Extended thermal cycling of PV modules - Test procedure

IEC 62892:2019 defines a test sequence that extends the thermal cycling test of IEC 61215-2. It is intended to differentiate PV modules with improved durability to thermal cycling and evaluate modules for deployment in locations most susceptible to thermal cycling type stress. This document is based on the ability for 95 % of the modules represented by the samples submitted for this test to pass an equivalency of 500 thermal cycles, as defined in IEC 61215‑2:2016, 4.11.3, with a maximum power degradation of less than 5 %. Provisions are also provided to reduce overall test time by increasing the maximum cycle temperature and/or the number of modules submitted for test.
The test procedure in this document was developed based on analysis of the stress on tin-lead solder bonds on crystalline silicon solar cells in a glass superstrate type package. Changes to lead-free solder have an effect on the acceleration factors but not enough to change the overall results of this test. Monolithic type modules with integral cell interconnection do not suffer from this specific type of stress but there are still electrical connections within the module, for example between the integrated cell circuit and the module bus bars, that may be subject to wear out from thermal cycling. Flexible modules (without glass) are not stressed in the same way as those with glass superstrates or substrates, therefore use of the equivalency factor employed in this document may not be applicable to these modules.

Cycle thermique étendu de modules PV - Procédure d'essai

l'IEC 62892:2019 définit une séquence d'essais qui étend l'essai de cycle thermique de l'IEC 61215-2. Il est destiné à différencier les modules photovoltaïques avec une meilleure durabilité par rapport au cycle thermique et à évaluer les modules pour un déploiement dans les lieux plus exposés aux contraintes de cycle thermique. Le présent document repose sur l'aptitude pour 95 % des modules représentés par les échantillons soumis à cet essai à supporter avec succès l'équivalent de 500 cycles thermiques, conformément à la procédure définie dans l'IEC 61215-2:2016, 4.11.3, avec une dégradation maximale de puissance inférieure à 5 %. Des dispositions sont également fournies pour réduire la durée totale des essais en augmentant la température maximale du cycle et/ou le nombre de modules soumis à l'essai.
La procédure d'essai décrite dans le présent document a été élaborée sur la base d'une analyse des contraintes exercées sur des assemblages soudés en alliage plomb-étain sur des cellules solaires en silicium cristallin au sein d'un ensemble de type superstrat de verre. Des modifications apportées à une soudure sans plomb ont un effet sur les facteurs d'accélération, mais pas de manière suffisante pour modifier les résultats globaux de cet essai. Les modules de type monolithique avec interconnexion intégrale des cellules ne souffrent pas de ce type de contrainte spécifique, mais il persiste des connexions électriques à l'intérieur du module, par exemple entre le circuit intégré de la cellule et les barres omnibus du module, qui peut subir une usure due aux cycles thermiques. Les modules souples (sans verre) ne subissent pas les mêmes contraintes que ceux qui comportent des superstrats ou des substrats de verre. Par conséquent, l'utilisation du facteur d'équivalence employé dans le présent document peut ne pas convenir à ces modules.

General Information

Status
Published
Publication Date
16-Apr-2019
Current Stage
PPUB - Publication issued
Completion Date
17-Apr-2019
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IEC 62892
Edition 1.0 2019-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Extended thermal cycling of PV modules – Test procedure
Cycle thermique étendu de modules PV – Procédure d'essai
IEC 62892:2019-04(en-fr)
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IEC 62892
Edition 1.0 2019-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Extended thermal cycling of PV modules – Test procedure
Cycle thermique étendu de modules PV – Procédure d'essai
INTERNATIONAL
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ICS 27.160 ISBN 978-2-8322-6598-7

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® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – IEC 62892:2019 © IEC 2019
CONTENTS

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

INTRODUCTION ..................................................................................................................... 5

1 Scope .............................................................................................................................. 6

2 Normative references ...................................................................................................... 6

3 Terms and definitions ...................................................................................................... 7

