LiDAR (Light Imaging, Detection, and Ranging) has been utilized in a wide variety of applications since it broke into the mainstream in 1971. It was initially introduced in the Apollo 15 mission when it was used to map the surface of the moon. LiDAR is a technology that uses the same principles as Sonar, instead replacing sound with laser pulses. These pulses strike the desired surface and bounce back, providing an accurate 3D model of the surfaces it strikes. Although most of LiDAR news we read today has to do with aerial LiDAR and mapping of the Earth’s surface, mobile LiDAR has been used to map millions of road miles but also to map inside mine shafts, dams and other man-made features.
One frequently overlooked application of LiDAR is the study of air currents and wind flow. LiDAR is a practical, cost-effective, and accurate method of collecting data for wind farm development. By studying operational wind turbine performance and wind pattern research using LiDAR, we can develop more efficient methods of producing renewable energy. This is increasingly important as we increase our renewable energy footprint.
Prior to using LiDAR, many of these wind studies were performed using meteorological masts (instruments strapped to tall poles). However, there are several advantages to using LiDAR to make many of these measurements without expensive masts. Ground based, upward looking LiDAR was first utilized by the wind industry. With the added portability LiDAR provides, researchers can much more easily collect data in multiple locations. Additionally, LiDAR can simultaneously collect data at several different heights. This provides copious amounts of information about wind flow across the entire turbine rotor area. Meteorological mast instruments also often have blind spots. LiDAR does not. LiDAR measurements have a much greater range up into the atmosphere extending much further than the height of a physical mast. This better sampling of meteorological conditions is important for engineering the future generation of large turbines which extend significantly above 100m in height. A final important advantage of meterological LiDAR is that it is environmentally non-invasive. That is, it measures the wind conditions without changing them. Physical masts are an obstacle to the wind flow and alter the atmospheric flow being measured. In the future, all wind turbines may be fitted with their own forward-looking nacelle based L to detect wind flow and notify the turbine operator when to activate the turbine.
Cornell University is on the cutting edge of using LiDAR technology for wind turbine studies. Researchers have acquired a pair of continuous wave ZephIR 300 wind lidars. This specialized LiDAR equipment is being used for ground-based remote sensing of wind flow in the atmosphere. The research is spearheaded by Professor Rebecca Barthelmie, Director of the Wind Energy Research Lab at Cornell University. Barthelmie has been cited for her extraordinary efforts and achievements in the field of wind energy research.
The ZephIR 300 is a continuous wave (CW) wind LiDAR which provides high resolution measurements 50 times per second anywhere from 10 to 200 meters up. CW wind LiDAR gives precise accurate measurements of wind speed, direction and other characteristics including Turbulence Intensity (TI). The effect of (TI) on wind turbines is of great interest to scientists in the field. The impact of irregular wind loading can affect both production from the turbine as well as the operating costs of the turbine with increased stresses and strains potentially reducing component life.
Power generation from wind energy is hard! Why? Because the energy source for a wind turbine is largely unknown until it (the wind) impacts the turbine. The main challenge in harvesting energy from wind comes from anticipating the incoming, unknown turbulent wind ﬁeld. The wind turbine controller tries to balance the competing interests of reduction in structural loads and increasing energy production to maximize turbine efficiency. Conventional wind turbines use feedback methods to meet these goals, reacting to wind disturbances after they have impacted the wind turbine. LiDAR sensors, on the other hand, enable the wind turbine to “see” the wind before it impacts the wind turbine. This, in turn, allows a controller to actuate the wind turbine in anticipation of an incoming wind disturbance. The result is greater efficiency.
LiDAR has proven to be a powerful new technology. Aerial Services has been using it to vastly increase the area and quality that can be mapped. It has vastly improved the efficiency of wind energy. And because of LiDAR’s versatility and the amazing ingenuity of America’s innovators, it remains a critical technology with new applications yet to be discovered.
Written by: Tom Britt, LiDAR Technician