For N-type Bifacial Technology, Dual Glass Structure is Preferred
Bifacial solar cells can be encapsulated in modules with either a glass/glass or a glass/ transparent backsheet structure. A glass/backsheet structure works well with conventional PERC modules due to its lightweight, whereas a glass/glass structure has the potential to generate additional energy for N-type modules under outdoor application conditions.
Dual glass is the preferred structure for the rear side cover of the N-type modules because the glass-glass version can maximize the advantages of the N-type. Compared to a transparent backsheet, the glass layer has better light transmittance (dual glass around 94% while transparent 89%), which means more add-on value to a higher bifacial factor of N-type technology that can absorb and transmit as much as possible sunlight from the rear sides of the module.
The reflectance and transmittance of n-type modules with glass/glass structures can maximize the higher bifacial Factor advantage of n-type TOPCon cell, providing approximately 10W more, as compared with glass/transparent backsheet modules using the same n-type TOPCon bifacial solar cells.
The life cycle of PV modules in general is primarily dependent on the cell degradation rate and encapsulation material used. Lower degradation of N-type versus p-type makes it can work well enough and reserve 87% power after 30 years. So N-type modules call for a more durable encapsulating configuration to match its slower degradation advantage. Besides， glass-glass bifacial modules could provide a minimum of 30 years thanks to the better resistance to corrosion, abrasion, extreme weather, shock, and vibration that ensures N-type module safety during production, transport, installation and long-term power generation and prevents new invisible cell cracking
In addition, the better resistance to vapor and heat penetration, as well as strengthened resistance to salt spray, acids, and alkalis corrosion of dual-glass configuration, avoid the potential concern of N-type that is PID and cells damage caused by long-term moisture penetration. Since glass has close to zero moisture penetration risk, so glass/glass version can better protect N-type cells which may be vulnerable to moisture, and extend their life expectancy. Furthermore, glass-glass structure design overcomes problems such as outdoor degradation-induced material aging and the power attenuation that frequently affects backsheets.
The distinctive weak point in dual glass modules is heavier weight compared to transparent backsheet. However, Thanks to improvements in module stiffness and the better support of dual-glass design, N-type TOPCon dual glass modules would have more excellent mechanical load level than transparent ones, what’s more, for example, Jinkosolar can provide the option of hail resistant solution with dual glass module to cater to special requirements from hail heavy-attacked regions.
From the long-term aspects, glass/glass version has better compatibility with 2000V modules, which will be an inevitable trend in the near future. Given that 2000V modules have higher requirements for reliability, the thicker transparent backsheet is necessary to guarantee the module quality, which will also inevitable bring the material cost increased.