SIST EN 62788-1-4:2017

Measurement procedures for materials used in photovoltaic modules - Part 1-4: Encapsulants - Measurement of optical transmittance and calculation of the solar-weighted photon transmittance, yellowness index, and UV cut-off frequency

This part of IEC 62788 provides a method for measurement of the optical transmittance of
encapsulation materials used in photovoltaic (PV) modules. The standardized measurements
in this procedure quantify the expected transmittance of the encapsulation to the PV cell.
Subsequent calculation of solar-weighted transmittance allows for comparison between
different materials. The results for unweathered material may be used in an encapsulation
manufacturer’s datasheets, in manufacturer’s material or process development, in
manufacturing quality control (material acceptance), or applied in the analysis of module
performance.
This measurement method can also be used to monitor the performance of encapsulation
materials after weathering, to help assess their durability. The standardized measurements
are intended to examine an interior region within a PV module, e.g., without the effects of
oxygen diffusion around the edges of the cells. Subsequent calculation of yellowness index
allows for quantification of durability and consideration of appearance. The change in
transmittance, yellowness index, and ultraviolet (UV) cut-off wavelength may be used by
encapsulation or module manufacturers to compare the durability of different materials.

Messverfahren für Werkstoffe, die in Photovoltaikmodulen verwendet werden - Teil 1-4: Verkapselungsstoffe - Messung der optischen Transmission und Berechnung der solargewichteten Photonentransmission, des Vergilbungsindex und der UV-Grenzfrequenz

Procédures de mesure des matériaux utilisés dans les modules photovoltaïques - Partie 1-4: Encapsulants - Mesurage du facteur de transmission optique et calcul du facteur de transmission photonique à pondération solaire, de l'indice de jaunissement et de la fréquence de coupure des UV

L'IEC 62788-1-4:2016 fournit une méthode de mesure du facteur de transmission optique des matériaux d'encapsulation utilisés dans les modules photovoltaïques (PV). Les mesurages normalisés de cette procédure permettent de quantifier le facteur de transmission prévu de l'encapsulation vers la cellule PV. Le calcul ultérieur du facteur de transmission à pondération solaire permet de comparer les différents matériaux. Les résultats concernant les matériaux non exposés aux intempéries peuvent être utilisés dans les fiches techniques d'un fabricant d'encapsulation, dans le développement des matériaux ou du procédé du fabricant, dans le contrôle de la qualité de fabrication (acceptation du matériau) ou être appliqués dans l'analyse des performances du module. Cette méthode de mesure peut également être utilisée pour contrôler les performances des matériaux d'encapsulation après exposition aux intempéries, afin d'évaluer leur durabilité.

Merilni postopki za materiale, uporabljene v fotonapetostnih modulih - 1-4. del: Enkapsulanti - Meritev optične prosojnosti in izračun solarno utežene prosojnosti, indeks porumenelosti in ultravijolične mejne frekvence

Ta del standarda IEC 62788 določa metodo za merjenje optične prosojnosti materialov za enkapsulacijo, ki se uporabljajo za fotonapetostne (PV) module. Standardizirane meritve v tem postopku količinsko opredeljujejo pričakovano prosojnost enkapsulacije na fotonapetostni celici.
Posledični izračun solarno utežene prosojnosti omogoča medsebojno primerjavo različnih materialov. Rezultati za materiale, ki niso bili izpostavljeni vremenskim vplivom, se lahko uporabljajo za tehnične liste proizvajalca za enkapsulacijo, za razvoj procesov ali materiala proizvajalca, za nadzor kakovosti proizvodnje (sprejemljivost materiala) ali za analizo učinkovitosti modula.
To merilno metodo je mogoče uporabljati tudi za nadzor učinkovitosti materialov za enkapsulacijo po izpostavljenosti vremenskim vplivom, na podlagi česar se poda ocena trajnosti. Namen standardiziranih meritev je preverjanje notranjega območja fotonapetostnega modula, npr. brez učinkov difuzije kisika okoli robov celic. Posledični izračun indeksa porumenelosti omogoča količinsko opredelitev trajnosti in upoštevanje videza. Spremembo prosojnosti, indeksa porumenelosti in ultravijolične (UV) mejne valovne dolžine lahko uporabljajo proizvajalci enkapsulacije ali modulov za primerjavo trajnosti različnih materialov.

