PWM and MPPT controllers have their own unique advantages and disadvantages. The choice of the scheme depends on the design characteristics, cost and external environment of the solar photovoltaic array. When we choose, we should focus on the following factors: 1) MPPT controller is more expensive than PWM controller, however, MPPT controller has higher charging efficiency, especially in cold weather conditions. MPPT controller also supports more photovoltaic (PV) panels wired in series (high voltage differential), which is also its major advantage. In this case, the cross-sectional area of the connecting cable can be greatly reduced, thus reducing the overall cost of the system. 2) Compared with MPPT controller, the biggest disadvantage of PWM controller is efficiency. PWM charging controller can not charge the maximum power generated by photovoltaic (PV) array. Its overall efficiency is usually between 65-85%. On the other hand, MPPT controller can ensure that the solar array is always in the best operating state. In some cases, such as cold weather, the charging efficiency provided by MPPT mode is 30% higher than that of PWM mode (high charging efficiency). 3) PWM mode has mature technology, simple and reliable circuit and low price, but the utilization rate of components is low. It is suitable for small systems. The temperature range of solar charging unit is 45-75 ℃. MPPT controller is a better choice for large systems, and its higher efficiency means good economic benefits. In addition, the MPPT controller supports users to obtain the maximum power from the photovoltaic (PV) array. When there is additional power demand and the space is limited, the size of the PV array cannot be expanded, the MPPT controller has obvious advantages in this case.