As components change in various ways, how do inverters adapt?

In the photovoltaic industry, cost reduction and efficiency improvement have always been the main theme of the industry. At present, the use of large silicon wafers is mainly to reduce the system BOS cost and LCOE, which has become an industry consensus. Whether 166 or 210 will dominate the market has become a long-standing debate in the industry. However, recently, industry insiders have reappeared a new point of view - 18X silicon wafers will subvert the monocrystalline silicon wafer market, and 500W+ ultra-high power modules have become the common choice of module leaders.

The increase in module power is not a linear development trajectory. In the early days of the photovoltaic industry around 2010, module power was mostly around 200W; the power increased by 5-10W each year, and it was not until around 2017 that 300W modules were born. Starting in 2018, a variety of technical routes emerged, and module power began to increase at an annual rate of 50W-100W. At the 2018 SNEC exhibition, 400W+ modules shined; in 2019, the SNEC exhibition became a stage for 500W+ modules to compete for splendor; in May, Jinko released a new product with a maximum power of 580W, and we see that 600W+ is waving to us. From the second half of 2020 to 2021, it is speculated that 600W+ modules may lead the way.

The continuous innovation of component manufacturers and the continuous increase in power have brought replacement pressure to inverter manufacturers to a certain extent. Inverter manufacturers need to match components and keep up with the trend of component development. The power increase of components is mainly reflected in the increase of voltage and current. So what parameters need to be adjusted between components and inverters?

There are two main parameters to match between the inverter and the components: string input voltage and string input current. For example, the voltage range of the string inverter is generally between 160-1000V, and multiple components need to be connected in parallel to match the voltage of the string within the voltage range of the inverter. Therefore, it is just a voltage increase, which has no effect on the inverter. It is just a change in the number of components in series, which has little to do with the power size of a single component; so the most important thing is the input current, because the current is the same when the components are connected in series, and the size of the input current of each string of the inverter determines whether high-efficiency components can be used.

Centralized inverters only have one stage of conversion. The capacity of an MPPT is more than 500kW. If there are 20 in a string, theoretically, components with a single component power below 25kW can be compatible, so there is no high-efficiency component compatibility problem in centralized inverters. String inverters generally have a two-stage structure, with a front-stage boost and a rear-stage inverter. The current of the component affects the input current of the front-stage boost circuit of the inverter.

The current of early modules was about 8A, so the input current of the inverter was generally around 9-10A. After 2018, new module technologies exploded. Various technologies such as half-cell, shingled, tiled, bifacial, PERC, HJT, MWT, etc. can be superimposed on each other, resulting in a significant increase in module current. The operating current of a 400W module has exceeded 11A, and the short-circuit current is close to 12A. The maximum input current of each string of Growatt's products has also reached 12.5A, which can meet the requirements of high-efficiency modules currently in mass production.

If the component power exceeds 600W and the component current exceeds 15A, can the existing inverter be used? This may be the issue that everyone is most concerned about. In fact, the solution to this problem is also very simple for the inverter. Even if there is no inverter with a maximum string input current of 15A, a slight modification to the existing inverter can meet the requirement.

For example, a 30-40kW inverter has two MPPTs, and the maximum input current of each MPPT is 34A/38A, and it can connect up to 4 strings. If you connect 600W/15A components, you can change the inverter to connect up to 2 strings per MPPT, so that the maximum current of each string can reach 17A or 19A. A 30kW inverter can connect 4 channels, each with 14 600W components, so it can connect 33.6kW components. A 40kW inverter can also connect 4 channels, each with 18 600W components, so it can connect 43.2kW components.

The maximum current of the inverter input depends on the capacity of the power device of the previous stage boost circuit. The capacity of the power device is still very large. For example, the commonly used Infineon DF225R12W2H3F_B11 module is designed with 3 MPPT inputs. Each MPPT can be connected to 2 string inputs. Each input can receive 12.5A. If larger components need to be connected, the power device manufacturer can be asked to change it to 2 MPPT inputs. In this way, each input can reach 18A, which can be connected to 600W bifacial components.

As the power of single components increases, the inverter can be easily over-equipped without increasing the number of strings. For example, for a 120kW system, if 300W components are used, 400 components are required, 20 of which are connected in series, and the inverter needs 20 inputs; if 370W components are used, 324 components are required, 18 of which are connected in series, and the inverter only needs 18 inputs; if 500W components are used, 240 components are required, 16 of which are connected in series, and the inverter only needs 15 inputs.

Summarize

The development of inverter and component technology corresponds to each other and develops together. If the power of the component increases, but the inverter power does not match, the electricity generated by the component will be wasted. If the power of the inverter increases, but the power of the component does not increase, the useful amount of DC cable will definitely increase, and the DC loss will also increase. In recent years, the high-power string type used in the project market has become larger and larger, which also depends on the increase in component power. The technological progress of component manufacturers and inverter manufacturers will jointly improve the power of components and inverters, reduce the system BOS cost and LCOE, and promote the development of the industry.