IEC 62788 1 5 Edition 1 0 201 6 06 INTERNATIONAL STANDARD NORME INTERNATIONALE Measurement procedures for materials used in photovoltaic modules – Part 1 5 Encapsulants – Measurement of change in l in[.]
Specimen preparation
To ensure quality, cut square specimens measuring 100 mm × 100 mm from a verified roll of encapsulation material that has been properly stored and is within its expiration date Specimens should be taken at least 200 mm from the roll's outer edges, using a uniform cutting technique to minimize size variation While the exact dimensions may vary slightly (± 5 mm), all specimens must remain smaller than the piece of aluminum foil.
Users may want to utilize the test procedure for additional purposes, such as checking the material's homogeneity across the width of an encapsulation roll In these instances, samples can be taken from various locations within the roll.
The specimens shall be handled without sudden movement, in a rigid manner during and after preparation to avoid undue stretching of the material
The machine direction (along the length of the roll) and transverse direction (across the width of the roll) shall be marked on each specimen
Once cut to size, any interleaf, liner, or release film shall be removed from the encapsulation specimens
The thickness of the encapsulation test specimen must be measured post-preparation This measurement should be the average of three values taken from various locations on the specimen, ideally positioned away from the cut edges to avoid any deformation effects caused by the cutting process.
Use of gloves is recommended during specimen preparation to avoid contaminating the specimens and/or roll of material
A consistent thickness measurement technique should be used for the thickness measurement, which is applied only for reference in this standard, because some encapsulation products are embossed or surface textured.
Number of specimens
A sample set shall be defined as three specimens taken from a separate location along the lateral (transverse) direction of the roll
For datasheet reporting, a minimum of six sample sets must be prepared, with each set containing three specimens These sample sets should be sourced from at least two separate rolls of material, with samples taken from the beginning, middle, and end of each roll, totaling 18 specimens Each set includes one specimen from the interior and two from the edges of the roll, as illustrated in Figure 1 Additionally, samples from the "beginning" and "end" of the roll must be collected at least 1 meter away from the roll's ends.
NOTE Only the sample set taken at the beginning of a roll is shown
Figure 1 – Schematic identifying the location of specimens within a sample set
For effective quality control using the datasheet value as a baseline, it is essential to consider several sampling factors These include establishing a time interval between samples to prevent consecutive rolls from being tested, sampling from various production lines when applicable, and determining an adequate sample size that enables the analysis of statistical variation.
For the purpose of quality control and manufacturing process control, different sampling quantities and sampling sets may be chosen by the material or module manufacturer
Cut edge of roll IEC
Machine extrusion direction Encapsulation specimen
Preconditioning of specimens
Specimens must not undergo any processing or preconditioning before testing It is essential to store and handle rolls of material according to the manufacturer's guidelines Prior to and following the test, specimens should be kept under laboratory conditions of 25 °C and 50% relative humidity, as specified in ISO 291 Testing should occur promptly, ideally within 8 hours after preparation.
To obtain representative results, the time between the test and sample preparation should be kept consistent
For each specimen in the sample set, the oven temperature must be set to the maximum processing temperature recommended by the encapsulation material manufacturer or the module manufacturer It is essential to allow the oven to stabilize at this temperature for a minimum of 5 minutes.
To assess materials with phase transitions and thermally facilitated cross-linking reactions, it is essential to evaluate them at a temperature that lies between the phase transition and cross-linking temperatures to determine the maximum size change Phase transitions should be analyzed according to ISO 11357-2 or ISO 11357-3 standards For instance, poly(ethylene-co-vinyl acetate) can be tested at around 100 °C, which is between its melting and curing temperatures Begin by placing a smooth, wrinkle-free piece of aluminum foil on a rack inside the oven, optionally supported by a tray or metal sheet for easier specimen removal Next, add a uniform layer of sand, approximately 2 mm to 4 mm thick, on top of the aluminum foil, ensuring its thickness is consistent by leveling it with a straight-edge tool Allow the sand's temperature to stabilize for at least 5 minutes in the oven, verifying the temperature at various locations, including the center of the substrate, using methods such as thermocouples or infrared thermometers Finally, accurately measure and record the dimensions of the test specimen in both the machine direction (MD) and transverse direction (TD), taking five separate measurements spaced evenly.