4 Sampling ......................................................................................................................... 7

5 Marking and documentation ............................................................................................. 7

6 Modifications ................................................................................................................... 8

7 Test procedure ................................................................................................................ 8

7.1 Initial evaluations .................................................................................................... 8

7.2 Thermal cycling test ................................................................................................ 8

7.2.1 Purpose ........................................................................................................... 8

7.2.2 Apparatus ........................................................................................................ 8

7.2.3 Procedure ........................................................................................................ 8

7.3 Final evaluations ..................................................................................................... 9

7.4 Requirements ....................................................................................................... 10

8 Reporting....................................................................................................................... 10

Annex A (normative) Calculation of the required number of thermal cycles .......................... 11

Annex B (informative) Acceleration factors based on deployed climate ................................ 14

Bibliography .......................................................................................................................... 17

Figure A.1 – Number of equivalent cycles as a function of maximum cycle temperature

over maximum module operating temperature ....................................................................... 11

Figure A.2 – Survivorship plot for a Weibull distribution with a shape parameter of 6

and a survivorship probability of 95% at 500 cycles .............................................................. 12

Figure B.1 – Plot of module cell temperature over the course of one day to illustrate

the maximum temperature, maximum temperature change and temperature reversal

terms .................................................................................................................................... 14

Figure B.2 – Combination of factors that indicate extended thermal cycling is advised

for a specific location ............................................................................................................ 15

Table 1 – Number of required thermal cycles, N ................................................................... 9

Table A.1 – Effect of sample size on test time ....................................................................... 13

Table B.1 – Cell temperature factors ..................................................................................... 15

Table B.2 – Module and mounting specific model parameters ............................................... 16

---------------------- Page: 4 ----------------------
IEC 62892:2019 © IEC 2019 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
EXTENDED THERMAL CYCLING OF PV MODULES –
TEST PROCEDURE
FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

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rights. IEC shall not be held responsible for identifying any or all such patent rights.

International Standard IEC 62892 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
82/1537/FDIS 82/1560/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.

---------------------- Page: 5 ----------------------
– 4 – IEC 62892:2019 © IEC 2019

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.

---------------------- Page: 6 ----------------------
IEC 62892:2019 © IEC 2019 – 5 –
INTRODUCTION

The IEC 61215 series defines test requirements for the design qualification of flat-plate PV

modules for long-term operation in general open-air climates. IEC TS 62941 provides technical

guidance in application of the type-approval testing.

This document, IEC 62892, supplements IEC 61215 by providing an extended thermal cycling

test intended to differentiate PV modules with improved durability to thermal cycling and

evaluate modules for deployment in locations most susceptible to thermal cycling type stress.

---------------------- Page: 7 ----------------------
– 6 – IEC 62892:2019 © IEC 2019
EXTENDED THERMAL CYCLING OF PV MODULES –
TEST PROCEDURE
1 Scope

This document defines a test sequence that extends the thermal cycling test of IEC 61215-2. It

is intended to differentiate PV modules with improved durability to thermal cycling and evaluate

modules for deployment in locations most susceptible to thermal cycling type stress . This

document is based on the ability for 95 % of the modules represented by the samples submitted

for this test to pass an equivalency of 500 thermal cycles, as defined in IEC 61215-2:2016,

4.11.3, with a maximum power degradation of less than 5 %. Provisions are also provided to

reduce overall test time by increasing the maximum cycle temperature and/or the number of

modules submitted for test.

