Effect of Wind Shear Coefficients on Electrical Energy Generation in Lunga, Zambia

Abstract

Sydney Mutale, Yong Wang, Jan Yasir, Aboubacar Traore and Mamadou Suoare

Wind measurements are usually conducted at lower heights due to economic constraints and, after that, extrapolated to higher heights to estimate the wind speed. In order to understand the effects of wind shear coefficients on electrical energy on the Lunga site, the values were taken using 10- minute wind speed data measured at 40, 50, and 60 meters above ground level. If a constant value of the wind shear coefficient is used, the actual and extrapolated wind speed measurements will significantly differ. The resulting errors will affect the energy yield analysis (EYA) of the wind turbines. Vergnet 0.2 MW and Vestas 3.45 MW wind turbine power curves were used to analyze the effect of wind shear coefficient from March 2017 to August 2021. Air temperature and surface pressure data were used to calculate the wind power density. Further, the study's mean air density was 1.108 kg/m3, and the mean wind shear coefficient calculated for the Lunga site was 0.246. The results of EYA for the two turbines show higher variation and uncertainty in electrical energy generated at lower heights than at higher heights due to higher wind shear coefficients at lower heights. The results of 0.143 power law and the actual wind shear coefficient results above ground level showed increased EYA and capacity factor for higher heights than lower heights. These findings will be important as guidance for analyzing the effects of wind shear coefficients on electrical energy generation in Zambia.

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