IEC 62788-2-1:2023

Measurement procedures for materials used in photovoltaic modules - Part 2-1: Polymeric materials - Frontsheet and backsheet - Safety requirements

IEC 62788-2-1:2023 specifies the safety requirements for flexible polymeric front- and backsheet constructions, which are intended for use as relied-upon insulation in photovoltaic (PV) modules. The specifications in this document define the specific requirements of polymeric front- or backsheet constructions on the component level and cover mechanical, electrical, visual and thermal characterization in an unexposed state and/or after ageing.
This document covers class II and class 0 modules, as defined in IEC 61730-1. Class III modules are out of scope. This document provides the requirements for qualification of front- and backsheets to be used in module safety qualification according to IEC 61730-1. Test method descriptions are provided in IEC TS 62788-2, along with additional characterization methods useful for performance or quality assurance.

Procédures de mesure des matériaux utilisés dans les modules photovoltaïques - Partie 2-1: Matériaux polymères - Face avant et face arrière - Exigences de sécurité

IEC 62788-2-1:2023 spécifie les exigences de sécurité pour les constructions souples de faces avant et de faces arrière polymères, prévues pour être utilisées comme isolation attendue dans les modules photovoltaïques (PV). Les spécifications du présent document définissent les exigences spécifiques des constructions des faces avant ou arrière polymères au niveau des composants et couvrent la caractérisation mécanique, électrique, visuelle et thermique des faces avant et arrière à l'état non exposé et/ou après vieillissement.
Le présent document couvre les modules de classe II et de classe 0 définis dans l'IEC 61730‑1. Les modules de classe III sont hors du domaine d'application.
Le présent document fournit les exigences de qualification des faces avant et arrière à utiliser pour la qualification pour la sûreté de fonctionnement du module conformément à l'IEC 61730‑1. Les descriptions des méthodes d'essai sont données dans l'IEC TS 62788-2, ainsi que des méthodes de caractérisation supplémentaires utiles pour assurer les performances ou la qualité.

General Information

• Status: Published
• Publication Date: 24-Aug-2023
• 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: 26-May-2023
• Completion Date: 25-Aug-2023

Standards Content (Sample)

IEC 62788-2-1
®

Edition 1.0 2023-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside


Measurement procedures for materials used in photovoltaic modules –
Part 2-1: Polymeric materials – Frontsheet and backsheet – Safety requirements

Procédures de mesure des matériaux utilisés dans les modules photovoltaïques –
Partie 2-1: Matériaux polymères – Face avant et face arrière – Exigences de
sécurité
IEC 62788-2-1:2023-08(en-fr)

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IEC 62788-2-1

®


Edition 1.0 2023-08




INTERNATIONAL



STANDARD




NORME


INTERNATIONALE
colour

inside










Measurement procedures for materials used in photovoltaic modules –

Part 2-1: Polymeric materials – Frontsheet and backsheet – Safety requirements



Procédures de mesure des matériaux utilisés dans les modules photovoltaïques –

Partie 2-1: Matériaux polymères – Face avant et face arrière – Exigences de

sécurité














INTERNATIONAL

ELECTROTECHNICAL

COMMISSION


COMMISSION

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ICS 27.160  ISBN 978-2-8322-6887-2




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– 2 – IEC 62788-2-1:2023 © IEC 2023
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 8
2 Normative references . 8
3 Terms, definitions and abbreviated terms . 9
3.1 General terms and definitions . 9
3.2 Sheet types and orientations . 9
3.3 Electrical insulation . 10
3.4 Temperatures . 11
3.5 Tensile properties . 11
4 Designation and ratings . 12
5 Requirements . 12
5.1 General . 12
5.1.1 Overview . 12
5.1.2 Single-layer constructions . 13
5.1.3 Multilayer constructions . 14
5.2 Insulation coordination . 14
5.2.1 General . 14
5.2.2 Breakdown voltage requirement for complete front- or backsheet . 14
5.2.3 Breakdown voltage requirements for individual layers . 15
5.2.4 Creepage distance requirements . 15
5.2.5 Distance through insulation requirements . 16
5.3 Thermal endurance . 16
5.4 Mechanical requirements . 17
5.5 Model and variant designation . 17
6 Evaluation of test results . 17
6.1 General . 17
6.2 Visual inspection – FBST 01 . 18
6.2.1 General . 18
6.2.2 Reporting . 18
6.3 Tensile properties – FBST 02 . 18
6.3.1 General . 18
6.3.2 Reporting . 18
6.4 Breakdown voltage – FBST 03 . 19
6.4.1 General . 19
6.4.2 Analysis . 20
6.4.3 Reporting . 20
6.5 Distance through insulation – FBST 04 . 21
6.5.1 General . 21
6.5.2 Analysis . 21
6.5.3 Reporting . 22
6.6 Material group – FBST 05 . 22
6.6.1 General . 22
6.6.2 Reporting . 23
6.7 Thermal endurance – FBST 06 . 23
6.7.1 General . 23

