Solar is the lowest maintenance source we have, so yeah, make sure to add maintenance. (It's more expensive with batteries, but compared with diesel, it's ridiculously cheap.)
1. The inverter and other electrical systems do fail (surprisingly frequently).
2. Solar is very spread-out: maintaining a geographically large facility is not trivial (vegetation, water drainage, cables etc.)
3. Batteries also require maintenance, and are an inherent part of any independent PV installation (if the site relies on the grid, it is no longer independent).