ISO 9846:2025

Solar energy — Calibration of a pyranometer using a pyrheliometer

This document specifies calibration methods for a pyranometer using a pyrheliometer as a reference instrument. Three methods are specified in this document. a) Alternating sun and shade method. This method uses a shading disc to alternately shade and unshade a pyranometer to compare with the tracking pyrheliometer. The test pyranometer can be horizontal, on a fixed tilt or tracking alongside the pyrheliometer. b) Continuous sun and shade method. In this method, a shaded calibrated reference pyranometer is used in addition to the reference pyrheliometer. The test pyranometer can be horizontal, on a fixed tilt or tracking alongside the reference pyrheliometer, but the reference pyranometer must be mounted in the same plane as the test pyranometer (most often on the horizontal). c) Collimation tube method. In this method, the test pyranometer is mounted on a solar tracker and is equipped with a collimation tube designed to allow the test pyranometer to have the same geometric view as the reference pyrheliometer for a direct comparison of the two instruments. The methods in this document are applicable for calibration of all pyranometers provided that a proper uncertainty evaluation is performed. Unlike spectrally flat pyranometers, non-spectrally flat pyranometers have a sensitivity that strongly depends on the solar spectrum. Therefore, the calibration result can be valid under a more limited range of conditions. The result of a calibration is the instrument sensitivity accompanied by an uncertainty. This document includes suggestions for uncertainty evaluation.

Énergie solaire — Étalonnage d'un pyranomètre utilisant un pyrhéliomètre

General Information

• Status: Published
• Publication Date: 07-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: 08-Aug-2025
• Due Date: 17-Aug-2025
• Completion Date: 08-Aug-2025

Relations

• Revises: ISO 9846:1993 - Solar energy — Calibration of a pyranometer using a pyrheliometer
• Effective Date: 06-Jun-2022

Standards Content (Sample)

International
Standard
ISO 9846
Second edition
Solar energy — Calibration of a
2025-08
pyranometer using a pyrheliometer
Énergie solaire — Étalonnage d'un pyranomètre utilisant un
pyrhéliomètre
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 Selection of methods . 7
5 Alternating sun-and-shade method (shade/unshaded method) . 8
5.1 Principle .8
5.2 Apparatus .9
5.2.1 Pyranometer .9
5.2.2 Pyrheliometer .9
5.2.3 Solar tracker .9
5.2.4 Shade device .10
5.2.5 Data acquisition system .11
5.3 Measurement conditions .11
5.4 Measurement site . 12
5.5 Installation . 12
5.6 Calibration procedure . 13
5.6.1 Preparatory phase . 13
5.6.2 Measurement phase (single series) . 13
5.6.3 Data sampling . 15
5.7 Calculation of sensitivity . 15
5.7.1 Initial data rejection and filtering . 15
5.7.2 Calculation of individual sensitivity values .16
5.7.3 Computation of the sensitivity of the test pyranometer .16
5.7.4 Evaluation of the final results .17
6 Continuous sun-and-shade method (component sum) . 17
6.1 Principle .17
6.2 Apparatus .18
6.2.1 Pyranometers.18
6.2.2 Pyrheliometer .18
6.2.3 Solar tracker .18
6.2.4 Shade device .18
6.2.5 Data acquisition system .18
6.3 Measurement conditions .18
6.4 Measurement site .18
6.5 Installation .19
6.6 Calibration procedure .19
6.6.1 Preparatory phase .19
6.6.2 Measurements .19
6.6.3 Data sampling .19
6.7 Calculation of sensitivity .19
6.7.1 Initial data rejection and filtering .19
6.7.2 Calculation of individual sensitivity values .19
6.7.3 Computation of the sensitivity of the test pyranometer . 20
6.7.4 Evaluation of the final results . 20
7 Collimation tube method .20
7.1 Principle . 20
7.2 Apparatus .21
7.2.1 Pyranometer .21
7.2.2 Pyrheliometer .21
7.2.3 Solar tracker .21

