Influence of different domain configurations on WRF solar irradiance estimation at Badajoz (Spain)

Over the last decades, numerical prediction models, such as the Weather Research and Forecasting (WRF), have emerged as one of the most powerful tools for solar radiation exploitation as renewable energy. A reliable forecast of solar radiation is an effective method to account for its variability and facilitate its integration into the grid. This study analyzes the influence of different domain configurations and spatial resolutions on the WRF solar radiation estimation. To this aim, different domain configurations centered on the city of Badajoz (Spain) have been tested. Thus, three different combinations of two nested domains (D01; higher domain; D02; inner domain) defined on a Lambert Conformal projection have been analyzed. Configurations C1 and C2 use the same domains but differ in the resolution of the nested domain (D02): 9 km for C1 and 3 km for C2. C3 has been defined to perform simulations at a higher resolution, consisting of two nested domains of 9 km for D01 and 1 km for D02. Due to WRF’s requirements on grid ratio between nested domains and computational efficiency criteria, this third configuration uses the same D02 dimensions as C1 and C2, but notably smaller D01 dimensions. All these configurations have employed the same WRF parameterizations. The initial and lateral boundary conditions for the meteorological fields are obtained from the reanalysis ERA5. Finally, the estimated solar radiation for the inner domains at 9, 3 and 1 km has been compared with ground-based solar radiation measurements. The results show a good performance of all the analyzed configurations, with an average relative MABE value of 14.95% and mean relative RMSE of 23.7%. Linear regression analysis between simulated and reference ground measurements have reported a slope of 0.83 for C1, 0.80 for C2 and 0.77 for C3. C3 tends to overestimate the reference measurements, while C1 and C2 tend to underestimate them. This underestimation is more remarkable for C2, likely due to the higher grid ratio in this configuration, 1:9 versus 1:3 in C1. Additionally, the analysis of differences between WRF simulation and reference data with respect to geometrical factors and sky conditions have reported differences between configurations. All these results reveal that different aspects related to the domain configuration, and not only final resolution, can influence the solar radiation forecasting and point out the need to find the most suitable configuration for each specific problem. Acknowledgments. This work is partially funded by FEDER/Ministerio de Ciencia, Innovación y Universidades-Agencia Estatal de Investigación of Spain through project RTI 2018-097332-B-C22, and by Junta de Extremadura-FEDER through project GR18097.