The results provide evidence that nacelle-mounted lidars can be used on complex sites and that they can provide valuable information on turbine performance in such situations. [1] IEC 61400-12-1:2017 [2] Medici et al, <em>Wind Energy</em> <strong>14</strong>, 691 (2011) [3] Borraccino et al, <em>Wind Energy Science</em> <strong>2</strong>, 269 (2017)
description: Wind Energy Science Conference (WESC 2019),