Comparison of daily diffuse radiation models in regions of China without solar radiation measurement

Considering diffuse solar radiation is essential for thermal environment construction and solar energy applications. Due to lack of solar radiation measurement in China, developing appropriate models for data estimation is becoming more and more important. In areas that lack solar radiation measurement, using estimated global solar radiation values or extraterrestrial solar radiation is a key problem. In this study, data obtained between 2000 and 2017 from 17 stations were selected to develop and verify 18 diffuse solar radiation models and three global solar radiation models. The models were evaluated using the mean bias error, mean absolute bias error, root mean squared error, and Nash-Sutcliffe efficiency coefficient. The results showed that the diffuse fraction models based on measured and calculated global solar radiation performed better than diffuse coefficient models. Models containing both clearness index and relative sunshine duration and four parameters (clearness index, relative sunshine duration, mean air temperature and relative humidity) obtained the best performance among all of models. Choosing a precise and suitable global radiation model is essential for estimating daily diffuse radiation in areas without global radiation measurement, especially in areas with low clearness index. A simplified model based only on clearness index can be applied to calculate daily diffuse radiation in Northern China. In areas with lower clearness index and those in Southern China, global radiation models that include multiple parameters (clearness index, temperature difference, and atmospheric pressure) are the optimal options. (C) 2019 Elsevier Ltd. All rights reserved.