Monitoring systems are essential to maintain optimal performance of photovoltaic (PV) systems. A critical aspect in such monitoring systems is the fault diagnosis technique being used. The role of a fault detection and diagnosis technique is to identify the causes affecting the real-time energy production and/or smooth functioning of PV systems. Over the past decade, various fault detection methods were reported in literature. Among all the fault detection techniques reported, some paid significant attention only on faults that occur in the PV system, some on faults on DC side of the PV system while the rest focused on AC side faults. For the first time, this paper provides a comprehensive review of popular fault detection techniques, addressing all major types of faults in PV systems. Detailed insights of PV fault detection techniques along with their relative performances are covered. A new fault detection technique is also proposed to identify the type and location (module level) of a fault. This review enables the reader to get acquaintance with major aspects/considerations in developing/choosing an effective yet viable fault detection technique for small and medium scale PV systems.