Off-grid power systems must be equipped with batteries. The task of the battery is to store energy, ensure the stability of the system power, and ensure the load power consumption at night or in cloudy and rainy days.

The system can only generate electricity when there is sunlight. Usually, the power generation is the highest at noon. However, at noon, the demand for electricity is not high. Many households need the electricity at night. So we need to store up energy, this energy storage device is the battery. Wait until the peak of electricity consumption, such as seven or eight o'clock in the evening, it can release the power.

In the other hand, photovoltaic power generation is extremely unstable due to the influence of radiation. And the load is not stable, such as air conditioners and refrigerators, the starting power is very large, and the operating power is usually less. If the photovoltaic is directly loaded, the system will be unstable, and the voltage will fluctuate. The battery is a power balance device. When the photovoltaic power is greater than the load power, the controller sends the excess energy to the battery pack for storage. When the photovoltaic power cannot meet the load demand, the controller sends the battery power to the load.