Technically, that's a PV output circuit conductor. Right? PV source circuits enter the combiner. A PV output circuit exits the combiner, after the source circuits are aggregated.
The basic process of sizing any dc PV power circuit is the same. As described in 690.8(B)(1) and (2), there's basically a two-step evaluation process. You use the largest minimum conductor size indicated in these two steps.
This article describes the process and includes example calculations:
Code-Compliant Conductor Sizing