Solar photovoltaic has been developed and promoted globally, and the use of inverters in solar photovoltaic power plants is particularly important. Since the derating of different brands of inverters is also different, the use of small-scale derating is not a big problem. However, the large-scale derating will not only result in waste of inverter cost, but also cannot obtain the ideal power generation, and it is not conducive to the long-term use of resistors and shunts. The specific impact is as follows:


First, the impact of inverter start-up and downtime

After the string voltage is reduced, the time for the inverter to start in the morning is pushed back, the time for shutting down in the evening is advanced, the daily power generation time is shortened, and the power generation is reduced! This is a direct result of power transmission loss and a certain economic loss for the power plant.


Second, the impact on the operating mode of the inverter

The string inverter consists of two stages of power conversion units. The front stage DC/DC implements the MPPT function, and the rear stage DC/AC implements the inverter function. Among them, the pre-stage DC/DC is realized by the boost topology, and its working time is determined by the string input voltage level.When the input voltage is lower than the set value, it works. When the input voltage is higher than the set value, it stops. After the string voltage is reduced, the DC/DC module operating time is increased, and the working time of the built-in resistor and the shunt is also lengthened, which also causes the average conversion efficiency of the inverter to decrease, resulting in a decrease in the overall power generation. 


 It can be seen that the derating of the inverter is realized at the cost of shortening the string length and reducing the string input voltage. The advantage is that the inverter is used in a reduced size, and the inverter is operated in a light load state for a long time, and its life is also prolonged; the disadvantage is that derating use not only wastes inverter resources, but also not conducive to the more efficient operation of the precision resistors and shunts in the inverter, resulting in a reduction in overall power generation!