**(1) Power selection principle of off-grid inverter**The power selection of off-grid inverters is mainly considered from the following aspects:

1) When the load is working continuously, the maximum load should consider the load power factor.

2) For the inductive load, the maximum power of the load at the moment of starting should be considered.

3) The rated power of the inverter should exceed 15%~20% of the maximum load value during continuous operation to prevent insufficient power caused by increased load. At the same time, the inverter should also provide suitable overload capacity. The overload capacity of domestic inverters is 150%, not more than 2s. The overload capacity of imported inverters is 250% to 300%, no more than 5s.

Example 1 A family uses loads such as 160W light bulbs, 100W refrigerators, and 120W TVs. When the three loads work normally at the same time, the total power is close to 400W. It works for 6-8 hours a day, and the average power factor is 0.85. The refrigerator needs 8 to 10 times the rated power to start. , TV starting needs twice the rated power, the overload capacity of ordinary inverter is 150%, not more than 2s. Please select an inverter.

Solution: The maximum load power during continuous operation is 400W/0.85=470V·A

100W refrigerator needs at least 100W x 10=1000W to start alone

Therefore, if the three loads do not start at the same time, just select the inverter: 1000W/150%=700W

If the three loads are started at the same time, the total starting power is 100w x10 + 120Wx2 + 160W = 1400W.

Need to choose inverter (W): 1400W/150% = 1000w or choose capacity inverter (V.A): 1000W/0.85 =1176V .A

W is the active power unit, kV.·A, V·A apparent power unit.

**(2) The power consumption of the off-grid inverter itself**The power consumption of the off-grid inverter itself is the most critical factor in determining the efficiency of the system. The power consumption of the inverter itself is constant. The national standard requires that the power consumption of the inverter itself is not allowed to exceed 3% of the rated power. The domestic inverter does not have a standby mode, which means that the domestic inverter generates its own power consumption 24h.

**(3) Influence of load on inverter**The inverter efficiency of the inverter changes with the change of the load. When selecting, the inverter efficiency corresponding to the long-term operating point of the load can be considered, and the load fluctuation is very large. When the household output is small (long-term operation), the inverter is inverting. device efficiency.

**(4) Other factors to consider**Including precise discharge management of batteries, management of access to diesel engines or external power grids, and load priority management, etc.