Glass/glass photovoltaic module reliability and degradation: a review

Abstract

Glass/glass (G/G) photovoltaic (PV) module construction is quickly rising in popularity due to increased demand for bifacial PV modules, with additional applications for thin-film and building-integrated PV technologies. G/G modules are expected to withstand harsh environmental conditions and extend the installed module lifespan to greater than 30 years compared to conventional glass/backsheet (G/B) modules. With the rapid growth of G/G deployment, understanding the outdoor performance, degradation, and reliability of this PV module construction becomes highly valuable. In this review, we present the history of G/G modules that have existed in the field for the past 20 years, their subsequent reliability issues under different climates, and methods for accelerated testing and characterization of both cells and packaging materials. We highlight some general trends of G/G modules, such as greater degradation when using poly(ethylene-co-vinyl acetate) encapsulants, causing the industry to move toward polyolefin-based encapsulants. Transparent backsheets have also been introduced as an alternative to the rear glass for decreasing the module weight and aiding the effusion of trapped gaseous degradation products in the laminate. New amendments to IEC 61215 standard protocols for G/G bifacial modules have also been proposed so that the rear side power generation and UV exposure will be standardized. We further summarize a suite of destructive and non-destructive characterization techniques, such as current–voltage scans, module electro-optical imaging, adhesion tests, nanoscale structural/chemical investigation, and forensic analysis, to provide deeper insights into the fundamental properties of the module materials degradation and how it can be monitored in the G/G construction. This will set the groundwork for future research and product development.

Electrochemical degradation modes in bifacial silicon photovoltaic modules

“…The two leading choices for bifacial PV packaging are glass/glass (G/G) or glass/transparent backsheet (G/TB) constructions, though it is currently unclear which choice will produce the lowest module degradation rates. 4,5 Scheme 1a highlights several different degradation pathways possible in G/G versus G/TB structures. G/G construction promises greater mechanical rigidity 6,7 and low rates of moisture/ atmospheric ingress, [8][9][10] leading to community recommendations to use G/G in harsh environments and extreme climates.…”

“…4,11 However, older generations of G/G modules containing poly (ethylene-co-vinyl acetate) (EVA) suffered from entrapment of encapsulant degradation products (e.g., acetic acid), historically causing encapsulant discoloration, package delamination, and metallization corrosion. 5,12,13 These degradation modes could be mitigated by using higher quality formulations, different encapsulants that produce less detrimental degradation products (e.g., polyolefins [POE]), or, to some extent, by using TBs that may allow out-diffusion of degradation products. 5 G/TB constructions also promise lower module operating temperatures, 14,15 lower weight (i.e., easier installation), 11 and less susceptibility to some types of potential-induced degradation (PID).…”

Review on the Sources of Power Loss in Monofacial and Bifacial Photovoltaic Technologies

“…Albadwawi et al [16] found that in extreme desert conditions, the front side discoloration can cause a degradation of 1.3-1.88% per year while for the rear side, this degradation is around 0.39-0.78% per year. Additionally, as BPV modules use common double glass technology, they showed to be more likely to trap acetic acid and gases produced during the degradation of the encapsulant as the glass layer is less breathable than a back sheet [63].…”

Smart Glass Coatings for Innovative BIPV Solutions

“…It is, therefore, clear that one of the requirements is a correspondingly long service life. In addition, it has already been shown in the literature that glass-glass modules have a longer service life than glass-foil modules [10,22,23].…”