Photovoltaic modules - Extended-stress testing - Part 2: Polymeric component materials

IEC TS 63209-2:2022 includes a menu of tests to use for evaluation of the long-term reliability of materials used as backsheets and encapsulants in PV modules. It is intended to provide information to supplement the baseline testing defined in IEC 61215 and IEC 61730, which are qualification tests with pass-fail criteria. used for reliability analysis and is not intended to be used as a pass-fail test procedure. This document addresses polymeric materials in the crystalline silicon module laminates, specifically backsheets and encapsulants in Glass/Glass or Glass/Backsheet modules. The included environmental stress tests are intended to cause degradation that is most relevant to field experience, but these may not capture all failure modes which may be observed in various locations.

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Publication Date
16-Aug-2022
Current Stage
PPUB - Publication issued
Completion Date
17-Aug-2022
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IEC TS 63209-2
Edition 1.0 2022-08
TECHNICAL
SPECIFICATION
colour
inside
Photovoltaic modules – Extended-stress testing –
Part 2: Polymeric component materials
IEC TS 63209-2:2022-08(en)
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---------------------- Page: 2 ----------------------
IEC TS 63209-2
Edition 1.0 2022-08
TECHNICAL
SPECIFICATION
colour
inside
Photovoltaic modules – Extended-stress testing –
Part 2: Polymeric component materials
INTERNATIONAL
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® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC TS 63209-2:2022 © IEC 2022
CONTENTS

FOREWORD ........................................................................................................................... 3

INTRODUCTION ..................................................................................................................... 5

1 Scope .............................................................................................................................. 6

2 Normative references ...................................................................................................... 6

3 Terms and definitions ...................................................................................................... 7

4 Failure modes and component interactions ...................................................................... 8

5 Selection of tests ............................................................................................................. 9

6 Single component testing ................................................................................................ 9

6.1 Extended test procedures ....................................................................................... 9

6.2 Reporting of single component durability properties .............................................. 10

6.2.1 Product identification ..................................................................................... 10

6.2.2 Reliability test data ........................................................................................ 10

7 BOM specific testing ...................................................................................................... 11

7.1 Test procedures – test coupons ............................................................................ 11

7.2 Test procedure – mini-modules ............................................................................. 13

7.2.1 Mini-module design........................................................................................ 13

7.2.2 Mini-module testing ....................................................................................... 14

7.3 Reporting of BOM specific tests ............................................................................ 15

7.3.1 Product identification ..................................................................................... 15

7.3.2 Reliability test data ........................................................................................ 15

8 Uniform Characterization Form ...................................................................................... 16

8.1 General ................................................................................................................. 16

8.2 Material test results and reporting requirements .................................................... 17

Bibliography .......................................................................................................................... 20

Figure 1 – Mini-module design parameters, 1-cell and 4-cell ................................................. 14

Table 1 – Encapsulant and backsheet failure modes ............................................................... 9

Table 2 – Single component testing ...................................................................................... 10

Table 3 – BOM specific tests for Glass/Backsheet cSi modules ............................................ 12

Table 4 – BOM specific tests for Glass/Glass cSi modules .................................................... 13

Table 5 – Mini-module design parameters ............................................................................. 15

Table 6 – Uniform Characterization Form – Part 1 ................................................................ 18

Table 7 – Uniform Characterization Form – Part 2 ................................................................ 19

---------------------- Page: 4 ----------------------
IEC TS 63209-2:2022 © IEC 2022 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
PHOTOVOLTAIC MODULES – EXTENDED-STRESS TESTING –
Part 2: Polymeric component materials
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

co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and

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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 TS 63209-2 been prepared by IEC technical committee 82: Solar photovoltaic energy

systems. It is a Technical Specification.
The text of this Technical Specification: is based on the following documents:
Draft Report on voting
82/2015/DTS 82/2058A/RVDTS

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 Technical Specification is English.