Measurements with a nominal separation of 20 mm will be conducted along the machine direction (MD) from points A to A’, B to B’, C to C’, D to D’, and E to E’, as well as the transverse direction (TD) from points a to a’, b to b’, c to c’, d to d’, and e to e’ At least two of the five measurements must be taken at least 10 mm away from the corners of the specimens, as illustrated in Figure 2 All measurements should be conducted at least 10 mm within the specimen's periphery To ensure consistency, the specimens will be marked with a soft-tip marker to allow for the same measurement locations to be used before and after heat treatment.
Figure 2 – Schematic identifying the designated measurement locations (AA’, BB’, CC’,
DD’, EE’, aa’, bb’, cc’, dd’, and ee’) for each specimen f) Open the oven door, place the encapsulation specimen on top of the sand, and close the oven door
Multiple specimens can be conditioned simultaneously in the same oven, provided there is adequate space It is important to load the specimens quickly to minimize the impact on the oven chamber temperature After 300 seconds, carefully remove the aluminum foil that supports the sand and test specimen from the heated oven Next, place the aluminum foil, along with the sand and test specimen, in a separate location to cool to ambient temperature, which can be verified by measuring the sand temperature Finally, remove the specimen from the sand and measure and record its dimensions along the machine direction (MD) and transverse direction (TD) at the same locations as before heating.
7 Calculation and expression of results
To calculate the percent size change (∆L), use the formula (1) by subtracting the final measurement (L_f) from the initial measurement (L_i) at the same location and in the same direction Next, divide the difference by the initial measurement at each corresponding site and multiply the result by 100.
A positive change in length (∆ L) indicates that the specimen has grown when the initial measurement is less than the final measurement Conversely, a negative ∆ L value signifies that the specimen has shrunk if the initial measurement exceeds the final measurement.
From the six distinct sample sets, identify the maximum value of ∆ L from the ninety values and calculate the corresponding range, which is the difference between the highest and lowest ∆ L values in each direction.
From the six different set samples, determine the mean ∆ L and corresponding standard deviation (of all ninety ∆ L values) in each direction
The repeatability and reproducibility of the method are described in [2] 1
A test report prepared by the test agency in accordance with ISO/IEC 17025 must include essential details such as the title, laboratory name and address, unique report identification, and client information It should describe the tested item, including its thickness, characterization, test conditions, and relevant dates The report must identify the test method used, reference the sampling procedure, and note any deviations or additional information pertinent to the tests It should present measurements and results supported by appropriate visuals, including maximum and mean values with standard deviations Additionally, the report must include a statement of estimated uncertainty, signatures of responsible individuals, and a disclaimer that results pertain only to the tested items, along with a note on reproduction restrictions without laboratory approval.
