IEC 60904-2:2023
(Main)Photovoltaic devices - Part 2: Requirements for photovoltaic reference devices
Photovoltaic devices - Part 2: Requirements for photovoltaic reference devices
IEC 60904-2:2023 gives requirements for the classification, selection, packaging, marking, calibration and care of photovoltaic reference devices. This document applies to photovoltaic (PV) reference devices that are used to measure the irradiance of natural or simulated sunlight for the purpose of quantifying the electrical performance of photovoltaic devices (cells, modules and arrays). It does not cover photovoltaic reference devices for use under concentrated sunlight. This fourth edition cancels and replaces the third edition published in 2015. This edition includes the following significant technical changes with respect to the previous edition:
a) added calibration procedures for calibrating PV devices at maximum power by extending the respective Clauses 12 and 13;
b) revised requirements for mandatory measurement of spectral responsivity, temperature coefficients and linearity, depending on usage and allowing some measurements on equivalent devices;
c) revised requirements for built-in shunt resistor;
d) added requirements for traceability of calibration explicitly.
Dispositifs photovoltaïques - Partie 2: Exigences applicables aux dispositifs photovoltaïques de référence
L'IEC 60904-2:2023 donne les exigences relatives à la classification, à la sélection, au conditionnement, au marquage, à l’étalonnage et aux précautions d’utilisation des dispositifs photovoltaïques de référence. Le présent document s’applique aux dispositifs photovoltaïques (PV) de référence utilisés pour mesurer l’irradiance de la lumière solaire naturelle ou simulée afin de quantifier les performances électriques des dispositifs PV (cellules, modules et panneaux). Il ne couvre pas les dispositifs photovoltaïques de référence pour une utilisation sous éclairement solaire concentré. Cette quatrième édition annule et remplace la troisième édition parue en 2015. Cette édition inclut les modifications techniques majeures suivantes par rapport à l’édition précédente:
a) ajout de procédures d’étalonnage des dispositifs PV à la puissance maximale en développant les Articles 12 et 13) correspondants;
b) révision des exigences applicables au mesurage obligatoire de la sensibilité spectrale, des coefficients de température et de la linéarité, en fonction de l’usage et en permettant certains mesurages sur des dispositifs équivalents;
c) révision des exigences applicables aux résistances de shunt intégrées;
d) ajout d’exigences pour la traçabilité de l’étalonnage de manière explicite.
General Information
Relations
Overview - IEC 60904-2:2023 (Photovoltaic reference devices)
IEC 60904-2:2023 specifies requirements for the classification, selection, packaging, marking, calibration and care of photovoltaic (PV) reference devices used to measure irradiance from natural or simulated sunlight. This fourth edition replaces IEC 60904-2:2015 and explicitly adds calibration traceability requirements. The standard applies to reference cells, modules and arrays used to quantify electrical performance of PV devices under normal (non-concentrated) sunlight conditions. It does not cover reference devices for concentrated sunlight.
Key topics and technical requirements
The standard defines mandatory technical areas and test procedures for PV reference devices, including:
- Classification and selection
- Definitions for primary, secondary and working reference devices and their intended roles in calibration chains.
- Calibration and calibration traceability
- Requirements to tie calibration values to SI units via documented, unbroken traceability chains (see IEC 60904-4 for traceability procedures).
- New procedures for calibrating PV devices at maximum power (added to Clauses 12 and 13).
- Spectral responsivity, temperature coefficients and linearity
- Revised rules on when these measurements are mandatory; allows some measurements on equivalent devices.
- Built-in shunt resistor
- Updated requirements for devices that include internal shunt resistors.
- Usage, care, packaging and marking
- Recommended packaging for natural and simulated sunlight use, marking and documentation requirements.
- Measurement clauses
- Temperature measurement, electrical connections, and test procedures for calibrating secondary and working references (Clauses 7, 12–14).
Applications - who uses IEC 60904-2
IEC 60904-2 is essential for:
- PV calibration and testing laboratories establishing irradiance reference standards.
- Solar simulator manufacturers and test facilities setting and verifying simulator irradiance.
- PV module and cell manufacturers conducting performance measurements and quality control.
- Certification bodies and conformity assessment organizations ensuring consistent irradiance measurement practices.
- Research institutions performing inter-laboratory comparisons and traceable PV measurements.
Using this standard helps ensure reliable irradiance measurements, consistent I‑V and power testing, and validated calibration chains for accurate PV performance characterization.
Related standards
IEC 60904-2 is part of the IEC 60904 series. Closely related documents include:
- IEC 60904-1, -3, -4, -5, -7, -8, -9, -10 (measurement principles, traceability, spectral responsivity, solar simulator performance, linearity)
- IEC TS 61836 (terms, definitions, symbols)
Keywords: IEC 60904-2:2023, photovoltaic reference devices, PV reference devices, calibration traceability, spectral responsivity, solar simulator, irradiance measurement, reference cell.
Frequently Asked Questions
IEC 60904-2:2023 is a standard published by the International Electrotechnical Commission (IEC). Its full title is "Photovoltaic devices - Part 2: Requirements for photovoltaic reference devices". This standard covers: IEC 60904-2:2023 gives requirements for the classification, selection, packaging, marking, calibration and care of photovoltaic reference devices. This document applies to photovoltaic (PV) reference devices that are used to measure the irradiance of natural or simulated sunlight for the purpose of quantifying the electrical performance of photovoltaic devices (cells, modules and arrays). It does not cover photovoltaic reference devices for use under concentrated sunlight. This fourth edition cancels and replaces the third edition published in 2015. This edition includes the following significant technical changes with respect to the previous edition: a) added calibration procedures for calibrating PV devices at maximum power by extending the respective Clauses 12 and 13; b) revised requirements for mandatory measurement of spectral responsivity, temperature coefficients and linearity, depending on usage and allowing some measurements on equivalent devices; c) revised requirements for built-in shunt resistor; d) added requirements for traceability of calibration explicitly.
IEC 60904-2:2023 gives requirements for the classification, selection, packaging, marking, calibration and care of photovoltaic reference devices. This document applies to photovoltaic (PV) reference devices that are used to measure the irradiance of natural or simulated sunlight for the purpose of quantifying the electrical performance of photovoltaic devices (cells, modules and arrays). It does not cover photovoltaic reference devices for use under concentrated sunlight. This fourth edition cancels and replaces the third edition published in 2015. This edition includes the following significant technical changes with respect to the previous edition: a) added calibration procedures for calibrating PV devices at maximum power by extending the respective Clauses 12 and 13; b) revised requirements for mandatory measurement of spectral responsivity, temperature coefficients and linearity, depending on usage and allowing some measurements on equivalent devices; c) revised requirements for built-in shunt resistor; d) added requirements for traceability of calibration explicitly.
IEC 60904-2:2023 is classified under the following ICS (International Classification for Standards) categories: 27.160 - Solar energy engineering. The ICS classification helps identify the subject area and facilitates finding related standards.
IEC 60904-2:2023 has the following relationships with other standards: It is inter standard links to IEC 60904-2:2015. Understanding these relationships helps ensure you are using the most current and applicable version of the standard.
