Maintenance Indicators
A key indicator that your solar panels require maintenance is performance. If you have noticed an extended period of low energy production — sans any substantial seasonal changes — a cleaning, debris check, or professional inspection could be required.
Monitor and track your energy output. If your panels are still relatively new, fluctuations in output likely indicate an immediate issue that needs to be addressed.
Additionally, if you have experienced any amount of severe weather, it is a good idea to check out your solar panels regardless of productivity to ensure there is no superficial or structural damage that may compromise your system.