iii
7.2.4 Collimation tube .21
7.2.5 Data acquisition system . 22
7.3 Measurement conditions . 23
7.4 Measurement site . 23
7.5 Installation . 23
7.6 Calibration procedure . 23
7.6.1 Preparatory phase . 23
7.6.2 Measurements . 23
7.6.3 Data sampling . 23
7.7 Calculation of sensitivity . 23
7.7.1 Initial data rejection and filtering . 23
7.7.2 Calculation of individual sensitivity values .24
7.7.3 Computation of the sensitivity of the test pyranometer .24
7.7.4 Evaluation of the final results .24
8 Calibration uncertainty .24
9 Certificate of calibration .25
Annex A (informative) Shade disc devices and solar tracker alignment .27
Annex B (informative) Calculation of the sun incidence angle on an inclined plane .
...

FINAL DRAFT
International
Standard
ISO/FDIS 9846
ISO/TC 180/SC 1
Solar energy — Calibration of a
Secretariat: SA
pyranometer using a pyrheliometer
Voting begins on:
Énergie solaire — Étalonnage d'un pyranomètre utilisant un 2025-05-16
pyrhéliomètre
Voting terminates on:
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 9846:2025(en) © ISO 2025

FINAL DRAFT
ISO/FDIS 9846:2025(en)
International
Standard
ISO/FDIS 9846
ISO/TC 180/SC 1
Solar energy — Calibration of a
Secretariat: SA
pyranometer using a pyrheliometer
Voting begins on:
Énergie solaire — Étalonnage d'un pyranomètre utilisant un
pyrhéliomètre
Voting terminates on:
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 9846:2025(en) © ISO 2025

ii
ISO/FDIS 9846:2025(en)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Selection of methods . 7
5 Alternating sun-and-shade method (shade/unshaded method) . 8
5.1 Principle .8
5.2 Apparatus .9
5.2.1 Pyranometer .9
5.2.2 Pyrheliometer .9
5.2.3 Solar tracker .9
5.2.4 Shade device .10
5.2.5 Data acquisition system .11
5.3 Measurement conditions .11
5.4 Measurement site . 12
5.5 Installation . 12
5.6 Calibration procedure . 13
5.6.1 Preparatory phase . 13
5.6.2 Measurement phase (single series) . 13
5.6.3 Data sampling . 15
5.7 Calculation of sensitivity . 15
5.7.1 Initial data rejection and filtering . 15
5.7.2 Calculation of individual sensitivity values . 15
5.7.3 Computation of the sensitivity of the test pyranometer .16
5.7.4 Evaluation of the final results .16
6 Continuous sun-and-shade method (component sum) . 17
6.1 Principle .17
6.2 Apparatus .18
6.2.1 Pyranometers.18
6.2.2 Pyrheliometer .18
6.2.3 Solar tracker .18
6.2.4 Shade device .18
6.2.5 Data acquisition system .18
6.3 Measurement conditions .18
6.4 Measurement site .18
6.5 Installation .18
6.6 Calibration procedure .18
6.6.1 Preparatory phase .18
6.6.2 Measurements .19
6.6.3 Data sampling .19
6.7 Calculation of sensitivity .19
6.7.1 Initial data rejection and filtering .19
6.7.2 Calculation of individual sensitivity values .19
6.7.3 Computation of the sensitivity of the test pyranometer . 20
6.7.4 Evaluation of the final results . 20
7 Collimation tube method .20
7.1 Principle . 20
7.2 Apparatus . 20
7.2.1 Pyranometer . 20
7.2.2 Pyrheliometer . 20
7.2.3 Solar tracker . 20

iii
ISO/FDIS 9846:2025(en)
7.2.4 Collimation tube . 20
7.2.5 Data acquisition system . 22
7.3 Measurement conditions . 22
7.4 Measurement site . 22
7.5 Installation . 22
7.6 Calibration procedure . 23
7.6.1 Preparatory phase . 23
7.6.2 Measurements . 23
7.6.3 Data sampling . 23
7.7 Calculation of sensitivity .
...

