Research on Improved Algorithm of Hourly Diffuse Radiation Model

In this paper, the hourly solar radiation data of 2011 in Beijing and Wuhan are collected in order to predict the diffuse irradiation ratio more accurately. First, the local solar energy resources are evaluated according to three indicators. Then the applicability of the Erbs model has been tested. Finally, a new model based on sky clearness index and solar altitude angle are used to modify the Erbs model. The results show that the total radiation in Beijing is 5189.36 MJ/m2 and it is single peak. The stability is 0.32. Direct ratio is 0.5. And the total radiation in Wuhan is 4261.93 MJ/m2 and it is double peak. The stability is 0.34. Direct ratio is 0.39. The shape of the data distribution of the hourly diffuse irradiation ratio is similar to that of the Erbs model. However, the measured values are not only related to the clearness index, but also to the solar altitude angle. The revised models improve the prediction accuracy. It provides an important basis for the design of photovoltaic system.