IEC TS 62788-2:2017

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

IEC TS 62788-2:2017(E) defines test methods and datasheet reporting requirements for safety and performance related properties (mechanical, electrical, thermal, optical and chemical) of non-rigid polymeric materials intended for use in terrestrial photovoltaic modules as polymeric frontsheets and backsheets. The test methods define how to characterize backsheet and frontsheet 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 encapsulant or adhesives. The methods described in this document support the safety and performance related tests defined on PV module level as defined in the series IEC 61730 and IEC 61215. This document also defines test methods for assessment of inherent material characteristics of polymeric backsheets and frontsheets or their components.

General Information

• Status: Published
• Publication Date: 15-Aug-2017
• ICS: 01 - GENERALITIES. TERMINOLOGY. STANDARDIZATION. DOCUMENTATION
• ICS: 27.160 - Solar energy engineering
• Technical Committee: TC 82 - Solar photovoltaic energy systems
• Drafting Committee: WG 2 - TC 82/WG 2
• Current Stage: PPUB - Publication issued
• Start Date: 29-Aug-2017
• Completion Date: 16-Aug-2017

Relations

• Revised: IEC TS 62788-2:2024 - Measurement procedures for materials used in photovoltaic modules - Part 2: Polymeric materials - Frontsheets and backsheets
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC TS 62788-2 ®
Edition 1.0 2017-08
TECHNICAL
SPECIFICATION
colour
inside
Measurement procedures for materials used in photovoltaic modules –
Part 2: Polymeric materials – Frontsheets and backsheets
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.

IEC Central Office Tel.: [phone]
3, rue de Varembé Fax: [phone]
CH-1211 Geneva 20 [e-mail]
Switzerland www.iec.ch
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigenda or an amendment might have been published.

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IEC TS 62788-2 ®
Edition1.0 2017-08
TECHNICAL
SPECIFICATION
colour
inside
Measurement procedures for materials used in photovoltaic modules –

Part 2: Polymeric materials – Frontsheets and backsheets

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.160 ISBN 978-2-8322-4673-3

– 2 – IEC TS 62788-2:2017 © IEC 2017
CONTENTS
FOREWORD . 6
INTRODUCTION . 8
1 Scope . 10
2 Normative references . 10
3 Terms and definitions . 13
4 Test procedures . 16
4.1 General . 16
4.2 Mechanical characteristics . 17
4.2.1 General . 17
4.2.2 Thickness . 17
4.2.3 Area weight . 18
4.2.4 Tensile strength / elongation at break . 19
4.2.5 Curling . 22
4.3 Adhesion testing . 22
4.3.1 Purpose . 22
4.3.2 General . 22
4.3.3 Sample preparation . 23
4.3.4 Sample conditioning . 24
4.3.5 Apparatus and procedure . 24
4.3.6 Adhesion tests for interfaces of backsheet and frontsheet . 24
4.3.7 Reporting requirements . 27
4.4 Thermal characteristics . 28
4.4.1 Thermal endurance . 28
4.4.2 Dimensional stability . 28
4.4.3 Relative thermal expansion (CTE) . 30
4.4.4 Thermal conductivity . 31
4.5 Electrical characteristics . 31
4.5.1 Breakdown voltage . 31
4.5.2 Distance through insulation (dti) . 32
4.5.3 Comparative Tracking Index (CTI) . 37
4.5.4 Volume resistivity . 38
4.6 Optical characteristics . 39
4.6.1 General . 39
4.6.2 Specimen preparation . 40
4.6.3 Visual Inspection . 40
4.6.4 Optical transmittance of frontsheets and backsheets . 41
4.6.5 Optical reflectance of backsheets . 42
4.6.6 Yellowness index (YI) . 42
4.6.7 Colour measurement (L*, a*, b*) . 43
4.6.8 Surface gloss. 44
4.7 Diffusion characteristics . 45
4.7.1 Permeability of water vapour . 45
4.7.2 Permeability of oxygen . 46
4.8 Chemical characteristics . 46
4.8.1 Resistance to solvents . 46

