Global solar radiation measurements in Maceió, Brazil

This work focuses on the variability of the global solar radiation over the area of Maceió (9°40′S, 35°42′W, 127 m), located in Northeastern State of Alagoas, Brazil, during the1997-1999 period. Solar radiation variability was evaluated on 5 min, hourly, daily, monthly and seasonal scales. The results showed that the maximum values of the hourly global solar irradiation, Hgh, in the dry (September-February) and rainy (March-August) seasons were 3.18 and 2.50 MJ m−2, respectively. The peaks of the hourly average, H¯gh, for both periods were 2.79 MJ m−2 and the daily average of the global solar irradiation, H¯gd, was 19.89 MJ m−2. The daily clearness index, Ktd, was found to be 0.53 (rainy period) and 0.59 (dry period). In clear, partially cloudy (the most frequent) and overcast days, the daily averages of global solar irradiation were 25.20, 19.00 and 8.00 MJ m−2, respectively. On an annual scale the global solar irradiation changed from 15.00 MJ m−2 by August to 24.04 MJ m−2 by November.