Measurement procedures for materials used in photovoltaic modules - Part 7-3: Accelerated stress tests - Methods of abrasion of PV module external surfaces

IEC 62788-7-3:2022 defines the test methods that can be used for evaluating the abrasion of materials and coatings in photovoltaic modules or other solar devices. This document may be applied to components on the incident surface (including coatings, frontsheet, and glass) as well as the back surface (including backsheets or back glass). This document is intended to address abrasion of PV module surfaces and any coatings present using representative specimens (e.g. which can be centimetres in size); the methods and apparatus used here can also be used on PV module specimens (e.g. meters in size).

Procédures de mesure des matériaux utilisés dans les modules photovoltaïques - Partie 7-3: Essais sous contraintes accélérés - Méthodes d’abrasion des surfaces externes des modules photovoltaïques

IEC 62788-7-3:2022 définit les méthodes d’essai qui peuvent être utilisées pour l’évaluation de l’abrasion des matériaux et revêtements des modules photovoltaïques ou autres dispositifs solaires. Le présent document peut être appliqué aux composants présents tant sur la surface concernée (y compris les revêtements, la feuille avant et le verre), que sur la face arrière (y compris les feuilles arrière ou le verre face arrière). Le présent document est destiné à traiter de l’abrasion des surfaces de modules photovoltaïques et tout revêtement présent au moyen d’éprouvettes représentatives (par exemple, dont la taille peut se mesurer en centimètres).

General Information

Status
Published
Publication Date
21-Feb-2022
Current Stage
PPUB - Publication issued
Completion Date
22-Feb-2022
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IEC 62788-7-3
Edition 1.0 2022-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Measurement procedures for materials used in photovoltaic modules –
Part 7-3: Accelerated stress tests – Methods of abrasion of PV module external
surfaces
Procédures de mesure des matériaux utilisés dans les modules
photovoltaïques –
Partie 7-3: Essais sous contraintes accélérés – Méthodes d’abrasion des
surfaces externes des modules photovoltaïques
IEC 62788-7-3:2022-02(en-fr)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 62788-7-3
Edition 1.0 2022-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Measurement procedures for materials used in photovoltaic modules –
Part 7-3: Accelerated stress tests – Methods of abrasion of PV module external
surfaces
Procédures de mesure des matériaux utilisés dans les modules
photovoltaïques –
Partie 7-3: Essais sous contraintes accélérés – Méthodes d’abrasion des
surfaces externes des modules photovoltaïques
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.160 ISBN 978-2-8322-1081-5

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 62788-7-3:2022 © IEC 2022
CONTENTS

FOREWORD ........................................................................................................................... 4

INTRODUCTION ..................................................................................................................... 6

1 Scope .............................................................................................................................. 7

2 Normative references ...................................................................................................... 7

3 Terms and definitions ...................................................................................................... 8

4 Artificial linear machine abrasion test (SAT01)................................................................. 8

4.1 Principle ................................................................................................................. 8

4.2 Apparatus ............................................................................................................... 8

4.2.1 Artificial linear machine abrasion apparatus ..................................................... 8

4.2.2 Brush ............................................................................................................... 9

4.2.3 Abrasive medium (dry) ..................................................................................... 9

4.2.4 Abrasive medium (wet slurry) ......................................................................... 10

4.3 Test specimens ..................................................................................................... 10

4.3.1 Materials and geometry ................................................................................. 10

4.3.2 Number of replicate specimens ...................................................................... 11

4.3.3 Reference material ........................................................................................ 11

4.4 Test procedure ...................................................................................................... 11

4.4.1 Setting up the apparatus and specimen ......................................................... 11

4.4.2 Performing the abrasion test .......................................................................... 12

4.5 Specimen preparation for examination after testing ............................................... 12

5 Artificial rotary machine abrasion test (SAT02) .............................................................. 13

5.1 General ................................................................................................................. 13

5.2 Apparatus ............................................................................................................. 13

5.2.1 Artificial rotary machine abrasion apparatus .................................................. 13

5.2.2 Brush ............................................................................................................. 14

