Glass vs Transparent Backsheets

Today Module Manufacturers Can Choose Between Glass And Transparent Backsheets For The Rear Cover of Their Bifacial Products

Glass vs Transparent Backsheets

Pricier than glass: While transparent backsheets have evolved in terms of reliability attributes, their major bottleneck is still the price difference to glass. The transparent CPC configuration comes closest to glass prices. (Source: Jolywood)

  • Transparent backsheet, replacing the glass in bifacial modules, has several advantages – less weight, better heat dissipation and requiring no changes to BOM and process
  • Glass-glass had a USP of 30 years power warranty, which is now also offered by a few transparent backsheet based suppliers
  •  During the recent short supply of glass, several module makers turned to transparent backsheets, an indication that transparent backsheet is at par with glass at all aspects, while further cost down is necessary to its wide spread
  • In the meantime, glass prices have dropped again, which makes the product more attractive again for bifacial module makers

Transparent backsheets is one of the most interesting topic in the area of backsheets. What has brought about this increased traction and attention to transparent backsheets is their application in a very rapidly developing sector of PV — bifacial. It is a technology that improves the energy yield of the PV system with minimal effort, ultimately reducing LCOE of a PV system. The ease of manufacturing, especially at the cell level, is the key to its widespread appeal. Any advanced technology beyond PERC is naturally bifacial and PERC, as well, can be tweaked to bifacial without involving additional costs.

At the module level, the most important change is naturally to make the rear cover transparent. Glass has been the natural and predominant choice in this regard. 2018-ish, during the commercialization phase of bifacial technology, there was no competent polymer solution available that could meet the needs of bifacial panels. As the bifacial trend took hold, so did the focus on transparent backsheets. The result — now there are reliable clear variants of backsheets available from nearly all leading companies.

In fact, using a transparent backsheet as rear cover of a bifacial module is an interesting alternative to glass. This approach also comes with several advantages. Unlike the heavy glass-glass modules, the polymer-based products weigh the same as standard modules, eliminating any extra care required in transportation, handling and installation. In addition, the manufacturing process, along with other materials used in module making, remains unchanged. This offers the manufacturer the ease of switching production between monofacial and bifacial module varieties depending on market demand (see So Many Backsheet Components).

Conversely, adding an extra glass loader to make glass-glass modules is not an expensive affair these days. Line throughput could favor the transparent backsheet based process, as the glass structure requires longer lamination cycle times compared to polymers. The observed drop in productivity for a plant using a glass rear cover is about 10% which, however, is not attractive enough to lure module makers into polymer based solutions. Using glass requires a change in BOM. It is not as simple as adding a sheet of glass, but it requires a high PID-resistant encapsulant such as POE at least on one side – the rear side for PERC. Unlike glass, the polymer backsheet modules are “breathable,” which means they allow moisture and free radicals formed, if any, to escape. It also makes sense to use backsheet panels in hot regions, which dissipate heat better than glass, thus helping to lower the cell operating temperature by 5 to 10 °C, making them more efficient.

One of the USPs for glass-glass modules has been the 30-year performance warranty. With its strong track record in reliability tests for mechanical loading and damp heat performance, this structure built enough equity for itself among module makers that it was the go-to solution in applications for very long times of use. Its exclusivity, however, has already been challenged. There are transparent backsheet modules available in the market now that match the 30-year power warranty of glass-glass panels, notably from JinkoSolar and Jolywood. A lot of the credit can be attributed to DuPont — the lone source of PVF Tedlar and a strong advocate of transparent backsheets for bifacial applications. JinkoSolar, one of the 3 world’s largest module makers, was convinced and started offering commercial transparent backsheet modules based on Clear Tedlar with a 30-year power warranty. Following this lead, Jolywood also commercialized the polymer rear cover modules with the 30-year warranty. Jolywood is somewhat different in this context. In addition to being a high-efficiency TOPCon cell and module manufacturer, Jolywood’s core business is supplying backsheets. It is in fact the world’s leading backsheet supplier in 2021, according to shipment data.  However, the lower warranty span does not seem to be a showstopper. Talesun and LG, for example, even started offering transparent backsheet modules with a 25-year power warranty. All leading companies have evaluated, tested and also completed the certification process. JA Solar, Suntech and Yingli have already put their transparent backsheets into commercial production, according to Fumotech’s Wei. Jolywood added a few more names to the list – Chint-Astronergy, Hyundai Solar and Indian module maker Vikram Solar (see Top 2 Took More Than 1/3rd).

The industry and its participants have a thorough understanding of the pros and cons of transparent backsheets versus glass. In other words, there are no pressing issues with transparent backsheets. The selection criterion now simply boils down to costs. This is evident from the fact that during the second half of 2020, when glass was in short supply and the prices were high, the industry rushed towards transparent backsheets, a trend acknowledged by all backsheet suppliers. But of late, with the fall in glass prices, glass has more than found the favor it had lost among the manufacturers. In the long run though, as costs go down, many backsheet makers expect the share of transparent backsheet to rise quickly.

The Text is an excerpt from TaiyangNews’ recent Market Survey on Backsheet and Encapsulation Materials, which can be downloaded for free here

An overview of the survey was presented during TaiyangNews Conference on Reliable PV Module Design. To learn more about the conference and view the presentations click here

About The Author

Shravan Chunduri

Shravan Chunduri is Head of Technology at TaiyangNews.

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