Comparison of methods for estimating daily and hourly diffuse solar radiation

Daily and hourly diffuse radiations measured using a pyranometer and shading ring have been compared with the values calculated using several correlations. For the daily diffuse radiation, the correlation of Duffie & Beckman (Solar Engineering of Thermal Processes, John Wiley, 1980), Liu & Jordan (Solar Energy, 4(3) (1960) 1–19), Erts et al., (Solar Energy, 28 (1982) 293) and Bruno (Solar Energy, 20(1) (1978) 97–100) have been used while the hourly diffuse radiation was calculated using the correlations of Hottel, Orgill & Holland (Solar Energy, 19 (1977) 357) and Liu & Jordan. It has been uniformly observed that Liu & Jordanʹs method may be considered a suitable method for the estimation of daily and hourly diffuse radiations in clear-sky conditions in the plain areas of northern India.