Frequency and probability of occurrence of clearness index for the region of Maceió-Alagoas

Abstract

Solar radiation is essential because its distribution around the planet establishes the variations of all the meteorological elements, determining the atmospheric and oceanic circulation patterns and configuring the terrestrial climate, besides being currently widely used for the production of alternative energy. Thus, the objective of this work is to analyze the solar radiation through frequency and probability of occurrence of clearness index in different seasonal periods for the region of Maceió, state of Alagoas. The RG was obtained from data from the INMET automatic stations for the city of Maceió, from January 2014 to December 2017. The Ro was calculated through the solar constant, vector radius of the Earth's orbit and zenith angle. KT was calculated by the ratio of RG to Ro. Histograms of frequencies and accumulatedfrequencies of KT were made. For the seasonal analysis of the solar radiation and KT conditions the data were separated in different seasonal periods. The hourly frequency of KT observed in the dry and rainy season had the highest occurrence in partially cloudy sky conditions, with an average of 53.62% of the total values for both seasons. The frequency of daily KT for the seasons had higher occurrence in partially cloudy sky conditions with an average of 79.74% of the data and the probability of annual occurrence was also higher for partially cloudy sky conditions with 57.21% for the values and 83.29% for daily values.