Photovoltaic devices - Part 4: Photovoltaic reference devices - Procedures for establishing calibration traceability

IEC 60904-4:2019 is available as IEC 60904-4:2019 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.
IEC 60904-4:2019 sets the requirements for calibration procedures intended to establish the traceability of photovoltaic (PV) reference devices to SI units as required by IEC 60904-2. This document applies to PV reference devices that are used to measure the irradiance of natural or simulated sunlight for the purpose of quantifying the performance of PV devices. The use of a PV reference device is required in many standards concerning PV (e.g. IEC 60904-1 and IEC 60904-3). This document has been written with single-junction PV reference devices in mind, in particular crystalline silicon, but it is sufficiently general to include other single-junction technologies. This second edition cancels and replaces the first edition published in 2009. This edition includes the following significant technical changes with respect to the previous edition:
modification of standard title;
- inclusion of working reference in traceability chain;
- update of WRR with respect to SI;
- revision of all methods and their uncertainties in annex
- harmonization of symbols and formulae with other IEC standards.
The contents of the corrigendum of September 2020 have been included in this copy.

Dispositifs photovoltaïques - Partie 4: Dispositifs photovoltaïques de référence - Procédures pour établir la traçabilité de l'étalonnage

IEC 60904-4:2019 est disponible sous forme de IEC 60904-4:2019 RLV qui contient la Norme internationale et sa version Redline, illustrant les modifications du contenu technique depuis l'édition précédente.
L’IEC 60904-4:2019 fixe les exigences relatives aux procédures d'étalonnage dans le but d'établir la traçabilité des dispositifs photovoltaïques (PV) de référence en unités SI, comme cela est exigé par l’IEC 60904-2. Le présent document s'applique aux dispositifs PV de référence utilisés pour mesurer l'éclairement énergétique de la lumière solaire naturelle ou simulée afin de quantifier les performances des dispositifs PV. L'utilisation d'un dispositif PV de référence est exigée dans de nombreuses normes relatives aux dispositifs PV (par exemple, l’IEC 60904-1 et l’IEC 60904-3). Le présent document a été rédigé en prenant en considération les dispositifs PV de référence à jonction unique, en particulier le silicium cristallin, mais il est suffisamment général pour inclure d’autres technologies à jonction unique. Cette deuxième édition annule et remplace la première édition parue en 2009. Cette édition inclut les modifications techniques majeures suivantes par rapport à l’édition précédente:
- modification du titre de la norme;
- incorporation de la référence de travail à la chaîne de traçabilité;
- mise à jour de la WRR (world radiometric reference - référence radiométrique mondiale) par rapport au SI;
- révision de toutes les méthodes et de leurs incertitudes à l’annexe:
- harmonisation des symboles et formules avec les autres normes IEC.
Le contenu du corrigendum de septembre 2020 a été pris en considération dans cet exemplaire.

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Status
Published
Publication Date
11-Nov-2019
Current Stage
PPUB - Publication issued
Completion Date
12-Nov-2019
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IEC 60904-4
Edition 2.0 2019-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Photovoltaic devices –
Part 4: Photovoltaic reference devices – Procedures for establishing calibration
traceability
Dispositifs photovoltaïques –
Partie 4: Dispositifs photovoltaïques de référence – Procédures pour établir
la traçabilité de l'étalonnage
IEC 60904-4:2019-11(en-fr)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 60904-4
Edition 2.0 2019-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Photovoltaic devices –
Part 4: Photovoltaic reference devices – Procedures for establishing calibration
traceability
Dispositifs photovoltaïques –
Partie 4: Dispositifs photovoltaïques de référence – Procédures pour établir
la traçabilité de l'étalonnage
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.160 ISBN 978-2-8322-7531-3

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® Registered trademark of the International Electrotechnical Commission
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---------------------- Page: 3 ----------------------
– 2 – IEC 60904-4:2019 © IEC 2019
CONTENTS

FOREWORD ........................................................................................................................... 4

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

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

3 Terms and definitions ...................................................................................................... 6

4 Requirements for traceable calibration procedures of PV reference devices .................... 9

5 Uncertainty analysis ........................................................................................................ 9

6 Calibration report ........................................................................................................... 10

7 Marking ......................................................................................................................... 10

Annex A (informative) Examples of validated calibration procedures .................................... 11

A.1 General ................................................................................................................. 11

A.1.1 Overview ....................................................................................................... 11

