1. Classification of the solar inverters.
Inverters can be divided into two categories: 1. Off-grid Inverters 2. On-grid Inverters (mainly used to generate electricity for the State Grid’s use).

2. Off-grid inverters can be classified into: 1. High frequency inverters 2. Low / power frequency inverters.
(1) Compared with power frequency, high frequency inverters have the advantages of small size, light weight and low price. At present, high frequency inverters are the mainstream in the market.
(2) Advantages of power frequency inverters: They are mainly used in industrial power supply, standby power supply. Compared with high frequency, the low/power frequency inverter is more stable in places where the using conditions are bad. At present, the use of power frequency is relatively stable.

3. Off-grid inverters can be divided into: 1. Pure sine wave inverters 2. Modified sine wave (square wave) inverters.
(1) The specific difference between the application of pure sine wave and modified wave is shown in the appendix (1).
Summary: (1) Ac output by pure sinusoidal is of the same high quality as that by grid power, so it is suitable for any load with a wide range of use, meanwhile there is no damage to any load of electrical appliance.
(2) The output of modified wave is still rectangular wave, which can not completely normally drive non-resistive load and will cause abnormal inductive and capacitive load, such as no start-up, high heat, abnormal noise, over-current, breakdown, etc., and even may burn down the inverter or load. Long-term use will cause damage to electrical equipment, so considering low cost, some common resistive load can use modified wave inverters.