SIST EN IEC 61724-1:2021

SLOVENSKI STANDARD
01-november-2021
Nadomešča:
SIST EN 61724-1:2017
Zmogljivost fotonapetostnega sistema - 1. del: Spremljanje in nadzorovanje
Photovoltaic system performance - Part 1: Monitoring
Betriebsverhalten von Photovoltaik-Systemen - Teil 1: Überwachung
Performance d'un système photovoltaïque - Partie 1: Surveillance
Ta slovenski standard je istoveten z: EN IEC 61724-1:2021
ICS:
27.160 Sončna energija Solar energy engineering
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 61724-1

NORME EUROPÉENNE
EUROPÄISCHE NORM
August 2021
ICS 27.160 Supersedes EN 61724-1:2017 and all of its amendments
and corrigenda (if any)
English Version
Photovoltaic system performance - Part 1: Monitoring
(IEC 61724-1:2021)
Performances des systèmes photovoltaïques - Partie 1: Betriebsverhalten von Photovoltaik-Systemen - Teil 1:
Surveillance Überwachung
(IEC 61724-1:2021) (IEC 61724-1:2021)
This European Standard was approved by CENELEC on 2021-08-25. 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 CEN-CENELEC
Management Centre 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 CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2021 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 61724-1:2021 E

European foreword
The text of document 82/1904/FDIS, future edition 2 of IEC 61724-1, prepared by IEC/TC 82 “Solar
photovoltaic energy systems” was submitted to the IEC-CENELEC parallel vote and approved by
CENELEC as EN IEC 61724-1:2021.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2022–05–25
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2024–08–25
document have to be withdrawn
This document supersedes EN 61724-1:2017 and all of its amendments and corrigenda (if any).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 61724-1:2021 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following note has to be added for the standard indicated:
IEC 60904-3 NOTE Harmonized as EN IEC 60904-3
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 1 Where an International Publication has been modified by common modifications, indicated by (mod), the
relevant EN/HD applies.
NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is available
here: www.cenelec.eu.
Publication Year Title EN/HD Year
IEC 60050-131 - International Electrotechnical Vocabulary - -
(IEV) - Part 131: Circuit theory
IEC 60904-2 - Photovoltaic devices - Part 2: EN 60904-2 -
Requirements for photovoltaic reference
devices
IEC 60904-5 - Photovoltaic devices - Part 5: EN 60904-5 -
Determination of the equivalent cell
temperature (ECT) of photovoltaic (PV)
devices by the open-circuit voltage method
IEC 60904-7 - Photovoltaic devices - Part 7: Computation EN IEC 60904-7 -
of the spectral mismatch correction for
measurements of photovoltaic devices
IEC 61215 series Terrestrial photovoltaic (PV) modules - EN IEC 61215 series
Design qualification and type approval
IEC 61557-12 - Electrical safety in low voltage distribution - -
systems up to 1 000 V AC and 1 500 V DC
- Equipment for testing, measuring or
monitoring of protective measures - Part
12: Power metering and monitoring
devices (PMD)
IEC/TS 61724-2  Photovoltaic system performance - Part 2:
Capacity evaluation method
IEC/TS 61724-3  Photovoltaic system performance - Part 3:
Energy evaluation method
IEC/TS 61836  Solar photovoltaic energy systems -  -
Terms, definitions and symbols
IEC 62053-22 - Electricity metering equipment - Particular EN IEC 62053-22 -
requirements - Part 22: Static meters for
AC active energy (classes 0,1S, 0,2S and
0,5S)
IEC 62670-3 - Photovoltaic concentrators (CPV) – EN 62670-3 -
Performance testing - Part 3: Performance
measurements and power rating
IEC 62817 2014 Photovoltaic systems - Design qualification EN 62817 2015
of solar trackers
ISO/IEC Guide 98-1 - Uncertainty of measurement – Part 1: - -
Introduction to the expression of
uncertainty in measurement
ISO/IEC Guide 98-3 - Uncertainty of measurement - Part 3: - -
Guide to the expression of uncertainty in
measurement (GUM:1995)
ISO 9060 2018 Solar energy - Specification and
classification of instruments for measuring
hemispherical solar and direct solar
radiation
ISO 9488  Solar energy - Vocabulary EN ISO 9488

