After a solar PV system is installed very very little is ever needed in
maintenance. In fact if you have a grid tied system that has no batteries,
you essentially have a system with no moving parts and no maintenance.
If you have batteries then you add some maintenance expenses as
batteries will need replacement periodically but still we are talking about
no moving parts and low maintenance. So basically the only aspect of
the system that you should assume will need replacement is the
inverters. They may need to be replace in 15 years at a cost of a few
thousand dollars, but that would be about it.