A new anisotropic diffuse radiation model

Through the analysis of distribution of diffuse radiation in the sky, the sky diffuse radiation is divided into four zones. Based on the concept of radiation intensity and solid angle, the corresponding integral equation is established in each zone to build a new theoretical model of anisotropic diffuse radiation. Radiation enhancement coefficients in the new theoretical model are solved from the instantaneous diffuse radiation data received by 30°, 45°, 60° inclined planes, then new model and existing models are compared with the diffuse radiation data received by 90° inclined planes. The results demonstrate that for existing models, Perez model is the most accurate, followed by Liu and Jordan model. Among the second generation models, Klucher model, Hay model, Skartveit and Olseth model are relatively accurate. While compared with existing models, NADR model is more consistent with the measured values. Further comparative analysis shows that for east and north orientations, Perez model and NADR model are more accurate; for south and west orientations, Liu and Jordan model and NADR model are more accurate. Klucher model is well agreed with the measured data in different inclinations. Hay model and Skartveit and Olseth model are relatively accurate on 30° tilt surface, and Temps and Coulson model is also relatively accurate on 45° tilt surface. NADR model is in good agreement with the measured data on 60° and 90° tilt surface. On the whole, NADR model is more accurate than the existing models.