You can purchase IEC 60904-2:2023 directly from iTeh Standards. The document is available in PDF format and is delivered instantly after payment. Add the standard to your cart and complete the secure checkout process. iTeh Standards is an authorized distributor of IEC standards.
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Photovoltaic devices –
Part 2: Requirements for photovoltaic reference devices
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IEC 60904-2 ®
Edition 4.0 2023-06
COMMENTED VERSION
INTERNATIONAL
STANDARD
colour
inside
Photovoltaic devices –
Part 2: Requirements for photovoltaic reference devices
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.160 ISBN 978-2-8322-7145-2
– 2 – IEC 60904-2:2023 CMV © IEC 2023
CONTENTS
FOREWORD .3
1 Scope .5
2 Normative references .5
3 Terms and definitions .6
4 Selection of reference device .9
4.1 General requirements .9
4.2 Additional requirements for single reference cell in a multi-cell package . 10
4.3 Additional requirements for reference modules . 10
4.4 Requirements for built-in shunt resistors. 11
5 Temperature measurement . 12
6 Electrical connections . 12
7 Calibration . 12
7.1 General requirements . 12
7.2 Calibration value(s) . 12
7.3 Spectral responsivity . 12
7.4 Temperature coefficients. 13
7.5 Linearity . 13
8 Documentation and report . 13
8.1 General . 14
8.2 Device documentation . 14
8.3 Calibration report . 14
9 Marking . 15
10 Packaging . 15
10.1 Recommended packaging for use in natural sunlight . 15
10.2 Recommended packaging for use under solar simulators . 15
10.3 Single cell package . 15
11 Care of reference devices . 16
12 Usage of reference devices . 16
13 Calibration of secondary reference devices against a primary reference cell . 17
13.1 General . 17
13.2 Natural sunlight . 17
13.3 Simulated sunlight . 18
13.4 Test procedure . 18
13.5 Additional measurements . 20
13.5.1 Spectral responsivity . 20
13.5.2 Temperature coefficient(s) . 20
13.5.3 Linearity . 20
14 Calibration of working reference device against a secondary reference device . 20
Bibliography . 22
List of comments . 23
Figure 1 – Single cell package .8
Figure 2 – Single reference cell in a multi-cell package . 10
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
PHOTOVOLTAIC DEVICES –
Part 2: Requirements for photovoltaic reference devices
FOREWORD
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This commented version (CMV) of the official standard IEC 60904-2:2023 edition 4.0
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This publication contains the CMV and the official standard. The full list of comments is
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– 4 – IEC 60904-2:2023 CMV © IEC 2023
IEC 60904-2 has been prepared by IEC technical committee 82: Solar photovoltaic energy
systems. It is an International Standard.
This fourth edition cancels and replaces the third edition published in 2015. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) added calibration procedures for calibrating PV devices at maximum power by extending
the respective Clauses 12 and 13;
b) revised requirements for mandatory measurement of spectral responsivity, temperature
coefficients and linearity, depending on usage and allowing some measurements on
equivalent devices;
c) revised requirements for built-in shunt resistor;
d) added requirements for traceability of calibration explicitly.
The text of this International Standard is based on the following documents:
Draft Report on voting
82/2127/FDIS 82/2151/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
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at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
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
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PHOTOVOLTAIC DEVICES –
Part 2: Requirements for photovoltaic reference devices
1 Scope
This part of IEC 60904 gives requirements for the classification, selection, packaging, marking,
calibration and care of photovoltaic reference devices.
This document covers applies to photovoltaic (PV) reference devices that are used to determine
measure the irradiance of natural or simulated sunlight for the purpose of quantifying the
electrical performance of photovoltaic devices (cells, modules and arrays under natural and
simulated sunlight). It does not cover photovoltaic reference devices for use under concentrated
sunlight.
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 60891, Photovoltaic devices – Procedures for temperature and irradiance corrections to
measured I-V characteristics
IEC 60904-1, Photovoltaic devices – Part 1: Measurement of photovoltaic current-voltage
characteristics
IEC 60904-3, Photovoltaic devices – Part 3: Measurement principles for terrestrial photovoltaic
(PV) solar devices with reference spectral irradiance data
IEC 60904-4, Photovoltaic devices – Part 4: Reference solar Photovoltaic reference devices –
Procedures for establishing calibration traceability
IEC 60904-5, Photovoltaic devices – Part 5: Determination of the equivalent cell temperature
(ECT) of photovoltaic (PV) devices by the open-circuit voltage method
IEC 60904-7, Photovoltaic devices – Part 7: Computation of the spectral mismatch correction
for measurements of photovoltaic devices
IEC 60904-8, Photovoltaic devices – Part 8: Measurement of spectral responsivity of a
photovoltaic (PV) device
IEC 60904-9, Photovoltaic devices – Part 9: Classification of solar simulator performance
requirements characteristics
IEC 60904-10, Photovoltaic devices – Part 10: Methods of linear dependence and linearity
measurements
IEC TS 61836, Solar photovoltaic energy systems – Terms, definitions and symbols
– 6 – IEC 60904-2:2023 CMV © IEC 2023
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC TS 61836 and the
following apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1
calibration traceability
traceability as defined in IEC 60904-4
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 1
Note 1 to entry: Photovoltaic reference devices are distinguished by their position in a chain of calibration
traceability.
[SOURCE IEC 60904-4:2019, 3.6, modified – The term "traceability" has been replaced with
"calibration traceability" and Note 1 to entry has been replaced.]
3.2
reference device
specially calibrated photovoltaic devices which are used to measure natural or simulated
irradiance or to set simulator irradiance levels for measuring the performance of other
photovoltaic devices
traceably calibrated photovoltaic device
Note 1 to entry: Normally used to measure natural or simulated solar irradiance or to set solar simulator irradiance
levels for measuring the performance of other photovoltaic devices. 2
3.3
primary reference device
photovoltaic reference device whose calibration is based on a radiometer or standard detector
or standard light source with calibration based on a secondary standard for irradiance 3
traceable to SI units as defined in IEC 60904-4
Note 1 to entry: Typically, a PV cell is used as a reference device for the measurement of natural or simulated solar
irradiance.
Note 2 to entry: Primary references are normally used by calibration and testing laboratories to calibrate secondary
references.
Note 3 to entry: Normally calibrated at periodic intervals. 4
3.4
secondary reference device
photovoltaic reference device calibrated in natural or simulated sunlight against a primary
reference device
Note 1 to entry: Secondary references are normally used by calibration and testing laboratories to calibrate working
references, but also for daily routine measurements, in industrial production and in monitoring.
Note 2 to entry: Normally calibrated at periodic intervals. 5
3.5
working reference device
photovoltaic reference device calibrated in natural or simulated sunlight against a secondary
reference device
Note 1 to entry: Working references are normally used for daily routine measurements, in industrial production and
in monitoring.
Note 2 to entry: Normally calibrated at periodic intervals. 6
3.6
reference cell
single photovoltaic cell used primarily for transfer of calibration values
reference device consisting of a single photovoltaic cell 7
Note 1 to entry: For practical reasons, such cells are small in surface area, and are usually mounted on a fixture
which ensures reproducibility in mounting, thermal control, electrical connections and protects the device. A typical
sample is sketched in Figure 1.
