Presentations

Abstract

The IEC 61400-50-3 prescribes for nacelle lidars to be calibrated at the level of the indivdual LOS measurements. This poses much tighter conditions on the valid wind direction sectors compared with ground based lidar calibrations. Also, since the test is ideally conducted a shallow elevation angles to minimise the impact of vertical wind speeds on the calibration, the tests are typically conducted at low heights, where the mean wind speed is lower than for a typical vertical profiling lidar calibration. Accordingly, it can be a long wait for a strong wind event to occur from the correct wind direction to complete the measurement data base for the higher wind speed bins, in DNV's recent experience calibration campaigns can last up to 6 months. DNV has therefore developed a pragmatic approach to extrapolate (or interpolate if required) uncertainties for missing wind speed bins. This approach has been tested on a track record of more than 30 lidar calibrations and two different lidar types, to provide a conservative but realistic estimate of lidar uncertainty for cases where project time pressure and adverse wind conditions require tests to be aborted before the data base is completed. The paper describes the study, the method and it's implementation.