I would support everything a number of replies have indicated,
including Timothy's.

We recently had a need to validate the effectiveness of shading in
EnergyPlus versus IES VE. Once input assumptions were aligned, the
output was very similar for clear sunny days which is what you would
expect given they have both been BESTEST'd. We did observe
differences under highly diffuse conditions or where shortwave gains
were dominated by ground reflectance or sky model differences. Think
of a north facade in summer at 30 Degrees latitude with a horizontal
shade fully shading from beam radiation. In these cases there were
differences which at those points in time appeared significant, but
the differences were small in the context of the shading that was
occurring on the beam component or on the annual solar gains. If you
looked at annual cooling numbers the differences observed under
diffuse or ground reflected conditions were noise compared to
differences that may arise in the simulation due to other factors ...

Regards
Graham