Wind-Farm-Scale Measurements Using Mobile-Based LiDAR

In wind farms, wakes – that is the relatively low speed, high turbulence flow region downstream of a wind turbine – result in 10-20% lower energy yields of wind farms and up to 80% higher fatigue loads on wind turbines that operate in wakes. The lower energy yields translate into lower revenues for operators of wind farms, and the higher loads result in increased maintenance costs. An improved knowledge of the characteristics of wakes is thus important in the design and operation of wind farms. As the physical processes in the wakes, such as turbulent mixing, entrainment, etc. are dependent on length-scale, wind tunnels are of limited usefulness in supporting efforts to improve our knowledge of wakes in utility-scale wind farms. We have designed and built a mobile laboratory, windRoverII, to make measurements in utility-scale wind farms. windRoverII is equipped with a 3D scanning LiDAR system to measure wind field over an area of up to 6km by 6km, and heights of up to 250m. As a LiDAR measures the wind speed along its line-of-sight, we have developed fully automated software, that determines the optimum scanning positions in a given area or wind farm, directs the driver of windRoverII to specified positions, determines and executes scan pattern of measurements from each position, and visualises the measurements in real-time. Predictions from numerical simulations and semi-empirical wake models are being compared with our utility-scale measurements in order to further improve these modeling tools. Thus, our new measurement approach is well suited to help in the reduction of the cost of wind-generated electricity in new wind farms.