General Information

• Status: Published
• Publication Date: 16-Jan-2017
• ICS: 17.180.99 - Other standards related to optics and optical measurements
• ICS: 27.160 - Solar energy engineering
• Technical Committee: PVS - Solar photovoltaic energy systems
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 11-Jan-2017
• Due Date: 18-Mar-2017
• Completion Date: 17-Jan-2017
• Ref Project: EN 62788-1-4:2016 - Measurement procedures for materials used in photovoltaic modules - Part 1-4: Encapsulants - Measurement of optical transmittance and calculation of the solar-weighted photon transmittance, yellowness index, and UV cut-off wavelength

Relations

• Amended By: SIST EN 62788-1-4:2017/A1:2021 - Measurement procedures for materials used in photovoltaic modules - Part 1-4: Encapsulants - Measurement of optical transmittance and calculation of the solar-weighted photon transmittance, yellowness index, and UV cut-off wavelength
• Effective Date: 01-Jan-2021

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN 62788-1-4:2017
01-februar-2017
0HULOQLSRVWRSNL]DPDWHULDOHXSRUDEOMHQHYIRWRQDSHWRVWQLKPRGXOLKGHO
(QNDSVXODQWL0HULWHYRSWLþQHSURVRMQRVWLLQL]UDþXQVRODUQRXWHåHQHSURVRMQRVWL
LQGHNVSRUXPHQHORVWLLQXOWUDYLMROLþQHPHMQHIUHNYHQFH
Measurement procedures for materials used in photovoltaic modules - Part 1-4:
Encapsulants - Measurement of optical transmittance and calculation of the solar-
weighted photon transmittance, yellowness index, and UV cut-off frequency
Ta slovenski standard je istoveten z: EN 62788-1-4:2016
ICS:
17.180.99 'UXJLVWDQGDUGLY]YH]L] Other standards related to
RSWLNRLQRSWLþQLPLPHUMHQML optics and optical
measurements
27.160 6RQþQDHQHUJLMD Solar energy engineering
SIST EN 62788-1-4:2017 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 62788-1-4:2017

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SIST EN 62788-1-4:2017


EUROPEAN STANDARD EN 62788-1-4

NORME EUROPÉENNE

EUROPÄISCHE NORM
December 2016
ICS 27.160

English Version
Measurement procedures for materials used in photovoltaic
modules - Part 1-4: Encapsulants - Measurement of optical
transmittance and calculation of the solar-weighted photon
transmittance, yellowness index, and UV cut-off wavelength
(IEC 62788-1-4:2016)
Procédures de mesure des matériaux utilisés dans les Messverfahren für Werkstoffe, die in Photovoltaikmodulen
modules photovoltaïques - Partie 1-4: Encapsulants - verwendet werden - Teil 1-4: Verkapselungsstoffe -
Mesurage du facteur de transmission optique et calcul du Messung der optischen Transmission und Berechnung der
facteur de transmission photonique à pondération solaire, solargewichteten Photonentransmission, des
de l'indice de jaunissement et de la fréquence de coupure Vergilbungsindex und der UV-Grenzfrequenz
des UV (IEC 62788-1-4:2016)
(IEC 62788-1-4:2016)
This European Standard was approved by CENELEC on 2016-11-01. 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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, 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: Avenue Marnix 17, B-1000 Brussels
© 2016 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
 Ref. No. EN 62788-1-4:2016 E

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SIST EN 62788-1-4:2017
EN 62788-1-4:2016
European foreword
The text of document 82/1148/FDIS, future edition 1 of IEC 62788-1-4, prepared by IEC/TC 82 "Solar
photovoltaic energy systems" was submitted to the IEC-CENELEC parallel vote and approved by
CENELEC as EN 62788-1-4:2016.

