SIST EN IEC 62788-6-2:2020

SLOVENSKI STANDARD
SIST EN IEC 62788-6-2:2020
01-julij-2020
Merilni postopki za materiale, uporabljene v fotonapetostnih modulih - 6-2. del:
Splošni preskusi - Preskušanje pronicanja vlage pri polimernih materialih
Measurement procedures for materials used in photovoltaic modules - Part 6-2: General
tests - Moisture permeation testing with polymeric materials
Messverfahren für Werkstoffe, die in Photovoltaik-Modulen verwendet werden - Teil 6-2:
Allgemeine Prüfungen - Permeationsprüfung mit polymeren Materialien
Procédures de mesure des matériaux utilisés dans les modules photovoltaïques - Partie
6-2: Essais génériques - Essais de perméation à l’humidité des matériaux polymères
Ta slovenski standard je istoveten z: EN IEC 62788-6-2:2020
ICS:
27.160 Sončna energija Solar energy engineering
83.080.01 Polimerni materiali na Plastics in general
splošno
SIST EN IEC 62788-6-2:2020 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN IEC 62788-6-2:2020


EUROPEAN STANDARD EN IEC 62788-6-2

NORME EUROPÉENNE

EUROPÄISCHE NORM
May 2020
ICS 27.160

English Version
Measurement procedures for materials used in photovoltaic
modules - Part 6-2: General tests - Moisture permeation testing
of polymeric materials
(IEC 62788-6-2:2020)
Procédures de mesure des matériaux utilisés dans les Messverfahren für Werkstoffe, die in Photovoltaik-Modulen
modules photovoltaïques - Partie 6-2: Essais génériques - verwendet werden - Teil 6-2: Allgemeine Prüfungen -
Essais de perméation à l'humidité des matériaux polymères Permeationsprüfung mit polymeren Materialien
(IEC 62788-6-2:2020) (IEC 62788-6-2:2020)
This European Standard was approved by CENELEC on 2020-04-23. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.


European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2020 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
 Ref. No. EN IEC 62788-6-2:2020 E

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EN IEC 62788-6-2:2020 (E)
European foreword
The text of document 82/1659/FDIS, future edition 1 of IEC 62788-6-2, prepared by IEC/TC 82 "Solar
photovoltaic energy systems" was submitted to the IEC-CENELEC parallel vote and approved by
CENELEC as EN IEC 62788-6-2:2020.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2021-01-23
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2023-04-23
document have to be withdrawn

Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.

Endorsement notice
The text of the International Standard IEC 62788-6-2:2020 was approved by CENELEC as a
European Standard without any modification.
In the official version, for Bibliography, the following note has to be added for the standard indicated:
IEC 61730-1 NOTE Harmonized as EN IEC 61730-1


2

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EN IEC 62788-6-2:2020 (E)
Annex ZA
(normative)

Normative references to international publications
with their corresponding European publications
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.
NOTE 1  Where an International Publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.
NOTE 2  Up-to-date information on the latest versions of the European Standards listed in this annex is available here:
www.cenelec.eu.
Publication Year Title EN/HD Year
ISO 2528 - Sheet materials - Determination of water - -
vapour transmission rate - Gravimetric (dish)
method
ISO 9932 - Paper and board - Determination of water - -
vapour transmission rate of sheet materials -
Dynamic sweep and static gas methods
ISO 15106-1 - Plastics - Film and sheeting - Determination EN ISO 15106-1 -
of water vapour transmission Rate - Part 1:
Humidity detection sensor method
ISO 15106-2 - Plastics - Film and sheeting - Determination EN ISO 15106-2 -
of water vapour transmission Rate - Part 2:
Infrared detection sensor method
ISO 15106-3 - Plastics - Film and sheeting - Determination EN ISO 15106-3 -
of water vapour transmission Rate - Part 3:
Electrolytic detection sensor method
ISO 15106-4 - Plastics - Film and sheeting - Determination - -
of water vapour transmission Rate - Part 4:
Gas-chromatographic detection sensor
method
IEC/TS 61836 - Solar photovoltaic energy systems - Terms, - -
definitions and symbols
ASTM F1249-06 - Standard test method for water vapour - -
transmission rate through plastic film and
sheeting using a modulated infrared sensor



