Abstract: Based on the Angstrom-Prescott model and spatial interpolation method, an estimation method of monthly solar radiation in Shandong Province is constructed herein, and the accuracy of the proposed method is verified using the radiation observation data from three national stations （Jinan, Juxian, and Fushan） and those from Heze, Liaocheng, Zibo, and Qingdao. First, based on the observation data of radiation and sunshine percentage between 1992 to 2015 from the three national stations, the Angstrom-Prescott model coefficients (A-P coefficients) in different months are obtained using the least square fitting method and verified using the observation data in 2016. Then, the solar radiation in Heze, Liaocheng, Zibo, and Qingdao is estimated using different spatial interpolation methods, and an optimal spatial interpolation method is selected based on these results. Finally, this method is compared with other methods in literature. The estimation results of monthly solar radiation in the national stations in 2016 show that the monthly average σMRE is approximately 3.5%, and the monthly average σ_RMSE is approximately 17 MJ/m²~24 MJ/m², proving that the A-P coefficient has a high accuracy. From the estimation results of monthly solar radiation in Heze, Liaocheng, Zibo, and Qingdao stations, the minimum curvature method with the least error (σ_MRE is approximately 7.22%, σ_RMSE is approximately 16 MJ/m²~69 MJ/m²) is selected as the optimal spatial interpolation method. Compared with other methods in literature, results show that the accuracy of monthly solar radiation estimation based on the proposed method is higher, and it can be extended to other regions.

Key words: total monthly solar radiation, Angstrom-Prescott model, spatial interpolation, Shandong Province