Analysis of satellite-measured insolation in Brazil

Incoming solar radiation, insolation, is an important factor in many processes occuring at the earth surface. These include natural processes such as energy and moisture flux, photosynthesis, evapotranspiration, as well as quantities of interest in solar energy applications, such as energy available for focusing and non-focusing solar collectors and photovoltaic cells. In Brazil, solar radiation has been measured from 1978 through a network of pyranometers distributed all over the country. In the area limited by 15° and 34°S latitude and 40° and 67°W longitude, insolation estimates have been made using the geostationary satellite (GOES) from May 1982 to June 1984. It was thus possible to compare the simultaneous daily values of global solar radiation corresponding to the Southern part of Brazil during 1982 and 1983. The purpose of this paper is to analyse the accuracy of the estimates, presenting the results of the comparison. They show that standard error of the satellite-derived daily insolation values when compared against pyranometers is in the range of 15–30% of the mean values. Therefore, operational estimation of surface insolation in this region using GOES data appears normally feasible.