Wind Minds‘ LIDAR system measures the vertical wind profile up to a height of 200 meter, allowing for the best possible data basis for yield assessments to be generated. Laser-based wind measurement technology provides highly reliable wind data, comparable to the accuracy of first class cup anemometers. With respect to data availability LIDAR measurements reach excellent results, especially in combination with MMS – the measurement monitoring system developed by Wind Minds.
Due to their flexibility LiDAR devices can easily be relocated to measure the wind at various points in the project area for a certain period of time. By means of horizontal cross predictions between the mast position and the various LiDAR locations the validity of the theoretical model can be checked. Potential deviations can be detected and adjusted – and uncertainties regarding the energy yields can be diminished. This provides major advantages compared to a measurement campaign conducted with a single met mast.
The benefit of combined measurements is the information on the shear for the extrapolation up to the planned hub height and the decrease of the associated partial uncertainty for the vertical extrapolation. Furthermore, it allows a horizontal cross prediction between the different measurement positions. That facilitates the calibration of the theoretical flow model until it performs more realistically with much less uncertainty in the horizontal extrapolation. Thus uncertainties are reduced and energy yield prognosis are refined which obviously results in an increased project value.
Another very important benefit of LiDAR measurements is the possibility to measure up to 200 meters above sea level and even higher, covering the whole rotor swept area of the highest turbines. This provides important information about the shear and avoids misinterpretations. Therefore, a temporary additional LiDAR measurement that is used for the vertical extrapolation of the shear using basic data coming from a lower altitude mast measurement provides safe and at the same time cost-saving solution.
With respect to power performance measurement and AEP assessment the rotor equivalent wind speed has become a focus of interest. By the use of LiDAR technology, the uncertainties in an AEP estimation can be reduced significantly. Even though the current applicable IEC standard does not yet account for the whole rotor swept area but only demands the measurement at hub height – the draft of the upcoming revision of the IEC 61400-12-1 is already incorporating the specification of the rotor equivalent wind speed and will allow the use of wind LiDARs for the measurement.
In order to acquire reliable data from a RSD it is crucial to regularly verify its performance and data output. The objectives of a LiDAR verification test are first and foremost to provide a proof of the measurement precision and secondly the estimation of deviations. Knowing this, the deduction of a correction factor and the determination of a corresponding uncertainty is feasible. Wind LiDARs are not calibrated like cup anemometers in wind tunnels but their performance is tested against a classical wind measurement mast which is equipped with cup anemometers and wind vanes. The cup anemometers and wind vanes serve as the reference sensors and should be ‘first class’ instrumentation, classified by the IEC 61400-12-1. Procedures applied in LiDAR verification tests and associated analyses are in accordance with the guidelines of International Energy Agency.