Photovoltaic system performance - Part 1: Monitoring

IEC 61724-1:2021 is available as IEC 61724-1:2021 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.
IEC 61724-1:2021 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. This document defines classes of photovoltaic (PV) performance monitoring systems and serves as guidance for monitoring system choices. This second edition cancels and replaces the first edition, published in 2017. 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.

Performances des systèmes photovoltaïques - Partie 1: Surveillance

IEC 61724-1:2021 est disponible sous forme de IEC 61724-1:2021 RLV qui contient la Norme internationale et sa version Redline, illustrant les modifications du contenu technique depuis l'édition précédente.
L'IEC 61724-1:2021 présente une terminologie, des équipements et des méthodes relatifs à la surveillance des performances et à l’analyse des systèmes photovoltaïques (PV). Elle sert également de base à d’autres normes qui s’appuient sur les données collectées. Cette deuxième édition annule et remplace la première édition parue en 2017. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
- Présentation de la surveillance des modules PV bifaciaux.
- Mise à jour des exigences relatives aux capteurs d’éclairement énergétique.
- Mise à jour du mesurage de l’encrassement pour tenir compte des nouvelles technologies.
- Suppression des systèmes de surveillance de classe C.
- Mise à jour de différentes exigences, recommandations et notes explicatives.

General Information

Status
Published
Publication Date
20-Jul-2021
Current Stage
PPUB - Publication issued
Completion Date
21-Jul-2021
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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
IEC 61724-1:2021-07(en-fr)
---------------------- Page: 1 ----------------------
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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

Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 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

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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

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– 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

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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

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– 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

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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.
---------------------- Page: 8 ----------------------
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.
---------------------- Page: 9 ----------------------
– 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

...

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