IEC 61724-1 ®
Edition 2.0 2021-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Photovoltaic system performance –

Part 1: Monitoring
Performances des systèmes photovoltaïques –

Partie 1: Surveillance
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.160 ISBN 978-2-8322-1002-5

– 2 – IEC 61724-1:2021 © IEC 2021
CONTENTS
FOREWORD . 6
INTRODUCTION . 8
1 Scope . 10
2 Normative references. 10
3 Terms and definitions . 11
4 Monitoring system classification . 15
5 General . 16
5.1 Measurement precision and uncertainty . 16
5.2 Calibration . 16
5.3 Repeated elements . 16
5.4 Power consumption . 16
5.5 Documentation . 16
5.6 Inspection . 16
6 Data acquisition timing and reporting . 16
6.1 Samples, records, and reports . 16
6.2 Timestamps . 18
6.3 Parameter names . 18
7 Required measurements . 18
8 Irradiance . 23
8.1 Sensor types . 23
8.2 General requirements . 23
8.2.1 Overview . 23
8.2.2 Sensor requirements . 23
8.2.3 Sensor locations . 24
8.2.4 Recalibration. 25
8.2.5 Soiling mitigation . 25
8.2.6 Dew and frost mitigation . 25
8.2.7 Inspection and maintenance . 26
8.2.8 Sensor alignment . 26
8.3 Measurements . 26
8.3.1 Global horizontal irradiance . 26
8.3.2 In-plane irradiance . 26
8.3.3 In-plane rear-side irradiance . 27
8.3.4 In-plane rear-side irradiance ratio . 27
8.3.5 Horizontal albedo . 27
8.3.6 Direct normal irradiance . 27
8.3.7 Diffuse horizontal irradiance . 27
8.3.8 Spectrally matched irradiance . 27
8.3.9 In-plane irradiance for concentrator systems . 28
8.3.10 Spectral irradiance for concentrator systems . 29
8.3.11 Circumsolar measurements for concentrator systems . 29
8.3.12 Satellite remote sensing of irradiance . 30
9 Environmental factors . 31
9.1 PV module temperature . 31
9.2 Ambient air temperature . 31

IEC 61724-1:2021 © IEC 2021 – 3 –
9.3 Wind speed and direction . 32
9.4 Soiling ratio . 32
9.5 Rainfall . 33
9.6 Snow . 33
9.7 Humidity . 33
10 Tracker system . 33
10.1 Single-axis trackers . 33
10.2 Dual-axis trackers . 33
10.2.1 Monitoring . 33
10.2.2 Pointing error sensor alignment . 33
11 Electrical measurements . 34
11.1 Inverter-level measurements . 34
11.2 Plant-level measurements . 34
12 Data processing and quality check . 35
12.1 Night . 35
12.2 Quality check . 35
12.2.1 Removing invalid readings . 35
12.2.2 Treatment of missing data . 35
13 Calculated parameters . 36
13.1 Overview. 36
13.2 Summations . 36
13.3 Irradiation . 36
13.4 Electrical energy . 37
13.4.1 General . 37
13.4.2 DC output energy . 37
13.4.3 AC output energy . 37
13.5 Array power rating . 37
13.5.1 DC power rating . 37
13.5.2 AC power rating . 38
13.6 Yields . 38
13.6.1 General . 38
13.6.2 PV array energy yield . 38
13.6.3 Final system yield . 38
13.6.4 Reference yield . 39
13.6.5 Bifacial reference yield . 39
13.7 Yield losses . 39
13.7.1 General . 39
13.7.2 Array capture loss . 39
13.7.3 Balance of systems (BOS) loss. 40
13.8 Efficiencies . 40
13.8.1 Array (DC) efficiency . 40
13.8.2 System (AC) efficiency . 40
13.8.3 BOS efficiency . 40
14 Performance metrics . 41
14.1 Overview. 41
14.2 Summations . 41
14.3 Performance ratios . 41
14.3.1 Performance ratio . 41