Note 2 to entry: Normally the reference cells are also provided with a protective window and embedded in an
encapsulant.
Note 3 to entry: Recommended use: as a laboratory primary, secondary and working reference.
Note 4 to entry: If the encapsulation system has been demonstrated to withstand long-term outdoor exposure,
applying test levels according to the IEC 61215 series [1], such reference cells can also be suitable to be used as a
monitoring device for long-term assessment of operational PV arrays.
Note 5 to entry: If the reference cell is provided with a protective window but without encapsulant, then it should
only be used when measuring the performance of other PV devices using direct beam natural or simulated sunlight. 8
– 8 – IEC 60904-2:2023 CMV © IEC 2023
Wiring space
Window receptacle
Solar cell cavity
Voltage and
Cable
current leads
clamp
Field of view not
less than 160°
IEC
Figure 1 – Single cell package
3.6.1
reference cell with protective cover but without encapsulant
photovoltaic reference cell similar to 3.6, but provided with a protective cover
Note 1 to entry: Recommended use: as a laboratory primary, secondary and working reference, in particular when
measuring the performance of other photovoltaic devices using solar simulators or natural sunlight with direct beam
only. 9
3.6.2
encapsulated reference cell
photovoltaic reference cell similar to 3.6, but encapsulated in a protective assembly so as to
withstand short-term outdoor exposure
Note 1 to entry: Recommended use: as a laboratory primary, secondary and working reference, in particular when
measurements of the performance of other photovoltaic devices under natural sunlight are performed.
Note 2 to entry: If the encapsulation system has been demonstrated to withstand long-term outdoor exposure,
applying test levels according to IEC 61215, such reference cells may also be suitable to be used as a monitoring
device for long-term assessment of operational photovoltaic arrays. 10
3.7
multi-cell reference devices
photovoltaic device consisting of several photovoltaic cells
Note 1 to entry: Recommended use: as the diffuse component of natural sunlight and non-normal incidence of
simulated sunlight interact with encapsulants and back sheets of a module and influence the amount of irradiance
which a particular cell receives, it is recommended that reference devices used for measuring sub-assemblies of
modules and arrays be encapsulated in a multi-cell package, matching the mechanical and optical features of the
test specimen (module, sub-assemblies of modules, arrays) so as to respond to variations in the geometrical
distribution of the incident radiation in the same way as the test specimen. 11
3.7
single reference cell in a multi-cell package
reference device consisting of a single photovoltaic cell mounted in a package such that frame,
encapsulation system, shape, size and spacing of the cells surrounding it are the same as in
the PV module to be tested
Note 1 to entry: The surrounding cells may be real or dummies that have the same optical properties.
3.8
reference module
photovoltaic module consisting of the encapsulation of a series and/or parallel connection of
photovoltaic cells
reference device consisting of a photovoltaic module 12
Note 1 to entry: Recommended use: for measuring other modules in order to achieve correspondence of
dimensions, mechanical construction, optical properties and electrical circuitry of the reference module and test
module, so as to minimize discrepancies due to solar simulator spatial non-uniformity, internal reflections or,
temperature distribution and spectral mismatch.
Note 2 to entry: As the diffuse component of natural sunlight and non-normal incidence of simulated sunlight interact
with encapsulants and back sheets of a PV module and influence the amount of irradiance which a particular cell
receives, it is recommended that reference devices used for measuring PV modules, sub-assemblies of PV modules
and PV arrays be encapsulated matching the mechanical and optical features of the device under test. 13
3.9
built-in shunt resistor
resistor connected across the output terminals of photovoltaic devices including connection
wiring
Note 1 to entry: The resistor shunts the output of the photovoltaic device providing an output voltage to be measured
and avoiding user-provided means of establishing short-circuit condition.
Note 2 to entry: For details consult 4.4.
4 Selection of reference device
4.1 General requirements
Depending on their intended use, reference devices need to meet different requirements in
terms of their spectral responsivity, mechanical construction, optical properties, dimensions and
electrical circuit. The spectral responsivity of the reference device, for example, is determined
by the transmission of any protective cover window in front of the device and the spectral
responsivity of the device itself. Therefore, the overall spectral responsivity can be adapted by
using suitable filters as or in addition to the protective cover window.
A reference device shall meet the following requirements:
a) photovoltaic characteristics shall be stable according to the requirements in Clause 11;
– 10 – IEC 60904-2:2023 CMV © IEC 2023
b) the output signal of the reference device shall vary linearly with irradiance, as defined in
IEC 60904-10, over the range of interest. 14
Reference devices should be made using a PV technology that is known to be stable with time.
In particular, the calibration value should not change after the reference device has been
exposed to solar irradiation, device temperatures different from its calibration temperature
and/or extended storage in the dark. The photovoltaic characteristics of a reference device shall
be stable according to the requirements in Clause 11. 15
The reference device shall be constructed such that the photovoltaic performance parameters,
in particular short-circuit current and maximum power, can be measured. The only exception
are devices with a built-in shunt resistor, see 4.4.
4.2 Additional requirements for single reference cell in a multi-cell package
The dotted line in Figure 2 indicates the minimum acceptable size of a multi-cell package. For
other cell arrangements, such as half-cut cells, an analogous configuration applies.
Figure 2 – Single reference cell in a multi-cell package
4.3 Additional requirements for reference modules
Additional requirements apply to reference modules.
a) Bypass diodes:
• general reference modules, which are used to measure a range of module types and
geometries, should not contain bypass diodes. The presence or absence of bypass
diodes shall be noted and considered in conjunction with the measurement conditions,
in particular spatial non-uniformity of the irradiance on the module during measurement;
• for reference modules, which are intended to be matched to the module under test, the
number, type and connection of bypass diodes (if present) shall match those in the
module under test.
b) If they are made from discrete cells, these shall should 16 be matched as follows depending
on the intended use of the reference module:
• if only the short-circuit current of the reference module will be used, the short-circuit
current of the individual cells shall should 17 be matched to within ±1 %;
• if other parameters (such as maximum power) are used additionally or exclusively, both
the short-circuit current and the fill factor of the individual cells shall should 18 be
matched to within ±1 %.
The matching of the individual cells is the responsibility of the manufacturer of the reference
module, bearing in mind that matching may can also be influenced by encapsulation or
lamination. The cell matching need not be checked by the calibration laboratory. However, if I-
V curves of the reference module indicate inconsistent response (i.e. obvious steps are noted
in the I-V curve), the I-V curve should be measured under light that is known to be uniform (e.g.
natural sunlight) to determine whether there is evidence that the cells within the module are
matched within 1 % this should be discussed between calibration laboratory and the client
supplying the module before proceeding with calibration. If the module exhibits evidence of >
1 % mismatch between cells, the module shall not be used as reference module. 19
4.4 Requirements for built-in shunt resistors
The built-in shunt resistor (see 3.9) shall should 20 be chosen such as to ensure that the
reference device operates sufficiently near to short-circuit condition, meeting the requirement
in Formula (1):
I × R < 0,03 × V
SC CAL OC
0,2 ×V
OC
R <
(1)
CAL
I
SC
where
R is the built-in shunt resistor;
CAL
I is the short-circuit current of the reference device at desired reference conditions;
SC
V is the open circuit voltage of the reference device at desired reference conditions.
