SIST EN ISO 9488:2022
(Main)Solar energy - Vocabulary (ISO 9488:2022)
Solar energy - Vocabulary (ISO 9488:2022)
This document defines basic terms relating to the work of ISO/TC 180. The committee covers
standardization in the field of the measurement of solar radiation and solar energy utilization in
space and water heating, cooling, industrial process heating and air conditioning. Consequently,
the vocabulary within this document is focussed on definitions relating to those measurement and
utilisation technologies.
Since the 1999 version of this document there has been considerable development in solar photovoltaic
technologies and high temperature solar thermal technologies that use heat to produce electricity or to
provide high temperatures for processes that require elevated temperatures. This standard has some
definitions that are useful also for those technologies; however, there are other documents that cover
vocabulary for these technologies in more detail.
Sonnenenergie - Vokabular (ISO 9488:2022)
Diese Internationale Norm definiert grundlegende Begriffe im Bereich der Sonnenenergie.
Énergie solaire - Vocabulaire (ISO 9488:2022)
Le présent document définit les termes de base relatifs aux travaux de l'ISO/TC 180. Le comité couvre la normalisation dans le domaine de la mesure du rayonnement solaire et de l'utilisation de l'énergie solaire pour le chauffage de l’eau et des locaux, ainsi que pour la réfrigération, les procédés thermiques indutrielset la climatisation. Par conséquent, le vocabulaire contenu dans le présent document est axé sur les définitions relatives à ces technologies de mesure et d'utilisation.
Depuis la version de 1999 du présent document, les technologies solaires photovoltaïques et les technologies solaires thermiques à haute température qui utilisent la chaleur pour produire de l'électricité ou pour fournir des températures élevées pour des processus qui le nécessitent, ont connu un développement considérable. La présente norme fournit des définitions qui sont utiles également pour ces technologies ; cependant, il existe d'autres documents qui couvrent le vocabulaire de ces technologies de manière plus détaillée.
Sončna energija - Slovar (ISO 9488:2022)
Ta dokument določa osnovne izraze v zvezi z delom, skladne s standardom ISO/TC 180. Odbor zagotavlja standardizacijo na področju merjenja sončnega sevanja oziroma izkoriščanja sončne energije za ogrevanje prostorov in vode, hlajenje, ogrevanje industrijskih procesov ter klimatizacijo. Posledično se besedišče v tem dokumentu osredotoča na definicije, povezane z navedenimi tehnologijami merjenja in uporabe.
Od različice tega dokumenta iz leta 1999 je prišlo do precejšnjega razvoja solarnih fotonapetostnih
tehnologij in visokotemperaturnih solarnih toplotnih tehnologij, ki uporabljajo toploto za proizvodnjo električne energije ali
za zagotavljanje visokih temperatur za procese, za katere so potrebne povišane temperature. Ta standard vsebuje nekaj
definicij, ki so uporabne tudi za te tehnologije; obstajajo pa tudi drugi dokumenti, ki
besedišče v zvezi s temi tehnologijami obravnavajo podrobneje.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN ISO 9488:2022
01-julij-2022
Nadomešča:
SIST EN ISO 9488:2000
Sončna energija - Slovar (ISO 9488:2022)
Solar energy - Vocabulary (ISO 9488:2022)
Sonnenenergie - Vokabular (ISO 9488:2022)
Énergie solaire - Vocabulaire (ISO 9488:2022)
Ta slovenski standard je istoveten z: EN ISO 9488:2022
ICS:
01.040.27 Prenos energije in toplote Energy and heat transfer
(Slovarji) engineering (Vocabularies)
27.160 Sončna energija Solar energy engineering
SIST EN ISO 9488:2022 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN ISO 9488:2022
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SIST EN ISO 9488:2022
EN ISO 9488
EUROPEAN STANDARD
NORME EUROPÉENNE
April 2022
EUROPÄISCHE NORM
ICS 01.040.27; 27.160 Supersedes EN ISO 9488:1999
English Version
Solar energy - Vocabulary (ISO 9488:2022)
?nergie solaire - Vocabulaire (ISO 9488:2022) Sonnenenergie - Vokabular (ISO 9488:2022)
This European Standard was approved by CEN on 31 January 2022.
CEN 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 CEN-CENELEC Management Centre or to any CEN
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 CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2022 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 9488:2022 E
worldwide for CEN national Members.
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SIST EN ISO 9488:2022
EN ISO 9488:2022 (E)
Contents Page
European foreword . 3
2
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SIST EN ISO 9488:2022
EN ISO 9488:2022 (E)
European foreword
This document (EN ISO 9488:2022) has been prepared by Technical Committee ISO/TC 180 "Solar
energy" in collaboration with Technical Committee CEN/TC 312 “Thermal solar systems and
components” the secretariat of which is held by NQIS/ELOT.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by October 2022, and conflicting national standards shall
be withdrawn at the latest by October 2022.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 9488:1999.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
Endorsement notice
The text of ISO 9488:2022 has been approved by CEN as EN ISO 9488:2022 without any modification.
