Presentations

Abstract

Historically, partially due to a lack in (pre-normative) guidance, Turbulence Intensity (TI) data acquired via floating lidar systems (FLS) have been treated as indicative only and not suitable for energy yield or structural analysis. This lack of standardized measurement capability has led to over-conservative approaches to assigning TI to an offshore wind project.    However, establishing a conservative approach to TI estimation is difficult for wind energy applications. For yield work a low TI can be seen as conservative as some common wake models will return higher wake losses. For structural analysis and fatigue loading however, a higher TI is seen as a conservative position. This conflicting need may lead to a project taking a different approach for different engineering disciplines that may, at some point, lead to some confusion at a later stage in the project or under review.    Industry initiatives have started to address this ( [1] [2]), however the metrics being used and the target values (e.g. [2] & [3]) are not uniformly agreed and adopted.    In 2016 The Carbon Trust Offshore Wind Accelerator recognised the need for guidance on the use of FLS for offshore wind resource assessment, with the latest version being published in 2018 [4]. In 2023 The Carbon Trust commissioned a project to look at the state of the art in FLS TI measurement and to derive a testing protocol based on available public evidence with a view to standardising approaches to assessing TI measurement quality.    The update introduces a new designation to the existing pre-commercial stage evaluation. The ‘+’ designation is added to denote the system has been tested for TI measurement capability with the error metrics used in the evaluation presented. There are no changes to the well understood normal stage acceptance criteria.     To test the new approach, data from 20 campaign cases submitted by 5 FLS OEMS comprising of onshore and offshore tests against reference met masts and reference lidars were analysed.  An overview of these results presented in this contribution.    The contribution will present the error metrics and method of testing as well as the evidence which form the basis of the update to The Carbon Trust OWA Roadmap for the Commercial Acceptance of Floating LiDAR Technology  version 3.0.    [1] CFARS, “An open source approach to evaluate the performance of remote sensing devices (RSD) Turbulence Intensity measurements & accelerate industry adoption of RSDs for turbine Site Suitability Assessment.,” CFARS White Paper, 2021.  [2] DNV, “Lidar-measured turbulence intensity for wind turbines,” DNV RP-0661 [Paywall], 2023.  [3] NEDO, “Offshore Wind Measurement Guidebook,” NEDO, Tokyo, 2023.  [4] The Carbon Trust: Offshroe Wind Accelerator, “Roadmap for the Commerical Acceptance of Flotaing LiDAR Technology,” The Carbon Trust, London, 2018.