A.1.2 Examples of validated methods ..................................................................... 11

A.1.3 List of common symbols ................................................................................ 11

A.1.4 Common formulae ......................................................................................... 12

A.1.5 Reference documents .................................................................................... 13

A.2 Global sunlight method (GSM) .............................................................................. 13

A.2.1 General ......................................................................................................... 13

A.2.2 Equipment ..................................................................................................... 14

A.2.3 Measurements ............................................................................................... 15

A.2.4 Data analysis ................................................................................................. 15

A.2.5 Uncertainty estimates .................................................................................... 16

A.2.6 Reference documents .................................................................................... 17

A.3 Differential spectral responsivity calibration (DSR) ................................................ 17

A.3.1 General ......................................................................................................... 17

A.3.2 Equipment ..................................................................................................... 18

A.3.3 Test procedure .............................................................................................. 18

A.3.4 Data analysis ................................................................................................. 20

A.3.5 Uncertainty estimate ...................................................................................... 20

A.3.6 Reference documents .................................................................................... 22

A.4 Solar simulator method (SSM) .............................................................................. 23

A.4.1 General ......................................................................................................... 23

A.4.2 Equipment ..................................................................................................... 23

A.4.3 Calibration procedure .................................................................................... 23

A.4.4 Data analysis ................................................................................................. 24

A.4.5 Uncertainty estimate ...................................................................................... 24

A.4.6 Reference documents .................................................................................... 25

A.5 Direct sunlight method (DSM) ............................................................................... 25

A.5.1 General ......................................................................................................... 25

A.5.2 Equipment ..................................................................................................... 26

A.5.3 Measurements ............................................................................................... 26

A.5.4 Data analysis ................................................................................................. 26

A.5.5 Uncertainty estimate ...................................................................................... 27

A.5.6 Reference documents .................................................................................... 27

Bibliography .......................................................................................................................... 28

---------------------- Page: 4 ----------------------
IEC 60904-4:2019 © IEC 2019 – 3 –
Figure 1 – Schematic of most common reference instruments and transfer methods

used in the traceability chains for solar irradiance detectors ................................................... 9

Figure A.1 – Block diagram of differential spectral responsivity calibration

superimposing chopped monochromatic radiation DE(l) and DC bias radiation E ................. 21

Figure A.2 – Optical arrangement of differential spectral responsivity calibration .................. 22

Figure A.3 – Schematic apparatus of the solar simulator method .......................................... 25

Table 1 – Examples of reference instruments used in a traceability chain of solar

irradiance ............................................................................................................................... 8

Table A.1 – Typical uncertainty components (k = 2) of global sunlight method ...................... 17

Table A.2 – Uncertainty components (k = 2) of differential spectral responsivity

calibration method on PV reference devices ......................................................................... 21

Table A.3 – Example of uncertainty components (k = 2) of a solar simulator method

calibration ............................................................................................................................. 24

Table A.4 – Typical uncertainty components (k = 2) of a solar simulator method

calibration when WRR traceable cavity radiometer is used.................................................... 24

Table A.5 – Typical uncertainty components (k = 2) of a direct sunlight method using

temperature dependent spectral correction factor (Formula (A.16)), without applying a

correction factor for the WRR to SI scale .............................................................................. 27

---------------------- Page: 5 ----------------------
– 4 – IEC 60904-4:2019 © IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
PHOTOVOLTAIC DEVICES –
Part 4: Photovoltaic reference devices –
Procedures for establishing calibration traceability
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

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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

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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National

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6) All users should ensure that they have the latest edition of this publication.

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expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC

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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 60904-4 has been prepared by IEC technical committee 82: Solar

photovoltaic energy systems.

This second edition cancels and replaces the first edition published in 2009. This edition

constitutes a technical revision.

This edition includes the following significant technical changes with respect to the previous

edition:
a) modification of standard title;
b) inclusion of working reference in traceability chain;
c) update of WRR with respect to SI;
d) revision of all methods and their uncertainties in Annex A;
e) harmonization of symbols and formulae with other IEC standards.
---------------------- Page: 6 ----------------------
IEC 60904-4:2019 © IEC 2019 – 5 –
The text of this International Standard is based on the following documents:
FDIS Report on voting
82/1618/FDIS 82/1638/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.

A list of all parts in the IEC 60904 series, published under the general title Photovoltaic

devices, can be found on the IEC website.

