When troubleshooting solar panels, there are several ways that you can check whether a solar panel is working the way it should be or not. A common issue with solar panels that is usually reported is when a solar panel is under-producing. Other issues that are also reported are delamination on the panels and "snail trails" on the panels. Physical damage to the solar panels can also be an issue that could affect the functionality of the solar panels depending on the severity of the damage.
In order to check if a solar panel is under-producing, you would need a multimeter that can measure and display DC voltage and amperage readings. Using the multimeter, you would place the positive and negative multimeter leads on the positive and negative MC4 connector ends of the solar panel wires. If the Voc and Isc values you obtain from the panel are significantly lower than the rated values on the label of the panel, then your panel is under-producing. Other tips when testing the panel using this method include tilting the panel at an angle towards direct sunlight and making sure there is no shading blocking the sunlight from the solar cells. Sometimes when there is delamination and snail trails on a panel, it may start having issues with functionality as well. After testing a solar panel with a multimeter, another way you can test to see if the panel is functioning the way it should would be to connect it to an off-grid system with a controller and battery bank, and check on the controller if the PV power, voltage, or amps being received is acceptable or not if your controller has a screen and ability to display PV input information.