I've been testing the amazing HDRI time-lapse image sequences that are under development by the folks at
and I am loving them.
Every Arch Viz pro out there has had to do a visual sun study, and though they can be done to convey not just realistic expectations of insolation, shading and shadow forms and motion, they often feel very… stark.
By using these HDRI sky time lapses, and using them as the IBL as well as the backdrop, you get intensely realistic lighting, and due to the real world changes in conditions due to ephemeral clouds passing, and the variation in shadow sharpness that this engenders, you end up with a much more emotive visual.
I threw this beta of one of their HDRI timelapses into a test file I created some time back, and here's what the result looks like.