OC
If a shunted reference cell does not meet the requirement of formula (1), it shall only be used
at irradiances (± 5 %) and temperatures (± 2 ºC) at which it was calibrated. 21
The long-term stability of such resistors the built-in shunt resistor shall also meet the stability
requirements of the reference device. Calibration values of such reference devices shall be
measured as the voltage drop across the built-in shunt resistor and stated with the dimension
[V] at standard test conditions (see Clause 7). The temperature coefficient of the built-in shunt
resistor is part of the temperature coefficient of the calibration value of the reference device.
As the uncertainty in the calibration may can be strongly dependent on the built-in shunt resistor
stability and temperature coefficient, respective values should be provided with the reference
cell data sheet.
If a shunted reference cell is to be used for low irradiance measurements, either a dedicated
cell can be constructed with the restriction of formula (1), where the short circuit current is
considered at the desired low irradiance rather than at STC. Alternatively a shunted cell can
have a larger shunt resistor, but requires a separate calibration for each irradiance and
temperature it is to be used at. 22
It is recommended that the shunt resistor be a removable 4-wire resistor, to allow for standard
(current-based) measurements of spectral responsivity and periodic checking of the reference
device stability by taking measuring an I-V curve per in accordance with IEC 60904-1. However,
the reproducibility of the electrical connection shall be maintained.
Formula (1) means that the measured output voltage of a shunted reference cell shall should
be less than 3 20 % 23 of its open circuit voltage. For typical crystalline silicon this equates to
about 20 120 mV output.
– 12 – IEC 60904-2:2023 CMV © IEC 2023
5 Temperature measurement
Means shall be provided for determining the reference cell temperature or, for reference
modules, the equivalent cell temperature (ECT), according to IEC 60904-5. Temperature
sensors and instrumentation shall have instrumental measurement uncertainty of 1 °C or less 24.
The required uncertainty for temperature measurements for the cell junction shall be less than
± 2,0 °C for all reference devices. A minimum accuracy of ±1,0 °C for the temperature sensor
is suggested to achieve this uncertainty in the temperature measurement.
6 Electrical connections
The electrical connections to reference cells without built-in shunt resistor shall consist of a
four-wire contact system (Kelvin probe). Care shall be taken to avoid Measurement errors due
to voltage drops along the cell’s contact bars and the package wiring shall be avoided.
The electrical connections to the reference module shall be designed to meet the requirements
of IEC 60904-1.
7 Calibration
7.1 General requirements
Each calibration of a reference device shall be made with a calibration procedure that is
traceable according to IEC 60904-4. Any measurement instrument used in the calibration
procedure shall be an instrument with an unbroken traceability chain. 25
The laboratory performing the calibration of the reference device shall maintain a documented
uncertainty analysis as well as documented repeatability and results from interlaboratory
comparisons.
7.2 Calibration value(s)
Each reference device shall be calibrated in terms of its calibration value(s) at the desired
–2
reference conditions, normally standard test conditions (STC) (1 000 W·m , 25 ºC device
temperature with the reference spectral irradiance distribution as defined in IEC 60904-3).
Calibration values shall be reported together with the three main parameters of total irradiance,
device junction temperature and spectral irradiance. The most common calibration conditions
are standard test conditions (STC). A calibration at STC shall refer to a total irradiance of
−2
1 000 W m , a device junction temperature of 25 °C and the reference spectral irradiance
distribution as defined in IEC 60904-3. Sometimes calibration is required at other conditions. A
reference device can have multiple calibration values for different desired reference conditions.
In particular, IEC 61853-1 [2] requires the use of a reference device at a range of irradiances
and temperatures and therefore the calibration at the respective conditions. 26
Methods for calibrating primary reference devices are included in IEC 60904-4. A method
procedure of calibrating secondary reference devices is described in Clause 13. The calibration
of working reference devices is treated in Clause 14.
7.3 Spectral responsivity
In general, the spectral responsivity at short-circuit current conditions of each reference device
shall be measured in accordance with IEC 60904-8. If for reference modules this cannot be
measured directly, it shall be deduced from measurements made on representative
encapsulated photovoltaic cells. For exceptions related to working references, see Clause 14. 27
___________
Numbers in square brackets refer to the Bibliography.
7.4 Temperature coefficients
eference device shall be measured
The determination of the temperature coefficient(s) of each r
in accordance with IEC 60891 is in general optional but depending on usage might be
mandatory, and in any case is strongly recommended. If the temperature coefficient(s) are
determined, also their linear dependence in accordance with IEC 60904-10 shall be reported.
For exceptions related to working references, see Clause 14. 28
7.5 Linearity
n general optional but
The determination of linearity in accordance with IEC 60904-10 is i
depending on usage might be mandatory, and in any case is strongly recommended. For
exceptions related to working references, see Clause 14. 29
8 Documentation and report 30
Each time a reference device is calibrated, the following information shall be recorded on a data
sheet:
– Identification number
– Type (primary reference cell; secondary reference device, working reference device)
– Cell manufacturer
– Material type
– Type of package
– Type and dimension of cell(s)
– Circuit diagram, in particular of any connectors
– Calibration organization
– Site and date of calibration
– Method of calibration (refer to standard)
– Radiometer or standard lamp characteristics (where applicable)
– Primary reference cell identification (where applicable)
– Simulator characteristics (where applicable)
– Type of temperature sensor (where applicable)
– Spectral responsivity
– Temperature coefficient of calibration value
– Calibration value at reference conditions
– Reference conditions
– Estimated uncertainty
– Shunt resistor nominal resistance and temperature coefficient (where applicable)
– Either the mismatch correction value used in the measurement or an estimate of the
uncertainty introduced by using the mismatched reference device.
For reference cells without fixed electrical connection to the cell, the following information shall
be recorded on the data sheet:
– Illustration of type, shape and location of electrical contacts during calibration.
For reference modules, the following information shall be recorded in addition on the data sheet:
– manufacturer
– model designation
– serial number
– 14 – IEC 60904-2:2023 CMV © IEC 2023
– cell technology
– construction and dimensions of module
– electrical circuit layout
– presence or absence of bypass diodes and if present their number and type.
8.1 General
The information given in 8.2 and 8.3 shall be recorded for each reference device.
8.2 Device documentation
The data sheet shall be compiled by the manufacturer of the reference device and contain the
following information:
a) unique identification of the device;
b) cell manufacturer and device manufacturer;
c) material type;
d) type of package;
e) type and dimension of cell(s);
f) circuit diagram, in particular of any connectors;
g) type of temperature sensor (where applicable) and its uncertainty;
h) shunt resistor type, nominal resistance and temperature coefficient (where applicable).
For reference modules, the following information shall be recorded in addition:
a) manufacturer of module;
b) model designation;
c) serial number;
d) cell technology;
e) construction and dimensions of module;
f) electrical circuit layout;
g) presence or absence of bypass diodes and if present their number and type.