3
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SIST EN ISO 9488:2022
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SIST EN ISO 9488:2022
INTERNATIONAL ISO
STANDARD 9488
Second edition
2022-03
Solar energy — Vocabulary
Sonnenenergie — Vokabular
Énergie solaire — Vocabulaire
Reference number
ISO 9488:2022(E)
© ISO 2022
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SIST EN ISO 9488:2022
ISO 9488:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022
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
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Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
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SIST EN ISO 9488:2022
ISO 9488:2022(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 Terms for solar geometry. 1
3.2 Radiation terms and quantities . 4
3.3 Radiation measurement . 10
3.4 Radiation properties and processes . 11
3.5 Indoor and outdoor climates . 13
3.6 Collector types . 13
3.7 Collector components and related quantities . 15
3.8 Types of solar heating systems . 22
3.9 System components and related quantities (other than collectors) . . 24
3.10 Non-solar-specific terms .25
Bibliography .28
Index .29
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SIST EN ISO 9488:2022
ISO 9488:2022(E)
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 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).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
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, in collaboration with
the European Committee for Standardization (CEN) Technical Committee CEN/TC 312, Thermal solar
systems and components, in accordance with the Agreement on technical cooperation between ISO and
CEN (Vienna Agreement).
This second edition cancels and replaces the first edition (ISO 9488:1999), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— update of definitions;
— addition of several new terms, according to the development of new standards for solar thermal
technology in the past two decades.
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.
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SIST EN ISO 9488:2022
INTERNATIONAL STANDARD ISO 9488:2022(E)
Solar energy — Vocabulary
1 Scope
This document defines basic terms relating to the work of ISO/TC 180. The committee covers
standardization in the field of the measurement of solar radiation and solar energy utilization in
space and water heating, cooling, industrial process heating and air conditioning. Consequently,
the vocabulary within this document is focussed on definitions relating to those measurement and
utilisation technologies.
Since the 1999 version of this document there has been considerable development in solar photovoltaic
technologies and high temperature solar thermal technologies that use heat to produce electricity or to
provide high temperatures for processes that require elevated temperatures. This standard has some
definitions that are useful also for those technologies; however, there are other documents that cover
vocabulary for these technologies in more detail.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1 Terms for solar geometry
3.1.1
aphelion
point in the Earth's orbit at which it is furthest from the Sun
6
Note 1 to entry: At the aphelion, the Earth is approximately 152 × 10 km from the Sun.
3.1.2
perihelion
point in the Earth's orbit at which it is closest to the Sun
6
Note 1 to entry: At the perihelion, the Earth is approximately 147 × 10 km from the Sun.
3.1.3
solar declination
δ
angle subtended between the Earth-sun line and the plane of the equator (north positive)
Note 1 to entry: The solar declination is zero on equinox dates, varying between +23,45° (June 22) and -23,45°
(December 22).
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SIST EN ISO 9488:2022
ISO 9488:2022(E)
3.1.4
solar azimuth angle
solar azimuth
γ
S
angular displacement from the chosen reference direction of the projection of a straight line from the
apparent position of the sun to the point of observation, onto the horizontal plane
Note 1 to entry: To avoid errors, the same definition (reference direction and measuring direction) must be used
for both solar azimuth and inclined surface azimuth.
Note 2 to entry: The reference direction can be either North or South and the azimuth angular displacement from
the reference direction can range from 0° to 360° or -180° to +180°.
Note 3 to entry: The geographic azimuth is measured clockwise from due north 0° to 360°.
Note 4 to entry: The two most common definitions in use for solar energy applications are:
o
1) Solar azimuth is 0° for a northern hemisphere location (north of the tropics at latitude angles > +23,45 )
at solar noon (3.1.9). Angular displacements east are negative and west are positive, i.e. -180° ≤ γ ≤ +180°.
S
This definition results in a simple set of equations; however, it leads to counter intuitive values for southern
o
hemisphere locations (outside of the tropics at latitude angles < -23,45 ), the solar azimuth angle being 180°
for a north facing inclined solar collector (3.6.1) in the southern hemisphere (see Reference [3]).
2) Solar azimuth angle is 0° at solar noon (3.1.9) for both Northern & Southern hemispheres (outside the tropics).
Angular displacements east are negative and west are positive, i.e. -180° ≤ γ ≤ +180°. For this definition, the
S
solar azimuth angle of a solar collector (3.6.1) tilted towards the equator at solar noon (3.1.9) in both north
and south hemispheres is 0° (outside the tropics).
3.1.5
zenith
point vertically above the observer
3.1.6
solar zenith angle
θ
z
angular distance of the sun from the vertical
3.1.7
solar altitude angle
solar elevation angle
h
complement of the solar zenith angle (3.1.6)
h = 90° - θ
z
3.1.8
solar hour angle
ω
angle between the sun projection on the equatorial plane at a given time and the sun projection on the
same plane at solar noon (3.1.9)
Note 1 to entry: The solar hour angle changes by approximately 360° within 24 h (approximately 15° within 1 h).
This angle is negative for morning hours and positive for afternoon hours, i.e. ω (in degrees) ≈ 15 (t -12) where
Hr
t is the solar time (3.1.10) in hours.
Hr
3.1.9
solar noon
local time of day at which the sun crosses the observer's meridian
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SIST EN ISO 9488:2022
ISO 9488:2022(E)
3.1.10
solar time
t
sol
hour of the day as determined by the apparent angular motion of the sun across the sky, with solar noon
(3.1.9) as the reference point for 12:00 h
Note 1 to entry: t = t + 4 (L - L ) + E, where t is the standard time, L is the longitude of the standard
sol st st loc st st
meridian for the local time zone and L is the longitude of the location in question with both longitudes specified
loc
o
in degrees west (0° ≤ L° ≤ 360 ). E is the equation of time, which takes into account the perturbations in the
Earth's rate of rotation around the sun that affect the time at which the sun crosses the observer's meridian.
Note 2 to entry: The correction 4 (L - L ) + E is expressed in minutes. An additional correction is needed if the
st loc
standard time is a daylight saving time.