3

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SIST EN IEC 62788-6-2:2020




IEC 62788-6-2

®


Edition 1.0 2020-03




INTERNATIONAL



STANDARD




NORME



INTERNATIONALE
colour

inside










Measurement procedures for materials used in photovoltaic modules –

Part 6-2: General tests – Moisture permeation testing of polymeric materials




Procédures de mesure des matériaux utilisés dans les modules

photovoltaïques –

Partie 6-2: Essais génériques – Essais de perméation à l’humidité des matériaux


polymères













INTERNATIONAL

ELECTROTECHNICAL

COMMISSION


COMMISSION

ELECTROTECHNIQUE


INTERNATIONALE




ICS 27.160 ISBN 978-2-8322-7921-2




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

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale

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CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms, definitions and symbols. 7
3.1 Terms and definitions . 7
3.2 Symbols . 7
4 Apparatus . 8
5 Test specimens . 8
6 Procedure . 9
7 Calculations . 10
7.1 Determination of diffusivity and solubility of moisture . 10
7.2 Determination of breakthrough constant . 11
7.3 Variable temperature measurement . 12
7.4 Variable relative humidity measurement . 13
8 Test report . 13
Annex A (informative) Example data . 15
A.1 Example of Fickian diffusion . 15
A.2 Example of failed measurement of Fickian diffusion . 16
A.3 Example of non-Fickian diffusion . 17
Bibliography . 19

Figure 1 – Diagram of a diffusion cell . 9
Figure A.1 – Example of Fickian diffusion in EVA at 85 °C and 100 % RH with a 2,84
mm thick film . 16
Figure A.2 – Example of a failed data set for Fickian diffusion in polyethylene
terepthalate at 22 °C and 100 % RH . 17
Figure A.3 – Example of non–Fickian diffusion in a desiccant filled polyisobutylene
material used as an edge seal . 18

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IEC 62788-6-2:2020 © IEC 2020 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

MEASUREMENT PROCEDURES FOR MATERIALS
USED IN PHOTOVOLTAIC MODULES –

Part 6-2: General tests –
Moisture permeation testing of polymeric 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
in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,
Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their
preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
may participate in this preparatory work. International, governmental and non–governmental organizations
liaising with the IEC also participate in this preparation. IEC collaborates closely with the International
Organization for Standardization (ISO) in accordance with conditions determined by agreement between the two
organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence between
any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
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.
International Standard IEC 62788-6-2 has been prepared by IEC technical committee 82: Solar
photovoltaic energy systems.
The text of this International Standard is based on the following documents:
FDIS Report on voting
82/1659/FDIS 82/1690/RVD

Full information on the voting for the approval of this International Standard 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.

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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 "http://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 publication 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.

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IEC 62788-6-2:2020 © IEC 2020 – 5 –
INTRODUCTION
This part of IEC 62788 describes methods to measure the permeation properties of polymeric
materials. The degradation of PV modules is known to go through many different corrosion
processes. These degradation processes may depend upon moisture ingress into the
encapsulant, edge seal, frontsheet, or backsheet materials. Typical polymeric materials used
include (amongst other polymers) ethylene-vinyl acetate (EVA) and polyolefins for
encapsulants, polyisobutylene (PIB) for edge seals, and polyethylene terephthalate (PET),
polyvinyl fluoride (PVF), or polyvinylidine fluoride (PVDF) for backsheets. Therefore, knowing
the moisture permeation characteristics of polymeric materials is relevant for module design.
These properties can be determined as a function of temperature and relative humidity. With
these parameters, simple scaling rules for time and distance can be used to extrapolate to the
use environments.

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MEASUREMENT PROCEDURES FOR MATERIALS
USED IN PHOTOVOLTAIC MODULES –

Part 6-2: General tests –
Moisture permeation testing of polymeric materials



1 Scope
This document provides methods for measuring the steady-state water vapour transmission
rate (WVTR), water vapour permeability (P), diffusivity (D), solubility (S), and moisture
breakthrough time (Ƭ ) (defined as the time to reach 10 % of the steady state WVTR) for
10
polymeric materials such as encapsulants, edge seals, frontsheets and backsheets. These
measurements can be made at selected temperatures and humidity levels as deemed
appropriate for evaluation of their performance in PV modules. Measurement is accomplished
by inspection of the transient WVTR curve and by fitting it to a theoretical Fickian model. This
document is best applied to monolithic films. If multilayer films are used, the D and S values are
only apparent values, but the steady-state values can still be measured.
This document was written for the measurement of water permeation, but it can equally be used
for other permeants such as O . In this case the same diffusion equations, fitting procedures,
2
and scaling arguments are used.
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 61836, Solar photovoltaic energy systems – Terms, definitions and symbols
ISO 2528, Sheet materials – Determination of water vapour transmission rate (WVTR) –
Gravimetric (dish) method
ISO 9932, Paper and board – Determination of water vapour transmission rate of sheet
materials – Dynamic sweep and static gas methods
ISO 15106-1, Plastics – Film and sheeting – Determination of water vapour transmission Rate
– Part 1: Humidity detection sensor method
ISO 15106-2, Plastics – Film and sheeting – Determination of water vapour transmission Rate
– Part 2: Infrared detection sensor method
ISO 15106-3, Plastics – Film and sheeting – Determination of water vapour transmission Rate
– Part 3: Electrolytic detection sensor method
ISO 15106-4, Plastics – Film and sheeting – Determination of water vapour transmission Rate
– Part 4: Gas-chromatographic detection sensor method
ASTM F1249-06, Standard test method for water vapour transmission rate through plastic film
and sheeting using a modulated infrared sensor