A list of all parts in the IEC 63209 series, published under the general title Photovoltaic modules

– Extended-stress testing, can be found on the IEC website.
---------------------- Page: 5 ----------------------
– 4 – IEC TS 63209-2:2022 © IEC 2022

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 http://www.iec.ch/standardsdev/publications.

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.

IMPORTANT – The "colour inside" logo on the cover page of this document indicates that it

contains colours which are considered to be useful for the correct understanding of its

contents. Users should therefore print this document using a colour printer.
---------------------- Page: 6 ----------------------
IEC TS 63209-2:2022 © IEC 2022 – 5 –
INTRODUCTION

This document is intended as a guide for component suppliers, module manufacturers and

downstream durability assessments, and focuses on polymeric materials in crystalline silicon

module laminates.

IEC TS 63209 series describes environmental stress tests which provide data for evaluation of

the long-term reliability of PV modules, probing areas not addressed in the IEC 61215 and

IEC 61730 series. IEC TS 63209-1 provides a menu of extended environmental stress tests for

PV modules, and this document, IEC TS 63209-2, describes complementary component level

testing which probes degradation modes which are not easily understood or addressed by

module level testing. This document additionally describes an overlapping suite of component

level tests useful for screening individual components and component combinations for a

specific bill of materials (BOM).

The testing in this document is intended for reliability evaluation only, with no pass/fail

requirements.

This document does not describe any new test or stress exposures, but takes the single

component testing described in the IEC 62788 series as a base line for stress exposures which

are then extended. As degradation of one component can be influenced by other components

(e.g. some backsheets tested with one encapsulant may perform differently than with another,

and vice versa), a slate of BOM-specific tests and related stress exposures are included which

are described in IEC 62788 component standards, but are not typically part of component data

sheets.

This document details component level stress sequences, sample construction and evaluation

test methods which can assist in a durability analysis. A particular focus is given to UV stress

alone and in combination with other stressors. UV exposures, in particular, are difficult to

perform accurately at the module level due to time and space constraints. Polymeric

components are known to have UV-induced degradation modes which progress relatively

slowly. Testing at a component level allows for smaller sample sizes, longer stress exposures,

and test coupons designed to target relevant properties after applied stress.
---------------------- Page: 7 ----------------------
– 6 – IEC TS 63209-2:2022 © IEC 2022
PHOTOVOLTAIC MODULES – EXTENDED-STRESS TESTING –
Part 2: Polymeric component materials
1 Scope

This part of IEC TS 63209 includes a menu of tests to use for evaluation of the long-term

reliability of materials used as backsheets and encapsulants in PV modules. It is intended to

provide information to supplement the baseline testing defined in IEC 61215 and IEC 61730,

which are qualification tests with pass-fail criteria. It may be used by PV stakeholders in

conjunction with IEC TS 63209-1, to provide more extended stress testing of the component

materials than can practically be accomplished with PV modules. The data set resulting from

testing is used for reliability analysis and is not intended to be used as a pass-fail test

procedure. This document addresses polymeric materials in the crystalline silicon module

laminates, specifically backsheets and encapsulants in Glass/Glass or Glass/Backsheet

modules. Although not specifically addressed, it is expected to also have applicability to thin

film technologies.

The included environmental stress tests are intended to cause degradation that is most relevant

to field experience, but these may not capture all failure modes which may be observed in

various locations.

The individual component standards provide a starting point for testing, and baseline data for

reference in this document may be available from a characterization sheet developed in

accordance with the Uniform Characterization Forms (UCF) of IEC TS 62788-2 and
IEC 62788-1-1. Extended tests using the same methods allows for trend analysis.

Additional testing is included to address interactions with other polymeric packaging material,

as individual components can perform differently depending on adjacent materials. These tests

are designed with BOM-specific coupons and mini-modules, intended to complement the

specific module bill of materials used in the IEC TS 63209-1 module tests.

As both test specimen form factor and I-V characteristics can play a role in degradation, some

multicomponent tests are designed to use a polymeric stack, while others use mini-modules.