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: 7 ----------------------
– 6 – IEC 60904-4:2019 © IEC 2019
PHOTOVOLTAIC DEVICES –
Part 4: Photovoltaic reference devices –
Procedures for establishing calibration traceability
1 Scope

This part of IEC 60904 sets the requirements for calibration procedures intended to establish

the traceability of photovoltaic (PV) reference devices to SI units as required by IEC 60904-2.

This document applies to PV reference devices that are used to measure the irradiance of

natural or simulated sunlight for the purpose of quantifying the performance of PV devices.

The use of a PV reference device is required in many standards concerning PV (e.g.

IEC 60904-1 and IEC 60904-3).

This document has been written with single-junction PV reference devices in mind, in

particular crystalline silicon, but it is sufficiently general to include other single-junction

technologies.
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 60904-1, Photovoltaic devices – Part 1: Measurement of photovoltaic current-voltage

characteristics

IEC 60904-2, Photovoltaic devices – Part 2: Requirements for photovoltaic reference devices

IEC 60904-3, Photovoltaic devices – Part 3: Measurement principles for terrestrial

photovoltaic (PV) solar devices with reference spectral irradiance data
IEC TS 61836, Solar photovoltaic energy systems – Terms, definitions and symbols

ISO/IEC Guide 98-3: 2008, Uncertainty of measurement – Part 3: Guide to the expression of

uncertainty in measurement (GUM: 1995)
3 Terms and definitions

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

following apply.

NOTE The different reference instruments for the traceability chain of solar irradiance are defined in this clause.

Typical examples for each category are listed in Table 1, which also refers to relevant standards (where available).

Figure 1 then shows schematically the most common traceability chains linking these instruments and the relevant

standards (where available). Methods for the implementation of this document are described in Annex A.

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
• IEC Electropedia: available at http://www.electropedia.org/
---------------------- Page: 8 ----------------------
IEC 60904-4:2019 © IEC 2019 – 7 –
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
primary standard

standard that is designated or widely acknowledged as having the highest metrological

qualities and whose value is accepted without reference to other standards of the same

quantity

Note 1 to entry: The concept of a primary standard is equally valid for base quantities and derived quantities.

Note 2 to entry: A primary standard is never used directly for measurement other than for comparison with other

primary standards or secondary standards.

Note 3 to entry: Primary standards are usually maintained by national metrology institutes (NMIs) or similar

organizations entrusted with maintenance of standards for physical quantities. Often referred to also just as the

«primary», the physical implementation is selected such that long-term stability, accuracy and repeatability of

measurement of the quantity it represents are guaranteed to the maximum extent possible by current technology.

Note 4 to entry: The World Radiometric Reference (WRR) as realized by the World Standard Group (WSG) of

cavity radiometers is the accepted primary standard for the measurement of solar irradiance.

3.2
secondary standard

device which, by periodical comparison with a primary standard, serves to maintain conformity

to SI units at other places than that of the primary standard

Note 1 to entry: A secondary standard does not necessarily use the same technical principles as the primary

standard, but strives to achieve similar long-term stability, accuracy and repeatability.

Note 2 to entry: Typical secondary standards for solar irradiance are cavity radiometers which participate

periodically (normally every 5 years) in the International Pyrheliometer Comparison (IPC) with the WSG, thereby

giving traceability to WRR. Direct traceability to SI radiometric scale can also be available for these instruments.

3.3
primary reference

instrument which a laboratory uses to calibrate secondary references, compared at periodic

intervals to a secondary standard

Note 1 to entry: Often primary references can be realized at much lower costs than secondary standards.

Note 2 to entry: Typically, a PV cell is used as a reference device for the measurement of natural or simulated

solar irradiance. Primary references are normally used by calibration and testing laboratories.