3.1.11
angle of incidence
incidence angle
θ
angle between the line joining the centre of the solar disc to a point on an irradiated surface and the
outward normal to the irradiated surface
3.1.12
solar tracker
sun tracker
power-driven or manually operated movable support which may be employed to keep a device oriented
toward a given direction with respect to the sun.
3.1.13
equatorial tracker
sun-following device having an axis of rotation parallel to the Earth's axis
Note 1 to entry: The parameters of motion are the hour angle and the declination of the sun.
3.1.14
altazimuth tracker
sun-following device which uses the solar elevation angle (3.1.7) and the azimuth angle (3.1.4) of the sun
as coordinates of movement
3.1.15
sun-path diagram
graphic representation of solar altitude (3.1.7) versus solar azimuth (3.1.4), showing the position of the
Sun as a function of time for various dates of the year
Note 1 to entry: If solar time (3.1.10) is used, the diagram is valid for all locations of the same latitude.
3.1.16
heliodon
solar-angle simulator for conducting shading assessments on buildings or collector arrays, usually
having a model table which tilts for the latitude and rotates for the hour of day, and a lamp to represent
the sun, mounted at some distance away on a vertical rail, allowing adjustment for declination
3.1.17
solarscope
device similar to a heliodon (3.1.16), but having a fixed horizontal model table and a light source movable
to any solar altitude and azimuth
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SIST EN ISO 9488:2022
ISO 9488:2022(E)
3.2 Radiation terms and quantities
3.2.1
radiation
emission and transfer of energy in the form of electromagnetic waves or particles
[4]
[SOURCE: WMO R0260 ]
Note 1 to entry: Radiation can also be used to refer to multiple quantities used to describe the process called
radiation. For example, radiation could mean energy or irradiance (3.2.5) (see Reference [5]).
3.2.2
radiant energy
quantity of energy transferred by radiation (3.2.1)
[4]
[SOURCE: WMO R0200 ]
3.2.3
radiant flux
radiation flux
flux of radiation
Φ
power emitted, transferred or received in the form of radiation (3.2.1)
3.2.4
radiance
radiant flux (3.2.3) emitted, transmitted, reflected or received by a given surface, per unit of solid angle
per unit of projected area
−2 −1
Note 1 to entry: Unit: W·m ·sr .
3.2.5
irradiance
G
quotient of the radiant flux (3.2.3) incident on the surface and the area of that surface, or the rate at
which radiant energy (3.2.2) is incident on a surface, per unit area of that surface
-2
Note 1 to entry: Unit: W∙m .
3.2.6
irradiation
DEPRECATED: insolation
H
incident energy per unit area of a surface, found by integration of solar irradiance (3.2.5) over a specified
time interval
3.2.7
radiant exitance
M
radiant flux (3.2.3) leaving the element of the surface, divided by the area of
that element
Note 1 to entry: Formerly called radiant emittance.
Note 2 to entry: The radiant energy (3.2.2) may leave the surface by emission, reflection and/or transmission.
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SIST EN ISO 9488:2022
ISO 9488:2022(E)
3.2.8
ultraviolet radiation
electromagnetic radiation of wavelength in the range of 10 nm to 400 nm
Note 1 to entry: UVA radiation has a wave-length range of 315 nm to 400 nm; UVB radiation has a wavelength
range of 280 nm to 315 nm; UVC radiation (wavelength range 280 nm to X-rays) cannot be detected by solar
energy technologies.
3.2.9
visible radiation
light
electromagnetic radiation of wavelengths causing visual sensations for humans
Note 1 to entry: Visible radiation is generally accepted to be within the wavelength band of 380 nm to 780 nm
3.2.10
infrared radiation
electromagnetic radiation of wavelengths longer than those of visible radiation (3.2.9) and shorter than
about 1 mm
3.2.11
shortwave radiation
radiation of wavelength shorter than 3 μm but longer than 280 nm
Note 1 to entry: This definition is linked to radiation typically measured with pyrheliometers (3.3.5) and
pyranometers (3.3.4) that are often considered as measuring solar irradiance (3.2.5) even though the wavelength
range excludes a small part of the solar spectrum (3.2.16).
Note 2 to entry: This term is specific to solar energy applications
3.2.12
longwave radiation
radiation of wavelength greater than 3 μm, typically originating from sources at terrestrial
temperatures
Note 1 to entry: Examples of sources of longwave radiation are clouds, atmosphere, ground and terrestrial
objects.
Note 2 to entry: Sometimes is called thermal radiation.
Note 3 to entry: This definition is linked to radiation typically measured with pyrgeometers (3.3.7) that are
considered as measuring irradiance (3.2.5) from sources at terrestrial temperatures even though the wavelength
range includes a small part of the solar spectrum (3.2.16).
Note 4 to entry: This term is specific to solar energy applications.
3.2.13
solar radiation
DEPRECATED: shortwave radiation
DEPRECATED: insolation
radiation (3.2.1) emitted by the sun
3.2.14
solar energy
energy emitted by the sun in the form of electromagnetic waves
Note 1 to entry: Solar energy is primarily in the wavelength region from 0,3 μm to 3,0 μm.
Note 2 to entry: Solar energy is generally understood to mean any energy made available by the capture and
conversion of solar radiation (3.2.13).
