Solar panels are a relatively care-free investment but it's better to clean them every once in a while — the frequency depends on the area where you live. When panels are installed on the roof, rain more or less takes care of them, but eventually they'll need a proper cleaning anyway. When panels are on the ground, debris and dirt are much more of a nuisance and it's almost mandatory to clean them at least once a year or it results in a decrease of efficiency. Monitoring system lets you know when it's time for a scrub — if the efficiency of panels dropped, the dirt or fallen leaves are the most obvious reason. Again, solar panels don't like thick layers of snow on them — not only does it decrease the amount of sunlight they are able to receive at the given time, it increases the rate of degradation. If snow doesn't slide off the panels, you have to clean them yourself or call for a special service. If you want to learn more about cleaning solar panels, here is another article for you
Keep in mind that while solar panels themselves last for a long time, other components of the system might want a replacement much sooner. An inverter, for example, can last for 10-15 years and the lifespan of some models can exceed 20 years. Solar charge controllers also work reliably for 15 years on average. The life of a battery, however, highly depends on its properties and maintenance, and might serve you from a decade to several months.