If you find there are issues with your system you should contact your installer and work with them to get the issue resolved. You should have an online monitoring portal available to you. This will show you the amount of energy you generate. You can use this information to verify if your system is still producing energy in the quantity it did before. Keep in mind that energy production fluctuates from day to day, month to month, and year to year based on weather conditions and other factors. Despite those fluctuations, you should see a consistent curve of energy production over time.