A well-installed solar system should require very little maintenance over its expected 25 plus year lifetime. The main reason is that solar systems have no moving parts that wear out over time. Second, solar panels use tempered glass and anodized aluminum, typically rated to withstand hurricane force winds and large hail storms, which is better than most windows.
In addition, Tier-1 panel manufacturers typically provide warranties of 25 years (we strongly recommend not purchasing solar panels from non-mainstream manufacturers).
It is important to note, however, that solar panel do degrade over time which impacts electricity production levels. The industry rule of thumb is that a solar panel's output will decrease by 0.5% per year, which means that even after 20 years a panel will still produce about 80% of the amount electricity it generated when new. Some manufacturers claim lower degradation levels.
The other important expense to consider is the inverter or micro inverter which converts the direct current from the solar panels to alternating current that comes out of a typical wall outlet. Inverters usually have a warranty of about 10 years. Micro Inverters typically have a warranty of about 20 years. String inverters typically need replacement after 10 to 15 years.
In terms of performance, there are online services available to help you keep track of energy output and other essential details, including sending email or text alerts to make you aware of any system performance problems.