Increasing module power using larger wafers has become a very important and prominent trend in today's PV business. With the introduction of its new Hi-MO 5 module series with 540 W output, leading vertically integrated PV manufacturer LONGi Solar has officially joined the 500W+ league. Hongbin Fang, director of Product Marketing and Chang Liu, product strategy director at LONGi Solar talked to TaiyangNews, to explain background, competitive advantages and product positioning of the new Hi-MO 5 module series.
TaiyangNews: Now, module makers are increasingly showing interest to come out with 500+ W module products, even LONGi just came out with one. What is the motivation behind the industry going after this power rush?
LONGi: When you are in the module manufacturing business, it is like you are in a race to facilitate our customers to attain the lowest LCOE. We have been in this race for 10 to 20 years following different approaches. Previously, we were focusing on improving the cell efficiency and improving cell packing densities. This may not continue for long as PERC cell production efficiencies are at 22.5% to 23%. That means it is getting closer to the limit. In the last few years, the industry has proven that not only improving efficiency, but increasing power by increasing module size also brings tremendous value to customers, especially in reducing BOS costs.
For example, compared to our previous Hi-MO 3 series that had a rated power of 380 W to 385 W, last year we launched Hi-MO 4, which is based on M6 wafers; the module power jumped to 430 W to 450 W. This is an about 15% increase in rated power. Though the module size grows proportionately, such a shift still enables significant BOS cost savings.
At the same time, there are several associated questions, one of which is what the optimal size is? At LONGi, we have broader visibility – from the manufacturing of single wafers, to cell, module and system integration. We even take factors like logistics (module transportation) into consideration. If you look at the historical development at LONGi, we started with monocrystalline wafers, went to PERC, implemented half-cell, then M6. So, all this due diligence went into the design of Hi-MO 5.
TaiyangNews: Can you explain more about Hi-MO 5?
LONGi: The Hi-MO 5 module is a series of ultra-high-power modules designed by LONGi for large utility PV projects, with a maximum power of 540 W and an efficiency of 21.1%. The series comes in both monofacial and bifacial variants. This is the result of several developments and innovations for wafers, cells and modules. Starting at the wafer level, the Hi-MO 5 is built with M10, 182 mm wafer format. LONGi has played an instrumental role in the process of proposing this M10 wafer format as the standard by a group of 7 leading solar cell and module manufacturing companies. Gallium doping technology is incorporated into the p-PERC cells that are used for this module series, minimizing if not eradicating LID. As for the innovations at module level, Hi-MO 5 features 9 busbars, half cells and "Smart Soldering" technology to improve efficiency and reliability. The module maintains the original 6-row, 144 half-cell design. Hi-MO 5 modules maintain the same Voc as Hi-MO 4, thus the same string length is attained. With 20% higher power per module, the power output per string increases by 20%, thereby enabling significant reduction in both electrical and mechanical BOS costs, as well as installation labor costs.
TaiyangNews: What is the background for selecting 182 mm as wafer size?
LONGi: Hi-MO 5 is based on the new standard M10 wafers with dimensions of 182 mm x 182 mm. As for the reason for opting for this particular size, LONGi analyzed the boundary conditions in ingot/wafer/cell/module manufacturing and module deployment processes. One of the practical real-world limits on further increase of a module size is the height of the standard 40 feet HC shipping container used in global logistics. This limits the width of the module to about 1.13 m. With a 6-row cell design, the optimal size of the silicon wafer is 182 mm.
TaiyangNews: What is LONGi's Smart Soldering technology? What are its advantages?
LONGi: LONGi's 'Smart Soldering' includes two technologies working in tandem: "Integrated segmented ribbon" and "Micro-gap" cell technologies. The triangular section of the ribbon maximizes capture of incident light, while the flat section enables the micro-gap connection of cells (cell spacing is reduced by more than 2/3). Smart soldering increases module efficiency by 0.3% compared with conventional multi-busbar modules, while reducing the tensile stress of the cell by 20% for long-term reliability.
TaiyangNews: What is the difference between Smart Soldering and the existing Stitch Soldering technology in the market?
LONGi: The typical MBB uses circular wires for interconnection of cells. During the soldering process, the soldering wires are locally flattened at overlapping areas in a way that the connection of cells is a sandwich structure of 'cell-flattened connecting media-cell'. Smart Soldering technology uses the flat section of the integrated segmented ribbon to achieve micro-gap interconnections. The tensile stress of the cell is significantly lower than that of conventional modules. Smart soldering technology deliver modules of higher efficiency, better reliability, better mass production stability and yield.
TaiyangNews: What is the product positioning of Hi-MO 5?
LONGi: Hi-MO 5 is designed for ultra-large power plants worldwide and the bifacial variant is the lead product. Hi-MO 5 is expected to account for 30% of LONGi's shipment in 2021, while the balance would be Hi-MO 4, which continues to be a prominent part of LONGi's product portfolio.
TaiyangNews: As you know there are also high power modules from other suppliers that are based on 210 mm wafer formats; what are the advantages of Hi-MO 5 over such products?
LONGi: First, at LONGi we don't agree that "the bigger the better." As a matter of fact, we have also carefully evaluated the 210 mm size. We made an incredibly detailed technology analysis for 210 mm wafer all along the value chain – production lines from ingots, wafers, cells and modules. We found that moving to 210 mm would require dramatic changes on manufacturing equipment and process, with significantly higher capital investment. The 210 mm technology is not yet mature, and we believe that instead of just increasing the wafer size to 182 mm, there is untapped potential to increase the module power and efficiency. This is also reflected in Hi-Mo 5.
The primary advantage of Hi-MO 5 is the reduction in BOS cost due to its power, efficiency and electrical characteristics. Hi-MO 5 can reduce BOS cost by $0.005 to $0.01 per W compared with the 500W module using 210 mm wafers. The 1/3 cut cells increase the risk of damaged surfaces and micro cracks, as well as cell mismatch. Last but not the least, Hi-MO 5 has a beautiful symmetrical 6-row design while the module using 1/3 cells based on 210 mm wafer has an asymmetrical 5-row design, which requires extra interconnect ribbon compromising on cost and module layout.
TaiyangNews: What are the advantages of Hi-MO5 on the application side of the system?
LONGi: On the application side, Hi-MO 5 offers significant advantages as well. Starting from logistics, Hi-MO 5 is designed to maximize on container space utilization, thus lowering transportation cost. More significant advantages of Hi-MO 5 modules are from BOS cost savings. As open circuit voltage is maintained consistent with conventional modules, same string length can be attained with Hi-MO 5 modules. With a significantly higher power rating (530 W to 540 W) of each Hi-MO 5 module, the power per string is proportionately higher. This enables significant savings on both electrical and mechanical BOS costs, as well as installation labor.
TaiyangNews: What is LONGi's technology roadmap?
LONGi: Our technology direction is based on how we bring better value to our customers, meaning lower BOS and LCOE. Based on thorough evaluation across the value and supply chain, we went a step forward from M6 to M10. We will continue to develop new technologies to improve cell and module efficiency, not only the wafer size.
TaiyangNews: Thank you for the interview.
Longi Solar will present the latest on its new HI-MO 5 panel during TaiyangNews' Virtual Conference on 500W+ Solar Modules on July 29 & 30, 2020. Longi Solar VP and Head of Mouldes Jun Lv will participate in the Exec Panel on July 30. Registrations free here.