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IEC 62788-2-1:2023 © IEC 2023 – 3 –
6.7.2 Reporting . 23
6.8 Accelerated ageing tests . 23
6.8.1 Damp heat – FBST 07 . 23
6.8.2 UV weathering – FBST 08 . 23
6.8.3 Reporting . 24
6.9 Overview tables . 25
7 Evaluation report . 26
7.1 Report. 26
8 Documentation and testing for similar materials . 26
8.1 General . 26
8.2 Alternate constituent layers . 27
8.3 Thickness variants . 27
8.4 Color variants . 27
8.5 Reporting for similar materials with different color or thickness . 28
Annex A (informative) Chemical analytical material identification . 30
A.1 General . 30
A.2 Examples of fingerprint techniques . 30
Bibliography . 31


Figure 1 – Schematic diagrams of typical constructions of front- or backsheets . 13
Figure 2 – Examples of calculations for determination of DTI ratio and adjusted
breakdown voltage . 20
Figure 3 – Determining distance through insulation from lamination protrusion test as a
function of temperature rating . 22
Figure 4 – Schematic of lamination protrusion test result for determining which
surfaces will be evaluated for minimum creepage distance in the IEC 61730 module
design review . 23

Table 1 – Minimum breakdown voltage requirements for basic and double/reinforced
insulation before and after accelerated aging . 15
Table 2 – Minimum distance through insulation requirements. 16
Table 3 – UV exposure conditions . 24
Table 4 – Evaluations and requirements overview for individual layers . 25
Table 5 – Evaluations and requirements overview for complete front- and/or
backsheets . 25

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– 4 – IEC 62788-2-1:2023 © IEC 2023
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

MEASUREMENT PROCEDURES FOR MATERIALS
USED IN PHOTOVOLTAIC MODULES –

Part 2-1: Polymeric materials –
Frontsheet and backsheet – Safety requirements

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
IEC 62788-2-1 has been prepared by IEC technical committee 82: Solar photovoltaic energy
systems. It is an International Standard.
The text of this International Standard is based on the following documents:
Draft Report on voting
82/2123/FDIS 82/2148/RVD

Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.

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IEC 62788-2-1:2023 © IEC 2023 – 5 –
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
A list of all parts in the IEC 62788 series, published under the general title Measurement
procedures for materials used in photovoltaic modules, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

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contents. Users should therefore print this document using a colour printer.

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– 6 – IEC 62788-2-1:2023 © IEC 2023
INTRODUCTION
This document provides test procedures and specifications for polymeric front- and backsheet
constructions employed in a PV module for safety qualification on a component level. Test
methods have been compiled to match the general requirements for polymeric materials used
as relied-upon insulation defined in the IEC 61730 standard series in consideration of test
methods in IEC TS 62788-2 (characterization of front- and backsheets), IEC TS 62788-7-2
1
[4] (UV weathering test) and the retesting guidelines IEC TS 62915. This document provides
clarifications on definitions of front- and backsheet construction types and related test
requirements, and additional environmental stress testing, to which IEC 61730-1 refers.
Separating out the component level testing into this document was considered to limit the
complexity of the IEC 61730 standard series, also in view of the implementation of the test
methods in the frame of IEC System of Conformity Assessment Schemes for Electrotechnical
Equipment and Components (IECEE).
Test methods on a component level and PV module level are different for practical reasons. On
a component level, the daylight filtered xenon test (IEC TS 62788-7-2) is applied for UV
weathering, which is regarded as more representative to assess the durability of polymeric
materials under outdoor weather conditions than the UVA test of IEC 61215-2. The latter has
been developed in view of practicality of applying UV exposure to larger scale PV modules.
This document focusses on the safety relevant properties of front- and backsheets as required
by IEC 61730.
The lamination protrusion test (aka DTI test) is required to measure the thickness of relied-upon
insulation on the component level. The thickness of the RUI layer(s) is verified by MST 04 of
IEC 61730-2 on PV module level. The test provides additional information needed for evaluation
of the Comparative Tracking Index (CTI) and dielectric strength / breakdown voltage.
– The lamination protrusion test applies default lamination conditions, that are representative
for a typical PV module manufacturing process. Using a 800 µm diameter solder wire that
mimics severe solder peaks and/or slanted ribbons, the test serves as worst case scenario
for measurement of potential displacement of material under lamination conditions. Even
more harsh lamination process conditions can be selected as recommended by the
manufacturer of the front- or backsheet.
– The lamination protrusion test is also used to identify additional inner layers of the front- or
backsheet that potentially may be in contact with live parts and for which CTI shall be
determined. Additional layers may require CTI depending on the construction of the PV
module, e.g., due to specific sheet openings and through wiring for junction box connections
with background provided in IEC 61730-1.
– The ratio of the measured distance through insulation (t ) to the total thickness is used to
DTI
calculate the effective dielectric strength or required withstand voltage when measured on
final products that contain inner layers, which can be displaced under lamination conditions
(see breakdown voltage test in 6.4).
– Because of the relationship with thermal endurance, t can be listed as a function of the
DTI
module operating temperature rating.
___________
1
 Numbers in square brackets refer to the Bibliography.

