Measurement procedures for materials used in photovoltaic modules - Part 5-2: Edge seals - Durability evaluation guideline

IEC TS 62788-5-2:2020 provides guidelines to assess the ability of an edge seal to prevent moisture ingress from the edges of PV modules. This document does not cover frame adhesives (sometimes colloquially referred to as edge seals) which by design do not serve to prevent moisture ingress to a meaningful degree. Edge seals should keep moisture out, remain adhered, and maintain electrically insulation from the environment. Much of the testing can be done on the material level, but given the fact that there are multiple surfaces, materials interactions, and mechanical stresses, testing on mini modules or modules is necessary. To accomplish this, this document contains three types of test sample types, materials, mini-modules, and full-size modules. It is intended that a quick evaluation and comparison can be made using materials only. This would be followed up by more rigorous tests using mini-modules where all the interfaces are correctly represented. And finally, full-size module tests are used to evaluate the actual construction process to allow unanticipated concerns to be addressed.

General Information

Status
Published
Publication Date
21-Jun-2020
Current Stage
PPUB - Publication issued
Completion Date
22-Jun-2020
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IEC TS 62788-5-2
Edition 1.0 2020-06
TECHNICAL
SPECIFICATION
colour
inside
Measurement procedures for materials used in photovoltaic modules –
Part 5-2: Edge seals – Durability evaluation guideline
IEC TS 62788-5-2:2020-06(en)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC TS 62788-5-2
Edition 1.0 2020-06
TECHNICAL
SPECIFICATION
colour
inside
Measurement procedures for materials used in photovoltaic modules –
Part 5-2: Edge seals – Durability evaluation guideline
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.160 ISBN 978-2-8322-8387-5

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC TS 62788-5-2:2020  IEC 2020
CONTENTS

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

1 Scope .............................................................................................................................. 5

2 Normative references ...................................................................................................... 5

3 Terms and definitions ...................................................................................................... 6

4 Testing ............................................................................................................................ 7

4.1 General ................................................................................................................... 7

4.2 Material level tests .................................................................................................. 7

4.2.1 Moisture ingress .............................................................................................. 7

4.2.2 Adhesion ......................................................................................................... 7

4.2.3 Dielectric strength ............................................................................................ 7

4.2.4 Material specimen UV exposure conditions ...................................................... 7

4.2.5 Volume resistivity ............................................................................................ 8

4.3 Mini-module testing ................................................................................................. 9

4.4 Full-size module testing ........................................................................................ 11

5 Test report ..................................................................................................................... 12

Annex A (informative) Example of breakthrough time extrapolation ...................................... 14

Figure 1 – Material specimen test flow diagram ...................................................................... 8

Figure 2 – Mini-module test flow diagram .............................................................................. 10

Figure 3 – Module test flow diagram ..................................................................................... 12

Figure A.1 – Example plot of transient WVTR through a 1 mm thick film of a desiccant

filled polyisobutylene based edge seal at 100 % RH at 85 °C and at 60 °C ........................... 15

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IEC TS 62788-5-2:2020  IEC 2020 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MEASUREMENT PROCEDURES FOR MATERIALS
USED IN PHOTOVOLTAIC MODULES –
Part 5-2: Edge seals –
Durability evaluation guideline
FOREWORD

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Technical Specifications are subject to review within three years of publication to decide

whether they can be transformed into International Standards.

IEC TS 62788-5-2, which is a Technical Specification, has been prepared by IEC technical

committee 82: Solar photovoltaic energy systems.
---------------------- Page: 5 ----------------------
– 4 – IEC TS 62788-5-2:2020  IEC 2020
The text of this Technical Specification is based on the following documents:
DTS Report on voting
82/1665/DTS 82/1712A/RVDTS

Full information on the voting for the approval of this Technical Specification can be found in

the report on voting indicated in the above table.

This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

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 publication will remain unchanged until the

stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to

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---------------------- Page: 6 ----------------------
IEC TS 62788-5-2:2020  IEC 2020 – 5 –
MEASUREMENT PROCEDURES FOR MATERIALS
USED IN PHOTOVOLTAIC MODULES –
Part 5-2: Edge seals –
Durability evaluation guideline
1 Scope

This part of IEC TS 62788 provides guidelines to assess the ability of an edge seal to prevent

moisture ingress from the edges of PV modules. This document does not cover frame adhesives

(sometimes colloquially referred to as edge seals) which by design do not serve to prevent

moisture ingress to a meaningful degree. Edge seals should keep moisture out, remain adhered,

and maintain electrically insulation from the environment. Much of the testing can be done on

the material level, but given the fact that there are multiple surfaces, materials interactions, and

mechanical stresses, testing on mini modules or modules is necessary. To accomplish this, this

document contains three types of test sample types, materials, mini-modules, and full-size

modules. It is intended that a quick evaluation and comparison can be made using materials

only. This would be followed up by more rigorous tests using mini-modules where all the

interfaces are correctly represented. And finally, full-size module tests are used to evaluate the

actual construction process to allow unanticipated concerns to be addressed.

