Against the background of global trend towards grid parity, the upgrading of solar wafer size from 156.78mm to larger sizes — including 158.75mm, 166mm, or even 210mm — has become a controversial topic in the PV industry. Top module and cell suppliers, including Jinko, JA Solar, Trina Solar and Aiko Solar, have retrofitted their in-house cell production lines to be compatible with the full square mono 158.75mm wafers, while Longi and Zhonghuan promote 166mm and 210mm wafers respectively. As the solar industry moves to adopt the larger wafers, no consensus has been reached between the producers on wafer sizes.
PVInfolink predicts that “158.75 modules” (modules with full square mono 158.75mm cells) will dominate the market in the first half of 2020, and the market is expected to see an increase of “166 modules” (modules with 166mm cells) in the second half of 2020 when Longi, Canadian Solar, Risen Energy put 166 products into mass production. However, it is still unclear whether or not more producers will follow suit. Industry estimates that the market share of 158.75 modules could reach 60%, and M2(156.75mm) series are expected to exit the market within three years.
Why can modules with full square mono 158.75mm cells dominate the market in 2020?
According to Zhiyu Zhang, an analyst from Solarwit, “Module with full square mono 158.75mm cells is bound to dominate the market with the constant declining crystal growth techniques cost, making the benefits outweigh costs while shifting pseudo-square wafer to full square wafer. Full square wafers fit the PV module in an optimal way and raise the conversion efficiency significantly.” Zhang added that the 158.75mm square wafer is 3.14% larger than M2, and increases the power of the same-size cell by around 0.15W. In other words, with little change to the size of modules, the 158.75mm wafers raise the power of conventional 60-cell modules from 310W to 320W, and enable 72-cell modules to reach 410W.
In summary, module with full square mono 158.75mm cells has a larger light receiving area and higher power with very little incremental cost.
Industry experts concur that the increase of wafer size is an inevitable trend, but an excessive increase in the size would exert great pressure on manufacturers. When compared to larger sizes of 166mm and 210mm, moderate retrofitting is required to current production lines to be compatible with 158.75mm products. For cell production, adjustments are mainly made in automation equipment and fixtures, the cost of which is rather low when shared equally in cost per watt; for modules, all changes are made in the carrier and welding segments of the production line, and the size of auxiliary materials including EVA, back sheet and glass will increase.
In contrast, the cost to retrofit the production line to be compatible with 166mm is much higher, as a part of the process needs new equipment. Cell production requires updating of the automation equipment, and purchasing of new tubular PECVD equipment and auxiliary equipment.
For the production of 166 modules, machines for series welding, stitch welding, laminating, framing need to be replaced, and the assembly line need to be upgraded and retrofitted. Data from PVInfolink shows that the retrofitting cost of 166mm cells and modules is 2-3 times higher than that of the 158.75mm. As such, that explains why Longi and its downstream cell factories are the only producers of 166mm products at present.
In addition, solar manufacturers face more challenges during the mass production of 166mm and 210mm wafers and cells, including (i) higher breakage rate during the wafer slicing process; (ii) higher risks of wafer distortion; (iii) wafer cohesion in neighboring quartz boats in the diffusion process; and (iv) lower cell efficiency caused by uneven surfaces during the texturing and coating processes. Although the yield of 166mm production line can be improved through retrofitting, it would result in a loss of 20% if it’s upgraded from a production line of 156.75mm products.
With the analysis of the pros and cons of the technologies, the market seems to be moving forward with 158.75mm as the mainstream size at the current stage, given its advantages of low retrofitting cost, lower cost per watt, and higher power output by increasing the wafer size through shifting pseudo-square wafer to full square wafer. It represents the best choice for investors pursuing solar modules with high efficiency, high power and high cost performance.