Photovoltaic devices - Part 4: Reference solar devices - Procedures for establishing calibration traceability

IEC 60904-4:2009 sets the requirements for calibration procedures intended to establish the traceability of photovoltaic reference solar devices to SI units as required by IEC 60904-2. Applies to photovoltaic (PV) reference solar 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 solar device is required in the application of IEC 60904-1 and IEC 60904-3.

Photovoltaische Einrichtungen - Teil 4: Referenz-Solarelemente - Verfahren zur Feststellung der Rückverfolgbarkeit der Kalibrierung

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

La CEI 60904-4:2009 fixe les exigences relatives aux procédures d'étalonnage, dans le but d'établir la traçabilité des dispositifs solaires photovoltaïques de référence en unités SI, comme cela est stipulé par la CEI 60904-2. La présente norme s'applique aux dispositifs solaires photovoltaïques (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 solaire PV de référence est requise lors de l'application des CEI 60904-1 et CEI 60904-3.

Fotonapetostne naprave - 4. del: Postopki za vzpostavljanje sledljivosti kalibracije referenčnih sončnih naprav (IEC 60904-4:2009)

Ta del IEC 60904 postavlja zahteve za kalibracijske postopke, ki so namenjeni vzpostavljanju sledljivosti fotonapetostnih referenčnih sončnih naprav v enote SI, kot zahteva IEC 60904-2. Ta standard velja za fotonapetostne (PV) referenčne sončne naprave, ki se uporabljajo za merjenje obsevanja z naravno ali simulirano sončno svetlobo za količinsko ovrednotenje zmogljivosti fotonapetostnih naprav. Uporaba fotonapetostne referenčne sončne naprave se zahteva pri uporabi IEC 60904-1 in IEC 60904-3. Ta standard je napisan z upoštevanjem enostičnih fotonapetostnih referenčnih sončnih naprav, zlasti kristalnega silikona. Vendar je glavni del standarda dovolj splošen, da vključuje druge tehnologije. Metode, opisane v Dodatku A, so omejene na enostične tehnologije.

General Information

Status
Published
Publication Date
29-Nov-2009
Drafting Committee
Parallel Committee
Current Stage
6060 - Document made available
Completion Date
30-Nov-2009

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SLOVENSKI STANDARD
SIST EN 60904-4:2010
01-februar-2010

)RWRQDSHWRVWQHQDSUDYHGHO3RVWRSNL]DY]SRVWDYOMDQMHVOHGOMLYRVWLNDOLEUDFLMH

UHIHUHQþQLKVRQþQLKQDSUDY ,(&

Photovoltaic devices -- Part 4: Procedure for establishing the traceability of the

calibration of reference solar devices
Photovoltaische Einrichtungen - Teil 4: Referenz-Solarelemente - Verfahren zur
Feststellung der Rückverfolgbarkeit der Kalibrierung

Dispositifs photovoltaïques -- Partie 4: Procédures pour établir la traçabilité de

l'étalonnage des dispositifs solaires de référence
Ta slovenski standard je istoveten z: EN 60904-4:2009
ICS:
27.160 6RQþQDHQHUJLMD Solar energy engineering
SIST EN 60904-4:2010 en,fr

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST EN 60904-4:2010
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SIST EN 60904-4:2010
EUROPEAN STANDARD
EN 60904-4
NORME EUROPÉENNE
November 2009
EUROPÄISCHE NORM
ICS 27.160
English version
Photovoltaic devices -
Part 4: Reference solar devices -
Procedures for establishing calibration traceability
(IEC 60904-4:2009)
Dispositifs photovoltaïques - Photovoltaische Einrichtungen -
Partie 4: Dispositifs solaires de référence - Teil 4: Referenz-Solarelemente -
Procédures pour établir Verfahren zur Feststellung
la traçabilité de l'étalonnage der Rückverfolgbarkeit der Kalibrierung
(CEI 60904-4:2009) (IEC 60904-4:2009)

This European Standard was approved by CENELEC on 2009-09-01. CENELEC members are bound to comply

with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard

the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on

application to the Central Secretariat or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other

language made by translation under the responsibility of a CENELEC member into its own language and notified

to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Cyprus, the

Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,

Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,

Sweden, Switzerland and the United Kingdom.
CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
Central Secretariat: Avenue Marnix 17, B - 1000 Brussels

