IEC 62788-1-4:2016/AMD1:2020

IEC 62788-1-4 ®
Edition 1.0 2020-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
A MENDMENT 1
AM ENDEMENT 1
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
IEC 62788-1-4:2016-09/AMD1:2020-10(en-fr)

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IEC 62788-1-4 ®
Edition 1.0 2020-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
A MENDMENT 1
AM ENDEMENT 1
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 978-2-8322-8874-0
– 2 – IEC 62788-1-4:2016/AMD1:2020
© IEC 2020
FOREWORD
This amendment has been prepared by IEC technical committee 82: Solar photovoltaic energy
systems.
The text of this amendment is based on the following documents:
FDIS Report on voting
82/1767/FDIS 82/1791/RVD
Full information on the voting for the approval of this amendment can be found in the report on
voting indicated in the above table.
The committee has decided that the contents of this amendment and the base 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• withdrawn,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.
_____________
1 Scope
In the second sentence of the second paragraph, replace:
around the edges
by:
at the periphery
4 Principle
In the last sentence, replace:
concentration
by:
optical concentration
© IEC 2020
6.1 Nominal (and unweathered) transmittance to the cell
In the fifth paragraph, replace:
The nominal thickness of the encapsulation specimens
by:
The nominal thickness of the encapsulant specimens

6.2 Weathering studies
Replace the existing third paragraph by the following:
The minimum size of 7,5 cm × 7,5 cm is recommended for weathering specimens based on
previous examinations of poly (ethylene-co-vinyl acetate).

In the eighth paragraph, replace:
The nominal thickness of the encapsulation specimens
by:
The nominal thickness of the encapsulant specimens

6.3 Glass for superstrates/substrates
Replace the existing second paragraph by the following:
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 ± 1) % between 280
nm and 2 500 nm, because the reduction in transmittance comes from reflections at the
surfaces. The UV cut-off wavelength for silica should be less than 225 nm. As in [1] and [12],
the transmittance of the glass should be greater than 90 % at 280 nm.
Replace the existing fourth paragraph by the following:
Subsequent examination beyond that intended for the encapsulation material datasheet
(including performance and weathering), such as for the purpose of quality control for
production monitoring, 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 soda-lime PV glass.
Add, at the end of the subclause, the following:
The process of solarization, where a redox reaction of trace impurities affects the UV cut-off
wavelength and corresponding range of transmittance, can occur if glass other than silica is
used [14]. It is therefore advised for weathering studies to UV condition substrate and
superstrate materials, other than silica, prior to lamination.

– 4 – IEC 62788-1-4:2016/AMD1:2020
© IEC 2020
NOTE Silica glass is more durable than soda-lime glass and will better resist glass corrosion in accelerated tests.

6.5 Preconditioning of specimens
In the title of the subclause, replace:
preconditioning
by
conditioning
In the first sentence, replace:
(23 ± 2) °C, (50 ± 5) % RH for at least 24 h, as recommended in ISO 291, prior to optical
measurement.
by:
(23 ± 2) °C, (50 ± 10) % RH for at least 24 h, as specified per Class 2 in ISO 291, prior to optical
measurement.
7.2 Specimen preparation
Replace the first sentence by the following:
Prior to measurement, specimens should be free of dust, grease or other contaminants.
Specimens may be wiped with a solution of deionized water and mild soap for cleaning prior to
measurement using a cleanroom wipe or lint free cloth.

7.4 Specimen measurements
In the first sentence of the fourth paragraph, replace:
durability
by:
weathering durability
© IEC 2020
7.5 Witness measurements
Add the following new subclause:
7.5.1 Witness specimen(s)
The witness specimens may include a traceable standard specimen, laboratory working witness
specimen, or the silica superstrate/substrate material. Witness specimen(s) for control
measurements may also include a non-weathered glass working witness specimen of the same
construction used in module representative test specimen(s) or reference (glass or polymeric
superstrate) specimen(s). When not being used for control measurements, a working witness
specimen shall be stored in the dark at 23 °C and 50 % humidity as specified per Class 2 in
ISO 291.
7.5.2 Procedure for the witness specimen prior to the test specimen(s)
After instrument equilibration and baselining, perform the transmittance measurements on a
witness specimen at the beginning of each measurement session to ensure proper operation of
the instrument and minimize the measurement error. Perform the transmittance measurements
of the witness specimen using the same procedure that will be applied to the test specimen(s).
The verification wavelengths for the working reference shall be ± 50 nm from the instrument
transitions for the source, detector, and gratings. Because of the limitations of measurement,
including noise from scattering at short wavelengths, the verification wavelengths shall not
extend below 225 nm. In the case of many commercial instruments where the source, detector,
and grating transitions occur at 350 nm, 800 nm, and 800 nm, respectively, the verification
wavelengths should include the ranges 250 nm to 300 nm, 400 nm to 750 nm and 850 nm to
2500 nm (in the case of standard measurements) or 225 nm to 300 nm, 400 nm to 750 nm and
850 nm to 2 500 nm (in the case of measurements of weathered specimens).
The transmittance at each of the verification wavelengths should be within 0,25 % of the known
transmittance (or laboratory running average) for the witness specimen. If the transmittance at
each verification wavelength is not within 0,25 % of the known transmittance, the instrument
baseline shall be performed again (including as many as three times) and the witness specimen
shall be remeasured. If the transmittance at each wavelength continues to be greater than
0,25 % of the known transmittance, the instrument sho
...