IEC 61427-2:2015/AMD1:2024

IEC 61427-2 ®
Edition 1.0 2024-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
AMENDMENT 1
AMENDEMENT 1
Secondary cells and batteries for renewable energy storage – General
requirements and methods of test –
Part 2: On-grid applications
Accumulateurs pour le stockage de l'énergie renouvelable – Exigences
générales et méthodes d'essais –
Partie 2 : Applications en réseau
IEC 61427-2:2015-08/AMD1:2024-03(en-fr)

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.

Droits de reproduction réservés. Sauf indication contraire, aucune partie de cette publication ne peut être reproduite ni
utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie et
les microfilms, sans l'accord écrit de l'IEC ou du Comité national de l'IEC du pays du demandeur. Si vous avez des
questions sur le copyright de l'IEC ou si vous désirez obtenir des droits supplémentaires sur cette publication, utilisez
les coordonnées ci-après ou contactez le Comité national de l'IEC de votre pays de résidence.

IEC Secretariat Tel.: +41 22 919 02 11
3, rue de Varembé info@iec.ch
CH-1211 Geneva 20 www.iec.ch
Switzerland
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigendum or an amendment might have been published.

IEC publications search - webstore.iec.ch/advsearchform IEC Products & Services Portal - products.iec.ch
The advanced search enables to find IEC publications by a Discover our powerful search engine and read freely all the
variety of criteria (reference number, text, technical publications previews, graphical symbols and the glossary.
committee, …). It also gives information on projects, replaced With a subscription you will always have access to up to date
and withdrawn publications. content tailored to your needs.

IEC Just Published - webstore.iec.ch/justpublished
Electropedia - www.electropedia.org
Stay up to date on all new IEC publications. Just Published
The world's leading online dictionary on electrotechnology,
details all new publications released. Available online and once
containing more than 22 500 terminological entries in English
a month by email.
and French, with equivalent terms in 25 additional languages.

Also known as the International Electrotechnical Vocabulary
IEC Customer Service Centre - webstore.iec.ch/csc
(IEV) online.
If you wish to give us your feedback on this publication or need

further assistance, please contact the Customer Service
Centre: sales@iec.ch.
A propos de l'IEC
La Commission Electrotechnique Internationale (IEC) est la première organisation mondiale qui élabore et publie des
Normes internationales pour tout ce qui a trait à l'électricité, à l'électronique et aux technologies apparentées.

A propos des publications IEC
Le contenu technique des publications IEC est constamment revu. Veuillez vous assurer que vous possédez l’édition la
plus récente, un corrigendum ou amendement peut avoir été publié.

Recherche de publications IEC -  IEC Products & Services Portal - products.iec.ch
webstore.iec.ch/advsearchform Découvrez notre puissant moteur de recherche et consultez
La recherche avancée permet de trouver des publications IEC gratuitement tous les aperçus des publications, symboles
en utilisant différents critères (numéro de référence, texte, graphiques et le glossaire. Avec un abonnement, vous aurez
comité d’études, …). Elle donne aussi des informations sur les toujours accès à un contenu à jour adapté à vos besoins.
projets et les publications remplacées ou retirées.

Electropedia - www.electropedia.org
IEC Just Published - webstore.iec.ch/justpublished
Le premier dictionnaire d'électrotechnologie en ligne au monde,
Restez informé sur les nouvelles publications IEC. Just
avec plus de 22 500 articles terminologiques en anglais et en
Published détaille les nouvelles publications parues.
français, ainsi que les termes équivalents dans 25 langues
Disponible en ligne et une fois par mois par email.
additionnelles. Egalement appelé Vocabulaire

Electrotechnique International (IEV) en ligne.
Service Clients - webstore.iec.ch/csc

Si vous désirez nous donner des commentaires sur cette
publication ou si vous avez des questions contactez-nous:
sales@iec.ch.
IEC 61427-2 ®
Edition 1.0 2024-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
AMENDMENT 1
AMENDEMENT 1
Secondary cells and batteries for renewable energy storage – General

requirements and methods of test –

Part 2: On-grid applications
Accumulateurs pour le stockage de l'énergie renouvelable – Exigences

générales et méthodes d'essais –

Partie 2 : Applications en réseau

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.220.20  ISBN 978-2-8322-8382-0