© 2009 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 60904-4:2009 E
---------------------- Page: 3 ----------------------
SIST EN 60904-4:2010
EN 60904-4:2009 - 2 -
Foreword

The text of document 82/533/CDV, future edition 1 of IEC 60904-4, prepared by IEC TC 82, Solar

photovoltaic energy systems, was submitted to the IEC-CENELEC parallel vote and was approved by

CENELEC as EN 60904-4 on 2009-09-01.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2010-06-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2012-09-01
Annex ZA has been added by CENELEC.
__________
Endorsement notice

The text of the International Standard IEC 60904-4:2009 was approved by CENELEC as a European

Standard without any modification.

In the official version, for Bibliography, the following notes have to be added for the standards indicated:

IEC 60891 NOTE Harmonized as EN 60891:1994 (not modified).
IEC 60904-1 NOTE Harmonized as EN 60904-1:2006 (not modified).
IEC 60904-3 NOTE Harmonized as EN 60904-3:2008 (not modified).
IEC 60904-7 NOTE Harmonized as EN 60904-7:2009 (not modified).
IEC 60904-8 NOTE Harmonized as EN 60904-8:1998 (not modified).
IEC 60904-9 NOTE Harmonized as EN 60904-9:2007 (not modified).
IEC 61836 NOTE Harmonized as CLC/TS 61836:2009 (not modified).
__________
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SIST EN 60904-4:2010
- 3 - EN 60904-4:2009
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

The following referenced documents are indispensable for the application of this document. For dated

references, only the edition cited applies. For undated references, the latest edition of the referenced

document (including any amendments) applies.

NOTE When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD

applies.
Publication Year Title EN/HD Year
1) 2)
IEC 60904-2 - Photovoltaic devices - EN 60904-2 2007
Part 2: Requirements for reference solar
devices
1) 2)
ISO/IEC 17025 - General requirements for the competence of EN ISO/IEC 17025 2005
testing and calibration laboratories
ISO/IEC Guide 98-3 2008 Uncertainty of measurement - - -
Part 3: Guide to the expression of uncertainty
in measurement (GUM:1995)
ISO 9059 - Solar energy - Calibration of field - -
pyrheliometers by comparison to a reference
pyrheliometer
ISO 9846 - Solar energy - Calibration of a pyranometer - -
using a pyrheliometer
Undated reference.
Valid edition at date of issue.
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SIST EN 60904-4:2010
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SIST EN 60904-4:2010
IEC 60904-4
Edition 1.0 2009-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Photovoltaic devices –
Part 4: Reference solar devices – Procedures for establishing calibration
traceability
Dispositifs photovoltaïques –

Partie 4: Dispositifs solaires de référence – Procédures pour établir la traçabilité

de l'étalonnage
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX
ICS 27.160 ISBN 2-8318-1044-6
® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 7 ----------------------
SIST EN 60904-4:2010
– 2 – 60904-4 © IEC:2009
CONTENTS

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

1 Scope and object..............................................................................................................5

2 Normative references .......................................................................................................5

3 Terms and definitions .......................................................................................................5

4 Requirements for traceable calibration procedures of PV reference solar devices ............7

5 Uncertainty analysis .........................................................................................................8

6 Calibration report..............................................................................................................8

7 Marking ............................................................................................................................8

Annex A (informative) Examples of validated calibration procedures....................................10

Bibliography..........................................................................................................................24

Figure 1 – Schematic of most common reference instruments and transfer methods

used in the traceability chains for solar irradiance detectors. ..................................................7

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

superimposing chopped monochromatic radiation DE(l) and DC bias radiation E ................18

Figure A.2 – Optical arrangement of differential spectral responsivity calibration. .................19

Figure A.3 – Schematic apparatus of the solar simulator method. .........................................21

Table 1 – Examples of reference instruments, used in a traceability chain of time and

solar irradiance.......................................................................................................................7

Table A.1 – Typical uncertainty components (k = 2) of global sunlight method ......................15

Table A.2 – Typical uncertainty components (k = 2) of a differential spectral

responsivity calibration .........................................................................................................18

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

calibration.............................................................................................................................21

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

calibration when WRR traceable cavity radiometer is used ...................................................21

Table A.5 – Typical uncertainty components (k = 2) of a direct sunlight method ....................23

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SIST EN 60904-4:2010
60904-4 © IEC:2009 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
PHOTOVOLTAIC DEVICES –
Part 4: Reference solar 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

this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,

Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC

Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested

in the subject dealt with may participate in this preparatory work. International, governmental and non-

governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely

with the International Organization for Standardization (ISO) in accordance with conditions determined by

agreement between the two organizations.

