<p>Solar photovoltaic (PV) systems play a vital role in sustainable energy generation; however, their reliability and performance are often challenged by various operational issues. Traditional monitoring methods frequently fail to detect many of these problems, leading to reduced energy output and increased safety risks. Therefore, intelligent, accurate and reliable fault detection and diagnostic techniques are essential to ensure system dependability and optimize power generation. PV system failures are broadly categorized into electrical, physical and environmental types. Electrical effects such as temperature fluctuations, dust accumulation, snow and partial shading cause mismatch losses and overall performance deterioration. Physical defects, including cell cracks, delamination, corrosion, discoloration and hotspots, result from structural or material degradation and can irreparably damage PV modules. Electrical faults significantly impact system safety and functionality, with DC-side faults including open-circuit, short-circuit, line-to-line, ground faults, arc faults and reverse current flow. AC-side issues involve inverter failures, synchronization errors and abnormal voltage variations. Additionally, defects in protective components like bypass diodes and fuses reduce power output and increase fire risks. A fault is able to be acute, chronic, temporary or permanent, depending on their duration and impact. Timely and accurate detection of these faults is crucial to maintain the reliability, safety and efficiency of PV installations. Therefore, this review mainly focuses on the identification, classification, diagnosis and protection of faults in PV systems, with particular emphasis on recent intelligent fault detection techniques.</p>