Estimation of mean monthly and hourly global solar radiation on surfaces tracking the sun: Case study: Tehran

Monthly average daily global solar radiation data are essential in the design and study of solar energy conversion devices. In this regard, modified Angström model was selected to estimate mean monthly global solar radiation for Tehran (35.68°N, 51.32°E). The results were compared with measured data. A good agreement (greater than 90%) was observed between the measured and the predicted values. This model is extremely recommended to estimate monthly average daily global solar radiation for Tehran and in elsewhere with similar climatic conditions where the radiation data is missing or unavailable. The results can also be used for elsewhere with similar climatic conditions that the radiation data is missing or unavailable. In addition, the values of monthly average and hourly clearness indices were determined during 2003 and 2009. Hourly solar radiation data required for solar energy system design and performance studies are generally not available for a number of sites especially in remote locations. Scientists have developed several methods to achieve hourly radiation using different input parameters. The Collares-Pereira and Rabl model has been used in this paper to predict hourly global solar radiation for the average day of each month. Three components of hourly solar radiation include beam, diffuse and ground reflected radiation were determined on surfaces tracking the sun.