5.2.3 Abrasive medium (dry) ................................................................................... 14

5.2.4 Abrasive medium (wet/slurry) ......................................................................... 15

5.3 Test specimens ..................................................................................................... 15

5.4 Test procedure ...................................................................................................... 15

5.5 Specimen preparation for examination after testing ............................................... 15

6 Falling sand test (SAT03) .............................................................................................. 15

6.1 Principle ............................................................................................................... 15

6.2 Apparatus ............................................................................................................. 15

6.2.1 Falling sand apparatus .................................................................................. 15

6.2.2 Abrasive medium ........................................................................................... 16

6.3 Test specimens ..................................................................................................... 16

6.3.1 General ......................................................................................................... 16

6.3.2 Number of replicate specimens ...................................................................... 16

6.4 Test procedure ...................................................................................................... 16

6.5 Specimen preparation for examination after testing ............................................... 17

7 Forced sand impingement test (SAT04) ......................................................................... 17

7.1 Principle ............................................................................................................... 17

7.2 Apparatus ............................................................................................................. 17

7.2.1 Forced sand impingement apparatus ............................................................. 17

7.2.2 Abrasive medium ........................................................................................... 17

---------------------- Page: 4 ----------------------
IEC 62788-7-3:2022 © IEC 2022 – 3 –

7.3 Test specimens ..................................................................................................... 18

7.4 Procedure ............................................................................................................. 18

7.5 Specimen preparation for examination after testing ............................................... 18

8 Test report ..................................................................................................................... 18

Annex A (informative) References describing the durability of materials to linear

abrasion................................................................................................................................ 20

Bibliography .......................................................................................................................... 21

Figure 1 – Schematic showing the arrangement of bristle tufts on the rotary brush ............... 14

---------------------- Page: 5 ----------------------
– 4 – IEC 62788-7-3:2022 © IEC 2022
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MEASUREMENT PROCEDURES FOR MATERIALS
USED IN PHOTOVOLTAIC MODULES –
Part 7-3: Accelerated stress tests –
Methods of abrasion of PV module external surfaces
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

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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.

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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.

IEC 62788-7-3 has been prepared by IEC technical committee 82:Solar photovoltaic energy

systems. It is an International Standard.
The text of this International Standard is based on the following documents:
Draft Report on voting
82/1987/FDIS 82/2009/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.
---------------------- Page: 6 ----------------------
IEC 62788-7-3:2022 © IEC 2022 – 5 –

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 62788 series, published under the general title Measurement

procedures for materials used in photovoltaic modules, 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: 7 ----------------------
– 6 – IEC 62788-7-3:2022 © IEC 2022
INTRODUCTION

There is a need for abrasion test methods in the PV industry, particularly for the front and back

surfaces of PV modules. This document defines a set of test methods to be used for evaluating

the abrasion of materials and coatings in photovoltaic modules or other solar devices. Linear

and rotary machine abrasion methods are specified that can be used to address durability to

abrasion with respect to the cleaning of solar devices. Linear abrasion is intended to emulate

traditional manual methods of cleaning, where the cleaning equipment typically acts

perpendicular to the surface, giving a scratching motion. Rotary abrasion is intended to emulate

popular robotic methods of cleaning, where the cleaning element often may act along the

surface in a swiping motion. Relative to DIN 53778-2 and ASTM D2486, application specific

modifications for the machine abrasion tests include the longer bristle length, use of abrasive

(test dust) of the size encountered in PV, the use of dry or wet abrasive as may be encountered

during cleaning modules, and the number of test cycles relative to the maintenance of PV

systems. A falling sand method is specified that can be used to address durability to abrasion

with respect to damage from ordinary use in the application environment, i.e., typically

meteorological events. Relative to DIN 52348, modifications include the quantity of test sand,

which is intended for examination of PV surfaces and coatings. A forced sand impingement

method is specified that can be used to address durability to abrasion from severe weather

events and/or the most challenging locations of use. Relative to IEC 60068-2-68, modifications

include the composition of test sand that may be compared to the PV application and the falling

sand test in this document as well as the specified carrier velocities based on the PV

application. The methods in this document can be used to aid performance analysis and/or for

the purpose of material design/selection. Comparing the linear brush, rotary brush, falling sand,

and forced impingement methods, different rates of abrasion and/or damage morphology can

occur between the different test methods – they are not expected to produce the same result.

