ISO 9059:2025

Solar energy — Calibration of pyrheliometers by comparison to a reference pyrheliometer

This document specifies methods for calibration of pyrheliometers using reference pyrheliometers and specifies the calibration procedures for the transfer of the calibration. This document is applicable for use by calibration service providers and test laboratories to enable a uniform quality of accurate calibration sensitivities to be achieved.

Énergie solaire — Étalonnage des pyrhéliomètres par comparaison à un pyrhéliomètre de référence

General Information

• Status: Published
• Publication Date: 06-Aug-2025
• ICS: 27.160 - Solar energy engineering
• Technical Committee: ISO/TC 180/SC 1 - Climate - Measurement and data
• Drafting Committee: ISO/TC 180/SC 1 - Climate - Measurement and data
• Current Stage: 6060 - International Standard published
• Start Date: 07-Aug-2025
• Due Date: 17-Aug-2025
• Completion Date: 07-Aug-2025

Relations

• Revises: ISO 9059:1990 - Solar energy — Calibration of field pyrheliometers by comparison to a reference pyrheliometer
• Effective Date: 06-Jun-2022

Standards Content (Sample)

International
Standard
ISO 9059
Second edition
Solar energy — Calibration of
2025-08
pyrheliometers by comparison to a
reference pyrheliometer
Énergie solaire — Étalonnage des pyrhéliomètres par
comparaison à un pyrhéliomètre de référence
Reference number
© ISO 2025
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Pyrheliometer calibration . 5
4.1 Reference pyrheliometers .5
4.2 Pyrheliometer sensitivity, measurement equation, measurand .5
4.3 Comparison of outdoor and indoor calibration .6
4.4 Method validation .7
4.5 Calibration uncertainty .7
4.5.1 General .7
4.5.2 Calibration uncertainty in indoor calibration .7
4.5.3 Calibration uncertainty in outdoor calibration .7
5 Outdoor calibration . 8
5.1 General .8
5.2 Radiation source .8
5.3 Meteorological variables .8
5.3.1 Wind speed and direction .8
5.3.2 Ambient air temperature .9
5.3.3 Sky conditions .9
5.4 Measuring equipment .9
5.4.1 Reference pyrheliometer.9
5.4.2 Solar tracker .9
5.4.3 Data acquisition systems and recording .11
5.5 Outdoor calibration procedure . 12
5.5.1 General . 12
5.5.2 Preparation . 12
5.5.3 Installation and adjustment . 12
5.6 Data sampling . 12
5.7 Mathematical treatment . 13
5.7.1 Initial data rejection and filtering . 13
5.7.2 Calculation of individual sensitivity values . 13
5.7.3 Computation of the sensitivity of the test pyrheliometer .14
5.7.4 Uncertainty evaluation . 15
6 Indoor calibration .15
6.1 General . 15
6.2 Radiation source . 15
6.3 Meteorological variables . 15
6.4 Measuring equipment . 15
6.4.1 Reference pyrheliometer. 15
6.4.2 Calibration system . 15
6.4.3 Data acquisition systems and recording .16
6.5 Indoor calibration procedure .16
6.5.1 General .16
6.5.2 Installation and adjustment .16
6.6 Data sampling .16
6.7 Mathematical treatment .17
6.7.1 Calculation of sensitivity.17
6.7.2 Uncertainty evaluation .18
7 Calibration certificate .18
Annex A (informative) Effects of circumsolar radiation . 19

iii
Annex B (informative) Introduction of a new Pyrheliometer sensitivity .22
Annex C (informative) Uncertainty evaluation for pyrheliometer calibration .24
Annex D (informative) Example of correction terms for an improved sensitivity value .26
Annex E (informative) Determination of number of days for calibration .28
Bibliography .30

iv
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 180, Solar energy, Sub-Committee SC 1, Climate
– Measurement and data.
This second edition cancels and replaces the first edition (ISO 9059:1990) which has been technically
revised.
The main changes are as follows:
— focus on current calibration practices;
— adapted recommendations for mathematical treatment of data;
[2]
— revised terminolog
...