– 4 – IEC 61724-1:2021 © IEC 2021
14.3.2 Temperature-corrected performance ratios . 42
14.3.3 Bifacial performance ratios . 44
14.4 Performance indices . 44
15 Data filtering . 45
15.1 Use of available data . 45
15.2 Filtering data to specific conditions . 45
15.3 Reduced inverter, grid, or load availability . 45
Annex A (informative) Sampling interval . 46
A.1 General considerations . 46
A.2 Time constants . 46
A.3 Aliasing error . 46
A.4 Example. 47
Annex B (informative) Module temperature sensor selection and attachment . 48
B.1 Objective . 48
B.2 Sensor and material selection . 48
B.2.1 Optimal sensor types . 48
B.2.2 Optimal tapes . 48
B.2.3 Cyanoacrylate adhesives and backsheet integrity . 49
B.3 Sensor attachment . 49
B.3.1 Permanent versus temporary . 49
B.3.2 Attachment location . 49
B.3.3 Bifacial modules . 49
B.3.4 Method . 49
Annex C (normative) Soiling measurement using clean and soiled PV reference device
pair . 52
C.1 Overview. 52
C.2 Equipment . 52
C.3 Normalization . 52
C.4 Measurement method 1 – max power reduction due to soiling . 53
C.5 Measurement method 2 – short-circuit current reduction due to soiling . 53
C.6 Non-uniform soiling . 53
C.7 Daily average value . 54
C.8 Renormalization . 54
Annex D (informative) Derate factors . 55
Annex E (normative) Systems with local loads, storage, or auxiliary sources . 57
E.1 System types . 57
E.2 Parameters and formulas . 59
Bibliography . 66

Figure 1 – Possible elements of PV systems . 8
Figure 2 – Samples, records and reports . 17
Figure B.1 – Sensor attachment, permanent . 50
Figure B.2 – Sensor attachment, temporary . 50
Figure B.3 – Sensor element wire strain relief . 51
Figure E.1 – Energy flow between possible elements of different PV system types . 57

Table 1 – Sampling and recording interval requirements . 18

IEC 61724-1:2021 © IEC 2021 – 5 –
Table 2 – Measured parameters and requirements . 20
Table 3 – Multiplier referenced in Table 2 . 23
Table 4 – Irradiance sensor requirements . 24
Table 5 – Inverter-level electrical measurement requirements . 34
Table 6 – Plant-level AC electrical output measurement requirements . 34
Table 7 – Calculated parameters . 36
Table 8 – Performance metrics . 41
Table E.1 – Elements of different PV system types . 58
Table E.2 – Parameters and formulas for different system types . 59

– 6 – IEC 61724-1:2021 © IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
PHOTOVOLTAIC SYSTEM PERFORMANCE –

Part 1: Monitoring
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 itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
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 61724-1 has been prepared by IEC technical committee 82: Solar
photovoltaic energy systems.
This second edition cancels and replaces the first edition, published in 2017. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
• Monitoring of bifacial systems is introduced.
• Irradiance sensor requirements are updated.
• Soiling measurement is updated based on new technology.
• Class C monitoring systems are eliminated.
• Various requirements, recommendations and explanatory notes are updated.

IEC 61724-1:2021 © IEC 2021 – 7 –
The text of this standard is based on the following documents:
FDIS Report on voting
82/1904/FDIS 82/1925/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
A list of all parts in the IEC 61724 series, published under the general title Photovoltaic system
performance, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 8 – IEC 61724-1:2021 © IEC 2021
INTRODUCTION
This document defines classes of photovoltaic (PV) performance monitoring systems and
serves as guidance for monitoring system choices.
Figure 1 illustrates major elements comprising different PV system types. The main clauses of
this document are written for grid-connected systems without local loads, energy storage, or
auxiliary sources, as shown by the bold lines in Figure 1. Annex E includes some details for
systems with additional components.
The PV array may include both fixed-axis and tracker systems and both flat-plate and
concentrator systems.
Key
RNE: renewable energy
PCE: power conditioning equipment
BDI: bi-directional inverter
GCI: grid-connected inverter
Bold lines denote simple grid-connected system without local loads, energy storage, or auxiliary sources.
Figure 1 – Possible elements of PV systems

