ARIMA and regression models for prediction of daily and monthly clearness index

Hourly and daily measurements of total and diffuse solar radiation and sunshine duration are analyzed. Three-year measurements of the available meteorological data in Mosul (latitude 36° 19′ N, longitude 43° 09′ E and 223 m above mean sea level) are used in this study. The present work involves two parts; in the first one, monthly mean daily and hourly of total and diffuse solar radiation are analyzed. The results show that the annual mean of the daily total and diffuse solar radiation is 5.11 and 1.6 kWh/m2 respectively. 57% of the days of the year are clear, while only 11.5% of the days are cloudy. Several empirical equations for estimating monthly mean daily global and diffuse solar radiation have been developed and compared with other available models. Ratio of average hourly to daily total solar radiation, for each month of the year is studied and compared with the theoretical results. In the second part, time-series model building using Box–Jenkins procedure to the daily clearness index is performed. The ARIMA(2,1,1) is developed for predication of daily clearness index.