The problem is that you can use the volumetric fog to simulate sun rays trough the clouds. It works perfectly but only in really small scales. There isnt a reason why this shoudnt work on a real scale since the resolution of the shadows and the volumetric fog still the same. Also the draw distance of 100,000,000 is just as an example in an empty scene, unfortunately it breaks much earlier in a standard game scene with lots of assets.