FINAL DRAFT
International
Standard
ISO/FDIS 9059
ISO/TC 180/SC 1
Solar energy — Calibration of
Secretariat: SA
pyrheliometers by comparison to a
Voting begins on:
reference pyrheliometer
2025-05-16
Énergie solaire — Étalonnage des pyrhéliomètres par
Voting terminates on:
comparaison à un pyrhéliomètre de référence
2025-07-11
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
ISO/FDIS 9059:2025(en) © ISO 2025

FINAL DRAFT
ISO/FDIS 9059:2025(en)
International
Standard
ISO/FDIS 9059
ISO/TC 180/SC 1
Solar energy — Calibration of
Secretariat: SA
pyrheliometers by comparison to a
Voting begins on:
reference pyrheliometer
Énergie solaire — Étalonnage des pyrhéliomètres par
Voting terminates on:
comparaison à un pyrhéliomètre de référence
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2025
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ISO/FDIS 9059:2025(en) © ISO 2025

ii
ISO/FDIS 9059:2025(en)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Pyrheliometer calibration . 5
4.1 Reference pyrheliometers .5
4.2 Pyrheliometer sensitivity, measurement equation, measurand .5
4.3 Comparison of outdoor and indoor calibration .6
4.4 Method validation .7
4.5 Calibration uncertainty .7
4.5.1 General .7
4.5.2 Calibration uncertainty in indoor calibration .7
4.5.3 Calibration uncertainty in outdoor calibration .7
5 Outdoor calibration . 8
5.1 General .8
5.2 Radiation source .8
5.3 Meteorological variables .9
5.3.1 Wind speed and direction .9
5.3.2 Ambient air temperature .9
5.3.3 Sky conditions .9
5.4 Measuring equipment .9
5.4.1 Reference pyrheliometer.9
5.4.2 Solar tracker .10
5.4.3 Data acquisition systems and recording .11
5.5 Outdoor calibration procedure . 12
5.5.1 General . 12
5.5.2 Preparation . 12
5.5.3 Installation and adjustment . 12
5.6 Data sampling . 12
5.7 Mathematical treatment . 13
5.7.1 Initial data rejection and filtering . 13
5.7.2 Calculation of individual sensitivity values . 13
5.7.3 Computation of the sensitivity of the test pyrheliometer .14
5.7.4 Uncertainty evaluation . 15
6 Indoor calibration .15
6.1 General . 15
6.2 Radiation source . 15
6.3 Meteorological variables . 15
6.4 Measuring equipment . 15
6.4.1 Reference pyrheliometer. 15
6.4.2 Calibration system . 15
6.4.3 Data acquisition systems and recording .16
6.5 Indoor calibration procedure .16
6.5.1 General .16
6.5.2 Installation and adjustment .16
6.6 Data sampling .16
6.7 Mathematical treatment .17
6.7.1 Calculation of sensitivity.17
6.7.2 Uncertainty evaluation .18
7 Calibration certificate .18
Annex A (informative) Effects of circumsolar radiation . 19

iii
ISO/FDIS 9059:2025(en)
Annex B (informative) Introduction of a new Pyrheliometer sensitivity .22
Annex C (informative) Uncertainty evaluation for pyrheliometer calibration .24
Annex D (informative) Example of correction terms for an improved sensitivity value .26
Annex E (informative) Determination of number of days for calibration .28
Bibliography .30

iv
ISO/FDIS 9059:2025(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that t
...