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SIST EN ISO 9488:2022
ISO 9488:2022(E)
3.2.15
solar flux
radiant flux (3.2.3) originating from the sun
3.2.16
solar spectrum
distribution by wavelength (or frequency) of electromagnetic radiation emitted from the sun
3.2.17
direct radiation
direct solar radiation
beam radiation
beam solar radiation
solar radiation (3.2.13) incident on a given plane, and originating from a small solid angle centred on the
sun's disk
Note 1 to entry: In general, direct solar radiation is measured by instruments with field-of-view angles (3.3.6)
of up to 6°. Therefore, a part of the scattered radiation around the sun's disk [circumsolar radiation (3.2.18)] is
included, as the solar disk itself has a field-of-view angle (3.3.6) of about 0,5°.
Note 2 to entry: Direct radiation is usually measured at normal incidence.
Note 3 to entry: Approximately from 97 to 99 % of the direct solar radiation received at the ground is contained
within the wavelength range from 0,3 μm to 3 μm (see Reference [6]).
Note 4 to entry: Further details on circumsolar radiation (3.2.18) and its role for direct radiation are provided in
irradiance (3.2.5), circumsolar irradiance (3.2.19), circumsolar contribution (3.2.20), sunshape (3.2.21) and direct
solar irradiance (3.2.28).
3.2.18
circumsolar radiation
radiation (3.2.1) scattered by the atmosphere so that it appears to originate from an area of the sky
immediately adjacent to the sun
Note 1 to entry: Circumsolar radiation causes the solar aureole.
Note 2 to entry: Further details on circumsolar radiation and its role for direct radiation (3.2.17) are provided
in circumsolar irradiance (3.2.19), circumsolar contribution (3.2.20), sunshape (3.2.21) and direct solar irradiance
(3.2.28).
3.2.19
circumsolar irradiance
quotient of the radiant flux (3.2.3) of the circumsolar radiation (3.2.18) on a given plane receiver (3.7.3)
surface to the area of that surface
Note 1 to entry: If the receiver (3.7.3) plane is perpendicular to the axis of the solid angle, the circumsolar
irradiance is called circumsolar normal irradiance. Circumsolar irradiance is usually measured at normal
incidence.
3.2.20
circumsolar contribution
contribution of a specific portion of the circumsolar normal irradiance to the direct normal irradiance
Note 1 to entry: The circumsolar contribution refers to a specific ring-shaped angular region described by an
inner and the outer angular distance from the centre of the sun.
Note 2 to entry: If the inner angle describing this angular region is the half-angle of the sun disk the circumsolar
contribution is also called circumsolar ratio.
Note 3 to entry: Depending on the circumsolar irradiance (3.2.19) measurement instrument or the solar technology
involved, different wavelength ranges are included. In order to describe circumsolar irradiance (3.2.19) correctly,
the wavelength range or the spectral response of the instrument or the involved technology has to be specified.
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SIST EN ISO 9488:2022
ISO 9488:2022(E)
3.2.21
sunshape
azimuthal average radiance profile as a function of the angular distance from the centre of the solar
disc, normalized to 1 at the centre of the disc and considering the wavelength range of shortwave
radiation (3.2.11).
3.2.22
hemispherical radiation
hemispherical solar radiation
solar radiation (3.2.13) received by a plane surface from a solid angle of 2π·sr
Note 1 to entry: The tilt angle (3.10.1) and the azimuth (3.10.2) of the surface should be specified, e.g. horizontal.
Note 2 to entry: Hemispherical solar radiation is composed of direct solar radiation and diffuse solar radiation
(solar energy scattered in the atmosphere as well as solar radiation reflected by the ground).
Note 3 to entry: Solar engineers commonly use the term global radiation (3.2.23) in place of hemispherical
radiation. This use is a source of confusion if the referenced surface is not horizontal.
Note 4 to entry: Approximately 97 % to 99 % of the hemispherical solar radiation incident at the Earth's surface
is contained within the wavelength range from 0,3 μm to 3 μm (see Reference [6]).
3.2.23
global radiation
global solar radiation
hemispherical solar radiation received by a horizontal plane on the Earth’s surface
Note 1 to entry: Approximately 97 % to 99 % of the global solar radiation incident at the Earth’s surface is
contained within the wavelength range from 0,3 μm to 3 μm (see Reference [6]).
Note 2 to entry: Solar engineers commonly use the term global radiation in place of hemispherical radiation
(3.2.22). This use is a source of confusion if the referenced surface is not horizontal.
3.2.24
diffuse radiation
diffuse solar radiation
hemispherical solar radiation minus direct solar radiation
Note 1 to entry: For the purposes of solar energy technology, diffuse radiation includes a part of solar radiation
scattered in the atmosphere as well as a part of solar radiation reflected by the ground, depending on the tilt
angle (3.10.1) of the receiver surface.
Note 2 to entry: The tilt angle (3.10.1) and the azimuth (3.10.2) of the receiver surface should be specified, e.g.
horizontal.
3.2.25
atmospheric radiation
DEPRECATED: sky radiation
longwave radiation (3.2.12) emitted by and propagated through the atmosphere
[4]
[SOURCE: WMO A2940 ]
3.2.26
extra-terrestrial solar radiation
solar radiation (3.2.13) received at the limit of the Earth's atmosphere
[4]
[SOURCE: WMO E1370 ]
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SIST EN ISO 9488:2022
ISO 9488:2022(E)
3.2.27
solar constant
G
sc
solar irradiance outside the Earth's atmosphere on a plane normal to the direction of this radiation,
6
when the Earth is at its mean distance from the sun (149,5 × 10 km)
-2 -2
Note 1 to entry: Historically the solar constant is considered to be 1 367 W∙m ± 7 W∙m . The new value of
-2
1 361,1 W∙m , from the most recent determination of the solar constant, is currently under consideration, see
Reference [7].
