Influence of polymeric encapsulation materials on quality and reliability of PV modules

Marlene Knausz

Research output: ThesisDoctoral Thesis

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Abstract

The presented work aimed at improvements in the reliability of PV modules. To achieve these goals, investigations in the short-term behavior, the long-term behavior and permeation properties of several polymeric materials used in PV modules were carried out. To examine the short-term behavior of polymeric encapsulation materials, systematic investigations in the thermal expansion behavior of various encapsulants were made. In this work, an overview of the thermal expansion behavior for nine different encapsulants is firstly presented. It revealed highly relevant influences of the thermal expansion behavior of polymeric encapsulants on PV module lamination processes. Thermo-Mechanical Analysis proved to be a suitable method for applicability but also for quality control of solar cell encapsulation films. Additionally the influence of lamination process and accelerated aging conditions on a polyamide-based backsheet was investigated. Only a physical change in the polyamide, which can be attributed to a partial re-crystallization process, was detected. It was confirmed that the re-crystallization process influences the elongation at break significantly. Considering thermal loads of the lamination process and of hot climate zones, only limited influence of weathering-induced re-crystallization on the mechanical stability of the backsheet, and consequently the PV module reliability, can be expected. A remaining question in reliability testing of components for PV modules is about material (in)compatibilities and synergistic effects and thus, how the results of singly tested materials correlate with materials aged within PV modules, two accelerated aging methods were used on single and module samples. Therefore, test modules (module samples) using the same components (glass, encapsulant, solar cells etc.), varying only in the backsheet used, were produced. Two accelerated aging conditions were chosen: the DH (85°C/ 85 % RH) aging according to the standard IEC 61215, but with extended exposure time up to 2000 h, and the simultaneously impact load of enhanced temperature (50°C), humidity (80 %) and irradiation (300-2800 nm, 1000 W/m²) (climate) for 1000 h. The results indicated post-crystallization (physical aging) and hydrolytic degradation (chemical aging) of PET under DH and to a smaller extent under climate conditions. From the results it can be stated that for reliability testing of PET based backsheets under DH conditions, investigations on single sheets yield meaningful results which can be directly correlated to the behavior of the backsheets laminated within a module. For reliability testing of backsheets under climate conditions, the interpretation is more difficult as irradiation warming induced a different microclimate on modules (higher temperature) compared to the single sheets. In c-Si PV modules permeation of water vapor and oxygen play a major role on reliability. Hence, the water vapor (WVTR) and oxygen transmission rates (OTR) of six backsheets were investigated in their initial and accelerated aged states. Also, different measurement techniques for determination of OTR and WVTR were compared. It clearly pointed out the difficulties when permeation results of different techniques are compared. The results of OTR and WVTR gave an overview on the general permeation properties of the investigated backsheets. Changes in the course of aging are not negligible and revealed increases in OTR. As PV modules operate at different temperatures due to diurnal and seasonal cycles, but also to operation in different climate zones, special emphasis was given to the temperature dependence of OTR and WVTR of four backsheets. It was seen that temperature dependency significantly influences the resulting transmission rate and followed the Arrhenius approach. The results revealed generally lower energies necessary for inducing oxygen permeation. Changes of the temp
Translated title of the contributionEinfluss polymerer Einkapselungsmaterialien auf die Qualität und Zuverlässigkeit von PV Modulen
Original languageEnglish
QualificationDr.mont.
Supervisors/Advisors
  • Leising, Günther, Assessor B (external), External person
  • Oreski, Gernot, Co-Supervisor (internal)
  • Pinter, Gerald, Assessor A (internal)
Publication statusPublished - 2015

Bibliographical note

embargoed until null

Keywords

  • reliability
  • quality
  • PV module
  • polymeric encapsulation
  • accelerated aging

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