The following dates are fixed:
(dop) 2017-08-01
• latest date by which the document has to be
implemented at national level by
publication of an identical national
standard or by endorsement
• latest date by which the national (dow) 2019-11-01
standards conflicting with the
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 [and/or CEN] shall not be held responsible for identifying any or all such
patent rights.

Endorsement notice
The text of the International Standard IEC 62788-1-4:2016 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/TS 61836 NOTE Harmonized as CLC/TS 61836.
2

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SIST EN 62788-1-4:2017
EN 62788-1-4:2016
Annex ZA
(normative)

Normative references to international publications
with their corresponding European publications

The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.

NOTE 1 When 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

IEC 60904-3 -  Photovoltaic devices - EN 60904-3 -
Part 3: Measurement principles for
terrestrial photovoltaic (PV) solar devices
with reference spectral irradiance data
ISO 291 2008 Plastics - Standard atmospheres for EN ISO 291 2008
conditioning and testing
ISO 11664-1 2007 Colorimetry - EN ISO 11664-1 2011
Part 1: CIE standard colorimetric observers
ISO 11664-2 2007 Colorimetry - EN ISO 11664-2 2011
Part 2: CIE standard illuminants
ISO 13468-2 1999 Plastics - Determination of the total EN ISO 13468-2 2006
luminous transmittance of transparent
materials - Part 2: Double-beam instrument
ISO 17223 2014 Plastics - Determination of yellowness - -
index and change in yellowness index
1)
ASTM E424-71 2007 Standard test methods for solar energy - -
transmittance and reflectance (Terrestrial)
of sheet materials


1)
Superseded by ASTM E424-71:2015.
3

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SIST EN 62788-1-4:2017

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SIST EN 62788-1-4:2017



IEC 62788-1-4

®


Edition 1.0 2016-09




INTERNATIONAL



STANDARD




NORME



INTERNATIONALE











Measurement procedures for materials used in photovoltaic modules –

Part 1-4: Encapsulants – Measurement of optical transmittance and calculation

of the solar-weighted photon transmittance, yellowness index, and UV cut-off


wavelength



Procédures de mesure des matériaux utilisés dans les modules


photovoltaïques –

Partie 1-4: Encapsulants – Mesurage du facteur de transmission optique

et calcul du facteur de transmission photonique à pondération solaire,

de l'indice de jaunissement et de la fréquence de coupure des UV









INTERNATIONAL

ELECTROTECHNICAL

COMMISSION


COMMISSION

ELECTROTECHNIQUE


INTERNATIONALE




ICS 27.160 ISBN 978-2-8322-3634-5



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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SIST EN 62788-1-4:2017
– 2 – IEC 62788-1-4:2016  IEC 2016
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references. 5
3 Terms and definitions . 6
4 Principle . 7
5 Apparatus . 7
6 Test specimens . 7
6.1 Nominal (and unweathered) transmittance to the cell . 7
6.2 Weathering studies . 8
6.3 Glass for superstrates/substrates . 9
6.4 Number of specimens . 9
6.5 Preconditioning of specimens . 9
7 Measurement procedure . 9
7.1 General . 9
7.2 Specimen preparation . 9
7.3 Instrument calibration (baseline measurements) . 9
7.4 Specimen measurements . 10
7.5 Witness measurements . 10
8 Calculation and expression of results . 10
8.1 Post-processing of data . 10
8.2 Calculation of weighted transmittance . 10
8.3 Calculation of the Yellowness Index (YI) . 11
8.4 Calculation of the UV cut-off wavelength . 11
9 Uncertainty of measurements . 11
10 Test report. 12
Annex A (informative) Advanced analysis of transmittance (absorption coefficients) . 14
Annex B (informative) Applying the quantum efficiency of a specific cell technology . 16
Bibliography . 18

