With a non GWR signal box or similar (by the finials) just adjacent to the shed yard and RR no 82 on shed it should be possible to work out where this is.
As a suggestion this could be outside Barry Works, looking towards the loco shed. We have never seen a similar view to compare but the bridge abutment on the right would be approximately correct for the tunnel to the docks. We have found evidence of a similar telegraph pole in the area, but on the downside there was no signal box for the finial, however, there were various other railway buildings in that area. Otherwise it would appear the locos are all dead.