8.3 Calibration report
Each time a reference device is calibrated, the calibration report shall contain the following
information:
a) unique identification of the device;
b) indication that the device has a built-in shunt resistor (where applicable);
c) type (primary reference cell; secondary reference device, working reference device);
d) calibration organization;
e) site and date of calibration;
f) method of calibration (refer to standard);
g) identification of the reference device used for the calibration and its traceability according
to IEC 60904-4;
h) simulator type and classification (where applicable);
i) calibration value(s) and corresponding reference conditions (total irradiance, device junction
temperature, spectral irradiance); in case of calibration via current-voltage characteristics
both short-circuit current and maximum power shall be reported; the open-circuit voltage
should also be reported;
j) spectral responsivity (where applicable);
k) temperature coefficient of calibration value(s) as well as linear dependence (where
applicable);
l) linearity (where applicable);
m) uncertainties for items i), j), k) and l);
n) either the spectral mismatch correction value used in the measurement or an estimate of
the uncertainty introduced by using an equivalent device;
o) statement that measurements originate from an equivalent device and an identification of
which measurements these are (where applicable);
p) unique identification of the equivalent device(s) (where applicable).
For reference cells without fixed electrical connection to the cell, the following information shall
be provided:
q) illustration of type, shape and location of electrical contacts during calibration.
9 Marking
The reference device shall carry a clear, indelible serial or identification number for cross-
reference to its data sheet.
10 Packaging
10.1 Recommended packaging for use in natural sunlight
The reference device used for measurement in natural sunlight should respond to variations in
the geometrical distribution of the incident radiation in the same way as the device under test
specimens (cells, sub-assemblies of cells, modules). As encapsulants and back sheets respond
to the diffuse component of natural sunlight, it is recommended that reference cells used for
measuring modules be enclosed in a multi-cell package (see Figure 2), simulating the
neighbouring optical parameters of a module.
In this case, the frame, the encapsulation system, the shape, and the size and spacing of the
cells surrounding the reference cell shall be the same as in the module to be tested. The
surrounding cells may be real or dummies that have the same optical properties. The dotted
line in Figure 2 indicates the minimum acceptable size of the multi-cell package for outdoor
testing.
10.2 Recommended packaging for use under solar simulators
In some solar simulators which allow multiple reflections of light to and from the device under
test specimen, the irradiance in the test plane may can change depending on whether or not
the device under test specimen is present. Therefore, in order to measure accurately the
irradiance that will be present when the device under test specimen is in place, the reference
devices used in such solar simulators shall should be packaged in the same way as the device
under test specimen, so that the change in irradiance due to multiple reflections is the same for
both the reference device and the device under test specimen.
Reference cells used for measurements in solar simulators designed to minimize any error from
multi-reflected light may be packaged singly or, if not intended for day-to-day use, mounted in
the unpackaged state on a temperature-controlled block.
Alternatively, the requirements given for reference cells for use in natural sunlight may be
followed.
10.3 Single cell package
If a single cell package is used, the following recommendations are made.
– 16 – IEC 60904-2:2023 CMV © IEC 2023
a) The field of view should be at least 160°. In case of a protective window the optical
properties of the latter have to be considered in determining the effective field of view of the
photovoltaic cell. The field of view is particularly important for measurements under natural
sunlight, whereas for usage on solar simulators with a limited range of angles of incidence,
it is less critical. 31
b) All surfaces in the package within the cell’s field of view should be non-reflective, with an
absorption a spectral absorptance of at least 0,95 in the cell’s wavelength responsivity band.
c) The material used for bonding the cell to the holder should be resistant to degradation,
either electrically or optically. Its physical characteristics should remain stable over the
entire period of intended use.
d) The use of a protective window is recommended. If encapsulated, the space between the
window and the cell should be filled with a stable encapsulant. Both the protective window
and the encapsulant should be transparent over the wavelength range in which the PV
reference device has a non-zero spectral responsivity. The refractive index of the
encapsulant should be similar (within 10 %) to that of the window to minimize errors due to
the internal reflection of light. The transparency, homogeneity and adhesion of the
encapsulant should not be adversely affected by ultra-violet light and operational
temperatures.
e) The protective window may embody a filter to match the spectral responsivity of the
reference cell to that of the device under test specimen, provided that the other requirements
recommendations of d) are met.
Figure 1 shows an example of a suitable single cell package. Other suitable single cell
packages can be found in JIS C8910 [3] or the World Photovoltaic Scale [4].
11 Care of reference devices
It is recommended that reference devices be recalibrated on an annual basis.
The window of a packaged reference device shall be kept clean and scratch-free.
Uncovered reference cells shall be preserved against damage, contamination and degradation.
A reference device exhibiting any defect which might impair its function shall not be used.
The calibration value of a reference device might change
...
IEC 60904-2 ®
Edition 4.0 2023-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Photovoltaic devices –
Part 2: Requirements for photovoltaic reference devices
Dispositifs photovoltaïques –
Partie 2: Exigences applicables aux dispositifs photovoltaïques de référence
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IEC 60904-2 ®
Edition 4.0 2023-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Photovoltaic devices –
Part 2: Requirements for photovoltaic reference devices
Dispositifs photovoltaïques –
Partie 2: Exigences applicables aux dispositifs photovoltaïques de référence
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.160 ISBN 978-2-8322-6948-0
– 2 – IEC 60904-2:2023 © IEC 2023
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 6
4 Selection of reference device . 8
4.1 General requirements . 8
4.2 Additional requirements for single reference cell in a multi-cell package . 8
4.3 Additional requirements for reference modules . 9
4.4 Requirements for built-in shunt resistors . 9
5 Temperature measurement . 10
6 Electrical connections . 10
7 Calibration . 10
7.1 General requirements . 10
7.2 Calibration value(s) . 10
7.3 Spectral responsivity . 11
7.4 Temperature coefficients . 11
7.5 Linearity . 11
8 Documentation and report . 11
8.1 General . 11
8.2 Device documentation . 11
8.3 Calibration report . 12
9 Marking . 12
10 Packaging . 12
10.1 Recommended packaging for use in natural sunlight . 12
10.2 Recommended packaging for use under solar simulators . 13
10.3 Single cell package . 13
11 Care of reference devices . 13
12 Usage of reference devices . 14
13 Calibration of secondary reference devices against a primary reference cell . 14
13.1 General . 14
13.2 Natural sunlight . 15
13.3 Simulated sunlight . 15
13.4 Test procedure . 15
13.5 Additional measurements . 17
13.5.1 Spectral responsivity . 17
13.5.2 Temperature coefficient(s) . 17
13.5.3 Linearity . 17
14 Calibration of working reference device against a secondary reference device . 17
Bibliography . 19
Figure 1 – Single cell package . 7
Figure 2 – Single reference cell in a multi-cell package . 8
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
PHOTOVOLTAIC DEVICES –
Part 2: Requirements for photovoltaic reference devices
FOREWORD
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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.
IEC 60904-2 has been prepared by IEC technical committee 82: Solar photovoltaic energy
systems. It is an International Standard.
