Typically, solar thermal systems need valves replaced every 3-5 years and storage tanks replaced every 10 years. Collector life is usually in excess of 15 years. This assumes "good" water quality is used in your system, and it was properly installed.
Solar electric (PV) systems typically do not require maintenance, other than periodic cleaning of the solar panels. PV panel life is typically 25 years. If you have a battery system, the bateries may require periodic maintenance such as "equalization" or water topping off.
Go to www.solar-estimate.org