I suspect, that SDS paths have a big impact here, so here is a render with corrected glass opacity but with BiDir Metro:
(eye and light paths both set to 20)
BiDir can't do sds, even with metropolis it fails, and if we add volumes it get's even worse..
I generally don't like bidir at all, it's just terrible and slow... There are better and faster solutions and I think Dade is on a good way to getting them to luxcore
Please take into consideration, that these are transparent, translucent and reflective materials, so environment is very important here. For example the gradient of the middle glass in your image was effected from the two other next to it.
No, not really. All three glasses are directly exposed to sun so all volumes should be lit as well
Edit: ...and the color/brightness highly dependent from the background!
it only adds bounce light in your case, so things seem brighter but that's all
The only thing that really can do it currently is caustic cache (and I'm not even sure that it is doing it right either)
But no one will ever use this in production, it's pain to setup and it's slow and only God or Dade knows if it can even converge to an acceptable result in thousand years.
EDIT: I left it rendering.. and it actually looks like caustic cache is just putting caustic to the volume but still no sunlight gets through glass it seems.
I think we gonna need lighttracing+VM+transparent shadows and everything will be correct and fast.