Table 1 – Details of the solar weight transmittance parameters . 11

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SIST EN 62788-1-4:2017
IEC 62788-1-4:2016  IEC 2016 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

MEASUREMENT PROCEDURES FOR MATERIALS
USED IN PHOTOVOLTAIC MODULES –

Part 1-4: Encapsulants – Measurement of optical transmittance and
calculation of the solar-weighted photon transmittance,
yellowness index, and UV cut-off wavelength

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 62788-1-4 has been prepared by IEC technical committee 82:
Solar photovoltaic energy systems.
The text of this standard is based on the following documents:
FDIS Report on voting
82/1148/FDIS 82/1165/RVD

Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.

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SIST EN 62788-1-4:2017
– 4 – IEC 62788-1-4:2016  IEC 2016
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.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
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 the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

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SIST EN 62788-1-4:2017
IEC 62788-1-4:2016  IEC 2016 – 5 –
MEASUREMENT PROCEDURES FOR MATERIALS
USED IN PHOTOVOLTAIC MODULES –

Part 1-4: Encapsulants – Measurement of optical transmittance and
calculation of the solar-weighted photon transmittance,
yellowness index, and UV cut-off wavelength



1 Scope
This part of IEC 62788 provides a method for measurement of the optical transmittance of
encapsulation materials used in photovoltaic (PV) modules. The standardized measurements
in this procedure quantify the expected transmittance of the encapsulation to the PV cell.
Subsequent calculation of solar-weighted transmittance allows for comparison between
different materials. The results for unweathered material may be used in an encapsulation
manufacturer’s datasheets, in manufacturer’s material or process development, in
manufacturing quality control (material acceptance), or applied in the analysis of module
performance.
This measurement method can also be used to monitor the performance of encapsulation
materials after weathering, to help assess their durability. The standardized measurements
are intended to examine an interior region within a PV module, e.g., without the effects of
oxygen diffusion around the edges of the cells. Subsequent calculation of yellowness index
allows for quantification of durability and consideration of appearance. The change in
transmittance, yellowness index, and ultraviolet (UV) cut-off wavelength may be used by
encapsulation or module manufacturers to compare the durability of different materials.
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 60904-3, Photovoltaic devices – Part 3: Measurement principles for terrestrial
photovoltaic (PV) solar devices with reference spectral irradiance data
ISO 291:2008, Plastics – Standard atmospheres for conditioning and testing
ISO 11664-1:2007, Colorimetry – Part 1: CIE standard colorimetric observers
ISO 11664-2:2007, Colorimetry – Part 2: CIE standard illuminants
ISO 13468-2:1999, Plastics – Determination of the total luminous transmittance of transparent
materials – Part 2: Double-beam instrument
ISO 17223:2014, Plastics – Determination of yellowness index and change in yellowness
index
ASTM E424-71:2007, Standard test methods for solar energy transmittance and reflectance
(Terrestrial) of sheet material

