600W+ panels are just around the corner. Are PV inverters ready?

As soon as 440W modules became mainstream, 500W+ modules emerged like mushrooms after rain. With the approach of grid parity, the power of photovoltaic modules has doubled. Before 2018, the module side basically maintained an annual increment of 5W. However, since 2019, the output power of modules has begun to grow rapidly by a multiple of 10. The superposition of new technologies is bringing the module power to 500W+ or even 600W.

There is no doubt that as the largest part of the system cost, the continuous increase in module output power has a great driving force in reducing the cost of electricity. In addition to the increase in output power brought about by the continuous improvement of module conversion efficiency, bifacial modules, tracking brackets and even over-matching will directly increase the power generation of modules.

Industry insiders told PV People that owners are becoming more and more accepting of bifacial modules. If the transportation and installation issues of large-size bifacial modules can be solved, bifacial modules may become king in the future.

But no matter what form of gain, the final result is a significant increase in the power generation of the components. As a whole power generation system, the increase in the power generation of the components of the photovoltaic power station requires the matching of the entire operating system to maximize its value, which puts higher requirements on the compatibility of supporting equipment such as inverters.

Among these, the most important is the "brain" of the photovoltaic power station - responsible for the most important inverter and "control" links of photovoltaic power generation. How the inverter matches the component upgrade from the technical end has become a key factor for design institutes to refer to when selecting, and has also become one of the most important topics for the R&D department of inverter companies.

From the perspective of photovoltaic power station design and selection, a senior expert from a design institute told us that the most important factor to consider when selecting an inverter is the specific conditions of the project site. If bifacial components are used, large-scale (centralized) inverters are generally preferred. Centralized inverters are more adaptable when matched with tracking systems, bifacial components, large-size components, etc. String inverters may not match due to external terminal parameter restrictions.

“For example, a 175kW string inverter has 9 MPPTs and a DC-side access capacity of 10A. Normally, each channel should be connected to 2 strings of components, for a total of 18 strings. According to the 10A access capacity, each string is 5A. But if each channel is connected to 3 strings, then the access capacity of each string may be only 3.5A, so each channel must be limited,” the above expert explained.

This view was also recognized by the relevant person in charge of the Electrical Department of another professional design institute. "High-power components will increase the voltage and current, and sometimes the impact of back-side gain on current increase needs to be superimposed. When selecting an inverter, designers will mainly consider the inverter's overload capacity, starting voltage, open-circuit voltage, inverter cost, and DC side incoming line circuit breaker selection."

"For centralized inverters with a 1500V DC side connection, due to the combining function of the combiner box, the power, voltage and current changes of the components have relatively little impact on them, and they have strong adaptability. However, for string inverters, since they have to adapt to the access of components of different specifications and different capacity ratios, the requirements for the number of incoming line loops vary greatly, so Y-terminal products have appeared in the market to solve the problem of DC side access," the aforementioned person in charge added.

At present, the DC input current capacity of mainstream string inverters on the market is around 12-13A. However, in response to the development of the industry, mainstream inverter manufacturers have also increased the speed of upgrading and improving the software and hardware of their products. In addition to the increase in DC input current mentioned above, it also includes the improvement of overload capacity and power factor.

From the perspective of the R&D and production of the inverter manufacturing industry, a senior inverter product manager told PV people, "The connection between the module and the inverter is mainly reflected on the DC side, specifically in terms of current and voltage. The higher the module power, the higher the corresponding voltage and current, and the inverter must also be upgraded accordingly. In addition, the safety issues caused by the increase in DC input voltage and current caused by high-power modules are also what inverter manufacturers should focus on. For example, AFCI (arc fault circuit breaker) functions should become standard in the near future."

Although the proportion of inverters in the entire photovoltaic power station system has dropped to about 2%, it must be emphasized that inverters are crucial to the operation of photovoltaic power stations throughout their life cycle. Inverter damage will not only reduce the annual power generation of photovoltaic power stations, but more importantly, it may also lead to serious safety accidents.

“Although the cost proportion of the inverter itself is relatively small in the overall power station, in the long run, a good inverter can ensure stable operation for 5-10 years, and then upgrade or replace the product. Considering only the aspects of safe operation and maintenance, the inverter technology upgrade is actually very important, which is related to the effective service life of the entire power station,” added the above product manager.

Image: Global PV inverter market exceeds $9 billion in 2019, Source: IHS Markit

In fact, looking at the history of the industry, inverter product updates and upgrades are almost the most frequent, from 1000V to 1500V, from string type to super large models, the update of inverters is to better adapt to the development of the industry. "No company can conquer the world with one inverter. If it does not upgrade or upgrades slowly, it will be eliminated by the industry." A senior inverter practitioner commented that those products that cannot adapt or are not upgraded in time are almost submerged in the torrent of industry development.

"After grid parity, the future is just the beginning." While the cost of photovoltaic power stations is continuously optimized, it will lead a new round of inverter technology innovation. At the same time, the most promising areas in the future market, such as energy storage, digital energy services, and operation management and regionalized power supply, are also inseparable from the intelligent "brain" - the energy allocation and management of the inverter. This ensures both comprehensive technological innovation and quality service, so that inverter companies can thrive in the competition.