IEC 61724-1:2021 © IEC 2021 – 9 –
The purposes of a performance monitoring system are diverse and could include comparing
performance to design expectations and guarantees as well as detecting and localizing faults.
For comparing performance to design expectations and guarantees, the focus should be on
system-level data and consistency between prediction and test methods.
For detecting and localizing faults there should be greater resolution at sub-levels of the system
and an emphasis on measurement repeatability and correlation metrics.
The monitoring system should be adapted to the PV system's size and user requirements. In
general, larger PV systems should have more monitoring points and higher accuracy sensors
than smaller and lower-cost PV systems.

– 10 – IEC 61724-1:2021 © IEC 2021
PHOTOVOLTAIC SYSTEM PERFORMANCE –

Part 1: Monitoring
1 Scope
This part of IEC 61724 outlines terminology, equipment, and methods for performance
monitoring and analysis of photovoltaic (PV) systems. It also serves as a basis for other
standards which rely upon the data collected.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 60050-131, International Electrotechnical Vocabulary (IEV) – Part 131: Circuit theory
IEC 60904-2, Photovoltaic devices – Part 2: Requirements for photovoltaic reference devices
IEC 60904-5, Photovoltaic devices – Part 5: Determination of the equivalent cell temperature
(ECT) of photovoltaic (PV) devices by the open-circuit voltage method
IEC 60904-7, Photovoltaic devices – Part 7: Computation of the spectral mismatch correction
for measurements of photovoltaic devices
IEC 61215 (all parts), Terrestrial photovoltaic (PV) modules – Design qualification and type
approval
IEC 61557-12, Electrical safety in low voltage distribution systems up to 1 000 V AC and
1 500 V DC – Equipment for testing, measuring or monitoring of protective measures – Part 12:
Power metering and monitoring devices (PMD)
IEC TS 61724-2, Photovoltaic system performance – Part 2: Capacity evaluation method
IEC TS 61724-3, Photovoltaic system performance – Part 3: Energy evaluation method
IEC TS 61836, Solar photovoltaic energy systems – Terms, definitions and symbols
IEC 62053-22, Electricity metering equipment – Particular requirements – Part 22: Static meters
for AC active energy (classes 0,1S, 0,2S and 0,5S)
IEC 62670-3, Photovoltaic concentrators (CPV) – Performance testing – Part 3: Performance
measurements and power rating
IEC 62817:2014, Photovoltaic systems – Design qualification of solar trackers
ISO/IEC Guide 98-1, Uncertainty of measurement – Part 1: Introduction to the expression of
uncertainty in measurement
IEC 61724-1:2021 © IEC 2021 – 11 –
ISO/IEC Guide 98-3, Uncertainty of measurement – Part 3: Guide to the expression of
uncertainty in measurement (GUM:1995)
ISO 9060:2018, Solar energy – Specification and classification of instruments for measuring
hemispherical solar and direct solar radiation
ISO 9488, Solar energy – Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-131,
IEC TS 61836, ISO 9488, and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
sample
data acquired from a sensor or measuring device
3.2
sampling interval
time between samples
3.3
record
data recorded and stored
3.4
recording interval
τ
time between records
3.5
report
aggregate value based on series of records
3.6
reporting period
time between reports
3.7
front side
side of a surface which normally faces the sky
3.8
rear side
side of a surface which normally faces the ground
3.9
monofacial PV device
PV device in which only the front side is used for power generation

