Over the past few months, leading module makers have been in a race to bring higher power modules to the market, raising the bar for utility-scale panel power to 500 W and more. Acknowledging the trend, TaiyangNews organized a virtual conference on the topic: 500W+ Solar Modules - How to Boost PV Panel Power to the Next Level (see TaiyangNews Virtual Conference on 500W+ Solar Modules). All leading module producers that had announced 500 W+ modules in H1/2020 took part in the event and presented details of their technologies. We are summarizing the company presentations at the event and also include the Q&A parts—here, for Risen Energy.
Risen Energy was the first company to introduce a 500 W+ module product based on a larger wafer size in Dec 2019. And only a little more than half a year later, in July 2020, the Chinese cell and module maker bettered itself by introducing a next generation 600 W module series by tweaking the previous generation design. At TaiyangNews Virtual Conference on 500W+ Solar Modules, Yafeng Liu, Senior R&D Director of Risen Energy, in addition to presenting the technicalities and key differences between the two generations of Titan module series, also discussed the roadmap to 700 W modules.
Development in brief
To provide some background, Liu first discussed the key areas that are driving module development, which are high module power, reducing module costs including materials, reducing LCOE and, last but not the least, high reliability. Module power can be increased in two ways—optical and electrical. Improvements in the transparency of glass and encapsulation materials, reflection from the rear cover such as backsheet or rear encapsulants, employing reflecting ribbons are ways to improve the optical characteristics of the modules. When it comes to improving power, the electrical resistance of module components, including cells and interconnection media, has to be reduced. Technologies such as half-cell and MBB can effectively reduce the internal resistance of the module. Bifacial is one key technology that has a considerable positive impact on lowering LCOE, "though the technology reduces the module power itself by about 10 W," according to Liu. However, bifacial technology increases the power yield of the PV system. Increasing the wafer size to improve module power is yet another important way to lower LCOE. "You can't call it a technology, but it is a product based on larger cells," emphasized Liu. Increasing the wafer size also upsurges module power. Though there are no real performance improvements with larger cells such as high efficiency, the approach is still beneficial. Larger wafers improve the productivity of manufacturing lines and, in turn, reduce costs. Of course, one could build high power modules by integrating a greater number of cells, but such a module misses on the low-cost advantage and module Voc also goes up, increasing BOS costs. Risen has incorporated all these aspects into its latest module products.
Titan G5 with 5 strings
Risen has developed two generations of high-power module products. Its first product is called Titan G5 with a power range of 490 W to 510 W and is offered in both monofacial and bifacial configurations; it is based on 5-string layout. According to Liu, the reason for finalizing on such a design was mainly to make the module series compatible with mainstream BOS, especially the string inverter. That said, the design has one shortcoming – it has a high Voc of 51 V. Risen has also evaluated half-cut cell design, which has a low Voc of 34 V. Low Voc plays a pivotal role in reducing BOS costs. According to Liu, BOS costs decrease by 0.1 US cent for a 2 V reduction in module Voc for a fixed mount system, and the benefits are even higher with trackers. The high current of 18 A in such a configuration, however, requires a special junction box and optimized inverter design, which were not ready at that time. The G5 is already in mass production and shipments have commenced from March 2020.
G6 with low voltage
Risen has addressed the aforementioned concerns with its latest Titan G6 series. The module comes in two power classes—600 W and 660 W. The major change with these modules is that they are based on the 6-string layout. And despite being ultra-high-power modules, both module series have a relatively low Voc of less than 40 V. This increases the current to 18.5 A for the 600 W module and to 20.2 A for the 660 W modules. Such modules require high current junction boxes, which are ready, according to Liu. As for inverters, Titan G6 modules have no compatibility issues with central inverters. However, the typical string inverters with 26 A are not compatible to these high current modules. According to Liu, new string inverters from leading suppliers such as Sungrow, Huawei, SMA and Ginlong have the current at MPPT increased from 26 A to 60 A.
However, both the generations of Titan series share the same module technology platform—MBB and half-cut cells. While the triple cut based G5 series uses 9 wires, the upgraded half-cut module employs 12 wires for interconnection. The company is employing a non-destructive method to slice the cells.
Benefits
Liu presented a financial analysis of the PV systems based on modules using different wafer sizes. Taking 410 W modules based on 158.75 mm as the baseline, Liu estimated that the G6 600 W module helps in reducing module costs by 9.14%, BOS cost by 4.42%, and 6.63% in total system costs, which finally leads to a decrease in LCOE by 5.56%. These savings are referring to a fixed tilt mounting system. The benefits are even higher for tracking systems where the highest savings of 12% or more is achieved in BOS savings, resulting in LCOE reduction of 9.51%.
Product and power roadmap
As an ending note, Liu presented the roadmap for product and module power. The key product developments till 2018 were dual glass, half-cell and bifacial. Modules based on larger wafers started hitting the market in 2018, increasing the power to 400 W and to 500 W in 2019. The year 2020 would see more and more of 600 W modules announcing their arrival in the market. In addition to larger wafers, high efficiency cell technologies such as HJT and TOPCon will also be introduced starting this year and will gradually be adapted to larger wafer formats. Future product developments are mainly focused on lowering LCOE, according to Liu. On this account, HJT cell technology using 210 mm wafers will be the module product of the future, underscored Liu. Historical power increase rates of 5 to 10 W per year appear measly in front of the recent rate of 60 W per year. However, according to Liu, the module power improvement will be slowed down due to module size limitations. As such, power increase will take incremental steps of 20 W per year reaching 660 W in 2021 and 700 W in 2023.
