Properties and degradation behaviour of polyolefin encapsulants for photovoltaic modules

Abstract

Various types of next-generation encapsulation films based on polyolefins have recently been introduced and could attract market attention. These material innovations can be classified as polyolefin elastomer (POE) and thermoplastic polyolefin (TPO) encapsulants, both of which consist of a polyethylene backbone with different side groups. The main advantage of these materials is the replacement of the vinyl acetate side groups of state-of-the-art encapsulant ethylene vinyl acetate (EVA) so that acetic acid cannot be formed. The main objective of this paper is to investigate the material properties of next-generation encapsulant films and compare them to an EVA reference. Two commercially available EVA alternatives (POE and TPO) have been selected. The material properties of single films as well as the electrical performance of test modules using these different encapsulants were investigated. The different films show comparable optical, thermal and thermo-mechanical properties, with slight differences in UV transparency and melting temperatures. Only shear viscosity values are higher for TPO than for POE and EVA, which requires adaption of the photovoltaic (PV) module lamination parameters. The test modules comprising the different encapsulation films show minor differences in the electrical performance after manufacturing; upon accelerated aging, no significant power loss is observed. But compared to TPO or POE, after 3000 h of damp heat exposure, test modules with EVA show the beginning of corrosion effects at the silver grid and above the ribbons. Based on the results, it can be stated that the new polyolefin encapsulation materials show great potential to be a valid replacement for EVA.

Environmental effects of stratospheric ozone depletion, UV radiation, and interactions with climate change: UNEP Environmental Effects Assessment Panel, Update 2020

“…The use of thermoplastic polyolefin (TPO) as an alternative to EVA as the encapsulant has been evaluated [ 483 , 484 ] and was found to have superior thermal stability, adhesive strength and resistance to discolouration. For instance, discolouration on exposure to UV radiation was ca nine times slower in TPO relative to EVA, and may also be easier to process.…”

Comparison of Degradation Behavior of Newly Developed Encapsulation Materials for Photovoltaic Applications under Different Artificial Ageing Tests

“…During DH exposure, instead, transmittance values decreased in the UV range as well as in the visible range below 500 nm indicating that the material’s yellowing was due to chromophore formation [ 33 ]. Formation of chromophores as well as migration of additives might have caused also the changes in transmittance below 390 nm, observable for POE and TPO [ 19 , 33 ].…”

“…Recently, an interest in new encapsulant materials has increased to overcome the issues due to the use of EVA and new formulations have been tested. In particular, Thermoplastic Polyolefines (TPO) and Polyolefin Elastomers (POE) have been introduced as alternatives to EVA as encapsulants for PV applications [ 8 , 15 , 16 , 17 , 18 , 19 ]. TPO and POE are polyethylene based materials, as well as EVA, but do not have vinyl acetate moieties.…”

“…Additionally, the lack of vinyl acetate units limits the occurrence of corrosion and PID [ 8 ]. In a work published recently, Oreski et al proved that module laminated with POE and TPO materials did not show signs of corrosion upon exposure to high temperatures and high humidity values [ 19 ].…”

Reshaping the Module: The Path to Comprehensive Photovoltaic Panel Recycling

“…EVA is a relatively cheap and easy-to-handle material with good optical transparency which has been used in solar module construction for many years [39,65]. It is nonetheless known to be prone to aging through long-term exposure to outdoor environmental conditions, leading to discolouration and the release of small amounts of acetic acid [66][67][68]. The latter in particular can cause module damage through corrosion of metal interconnects and busbars, prematurely reducing module performance [67,68].…”