IEC/TS 62788-2 Ed. 2.0 en:2024

Measurement procedures for materials used in photovoltaic modules - Part 2: Polymeric materials - Frontsheets and backsheets

IEC TS 62788-2:2024 defines test methods and datasheet reporting requirements for safety and performance-related properties (mechanical, electrical, thermal, optical, chemical) of non rigid polymeric materials intended for use in terrestrial photovoltaic modules as polymeric front- and backsheets.

The test methods in this document define how to characterize front- and backsheet materials and their components in a manner representative of how they will be used in the module, which eventually includes combination with other matched components such as encapsulants or adhesives.

Results of testing described in this document are called by IEC 62788-2-1 for safety qualification of polymeric front- and backsheets on component level and support the safety and performance-related tests defined on the PV module level as defined in the series IEC 61730 (for safety) and IEC 61215 (for performance).

This document also defines test methods for assessing inherent material characteristics of polymeric front- and backsheets or their components, which can be required in datasheet reporting or can be useful in the context of product development or design of PV modules.

This second edition cancels and replaces the first edition published in 2017. This edition includes the following significant technical changes with respect to the previous edition:

• a) With revision of IEC 61730-1 the requirements for the polymeric front- and backsheet have been moved from IEC 61730-1 into IEC 62788-2-1. This is reflected accordingly.
• b) The tensile testing method has been refined based on findings of round robin tests, including updated drawings.
• c) A thermal pre-exposure method has been introduced to be equivalent to the thermal effects of a "lamination" cycle. This pre-exposure defines the "fresh" state of the front- or backsheet in final application for evaluation of changes in ageing tests. For practical reasons, an oven exposure has been defined as an equivalent test.
• d) The multiple functions of the lamination protrusion test (previously DTI test) have been clarified, to identify and measure RUI layer thickness as well as to identify layers for which the comparative tracking index (CTI) needs to be determined. Also the content of IEC 62788-2-1 has been updated, by which the lamination protrusion test and MST 04 are additionally set in perspective to each other via engineering judgement.
• e) The DC breakdown voltage test method has been updated and the option to perform a withstand voltage test has been added (to reduce the required measurement voltage). The correction of DC breakdown voltage ( ) measurements, needed in the presence of non RUI layers and after the lamination protrusion test, has been defined more precisely.
• f) Details for thickness measurement have been added (engineered surface roughness due to embossing).
• g) The adhesion test methods have been reviewed and updated. The single cantilevered beam test has been added. Figures have been updated to align with IEC 62788-1-1.
• h) The thermal failsafe test has been added as a test method based on discussion in the parallel project for IEC 62788-2-1. The test method offers a single temperature-point evaluation to include elongation at break to the thermal endurance evaluation.
• i) A sequential UV/TC test ("solder bump test") has been added.