Posters

Abstract

The upcoming modern wind turbines have a clear tendency to increase rapidly the rotor diameter, hub height and rated power, and the investment for one individual turbine is increasing. Therefore, the accurate Power Performance Testing (PPT) and the wind field monitoring become critical, especially for the large-scale offshore wind farm. However, given the high financial costs of building a tall or offshore met mast, Nacelle-Mounted Lidar (NML) is a natural solution for PPT thanks to the easy deployment and the accurate wind measurement for the whole rotor area. Wind shear is one key parameter for wind field monitoring, as the big wind shear could reduce the power generation and even lead to safety incidents. IEC 61400-12-1 highlights the importance of the wind shear for the accurate PPT measurement and define the calculation of REWS (Rotor Equivalent Wind Speed). The wind shear and REWS are the important wind-related parameters to characterise the vertical difference of the coming wind flow toward wind turbine. One NML is installed on the nacelle roof, while GBL is deployed on the ground in front of wind turbine. The measurement directions of two device are different, so the wind shear comparison needs to select the suitable wind sector. Raw data is shown by Fig. 1 (https://zhiliang.s3.ap-northeast-2.amazonaws.com/WindShear/Figure_01.png [https://zhiliang.s3.ap-northeast-2.amazonaws.com/WindShear/Figure_01.png]), which demonstrates the good wind measurement for two different types of wind lidars (GBL and NML) and the proper methodology used in this study. The field evaluations are taken at two operational wind farms in US, comparing the wind shear measurement by NML and Ground-Based Lidar (GBL). The result shows that the correlation coefficient by two devices is very good: 0.9718 and 0.9714 with slopes of 1.040 and 0.984 in two campaigns by Fig. 2 (https://zhiliang.s3.ap-northeast-2.amazonaws.com/WindShear/Figure_02.PNG [https://zhiliang.s3.ap-northeast-2.amazonaws.com/WindShear/Figure_02.PNG]). The good result proofs wind shear measurement by NML is accurate. More investigation on the impact of wind shear to wind turbine power performance has conducted. Fig.3 shows the main results (https://zhiliang.s3.ap-northeast-2.amazonaws.com/WindShear/Figure_03.PNG [https://zhiliang.s3.ap-northeast-2.amazonaws.com/WindShear/Figure_03.PNG]). Fig.3(a) and Fig.3(b) shows the turbine power is affected significantly by the wind shear and atmospheric stability. Therefore, we classify the 4 different statuses of atmospheric stability in Fig.3(d) and Fig.(d) and the difference of the turbine power curves has been studied. This study provides a good understanding and the solid result from field measurement for the usage of the Nacelle-Mounted Lidars on wind shear measurement. The conclusions are below, (1) Nacelle-Mounted Lidar is an efficient way to measurement the wind flow for wind turbine and has a good accuracy of the wind shear measurement; (2) power performance of wind turbine is affected significantly by the atmospheric condition of the wind shear and stability, because the different vertical distribution of wind field has the different energy in the whole rotor plane, even when the wind speed at the hub height is the same. The future of the research and application of NML to evaluate the wind flow in front wind turbine is very promising.