Re-Deployment Performance Validations
Before ZephIR systems are deployed on wind study projects in either complex terrain or simple sites, they are assessed against a 91.5m mast in flat terrain at the IEC compliant UK Remote Sensing Test Site (Pershore, UK) as part of an industry-approved and well-documented performance validation. The mean and standard deviation of 10-min horizontal wind speed correlation parameters, gradient and R2, have been calculated from over 170 performance validations of ZephIR 300s to investigate the consistency of lidar performance, pre-deployment (Table 1). The regression slopes show a standard deviation for the ZephIRs of <1% at all heights, with current IEC standards for cup anemometers allowing for almost double that variation, at <2%. Comparison of paired cups is used to provide a robust method for identifying any problems with the mast instrumentation. The comparisons also include any effects of differing weather conditions in addition to lidar and cup calibration effects.
Table 1: Batch comparison of more than 170 performance verifications of ZephIR 300
Figure 1: Correlation plots of 10-minute averaged horizontal velocity, ZephIR speed versus mast speed. Data are shown from the 4 measurement heights ranging from 20.5m up to 91.5m.
The long-term stability and accuracy of ZephIR has been demonstrated not only through an assessment of ZephIR calibration accuracy, but also through repeatability trials in real-world conditions. An analysis of the factors that the ZephIR velocity calibration depends on shows that the possibility of any drift of critical parameters over time is negligible. Two wind study trials, separated by a long time period, were carried out with the same ZephIR 300 next to the Pershore mast. The resulting percentage change in gradients of the 10-min horizontal wind speed correlation were <0.5% at all heights.
Figure 2: Percentage change in gradient of 10-min horizontal wind speed from 2 trials separated in time from the same ZephIR 300.
Calibrated Wind Tunnel Testing
In addition to the pre-deployment performance validations, batch comparisons and demonstrable performance in all terrains, in an experimental wind study investigation by LM Windpower, DTU Wind Energy (Risø) and NKT Photonics, a ZephIR 300 system was configured to stare directly along the flow in a high-performance wind tunnel. The world-first results showed unprecedented performance at the theoretical limit when compared against the wind tunnel instrumentation across a speed range of 5 to 75m/s.
The correlation was extremely high with R2 >0.9999, and the gradient of the comparison plot differs from unity by less than 0.5%, comparable to the expected accuracy of the pitot sensor used to calibrate the tunnel itself.