Is this a code inspected application? If it is then no, ground needs to be factory colored the correct color (as stated anbove) and cannot be recoded as green/ground unless size 4AWG or above.
NEC answer:
Yes, if you remove all of the insulation from it.
But, I wouldn't recommend it.
Save your PV wire for future PV wire needs.
A properly sized green insulated EGC is going to be less expensive.