I output the hourly solar altitude angle, solar azimuth angle, and the cosine value of the Surface Outside Face Beam Solar Incident Angle for a window facing south. I found that the cosine value of the surface outside face beam solar incident angle has some deviations.

Especially, at 04/11 16:30, the incident angle cosine value output from EnergyPlus is negative. However, based on the solar altitude angle and azimuth angle, it should be positive. This is because the solar azimuth angle is less than 270 degrees, indicating that the direct solar beam can hit the south facade.