ISO/FDIS 9846
ISO/TC 180/SC 1/WG4
Secretariat: SA
Date: 20242025-05-02-26
Solar energy — Calibration of a pyranometer using a pyrheliometer
Énergie solaire — Étalonnage d'un pyranomètre utilisant un pyrhéliomètre
FDIS stage
ISO/FDIS 9846:2025 (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/FDIS 9846:2025(en)
Contents
Foreword . v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and Definitions . 2
4 Selection of methods . 7
5 Alternating sun-and-shade method (shade/unshade method) . 9
5.1 Principle . 9
5.2 Apparatus . 9
5.2.1 Pyranometer . 9
5.2.2 Pyrheliometer . 9
5.2.3 Solar tracker . 10
5.2.4 Shade device . 10
5.2.5 Data acquisition system . 11
5.3 Measurement conditions . 11
5.4 Measurement site . 12
5.5 Installation . 12
5.6 Calibration procedure . 13
5.6.1 Preparatory phase . 13
5.6.2 Measurement phase (single series) . 13
5.6.3 Data sampling . 15
5.7 Calculation of sensitivity . 15
5.7.1 Initial data rejection and filtering . 15
5.7.2 Calculation of individual sensitivity values . 16
5.7.3 Computation of the sensitivity of the test pyranometer . 16
5.7.4 Evaluation of the final results . 17
6 Continuous sun-and-shade method (component sum) . 17
6.1 Principle . 17
6.2 Apparatus . 18
6.2.1 Pyranometers . 18
6.2.2 Pyrheliometer . 18
6.2.3 Solar tracker . 18
6.2.4 Shade device . 18
6.2.5 Data acquisition system . 18
6.3 Measurement conditions . 18
6.4 Measurement site . 18
6.5 Installation . 18
6.6 Calibration procedure . 19
6.6.1 Preparatory phase . 19
6.6.2 Measurements . 19
6.6.3 Data sampling . 19
6.7 Calculation of sensitivity . 19
6.7.1 Initial data rejection and filtering . 19
6.7.2 Calculation of individual sensitivity values . 19
6.7.3 Computation of the sensitivity of the test pyranometer . 20
6.7.4 Evaluation of the final results . 20
7 Collimation tube method . 20
7.1 Principle . 20
iii
ISO/FDIS 9846:2025 (en)
7.2 Apparatus . 20
7.2.1 Pyranometer . 20
7.2.2 Pyrheliometer . 21
7.2.3 Solar tracker . 21
7.2.4 Collimation tube . 21
7.2.5 Data acquisition system . 22
7.3 Measurement conditions . 22
7.4 Measurement site . 22
7.5 Installation . 23
7.6 Calibration procedure . 23
7.6.1 Preparatory phase . 23
7.6.2 Measurements . 23
7.6.3 Data sampling . 23
7.7 Calculation of sensitivity . 23
7.7.1 Initial data rejection and filtering . 23
7.7.2 Calculation of individual sensitivity values . 23
7.7.3 Computation of the sensitivity of the test pyranometer . 24
7.7.4 Evaluation of the final results . 24
8 Calibration uncertainty . 24
9 Certificate of calibration . 25
Annex A (informative) Shade disc devices and collimation tube . 26
A.1 Shade device matches pyrheliometer geometry. . 26
A.2 Basic description of shading devices component. . 26
A.3 Typical shading devices design . 26
A.4 Collimation tube matches pyrheliometer geometry . 27
A.5 Admissible misalignment of solar tracker . 27
Annex B (informative) Calculation of the sun incidence angle 𝜽 on an inclined plane . 29
Annex C (informative) Motivation on number of measurement days . 31
C.1 Analyses of the calibration results . 31
Annex D (informative) Extended version of the sun-and-shade method . 32
Annex E (informative) Sample averaging of the alternating sun-and-shade method . 33
Annex F (informative) The Forgan alternate method . 34
Annex G (informative) Comparison of the alternating sun-and-shade method (ASSM), the
continuous sun-and-shade method (CSSM) and Collimation Tube Method (CTM) . 36
Annex H (informative) Uncertainty evaluation for pyranometer calibration . 37
H.1 General remarks . 37
H.2 Possible contributions to be considered . 37
H.3 Use of correction factors or reduction formula . 39
Annex I (informative) Introduction of a new Pyranometer sensitivity . 40
Bibliography . 42

Foreword . vi
Introduction .vii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions .
...