Weathering stability of polymeric materials developed for PV modules operating in harsh climatic conditions

Antonia Omazic

Research output: ThesisDoctoral Thesis

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Abstract

An increased reliability represents one of the main challenges for current and future PV modules. However, an increased reliability has to be achieved within cost-reduction and sustainability frameworks, which makes it even more challenging. In order to meet an increased demand for reliability, cost-reduction and sustainability, some of the options are: 1) change of materials for PV components, 2) change in PV design and/or production process and 3) development of new or adjusting the current qualification and reliability tests. However, the influence of each of those steps on reliability of PV modules has to be well understood. Hence the main aims of this thesis are to understand the influence of the replacement of state-of-the-art materials with alternatives, PV design and customized climate-specific accelerated tests on reliability of PV modules. An in-depth literature review on the relation between degradation of polymeric PV components and climatic conditions is given in Chapter 1. The results of the feasibility study for replacement of state-of-the-art PET/fluoropolymer backsheets via alternative co-extruded polyolefin backsheets are presented in Chapter 2. The results of applied methods pointed to excellent weathering stability of the polyolefin backsheet even after extended aging, which could lead to reduced cracking and embrittlement in the field. Chapter 3 deals with weathering stability of alternative polyolefin encapsulants (thermoplastic polyolefin, TPO, and polyolefin elastomer, POE) on the PV module level. The special focus was on the influence of the microclimate within the module and permeation properties of the backsheet on their degradation. FTIR-ATR spectroscopy revealed strong influence of the type of the backsheet and microclimate within the test module on degradation of front encapsulants. As opposed to a polymeric backsheet, an impermeable glass backsheet prevents moisture and oxygen ingress towards cell and front encapsulant, which results in different degradation mechanisms. TPO showed very good weathering stability in both types of modules. The results of these investigations have confirmed that type of the backsheet plays an important role in the degradation of front encapsulants in PV modules. Chapter 4 deals with thermo-mechanical stability of state-of-the-art and alternative polyolefin encapsulants. In order to understand the influence of aging on thermo-mechanical behaviour of encapsulants, thermo-mechanical analysis (TMA) was conducted on laminated encapsulants before and after 1000h of damp heat aging. The results have shown strong influence of morphology, i.e. crystallinity on the thermo-mechanical behaviour of encapsulants. Due to the highest crystalline content, TPO showed the most stable thermo-mechanical behaviour among the investigated encapsulants before and after aging. On the other hand, EVA with the lowest crystalline content showed the highest thermal expansion, which could lead to the formation of stresses within the PV module during production and service time and give rise to different failure modes. According to the state-of-the-art IEC 61215 qualification test, damp heat testing of modules performed at 85°C and 85% RH for 1000h provides the most information on aging and degradation of encapsulation materials, but this test is recognized as not predictive of long term performance. Chapter 5 deals with the influence of climate-specific accelerated tests on degradation of EVA at the PV module level. The main focus in this part was on the application of non-destructive methods, whereas Raman confocal spectroscopy proved to be a great tool for fast and non-destructive qualitative and quantitative assessment of EVA degradation. The results showed significant difference in EVA degradation behaviour under different aging conditions compared to standard tests, which could be of great importance for the development
Translated title of the contributionWitterungsbeständigkeit von Kunststoffkomponenten für PV Module die unter rauen Klimabedienungen dienen
Original languageEnglish
QualificationDr.mont.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Erceg, Matko, Assessor B (external), External person
  • Pinter, Gerald, Assessor A (internal)
Publication statusPublished - 2019

Bibliographical note

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Keywords

  • PV modules
  • polymers
  • alternative materials
  • degradation
  • weathering stability
  • feasibility study

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