– 2 – IEC 61427-2:2015/AMD1:2024
© IEC 2024
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SECONDARY CELLS AND BATTERIES FOR RENEWABLE ENERGY
STORAGE – GENERAL REQUIREMENTS AND METHODS OF TEST –

Part 2: On-grid applications
AMENDMENT 1
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) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
respect thereof. As of the date of publication of this document, IEC had not received notice of (a) patent(s), which
may be required to implement this document. However, implementers are cautioned that this may not represent
the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
shall not be held responsible for identifying any or all such patent rights.
Amendment 1 to IEC 61427-2:2015 has been prepared by IEC technical committee 21:
Secondary cells and batteries.
The text of this Amendment is based on the following documents:
Draft Report on voting
21/1179/FDIS 21/1194/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
© IEC 2024
The language used for the development of this Amendment is English.
A list of all parts in the IEC 61427 series, published under the general title Secondary cells and
batteries for renewable energy storage, can be found on the IEC website.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications/.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn, or
• revised.
IMPORTANT – The "colour inside" logo on the cover page of this document 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.

___________
6 Battery endurance
6.1 General
Add the following at the end of 6.1:
Since the publication of this document in 2015, details of a complex pattern of energy exchange
in frequency-regulation duty, at 4 s intervals and over a 24 h period, have been published by
Pacific Northwest National Laboratory (PNNL) and Sandia National Laboratories (SAND) in the
PNNL-22010 Rev 2/ SAND 2016-3078 R Report.
In Annex B (informative) details of this energy exchange profile are made available for
evaluating, if useful, the service-induced decay of battery performance also with a more
randomized usage pattern compared to that offered by the symmetric 6.2 profile.
6.2 Test for endurance in frequency-regulation service
Add the following sentence as a new paragraph after the existing list item r).
See Annex B for supplemental test profile for frequency regulation duty service.

– 4 – IEC 61427-2:2015/AMD1:2024
© IEC 2024
Add the following new annex after Annex A:
Annex B
(informative)
Supplemental test profile for frequency regulation duty service
B.1 General
The batteries in on-grid electrical energy storage (EES) applications provide and accept the
energy needed to maintain the mains frequency within specified limits. This exchange of energy
results in multiple charge and discharge events per hour in the electrochemically active masses
of the battery. The order, intensity and duration of these events influences the stability and
activity of the involved active mass structures and hence the endurance of the batteries.
This additional test procedure for evaluating battery performance under frequency-regulation
service, is based on data acquired by actual monitoring of a regional transmission organization
grid frequency balancing signal by Pacific Northwest National Laboratory (PNNL) and Sandia
National Laboratories (SAND) in the USA.
The balancing signal data are reported in section 5.3.2 Frequency regulation duty cycle of the
document PNNL-22010 Rev 2 / SAND 2016-3078 R, Protocol for Uniformly Measuring and
Expressing the Performance of Energy Storage Systems and dated April 2016. This data is
available as a spreadsheet on the IEC website courtesy of the Pacific Northwest National
Laboratory, operated by Battelle for the U.S. Department of Energy. The spreadsheet,
SAND2013-7315P profile details.xlsx can be accessed via TC 21 supporting documents on the
IEC website – www.iec.ch/tc21/supportingdocuments. This information is given for the
convenience of users of this document and does not constitute an endorsement by IEC of the
data named.
The complex pattern of energy exchange and the associated procedures described in
Clause B.2, can be used as a tool to complement and reinforce, as appropriate or useful, the
information on the service-induced decay of battery performance gathered with the test profile
in 6.2. The profile in 6.2 remains however the required profile if product comparisons or
qualifications are carried out.
The test and associated test profile specified in Clause B.3 is optional; it is not necessary to
carry it out to claim conformance with this document.
However, if this test is carried out, it shall be executed as specified in Clause B.3.
B.2 The Annex B profile for evaluating battery endurance in
frequency-regulation duty
The Annex B profile consists of a sequence of 2 h average and 2 h aggressive signal levels
reflecting the deviation from the grid frequency dead band and the resulting demand to deliver
energy from or store in the battery of the frequency-regulation application. Each signal specifies
a constant power level for a duration of 4 s resulting in 1 800 signal levels per 2 h period. The
adjective of average and aggressive reflects the intensity of the energy flow to and from the
battery.
Over 24 h, the Annex B duty cycle consists of a sequence with three 2-h duration average signal
deviation levels, one 2-h duration aggressive signal deviation level, three 2-h duration average
signal deviation levels, one 2-h duration aggressive signal deviation level and four 2-h duration
average signal deviation levels. The values of average and aggressive deviation signal level,
forming the 24 h duty cycle as shown in Figure B.1, are listed in the abovementioned
spreadsheet on the IEC website.

