Presentations

Abstract

Vertically profiling lidars are now widely used for Energy Yield Assessment both onshore and offshore. Horizontal wind speed and direction measurements from multiple lidar device vendors and different lidar architectures have undergone thousands successful validations against co-located anemometry. Lidar turbulence intensity measurements (TI), however, have not yet gained acceptance as direct replacements for anemometry for turbine site suitability and loads validation. Profiling lidars tend to overestimate TI by roughly 10% compared to cup anemometers. Lidar TI errors arise from several different physical phenomena, including inter-beam effects and intra-beam effects. Inter-beam effects include the mismatch of the instantaneous turbulent eddies sampled at the different beam locations, and cross-contamination of the Cartesian turbulent components in the lidar's titled beams. Intra-beam effects include volume averaging of the flow field by the lidar's 20m pulse. In this study, different physics-based and model-based methods of computing lidar turbulence intensity are compared against co-located anemometry at various sites in Europe. The results of these comparisons are evaluated using passbands proposed in DNV Recommended Practice 0661: Lidar-measured turbulence intensity for wind turbines (DNV RP). Strengths, weaknesses, and sensitivities of the different physics-based and model-based types are discussed.