It is highly recommended that both encapsulation suppliers and module manufacturers maintain a copy of this report, which shall be kept for reference purposes
1 Numbers in square brackets refer to the Bibliography
Annex A (informative) Implementation and design of the test
Details that may aid in the implementation or understanding of the test may be found in the literature
[1 ] D.C Miller, L Ji, G Kelly, X.H Gu, N Nickel, P Norum, T Shioda, and G
Tamizhmani, and J.H Wohlgemuth, “Examination of Size-Change Test for PV Encapsulation Materials”, Proc SPIE, 201 2,pp 8472-29
[2] D C Miller, J Bokria, X.H Gu, C Honeker, N Nickel, K Sakurai, T Shioda, G
Tamizhmani, E Wang, S.Y Yang, T Yoshihara, O Zubillaga, and J.H Wohlgemuth,
“Verification of Size-Change Test for PV Encapsulation Materials”, Proc SPIE, 201 5
[3] IEC TS 62788-2, Measurement procedures for materials used in photovoltaic modules
– Part 2: Polymeric materials used for frontsheets and backsheets 2
5 Éprouvettes 1 8 5.1 Préparation de l'éprouvette 1 8 5.2 Nombre d'éprouvettes 1 9
7 Calcul et expression des résultats 22
Annexe A (informative) Mise en œuvre et conception de l'essai 25
Figure 1 – Schéma indiquant l'emplacement des éprouvettes d'un jeu d'échantillons 20
Figure 2 – Schéma indiquant les emplacements de mesure désignés (AA’, BB’, CC’, DD’, EE’, aa’, bb’, cc’, dd’, et ee’) pour chaque éprouvette 22
PROCÉDURES DE MESURE DES MATÉRIAUX UTILISÉS
Partie 1 -5: Encapsulants – Mesurage de la variation des dimensions linéaires des matériaux d'encapsulation en couches minces résultant des conditions thermiques appliquées
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Préconditionnement des éprouvettes
Test specimens should not undergo any treatment, such as thermal processing or preconditioning, prior to testing It is essential that the storage and handling of material rolls adhere to the manufacturer's recommendations Specimens must be kept in laboratory conditions, specifically at a temperature of 25 °C and a relative humidity of 50%, as specified in ISO 291, both before and after testing Additionally, specimens should be tested promptly within a specified timeframe.
Pour obtenir des résultats représentatifs, il convient de respecter un délai constant entre l'essai et la préparation des échantillons
The following procedure must be applied to each sample test: a) Set the oven temperature to the maximum processing temperature recommended by the encapsulation material manufacturer (or to the maximum processing temperature used by the module manufacturer) and allow the oven to stabilize at the designated temperature for at least 5 minutes.
For materials undergoing a phase transition and crosslinking reaction due to heat, it is essential to analyze the material at an intermediate temperature between the phase transition and crosslinking temperatures to determine the maximum dimensional variation The evaluation of phase transitions should be conducted in accordance with ISO 11357-2 or ISO 11357-3 standards For instance, poly(ethylene) serves as a relevant example in this context.
The extrusion direction of the co-acetate vinyl encapsulation material can be examined at approximately 100 °C, which is an intermediate temperature between its melting and curing points A smooth, wrinkle-free aluminum sheet should be placed on a support inside the oven or at the bottom of the chamber, with a metal tray or sheet used to support the aluminum and facilitate the removal of the specimens A uniform layer of sand, approximately 2 mm to 4 mm thick, should be spread over the aluminum sheet before closing the oven door The sand's surface can be leveled using a squeegee or similar tool to ensure consistent thickness It is essential to allow the sand temperature to stabilize for at least 5 minutes in the oven, and the substrate temperature should be checked at least once before testing, using a thermocouple, infrared thermometer, or other suitable methods Finally, accurately mark, measure, and record the dimensions of the specimen in both the machine direction (MD) and the transverse direction (TD).
Five distinct measurements, evenly spaced with a nominal separation of 20 mm, must be taken in the machine direction (from A to A’, B to B’, C to C’, D to D’, E to E’) and in the transverse direction (from a to a’, b to b’, c to c’, d to d’, e to e’) of the sample Two of these measurements should be taken at least 10 mm from the corners of the specimens, as shown in Figure 2 All measurements must be conducted at least 10 mm from the edges of the specimens The specimens should be marked with a fine-tipped marker to ensure that the same measurement locations can be used before and after thermal treatment.