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IEC 62788-2-1:2023 © IEC 2023 – 7 –
This document specifies a suite of environmental stress tests to characterize the durability of
the relied-upon insulation. In the evaluation of tensile testing a minimum elongation at break is
considered in addition to retention of tensile strength, as this allows to differentiate known-bad
and known-good materials. The thermal endurance performance, which is historically evaluated
by tensile strength and dielectric strength in terms of TI or RTE (RTI), is therefore
complemented by a thermal failsafe test to also evaluate elongation at break. The combination
of these elements, tests covering thermal, damp heat and UV weathering stresses and
evaluation of elongation at break, represents a step forward in safety testing of polymeric front-
and backsheets that is still balanced in terms or practicality (duration) of testing.
The requirements in this document for model or variant designations and (re)testing of similar
materials have been aligned with developments for the IEC TS 62915 module retesting
guidelines. The current requirements provide a first step towards more detailed requirements
which may be developed in a future revision of this document or a dedicated component
retesting standard.
A future revision of this document may consider sequential testing on engineering coupons with
(solder wire) bumps to better mimic the combination of UV and cyclic stress fatigue, that is
currently discussed as the next level in endurance testing of polymeric front- and backsheets
in IEC TS 62788-2 and IEC TS 63209-2[6]. However, method consolidation requires more time
than available for this project.
In view of requirements for material identification in the context of the retesting guidelines
(IEC TS 62915), approaches for “finger-printing” are provided in Annex A.
The requirements in this document may be used in the context of Manufacturing Quality
Assurance of polymeric front- and backsheets as explained in the guideline IEC 62941[5].

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– 8 – IEC 62788-2-1:2023 © IEC 2023
MEASUREMENT PROCEDURES FOR MATERIALS
USED IN PHOTOVOLTAIC MODULES –

Part 2-1: Polymeric materials –
Frontsheet and backsheet – Safety requirements



1 Scope
This document specifies the safety requirements for flexible polymeric front- and backsheet
constructions, which are intended for use as relied-upon insulation in photovoltaic (PV)
modules. The specifications in this document define the specific requirements of polymeric
front- or backsheet constructions on the component level and cover mechanical, electrical,
visual and thermal characterization in an unexposed state and/or after ageing.
This document covers class II and class 0 modules, as defined in IEC 61730-1. Class III
modules are out of scope.
For qualification to IEC 61730-1 of a PV module using a polymeric front- or backsheet, the sheet
must pass the requirements in this document for the specified module’s safety class, rated
system voltage, and module temperature rating.
Compliance with the safety requirements for a front- or backsheet on the component level does
not replace the need for a safety qualification of the complete PV module, in which the front- or
backsheet is integrated. The appropriate requirements for testing and qualification of PV
modules, are defined in IEC 61730-1 and IEC 61215-1 (or IEC TS 62915 in case of retesting),
with test methods provided by IEC 61730-2 and IEC 61215-2, respectively.
This document provides the requirements for qualification of front- and backsheets to be used
in module safety qualification according to IEC 61730-1. Test method descriptions are provided
in IEC TS 62788-2, along with additional characterization methods useful for performance or
quality assurance.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60216-1, Electrical insulating materials – Thermal endurance properties – Part 1: Ageing
procedures and evaluation of test results
IEC 60216-3, Electrical insulating materials – Thermal endurance properties – Part 3:
Instructions for calculating thermal endurance characteristics
IEC 60216-5, Electrical insulating materials – Thermal endurance properties – Part 5:
Determination of relative temperature index (RTI) of an insulating material
IEC 60664-1, Insulation coordination for equipment within low-voltage supply systems – Part 1:
Principles, requirements and tests
IEC 61215-1, Terrestrial photovoltaic (PV) modules – Design qualification and type approval –
Part 1: Test requirements

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IEC 62788-2-1:2023 © IEC 2023 – 9 –
IEC 61215-2, Terrestrial photovoltaic (PV) modules – Design qualification and type approval –
Part 2: Test procedures
IEC 61730-1, Photovoltaic (PV) module safety qualification – Part 1: Requirements for
construction
IEC 61730-2, Photovoltaic (PV) module safety qualification – Part 2: Requirements for testing
IEC TS 61836, Solar photovoltaic energy systems –
...