3.4
secondary reference

measurement device in use for daily routine measurements or to calibrate working references,

calibrated at periodic intervals against a primary reference

Note 1 to entry: The most common secondary references for the measurement of natural or simulated solar

irradiance are PV cells and PV modules. Secondary references are normally used by calibration and testing

laboratories, but sometimes also in industrial production.
3.5
working reference

measurement device in use for daily routine measurements, calibrated at periodic intervals

against a secondary reference

Note 1 to entry: The most common working references for the measurement of natural or simulated solar

irradiance are PV cells and PV modules.
Note 2 to entry: Working references are normally used in industrial production.
---------------------- Page: 9 ----------------------
– 8 – IEC 60904-4:2019 © IEC 2019
3.6
traceability

requirement for any PV reference device, to tie its calibration

value to SI units in an unbroken and documented chain of calibration transfers including

stated uncertainties

Note 1 to entry: The WRR has been compared several times to the SI radiometric scale. While in previous

comparisons the two scales were found to be indistinguishable within the uncertainty of the comparison, the latest

comparison of scales established that there is a systematic shift between the scales, with WRR reading 0,34 %

higher irradiance than the SI scale. The uncertainty of this shift was given as 0,18 % (k = 2). Therefore, traceability

to WRR automatically provides traceability to SI units. However, the shift between the scales may be corrected for

those measurements traceable to the WRR. The uncertainty of the scale comparison shall be included into the

uncertainty budget. Essentially there are two possibilities for those measurements traceable to SI units via the

WRR. Firstly, no correction is applied for the scale difference and a larger uncertainty of 0,3 % (rectangular

distribution) shall be used. Secondly an explicit correction of the scale difference amounting to 0,34 %. In this case

the uncertainty contribution is 0,18 % (k = 2). The value of 0,34 % for the scale difference is the latest available at

time of publication of this document. The scientific literature should be checked for possible updates of this

difference and its uncertainty. In particular, it is possible that in the future the WRR is adapted to take account of

this difference and bring it into line with SI units. In this case no further correction shall be applied.

[SOURCE: A Fehlmann, G Kopp, W Schmutz, R Winkler, W Finsterle, N Fox, metrologia 49

(2012) S34]
Table 1 – Examples of reference instruments used
in a traceability chain of solar irradiance
Reference instrument Solar irradiance

Primary standard Group of cavity radiometers constituting the World Standard Group (WSG) of the

World Radiometric Reference (WRR)
Cryogenic trap detector
Standard lamp

Secondary standard Commercially available cavity radiometers compared regularly (normally every 5

years) at the International Pyrheliometer Comparison (IPC)
Standard detector calibrated against a trap detector
Spectroradiometer calibrated against a standard lamp
Primary reference Normal incidence pyrheliometer (NIP) (ISO 9059)
PV reference device (IEC 60904-2 and IEC 60904-4)
Secondary reference Pyranometer (ISO 9846)
PV reference device (IEC 60904-2)
Working reference Pyranometer (ISO 9847)
PV reference device (IEC 60904-2)
---------------------- Page: 10 ----------------------
IEC 60904-4:2019 © IEC 2019 – 9 –
Figure 1 – Schematic of most common reference instruments and transfer methods
used in the traceability chains for solar irradiance detectors
4 Requirements for traceable calibration procedures of PV reference devices

A traceable calibration procedure is necessary to transfer calibration from a standard or

reference measuring solar irradiance and based on a physical principle other than PV effect

(such as cavity radiometer, pyrheliometer and pyranometer) to a PV reference device. The

requirements for such procedures are as follows:

a) Any measurement instrument required and used in the transfer procedure shall be an

instrument with an unbroken traceability chain.
b) A documented uncertainty analysis.

c) Documented repeatability, such as measurement results of laboratory intercomparison, or

documents of laboratory quality control.

d) Inherent absolute accuracy, given by a limited number of intermediate transfers.

Normally the transfer would be from a secondary standard to a PV reference device

constituting a primary reference.
The transfer from one PV reference device to another is covered by IEC 60904-2.
5 Uncertainty analysis

An uncertainty estimate according to ISO/IEC Guide 98-3: 2008 shall be provided for each

traceable calibration procedure. This estimate shall provide information on the uncertainty of

the calibration procedure and quantitative data on the following uncertainty factors for each

instrument used in performing the calibration procedure. In particular:
a) Component of uncertainty arising from random effects (Type A).
b) Component of uncertainty arising from systematic effects (Type B).

A full uncertainty analysis has to be performed for the implementation of the calibration

method by a particular laboratory. Annex A provides examples of the main uncertainty

components in some particular implementations. Due to the variety of methods available, it is

---------------------- Page: 11 ----------------------
– 10 – IEC 60904-4:2019 © IEC 2019

impossible to give a detailed guidance on how a particular uncertainty analysis should be

made. However, the following components shall be considered:
– uncertainty of all measurement instruments involved;
– offset and drift of all measurement instruments;
– uncertainty of all references used;
– uncertainty of measured device
...

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