ISO 9847:2023

INTERNATIONAL ISO
STANDARD 9847
Second edition
2023-01
Solar energy — Calibration of
pyranometers by comparison to a
reference pyranometer
Énergie solaire — Étalonnage des pyranomètres par comparaison à
un pyranomètre de référence
Reference number
© ISO 2023
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ii
Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Pyranometer calibration . 4
4.1 General . 4
4.2 Pyranometer sensitivity, measurement equation, measurand . 4
4.3 Indoor and outdoor calibration compared . 6
4.4 Method validation . 6
4.5 Calibration uncertainty . 6
5 Measuring equipment . 7
5.1 Data acquisition and recording. 7
5.2 Instrument platforms . 8
5.3 Pyranometers . 8
6 Indoor calibration (Type A) . 8
6.1 Introductory remarks on indoor calibration . 8
6.2 Reference pyranometers for indoor calibration . 8
6.3 Indoor calibration systems . 9
6.3.1 System with a direct beam source (type A1) . 9
6.3.2 Systems with an integrating sphere source (type A2) . 9
6.4 Indoor calibration procedures . 9
6.4.1 Calibration procedure requirements (types A1 and A2). 9
6.4.2 Indoor calibration procedures (types A1 and A2) . 9
6.4.3 Calculation of the sensitivity . 10
6.4.4 Calibration conditions and optional correction of reference operating
conditions . 11
6.4.5 Uncertainty evaluation . 11
7 Outdoor calibration (Type B) .12
7.1 Introductory remarks on outdoor calibration .12
7.2 Reference pyranometers for outdoor calibration .12
7.3 Outdoor calibration systems . 12
7.3.1 Site selection for outdoor calibration .12
7.3.2 Tracking for normal incidence calibration (type B3) .13
7.4 Outdoor calibration procedures . 13
7.4.1 Calibration procedure requirements (B1, B2, B3) .13
7.4.2 Outdoor horizontal calibration procedure (type B1) .13
7.4.3 Outdoor tilted calibration procedure (type B2) . 14
7.4.4 Outdoor normal incidence calibration procedure (type B3) .15
7.4.5 Calculation of the sensitivity . 15
7.4.6 Calibration conditions and optional correction of reference operating
conditions . 16
7.4.7 Uncertainty evaluation . 16
8 Calibration certificate .17
Annex A (informative) Examples of calibration systems using artificial sources .18
Annex B (informative) Calculation of daily average zenith angle .22
Annex C (informative) Introduction of a new pyranometer sensitivity .24
Annex D (informative) Data quality review for outdoor calibration .26
Annex E (informative) Uncertainty evaluation for outdoor calibration .29
iii
Annex F (informative) Uncertainty evaluation for indoor calibration .30
Bibliography .31
iv
Foreword
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described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents 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).
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www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 180, Solar energy, Subcommittee SC 1,
Climate – Measurement and data.
This second edition cancels and replaces the first edition (ISO 9847:1992) which has been technically
revised.
The main changes are as follows:
— focus on current calibration practices;
— adapted recommendations for mathematical treatment of data;
[1]
— adaptation of the terminology to the revised ISO 9060:2018 and ISO Guide 99 ;
[2]
— added comments on uncertainty evaluation of the calibration with reference to ASTM G213 and
ISO/IEC Guide 98-3;
— inclusion of reference to non-spectrally-flat pyranometers, that are now also included in ISO 9060.
Annexes A, B, C, D, E and F are given for information only.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
v
Introduction
Pyranometers are instruments used to measure the irradiance (power per unit area) received from the
sun for many purposes.
In recent years the application of hemispherical solar radiation measurement, using pyranometers,
has risen sharply. The main application of pyranometers now is no longer scientific research, but
assessment of the performance of solar power plants.
Accurate measurements of the hemispherical solar radiation are required for
a) the determination of the energy input to solar energy systems such as photovoltaic (PV) -, and solar
thermal systems, as a basis for performance assessment,
b) the testing and assessment of solar technologies,
c) the geographic mapping of solar energy resources, and
d) other applications such as agriculture, building efficiency, material degradation and reliability,
climate, weather, health, etc.
Today’s growing solar energy performance assessment markets demand the lowest possible
measurement uncertainties. To meet this demand, a measurement requires an uncertainty evaluation
[3]
and an accurate time stamp .
Calibration of measuring instruments is an essential part of the uncertainty evaluation and part of
any quality management system. Regular instrument re-calibration according to this standard helps
attaining the required low measurement uncertainties. Calibration usually will show the instrument is
stable and then serves as:
— confirmation that the measurement data collected over the time interval from the previous to the
present calibration are reliable
— the instrument is expected to remain stable, future measurement data are expected to be reliable.
Uncertainties mentioned in this document are expanded uncertainties with a coverage factor k = 2.
vi
INTERNATIONAL STANDARD ISO 9847:2023(E)
Solar energy — Calibration of pyranometers by
comparison to a reference pyranometer
1 Scope
This document specifies two preferred methods for the calibration of pyranometers using reference
pyranometers; indoor (Type A) and outdoor
...