Cost-effective & Reliable Coextruded Polyolefin-Based Encapsulation Solutions

The quality and reliability of encapsulation materials, such as encapsulants and backsheets, are as critical as the quality of solar cells in ensuring long-term PV module performance. In the current era of intense cost pressure, these materials face challenges in balancing cost-effectiveness and quality.

At the recent TaiyangNews Reliable PV Module Design 2024 virtual conference, Imco Goudswaard, Commercial Manager at Endurans Solar, shared some insights into the company’s innovative coextruded polyolefin-based backsheet and encapsulant solutions (see Endurans Solar's presentation here). A US-based leader in polymer technology, the company offers a product portfolio that includes polyolefin-based backsheets and single-layer encapsulants such as EVA, POE, and the newly developed multilayer EPE encapsulant.

Backsheet

Withstanding the pressure of cost reduction, driven by the consistent decline in module prices in the last 2 decades, the backsheet structure has evolved multiple times, majorly the outer layer fluorine quantity (gm/m²). The outer layer of fluorinated film, protecting the core layer of polyester with low cost and good electrical insulating properties, has experienced a drastic reduction in thickness and quantity compromising on quality. The encapsulation solution provider noted that the latest 2-side coated (CPC) backsheet structure, having a thin fluorinated outer layer of 15 µm thickness and less than 20 gm/m² fluorine quantity, poses serious long-term reliability risk for PV modules. The company has addressed this challenge by developing a coextruded polyolefin-based backsheet, which can offer all relevant features for future-proof modules. This polyolefin-based backsheet, made in a single coextrusion process instead of conventional multiple process steps of lamination, features cost-effectiveness, highly available polymer, inert to the outdoor environment, and good mechanical strength like polyester film. Additionally, the polyolefin-based core layer, having a good water and moisture barrier, can easily let any acidic acid, formed from EVA, migrate out during day time. From a sustainability perspective, polyolefin-based backsheets have multiple advantages, such as remelting after the end-of-life, a low carbon-intensive production process compared to glass, and even getting back the monomers with an efficiency of almost 90% after entering into a pyrolysis process, added the company.

Based on the above-mentioned strength of the coextruded polyolefin polymer, the company expects to launch the latest Endurans HP transparent backsheet for bifacial modules. This backsheet, based on the company's HPO technology, brings all the advantages of coextruded polyolefin, plus an additional light-trapping feature.

The ongoing trend of utilizing mesh with transparent backsheet or glass to get the added advantages of light trapping feature is fading due to the reduction of cell-to-cell gap or even gapless cell interconnection. However, the conventional transparent backsheet has limitations in achieving good transmission of rear-side low-angle diffused irradiation. Endurans Solar has addressed this challenge with this latest HPO technology-based transparent backsheet.

This bifacial backsheet, having good diffused irradiation transmittance property, leads to up to 3% additional power yield compared to traditional transparent backsheet. Additionally, this made-in-USA backsheet film is light and easy to handle compared to glass or mesh. On the reliability part, this new solution showed good mechanical retention value, such as elongation at the break in both MD and TD directions after multiple stress tests, including PCT, damp heat (DH), ultraviolet (UV), and dry oven tests. On top of that, the optical properties of this transparent backsheet showed promising value after different environmental aging tests. However, the laminate aging properties of a mini-module, equipped with the bifacial backsheet, show minor changes in EVA peel strength, yellowness index, and flash test.

EPE

Having previously launched single-layer encapsulants, such as EVA and POE, the company has recently launched multi-layer encapsulants, EPE. This EPE encapsulant, which combines the features of EVA and POE, has a few limitations in terms of high cost and risk of acid formation. To address this limitation, Endurans Solar has developed a proprietary EPE encapsulant technology by replacing the costly POE core layer with a higher melting PO. The added advantages of this latest technology are a higher moisture barrier for improved resiliency against acid formation, lower cell crack due to high stiffness and low shrinkage characteristics, low cost of the PO layer compared to the POE layer, and sustainability. This upcoming EPE encapsulant shows up to 40% additional reduction in water vapor transmission rate (WVTR) compared to commercial EPE and improved PID performance in an internal test facility. Moreover, this new encapsulant, with non-cross-linked property, offers good adhesion retention value in in-house testing, added the company.