Estimation of Diffuse Radiation from Sunshine Hours and Global Radiation

摘要

For the design and study of solar photovoltaic systems and solar thermal systems, the accurate information about the solar radiation components at a given place is needed. The diffuse radiation is one of the most important components of solar radiation. The diffuse radiation measured at a place gives an idea about the state of the atmosphere at the place. In this study, we have developed a regression model to estimate the monthly mean daily diffuse radiation from the monthly mean daily global radiation. The robust regression technique which is nothing but the weighted least squares method has been used to develop our model. The technique has been adopted since this method is vulnerable to the outliers in the data. The month wise regression models were developed using the data for a period of twenty years (1989-2008). The study site is Chennai (13°N, 80° 11'E), the capital city of TamilNadu, India. We evaluated the performance of the model by calculating the mean bias error (MBE), the root mean squared error (RMSE) and the mean absolute percentage error (MAPE). They were found to be 0.1221MJ/day/m~2, 0.6648 MJ/day/m~2 and 6.23% respectively.