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Bifacial Era: Double-Glass or Transparent Backsheet?


Bifacial Era: Double-Glass or Transparent Backsheet?

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Bifacial modules can greatly increase power generation, and the market share is expected to increase rapidly! There are two choices in front of customers: "Bifacial double glass" or "single glass + transparent backsheet"?

Bifacial double-glass modules benefit from reduced use of organic backsheet. The components have high fire safety class, low long-term degradation, resistance to moisture, corrosion, fire, sand and abrasion! However, the biggest bottleneck restricting their development is the heavy weight and high cost of the double glass modules.

1 、Deterministic ultra-thin glass 

As the photovoltaic glass of 2.0 mm and even ≤1.8mm gradually matures, the said two problems will be solved. In addition, the double-glass bifacial modules support the lifetime of the photovoltaic power station from the perspective of module manufacturing materials to further increase to 40 or 50 years, to generate electricity. It can be achieved that the photovoltaic power station becomes a long-term, effective, reliable and value-protected property. 

In the short-term expectable future, this historical trend is called the inorganic material stream of the module. 

To the double-sided power generating modules with 2.0mm photovoltaic front glass, which should be used on the back side, transparent backsheet or photovoltaic glass? This kind of discussion is still ongoing. Since the current bifacial modules mostly use the photovoltaic glass with a thickness of 2.5 mm, the "double-glass bifacial" and "single-glass + transparent back bifacial" are really hard to beat. From a long-term view, 2.0mm thick photovoltaic glass will eventually mature, it is only a manufacturing problem. However, the problem of transparent backsheet (organic matter) is the inherent problem of its characteristics. The problem of manufacturing is a time problem. It will be solved in a further research. The problem stemming from its characteristics is a biggest and unsolved problem. Therefore, as long as we change the view, the problem of "double glass VS transparent backsheet" which is now being debated will be judged clearly.

Regarding photovoltaic glass, one practical parameter: 125 square meters of 3.2mm thick photovoltaic glass corresponds to a weight of exactly 1 ton. That means photovoltaic glass 125㎡(3.2mm thickness) = 1t = 1000kg. According to that, a bifacial module with 2.5 mm thick glass has a glass thickness of 5 mm (2.5 x 2), and the area corresponding 1 ton is 80 ㎡

Instead of photovoltaic glass 80㎡(2.5mm x 2) = 1t = 1000kg, 2.0mm thick glass is used in bifacial modules, 100㎡   corresponds to 1 ton. According to the above simple correspondence, the weight of different module types can be calculated.

As showed in the above table, the standard unifacial 72-cell module with 3.2mm thick glass weighs about 21kg. when the 2.5mm thick glass is used in a bifacial module, the module weighs 27.75kg, and the weight increases by 6.75kg, which is 32.14% more than the standard weight. If the 2.0mm thick glass is used in a bifacial module, the weight is 22.9kg, which increases by only 1.89kg weight compared to the unifacial module. The increase is just 8.9% of the standard module. 

It is found that the industrial application of 2.0mm thick photovoltaic glass will effectively control the weight of double-glass bifacial modules, and solve the problems about the difficult installation of double-glass modules due to heavy weight. Therefore, the industrial debate on whether to choose "photovoltaic glass" or "transparent backsheet" on the back side will be determined by the maturity of ≤2.0mm thick photovoltaic glass.

2、the strategic choice under the stream of module inorganicization

1). From the perspective of photovoltaic glass manufacturers, the biggest factor that restricts the double- glass modules is the weight of the modules at present. If the 2.0mm thick photovoltaic glass tempering equipment can have a great progress and the cost is greatly reduced, the inorganicization of the modules will be greatly promoted. 

2).From the perspective of film manufacturers, double-glass modules must use POE as packaging material. The price of POE is 50% higher than EVA. And the fluidity is large (the corresponding cell string spacing must be wider). In addition, the lamination time is 90% longer than EVA (This means that double glass modules require more lamination machines). The high cost, high fluidity and long lamination time of POE film are important factors that restrict the inorganicization. If the film manufacturers could make some new breakthroughs in these directions, it would greatly contribute to the era of inorganicization of modules.

3). From the perspective of module manufacturers, the cost of silicon materials will continue to decrease in the future, but the cost of glass is difficult to decline significantly. The inorganic era means the full application of double-glass module. For a photovoltaic module, the cost proportion of glass in the total cost would continue to increase and the transportation cost of glass has to be taken seriously. As a module factory, more thinking about the glass purchase should be done on the location synergy of the “modules & glass”.

4). From the perspective of backsheet manufacturers, the challenges brought by the era of module inorganicization to the backsheet are obvious. But considering the expansion of the total market size, the application of the roof tiled power stations, and the acceptance and certification process of inorganic module concept, the backsheet  business will not suddenly disappear like the mortar cutting business in the past, but will maintain for a long time. As s backsheet enterprise, it may be the best policy to choose to maintain the business rather than expand.