EN 62979:2017

SLOVENSKI STANDARD
01-januar-2018
)RWRQDSHWRVWQLPRGXO2EYRGQDGLRGD3UHVNXVWHUPLþQHJDSREHJD
Photovoltaic module - Bypass diode - Thermal runaway test
Ta slovenski standard je istoveten z: EN 62979:2017
ICS:
27.160 6RQþQDHQHUJLMD Solar energy engineering
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN 62979
NORME EUROPÉENNE
EUROPÄISCHE NORM
October 2017
ICS 27.160
English Version
Photovoltaic module - Bypass diode - Thermal runaway test
(IEC 62979:2017)
Essai d'emballement thermique portant sur les diodes de Photvoltaik-Module - Bypass-Diode - Prüfung des
dérivation des modules photovoltaïques thermischen Durchgehens
(IEC 62979:2017) (IEC 62979:2017)
This European Standard was approved by CENELEC on 2017-09-14. 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,
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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
© 2017 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN 62979:2017 E
European foreword
The text of document 82/1269/FDIS, future edition 1 of IEC 62979, prepared by IEC/TC 82 “Solar
photovoltaic energy systems" was submitted to the IEC-CENELEC parallel vote and approved by
CENELEC as EN 62979:2017.
The following dates are fixed:
(dop) 2018-06-14
• 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) 2020-09-14
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 shall not be held responsible for identifying any or all such patent rights.
Endorsement notice
The text of the International Standard IEC 62979:2017 was approved by CENELEC as a European
Standard without any modification.
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 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/TS 61836 -  Solar photovoltaic energy systems - - -
Terms, definitions and symbols

IEC 62979 ®
Edition 1.0 2017-08
INTERNATIONAL
STANDARD
Photovoltaic modules – Bypass diode – Thermal runaway test

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.160 ISBN 978-2-8322-4587-3

– 2 – IEC 62979:2017 © IEC 2017
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Thermal runaway test . 7
4.1 Diode thermal runaway . 7
4.2 Test conditions . 8
4.3 Preparation of test specimen. 8
4.4 Test equipment . 9
4.5 Test procedure . 10
5 Pass or fail criteria. 12
6 Test report . 12

Figure 1 – Illustration of how thermal runaway occurs . 7
Figure 2 – Circuit for measurement of T and forward voltage . 9
lead
Figure 3 – Circuit for flowing a forward current to the bypass diode . 10
Figure 4 – Circuit for applying a reverse bias voltage to the bypass diode. 10
Figure 5 – The typical pattern of thermal runaway . 11
Figure 6 – The pattern of non-thermal runaway . 11

IEC 62979:2017 © IEC 2017 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
PHOTOVOLTAIC MODULES – BYPASS DIODE –
THERMAL RUNAWAY TEST
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.
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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 62979 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
82/1269/FDIS 82/1311/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.

– 4 – IEC 62979:2017 © IEC 2017
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.
A bilingual version of this publication may be issued at a later date.

IEC 62979:2017 © IEC 2017 – 5 –
INTRODUCTION
During the normal operation of PV modules the bypass diodes are reverse biased. When the
PV module is partially shaded (for example by utility poles, buildings, or leaves), some of the
cells in the PV module may not be able to produce the current being produced by the other
cells in the series string. The shaded cells are then driven into reverse bias so the bypass
diode of the shaded cell-string becomes forward bias protecting the shaded cells.
Under these circumstances, the temperature of the bypass diode increases due to the forward
current flowing through the diode. It is in this condition that the diodes are tested in
accordance with IEC 61215-2:2016, 4.18.1: Bypass diode thermal test. When the shade is
removed, operating conditions return to normal and the bypass diode is again reversed biased.
Some of the diodes utilized as bypass diodes in PV modules have characteristics where the
reverse bias leakage current increases with the diode temperature. So if the diode is already
at an elevated temperature when reverse biased, there will be a substantial leakage current
and the diode junction temperature can increase considerably. The worst case occurs when
this heating exceeds the cooling capability of the junction box in which the diode is installed.
As a result of this increasing temperature and leakage current, the diode can break down.
These phenomena are called “thermal runaway”. The thermal design of the bypass diode in
the junction box shall be verified to ensure that thermal runaway does not occur.

– 6 – IEC 62979:2017 © IEC 2017
PHOTOVOLTAIC MODULES – BYPASS DIODE –
THERMAL RUNAWAY TEST
1 Scope
This document provides a method for evaluating whether a bypass diode as mounted in the
module is susceptible to thermal runaway or if there is sufficient cooling for it to survive the
transition from forward bias operation to reverse bias operation without overheating.
This test methodology is particularly suited for testing of Schottky barrier diodes, which have
the characteristic of increasing leakage current as a function of reverse bias voltage at high
temperature, making them more susceptible to thermal runaway.
The test specimens which employ P/N diodes as bypass diodes are exempted from the
thermal runaway test required herein, because the capability of P/N diodes to withstand the
reverse bias is sufficiently high.
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
...