Solar panels are configured with batteries to maintain the number of days, usually the number of days that can be maintained by the battery's power supply without the PV array power supply.
In general, the determination of the number of days a solar panel is maintained is related to two factors: the degree to which the load is required for the power supply and the longest number of rainy days in which the PV system is installed. Generally, the maximum number of rainy days in the installation location of the PV system can be used as a reference for the number of days of maintenance used in the system design, but the load requirements for the power supply should be considered. For photovoltaic applications where the load is not very good for power supply, the number of days to be maintained in the design is 3 to 5 days. For photovoltaic systems with strict load requirements, the number of days in the design is usually 7 to 12 days. The so-called system with less stringent load requirements usually means that the user can adjust the load demand slightly to adapt to the inconvenience caused by bad weather. A system that requires strict requirements refers to the use of electrical loads, which are important for stopping power supply, such as military, communications, navigation, or important health facilities such as hospitals and clinics. In addition, consider where the PV system is installed. If you are in a remote area, you must design a larger battery capacity because maintenance personnel will take longer to reach the site.