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3 Terms, definitions and symbols
For the purposes of this document, the terms and definitions the terms and definitions given in
IEC TS 61836 and 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 Terms and definitions
3.1.1
edge seal
polymeric material designed to be placed between two impermeable (or with extremely low
permeability) frontsheet and backsheet materials to restrict moisture ingress from the sides
3.1.2
Fickian
material for which the diffusivity is constant, independent of concentration of the permeant
within the experimental uncertainty
3.1.3
permeability
state or quality of a material or membrane that causes it to allow liquids or gases to pass through
it
3.1.4
diffusivity
measure of the capability of a substance to be diffused or to allow something to pass by diffusion
3.2 Symbols
T temperature [°C] or [K]
t time from application of moisture or the start of the experiment [h]
instrumental delay time [h]
Ƭ
delay
Ƭ time for WVTR to reach 10 % of its steady-state value [h]
10
Ƭ time for WVTR to reach 50 % of its steady-state value [h]
1/2
l sample thickness [mm]
H relative humidity [%]
−2 −1
T water vapour transmission rate [g·m ·day ]
R
−2 −1
P water permeability [g·mm·m ·day ]
2 −1
D water diffusivity [cm ·s ]
−3
S water solubility [g·cm ]
−0,5
K moisture ingress breakthrough constant [cm·h ]
10
−2 −1
P Arrhenius permeability prefactor [g·mm·m ·day ]
o
−1
Ea Arrhenius permeability activation energy [kJ·mol ]
P
2 −1
D Arrhenius diffusivity prefactor [cm ·s ]
o
−1
Ea Arrhenius diffusivity activation energy [kJ·mol ]
D

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−3
S Arrhenius solubility prefactor [g·cm ]
o
−1
Ea Arrhenius solubility activation energy [kJ·mol ]
S
−0,5
K Arrhenius moisture ingress breakthrough constant prefactor [cm·h ]
o,10
−1
Ea Arrhenius moisture ingress breakthrough constant activation energy [kJ·mol ]
K10
4 Apparatus
Any instrument capable of measuring the transient permeation through a membrane shall be
used. Many examples of apparatus that are suitable for these measurements are described in
ASTM F1249-06, ISO 2528, ISO 9932, ISO 15106-1, ISO 15106-2, ISO 15106-3, and
ISO 15106-4. The key characteristics to look for are high precision and small timescales for the
response to changes. At low permeation rates, the amount of moisture adsorbed onto
instrument surfaces becomes a problem, because it limits the useful precision of some
instruments.
5 Test specimens
The suitable polymer film sample thickness will depend on the transient WVTR and the
instrumental setup. Typically, samples are between 0,25 mm and 2 mm thick, but other
thicknesses may be used. Very low-permeability materials, such as polychlorotrifluoroethylene
(PCTFE) may require much thinner films so that permeated water is detectable at low
temperatures. Conversely, high-diffusivity materials (such as silicones) may need to be several
millimetres thick to accurately separate the lag time, associated with transient diffusion in the
polymer, from the instrumental delay. For very thick samples, care shall be taken to assess
and/or minimize moisture ingress from, or egress to, the external environment from the sides
of the sample. Thickness variation shall be less than ±5 % over the sample area of interest.
2 2
The suggested sample test area is between 5 cm to 100 cm , but other areas may be used if
desired.
NOTE Masks can be provided by permeation equipment manufacturers and are typically made of an Al foil with an
2 2
adhesive on one side. These masks are typically designed to reduce the transmission area from 50 cm to 5 cm .
Samples shall be processed or cured (if applicable) in accordance with the manufacturer’s
specification. Verify that the sample does not change during measurement through loss of
volatiles or other chemical degradation processes in a way that could change the permeation
properties relative to the intended use environment. This can be verified by comparing initial
measurements with another set of measurements, made under the same conditions, on the
same film, at a later date. If permeation changes with aging, one shall either only use fresh
samples or aged samples and note the sample history in the test report.
Sample surfaces shall be smooth and flat with uniform thickness (< 5 % variation in thickness).
This can require curing (or thermal treatment) while being held between flat, planar surfaces.
Masking the samples or supporting them with a mesh can be necessary during testing at higher
temperatures to prevent sag or other deformations of the sample.
Some materials, particularly polyisobutylene-based edge seals, are very tacky and prone to
stick to the surfaces of the measurement instrument. In this case, a thin (preferably < 0,05 mm),
−2 −1
highly permeable (50 g·m ·day ), non–stick supporting film may be used. If a film like this is
used, verify that it does not impact the results by measuring films of at least two different
thicknesses. If the films do not impact the measurement, the steady-state WVTR will scale as
2
1/l and the transient time should scale as 1/l , where l is the sample thickness.

