Wind Turbulence Intensity Characteristics at 10m Above Ground Along the Cotonou Coast, Benin

Abstract

The characteristics of the wind turbulence intensity that are essential to know before installing a wind turbine at a site were investigated along the coast of Cotonou in Benin. The average speed, direction, roughness length, friction velocity, turbulence intensity and relationship between the roughness and wind turbulence intensity were evaluated as well. Using the estimators derived from a simple isotropic Gaussian model of turbulent wind fluctuations, we proposed modified models for estimating the turbulence intensity of wind components. Wind speed and direction data recorded at 10 m above ground level from 2011 to 2014 during the first Compact of the Millennium Challenge Account (MCA) in Benin were utilized. The results obtained indicated that the annual average roughness length is evaluated at 1.25×10-4 m, and the annual mean friction velocity is equal to 0.41 m.s-1. Peak values of the turbulence intensity vary from 0.3 to 0.6 except during the months of January, April, July, August and September. The high values obtained could jeopardize the production of wind energy during these months. The correlation between the turbulence intensity and roughness length ranging from 0.75 in January to 0.94 in August revealed that these two parameters are linked by an increasing linear function. Finally, modified formulations of the longitudinal and transversal wind turbulence intensity developed from the van den Hurk and de Bruin model and based on the best-fitting approach were proposed. The error estimators (MAE; RMSE) computed to validate these modified models vary respectively from (0.0099; 0.0141) to (0.0614; 0.0890).