In the spirit of the current standard, wind farm owners in North America are increasingly performing operational (non-contractual) power curve tests using ground-based Lidar alone. Certain Lidar models provide a very similar input to hub height IEC masts for assessing wind turbine performance in simple terrain sites, mimicking the role of the mast but with a much higher degree of flexibility and at a much lower cost. Resultant uncertainties on power performance are slightly higher but not significantly so, and the results of such a test give wind plant owners very similar benefits in understanding whether turbine performance meets, underwhelms, or exceeds expectations, and just as importantly whether far more costly and time-intensive actions such as formal IEC 61400-12-1 testing under the current standard will pay off.
As the exclusive North American distributor of the WINDCUBE Lidar manufactured by Leosphere SAS, we focus specifically on this Lidar model in an example of Lidar-based operational curve (OPC) test in practice in the Midwest USA. More than 500 WINDCUBE Lidars are used globally today for wind resource and wind turbine performance assessment. WINDCUBE Lidars record 10-minute average wind speed data at 12 user-selectable heights of measurement, allowing for flexibility to measure not only at turbine hub height but across the entire rotor swept area if desired. According to an independently issued statement from DNV GL, WINDCUBE’s measurement uncertainty in simple terrain is within the uncertainty of calibrated Class 1 anemometry. Every unit is tested and validated in such a way that its performance can be traced back to a reliable reference. The quality of measurement and performance stability and traceability allows WINDCUBE data to be “bankable” with limited if any on-site verification.
The real world Lidar-based test proved turbine underperformance to the wind farm owner and allowed them to proceed confidently with more costly formal testing per the IEC standard, with high confidence in the expected results. We present results from this initial test and also examine turbine efficiency as a function of shear and turbulence as measured by the Lidar.