The selection of inverter, first of all, must consider has enough rated capacity to meet the maximum load equipment requirements for electrical power. For a single device load inverter, the selection of rated capacity is relatively simple. When the electrical equipment is pure resistive load or power factor is greater than 0.9, the rated capacity of the inverter is 1.1~1.15 times the capacity of the electrical equipment. At the same time, the inverter should also have the ability to withstand capacitive and inductive load shocks. For general inductive loads, such as motors, refrigerators, air conditioners, washing machines and high-power pumps, when starting, the instantaneous power may be 5~6 times the rated power. At this time, the inverter will withstand great instantaneous surge. For such systems, the rated capacity of the inverter should be sufficient to ensure that the load can start reliably. The high-performance inverter can start continuously multiple full load without damaging the power device. For their own safety, small inverters sometimes need to adopt soft start or current-limiting start. In addition, the inverter also has a certain overload capacity. When the input voltage and output power are rated values and the ambient temperature is 25 °C, the continuous and reliable working time of the inverter should not be less than 4h. When the input voltage is the rated value and the output power is 125% of the rated value, the safe working time of the inverter should not be less than 1 min ; when the input voltage is the rated value and the output power is 150% of the rated value, the safe working time of the inverter should not be less than 10s.

Application example : 
In the photovoltaic system, the main load is 150W refrigerator, and the AC inverter with rated capacity of 180W can work reliably when it works normally. However, because the refrigerator is an inductive load, its power consumption can reach as much as 5~6 times of the rated power at the starting moment. Therefore, the output power of the inverter can reach 800W when the load starts. Considering the overload capacity of the inverter, 500W inverter can work reliably. When there are multiple loads in the system, the selection of inverter capacity should also consider the possibility of several electrical loads working at the same time, namely, “ load simultaneous coefficient ”.