The photovoltaic off-grid power generation system has the advantages of flexibility, strong applicability, and low construction cost. It is very suitable for use in areas with unstable power.

　　When designing a photovoltaic off-grid power generation system, it must be handled flexibly and not stuck to a certain fixed formula. The following are the four principles for designing photovoltaic off-grid power generation systems:

　　1. Confirm the power of the inverter according to the user's load type and power

　　Loads are generally divided into inductive loads and resistive loads. Loads with motors such as washing machines, air conditioners, and range hoods are inductive loads. Lighting lamps, heating elements, etc. are resistive loads.

　　The starting power of the inductive load is 5-7 times the rated power, and the starting power of the resistive load is equal to the rated power.

　　When calculating the power of the inverter, the starting power of these loads needs to be taken into consideration.

　　For ordinary households, considering that all loads cannot be turned on at the same time, the sum of the load power can be multiplied by a coefficient of 0.6-0.9.

　　2. Confirm the power of photovoltaic modules according to the user's daily power consumption

　　The design principle of photovoltaic modules is to meet the average weather conditions, the annual power generation should be equal to the user's annual power consumption.

　　Photovoltaic module design needs to be in the worst season, and energy storage batteries can basically be fully charged every day.

　　However, in some areas, the illuminance in the worst season is far below the annual average. If the formula design is rigidly applied, the annual power generation will be seriously exceeded, and eventually waste.

　　3. Consider the efficiency of the controller, the loss of the machine and the loss of the battery

　　There are two types of solar controllers: PWM and MPPT. The efficiency of the PWM controller is about 85% and the input voltage range is relatively narrow, but the price is relatively low. The efficiency of the MPPT controller is about 95% and the price is relatively high.

　　Lead-acid batteries will also have 10-15% loss during charging and discharging, while lithium batteries can be controlled within 3%.

　　The power available for off-grid systems = total component power * average solar power generation hours * controller efficiency * battery efficiency.

　　4. Determine the capacity of the energy storage battery according to the user's night power consumption or expected standby time

　　Battery design capacity = (load daily average power consumption * number of consecutive cloudy and rainy days) ÷ battery discharge depth.

　　For general loads, such as solar street lights, it can be selected based on experience or needs within 2 to 3 rainy days. Important loads such as communication, navigation, hospital treatment, etc. are selected within 3-7 rainy days. If you are in a remote place, the battery capacity should be designed to be larger, because it takes a long time for maintenance personnel to arrive on site.

　　In the photovoltaic power generation system, if all lead-acid batteries are used, the discharge depth is generally between 0.5-0.7; if the lithium iron phosphate battery is used, the discharge depth is generally between 0.8-0.9.