– 12 – IEC 61724-1:2021 © IEC 2021
3.10
bifacial PV device
PV device in which both front side and rear side are used for power generation
3.11
bifaciality coefficient
𝛗𝛗
ratio between an I-V characteristic of the rear side and the front side of a bifacial device,
typically at Standard Test Conditions (STC), unless otherwise specified
Note 1 to entry: Bifaciality coefficients include the short-circuit current bifaciality coefficient 𝜑𝜑 , the open-circuit
Isc
voltage bifaciality coefficient 𝜑𝜑 and the maximum power bifaciality coefficient 𝜑𝜑 .
Voc Pmax
Note 2 to entry: Bifaciality coefficients are defined in IEC TS 60904-1-2.
3.12
irradiance
G
incident flux of radiant power per unit area
−2
Note 1 to entry: Expressed in units of W·m .
3.13
in-plane irradiance
G or POA
i
sum of direct, diffuse, and ground-reflected irradiance incident upon the front side of an inclined
surface parallel to the plane of the modules in the PV array, also known as plane-of-array (POA)
irradiance
−2
Note 1 to entry: Expressed in units of W·m .
3.14
horizontal albedo
𝜌𝜌
𝐻𝐻
proportion of incident light reflected by a ground surface as measured in a horizontal plane
Note 1 to entry: It is a property of a ground surface and is a dimensionless quantity on a scale from 0 to 1.
3.15
in-plane rear-side irradiance ratio
𝜌𝜌
𝑖𝑖
ratio of the irradiance incident on the rear side of the modules in the PV array to the irradiance
incident on the front side
Note 1 to entry: It is a dimensionless quantity but can exceed a value of 1 since, in addition to reflected light, diffuse
and direct components of the solar resource may also be measured on the rear-side of the plane of array.
3.16
spectrally matched in-plane rear-side irradiance ratio
𝑆𝑆𝑆𝑆
𝜌𝜌
𝑖𝑖
in-plane rear-side irradiance ratio per 3.15 when both irradiance quantities are measured with
a spectrally matched reference device or with the application of spectral correction factors per
IEC 60904-7
3.17
spectrally matched reference device
reference device such as a PV cell or module with spectral response characteristics sufficiently
close to those of the PV modules in the PV array such that spectral mismatch errors are small
under the typical range of incident spectra

IEC 61724-1:2021 © IEC 2021 – 13 –
3.18
in-plane rear-side irradiance
rear
rear
G or POA
i
sum of direct, diffuse, and ground-reflected irradiance incident on the rear side of the modules
in the PV array, also known as rear-side plane-of-array irradiance
−2
Note 1 to entry: Expressed in units of W·m .
𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 𝑆𝑆𝑆𝑆
Note 2 to entry: (If measured via in-plane rear-side irradiance ratio): 𝐺𝐺 = 𝜌𝜌 × 𝐺𝐺 or 𝐺𝐺 = 𝜌𝜌 × 𝐺𝐺 .
𝑖𝑖 𝑖𝑖 𝑖𝑖 𝑖𝑖,𝑆𝑆𝑆𝑆 𝑖𝑖 𝑖𝑖
3.19
bifacial reference device
bifacial PV device, such as a cell or module, having substantially the same properties, with
respect to response to front-side and rear-side irradiance, as bifacial modules to be monitored
3.20
bifacial irradiance factor
BIF
dimensionless factor that can be directly multiplied by the front-side in-plane irradiance (G ) to
i
calculate the “effective” irradiance reaching a bifacial device from both the front and rear side
collectively
𝑠𝑠𝑠𝑠 𝑆𝑆𝑆𝑆
Note 1 to entry: 𝐵𝐵𝐵𝐵𝐵𝐵 = (1 +𝜑𝜑 × 𝜌𝜌 ) or 𝐵𝐵𝐵𝐵𝐵𝐵 = (1 +𝜑𝜑 × 𝜌𝜌 ). See 3.11, 3.15, 3.16.
𝑆𝑆𝑃𝑃𝑟𝑟𝑃𝑃 𝑖𝑖 𝑆𝑆𝑃𝑃𝑟𝑟𝑃𝑃 𝑖𝑖
Note 2 to entry: Rear-side POA irradiance can be measured simultaneously with front-side POA irradiance using a
𝐵𝐵𝑖𝑖𝐵𝐵𝑖𝑖 𝑅𝑅𝑟𝑟𝑅𝑅 𝐷𝐷𝑟𝑟𝐷𝐷𝑖𝑖𝐷𝐷𝑟𝑟
bifacial reference device. In that case, 𝐵𝐵𝐵𝐵𝐵𝐵 =𝐺𝐺 ÷𝐺𝐺 . For consistency, the front-side POA irradiance
𝑖𝑖
𝑖𝑖
should be measured with the same or similar type of device as the bifacial reference device.
Note 3 to entry: ”Effective” irradiance may include the effect of inhomogeneities in rear-side irradiance.
3.21
global horizontal irradiance
GHI
direct plus diffuse irradiance incident on the front side of a horizontal surface
−2
Note 1 to entry: Expressed in units of W·m .
Note 2 to entry: 𝐺𝐺𝐺𝐺𝐵𝐵 = 𝐷𝐷𝐷𝐷𝐵𝐵∙ cos𝑍𝑍 +𝐷𝐷𝐺𝐺𝐵𝐵 where Z is the solar zenith angle.
3.22
circumsolar
immediately surrounding the solar disk
3.23
direct normal irradiance
DNI
irradiance emanating from the solar disk and from the circumsolar region of the sky within a
subtended full angle of 5° falling on a plane surface normal to the sun’s rays
−2
Note 1 to entry: Expressed in units of W·m .
Note 2 to entry: 𝐺𝐺𝐺𝐺𝐵𝐵 = 𝐷𝐷𝐷𝐷𝐵𝐵∙ cos𝑍𝑍 +𝐷𝐷𝐺𝐺𝐵𝐵 where Z is the solar zenith angle.