The included stress tests are not designed to test to failure, but to be representative of stress

levels of the long-term application.

These tests are not intended to provide service life estimates, or to be indicative of fitness for

use in specific climate/mounting configurations. For example, the same module deployed in two

different locations or with different mounting methods may degrade in different ways, so a single

test protocol cannot be expected to exactly match the performance in both environments;

correlation to field will depend upon where and how the product is deployed.
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 TS 60904-13:2018, Photovoltaic devices – Part 13: Electroluminescence of photovoltaic

modules
---------------------- Page: 8 ----------------------
IEC TS 63209-2:2022 © IEC 2022 – 7 –

IEC 61215-1-1:2021, Terrestrial photovoltaic (PV) modules – Design qualification and type

approval -Part 1-1: Special requirements for testing of crystalline silicon photovoltaic (PV)

modules

IEC 61215-2:2021, Terrestrial photovoltaic (PV) modules – Design qualification and type

approval – Part 2: Test procedures

IEC 61730-2, Photovoltaic (PV) module safety qualification – Part 2: Requirements for testing

IEC TS 61836, Solar photovoltaic energy systems – Terms, definitions and symbols

IEC 62788-1-1, Measurement procedures for materials used in photovoltaic modules – Part 1-1:

Encapsulants – Polymeric materials used for encapsulants

IEC 62788-1-6, Measurement procedures for materials used in photovoltaic modules – Part 1-6:

Encapsulants – Test methods for determining the degree of cure in ethylene-vinyl acetate

IEC 62788-1-7:2020, Measurement procedures for materials used in photovoltaic modules –

Part 1-7: Encapsulants – Test procedure of optical durability

IEC TS 62788-2, Measurement procedures for materials used in photovoltaic modules – Part 2:

Polymeric materials – Frontsheets and backsheets

IEC TS 62788-6-3, Measurement procedures for materials used in photovoltaic modules – Part

6-3: Adhesion testing of interfaces within PV modules

IEC TS 62788-7-2:2017, Measurement procedures for materials used in photovoltaic modules

– Part 7-2: Environmental exposures – Accelerated weathering tests of polymeric materials

IEC TS 62804-1, Photovoltaic (PV) modules – Test methods for the detection of potential-

induced degradation – Part 1: Crystalline silicon

IEC TS 63209-1:2021, Photovoltaic modules – Extended-stress testing – Part 1: Modules

3 Terms and definitions

For the purposes of this document, the terms and definitions given in IEC TS 62788-2,

IEC 62788-1-1, IEC 62788-1-7, IEC TS 63209-1, IEC TS 61836 along with the following apply:

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
Bill of Materials
BOM

list of the specific materials used to build a specific PV module, excluding equal alternates

3.2
Uniform Characterization Form
UCF
list of properties to be evaluated according to the tests in this document
---------------------- Page: 9 ----------------------
– 8 – IEC TS 63209-2:2022 © IEC 2022
3.3
Single Cantilever Beam
SCB
adhesion test using a single cantilever beam as described in IEC TS 62788-6-3
4 Failure modes and component interactions

Degradation of polymeric materials can occur both by chemical changes to a specific material,

such as thermo-oxidative degradation, hydrolysis, photolysis, and by morphological changes,

such as reordering of type or degree of crystallinity, which can significantly alter key properties.

Subsequent mechanical, thermo-mechanical, or hydromechanical stresses such as obtained

with thermal cycling, coefficient of thermal expansion (CTE) differentials, or from volume

changes associated with moisture ingress/egress, can then induce physical degradation, such

as delamination and cracking. Observed failure modes for backsheets and encapsulants are

shown in Table 1.

Degradation of single components is evaluated by monitoring changes to key characteristics

after single stresses (exposure to damp heat (DH), thermal, and ultraviolet (UV) as specified in

the IEC 62788 series, using the Xe exposures defined in IEC TS 62788-7-2. In this document,

the UV stress is extended and includes multiple data points to observe changes and allow for

extrapolation to longer UV exposures. Specifics are detailed in the individual single component

sections.

