Spatial and temporal analysis of decomposition models in China

This study presents a comprehensive evaluation of 15 decomposition models (12 empirical and 3 atmospheric transmittance models) for estimating diffuse horizontal irradiance at 17 radiation sites in China, using hourly radiation data from 2011 to 2020. Our results show distinct patterns in model performance across different geographical regions, seasons, and sky conditions. The Liu model demonstrates the best overall performance with an RMSE of 78.20 W/m(2), while model accuracy shows significant geographical variation, performing best in South and Southeast China (RMSE<70 W/m(2)) and worst in the Qinghai-Tibet Plateau and Northwest China (RMSE>90 W/m(2)). Seasonal analysis reveals better performance in winter than in summer, with RMSE differences approaching 40 W/m(2), mainly due to the higher proportion of solar elevation angles exceeding 30 degrees in summer. Under different sky conditions (classified by clearness index: 0-0.35 for overcast, 0.35-0.65 for partly cloudy, 0.65-1 for clear skies), most models follow an RMSE pattern of partly cloudy > clear sky > overcast. However, the Reindl2, Boland, DIRINT, and DIRINDEX models deviate from this trend due to their formula structure and sensitivity to atmospheric parameters. To reduce these regional disparities, we propose a new region-specific model selection strategy: the DIRINDEX model for eastern regions, DIRINT for central areas, and Karatasou for western regions. This combined approach reduces the overall RMSE to 73.17 W/m(2). This research deepens our understanding of the application of decomposition models in China's complex geographical and climatic conditions, offering valuable references for solar radiation modeling and renewable energy forecasting in diverse climatic regions.