3.2.28
direct solar irradiance
G
b
quotient of the radiant flux (3.2.3) on a given plane receiver surface received from a small solid angle
centred on the sun's disk to the area of that surface
Note 1 to entry: If the plane is perpendicular to the axis of the solid angle, direct normal solar irradiance G is
bn
received.
-2
Note 2 to entry: Unit: W∙m .
Note 3 to entry: Approximately 97 % to 99 % of the direct solar radiation received at ground level is contained
within the wavelength range from 0,3 µm to 3 µm (see Reference [3]). Depending on the direct irradiance
measurement instrument or the solar technology involved, different wavelength ranges are included. In order
to describe direct irradiance correctly, the wavelength range or the spectral response of the instrument or the
involved technology has to be specified.
Note 4 to entry: In general, direct normal solar irradiance is measured by instruments with field-of-view angles
(3.3.6) of up to 6°.
...
SLOVENSKI STANDARD
oSIST prEN ISO 9488:2020
01-september-2020
Sončna energija - Slovar (ISO/DIS 9488:2020)
Solar energy - Vocabulary (ISO/DIS 9488:2020)
Sonnenenergie - Vokabular (ISO/DIS 9488:2020)
Énergie solaire - Vocabulaire (ISO/DIS 9488:2020)
Ta slovenski standard je istoveten z: prEN ISO 9488
ICS:
01.040.27 Prenos energije in toplote Energy and heat transfer
(Slovarji) engineering (Vocabularies)
27.160 Sončna energija Solar energy engineering
oSIST prEN ISO 9488:2020 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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oSIST prEN ISO 9488:2020
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oSIST prEN ISO 9488:2020
DRAFT INTERNATIONAL STANDARD
ISO/DIS 9488
ISO/TC 180 Secretariat: SA
Voting begins on: Voting terminates on:
2020-07-08 2020-09-30
Solar energy — Vocabulary
Énergie solaire — Vocabulaire
ICS: 27.160; 01.040.27
THIS DOCUMENT IS A DRAFT CIRCULATED
This document is circulated as received from the committee secretariat.
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
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WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
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RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
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©
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ii © ISO 2020 – All rights reserved
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ISO/DIS 9488:2020(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
3.1 Terms for solar geometry . 1
3.2 Radiation terms and quantities . 3
3.3 Radiation measurement . 9
3.4 Radiation properties and processes .10
3.5 Indoor and outdoor climates .11
3.6 Collector types .11
3.7 Collector components and related quantities .13
3.8 Types of solar heating systems .20
3.9 System components and related quantities (other than collectors) .21
3.10 Non-solar-specific terms .23
Bibliography .25
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ISO/DIS 9488:2020(E)
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
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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 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).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
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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.
This second edition cancels and replaces the first edition (ISO 9488:1999), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— update of definitions
— addition of several new terms, according to the development of new standards for solar thermal
technology in the past two decades.
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.
iv © ISO 2020 – All rights reserved
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DRAFT INTERNATIONAL STANDARD ISO/DIS 9488:2020(E)
Solar energy — Vocabulary
1 Scope
This International Standard defines basic terms relating to solar energy.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1 Terms for solar geometry
3.1.1
aphelion
point in the Earth's orbit at which it is furthest from the sun
6
Note 1 to entry: At the aphelion, the Earth is approximately 152 X 10 km from the Sun.
3.1.2
perihelion
point in the Earth's orbit at which it is closest to the sun
6
Note 1 to entry: At the perihelion, the Earth is approximately 147 x 10 km from the sun.
3.1.3
solar declination
δ
angle subtended between the Earth-sun line and the plane of the equator (north positive)
Note 1 to entry: The solar declination is zero on equinox dates, varying between +23.45 ° (June 22) and -23.45 °
(December 22).
3.1.4
solar azimuth angle
solar azimuth
γ
S
projected angle between a straight line from the apparent position of the sun to the point of observation
and due north, measured clockwise, using the projections on the local horizontal plane
Note 1 to entry: This is the same definition as the one of the geographical azimuth. It is valid over the whole globe.
3.1.5
zenith
point vertically above the observer
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3.1.6
solar zenith angle
θ
z
angular distance of the sun from the vertical
3.1.7
solar altitude angle
solar elevation angle
h
complement of the solar zenith angle
h = 90° - θ
z
3.1.8
solar hour angle
ω
angle between the sun projection on the equatorial plane at a given time and the sun projection on the
same plane at solar noon
Note 1 to entry: The solar hour angle changes by approximately 360° within 24 h (approximately 15° per hour).
This angle is negative for morning hours and positive for afternoon hours, i.e. ω (in degrees) ≈ 15 (Hr-12) where
Hr is the solar time in hours.
3.1.9
solar noon
local time of day at which the sun crosses the observer's meridian.
3.1.10
solar time
hour of the day as determined by the apparent angular motion of the sun across the sky, with solar noon
as the reference point for 12:00 h
Note 1 to entry: Solar time = standard time + 4 (L - L ) + E, where L is the longitude of the standard meridian
st loc st
for the local time zone, L is the longitude of the location in question and E is the equation of time, which takes
loc
into account the perturbations in the Earth's rate of rotation around the sun that affect the time at which the sun
crosses the observer's meridian. The correction 4 (L - L ) + E is expressed in minutes. An additional correction
st loc
is needed if the standard time is a daylight saving time.