Observed failure modes of backsheets and encapsulants include: frontside (through glass)

cracking, backside cracking, interlayer delamination, and discoloration as well as delamination

and increased optical absorption of the encapsulant.

Failure modes can be influenced by other module components (see Bibliography for references

providing pictures and more details). These interactions can result in both positive and negative

effects as shown in Table 1. BOM specific testing is used to evaluate these effects, and

adhesion.
---------------------- Page: 10 ----------------------
IEC TS 63209-2:2022 © IEC 2022 – 9 –
Table 1 – Encapsulant and backsheet failure modes
Component Degradation mode Interactions with other components
cell side yellowing
encapsulant
cell side cracking
plus: UV filter
minus: chemical interactions with base polymer,
backsheet / encapsulant delamination
additives or impurities
loss of transmission (clear)
interlayer delamination n/a
air side yellowing n/a
encapsulant, connectors, cells
Backsheet
• connectors provide localized stress points which
can induce cracks
• thickness and compliance of encapsulant can
mitigate the stress from cell edges/connectors
encapsulant, connectors, cells
cell side and air side cracking • connectors provide localized stress points
• additive effects
glass/backsheet
yellowing • oxygen transmission effects
• additive effects
backsheet
transmission loss (non-yellowing)
• additive effects
Encapsulant
glass
adhesion to glass
• glass treatment (adhesion promoter)
adhesion to cell – front side cell
adhesion to cell – back side cell
adhesion to backsheet backsheet
5 Selection of tests

This document contains a menu of tests, which are intended to supply information to supplement

the reliability data obtained in IEC TS 63209-1. Users can select relevant tests from this list

which are relevant to the targeted application. All test data is to be reported, with no pass/fail

criterion applied.
6 Single component testing
6.1 Extended test procedures

This clause describes test for encapsulants and backsheets. Evaluation methods and stress

exposure setpoints are the same as in the referenced IEC 62788 series specifications as shown

in Table 2, with some stress durations extended from the referenced specifications.

Properties which are useful for evaluation of long-term durability of backsheets include both

direct visual observations, e.g. of cracks or delamination, and secondary characteristics which

inform as to the propensity to crack or delaminate. Quantitative property measurements are

used to determine relative changes to project trends after stress exposures. Characterization

methods for backsheets are provided in IEC TS 62788-2.

Optical transmission is the primary property for evaluating long term durability of encapsulants

as a single component. This characterization method is provided in IEC 62788-1-7.

---------------------- Page: 11 ----------------------
– 10 – IEC TS 63209-2:2022 © IEC 2022

IEC TS 62788-2 and IEC 62788-1-1 specify environmental stress exposures for single

component testing of backsheets and encapsulants. This document provides extended stresses

for some of these tests, as shown in Table 2, in the column headed by “extended”.

Table 2 – Single component testing
Hours
Component Specimen Stress Evaluation methods Reference
base extended
visual, mechanical,
BS DH 1 000 h transmittance
A3 UVX
G/E1/E1/BS 4 000h 6 000 h
visual, transmittance
(front)
A3 UVX visual, mechanical,
G/E1/E1/(trm)/BS 4 000 h 6 000 h
3 2
(front) transmittance
A3 UVX visual, mechanical,
BS 2 000 h 4 000 h
3 2 IEC TS 62788-
(back) transmittance
Backsheet
either 180 peel
Inter layer
DH 1 000
adhesion
OR SCB
not
applicabl
RUI layers (RTI) thermal mechanical
RUI layers
(thermal failsafe) 120 °C 2 000 h mechanical
G/E1/G
Transmittance ,
Encapsulant(s
A3 UVX (front) 4 000 h 6 000 h visual, yellowness, IEC 62788-1-7
G/E2/G
UV cutoff

When called for, the encapsulant is considered representative of others with same UV cut-on wavelength

specified as in IEC TS 62788-2.
Property measured for clear backsheets and encapsulants.