2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international

consensus of opinion on the relevant subjects since each technical committee has representation from all

interested IEC National Committees.

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

Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC

Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any

misinterpretation by any end user.

4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications

transparently to the maximum extent possible in their national and regional publications. Any divergence

between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in

the latter.

5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any

equipment declared to be in conformity with an IEC Publication.

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

7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and

members of its technical committees and IEC National Committees for any personal injury, property damage or

other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and

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

Publications.

8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is

indispensable for the correct application of this publication.

9) 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.
The text of this standard is based on the following documents:
CDV Report on voting
82/533/CDV 82/561/RVC

Full information on the voting for the approval of this standard can be found in the report on

voting indicated in the above table.

This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

A list of all parts of IEC 60904 series, under the general title Photovoltaic devices, can be

found on the IEC website.
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SIST EN 60904-4:2010
– 4 – 60904-4 © IEC:2009

The committee has decided that the contents of this publication will remain unchanged until

the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in

the data related to the specific publication. At this date, the publication will be

• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
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SIST EN 60904-4:2010
60904-4 © IEC:2009 – 5 –
PHOTOVOLTAIC DEVICES –
Part 4: Reference solar devices –
Procedures for establishing calibration traceability
1 Scope and object

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

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

This standard applies to photovoltaic (PV) reference solar 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 solar device is required in the application of

IEC 60904-1 and IEC 60904-3.

This standard has been written with single junction PV reference solar devices in mind, in

particular crystalline Silicon. However, the main part of the standard is sufficiently general to

include other technologies. The methods described in Annex A, however, are limited to single

junction technologies.
2 Normative references

The following referenced documents are indispensable for the application 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 60904-2, Photovoltaic devices – Part 2: Requirements for reference solar devices

ISO/IEC 17025, General requirements for the competence of testing and calibration

laboratories

ISO 9059, Solar energy – Calibration of field pyrheliometers by comparison to a reference

pyrheliometer
ISO 9846, Solar energy – Calibration of a pyranometer using a pyrheliometer

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 following terms and definitions apply.

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

Table 1 lists and compares them with those in use for time. Figure 1 shows schematically the most common

traceability chains, based on the methods described in Annex A.
3.1
primary standard

a device, which implements physically one of the SI units or directly related quantities. They

are usually maintained by national metrology institutes (NMIs) or similar organisations

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, precision

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SIST EN 60904-4:2010
– 6 – 60904-4 © IEC:2009

and repeatability of measurement of the quantity it represents are guaranteed to the maximum

extent possible by current technology.

NOTE 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

a 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. It does not necessarily

use the same technical principles as the primary standard, but strives to achieve similar long-

term stability, precision and repeatability.

NOTE 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.

3.3
primary reference

the reference instrument which a laboratory uses to calibrate secondary references. It is

compared at periodic intervals to a secondary standard. Often primary references can be

realised at much lower costs than secondary standards.

NOTE Typically a solar cell is used as a reference solar device for the measurement of natural or simulated solar

irradiance.
3.4
secondary reference

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

references, calibrated at periodic intervals to a primary reference.

NOTE The most common secondary references for the measurement of natural or simulated solar irradiance are

solar cells and solar modules.
3.5
traceability

the requirement for any PV reference solar device, to tie its calibration value to SI units in an

unbroken and documented chain of calibration transfers including stated uncertainties.