© IEC 2024
SOURCE: Figure reproduced from PNNL-22010 Rev 2 / SAND 2016-3078 R, with the permission of Pacific Northwest
National Laboratory, operated by Battelle for the U.S. Department of Energy.
Figure B.1 – 24 h sequence of the Annex B profile for a supplemental evaluation of the
service-induced performance decay of a battery in frequency-regulation service
The exchanged power η is normalized with respect to the rated power of the EES application
where the positive value represents a discharge from the battery and negative value a charge
into the battery.
The longest duration at full discharge power or η = 1,0 is 52 s. The daily averaged power level
is 30 % of the rated power capability of the EES system. The amount of energy charged daily
into the battery (Wh-in) is equal to the daily amount of energy discharged (Wh-out).
This will result, due to a roundtrip Wh efficiency of < 1,0, in a slow walk-down of the battery
capacity over time requiring periodic auxiliary charge energy input to re-establish the proper
target level of operational state of charge (SoC ) required to fulfil all peak power demands.
OT
The SoC level is specific for each type of battery and application and is specified by the
OT
battery manufacturer.
It is recommended that the machine instructions or commands for the power levels during a full
24 h-duration duty cycle be broken down into the appropriate consecutive sequences of 2 h
with 1 800 signal levels each. This facilitates the upload and the execution of the power level
setting instructions by the control unit of the battery cycling equipment.
The overall composite 24 h instruction set is the following.
Start the 24 h sequence
– Go to data set of a 2 h sequence at average power level and execute set 3 times,
– Go to data set of a 2 h sequence at aggressive power level and execute set 1 time,
– Go to data set of a 2 h sequence at average power level and execute set 3 times,
– Go to data set of a 2 h sequence at aggressive power level and execute set 1 time,
– Go to data set of a 2 h sequence at average power level and execute set 4 times,
Stop the 24 h sequence.
– 6 – IEC 61427-2:2015/AMD1:2024
© IEC 2024
B.3 Test procedure
B.3.1 Annex B is informative in nature, i.e., it is given for information purposes only.
The test given in this Clause B.3 is optional; it is not necessary to carry it out to claim
conformance with this document.
However, if this test is carried out, it shall be executed as specified in Clause B.3.
The procedure makes reference to the requirements in Clause 5 and Clause 6 of this document
in order to provide boundary conditions comparable to those required for tests with the profile
in 6.2.
B.3.2 The full-sized battery (FSB) shall be selected according to 5.3 and meet the bidirectional
absolute power level requirements of η = 1,0 or 1 000 kW of the composite 24 h Annex B profile
at the selected initial SoC and within the voltage limits specified by the manufacturer. The
OT
battery shall be operated at an ambient temperature of + 25 °C ± 3 K or as appropriate for the
battery design.
B.3.3 The manufacturer shall report how many cells, modules or stacks make up such an FSB.
This value is termed n.
B.3.4 The manufacturer shall define the fraction of power (1 000 / n) kW such a cell, module
or stack will deliver or accept when it is part of the FSB and this battery meets the condition in
B.3.2.
B.3.5 The manufacturer shall assemble with x of such cells, modules or stacks the appropriate
test object battery (TOB) having at least:
1) four (4) cells in series (only if these cells are commercialized individually),
or
2) one or more modules that result in at least four (4) cells in series,
or
3) one stack with at least four (4) flow cells in series,
and incorporate the relevant BMS and BSS peripherals.
B.3.6 When a battery based EES application with different power capability and/or energy
content is required to be tested in accordance with this Annex B, then such a choice is
acceptable provided that all other testing provisions are fulfilled and this deviation is stated in
the test documentation.
B.3.7 The actual energy content E (in kWh) of this TOB, after the manufacturer-specified full
charge and thermal equilibration in air at +25 °C ± 3 K ambient temperature or as appropriate
for the battery design, shall be determined with a constant power discharge at the
(x × 500 / n) kW power level to the final voltage U or to the BMS mandated discharge limit
final
as specified by the manufacturer. The energy content value is for comparison purposes as
needed in other clauses.
B.3.8 The TOB shall then be fully recharged according to the manufacturer's specifications.
B.3.9 The TOB shall then be discharged to such a SoC that it can repetitively deliver and
OT
accept the fractional power and energy levels of the 24 h Annex B profile without exceeding the
manufacturer's specified operating voltage limits.

