As the solar industry debates over the right encapsulant for solar modules, Lithuania's SoliTek says its recent research prefers Polyolefin Elastomer (POE) as the encapsulant of choice for superior performance. It is particularly useful for modules based on n-type cells.
The current crop of p-type modules, however, uses Ethylene Vinyl Acetate (EVA) predominantly. In fact, it holds a dominant position out of the 3 main encapsulant material types with co-extruded EPE being the 3rd one.
SoliTek says estimates show that in 2023 the demand for EVA ranged from 1,480,000 to 1,530,000 metric tons (MT), while it was 390,000 to 420,000 MT for POE. The same is expected to grow to 1,450,000-1,530,000 MT for EVA and 520,000-580,000 MT for POE. This reflects the evolving preferences in the market.
Yet, SoliTek says its recent series of module durability tests, conducted in specific climatic chambers to test the difference between EVA and POE encapsulated modules, showed better results for POE-based modules.
The damp heat test applying 85°C ± 2°C with a relative humidity of 85% was performed for an uninterrupted cycle of up to 3,500 hours, up from the 1,000 hours required by IEC. The glass-backsheet modules with an EVA encapsulant exhibited a degradation rate of -7.90% after 2,500 hours, which is equivalent to 25 years.
Glass-glass modules under the same conditions with POE showed a -3.50% degradation after 3,500 hours, equivalent to 35 years.
"These tests suggest that POE encapsulated glass-glass modules could have lifespans exceeding 50 years, a stark contrast to the 25-year expectancy for modules with different materials," says SoliTek. "The superior moisture resistance, PID resistance, and UV protection of POE make it particularly suitable for high-efficiency, moisture-sensitive cells."
It does add that in real-life conditions, the modules will be subjected to various other elements well beyond the high temperatures and high humidity as these were exposed to in a controlled environment.
SoliTek does add, from its tests, that all glass-glass modules are not equivalent and/or superior to all glass-backsheet modules.
It clarifies, "However, it would be highly misleading to assume that all glass/glass modules are equivalent and superior to all glass/backsheet modules. While EVA or any film containing EVA in its composition has been a suitable choice for the lamination of glass/backsheet modules, it can pose significant issues when used in a glass/glass configuration."
In the case of EVA being used in a glass-glass configuration, the primary concern is related to the formation of acetic acid during lamination. This acetic acid evaporates in a backsheet, but gets trapped between the glass-glass layers leading to corrosion of cell metallization or delamination. It may lead to reliability concerns for the modules.
Nonetheless, SoliTek does not share any comparison between POE glass-glass and POE glass-backsheet.
"This breakthrough is especially significant in light of the global shift towards bifacial and n-type module technologies. POE's enhanced moisture resistance, superior PID resistance, and robustness against environmental factors position it as a highly effective alternative to EVA, especially for moisture-sensitive, high-efficiency solar cells," says the manufacturer that has been using POE films for its modules since 2013.
TaiyangNews covered the subject of encapsulants in its Market Survey on Backsheets and Encapsulation 2022-23 which is available for free download here.
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