ESTIMATION OF GLOBAL SOLAR RADIATION FROM THE INSOLATION DATA IN THE STATE OF PIAUÍ, BRAZIL

The quantification of global solar radiation requires the use of expensive sensors. Thus, this meteorological element is usually estimated by equations. The objective of this study was to obtain the coefficients a and b of the Angström-Prescott equation and their possession, to estimate the global solar radiation from the insolation data and to compare it with the data measured in municipalities located in the State of Piauí, namely: Paulistana, Picos, São João do Piauí, Floriano and Piripiri. The coefficients were determined in three periods: annual, rainy (January to May) and dry (June to December). From the coefficients found, the solar radiation was estimated and compared with the values measured in the annual period, rainy and dry. The values of a ranged from 0.2485 (Floriano) to 0.3280 (Piripiri) in the rainy season. In the dry period, the variation was from 0.2626 (Floriano) to 0.3399 (São João do Piauí). The values of b ranged from 0.3623 (Floriano) to 0.4748 (Paulistana) in the rainy season and from 0,3794 (Floriano) to 0,5079 (Paulistana) in the dry period. The estimates of global solar radiation from the insolation data using the Angström-Prescott equation using the coefficients a and b obtained, when compared with the measured values, presented good performance. It is possible to use global solar radiation data estimated from the insolation in the municipalities studied.