Performance and life prediction model for photovoltaic modules: Effect of encapsulant constitutive behavior Osama Hasan, A.F.M. Arif n Department of Mechanical Engineering, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia article info Article history: Received 9 May 2013 Received in revised form 3 November 2013 Accepted 11 November 2013 Available online 7 December 2013 Keywords: Encapsulant Life prediction Viscoelasticity Photovoltaic Finite element analysis abstract An encapsulant in a Photovoltiac (PV) module is a polymer used for binding all the components together. It also provides protection of cells and interconnects from moisture, foreign impurities and mechanical damage. In addition to this, the encapsulant must possess certain desirable characteristics such as low cost, high transmittance of light, good thermal conduction and long operating range. The provision of such properties makes it a vital component on which the performance of a PV module depends. Currently, the PV industry is dominated with Ethylene-Vinyl Acetate (EVA) as an encapsulant, mostly due to its low cost. Other polymers such as polydimethylsiloxane (PDMS), polyvinyl butyral (PVB), thermoplastic polyurethane (TPU) and Ionomer have gained interest and are being tested for better encapsulation of PV modules. The current work deals with the comparison of the mentioned encapsulants and selecting the optimum one based on its properties such as light transmittance, UV durability, electrical insulation, water vapor transmission rate and cost. The structural life of PV module is also compared by using these encapsulants. For this purpose, previously developed structural and thermal models are coupled with electrical and life-prediction models to determine efficiency and life of PV module for each encapsulant case. Life prediction of PV module encapsulant is based on a year's data of Jeddah, Saudi Arabia where the interconnect crack initiation defines failure. Under these assumptions, a detailed structural analysis has been carried out. Finally, the results of simulation combined with the other outcomes of literature are used in a decision matrix to give Ionomer to be an optimum encapsulant for PV module. & 2013 Elsevier B.V. All rights reserved. 1. Introduction The photovoltaic (PV) industry has shown rapid growth in the last few decades. Its expansion has led to the selection of such materials in its construction, which enables it to meet its require- ments efficiently. Now-a-days, research on PV modules is mainly focused on the encapsulant material, due to significant involve- ment of its properties over PV module performance. The structural performance of PV modules is enhanced due to the protective covering it provides to isolate silicon cells from the influence of the environment. At the same time, it also has to be transparent to light so as not to hinder the electrical performance of PV modules. In fact, it could also provide a medium to extract heat from the cells to increase their efficiency. So, the fulfillment of these requirements and others (discussed later) are important for an optimal performance of PV modules. During the 1960s and 1970s, polydimethylsiloxane (PDMS)/ silicone was used as an encapsulant for PV modules [1]. But from the 1980s till today, the PV industry is dominated with ethylene vinyl acetate (EVA) [2]. EVA was chosen over PDMS mainly due to its low cost. In the late 1990s, it was found that EVA turned yellow/ brown due to UV radiation from the sun thus decreased its transmittance. It has also been reported to lose adhesion under UV light [3]. Furthermore, EVA has the ability to concentrate water due to diffusion which makes it to react with moisture to form acetic acid. The acetic acid speeds up the corrosion process of the inner components of the PV module [4]. This raises a question of its operation under humid climates. The glass transition temperature (T g ) of EVA is  15 1C [5] and it comes in between the operating range of a PV module in cold regions. Thus, compliancy of EVA is an issue for modules operating in such regions. The mentioned concerns have recently revitalized the interest to study different polymers for PV module encapsulation. Such polymers include polyvinyl butyral (PVB), Ionomer, PDMS and thermoplastic polyurethane (TPU). The mentioned encapsulants have their merits and demerits over one another, but the best compromise amongst them needs to be chosen with respect to PV module performance and life. Failure is defined as the change in properties of a structure, machine or machine part that makes it inept to perform its intended functions. The occurrence of such failure is through physical means which are known as failure modes [6]. In the case of PV modules, Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/solmat Solar Energy Materials & Solar Cells 0927-0248/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.solmat.2013.11.016 n Corresponding author at: Department of Mechanical Engineering, King Fahd University of Petroleum and Minerals, P.O. Box 1467, Dhahran 31261, Saudi Arabia. Tel: +966 13 8602579. E-mail address: afmarif@kfupm.edu.sa (A.F.M. Arif). Solar Energy Materials & Solar Cells 122 (2014) 75–87