> Usually the exposed metallic parts will be “grounded” (bonded to the ground / protective earth / equipment grounding conductor / whatever your jurisdiction calls it at the inverter).

It’s not usually, all of the panels and also the metal racking must be bonded and grounded.

Supplementary grounds are allowed by the NEC, article 250.54

There are zero requirements for supplemental grounds, you could use a single 24AWG conductor bonded to a brad nail or a #6 bare copper conductor bonded to (3) 5/8” dia’ 10’ ground rods. The fact that there are no requirements should tell you something about the necessity of supplemental grounds.

> 250.54 Auxiliary Grounding Electrodes. One or more grounding electrodes shall be permitted to be connected to the equipment grounding conductors specified in 250.118 and shall not be required to comply with the electrode bonding requirements of 250.50 or 250.53(C) or the resistance requirements of 250.53(A)(2) Exception, but the earth shall not be used as an effective ground-fault current path as specified in 250.4(A)(5) and 250.4(B)(4).