Figure 2 – Schéma indiquant les emplacements de mesure désignés (AA’, BB’, CC’, DD’,
EE’, aa’, bb’, cc’, dd’, et ee’) pour chaque éprouvette f) Ouvrir la porte de l'étuve, placer l'éprouvette d'encapsulation sur le sable, puis fermer la porte de l'étuve
Multiple test tubes can be simultaneously conditioned in the same oven When space allows, ensure a quick loading of the test tubes to minimize the impact on the oven's temperature Wait 300 seconds before removing the aluminum sheet, which supports the sand and the test tube, from the heated oven Transfer the aluminum sheet with the sand and test tube to another location and allow it to cool sufficiently to reach room temperature, which can be confirmed by measuring the sand's temperature Finally, remove the test tube from the sand and measure and record the dimensions of the cooled test tube in both the machine direction and the transverse direction at the same locations used for measurements before heating.
7 Calcul et expression des résultats
To calculate the dimensional variation percentage, denoted as ∆L, use the formula (1) by subtracting the final measurement (L_f) from the initial measurement (L_i) at the corresponding location in the same direction Divide the difference by the initial measurement at each corresponding measurement location in each direction, and then multiply the result by 100.
If the initial measurement value is less than the final measurement value, a positive value of ∆L indicates an increase in the dimensions of the specimen.
Pourtour des éprouvettes Emplacements de mesure a b c d e a ′ b ′ c ′ d ′ e ′
(distance type) (distance type) supérieure à celle de la mesure finale, une valeur ∆ L négative indique un rétrécissement de l'éprouvette
Determine the maximum value of ∆L (the highest of the 90 values) and the corresponding range (the maximum ∆L value minus the minimum ∆L value) in each direction from the six different sample sets.
Déterminer la valeur ∆ L moyenne et l'écart-type correspondant (de l'ensemble des 90 valeurs
∆ L) dans chaque direction à partir des six jeux d’échantillons différents
La répétabilité et la reproductibilité de la méthode sont décrites en [2] 1
An test report must be prepared by the testing agency in accordance with ISO/IEC 17025, detailing the specific specifications applicable to the test specimens Each report should include at least the following information: a title; the name and address of the testing laboratory and the location of the tests; a unique identification for the report and each page; the client's name and address, if applicable; a description and identification of the tested item, including sample thickness; characterization and condition of the tested item, including test temperature and duration; the date of receipt of the tested item and the test dates, if applicable; identification of the testing method used; reference to the sampling procedure, if applicable; any deviations, additions, or exclusions from the testing method, along with other relevant information such as ambient conditions; measurements, examinations, and results presented in tables, graphs, sketches, and photographs as appropriate, including the maximum ∆L value and corresponding range measured for each specimen in both machine and transverse directions; the average ∆L value and corresponding standard deviation for each specimen in both directions; an indication of the estimated uncertainty of the test results, if applicable; the signature and title, or equivalent identification of the responsible individuals, along with the date of issuance; a note indicating that the results pertain only to the tested items; and a statement that the report must not be reproduced except in its entirety and with the written consent of the laboratory.
1 Les chiffres entre crochets se réfèrent à la bibliographie
It is highly recommended that both encapsulation material suppliers and module manufacturers retain a copy of this report for future reference.
Annexe A (informative) Mise en œuvre et conception de l'essai
Les informations détaillées de nature à faciliter la mise en œuvre ou la compréhension de l'essai peuvent être consultées dans les ouvrages de référence
[1 ] D.C Miller, L Ji, G Kelly, X.H Gu, N Nickel, P Norum, T Shioda, and G
Tamizhmani, and J.H Wohlgemuth, “Examination of Size-Change Test for PV Encapsulation Materials”, Proc SPIE, 201 2, pp 8472-29
[2] D C Miller, J Bokria, X.H Gu, C Honeker, N Nickel, K Sakurai, T Shioda, G
Tamizhmani, E Wang, S.Y Yang, T Yoshihara, O Zubillaga, and J.H Wohlgemuth,
“Verification of Size-Change Test for PV Encapsulation Materials”, Proc SPIE, 201 5
[3] IEC TS 62788-2, Measurement procedures for materials used in photovoltaic modules
– Part 2: Polymeric materials used for frontsheets and backsheets (disponible en anglais seulement) 2