Monthly-averaged daily global irradiation data are now easily available from NASA website. Using established models it is then possible to decompose the daily to averaged-hourly global irradiation. The missing link so far has been hourly averaged diffuse irradiation. In this article data was pooled from 10 UK locations to obtain a regression model to complete the above missing link. It was presently shown that the averaged-data regressions are distinctly different from previously available hour-by-hour regressions.

Practical application : The present work has explored a correlation between averaged-hourly diffuse and global irradiation using the diffuse ratio–clearness index envelope. Results show that a strong regression relationship is thus obtainable. The present work has therefore the potential for other similar research that may be followed up in a likewise manner.