3.1.11
angle of incidence
incidence angle
θ
angle between the line joining the centre of the solar disc to a point on an irradiated surface and the
outward normal to the irradiated surface
3.1.12
solar tracker
sun tracker
power-driven or manually operated movable support which may be employed to keep a device oriented
with respect to the sun
3.1.13
equatorial tracker
sun-following device having an axis of rotation parallel to the Earth's axis
Note 1 to entry: The parameters of motion are the hour angle and the declination of the sun.
3.1.14
altazimuth tracker
sun-following device which uses the solar elevation angle and the azimuth angle of the sun as
coordinates of movement
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3.1.15
sun-path diagram
graphic representation of solar altitude versus solar azimuth, showing the position of the Sun as a
function of time for various dates of the year
Note 1 to entry: If solar time is used, the diagram is valid for all locations of the same latitude.
3.1.16
heliodon
solar-angle simulator for conducting shading assessments on buildings or collector arrays, usually
having a model table which tilts for the latitude and rotates for the hour of day, and a lamp to represent
the sun, mounted at some distance away on a vertical rail, allowing adjustment for declination
3.1.17
solarscope
device similar to a heliodon, but having a fixed horizontal model table and a light source movable to any
solar altitude and azimuth
3.2 Radiation terms and quantities
3.2.1
radiation
transfer of energy in the form of electromagnetic waves
[SOURCE: WMO R0260]
Note 1 to entry: Radiation can also be used to refer to multiple quantities used to describe the process called
radiation. For example, radiation could mean energy or irradiance.
[SOURCE: WMO CIMO Guide, 2017]
3.2.2
radiant energy
quantity of energy transferred by radiation
[SOURCE: WMO R0200]
3.2.3
radiant flux
radiation flux
flux of radiation [SOURCE: WMO R0230]
Φ
power emitted, transferred or received in the form of radiation
[SOURCE: ISO 31-6]
3.2.4
radiance
radiant power emitted, transmitted, reflected or received by a given surface, per unit solid angle per
unit projected area.
−2 −1
Note 1 to entry: Radiance is expressed in watts per square metre per steradian (W·m ·sr ).
3.2.5
irradiance
G
Quotient of the radiant flux incident on the surface and the area of that surface, or the rate at which
radiant energy is incident on a surface, per unit area of that surface
-2
Note 1 to entry: Irradiance is expressed in watts per square metre (W∙m ).
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3.2.6
irradiation
DEPRECATED: insolation
H
incident energy per unit area of a surface, found by integration of irradiance over a specified time
interval.
3.2.7
radiant exitance
M
at a point on a surface, the radiant flux leaving the element of the surface, divided by the area of
that element
[SOURCE: ISO 31-6]
Note 1 to entry: Formerly called radiant emittance.
Note 2 to entry: The radiant energy may leave the surface by emission, reflection and/or transmission.
3.2.8
ultraviolet radiation
electromagnetic radiation of wavelength in the range of 10 nm to 400 nm
Note 1 to entry: UVA radiation has a wave-length range of 315 nm to 400 nm; UVB radiation has a wavelength
range of 280 nm to 315 nm; UVC radiation (wavelength range 280 nm to X-rays) cannot be detected by solar
energy technologies.
3.2.9
visible radiation
light
electromagnetic radiation of wavelengths causing visual sensations for humans
Note 1 to entry: Visible radiation is generally accepted to be within the wavelength band of 380 nm to 780 nm
3.2.10
infrared radiation
electromagnetic radiation of wavelengths longer than those of visible radiation and shorter than
about 1 mm
3.2.11
shortwave radiation
radiation of wavelength shorter than 3 μm but longer than 280 nm
3.2.12
longwave radiation
radiation of wavelength greater than 3 μm, typically originating from sources at terrestrial
temperatures
Note 1 to entry: Examples of sources of longwave radiation are clouds, atmosphere, ground and terrestrial
objects.
Note 2 to entry: Sometimes is called thermal radiation.
3.2.13
solar radiation
DEPRECATED: shortwave radiation
DEPRECATED: insolation
radiation emitted by the sun
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3.2.14
solar energy
energy emitted by the sun in the form of electromagnetic energy
Note 1 to entry: Solar energy is primarily in the wavelength region from 0,3 μm to 3,0 μm.
Note 2 to entry: Solar energy is generally understood to mean any energy made available by the capture and
conversion of solar radiation.
3.2.15
solar flux
radiant flux originating from the sun
3.2.16
solar spectrum
distribution by wavelength (or frequency) of electromagnetic radiation emitted from the sun
3.2.17
direct radiation
direct solar radiation
beam radiation
beam solar radiation
radiation incident on a given plane, and originating from a small solid angle centred on the sun's disk
Note 1 to entry: In general, direct solar radiation is measured by instruments with field-of-view angles of up to
6°. Therefore, a part of the scattered radiation around the sun's disk (circumsolar radiation) is included, as the
solar disk itself has a field-of-view angle of about 0,5°.
Note 2 to entry: Direct radiation is usually measured at normal incidence.
Note 3 to entry: Approximately from 97 to 99% of the direct solar radiation received at the ground is contained
within the wavelength range from 0,3 μm to 3 μm [SOURCE: Reference [1] ].
Note 4 to entry: Further details on circumsolar radiation and its role for direct radiation are provided in circumsolar
radiation, circumsolar irradiance, circumsolar contribution, sunshape and direct solar irradiance.
3.2.18
circumsolar radiation
radiation scattered by the atmosphere so that it appears to originate from an area of the sky immediately
adjacent to the sun
Note 1 to entry: Circumsolar radiation causes the solar aureole.