4.9 Other characteristics . 48
4.9.1 Ignitability – Purpose . 48
4.9.2 Flammability – Purpose . 48
4.10 Accelerated ageing tests . 48
4.10.1 Purpose . 48
4.10.2 Damp Heat (DH) testing at elevated heat and moisture . 49
4.10.3 Weathering at elevated levels of temperature and moisture . 50
5 Uniform characterization form (UCF) . 55
5.1 General . 55
5.2 Layer stack description . 55
5.3 Material test results and reporting requirements. 56
6 Data sheet . 58
6.1 Purpose . 58
6.2 Reporting requirements . 58
7 Product identification sheet (label) . 58
Annex A (informative) Overview of adhesion testing of frontsheet and backsheet . 59
A.1 Type of adhesion failure . 59
A.2 Characteristics of adhesion peel tests . 60
A.3 Characteristics of pluck and lap-shear tests . 60
A.4 Cross-hatch tape testing . 61
A.5 Other caveats . 61
A.6 Overview . 61
Annex B (normative) Adhesive bond strength test procedures in PV context . 64
B.1 180°peel adhesion test . 64
B.1.1 Specimens . 64
B.1.2 Procedure . 64
B.1.3 Measurement . 65
B.2 T-peel adhesion test . 66
B.2.1 Sample preparation . 66
B.2.2 Procedure . 67
B.2.3 Measurement . 67
B.3 Dynamic tensile (T-pluck). 68
B.3.1 Purpose . 68
B.3.2 Principle . 68
B.3.3 Specimens . 68
B.3.4 Measurement procedure . 69
B.3.5 Final measurements . 69
B.4 Dynamic overlap shear . 70
B.4.1 Purpose . 70
B.4.2 Principle . 70
B.4.3 Specimens . 70
B.4.4 Measurement procedure . 72
B.4.5 Final measurements . 72
B.5 Cross-hatch tape test . 73
B.5.1 Apparatus . 73
B.5.2 Procedure . 74
B.5.3 Final measurements . 74

– 4 – IEC TS 62788-2:2017 © IEC 2017
Annex C (normative) DC breakdo
...

IEC TS 62788-2 ®
Edition 1.0 2017-08
TECHNICAL
SPECIFICATION
colour
inside
Measurement procedures for materials used in photovoltaic modules –
Part 2: Polymeric materials – Frontsheets and backsheets

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form

or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or

your local IEC member National Committee for further information.

IEC Central Office Tel.: [phone]
3, rue de Varembé Fax: [phone]

CH-1211 Geneva 20 [e-mail]
Switzerland www.iec.ch
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigenda or an amendment might have been published.

IEC Catalogue - webstore.iec.ch/catalogue Electropedia - www.electropedia.org
The stand-alone application for consulting the entire The world's leading online dictionary of electronic and
bibliographical information on IEC International Standards, electrical terms containing 20 000 terms and definitions in
Technical Specifications, Technical Reports and other English and French, with equivalent terms in 16 additional
documents. Available for PC, Mac OS, Android Tablets and languages. Also known as the International Electrotechnical
iPad. Vocabulary (IEV) online.

IEC publications search - www.iec.ch/searchpub IEC Glossary - std.iec.ch/glossary
The advanced search enables to find IEC publications by a 65 000 electrotechnical terminology entries in English and
variety of criteria (reference number, text, technical French extracted from the Terms and Definitions clause of
committee,…). It also gives information on projects, replaced IEC publications issued since 2002. Some entries have been
and withdrawn publications. collected from earlier publications of IEC TC 37, 77, 86 and

CISPR.
IEC Just Published - webstore.iec.ch/justpublished

Stay up to date on all new IEC publications. Just Published IEC Customer Service Centre - webstore.iec.ch/csc
details all new publications released. Available online and If you wish to give us your feedback on this publication or
also once a month by email. need further assistance, please contact the Customer Service
Centre: [e-mail].
IEC TS 62788-2 ®
Edition1.0 2017-08
TECHNICAL
SPECIFICATION
colour
inside
Measurement procedures for materials used in photovoltaic modules –