NOTE The WRR has been compared twice to the SI radiometric scale and shown to be within their mutual

uncertainty levels. Therefore traceability to WRR automatically provides traceability to SI units. However, the

uncertainty of the ratio WRR/SI units needs to be taken into account. The World Radiation Center (WRC)

recommends a rectangular uncertainty distribution with 0,3 % half-width. A third comparison is currently underway

and should be published in the future.
J. Romero, N.P. Fox, C. Fröhlich metrologia 28 (1991) 125-8
J. Romero, N.P. Fox, C. Fröhlich metrologia 32 (1995/1996) 523-4
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SIST EN 60904-4:2010
60904-4 © IEC:2009 – 7 –
Table 1 – Examples of reference instruments, used in a traceability chain
of time and solar irradiance
Reference instrument Time Solar irradiance

Primary standard Cesium atomic clock at Group of cavity radiometers constituting the World Standard

National Metrology Institute Group (WSG) of the World Radiometric Reference (WRR)

(NMI)
Cryogenic trap detector
Standard lamp

Secondary standard Cesium atomic clock on GPS Commercially available cavity radiometers compared every 5

(Global Positioning System) years at the International Pyrheliometer Comparison (IPC)

satellites
Standard detector calibrated against a trap detector
Spectroradiometer calibrated against a standard lamp

Primary reference GPS receiver, set to show Normal incidence pyrheliometer (NIP) (ISO 9059)

time
Reference solar device (IEC 60904-2 and IEC 60904-4)
Secondary reference Quartz watch Pyranometer (ISO 9846)
Reference solar device (IEC 60904-2)
WSG Trap detector Standard lamp
Primary
standard
IPC
Secondary
Absolute radiometer Spectroradiometer
Standard detector
standard
ISO 9059 IEC 60904-4
Primary
Reference solar device
NIP
reference
IEC 60904-2
ISO 9846
Secondary Reference solar device
Pyranometer
reference
IEC 858/09

NOTE Direct traceability of absolute radiometers to SI radiometric scale may also be available.

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 solar
devices

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

reference measuring solar irradiance (such as cavity radiometer, pyrheliometer and

pyranometer) to a PV reference solar device. The requirements for such procedures are as

follows:
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SIST EN 60904-4:2010
– 8 – 60904-4 © IEC:2009

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 precision, given by a limited number of intermediate transfers.

NOTE 1 Normally the transfer would be from a secondary standard to a PV reference solar cell constituting a

primary reference.

NOTE 2 The transfer from one reference solar device to another is covered by IEC 60904-2.

5 Uncertainty analysis

An uncertainty estimate according to MISC UNCERT – ED. 1.0 (1995-01) 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).

Nevertheless a full uncertainty analysis has to be performed for the implementation of the

calibration method by a particular laboratory.
6 Calibration report

The calibration report shall conform to the requirements of ISO/IEC 17025 and shall normally

include at least the following information:
a) title (e.g. ”Calibration Certificate”);

b) name and address of laboratory, and location where the tests and/or calibrations were

carried out, if different from the address of the laboratory;

c) unique identification of the report (such as serial number) and of each page, the total

number of pages and the date of issue;
d) name and address of the client placing the order;

e) description and unambiguous identification of the item(s) tested or calibrated;

f) date of receipt of calibration item(s) and date(s) of performance of test or calibration, as

appropriate;

g) calibration results including the temperature of the device at which the calibration was

performed;

h) reference to sampling procedures used by the laboratory where these are relevant to the

validity or application of the results;

i) the name(s), title(s) and signature(s) or equivalent identification of person(s) authorising

the report;

j) where relevant, a statement to the effect that the results relate only to the items tested or

calibrated.
7 Marking

The calibrated reference solar device shall be marked with a serial number or reference

number and the following information attached or provided on an accompanying certificate:

a) date of (actual or present) calibration;
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SIST EN 60904-4:2010
60904-4 © IEC:2009 – 9 –
b) calibration value and its temperature coefficient (if applicable).
---------------------- Page: 15 ----------------------
SIST EN 60904-4:2010
– 10 – 60904-4 © IEC:2009
Annex A
(informative)
Examples of validated calibration procedures
A.1 General

This annex describes examples of calibration procedures for PV reference solar cells as

primary reference devices, together with their stated uncertainties. These procedures serve to

establish the traceability of reference solar devices to SI units as required by IEC 60904-2.

Primary reference devices calibrated in accordance with these procedures serve to establish

the traceability of further PV reference solar devices.

As already mentioned in Clause 1, the methods in this annex are limited to PV single junction

technology. Moreover, they have currently only been validated for crystalline Silicon

technology, although they should be applicable to other technologies.

The methods have been implemented in various laboratories around the world and validated

in international intercomparisons, most notably the World Photovoltaic Scale (WPVS).

However, the description in this standard is more generalised. For details of the various

implementations, the references in peer-reviewed publications are given at the end of each

procedure.

