Empirical correlations for estimating the ratios of monthly mean hourly to daily global solar radiation received on horizontal surfaces have been compared and their validities tested. The correlation of Collares-Pereira and Rabl [Solar Energy, 22, (1979) 155] yields the best results, while the...

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 &...