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SIST EN 62788-1-4:2017
– 6 – IEC 62788-1-4:2016  IEC 2016
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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
NOTE In cases where definitions already exist, refer to IEC TS 61836. Calculations related to these definitions
are given in Clause 8.
3.1
solar-weighted transmittance of photon irradiance
–2 –1 –1
proportion of the solar spectral photon irradiance (E , m ·s ·nm ) optically transmitted
pλ
through the specimen, throughout the range of the terrestrial solar spectrum (280 nm to
2 500 nm) (see Table 1)
–2 –1 –1
Note 1 to entry: The photon irradiance (E , m ·s ·nm ) accounts for the wavelength-specific energy of the
pλ
–2 –1
optical flux and should not be confused with spectral irradiance (E , W·m ·nm ).
λ
3.2
representative solar-weighted transmittance of photon irradiance
–2 –1 –1
proportion of the solar spectral photon irradiance (E , m ·s ·nm ) optically transmitted
pλ
through the specimen, throughout the range of the terrestrial solar spectrum (300 nm to
1 250 nm) (see Table 1)
Note 1 to entry: In the case of a PV device, the representative solar-weighted transmittance of photon irradiance
is defined throughout the range of the spectrum utilized by a representative PV device (which may not include
wavelengths as low as 280 nm or as great as 2 500 nm).
3.3
UV cut-off wavelength
λ
cUV
wavelength of light below which the encapsulation is considered optically absorbing and
above which the encapsulation is considered transmitting
Note 1 to entry: In this procedure, the absolute transmittance of 10 % (corresponding to the optical absorbance of
1
1) is considered as the threshold of the UV cut-off wavelength. As described further in [9] , the UV cut-off
wavelength may also be used to quantify the effects of weathering.
3.4
weathering
process of subjecting specimens to environmental conditions that could include ultra-violet
radiation, temperature, humidity, and ozone
Note 1 to entry: Weathering may occur in artificial or natural environments. Weathering could occur at the nominal
(field) or an accelerated rate.
3.5
yellowness index
YI
calculated value identifying the yellowness of the test specimen perceived by a human
observer (see ASTM E313-10)
Note 1 to entry: YI may be used to quantify the effects of weathering.
_____________
1
 Numbers in square brackets refer to the Bibliography.

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SIST EN 62788-1-4:2017
IEC 62788-1-4:2016  IEC 2016 – 7 –
4 Principle
The total spectral transmittance of laminated specimens, containing encapsulation material,
shall be measured using a spectrophotometer equipped with an integrating sphere. Solar-
weighted transmittance, yellowness index, and UV cut-off wavelength will be subsequently
calculated from the transmittance measurements.
The transmittance measured using this procedure may be used in a more advanced optical
analysis to improve the accuracy of PV performance analysis or distinguish between different
encapsulation materials, as described in Annex A. The transmittance measured using this
procedure may be used to estimate module performance (current yield) if the quantum
efficiency of the PV cell is known, as described in Annex B. The method does not attempt to
account for variations in transmittance with the angle of incidence, which may vary with time
of day, sky conditions, and geometry of the module, especially if concentration is used.
5 Apparatus
The test instrument shall consist of a double beam spectrophotometer equipped with an
integrating sphere. A single beam spectrophotometer may be used if the port reflectance can
be properly accounted for, as in Annex A and [2]. Details regarding the construction and
configurations of the test instrument may be found in ISO 13468-2 or ASTM E424-71. A
measurement range of at least 280 nm to 2 500 nm is required for calculation of the solar-
weighted transmittance using the AM1.5 global spectrum as in IEC 60904-3. A wavelength
increment no larger than 1 nm is preferred for the measurement, however increments up to
5 nm are permitted with linear interpolation to 1 nm.
An integrating sphere of at least 100 mm in diameter with a port area of < 5 %, as in [11], is
recommended to reduce the error in the measurement. The port area as in [9] should not
exceed 13 %.
6 Test specimens
6.1 Nominal (and unweathered) transmittance to the cell
Specimens shall be constructed using a laminate structure of glass/encapsulation, as
described in Annex A and [12].
The solar-weighted transmittance and representative solar-weighted transmittance, as
calculated in Clause 8, may be used for the purpose of reporting on an encapsulation
manufacturer’s datasheet.
The specimens shall contain an examination region free from visible flaws including:
scratches, pits, sink marks, bubbles, or other imperfections. The examination region shall be
at least 50 % larger in diameter than the measurement area of the test instrument.
NOTE 1 A spot size of 1 cm × 1 cm is common in many commercial spectrophotometer instruments. Use of
specimens at least 2 to 3 times this size will improve uniformity (resulting from fabrication) and handling (during
measurement).
The size (length and width) should be adequate to allow the specimen to fit inside the test
instrument.
The nominal thickness of the encapsulation specimens shall be equal to the thickness
intended for use in PV modules.
Specimens should be cured (if applicable) according to the manufacturer’s specification and
using a process as similar as possible to the method used in the intended manufacturing
process.