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If a thicker specimen is needed, multiple layers of film may be simply stacked together in the
test fixture as long as the air gap between layers is minimized. It is recommended that the
laminate be run through a roll laminator or some other means to create good contact between
films. This method yields acceptable results because the volume of the air gap is very low, the
mole fraction of water in air is typically low, and the diffusivity of moisture in air is very high. If
applying this method to other permeants, such as oxygen, small gaps between layers are likely
−1
to affect the results. Here, one shall verify the WVTR and the transient time scale as l and
−2
l respectively.
When measuring multilayer laminate films containing layers of different materials (e.g. a
backsheet consisting of a fluoropolymer/polyethylene terephthalate/ethylene vinyl acetate), this
film layering procedure shall not be used to increase the delay time for moisture ingress to
determine diffusivity and solubility. Provided sufficient instrument sensitivity is present in
accordance with the restrictions outlined in Clause 7, the steady-state values for WVTR and
permeability can still be obtained without layering, but, in some cases, estimates of the apparent
diffusivity and solubility might not be possible for a given instrument with the restrictions
outlined for the time scales on the transient curves.
6 Procedure
For moisture ingress testing, sample drying in a desiccated atmosphere (RH < 1 %) prior to
testing can be used to reduce the equilibration drying time in the instrument. The required drying
time and temperature will depend on the sample diffusivity. A drying temperature of 40 °C to
50 °C is recommended for at least 48 h to 72 h for most materials. Thicker samples, or samples
with low D, can take longer to dry. For samples such as edge seals with desiccants, drying
might not be possible. In this case, the materials shall be used as received while taking
precautions to minimize the exposure to moisture prior to testing. While being conditioned,
samples should not be stacked flat on top of each other, but air should be allowed to circulate
between them. Keep the sample dry until it is placed in the diffusion cell, which has been
previously dried by removing residual moisture and/or purging with dry nitrogen or similar dry
gas. After placing the sample in the diffusion cell, allow time for equilibration of the diffusion
cell to the desired temperature.
Pass dry gas (e.g. N ) over both sides of the sample to remove any residual moisture. Care
2
should be taken to ensure that the gas is at the desired temperature before passing it over the
film. When the cell is within ±0,5 °C of the desired temperature and the WVTR is at a steady
state near zero, within the detection limits of the instrument, turn off the external purge gas on
the permeant source side and start monitoring moisture permeation on the detector side (see
Figure 1).

Figure 1 – Diagram of a diffusion cell

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For testing at 100 % RH, inject (or otherwise apply moisture as a step change) 3 ml to 10 ml of
H O into the permeant source chamber of the cell and monitor the WVTR over time noting the
2
time H O was added. Water shall not be added to the point of filling up the chamber and
2
contacting the sample. The water should be equilibrated to the desired temperature within
±10 °C. More than 10 ml of water may be necessary for larger films so that there is enough
liquid to cover the bottom of the chamber. When the WVTR has reached steady state, the
experiment can be terminated.
Experiments may also be conducted at humidity levels below 100 %. Any method that can
produce a step change in humidity may be used. The step change in humidity shall be short
enough to reach at least 90 % of the desired value in a time less than 0,05 ∙ Ƭ , where Ƭ is
1/2 1/2
the time at which WVTR (Ƭ ) is half of the WVTR at steady state.
1/2
EXAMPLE Controlled humidity step change can be accomplished by placing the test cell in a chamber with
controlled temperature and humidity.
...