This document is structured to evaluate the ability of an edge seal and the overall packaging

design to prevent moisture ingress and to provide sufficient electrical insulation according to

accepted qualification standards. It seeks to uncover inadequacies in the permeation properties

of the edge seal, electrical safety issues, or delamination resulting in moisture ingress. Here it

is implied that mini-modules and full-size modules are constructed in accordance with

IEC 61730 series This document does not attempt to evaluate the predicted service life of a

module with respect to overall performance. It is designed to determine at the material level if

the edge seal can keep moisture out, and then to uncover potential failure modes and/or

evaluate the probable effect of manufacturing changes on the performance of edge seals. Test

conditions focus on stresses likely to produce safety, moisture ingress, and debonding related

failure modes.

For the purposes of this document, an edge seal is defined as a polymeric material designed to

be placed between two impermeable (or extremely low permeability) frontsheet and backsheet

materials to restrict moisture ingress from the sides. In some cases, an encapsulant with a

diffusivity much lower than is found in polyethylene-co-vinyl acetate (EVA) may also serve the

purpose of an edge seal and may be evaluated according to this document for comparison.

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 60904 (all parts), Photovoltaic devices

IEC 61215-1:2016, Terrestrial photovoltaic (PV) modules – Design qualification and type

approval – Part 1: Test requirements

IEC 61215-2:2016, Terrestrial photovoltaic (PV) modules – Design qualification and type

approval – Part 2: Test procedures
---------------------- Page: 7 ----------------------
– 6 – IEC TS 62788-5-2:2020  IEC 2020
IEC TS 61836, Solar photovoltaic energy systems – Terms, definitions and symbols

IEC TS 62782, Photovoltaic (PV) modules – Cyclic (dynamic) mechanical load testing

IEC 62788-1-2, Measurement procedures for materials used in photovoltaic modules – Part 1‑2:

Encapsulants – Measurement of volume resistivity of photovoltaic encapsulant and other

polymeric materials

IEC 62788-5-1, Measurement procedures for materials used in photovoltaic modules – Part 5‑1

Edge seals – Suggested test methods for use with edge seal materials

IEC 62788-6-2, Measurement procedures for materials used in photovoltaic modules – Part 6‑2:

General tests – Moisture permeation testing of polymeric materials

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

Part 7‑2: Environmental exposures – Accelerated weathering test of polymeric materials

ISO 10365, Adhesives – Designation of main failure patterns

ASTM D7869-13, Standard practice for xenon arc exposure test with enhanced light and water

exposure for transportation coatings

ASTM G154 – 12a, Standard practice for operating fluorescent ultraviolet (UV) lamp apparatus

for exposure of nonmetallic materials
3 Terms and definitions

For the purposes of this document, the terms and definitions given in IEC TS 61836 apply, as

well as the following.

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
edge seal

polymeric material designed to be placed between two impermeable (or extremely low

permeability) frontsheet and backsheet materials to restrict moisture ingress from the sides

3.2
backsheet

(combination of) outer layer(s) of the PV module, located on the back of PV module and

providing protection of the inner components of the PV module from external stresses and

weather elements, as well as electrical insulation
3.3
frontsheet

(combination of) outer layer(s) of the PV module, located on the front of PV module and

providing protection of the inner components of the PV module from external stresses and

weather elements, as well as electrical insulation
---------------------- Page: 8 ----------------------
IEC TS 62788-5-2:2020  IEC 2020 – 7 –
4 Testing
4.1 General

This document is separated into three different types of testing, materials, mini-modules, and

full-size modules as outlined in Figure 1, Figure 2 and Figure 3 respectively. Material testing

determines if the edge seal material is suitable for the application and provides some basic

information for a gross comparison of materials. Here some longer-term durability is evaluated

because of the ease with which this can be done on small material specimens.

Next, mini-module tests are designed to evaluate if the different materials can work together.

These samples consist of most or all of the materials used in the module, but just in a smaller

size consisting of a few cells or of one cell for crystalline Si modules, or a small number of small

cells for monolithically integrated thin film cells. This includes some UV, thermal and humidity

stress factors, but not mechanical stress. Because of its small size, significant UV exposure is

still possible.

Finally, full-size modules are evaluated because this enables a more accurate evaluation of the

response to mechanical stress factors, but because of the large size, there is a reduction in the

amount of UV stress. The intent here is to determine if the design is adequate and if the design

can be manufactured well.
4.2 Material level tests
4.2.1 Moisture ingress

Measure the permeation breakthrough time (τ ) from the transient permeation through a

F10 %

film of material according to IEC 62788-6-2. Measure the transient water vapour transmission

curve at (85 ± 2) °C and 100 % RH. An additional measurement at (60 ± 2) °C and 100 % RH

...

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