This fourth edition cancels and replaces the third edition published in 2015. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) added calibration procedures for calibrating PV devices at maximum power by extending
the respective Clauses 12 and 13;
b) revised requirements for mandatory measurement of spectral responsivity, temperature
coefficients and linearity, depending on usage and allowing some measurements on
equivalent devices;
c) revised requirements for built-in shunt resistor;
d) added requirements for traceability of calibration explicitly.
– 4 – IEC 60904-2:2023 © IEC 2023
The text of this International Standard is based on the following documents:
Draft Report on voting
82/2127/FDIS 82/2151/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
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.
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 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 document indicates
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PHOTOVOLTAIC DEVICES –
Part 2: Requirements for photovoltaic reference devices
1 Scope
This part of IEC 60904 gives requirements for the classification, selection, packaging, marking,
calibration and care of photovoltaic reference devices.
This document applies to photovoltaic (PV) reference devices that are used to measure the
irradiance of natural or simulated sunlight for the purpose of quantifying the electrical
performance of photovoltaic devices (cells, modules and arrays). It does not cover photovoltaic
reference devices for use under concentrated sunlight.
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 60891, Photovoltaic devices – Procedures for temperature and irradiance corrections to
measured I-V characteristics
IEC 60904-1, Photovoltaic devices – Part 1: Measurement of photovoltaic current-voltage
characteristics
IEC 60904-3, Photovoltaic devices – Part 3: Measurement principles for terrestrial photovoltaic
(PV) solar devices with reference spectral irradiance data
IEC 60904-4, Photovoltaic devices – Part 4: Photovoltaic reference devices – Procedures for
establishing calibration traceability
IEC 60904-5, Photovoltaic devices – Part 5: Determination of the equivalent cell temperature
(ECT) of photovoltaic (PV) devices by the open-circuit voltage method
IEC 60904-7, Photovoltaic devices – Part 7: Computation of the spectral mismatch correction
for measurements of photovoltaic devices
IEC 60904-8, Photovoltaic devices – Part 8: Measurement of spectral responsivity of a
photovoltaic (PV) device
IEC 60904-9, Photovoltaic devices – Part 9: Classification of solar simulator characteristics
IEC 60904-10, Photovoltaic devices – Part 10: Methods of linear dependence and linearity
measurements
IEC TS 61836, Solar photovoltaic energy systems – Terms, definitions and symbols
– 6 – IEC 60904-2:2023 © IEC 2023
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC TS 61836 and the
following apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1
calibration 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: Photovoltaic reference devices are distinguished by their position in a chain of calibration
traceability.
[SOURCE IEC 60904-4:2019, 3.6, modified – The term "traceability" has been replaced with
"calibration traceability" and Note 1 to entry has been replaced.]
3.2
reference device
traceably calibrated photovoltaic device
Note 1 to entry: Normally used to measure natural or simulated solar irradiance or to set solar simulator irradiance
levels for measuring the performance of other photovoltaic devices.
3.3
primary reference device
photovoltaic reference device with calibration based on a secondary standard for irradiance
traceable to SI units as defined in IEC 60904-4
Note 1 to entry: Typically, a PV cell is used as a reference device for the measurement of natural or simulated solar
irradiance.
Note 2 to entry: Primary references are normally used by calibration and testing laboratories to calibrate secondary
references.
Note 3 to entry: Normally calibrated at periodic intervals.
3.4
secondary reference device
photovoltaic reference device calibrated in natural or simulated sunlight against a primary
reference device
Note 1 to entry: Secondary references are normally used by calibration and testing laboratories to calibrate working
references, but also for daily routine measurements, in industrial production and in monitoring.
Note 2 to entry: Normally calibrated at periodic intervals.
3.5
working reference device
photovoltaic reference device calibrated in natural or simulated sunlight against a secondary
reference device
Note 1 to entry: Working references are normally used for daily routine measurements, in industrial production and
in monitoring.
Note 2 to entry: Normally calibrated at periodic intervals.
3.6
reference cell
reference device consisting of a single photovoltaic cell
Note 1 to entry: For practical reasons, such cells are small in surface area, and are usually mounted on a fixture
which ensures reproducibility in mounting, thermal control, electrical connections and protects the device. A typical
sample is sketched in Figure 1.
Note 2 to entry: Normally the reference cells are also provided with a protective window and embedded in an
encapsulant.
Note 3 to entry: Recommended use: as a laboratory primary, secondary and working reference.
Note 4 to entry: If the encapsulation system has been demonstrated to withstand long-term outdoor exposure,
applying test levels according to the IEC 61215 series [1], such reference cells can also be suitable to be used as a
monitoring device for long-term assessment of operational PV arrays.
Note 5 to entry: If the reference cell is provided with a protective window but without encapsulant, then it should
only be used when measuring the performance of other PV devices using direct beam natural or simulated sunlight.
Figure 1 – Single cell package
3.7
single reference cell in a multi-cell package
reference device consisting of a single photovoltaic cell mounted in a package such that frame,
encapsulation system, shape, size and spacing of the cells surrounding it are the same as in
the PV module to be tested
Note 1 to entry: The surrounding cells may be real or dummies that have the same optical properties.
3.8
reference module
reference device consisting of a photovoltaic module
Note 1 to entry: Recommended use: for measuring other modules in order to achieve correspondence of
dimensions, mechanical construction, optical properties and electrical circuitry of the reference module and test
module, so as to minimize discrepancies due to solar simulator spatial non-uniformity, internal reflections,
temperature distribution and spectral mismatch.
Note 2 to entry: As the diffuse component of natural sunlight and non-normal incidence of simulated sunlight interact
with encapsulants and back sheets of a PV module and influence the amount of irradiance which a particular cell
receives, it is recommended that reference devices used for measuring PV modules, sub-assemblies of PV modules
and PV arrays be encapsulated matching the mechanical and optical features of the device under test.
– 8 – IEC 60904-2:2023 © IEC 2023
3.9
built-in shunt resistor
resistor connected across the output terminals of photovoltaic devices including connection
wiring
Note 1 to entry: The resistor shunts the output of the photovoltaic device providing an output voltage to be measured
and avoiding user-provided means of establishing short-circuit condition.
Note 2 to entry: For details consult 4.4.
4 Selection of reference device
4.1 General requirements
Depending on their intended use, reference devices need to meet different requirements in
terms of their spectral responsivity, mechanical construction, optical properties, dimensions and
electrical circuit. The spectral responsivity of the reference device, for example, is determined
by the transmission of any protective window in front of the device and the spectral responsivity
of the device itself. Therefore, the overall spectral responsivity can be adapted by using suitable
filters as or in addition to the protective window.
Reference devices should be made using a PV technology that is known to be stable with time.
In particular, the calibration value should not change after the reference device has been
exposed to solar irradiation, device temperatures different from its calibration temperature
and/or extended storage in the dark. The photovoltaic characteristics of a reference device shall
be stable according to the requirements in Clause 11.
The reference device shall be constructed such that the photovoltaic performance parameters,
in particular short-circuit current and maximum power, can be measured. The only exception
are devices with a built-in shunt resistor, see 4.4.
4.2 Additional requirements for single reference cell in a multi-cell package
The dotted line in Figure 2 indicates the minimum acceptable size of a multi-cell package. For
other cell arrangements, such as half-cut cells, an analogous configuration applies.
