Parameterization of the Hargreaves & Samani and ångström-Prescott Equations for Estimating Solar Radiation in Goiânia-GO.

Abstract

Solar radiation is a climatological variable widely used in climate studies and can be measured using meteorological stations. Due to the high cost and complex maintenance of measurement equipment, it is possible to estimate it using mathematical models. Thus, the present study aimed to calibrate and validate the parameters of the ångström-Prescott and Hargreaves & Samani equation to estimate the solar radiation incident in Goiânia, Goiás. Daily maximum temperature historical data (T_max; °C) and minimum (T_min; °C), incident solar radiation (Rs, MJ m^-2 dia^-1) and sunshine duration (n, h dia^-1) in the region were used. The parameters were calibrated for monthly and seasonal periods using the least-squares method. The estimated parameters were validated using the Willmott index (d), the correlation coefficient (r), and the root of the mean square error (RMSE). The parameter k_Rs varied from 0.12 to 0.14, while the parameter a ranged between 0.06 and 0.43, and the b varied from 0.16 to 0.72. The estimates in the seasonal periods performed better when compared to the monthly ones. The obtained indices demonstrated satisfactory estimates for the seasonal periods' parameters, being adequate to estimate the solar radiation in the Goiânia.

Keywords
available energy; empirical coefficient; agrometeorology