Solar panels have more than 25 years guarantee or lifespan, but users should know that occasionally they need cleaning, dust and other environmental occurrences can dirty the surface of the panels thereby reducing their total power output.

Solar panels surfaces are water resistant and should be cleaned with detergent & cloth like once during raining seasons and repeatedly during dry and dusty seasons(the surface of the panels should be inspected regularly during the dry season and clean immediately)

On the roof, pv rails with bolts and nuts 

are used to hold firmly the solar panels depending on the customers demand (some customers don't want any nail or screw drilled to their zinc) and in this case binding wires can be used; so like once after two or three years replace these binding wires or the bolts and nuts and possibly the pv rails and too.

The DC wires from PV to where the system is should be checked especially where they are used to connect the panels together to parallel or series connections. If mc4 connectors, they should be examined too for lusting and loose connections between the male and female connectors

The battery should be check also, seal lead acid, gel or lithium batteries don't need maintenance but make sure they aren't place directly on top of cement or tiled floors and they are placed in a well ventilated area away from heat or sunshine or too much cold, normal room temperature should be maintained but tubular batteries require MAINTENANCE, distilled water should be topped  with six months interval or using the guage on them below

Watch the below video to see more reason why you should clean and maintain your solar system.