A PV system includes a plurality of PV strings configured to generate a string output power responsive to received solar irradiation, with a source conductor and a return conductor being provided from the PV strings. One or more DC voltage regulators are electrically connected to the PV strings on at least one of the source or return conductors, with the DC voltage regulator being configured to regulate the voltage of a respective PV string or group of strings. A controller selectively controls a voltage output by the DC voltage regulator and is programmed to periodically cause the DC voltage regulator to alter the voltage of a PV string or group of strings, detect a change in current in the respective PV string(s) responsive to the altering of the voltage, and perform at least one of a PV string degradation detection and causal diagnosis and a grounded conductor fault detection.