© IEC 2024
B.3.10 The manufacturer shall report this SoC level, expressed as a percentage of the
OT
actual energy content as determined in B.3.7 and ways to achieve it.
B.3.11 The TOB shall then be submitted, at an ambient temperature of +25 °C ± 3 K or as
appropriate for the battery design, to a 24 h Annex B profile consisting of a sequence of average
and aggressive power level periods as described in Clause B.2. The battery voltage and the
cumulative discharged and charged capacity (in Ah) and energy (in kWh) of the TOB shall be
monitored and recorded once at the end of each 4 s constant power segment.
B.3.12 After completing a 24 h Annex B test sequence, the TOB shall be immediately
discharged for 52 s at its actual temperature with a power equivalent to (1 000 / n) kW and the
reached final voltage level monitored and recorded.
B.3.13 If the TOB voltage in B.3.11 and B.3.12 exceeds the upper and lower limits of operating
voltages then the energy-delivery and energy-acceptance capability under frequency-regulation
service of the TOB and by derivation that of the FSB, shall be considered degraded and the
procedure B.3.14 carried out.
B.3.14 The proper functioning of the battery shall be re-established with a charge or discharge
whose power levels shall not exceed (1 000 / n) kW. The voltage levels encountered in this
charge or discharge shall not exceed the upper and lower limits of operating voltages defined
for the Annex B profile. The conditions of this performance recovery action shall be specified
by the manufacturer and take into consideration commercial viability, contractual and timing
constraints in frequency-regulation service.
B.3.15 Suggested metrics for the evaluation of the performance of a battery in simulated
frequency-regulation service with the 24 h Annex B profile sequence are:
1) Energy content level of the TOB as determined in B.3.7.
2) Voltage levels of the battery during a 24 h Annex B profile sequence.
3) Cumulated amount of capacity discharged in a 24 h Annex B profile sequence from the
battery.
4) Cumulated amount of capacity charged in a 24 h Annex B profile sequence into the battery.
5) SoC level at the conclusion of each 24 h Annex B profile sequence.
OT
6) Number of 24 h Annex B profile sequences carried out before conditions of B.3.13 are
encountered.
7) Plot of the achieved number of Annex B profile sequences vs elapsed days in the endurance
test.
8) Amount of energy (kWh) consumed to re-establish proper functioning of the battery as per
B.3.14.
9) Duration in minutes of the B.3.14 activity before the battery returns to regular Annex B
profile-based frequency-regulation service.
10) Power levels in the form of a W vs time profile of the B.3.14 activity.
11) Ampere hour capacity as per B.3.7 and/or internal resistance of the battery at selected
intervals to quantify capacity or internal conductivity degradation.
12) Any battery design-specific parameter revealing its actual status of health, or inversely, its
degree of performance degradation.
B.3.16 The endurance test steps B.3.11 to B.3.14 shall be carried until the planned service
life and commercial viability of the battery in frequency-regulation service has been
demonstrated based on the data gathered and analysed as per B.3.15.

– 8 – IEC 61427-2:2015/AMD1:2024
© IEC 2024
B.4 Examples of data acquired with the 6.2 and the 24 h Annex B sequence
Figure B.2 and Figure B.3 show examples of a graphical display of selected battery data
acquired with the 6.2 c profile and the 24 h Annex B profile sequences. A same battery type
was submitted to test conditions simulating frequency-regulation duty and in both cases the
acquired data revealed charge acceptance issues.
When tested with the 6.2 c profile, this deficiency is characterized by escalating on-charge
voltages which inhibit full SoC adaptations within the voltage window of the
OT
frequency-regulation installation.
When tested with the Annex B sequence profile, a decaying charge acceptance and SoC is
OT
observed that results in reduced operating time
...