摘要： The use of photovoltaic (PV) systems has increased in recent years due to the high demand for clean energy sources. PV systems can utilize abundant and free energy from the sun, which is a substantial advantage. However, compared with other renewable technologies, the PV system still faces major obstacles such as high cost and low efficiency. In addition, fluctuating incident energy from the sun creates harmonics in the generated power that might lead to undesirable system performance. Total harmonic distortion (THD) is the ratio of distorted power to the main power of the signal, and is most commonly used to indicate the amount of signal distortion. THD has become a serious concern as more PV systems are integrated into grid systems. Previous research and reviews have attempted to reduce THD and its effect, but unfortunately focused on reducing THD at individual parts of the PV system. For the first time, this study holistically and systematically reviews the advances in THD reduction techniques for the entire PV system. The causes of harmonics, current solutions, and research gaps for further investigation are described in detail. Moreover, the current THD reduction techniques used in each stage of the PV system are compared, including their main benefits and drawbacks. Finally, this study recommends the use of adaptive filters as a possible solution for THD reduction because these filters have effectively reduced noise and disturbance in other systems.