Posters

Abstract

Wind resource assessment for offshore wind projects relies heavily on the use of floating lidar systems (FLS) for pre-construction wind measurements on site. These instruments have been widely adopted and operated in accordance with a comprehensive set of pre-normative guidance, including the Carbon Trust roadmap for commercial acceptance and IEA Wind Task 32 recommended practices. In addition, the need to address overly conservative approaches to uncertainty evaluation has been discussed in the Carbon Trust Lidar Uncertainty Standard Review. These considerations and established best practice are now being codified in a forthcoming IEC standard, IEC TS 61400-50-4. This presentation provides an update on the progress and contents of this normative standard. A key challenge has been to maintain continuity with existing guidance and established best practice while formulating guidance that is compatible with the broader context of wind measurement guidance in the 614090-50 series of standards. This has entailed the development of a procedure for FLS classification which reflects industry experience of the discrete stages described in the Carbon Trust roadmap while supporting an evaluation of measurement uncertainty that is continuous and based upon sensitivity tests comparable to those used to classify other instruments, such as the procedure described in IEC 61400-50-2 for ground-based lidar. In addition, the possibility of operating with zero classification uncertainty given an adequate evidence base described for nacelle mounted lidars in IEC 61400-50-3 is extended to floating lidar systems, with classification uncertainty being incurred only under circumstances outwith the envelope of operational conditions for which there is an adequate evidence base that supports confidence in satisfactory performance with respect to accuracy. A systematic approach to identifying and evaluating the contributions to the uncertainty budget is described in terms of a hierarchy of uncertainties, from those pertaining to instrument type (classification), those that relate to an individual unit (calibration) and those associated with a particular deployment of that unit during a specific measurement campaign (configuration). Procedures are described for assessing these and for conducting measurement campaigns and maintaining individual instruments in order to ensure the test burden, validity of results, and uncertainty are managed effectively. An accelerated test protocol and set of events that trigger the requirement for a test are discussed. Conversely, a set of conditions that obviate the need for a test are also described. In general, the forthcoming standard has been written to support realistic rather than conservative uncertainty estimation and provide clear guidance for effective operation of floating lidar systems. In addition, the guidance is formulated in a manner that is compatible with the broader context of measurement standards to support meaningful intercomparison between measurements acquired using different technologies.