Figure 2 – Single reference cell in a multi-cell package
4.3 Additional requirements for reference modules
Additional requirements apply to reference modules.
a) Bypass diodes:
• general reference modules, which are used to measure a range of module types and
geometries, should not contain bypass diodes. The presence or absence of bypass
diodes shall be noted and considered in conjunction with the measurement conditions,
in particular spatial non-uniformity of the irradiance on the module during measurement;
• for reference modules, which are intended to be matched to the module under test, the
number, type and connection of bypass diodes (if present) shall match those in the
module under test.
b) If they are made from discrete cells, these should be matched as follows depending on the
intended use of the reference module:
• if only the short-circuit current of the reference module will be used, the short-circuit
current of the individual cells should be matched to within ±1 %;
• if other parameters (such as maximum power) are used additionally or exclusively, both
the short-circuit current and the fill factor of the individual cells should be matched to
within ±1 %.
The matching of the individual cells is the responsibility of the manufacturer of the reference
module, bearing in mind that matching can also be influenced by encapsulation or lamination.
The cell matching need not be checked by the calibration laboratory. However, if I-V curves of
the reference module indicate inconsistent response (i.e. obvious steps are noted in the I-V
curve), this should be discussed between calibration laboratory and the client supplying the
module before proceeding with calibration.
4.4 Requirements for built-in shunt resistors
The built-in shunt resistor (see 3.9) should be chosen such as to ensure that the reference
device operates sufficiently near to short-circuit condition, meeting the requirement in
Formula (1):
0,2×V
OC
R <
(1)
CAL
I
SC
where
R is the built-in shunt resistor;
CAL
I is the short-circuit current of the reference device at desired reference condition;
SC
V is the open circuit voltage of the reference device at desired reference condition.
OC
The long-term stability of the built-in shunt resistor shall also meet the stability requirements of
the reference device. Calibration values of such reference devices shall be measured as the
voltage drop across the built-in shunt resistor and stated with the dimension [V]. The
temperature coefficient of the built-in shunt resistor is part of the temperature coefficient of the
calibration value of the reference device. As the uncertainty in the calibration can be strongly
dependent on the built-in shunt resistor stability and temperature coefficient, respective values
should be provided with the reference cell data sheet.
It is recommended that the shunt resistor be a removable 4-wire resistor, to allow for standard
(current-based) measurements of spectral responsivity and periodic checking of the reference
device stability by measuring an I-V curve in accordance with IEC 60904-1. However, the
reproducibility of the electrical connection shall be maintained.
– 10 – IEC 60904-2:2023 © IEC 2023
Formula (1) means that the measured output voltage of a shunted reference cell should be less
than 20 % of its open circuit voltage. For typical crystalline silicon this equates to about 120 mV
output.
5 Temperature measurement
Means shall be provided for determining the reference cell temperature or, for reference
modules, the equivalent cell temperature (ECT), according to IEC 60904-5. Temperature
sensors and instrumentation shall have instrumental measurement uncertainty of 1 °C or less.
The required uncertainty for temperature measurements for the cell junction shall be less than
2,0 °C for all reference devices.
6 Electrical connections
The electrical connections to reference cells without built-in shunt resistor shall consist of a
four-wire contact system (Kelvin probe). Measurement errors due to voltage drops along the
cell’s contact bars and the package wiring shall be avoided.
The electrical connections to the reference module shall be designed to meet the requirements
of IEC 60904-1.
7 Calibration
7.1 General requirements
Each calibration of a reference device shall be made with a calibration procedure that is
traceable according to IEC 60904-4. Any measurement instrument used in the calibration
procedure shall be an instrument with an unbroken traceability chain.
The laboratory performing the calibration of the reference device shall maintain a documented
uncertainty analysis as well as documented repeatability and results from interlaboratory
comparisons.
7.2 Calibration value(s)
Each reference device shall be calibrated in terms of its calibration value(s) at the desired
reference conditions. Calibration values shall be reported together with the three main
parameters of total irradiance, device junction temperature and spectral irradiance. The most
common calibration conditions are standard test conditions (STC). A calibration at STC shall
−2
, a device junction temperature of 25 °C and the
refer to a total irradiance of 1 000 W m
reference spectral irradiance distribution as defined in IEC 60904-3. Sometimes calibration is
required at other conditions. A reference device can have multiple calibration values for different
desired reference conditions. In particular, IEC 61853-1 [2] requires the use of a reference
device at a range of irradiances and temperatures and therefore the calibration at the respective
conditions.
Methods for calibrating primary reference devices are included in IEC 60904-4. A procedure of
calibrating secondary reference devices is described in Clause 13. The calibration of working
reference devices is treated in Clause 14.
___________
Numbers in square brackets refer to the Bibliography.
7.3 Spectral responsivity
In general, the spectral responsivity at short-circuit current conditions of each reference device
shall be measured in accordance with IEC 60904-8. For exceptions related to working
references, see Clause 14.
7.4 Temperature coefficients
The determination of the temperature coefficient(s) of each reference device in accordance with
IEC 60891 is in general optional but depending on usage might be mandatory, and in any case
is strongly recommended. If the temperature coefficient(s) are determined, also their linear
dependence in accordance with IEC 60904-10 shall be reported. For exceptions related to
working references, see Clause 14.
7.5 Linearity
The determination of linearity in accordance with IEC 60904-10 is in general optional but
depending on usage might be mandatory, and in any case is strongly recommended. For
exceptions related to working references, see Clause 14.
8 Documentation and report
8.1 General
The information given in 8.2 and 8.3 shall be recorded for each reference device.
8.2 Device documentation
The data sheet shall be compiled by the manufacturer of the reference device and contain the
following information:
a) unique identification of the device;
b) cell manufacturer and device manufacturer;
c) material type;
d) type of package;
e) type and dimension of cell(s);
f) circuit diagram, in particular of any connectors;
g) type of temperature sensor (where applicable) and its uncertainty;
h) shunt resistor type, nominal resistance and temperature coefficient (where applicable).
For reference modules, the following information shall be recorded in addition:
i) manufacturer of module;
j) model designation;
k) serial number;
l) cell technology;
m) construction and dimensions of module;
n) electrical circuit layout;
o) presence or absence of bypass diodes and if present their number and type.
– 12 – IEC 60904-2:2023 © IEC 2023
8.3 Calibration report
Each time a reference device is calibrated, the calibration report shall contain the following
information:
a) unique identification of the device;
b) indication that the device has a built-in shunt resistor (where applicable);
c) type (primary reference cell; secondary reference device, working reference device);
d) calibration organization;
e) site and date of calibration;
f) method of calibration (refer to standard);
g) identification of the reference device used for the calibration and its traceability according
to IEC 60904-4;
h) simulator type and classification (where applicable);
i) calibration value(s) and corresponding reference conditions (total irradiance, device junction
temperature, spectral irradiance); in case of calibration via current-voltage characteristics
both short-circuit current and maximum power shall be reported; the open-circuit voltage
should also be reported;
j) spectral responsivity (where applicable);
k) temperature coefficient of calibration value(s) as well as linear dependence (where
applicable);
l) linearity (where applicable);
m) uncertainties for items i), j), k) and l);
n) either the spectral mismatch correction value used in the measurement or an estimate of
the uncertainty introduced by using an equivalent device;
o) statement that measurements originate from an equivalent device and an identification of
which measurements these are (where applicable);
p) unique identification of the equivalent device(s) (where applicable).
