Residential installations used to be high voltage, of up to 600VDC. Panels are wired in strings of perhaps 10 panels each, which then feed a string converter. Some converters have an electronic arc fault detector to shut down when an intermittent irregular current is detected.
Modern residential installations now use microinverters. Each panel is fitted with its own inverter, and the trunk is now AC instead of DC. This eliminates the hazard of DC arcing. And failure of a cell in a panel simply reduces that panel output.
Commercial installations use infrared camera to visually inspect each panel for hotspots caused by an individual cell getting weak. Large utility-scale installations do the survey with drones.