The test procedure in this document was developed based on analysis of the stress on tin-lead

solder bonds on crystalline silicon solar cells in a glass superstrate type package. Changes to

lead-free solder have an effect on the acceleration factors but not enough to change the overall

results of this test. Monolithic type modules with integral cell interconnection do not suffer from

this specific type of stress but there are still electrical connections within the module, for

example between the integrated cell circuit and the module bus bars, that may be subject to

wear out from thermal cycling. Flexible modules (without glass) are not stressed in the same

way as those with glass superstrates or substrates, therefore use of the equivalency factor

employed in this document may not be applicable to these modules.
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 61215-1:2016, Terrestrial photovoltaic (PV) modules – Design qualification and type

approval – Part 1: Test requirements

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

– Part 1-1: Special requirements for testing of crystalline silicon terrestrial photovoltaic (PV)

modules

IEC 61215-1-2, Terrestrial photovoltaic (PV) modules – Design qualification and type approval

– Part 1-2: Special requirements for testing of thin-film Cadmium Telluride (CdTe) based

photovoltaic (PV) modules

IEC 61215-1-3, Terrestrial photovoltaic (PV) modules – Design qualification and type approval

– Part 1-3: Special requirements for testing of thin-film amorphous silicon based photovoltaic

(PV) modules

IEC 61215-1-4, Terrestrial photovoltaic (PV) modules – Design qualification and type approval

– Part 1-4: Special requirements for testing of thin-film Cu(In,GA)(S,Se) based photovoltaic

(PV) modules
___________

Guidance is provided in Annex B to assess if this test is warranted for the targeted deployment location.

---------------------- Page: 8 ----------------------
IEC 62892:2019 © IEC 2019 – 7 –

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

approval – Part 2: Test procedures

IEC 61730-1, Photovoltaic (PV) module safety qualification – Part 1: Requirements for

construction

IEC 61730-2, Photovoltaic (PV) module safety qualification – Part 2: Requirements for testing

IEC TS 61836, Solar photovoltaic energy systems – Terms, definitions and symbols

IEC TS 62915, Photovoltaic (PV) modules – Type approval, design and safety qualification –

Retesting

IEC TS 62941:2016, Terrestrial photovoltaic (PV) modules – Guideline for increased confidence

in PV module design qualification and type approval
3 Terms and definitions

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

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
equivalent cycles
number of thermal cycles that imparts the same amount of solder fatigue damage
4 Sampling

Modules for these tests shall be taken at random from a production batch or batches of a module

type that is already certified to IEC 61215, IEC 61730-1 and IEC 61730-2. The modules shall

have been manufactured from specified materials and components in accordance with the

relevant drawings and process sheets and have been subjected to the manufacturer's normal

inspection, quality control and production acceptance procedures. The modules shall be

complete in every detail and shall be accompanied by the manufacturer's handling, mounting

and connection instructions.

The relation between the number of modules submitted for testing and the required number of

cycles is detailed Table 1 and Annex A. A minimum of three modules shall be submitted for

testing, two for the actual testing and one as control.

Because these tests are designed for accelerated stress testing of production modules,

engineering samples are not allowed.
5 Marking and documentation

Each module shall include clear and indelible markings as defined in IEC 61215-1. Modules

shall be supplied with documentation conforming to the requirements in IEC 61215-1.

Documentation consistent with the requirements of Clause 4 of IEC TS 62941:2016 shall also

be available for inspection by the test agency to ensure adequacy of the Quality Management

System.
---------------------- Page: 9 ----------------------
– 8 – IEC 62892:2019 © IEC 2019
6 Modifications

Changes in material selection, components and manufacturing process that would trigger

retesting of the 200 thermal cycles leg in IEC TS 62915 would also require retest to this

document.
7 Test procedure
7.1 Initial evaluations

a) Visual inspection in accordance with IEC 61215-2 Module Qualification Test (MQT) 01.

b) Maximum power determination in accordance with IEC 61215-2 MQT 02.
c) Insulation test in accordance with IEC 61215-2 MQT 03.
d) Wet current leakage test in accordance with IEC 61215-2 MQT 15.
7.2 Thermal cycling test
7.2.1 Purpose

