How to design an off-grid system?

The photovoltaic off-grid power generation system mainly consists of six parts: solar panels, brackets, solar controllers, off-grid inverters, batteries, and distribution boxes. After the solar cell module is connected to the solar controller, it first meets the user's load, and then stores the remaining power in the battery for use at night and on rainy days. When the battery is dead, most inverters can also support commercial power input (or a diesel generator) as a supplementary energy source to power the load.

The design of photovoltaic off-grid systems is different from the design of grid-connected power generation systems. It needs to consider the user's load size, daily power consumption, local climate conditions, and other factors. It is relatively complicated to choose different design solutions based on the actual needs of customers. To ensure the reliable operation of the off-grid system, it is necessary to conduct a preliminary customer demand survey. The design of photovoltaic off-grid systems mainly includes inverter selection, solar panel capacity design, and battery capacity design.

Inverter selection: Determine the inverter power according to the user load size and type

The selection of inverter power is generally no less than the total power of the load. However, considering the service life and subsequent expansion of the inverter, it is recommended to reserve a certain margin for the inverter power, generally 1.2~1.5 of the load power. times. In addition, if the load includes motor inductive loads similar to refrigerators, air conditioners, water pumps, range hoods, etc. (the starting power of the motor is 3 to 5 times the rated power). The starting power of the load should be considered, that is, the starting power of the load should be less than the maximum impact power of the inverter. The following is the calculation formula for frequency converter power selection for design reference.

Determination of component capacity: Determine component capacity based on the user’s daily power consumption and light intensity

Part of the electricity generated by the photovoltaic modules during the day is supplied to the load, while the remainder is used to charge the battery. At night or when there is insufficient solar radiation, the electrical energy stored in the battery will be released to the load for use. It can be seen that the electricity consumed by the load comes from the electricity generated by the photovoltaic modules during the day without commercial electricity/or diesel engines as supplementary energy. Considering that the light intensity is different in different regions and seasons, to ensure the reliable operation of the system, the capacity design of the photovoltaic panels should also meet the needs of the worst light season.

Determination of battery capacity: Determine battery capacity based on nighttime power consumption or backup time

The battery of the photovoltaic off-grid system is mainly used for energy storage to ensure that the load can still work normally when the solar radiation is insufficient. For photovoltaic off-grid systems with important loads, the design of battery capacity needs to take into account the local maximum rainy days. Ordinary photovoltaic off-grid systems do not require high-load power supplies. Considering the cost of the system, load usage can be adjusted based on actual light intensity rather than rainy weather.