Formal working reference materials are identified in this document. The purpose of the working

reference is to verify the apparatus is installed and working correctly. The characteristic(s) of

interest can be verified on a regular basis (monthly, weekly, etc.). The characteristic(s) of

interest and their values (with acceptance limits for precision) will be given in a referencing

document or future version of this document, based on the results of an interlaboratory precision

study.
---------------------- Page: 8 ----------------------
IEC 62788-7-3:2022 © IEC 2022 – 7 –
MEASUREMENT PROCEDURES FOR MATERIALS
USED IN PHOTOVOLTAIC MODULES –
Part 7-3: Accelerated stress tests –
Methods of abrasion of PV module external surfaces
1 Scope

This part of IEC 62788 defines the test methods that can be used for evaluating the abrasion

of materials and coatings in photovoltaic modules or other solar devices. This document may

be applied to components on the incident surface (including coatings, frontsheet, and glass) as

well as the back surface (including backsheets or back glass). This document is intended to

address abrasion of PV module surfaces and any coatings present using representative

specimens (e.g. which can be centimetres in size); the methods and apparatus used here can

also be used on PV module specimens (e.g. meters in size). A suite of tests and their methods

are identified in this document, including falling sand, forced sand impingement, and machine

(brush) abrasion. Materials and coatings can have different intended design purposes and

design lifetimes and therefore no specific pass/fail criteria are defined in this document. The

results of the testing can, however, be used to identify relative durability of coatings for various

outdoor environments and cleaning practices. The methods can be used for the purpose of

relative comparison, e.g. for the purpose of material or coating selection. The quantitative

correlation between artificial abrasion and field erosion (which will depend on factors including

climate or location of use as well as application, e.g., use of a tracker, rack-mount, roof-mount,

building integrated, or vehicle integrated PV) can be established for each specific material or

coating, which is beyond the scope of this document.

The correlation between the rates of degradation from the different test methods (linear brush,

rotary brush, falling sand, and forced impingement) is beyond the scope of this document and

may be covered in referencing documents. The correlation between the rates of degradation for

unaged and aged specimens is also beyond the scope of this document and may be covered in

referencing documents.

The methods related to the characterization of abraded specimens (which might include optical

transmittance, optical reflectance, surface roughness, and surface energy) are not defined in

this document; characterization methods from other standards (including optical transmittance,

optical reflectance, electrical performance, surface roughness, and surface energy) can be

applied to specimens abraded using the methods defined in this document. Methods for

examining the contamination of specimens, including artificial soiling, are not examined in this

document. Additional specimen conditioning can be applied prior to the methods in this

document. The abrasion tests in this document can be referenced and/or applied in conjunction

with an accelerated test or test sequence in other standards.
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 60068-2-68, Environmental testing – Part 2-68: Tests – Test L: Dust and sand
IEC TS 61836, Solar photovoltaic energy systems – Terms, definitions and symbols
ISO 291, Plastics – Standard atmospheres for conditioning and testing
---------------------- Page: 9 ----------------------
– 8 – IEC 62788-7-3:2022 © IEC 2022

ISO 12103-1, Road vehicles – Test contaminants for filter evaluation – Part 1: Arizona test dust

ASTM D2486, Standard test methods for scrub resistance of wall paints

DIN 52348:1985-02, Testing of glass and plastics; abrasion test; sand trickling method

DIN 53778-2:1983-08, Emulsion paints for interior use; evaluation of cleanability and of wash

and scrub resistance of coatings
MIL-STD-810G, Environmental engineering considerations and laboratory tests

VDI 3956, Evaluation of the soiling properties of surfaces – Test method for the dust soiling

behaviour of solar energy systems
3 Terms and definitions

For the purposes of this document, the terms and definitions given in IEC TS 61836 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
artificial abrasion

wear resulting from the cleaning of a PV device, including manual or robotic cleaning

3.2
natural erosion
wear resulting from the ordinary terrestrial use of a PV device

