At present, there are many models of inverters on the market. In order to simplify management and explore the advantages of centralized procurement, many EPC manufacturers often use limited inverter models to do as many field designs as possible, which will inevitably involve the reduction of inverters. Content usage issues. A small reduction in capacity is not a big problem; but a large reduction in capacity will not only waste the cost of the inverter, but also fail to obtain the ideal power generation.
1. Waste of resources
To give a simple example, if a 10kW solar inverter is originally used to carry a 6kW photovoltaic module, it means that the inverter only uses 60% of the workload, which will inevitably lead to waste of resources after a long time, which is not conducive to the overall cost of electricity ( LCOE) optimization. Of course, small cases are fine, but if it is a MW-level large case, waste cannot be ignored.
2. Shorten the string length and reduce the overall power generation
1. Not conducive to string optimization design
For an solar inverter of a certain power level, the number of DC input terminals is closely related to the rated power of its MPPT module. If the power of a 10kW MPPT module is to be derated to 6kW, the length of the module string will be shortened to 60% of the original, and the string is open. , The operating voltage is also reduced to 60% of the original, obviously this is not the optimal design!
2. It is not conducive to the efficient operation of the inverter
As mentioned above, with the open circuit of the string and the operating voltage reduced to 60% of the original, the use of derating will have a significant impact on the working behavior of the inverter.
Impact on the start-up and shutdown time of the inverter: After the string voltage is lowered, the start-up time of the inverter in the morning will be delayed, and the time for shutdown in the evening will be advanced, the daily power generation time will be shortened, and the power generation will be reduced!
Impact on the working mode of the inverter: The string inverter is composed of two stages of power conversion units, the front stage DC/DC realizes the MPPT function, and the latter stage DC/AC realizes the inverter function. Among them, the front-stage DC/DC is implemented by a boost topology (boost architecture), and its working time is determined by the input voltage of the string. It works when the input voltage is lower than the set value, and stops working when the input voltage is higher than the set value. . After the string voltage decreases, the working time of the DC/DC module increases, and the average conversion efficiency of the inverter decreases, 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 input voltage of the string. The advantage is to reduce the number of inverters used, and at the same time, the inverter will work in a light-load state for a long time, and its life will be extended to a certain extent; the disadvantage is that the use of reduced capacity will not only waste inverter resources, but also not conducive to inverter Work more efficiently, resulting in lower overall power generation!