The purpose of the thermal cycling test is to determine the ability of the PV modules to withstand

thermal mismatch, fatigue, and other stresses caused by rapid, non-uniform or repeated

changes of temperature.
7.2.2 Apparatus
In accordance with IEC 61215-2:2016, 4.11.2.
7.2.3 Procedure
In accordance with IEC 61215-2:2016, 4.11.3 with the following modifications:

a) The maximum temperature of the cycle (T ) may be increased above 85 °C to reduce the

MAX

number of required cycles according to Table 1. (T ) shall be specified by the submitting

MAX
party and recorded in the test report.

b) During the thermal cycling test set the continuous current flow during the heat up cycle to

the technology specified current in IEC 61215-2 at temperature from –40 °C to
(T ) –5 °C. During cool down, the –40 °C dwell phase and temperatures above
MAX
) –5 °C the continuous current shall be reduced to no more than 1,0 % of the
MAX
measured STC peak power current to measure continuity.

c) The number of cycles shall be as shown in Table 1. Annex A may be used to calculate the

required number of thermal cycles when more than 10 modules are submitted for test or

when T –85 °C>25 °C.
MAX
---------------------- Page: 10 ----------------------
IEC 62892:2019 © IEC 2019 – 9 –
Table 1 – Number of required thermal cycles, N
T –85 Number of modules submitted for test
MAX
°C 2 3 4 5 6 7 8 9 10
0 731 683 651 627 609 593 580 569 559
1 711 665 634 611 592 577 565 554 544
2 693 647 617 594 577 562 550 539 530
3 674 630 601 579 562 547 535 525 516
4 657 614 585 564 547 533 521 511 502
5 640 598 570 549 533 519 508 498 489
6 623 583 555 535 519 506 495 485 477
7 608 568 541 521 506 493 482 473 465
8 592 553 528 508 493 481 470 461 453
9 577 539 514 495 481 468 458 449 441
10 563 526 501 483 469 457 447 438 430
11 549 513 489 471 457 445 436 427 420
12 535 500 477 459 446 434 425 417 409
13 522 488 465 448 435 424 414 406 399
14 509 476 454 437 424 413 404 396 390
15 497 465 443 427 414 403 394 387 380
16 485 453 432 416 404 394 385 378 371
17 473 443 422 406 394 384 376 368 362
18 462 432 412 397 385 375 367 360 353
19 451 422 402 387 376 366 358 351 345
20 441 412 393 378 367 358 350 343 337
21 430 402 383 369 358 349 342 335 329
22 420 393 375 361 350 341 334 327 321
23 411 384 366 353 342 333 326 320 314
24 401 375 358 344 334 326 319 312 307
25 392 367 349 337 327 318 311 305 300

NOTE The relationship employed to calculate the number of required cycles in Table 1 is based on a Coffin-Manson

style empirical relationship for solder thermal fatigue and a one-parameter Weibull analysis and dictates that 95 %

of the modules represented by the samples submitted for this test will pass an equivalency of 500 qualification level

thermal cycles [1, 2] . This relationship is applicable for both PbSn and Pb-free solders. FEM simulations of a PV

module have demonstrated that this relationship results in a conservative estimate for equivalency [3]. These

simulations show that softening of the module’s encapsulant at high temperatures will result in a faster rate of solder

damage accumulation. Therefore, while prescribing a higher maximum cycle temperature will reduce the overall test

time, the equivalency of that test, or overall stress, may be greater than intended.

7.3 Final evaluations
a) Visual inspection in accordance with IEC 61215-2 MQT 01.
b) Maximum power determination in accordance with IEC 61215-2 MQT 02.
c) Insulation test in accordance with IEC 61215-2 MQT 03.
d) Wet leakage current test in accordance with IEC 61215-2 MQT 15.
e) Bypass diode functionality test in accordance with IEC 61215-2 MQT 18.2.
___________
Numbers in square brackets refer to the Bilbiography.
---------------------- Page: 11 ----------------------
– 10 – IEC 62892:2019 © IEC 2019

When implementing the tests from IEC 61215-2, the requirements of the technology specific

standards (IEC 61215-1-1, IEC 61215-1-2, IEC 61215-1-3 and IEC 61215-1-4) shall be taken

into account.
7.4 Requirements
The requirements are as follows:
– no interruption of current flow during the test;
– no evidence of major visual defects, as defined in IEC 61215-1:2016, Clause 7;

– the degradation of maximum output power shall not exceed 5 % of the value measured

before the test;

– insulation resistance shall meet the same requirements as for the initial measurements.

