One might think there's little room for further developments of backsheet and encapsulants, the polymers protecting the electric circuit of a solar module from the elements and mechanical stress. Indeed, there are products with over a dozen different material configurations for backsheets on offer for different applications and needs. While the encapsulant segment is fully dominated by EVA, which has some shortcomings, module manufacturers mostly know how to deal with the issues of the material that's in use for many decades.
However, the cost pressure on modules is not sparing material suppliers. And with module technology quickly evolving to improve power ratings through different means in recent times, there have been also new requirements for the backsheet/ encapsulant segment to cope with all those innovations. What's true for solar modules is also the case for its packaging materials – there is quite some innovation potential being released these days.
Today, the most popular backsheet in the market continues to have a PVDF film on the outer side, a fluorine coating on the inner side, and PET as the core layer. While there are different coatings/layers available, which could be used on both the inner and outer sides to reduce cost, this won't help a lot, let aside that such products are already available. The next step to reduce cost might be to replace PET as the backsheet's core. The alternative, PP has a lower density and higher water vapor transmission rate, enabling considerable savings on material use. Applying another production technology, coextrusion for making multi-layer backsheets in one single step directly from resin, instead of current state- of-the-art method lamination of films, offers further potential. While some European suppliers have been implementing coextrusion, the big Chinese companies have been shying away from this move so far.
Another big innovation push for backsheets has come from a non-polymer competitor – glass. With bifacial modules now quickly seeing traction in the market, and glass being the preferred material for the rear cover from the start when no appropriate transparent backsheets were available, companies have worked hard to address that weak flank. Not only are most backsheet manufacturers offering now transparent models for many different product compositions and have implemented reflective grids on the heels of glass manufacturers to improve power output of the rear cell sides; They have also started gearing up to address the solar glass manufacturer's prime selling proposition – longevity. After the world's largest module manufacturer Jinko started offering bifacial panels with transparent backsheet that have 30-year power warranties last spring, matching those of typical glass-glass panels, Jolywood Group, which is not only a leading producer of backsheets but also of high-efficiency modules, has followed suit. However, this move to longer warranties hasn't spilled over to many other module manufacturers offering bifacial products with transparent backsheet so far. While there are pros and cons for both back cover materials, for the moment, glass still enjoys the prime position in the quickly growing bifacial module market segment.
The positive development towards bifacial modules has also enabled the advent of POE in the encapsulation field. Unlike with EVA, there is no acid formation and the material is relatively PID resistant, although it brings up other concerns such as bubble formation and longer processing times. But its major disadvantage is cost, which is at least 25% higher than for the incumbent, EVA. Chinese backsheet/ encapsulant leaders have developed a coextruded encapsulation stack of EVA-POE-EVA that resolves the material and processing issues of pure POE films; and the cost structure is similar, if not cheaper. With all leading suppliers of POE entering the realm of coextrusion, multilayered encapsulation has a good chance to replace pure POE in bifacial module applications. There is also another interesting POE variant offered on the market – thermoplastic POE, which also reduces lamination time significantly and supports lower temperature lamination processes.
However, even long-time market dominator EVA has seen improvements lately. White EVA is a new bright spot with the promise of enhancing power output, especially when combined with advanced module technologies such as half-cell and MBB. Despite its 20% higher price tag, its performance will increasingly justify its application, thus it's likely to win market share in the coming years. Evidently, the room for further developments in the backsheet/ encapsulation field is not as limited as one might think at first sight.
This is the conclusions part from the TaiyangNews Market Survey on Backsheets & Encapsulation Materials 2020, which is for download free of charge here. It was launched during the TaiyangNews Reliable Module Design Conference, for which the presentation recording is accessible here. To learn more on the latest on High Efficiency Solar, where we will also launch our HJT 2020 report, register for the TaiyangNews conference on this topic on Dec. 1-4 here.