General Formulation of Ångström-Prescott Coefficients: A New Approach for Côte d’Ivoire

Abstract

In this study, we used calibrated annual Ångström-Prescott (AP) coefficients of nine (9) weather stations in Côte d'Ivoire to formalize two general equations expressing them as a function of the latitude and altitude. The aim is formalizing the general equations of Ångström-Prescott coefficients that can be used to increase the density of global horizontal irradiance. The Ångström-Prescott coefficients thus obtained were compared with the values calibrated using the root mean square error (RMSE), the mean bias error (MBE), the mean absolute bias error (MABE), the NSE coefficient and the statistical t-test (t-stat) with the following results for coefficients a and b respectively: 0.00935143, -0.00042828, 0.00825164, 0.99734601, 0.12129825 and 0.00633772, -0.00017254, 0.00471422, 0.7653197, 0.072056623. To improve the estimation of coefficient a, we linked it to the coefficient b by a polynomial function of degree two. This equation led to a significant decrease in the absolute estimation error of coefficient a resulting in low values of RMSE and MABE. RMSE decreased from 0.00935143 to 0.00498464 and MABE decreased from 0.00825164 to 0.00346367. The low values of the statistical t-test (t-stat) (0.45735957 for a and 0.07205623 for b) for the two equations show that the model agrees well with the data. The good agreement between the annual Angström-Prescott coefficients estimated and calibrated also confirmed by high NSE coefficients (0.99924593 for a and 0.7653197 for b) recommends the use of this model in any site in Côte d'Ivoire to predict global horizontal irradiance.