Note 2 to entry: Further details on circumsolar radiation and its role for direct radiation are provided in circumsolar
irradiance, circumsolar contribution, sunshape and direct solar irradiance
3.2.19
circumsolar irradiance
quotient of the radiant flux of the circumsolar radiation on a given plane receiver surface to the area of
that surface
Note 1 to entry: If the receiver plane is perpendicular to the axis of the solid angle, the circumsolar irradiance is
called circumsolar normal irradiance. Circumsolar irradiance is usually measured at normal incidence.
3.2.20
circumsolar contribution
contribution of a specific portion of the circumsolar normal irradiance to the direct normal irradiance.
The circumsolar contribution refers to a specific ring-shaped angular region described by an inner and
the outer angular distance from the centre of the sun.
Note 1 to entry: If the inner angle describing this angular region is the half-angle of the sun disk the circumsolar
contribution is also called circumsolar ratio.
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Note 2 to entry: Depending on the circumsolar irradiance measurement instrument or the solar technology
involved, different wavelength ranges are included. In order to describe circumsolar irradiance correctly, the
wavelength range or the spectral response of the instrument or the involved technology has to be specified.
3.2.21
sunshape
azimuthal average radiance profile as a function of the angular distance from the centre of the sun,
normalized to 1 at the centre of the sun and considering the wavelength range of shortwave radiation.
3.2.22
hemispherical radiation
hemispherical solar radiation
solar radiation received by a plane surface from a solid angle of 2π sr
Note 1 to entry: The tilt angle and the azimuth of the surface should be specified, e.g. horizontal.
Note 2 to entry: Hemispherical solar radiation is composed of direct solar radiation and diffuse solar radiation
(solar energy scattered in the atmosphere as well as solar radiation reflected by the ground).
Note 3 to entry: Solar engineers commonly use the term global radiation in place of hemispherical radiation. This
use is a source of confusion if the referenced surface is not horizontal (see global radiation).
Note 4 to entry: Approximately 97 % to 99 % of the hemispherical solar radiation incident at the Earth's surface
is contained within the wavelength range from 0,3 μm to 3 μm [SOURCE: Reference [1]].
3.2.23
global radiation
global solar radiation
hemispherical solar radiation received by a horizontal plane
Note 1 to entry: Approximately 97 % to 99 % of the global solar radiation incident at the Earth’s surface is
contained within the wavelength range from 0,3 μm to 3 μm [SOURCE: Reference [1]].
Note 2 to entry: Solar engineers commonly use the term global radiation in place of hemispherical radiation. This
use is a source of confusion if the referenced surface is not horizontal (see hemispherical radiation).
3.2.24
diffuse radiation
diffuse solar radiation
hemispherical solar radiation minus direct solar radiation
Note 1 to entry: For the purposes of solar energy technology, diffuse radiation includes solar radiation scattered
in the atmosphere as well as solar radiation reflected by the ground, depending on the tilt angle of the receiver
surface.
Note 2 to entry: The tilt angle and the azimuth of the receiver surface should be specified, e.g. horizontal.
3.2.25
atmospheric radiation
DEPRECATED: shortwave sky radiation
longwave radiation emitted by and propagated through the atmosphere
[SOURCE: WMO A2940]
3.2.26
extraterrestrial solar radiation
solar radiation received at the limit of the Earth's atmosphere
[SOURCE: WMO E1370]
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3.2.27
solar constant
I
0
solar irradiance outside the Earth's atmosphere on a plane normal to the direction of this radiation,
6
when the Earth is at its mean distance from the sun (149,5 x 10 km)
-2 -2
Note 1 to entry: Historically the solar constant is considered to be 1 367 W∙m ± 7 W∙m [SOURCE: Reference
-2
[2].]. The new value of 1361.1 W∙m , from the most recent determination of the solar constant, is currently
under consideration [SOURCE: Reference [3].].
3.2.28
direct solar irradiance
G
b
quotient of the radiant flux on a given plane receiver surface received from a small solid angle centred
on the sun's disk to the area of that surface
Note 1 to entry: If the plane is perpendicular to the axis of the solid angle, direct normal solar irradiance G is
bn
received.
-2
Note 2 to entry: Direct solar irradiance is expressed in watts per square metre (W∙m ).
Note 3 to entry: Approximately 97% to 99% of the direct solar radiation received at ground level is contained
within the wavelength range from 0,3 µm to 3 µm [SOURCE: Reference [1].]. Depending on the direct irradiance
measurement instrument or the solar technology involved, different wavelength ranges are included. In order
to describe direct irradiance correctly, the wavelength range or the spectral response of the instrument or the
involved technology has to be specified.
Note 4 to entry: In general, direct normal solar irradiance is measured by instruments with field-of-view angles
of up to 6°. The currently recommended instrument design uses 5° field-of-view [SOURCE: WMO CIMO guide
2017]. A part of the scattered radiation around the Sun's disk (circumsolar radiation) is included, as the solar disk
itself has a field-of-view angle of about 0,5°.