Part 2: Polymeric materials – Frontsheets and backsheets

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.160 ISBN 978-2-8322-4673-3

– 2 – IEC TS 62788-2:2017 © IEC 2017

CONTENTS
FOREWORD . 6

INTRODUCTION . 8

1 Scope . 10

2 Normative references . 10

3 Terms and definitions . 13

4 Test procedures . 16

4.1 General . 16

4.2 Mechanical characteristics . 17
4.2.1 General . 17
4.2.2 Thickness . 17
4.2.3 Area weight . 18
4.2.4 Tensile strength / elongation at break . 19
4.2.5 Curling . 22
4.3 Adhesion testing . 22
4.3.1 Purpose . 22
4.3.2 General . 22
4.3.3 Sample preparation . 23
4.3.4 Sample conditioning . 24
4.3.5 Apparatus and procedure . 24
4.3.6 Adhesion tests for interfaces of backsheet and frontsheet . 24
4.3.7 Reporting requirements . 27
4.4 Thermal characteristics . 28
4.4.1 Thermal endurance . 28
4.4.2 Dimensional stability . 28
4.4.3 Relative thermal expansion (CTE) . 30
4.4.4 Thermal conductivity . 31
4.5 Electrical characteristics . 31
4.5.1 Breakdown voltage . 31
4.5.2 Distance through insulation (dti) . 32
4.5.3 Comparative Tracking Index (CTI) . 37
4.5.4 Volume resistivity . 38
4.6 Optical characteristics . 39
4.6.1 General . 39

4.6.2 Specimen preparation . 40
4.6.3 Visual Inspection . 40
4.6.4 Optical transmittance of frontsheets and backsheets . 41
4.6.5 Optical reflectance of backsheets . 42
4.6.6 Yellowness index (YI) . 42
4.6.7 Colour measurement (L*, a*, b*) . 43
4.6.8 Surface gloss. 44
4.7 Diffusion characteristics . 45
4.7.1 Permeability of water vapour . 45
4.7.2 Permeability of oxygen . 46
4.8 Chemical characteristics . 46
4.8.1 Resistance to solvents . 46

4.9 Other characteristics . 48

4.9.1 Ignitability – Purpose . 48

4.9.2 Flammability – Purpose . 48

4.10 Accelerated ageing tests . 48

4.10.1 Purpose . 48

4.10.2 Damp Heat (DH) testing at elevated heat and moisture . 49

4.10.3 Weathering at elevated levels of temperature and moisture . 50

5 Uniform characterization form (UCF) . 55

5.1 General . 55

5.2 Layer stack description . 55
5.3 Material test results and reporting requirements. 56
6 Data sheet . 58
6.1 Purpose . 58
6.2 Reporting requirements . 58
7 Product identification sheet (label) . 58
Annex A (informative) Overview of adhesion testing of frontsheet and backsheet . 59
A.1 Type of adhesion failure . 59
A.2 Characteristics of adhesion peel tests . 60
A.3 Characteristics of pluck and lap-shear tests . 60
A.4 Cross-hatch tape testing . 61
A.5 Other caveats . 61
A.6 Overview . 61
Annex B (normative) Adhesive bond strength test procedures in PV context . 64
B.1 180°peel adhesion test . 64
B.1.1 Specimens . 64
B.1.2 Procedure . 64
B.1.3 Measurement . 65
B.2 T-peel adhesion test . 66
B.2.1 Sample preparation . 66
B.2.2 Procedure . 67
B.2.3 Measurement . 67
B.3 Dynamic tensile (T-pluck). 68
B.3.1 Purpose . 68
B.3.2 Principle . 68

B.3.3 Specimens . 68
B.3.4 Measurement procedure . 69
B.3.5 Final measurements . 69
B.4 Dynamic overlap shear . 70
B.4.1 Purpose . 70
B.4.2 Principle . 70
B.4.3 Specimens . 70
B.4.4 Measurement procedure . 72
B.4.5 Final measurements . 72
B.5 Cross-hatch tape test . 73
B.5.1 Apparatus . 73
B.5.2 Procedure . 74
B.5.3 Final measurements . 74
...