Diffuse radiation on a horizontal surfaces at Madras

The diffuse radiation falling on a horizontal surface at Madras, India has been analysed and the results presented. Five years of data have been used for the analysis and a correlation has been established between the daily average diffuse radiation with the monthly average clearness index. It has also been shown that there is an appreciable difference in the ratio of monthly average hourly diffuse to the monthly average daily diffuse radiation with respect to day length.