– 14 – IEC 61724-1:2021 © IEC 2021
3.24
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 (see ISO 9488)
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.
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.
3.25
circumsolar ratio
fraction of measured direct normal irradiance (DNI) emanating from the circumsolar region of
the sky, i.e. within the angular acceptance of the DNI sensor but outside the solar disk
3.26
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 (see ISO 9488)
3.27
diffuse horizontal irradiance
G or DHI
d
global irradiance on the front side of a horizontal surface excluding the portion emanating from
the solar disk and from the circumsolar region of the sky within a subtended full angle of 5°
−2
Note 1 to entry: Expressed in units of W·m .
Note 2 to entry: 𝐺𝐺𝐺𝐺𝐵𝐵 = 𝐷𝐷𝐷𝐷𝐵𝐵∙ cos𝑍𝑍 +𝐷𝐷𝐺𝐺𝐵𝐵 where Z is the solar zenith angle.
3.28
in-plane direct beam irradiance
G
i,b
in-plane irradiance incident upon the front side of an inclined surface parallel to the plane of
the modules in the PV array emanating from the solar disk and from the circumsolar region of
the sky within a subtended full angle of 5°
Note 1 to entry: The in-plane direct beam irradiance 𝐺𝐺 = cos(𝜃𝜃) ×𝐷𝐷𝐷𝐷𝐵𝐵, where 𝜃𝜃 is the angle between the sun
𝑖𝑖,𝑏𝑏
and the normal to the plane. When the plane of array is normal to the sun, 𝐺𝐺 =𝐷𝐷𝐷𝐷𝐵𝐵.
𝑖𝑖,𝑏𝑏
−2
Note 2 to entry: Expressed in units of W·m .
3.29
irradiation
H
irradiance integrated over a specified time interval
−2
Note 1 to entry: Expressed in units of kW-h·m .
3.30
standard test conditions
STC
-2
in-plane irradiance 1 000 W⋅m , normal incidence, PV cell junction temperature 25 °C, and the
reference spectral irradiance defined in IEC 60904-3

IEC 61724-1:2021 © IEC 2021 – 15 –
3.31
soiling ratio
SR
ratio of the actual power output of the PV array under given soiling conditions to the power that
would be expected if the PV array were clean and free of soiling
3.32
soiling level
SL
fractional power loss due to soiling, given by 1 – SR
3.33
soiling rate
rate of change of soiling ratio, typically expressed in percent per day
3.34
active power
P
under periodic conditions, mean value, taken over one period, of the instantaneous product of
current and voltage
Note 1 to entry: Under sinusoidal conditions, the active power is the real part of the complex power.
Note 2 to entry: Expre
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