Received: 20 December 2017 Revised: 19 June 2018 Accepted: 5 July 2018 DOI: 10.1002/pip.3069 RESEARCH ARTICLE Measurement and modelling of water ingress into double-glass photovoltaic modules David Wisniewski 1,2 Ruirui Lv 3 Selvakumar V. Nair 1,2 Jean-Nicolas Jaubert 3 Tao Xu 3 Harry E. Ruda 1,2 1 Centre for Advanced Nanotechnology, University of Toronto, 170 College Street, Toronto, Ontario M5S 3E3, Canada 2 Department of Materials Science and Engineering, University of Toronto, 184 College Street, Toronto, Ontario M5S 3E3, Canada 3 CSI Advanced Solar Inc., Changshu 215500, China Correspondence David Wisniewski, Centre for Advanced Nanotechnology, University of Toronto, 170 College Street, Toronto, Ontario M5S 3E3, Canada. Email: dave.wisniewski@mail.utoronto.ca Funding information Natural Sciences and Engineering Research Council of Canada (NSERC); Ontario Centres of Excellence (OCE) Abstract Polymer encapsulants are an essential component in photovoltaic (PV) devices, providing mechanical support, optical coupling, and electrical and physical isolation. However, moisture ingress into the module can degrade these polymers and subsequently the performance of the device. In this paper, we report experimental measurements of the temporal evolution of moisture content in ethylene-vinyl acetate (EVA) encapsulant in a double-glass PV module. Using physical properties of EVA as determined by water vapour transmission rate measurements, we simulate diffusion of water into the module using a finite element model. The model accounts for realistic geometry of our module and is used to simulate accelerated test conditions and outdoor operation in geographic locations. Using the calculated results, we propose two schemes using the accelerated test results to understand the behaviour of modules operating in humid climates. Finally, we show that the time needed to reach the saturation water concentration can be increased by as much as a factor of two by reducing the initial water content in EVA films. KEYWORDS double glass, EVA, humidity, moisture ingress, polymer encapsulant, solar cell, solubility 1 INTRODUCTION Crystalline silicon photovoltaic (PV) devices represent over 90% of the worldwide photovoltaic market. 1 These devices have a target lifetime of 30 years, 2 including situations where the module is exposed to harsh climatic conditions. In environments that are particularly hot or humid, water can permeate into the module and lead to performance degradation including corrosion at interconnects, 3 delamination at interfaces, 4 and discolouration of components. 5 Typically, this mois- ture ingress occurs through polymer components, since the diffusivity of water is much larger than that of other components exposed to the environment, such as glass. Polymer encapsulants are necessary for structural support, coupling between the cell and incident solar irradiation, physical and electri- cal isolation of components, and for ancillary electrical connections. 6 Presently, ethylene-vinyl acetate (EVA) is the most popular encapsu- lant used in crystalline silicon PV modules due to its low cost; however, it suffers from high water diffusivity and acetic acid production. 7 To understand and predict the failure mechanisms due to moisture ingress, and achieve a PV module capable of sustaining 30 years in the field, a strong understanding of the water ingress behaviour in EVA is required. In this paper, we consider the lateral water ingress into a double-glass PV module (Canadian Solar Inc., CS6K-P-FG) through the EVA (3M 9110T) encapsulant. This permeation can be a complex phe- nomenon influenced by many factors such as temperature, pressure differences, material properties, and concentration gradients of the dif- fusing species. 8,9 To move through a barrier, the water must undergo absorption to enter the material, followed by diffusion through that material. Absorption can be explained using permeation theory, while diffusion through EVA is well described using Fick's laws. 10 For com- plex geometries and instances where the concentration at the solid boundary changes, analytical methods become difficult to use, while finite element models can effectively describe the behaviour of the system. In this paper, we use both analytical and finite element tech- niques to examine the moisture ingress behaviour of our double-glass PV modules. We first determine the EVA properties (diffusivity, saturation concentration, solubility, and permeability) using water vapour trans- mission rate (WVTR) experiments. We then verify these parameters Prog Photovolt Res Appl. 2018;1–8. wileyonlinelibrary.com/journal/pip © 2018 John Wiley & Sons, Ltd. 1