Estimation of Dynamic Wind Shear Coefficient to Characterize Best Fit of Wind Speed Profiles under Different Conditions of Atmospheric Stability and Terrains for the Assessment of Height-Dependent Wind Energy in Libya

Abstract

Assessment of wind potential at a certain site requires an accurate estimate of wind speed at different heights other than that at the measured altitudes. Extrapolating wind data is affected, among other parameters, by the spacing height of the measured wind data. An estimate of the wind shear coefficient (WSC) is needed in order to develop the predicted wind speed profile. In this paper, the effect of spacing height of wind speed measurements on the WSC estimation is investigated using the power-law model, while taking into consideration the effect of the atmospheric stability. Estimation of WSC that would give the nearest value of the extrapolated wind speed to the measured value was performed at three different terrains and promising wind farm locations in Libya. The obtained results indicate the undeniable fact that WSC depends on time, altitude and the spacing height. The value of WSC of the lower measuring spacing height of 20–40 m gives best estimate to wind speed profiles for all atmospheric stability conditions for the two southern cities, while the second spacing height (40–60 m) gave best estimate of wind speed profile for the coastal site. Adopting the proposed WSC instead of the value of seventh in wind potential assessments, leads to an increase in the productivity of wind turbines at rates of 8 and 16% at hub heights of 50 and 100 m, respectively. This in turn will reduce the levelized cost of energy (LCOE) and enhance the competitiveness of wind energy in the energy market.