IEC TS 62788-2 refers to “air side” for back side exposures, and “sun-facing side” for front side exposures.

G: Glass; E: Encapsulant; BS: Backsheet, trm: transparent release material as in IEC TS 62788-2;

A3: UV Xe exposure condition in IEC TS 62788-7-2.
6.2 Reporting of single component durability properties
6.2.1 Product identification
The following information shall be included in the documentation:

a) If testing was performed as an extension to IEC TS 63209-1 testing for a specific module

model, include the module name, registered trade name, or registered trademark of

manufacturer, and type or model number designation.
b) Type designation of backsheet, encapsulant and cell.

c) Name, address and contact information of the component manufacturers or importers.

6.2.2 Reliability test data
Report all data from selected tests. No pass-fail criteria shall be applied.
UV/xenon testing as described in IEC TS 62788-7-2:2017.
Backsheets (IEC TS 62788-2).

UCF No. 1, 2 tensile strength and elongation at break (average and standard deviation)

• unexposed
---------------------- Page: 12 ----------------------
IEC TS 63209-2:2022 © IEC 2022 – 11 –
• after 1 000 h DH testing
• after 2 000 h, 4 000 h, and 6 000 h xenon weathering (front side exposures)
• after 2 000 h, 4 000 h xenon weathering (rear side exposures)
UCF No. 3, 4 interlayer adhesion
• unexposed
• after 1 000 h DH testing

UCF No. 5 (on individual RUI layers) RTE, RTI or TI (Elongation at break), OR thermal

failsafe test:
• unexposed
• after 2 000 h at 120 ˚C
UCF No. 6, 7, 8 colour or transmittance
• unexposed
• after 1 000 h DH testing
• after 2 000 h, 4 000 h, and 6 000 h xenon weathering (front side exposures)
• after 2 000 h, 4 000 h xenon weathering (rear side exposures)
Encapsulants (IEC 62788-1-1)
UCF No. 9 transmission or colour
• unexposed
• after 2 000 h, 4 000 h, 6 000 h xenon weathering.
7 BOM specific testing
7.1 Test procedures – test coupons

This clause describes test for encapsulants and backsheets and cells with the combination as

specified in a module’s Bill of Material (BOM). It is recommended that the same glass is used

in the test coupon as in the module; as this can be difficult, a different product of the same type

(base composition, surface texture, heat treatment) is allowed, if after solarization, the UV

cut-off is the same or lower than that of the module glass. If testing adhesion between

encapsulant and glass, same glass shall be used to get relevant information.

Evaluation methods and stress exposure setpoints are the same as in the referenced IEC 62788

series specifications as shown in Table 3 for glass/backsheet module designs, and Table 4 for

glass/glass designs. Stress durations are extended from the referenced specifications.

Properties which are useful for evaluation of long-term durability of backsheets/encapsulant

combinations include both direct visual observation, e.g. of cracks or delamination, and

adhesion. Test coupon preparations and characterization methods are referenced from

IEC TS 62788-2 and IEC 62788-1-1.

IEC TS 62788-2 and IEC 62788-1-1 specify environmental stress exposures for laminate

structures. This document provides extended stresses for some of these tests, as shown in the

column headed by “extended” in Table 3 for glass/backsheet modules, and in Table 4 for

glass/glass modules.
---------------------- Page: 13 ----------------------
– 12 – IEC TS 63209-2:2022 © IEC 2022
Table 3 – BOM specific tests for Glass/Backsheet cSi modules
Hours
Component,
Specimen Stress Evaluation methods Reference
failure mode
base extended
BS cracking G/E/E/BS
(back) (w/solder wire)
A3 1 000 /
2x 3x visual IEC TS 62788-2
BS cracking G/E/E/BS* 200 TC
(front) (w/solder wire)
DH200/
(A3 (back) 1 000/TC50/HF10), 3 times
BS cracking
(back), mini-modul
...

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