The maintenance of a solar installation concerns essentially the panels and the batteries.
In regard to the panels: Photovoltaic panels do not require major maintenance apart from cleaning of the surface. A photovoltaic cell exposed to unobstructed sunlight will more likely reach high efficiency performance figures.
In regard to the batteries: an annual maintenance may be necessary depending on the battery technology used. Some specific types of lead acid batteries may require an electrolyte refill, while the majority of lead acid and lithium ion batteries commonly used for solar applications is maintenance free.