The uncertainty estimates are based on U (coverage factor k = 2) for all single components.

The combined expanded uncertainty is calculated as the square root of the sum of squares of

all components. The uncertainties provided are simplified versions (restricted to the main

components) as provided by the laboratories having implemented the procedure. These

uncertainty calculations serve as guidelines and will have to be adapted to the particular

implementation of each procedure in a given laboratory. The uncertainties achieved by any

implementation of these methods might be considerably different. Uncertainties quoted have

to be based on an explicit analysis and cannot be taken by reference to the uncertainty

estimates in this standard.
A.1.1 Examples of validated methods
A. 2 Global sunlight method
A. 3 Differential spectral responsivity calibration
A. 4 Solar simulator method
A. 5 Direct sunlight method
A.1.2 List of common symbols
I short circuit current of reference cell
T temperature of reference cell
M irradiance correction factor (see below)
M temperature correction factor (see below)

T temperature coefficient α of the short-circuit current (IEC 60891) normalized to

coef
the short-circuit current at 25 °C and expressed in 1/ °C
MMF mismatch factor (see below)
λ wavelength
S(λ) spectral response of reference cell
s(λ) differential spectral responsivity of reference cell
E (λ) spectral irradiance distribution of natural or simulated sunlight

(λ) standard or reference spectral irradiance distribution according to IEC 60904-3

G direct irradiance
dir
G diffuse in-plane irradiance
dif
G total in-plane irradiance
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SIST EN 60904-4:2010
60904-4 © IEC:2009 – 11 –
E irradiance at STC (= 1 000 Wm )
STC
CV calibration value, i.e. I at STC
AM air mass
STC standard test conditions (1 000 W/m , 25 °C and E (λ))
P local air pressure
P 101 300 Pa
θ solar elevation angle
A.1.3 Common equations

The methods described in Clauses A.2, A.4 and A.5 have some common calculations, which

are detailed in this subclause. Details of the various implementations are then described in

each subclause.

The I is normally not measured at exactly 1 000 Wm , but at an irradiance level close to it.

Under the assumption that the I of the reference cell varies linearly with irradiance, the

following correction is made:
1000
−2 m
I (1 000 Wm ) = I M = I (A.1)
SC SC G SC

STC mandate a device temperature of 25 °C, but measurements will not always be taken at

this temperature. The deviations in temperature should be accounted for in the uncertainty

budget. It is also possible to correct I from the measurement temperature T to 25 °C by

SC j
multiplying with the temperature correction factor M defined by
I (T )
SC j
I (25 °C) = I (T )M = (A.2)
SC SC j T
1− T()25 °C − T
coef j

The correction for the difference in spectral sensitivity of the reference cell to be calibrated

and the device used to measure the irradiance can be described as a MMF
4000 nm 4000 nm
S(λ) ⋅ E (λ) ⋅ dλ E (λ) ⋅ dλ
s m
∫ ∫
300 nm 300 nm
MMF = (A.3)
4000 nm 4000 nm
S(λ) ⋅ E (λ) ⋅ dλ E (λ) ⋅ dλ
m s
∫ ∫
300 nm 300 nm

NOTE The integration range is taken based on the definition of E (λ). If the measurement range, in particular that

of E (λ), does not cover this entire range, suitable approximation, extrapolation or modelling can be used, but

needs to be accounted for in the uncertainty calculation.
The calibration value CV of the reference cell is then calculated as
CV = I M M MMF (A.4)
SC G T
A.1.4 References documents

– C. R. Osterwald et al. “The results of the PEP’93 intercomparison of reference cell

calibrations and newer technology performance measurements: Final Report”, NREL/TP-

520-23477 (1998) 209 pages.

– C. R. Osterwald et al. “The world photovoltaic scale: an international reference cell

calibration program”, Progress in Photovoltaics 7 (1999) 287-297.

– K. Emery “The results of the First World Photovoltaic Scale Recalibration”, NREL/TP-520-

27942 (2000) 14 pages.
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SIST EN 60904-4:2010
– 12 – 60904-4 © IEC:2009

– Winter el al.: “The results of the Second World Photovoltaic Scale Recalibration”, Proc. of

the 31 IEEE PVSC 3-7 January 2005, Orlando, Florida, USA, pp. 1011-1014.
A.2 Global sunlight method
The establishment of traceability is based on the c
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