Note 1 to entry: Sources of erosion may include particulate impingement, particulate transport (from wind or water),

or autonomous scraping (from snow or ice by gravity).
4 Artificial linear machine abrasion test (SAT01)
4.1 Principle

The machine abrasion methods are specified that can be used to address durability to abrasion

with respect to the cleaning of solar devices. Linear abrasion is intended to emulate traditional

manual methods of cleaning, where the cleaning equipment typically acts perpendicular to the

surface, giving a scratching motion. The test is typically applied to the irradiance incident

surface of a PV module. Because either dry or wet cleaning may be used to clean a PV module,

both dry and wet (slurry) abrasives may be used in this test. The test may simulate the cleaning

of fixed, tracked, or vehicle integrated PV.
4.2 Apparatus
4.2.1 Artificial linear machine abrasion apparatus

A linear abrasion apparatus fulfilling the requirements of ASTM D2486 or DIN 53778-2 shall be

used. Essential components of the apparatus include: a linear abrasion mechanism, a brush,

an abrasive dispenser (slurry or dry abrasive), and an enclosure (if applicable). An enclosure

is recommended for the apparatus to prevent spilling or spraying of abrasive (dry or wet slurry

abrasives) or the possibility of silicosis (with ventilation, for dry abrasive). Additional equipment

and containers for the management of waste abrasive and its disposal after the test is advised.

---------------------- Page: 10 ----------------------
IEC 62788-7-3:2022 © IEC 2022 – 9 –

The abrasion mechanism shall provide a brush stroke length of at least 14,5 cm. The brush may

operate at either a constant or varied velocity through each stroke. The brush velocity of

30 ± 3 cm⋅s shall be used for the through the central 7,5 cm test region on the specimen

during machine abrasion testing. Other test rates may be used for the purposes of research

and development.

NOTE For example, the brush velocity of 30 cm⋅s , when used with a stroke length of 25,4 cm corresponds to a

test rate of 37± 1 cycles per minute.

Specimens shall be rigidly mounted relative to the apparatus using mechanical springs or

clamps, tape or other means.

To ensure repeatability of results (i.e., avoid temperature-related effects related to the abrasion

process or abrasive) the apparatus shall be maintained, in a laboratory maintained at

(23 ± 2) °C, (50 ± 10) % RH, as specified per Class 2 in ISO 291.

The dispenser for dry dust shall be separated from the specimen surface by at least 10 cm to

provide clearance for the motion of the brush (in both linear and rotary configurations) and also

aid dispensing to the designated test area of the specimen.

The dispenser for wet slurry shall be separated from the specimen surface by at least 5 cm to

aid dispensing to the designated test area of the specimen.
4.2.2 Brush

The brush block shall be (35 ± 1) mm × (85± 1) mm in area and (13 ± 1) mm in thickness.

The brush bristles shall consist of polyamide 612, (0,23 ± 0,03) mm in diameter that extend

(38 ± 2) mm from the brush block. Brushes with bristles shorter than 35 mm in length shall be

replaced. The bristle profile shall be round, with no taper or other change in geometry along

their length. The lateral space of 12 mm shall be used for the bristle tuft columns along the

length of the brush, with a offset space of 4 mm between rows and lateral offset space of 6 mm

between adjacent bristle columns. The bristle tufts shall be staggered in a 5-4-5-4-... pattern

along the brush, with total of 59 tufts. The bristle count shall be (158 ± 6) tips⋅tuft

A 325 g external weight shall be used with the brush, as in ASTM D2486. The nominal brush

weight of 125 g includes the dry weight of brush block and bristles. The nominal brush net

weight (including 5 g attachment bolt) shall be 455 ± 10 g, including the dry weight of brush

block, bristles, external weight, fasteners, and holder. The nominal contact force of 4,46 N shall

result from the self-weight of the components; no spring or other external force shall be used.

4.2.3 Abrasive medium (dry)

The dry abrasive medium shall consist of A3 (medium) AZ test dust, as specified in

−2 −1

ISO 12103-1. The nominal abrasive concentration of (0,7) mg⋅cm ⋅cycle shall be used during

the test. To ensure
...

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