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 & Jordan's 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.