Characterisation of the Vertical Wind Profile According to the Stability Classes of the Atmosphere in Conakry, Guinea

The characteristics of the vertical wind profile and the wind potential study on the Conakry site for each atmospheric stability class were investigated in this study. Wind speed and air temperature data recorded over the period from January 2001 to December 2019 at 10 m and 50 m above the ground at daily (50 m) and hourly (10 m) scales were used. The wind shear parameters were determined from the logarithmic and power law. Based on the Newman and Klein wind shear model, a new formulation of this parameter was proposed as a function of the Obukhov length at order 2 and calibrated from the measurements using the simplex algorithm of Nelder and Mead. From the Weibull parameters obtained for the stable and unstable period of the atmosphere, the available wind potential at Conakry was estimated from 10 m to 80 m. The results indicate that the annual average of the ground roughness length is 1.7 x 10-2 m. The annual average of the ground friction velocity is 0.19 m.s-1. The atmosphere remains stable at the Conakry site from 09 p.m. to 10 a.m. and unstable from 10 a.m. to 09 p.m. The proposed wind shear formulation gives a better estimation of the wind speed in function of altitude with the lowest values of RMSE and MAE (4.5x10-4 ; 3.8x10-4) m.s-1 in stable and unstable periods (0.09 ; 0.07) m.s-1 compared to some models found in the literature. The mean annual wind shear coefficient in stable period is 0.26 and in unstable period 0.28. The annual mean shape parameter from 10 m to 80 m above ground in stable period is between 1.25 and 1.64, and during unstable period, it varies from 1.55 to 2.07. The annual mean scale parameter at 10 m and 80 m above ground is (3.9; 7.10) m.s-1 (unstable atmosphere) and (2.45; 4.41) m.s-1 when the atmosphere is stable. The annual average of the energy production under a convective atmosphere at 10 m and 80 m is estimated at 72 W.m-2 and 301 W.m-2 respectively. During the night cycle, this annual production varies from 28 W.m-2 (10 m) to 93 W.m-2 (80 m). Based on these results, the Conakry site is suitable to host medium-sized wind power plants for electricity and water production.