For reference cells without fixed electrical connection to the cell, the following information shall
be provided:
q) illustration of type, shape and location of electrical contacts during calibration.
9 Marking
The reference device shall carry a clear, indelible serial or identification number for cross-
reference to its data sheet.
10 Packaging
10.1 Recommended packaging for use in natural sunlight
The reference device used for measurement in natural sunlight should respond to variations in
the geometrical distribution of the incident radiation in the same way as the device under test
(cells, sub-assemblies of cells, modules). As encapsulants and back sheets respond to the
diffuse component of natural sunlight, it is recommended that reference cells used for
measuring modules be enclosed in a multi-cell package (see Figure 2), simulating the
neighbouring optical parameters of a module.
In this case, the frame, the encapsulation system, the shape, and the size and spacing of the
cells surrounding the reference cell shall be the same as in the module to be tested. The
surrounding cells may be real or dummies that have the same optical properties. The dotted
line in Figure 2 indicates the minimum acceptable size of the multi-cell package for outdoor
testing.
10.2 Recommended packaging for use under solar simulators
In some solar simulators which allow multiple reflections of light to and from the device under
test, the irradiance in the test plane can change depending on whether or not the device under
test is present. Therefore, in order to measure accurately the irradiance that will be present
when the device under test is in place, the reference devices used in such solar simulators
should be packaged in the same way as the device under test, so that the change in irradiance
due to multiple reflections is the same for both the reference device and the device under test.
Reference cells used for measurements in solar simulators designed to minimize any error from
multi-reflected light may be packaged singly or, if not intended for day-to-day use, mounted in
the unpackaged state on a temperature-controlled block.
Alternatively, the requirements given for reference cells for use in natural sunlight may be
followed.
10.3 Single cell package
If a single cell package is used, the following recommendations are made.
a) The field of view should be at least 160°. In case of a protective window the optical
properties of the latter have to be considered in determining the effective field of view of the
photovoltaic cell. The field of view is particularly important for measurements under natural
sunlight, whereas for usage on solar simulators with a limited range of angles of incidence,
it is less critical.
b) All surfaces in the package within the cell’s field of view should be non-reflective, with a
spectral absorptance of at least 0,95 in the cell’s wavelength responsivity band.
c) The material used for bonding the cell to the holder should be resistant to degradation,
either electrically or optically. Its physical characteristics should remain stable over the
entire period of intended use.
d) The use of a protective window is recommended. If encapsulated, the space between the
window and the cell should be filled with a stable encapsulant. Both the protective window
and the encapsulant should be transparent over the wavelength range in which the PV
reference device has a non-zero spectral responsivity. The refractive index of the
encapsulant should be similar (within 10 %) to that of the window to minimize errors due to
the internal reflection of light. The transparency, homogeneity and adhesion of the
encapsulant should not be adversely affected by ultra-violet light and operational
temperatures.
e) The protective window may embody a filter to match the spectral responsivity of the
reference cell to that of the device under test, provided that the other recommendations
of d) are met.
Figure 1 shows an example of a suitable single cell package. Other suitable single cell
packages can be found in JIS C8910 [3] or the World Photovoltaic Scale [4].
11 Care of reference devices
It is recommended that reference devices be recalibrated on an annual basis.
The window of a packaged reference device shall be kept clean and scratch-free.
Uncovered reference cells shall be preserved against damage, contamination and degradation.
A reference device exhibiting any defect which might impair its function shall not be used.
– 14 – IEC 60904-2:2023 © IEC 2023
The calibration value of a reference device might change systematically as a function of time
for successive calibrations. If the calibration value of a reference device has changed by more
than 1 % with respect to its previous calibration or by more than 5 % of its initial calibration, it
shall not be used as a reference device.
12 Usage of reference devices
Reference devices shall only be used at irradiances (±10 %) and temperatures (±5 °C) at which
they were calibrated. For the ranges given, use of a simple correction according to established
procedures provided in IEC 60891 with generic correction coefficients is acceptable, as long as
the additional uncertainties introduced are taken into account.
The usage of reference devices outside the ranges given above requires the following in
addition to the single calibration at one reference condition (normally STC):
a) a separate calibration for each desired reference condition it is to be used at; or
b) if to be used over a wider temperature range: a determination of the relevant temperature
coefficient(s) according to IEC 60891 (and their linear dependence according to
IEC 60904-10) and appropriate corrections for differences between the temperatures during
usage and the calibration temperature; and/or
c) if to be used over a wider irradiance range: a determination of the linearity (output versus
irradiance) over the relevant irradiance range according to IEC 60904-10 and appropriate
corrections for differences between the irradiance during usage and the calibration
irradiance.
The reference device can be used in the ranges of conditions mentioned above around the
additional reference conditions with a). Alternatively, it can be used with the calibration value
of the original reference condition over a wider temperature range with b) or a wider irradiance
range with c). If a usage over wider temperature and irradiance ranges is desired, b) and c) are
both required.
13 Calibration of secondary reference devices against a primary reference cell
13.1 General
This Clause 13 describes a procedure for calibrating a secondary reference device in natural
or simulated sunlight against a primary reference cell whose calibration is traceable to SI units
according to IEC 60904-4. The procedure described is an example and other calibration
procedures are acceptable as long as they meet the requirements of 7.1. In any case, the
spectral mismatch between the primary reference cell and that of the secondary reference
device under the irradiance used for the calibration shall be determined according to
IEC 60904‑7.
The primary reference cell is calibrated such that its output (short-circuit current or voltage
across a built-in shunt resistor in case of shunted cell) can be used to determine the irradiance
of the natural or simulated sunlight. The calibration value(s) of the secondary reference device
can be determined by measuring:
a) its output (short-circuit current or voltage across a built-in shunt resistor in case of a shunted
device). This is the most common calibration if the secondary reference device is a cell;
b) its current-voltage characteristics according to IEC 60904-1. This permits the calibration of
the maximum power and of the short-circuit current. This is the most common calibration if
the secondary reference device is a module.
For secondary reference devices with built-in shunt resistor only a) is applicable, as b) is not
possible. For secondary reference devices without built-in shunt resistor, the choice of
calibration depends on the intended use. For guidance on the use of short-circuit current or
maximum power of a reference device refer to IEC TR 60904-14 [5].
The procedure can be applied using both natural and simulated sunlight according to the
requirements in IEC 60904-1 with the restrictions given in 13.2 and 13.3.
13.2 Natural sunlight
Calibration in natural sunlight shall be carried out under the following conditions:
a) clear, sunny weather, with the diffuse irradiance not greater than 20 % of the global
irradiance. For determining the contribution of diffuse irradiance, see IEC 60904-4;
b) no observable cloud formations within 30° of the sun;
−2
c) total irradiance (sun + sky + ground reflection) not less than 80
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