ISO/FDIS 9059:2025(en)
ISO /TC 180/SC1/WG4SC 1
Secretariat: SA
Date: 2025-05-02-20
Solar energy — Calibration of pyrheliometers by comparison to a
reference pyrheliometer
Énergie solaire — Étalonnage des pyrhéliomètres par comparaison à un pyrhéliomètre de référence
FDIS stage
ISO/DISFDIS 9059:202X(E2025(en)
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying,
or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO
at the address below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
E-mail: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 20242025 – All rights reserved
ii
ISO/FDIS 9059:2025(en)
Contents
Foreword . v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Pyrheliometer calibration . 6
4.1 Reference pyrheliometers . 6
4.2 Pyrheliometer sensitivity, measurement equation, measurand . 6
4.3 Comparison of outdoor and indoor calibration . 7
4.4 Method validation . 8
4.5 Calibration uncertainty . 8
5 Outdoor calibration . 10
5.1 General. 10
5.2 Radiation source . 10
5.3 Meteorological variables . 10
5.4 Measuring equipment . 11
5.5 Outdoor calibration procedure . 16
5.6 Data sampling . 17
5.7 Mathematical treatment . 17
6 Indoor calibration. 20
6.1 General. 20
6.2 Radiation source . 20
6.3 Meteorological variables . 20
6.4 Measuring equipment . 20
6.5 Indoor calibration procedure. 21
6.6 Data sampling . 21
6.7 Mathematical treatment . 22
7 Calibration certificate . 23
Annex A (informative) Effects of circumsolar radiation . 25
Annex B (informative) Introduction of a new Pyrheliometer sensitivity . 30
Annex C (informative) Uncertainty evaluation for pyrheliometer calibration . 32
Annex D (informative) Example of correction terms for an improved sensitivity value . 35
Annex E (informative) Determination of number of days for calibration . 37
Bibliography . 40

Foreword . v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Pyrheliometer calibration . 7
4.1 Reference pyrheliometers . 7
© ISO 2025 – All rights reserved
iii
ISO/DISFDIS 9059:202X(E2025(en)
4.2 Pyrheliometer sensitivity, measurement equation, measurand . 7
4.3 Comparison of outdoor and indoor calibration . 8
4.4 Method validation . 8
4.5 Calibration uncertainty. 8
4.5.1 Calibration uncertainty in indoor calibration . 9
4.5.2 Calibration uncertainty in outdoor calibration . 9
5 Outdoor calibration .10
5.1 Radiation source .10
5.2 Meteorological variables .10
5.2.1 Wind speed and direction .10
5.2.2 Ambient air temperature .10
5.2.3 Sky conditions .10
5.3 Measuring equipment .11
5.3.1 Reference pyrheliometer .11
5.3.2 Solar tracker .11
5.3.3 Data acquisition systems and recording .13
5.4 Outdoor calibration procedure .14
5.4.1 Preparation .14
5.4.2 Installation and adjustment .14
5.5 Data sampling .15
5.6 Mathematical treatment .15
5.6.1 Initial data rejection and filtering .15
5.6.2 Calculation of individual sensitivity values .15
5.6.3 Computation of the sensitivity of the test pyrheliometer .16
5.6.4 Uncertainty evaluation .17
6 Indoor calibration .17
6.1 Radiation source .17
6.2 Meteorological variables .18
6.3 Measuring equipment .18
6.3.1 Reference pyrheliometer .18
6.3.2 Calibration system .18
6.3.3 Data acquisition systems and recording .18
6.4 Indoor calibration procedure .18
6.4.1 Installation and adjustment .19
6.5 Data sampling .19
6.6 Mathematical treatment .19
6.6.1 Calculation of sensitivity .19
6.6.2 Uncertainty evaluation .20
7 Calibration certificate .20
Annex A (informative) Effects of circumsolar radiation .22
A.1 Effects of aerosols .22
A.2 Effects of circumsolar radiation on pyrheliometers .23
Annex B (informative) Introduction of a new Pyrheliometer sensitivity .26
Annex C (informative) Uncertainty evaluation for pyrheliometer calibration .28
Annex D (informative) Example of correction terms for an improved sensitivity value .31
Annex E (informative) Determination of number of days for calibration .33
Bibliography .35

iv © ISO 20242025 – All rights reserved
iv
ISO/FD
...