Note 5 to entry: In order to describe direct normal solar irradiance accurately, it is necessary to specify how
circumsolar radiation is included in it using the following terms. B is the experimental direct normal irradiance.
n
α
2π
1
BP= ()ξϕ,,Ld()ξϕ coss()ξξin() ξdϕ.
n ∫∫
0 0
where
-2 -1
L(ξ,φ) is the broadband sky radiance - usually expressed in W· m sr - for an element of sky
whose angular position is defined by the angular distance ξ from the centre of the sun disk
and the azimuth angle φ in the sun disk and the circumsolar region;
P(ξ,φ) is the penumbra function of the measurement device that is sometimes also called “accept-
ance function”;
α is the greatest angular distance from the sun disk centre for which radiation is measured
l
by the instrument.
ideal ideal
In atmospheric radiation transfer models, another parameter is often used: B (α ). B (α ) is the direct
n l n l
normal irradiance up to the angular limit α which in this case mostly corresponds to the sun disk half-angle
l
ideal
(∼0,27°). B (α ) is calculated as B , the penumbra function being set equal to 1 [see also SOURCE: Reference
n l n
ideal
[4].]. In concentrating solar power plant models B (α ) or B might be used depending on the sunshape data
n l n
applied in the model. The angular limit α also has to fit to the applied sunshape data.
l
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3.2.29
hemispherical irradiance
hemispherical solar irradiance
DEPRECATED: incident solar radiation intensity
DEPRECATED: instantaneous insolation
DEPRECATED: insolation
DEPRECATED: incident radiant flux density
G
hem
quotient of the radiant flux on a given plane receiver surface received from a solid angle of 2π sr to the
area of that surface
Note 1 to entry: The tilt angle and the azimuth of the surface should be specified, e.g. horizontal.
-2
Note 2 to entry: Hemispherical irradiance is expressed in watts per square metre (W∙m ).
Note 3 to entry: Examples for hemispherical irradiance are global irradiance and the irradiance received in the
plane of solar collector [Plane of Array (POA) irradiance], also called "global tilted irradiance".
3.2.30
global irradiance
global solar irradiance
hemispherical solar irradiance on a horizontal plane G
h
-2
Note 1 to entry: Global irradiance is expressed in watts per square metre (W∙m ).
Note 2 to entry: Global irradiance always refers to a horizontal plane. Global irradiance should not be confused
with global tilted irradiance (see hemispherical irradiance, Note 3 to entry).
3.2.31
diffuse solar irradiance
G
d
irradiance of diffuse solar radiation on a given plane receiver surface
Note 1 to entry: The tilt angle and the azimuth of the receiving surface should be specified, e.g. horizontal.
-2
Note 2 to entry: Diffuse solar irradiance is expressed in watts per square metre (W∙m ).
3.2.32
spectral solar irradiance
E
λ
solar irradiance per unit wavelength interval at a given wavelength
-2 -1
Note 1 to entry: Spectral solar irradiance is expressed in watts per square metre per micrometre (W∙m ∙μm ).
3.2.33
isorad
curve, drawn on a map, indicating sites of equal solar irradiation during a given interval of time
3.2.34
isohel
curve, drawn on a map, indicating sites of equal sunshine duration during a given interval of time
3.2.35
sky temperature
equivalent blackbody radiation temperature of the atmospheric longwave radiation received at a
horizontal surface
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3.3 Radiation measurement
3.3.1
World Radiometric Reference
WRR
measurement standard defining the SI unit of total irradiance
Note 1 to entry: See the WMO Guide to Meteorological Instruments and Methods of Observation, 2017, subclause
7.1.2.2 .
Note 2 to entry: The WRR was adopted by the WMO and has been in effect since 1 July 1980.
Note 3 to entry: In order to ensure its long-term stability, the WRR is maintained by a group (known as the World
Standard Group) of at least four pyrheliometers of different design which are under the auspices of the WMO
World Radiation Centre at Davos, in Switzerland.
3.3.2
radiometer
instrument used for measuring radiation
Note 1 to entry: Depending on the construction of the instrument, the readout of the instrument will give either
irradiance or irradiation.
3.3.3
pyrradiometer
radiometer for measuring the overall radiation including shortwave and longwave radiations on a plane
surface from a solid angle of 2π sr
Note 1 to entry: Depending on the construction of the instrument, the readout of the instrument will give either
irradiance or irradiation.
3.3.4
pyranometer
radiometer designed for measuring the solar irradiance on a plane receiver surface
3.3.5
pyrheliometer
DEPRECATED: actinometer
radiometer using a collimated detector for measuring the direct solar irradiance under normal
incidence
Note 1 to entry: Its spectral response should be approximately constant in the wavelength range of 0,3 μm to 3
μm and the acceptance angle is recommended to be 5° [SOURCE: WMO CIMO guide, 2017].
3.3.6
field-of-view angle
full angle of the geometrical cone which is defined by the centre of the pyrheliometer
receiver surface and the border of its aperture
3.3.7
pyrgeometer
radiometer for measuring the longwave irradiance on a plane receiver surface
Note 1 to entry: This spectral range is similar to that of atmospheric longwave radiation and is only nominal. The
spectral response of a pyrgeometer depends largely on the material used for the dome(s) protecting its receiving
surface.
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3.3.8
diffusometer
radiometer designed for measuring the diffuse solar radiation, consisting usually of a pyranometer and
a shading structure which can be a shading ball, a shading disk, a shading ring, a rotating shadowband
or a shading mask.
Note 1 to entry: For details, see ISO 9060 and ISO 9846.
3.4 Radiation properties and processes
3.4.1
absorptance
absorption factor
α
ratio of the radiant flux absorbed by an element of a surface to that of the incident radiation
Note 1 to entry: The absorptance may apply to either a single wavelength or a wavelength range.
3.4.2
emittance
ε
ratio of radiant exitance of a body to that of a full radiator (blackbody) at the same temperature[SOURCE:
ISO 13731:2001].
Note 1 to
...
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