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SIST EN 62788-1-4:2017
– 8 – IEC 62788-1-4:2016  IEC 2016
The thickness of the encapsulation portion of the test specimen shall be measured after its
preparation. The thickness shall be taken as the average of three measurements obtained at
different locations on the test region of the specimen.
Glass plates shall be parallel with minimal edge pinch or edge flare. I.e. the encapsulation
thickness at any of the corners shall not be more than 10 % different than that in the centre of
the sample. In a typical bag laminator this will require the use of a frame around the samples
during lamination, but any other means of accomplishing this specification is acceptable.
The back surface of the specimens (the exposed encapsulation intended to face to the
integrating sphere) shall not be intentionally textured.
For additional resolution to more accurately distinguish between materials, subsequent
studies may utilize a thicker encapsulation layer that may be analysed to determine the
optical attenuation coefficient as described in Annex A.
If the encapsulation material is intended to be used with superstrates other than glass, the
same procedure may be used in a subsequent study. Specimens using polymeric superstrates
may be prone to optical polarization occurring within the instrument. As in [9] and [12], a
depolarizer should be used with the instrument to minimize the effects of polarization.
NOTE 2 The effect of haze in specimens prone to optical haze can be mitigated through the use of a diffusing
film, as described in [13].
6.2 Weathering studies
A glass/encapsulation/glass laminate specimen geometry is recommended.
The size (length and width) should be adequate to allow the specimen to fit inside the test
instrument.
As described in [14], the minimum size of 5 cm × 5 cm is recommended for weathering
specimens based on previous examinations of poly (ethylene-co-vinyl acetate).
Large specimens are preferred in weathering studies, because a test region may be
distinguished, where the diffusion of oxygen or moisture is limited.
Other geometries may be used with this procedure to evaluate the effects of weathering. For
example, a permeable polymeric backsheet facilitates the examination of moisture ingress.
Some PV modules make use of an edge seal to reduce moisture permeation.
Separate “blank” pieces of superstrate or substrate may be weathered with the test
specimens to quantify the degradation of those components.
The specimens shall contain an examination region free from visible flaws including:
scratches, pits, sink marks, bubbles or other imperfections. The examination region shall be
at least 50 % larger in diameter than the measurement area of the test instrument.
The nominal thickness of the encapsulation specimens shall be as intended for use in the PV
module. Specimens should be cured (if applicable) according to the manufacturer’s
specification and as similar as possible to the method used in the intended manufacturing
procedure.
The thickness of the encapsulation in the laminate may be controlled by inserting a removable
material around the specimen perimeter.

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SIST EN 62788-1-4:2017
IEC 62788-1-4:2016  IEC 2016 – 9 –
6.3 Glass for superstrates/substrates
Measurements of the nominal (unweathered) transmittance to the cell for the purpose of
encapsulation manufacturer’s datasheets shall be performed using (3 ± 0,2) mm thick silica
glass. The glass shall have smooth, defect-free surfaces that are sufficiently flat and parallel
such that the diffuse component of transmitted light is less than 1 % between 280 nm and
2 500 nm.
The solar-weighted transmittance of photon irradiance of silica glass, which may be used to
verify that the composition of the glass is appropriate, is approximately 93 %, because the
reduction in transmittance comes from reflections at the surfaces. As in [1] and [12], the
transmittance of the glass should be greater than 90 % at 280 nm.
The glass shall not be coated or contain antireflective layers. The glass shall not be
intentionally textured.
Subsequent examination beyond that intended for the encapsulation material datasheet,
including weathering, may be performed according to this procedure using other superstrate
and/or substrate materials that can incorporate other optical features, e.g., antireflective
coatings, surface texture, and untempered PV glass.
6.4 Number of specimens
A minimum of 3 replicates shall be used for the determination of the transmittance to the cell
or in weathering studies. Optical characteristics, including transmittance, YI, and the UV cut-
off wavelength shall be subsequently calculated using the average of the three separate
specimens, with the range of the measurements indicated to identify their variability.
6.5 Preconditioning of specimens
Specimens used for the pu
...