Free-air PV source circuit conductors are different. Once you are in conduit, there isn't a necessarily difference. Although, a lot of commercial PV systems will need 1,000-volt rated wire.
The difference isn't the conductor. The difference is the application. And if you study failures in PV systems, like the author of article I referenced earlier, you start to see trends. These failure trends result in Code changes, among other things. (In fact, Bill Brooks, who wrote that article, is on CMP-4, which is responsible for Articles 690 and 705; he's also on Mike Holt's videos.)
On these giant rooftop systems, there are a lot of opportunities for conductor damage. One of the things that contributes to damage is differential expansion and contraction. The expansion characteristics for copper or aluminum conductors are different than for metal conduit. In practice, this movement can chew through conductor insulation. This is why a lot of commercial rooftop systems are deployed using cable tray. This practice reduces field failures.