The surge in renewable electricity generation using photovoltaic (PV) systems was accompanied by an increased awareness of the fault conditions developing during the operational lifetime. Fault detection, diagnostics, and prognostics are such efforts to detect and classify a fault so the system operational expectations can be managed. Trending of the faults and prognostics also aid to evaluate expected remaining useful life so that mitigation actions can be evaluated and implemented. This paper aims to review the state of the art and practice of prognostics and health management (PHM) for the DC side of PV systems. Following a review of the PV industry current status, the study describes and classifies the different failure modes. Next, it summarizes the PV faults detection, diagnostics and prognostics approaches. A review of the PHM applications for PV systems paves the way to emphasize the key research gaps and challenges in the current practice. The available opportunities are also highlighted through a comprehensive understanding of the PV systems current performance, from where scholars and decision makers can integrate improvement strategies with promising directions for future research and practices.