The presentation was followed by a Q&A with the conference attendees, which we have listed below (selected questions, edited & summarized):
Question: As you are investing in HJT, is our understanding correct that in 2023 you will be able to offer a 700 W module based on the larger 210 mm wafer with HJT technology?
Yafeng Liu: Yes, that is our estimation. We will be able to develop such a product in our lab by next year and we will need another year, maybe 2022, to transfer the technology to mass production. This means in 2023, the 700 W module will be in mass production. HJT still needs 2 years to be in mass production, because the power benefits of HJT hardly outweigh the manufacturing costs. In the next 2 years, the costs of HJT would decrease quickly. That's why we estimate that it takes 2 to 3 years for the final HJT+210 wafers technology to be in mass production.
Question: Have you seen any uniformity issues in deposition for HJT with these larger wafers?
Yafeng Liu: With regards to uniformity, HJT cells fare better compared to PERC. Now we are manufacturing 210 wafers with PERC. A few may say that diffusion and deposition may have uniformity issues, but we are already in mass production and have attained good cell efficiency. Uniformity is not an issue. And as for HJT, there is no diffusion process and it is only PECVD deposition. In fact, diffusion of PERC for the large cell is a bigger challenge compared with HJT CVD. So, it is rather easy to increase the wafer size with HJT compared to PERC.
Question: Going back to the roadmap slide, you referred to both HJT and TOPCon. Are you pursuing both the paths or is it just showing the next generation of cells?
Yafeng Liu: It's about the market in general. Some manufacturers and experts lean towards TOPCon, and some towards HJT. My view is that TOPCon is okay in the short term, say 2 to 3 years, if you only focus on the cell efficiency or module power. TOPCon is easy to manufacture; you can add some equipment to the existing lines and then you can manufacture TOPCon cells. So, it is also low investment. But as I said, LCOE is the most important part. HJT has the highest advantages in terms of power generation. It is about 8% higher for the same module power, which means it can reduce LCOE significantly. Now the LCOE of HJT is already comparable with PERC and TOPCon. But when HJT manufacturing costs decrease sometime in the future, LCOE with HJT would far outweigh those of any contemporary technologies.
Question: It's clear that Risen has chosen the HJT path. Will you also have TOPCon in your portfolio?
Yafeng Liu: We have both HJT and TOPCon products. HJT needs completely new lines, which means we cannot dedicate the entire manufacturing capacity for HJT, but we can upgrade the PERC capacity to TOPCon. However, the future product would be HJT, thus we will consider HJT for new capacity.
Question: How will the high voltage of HJT influence large systems?
Yafeng Liu: This is the weak point of HJT that Voc will be higher; for the 158 mm wafer-based module, the Voc is around 5 V higher vis-à-vis the normal module. For large wafers, the difference in Voc can be adjusted with product design. High Voc can also be compensated with high power.
Question: What are the benefits of the 5-string design?
Yafeng Liu: The 5-string design does not bring any direct benefits, but it is rather a design aspect of the product. We have several designs for the Titan series with 210 mm cells—half cut, triple cut, four cuts and five cuts. However, last year we could only choose the triple cut design. We could not use the half cut, because we did not have a high current junction box and string inverter at that time. So, we had no choice than to choose the triple cut with 5-string. When we use triple cut with 5-string, we can have the Voc and Isc at a level that is compatible with the existing junction box and string inverter. If we use the triple cut cell in 6-string layout, the Voc will be much higher, which reduces the number of modules that can be connected per string. That's the reason why we chose the 5-string + triple cut 210 mm cell last year. This year, we have compatible components available in the market, and thus we chose the best module design, i.e. a 6-string module with half cut and 210 mm cells.
Question: Are you using any tiling or paving technologies for reducing cell gaps?
Yafeng Liu: We are not, because we think that tiling technology has some weak points. The cells are overlapped and, consequently, production yield is lower compared with the narrow gap cells or normal gap cell strings. In our opinion, paving is also not a good technology. Taking into consideration the module power, production yield and module efficiency, we chose narrow gaps for our Titan series.
Question: Are you also thinking about moving to gallium doping?
Yafeng Liu: I cannot speak on the topic of gallium doping. Suffice to say that there are some patents in this area. What I can say is that we have a low degradation cell technology.
Question: Can you talk, in general, about your roadmap in terms of capacities – where are you heading in terms of expansion?
Yafeng Liu: Now our capacity is about 15 GW and will be over 20 GW next year. Whether it will be 20 GW or 30 GW afterwards, I cannot say now.
Question: Are the cell sizes for G6 600 W and 660 W different?
Yafeng Liu: That is correct. There are some experts that have calculated and found that the cell sizes are different. With the G6 600 W module, the wafer size as well as module size are already at the limit. However, G6 660 W has not reached its limitation and is a pilot product.
TaiyangNews: Thank you for your presentation at the TaiyangNews 500W+ Solar Module Conference.
The Risen Energy presentation of Yafeng Liu can be viewed on the TaiyangNews YouTube Channel here.