– any by-pass diodes shall still function as diodes.

NOTE Electroluminescence imaging may be a useful technique to image the location of failed, or failing, solder

bonds.
8 Reporting

Following completion of the testing, a report of the tests, with measured performance

characteristics and details of any failures and re-tests, shall be prepared by the test agency.

The report shall contain the detail specification for the module. Each test report shall include at

least the following information:
a) a title;

b) name and address of the test laboratory and location where the tests were carried out;

c) unique identification of the report and of each page;
d) name and address of client, where appropriate;
e) description and identification of the item tested;
f) characterization and condition of the test item;
g) date of receipt of test item and date(s) of test, where appropriate;
h) reference to sampling procedure;

i) any deviations from, additions to, or exclusions from, the test method and any other

information relevant to a specific tests, such as environmental conditions and the test

procedure used to validate that the by-pass diodes were functional at the end of the test

sequence;

j) measurements, examinations and derived results supported by tables, graphs, sketches and

photographs as appropriate including maximum power loss observed after all of the tests,

dry and wet insulation resistance changes due to the tests and evidence of changes that

might ultimately lead to performance degradation;

k) a statement of the estimated uncertainty of the test results (where relevant);

l) a signature and title, or equivalent identification of the person(s) accepting responsibility for

the content of the report, and the date of issue;

m) where relevant, a statement to the effect that the results relate only to the items tested;

n) a statement that the report shall not be reproduced except in full, without the written

approval of the laboratory.
A copy of this report shall be kept by the manufacturer for reference purposes.
---------------------- Page: 12 ----------------------
IEC 62892:2019 © IEC 2019 – 11 –
Annex A
(normative)
Calculation of the required number of thermal cycles

There are two factors that together determine the required number of thermal cycles, N , as

tabulated in Table 1:
a) Maximum cycle temperature, T (°C).
MAX
b) Number of modules submitted for test, n.

The first step is to determine the equivalent number of cycles, N . It is a function of T . This

e MAX

number of cycles will impart an equivalent amount of solder fatigue damage as 500 qualification

level cycles (–40 °C to 85 °C) as defined in IEC 61215-2, MQT 11. The relationship between

T and N is:
MAX e
1414
( )
𝑁𝑁 = 150470𝑇𝑇 +40 exp� � (A.1)
𝑒𝑒 𝑀𝑀𝑀𝑀𝑀𝑀
𝑇𝑇 +273
𝑀𝑀𝑀𝑀𝑀𝑀

Formula (A.1) defines how increasing the maximum cycle temperature over 85 °C can reduce

the potential number of cycles and therefore overall test time, Figure A.1. This formula is based

on a Coffin-Manson style empirical relationship for solder thermal fatigue [1, 2]. This

relationship is applicable for both PbSn and Pb-free solders. FEM simulations of a PV module

have demonstrated that this relationship results in a conservative estimate for equivalency [3].

These simulations show that softening of the module’s encapsulant at high temperatures will

result in a faster rate of solder damage accumulation. Therefore, while prescribing a higher

maximum cycle temperature will reduce the overall test time, the equivalency, or overall stress,

of that test may be greater than intended.
500
450
400
350
300
0 5 10 15 20 25
T -85 (°C)
max
IEC
Figure A.1 – Number of equivalent cycles as a function of maximum
cycle temperature over maximum module operating temperature
Number of equivalent cycles, N
---------------------- Page: 13 ----------------------
– 12 – IEC 62892:2019 © IEC 201
...

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