Photovoltaic (PV) modules - Test methods for the detection of potential-induced degradation - Part 2: Thin-film

IEC TS 62804-2:2022 defines apparatus and procedures to test and evaluate the durability of photovoltaic (PV) modules to power loss by the effects of high voltage stress in a damp heat environment, referred to as potential-induced degradation (PID). This document defines a test method that compares the coulomb transfer between the active cell circuit and ground through the module packaging under voltage stress during accelerated stress testing with the coulomb transfer during outdoor testing to determine an acceleration factor for the PID.
This document tests for the degradation mechanisms involving mobile ions influencing the electric field over the semiconductor absorber layer or electronically interacting with the films such that module power is affected.

General Information

Status
Published
Publication Date
28-Mar-2022
Current Stage
PPUB - Publication issued
Completion Date
29-Mar-2022
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IEC TS 62804-2:2022 - Photovoltaic (PV) modules - Test methods for the detection of potential-induced degradation - Part 2: Thin-film
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IEC TS 62804-2
Edition 1.0 2022-03
TECHNICAL
SPECIFICATION
colour
inside
Photovoltaic (PV) modules – Test methods for the detection of potential-induced
degradation –
Part 2: Thin-film
IEC TS 62804-2:2022-03(en)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC TS 62804-2
Edition 1.0 2022-03
TECHNICAL
SPECIFICATION
colour
inside
Photovoltaic (PV) modules – Test methods for the detection of potential-
induced degradation –
Part 2: Thin-film
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.160 ISBN 978-2-8322-1093-6

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

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC TS 62804-2:2022  IEC 2022
CONTENTS

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

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

1 Scope .............................................................................................................................. 9

2 Normative references ...................................................................................................... 9

3 Terms and definitions .................................................................................................... 10

4 Samples ........................................................................................................................ 10

5 Tests ............................................................................................................................. 11

5.1 General ................................................................................................................. 11

5.2 Test procedures – Outdoor measurements ............................................................ 12

5.2.1 General ......................................................................................................... 12

5.2.2 Apparatus ...................................................................................................... 12

5.2.3 Optional monitoring ....................................................................................... 15

5.2.4 Test conditions .............................................................................................. 16

5.2.5 Procedure ...................................................................................................... 16

5.2.6 Acceleration by elevated system voltage testing outdoors .............................. 19

5.3 Test procedures – Accelerated testing in environmental chamber ......................... 21

5.3.1 General ......................................................................................................... 21

5.3.2 Test of modules in the dark and unpowered state .......................................... 22

5.3.3 Testing in chamber with light bias or current .................................................. 29

5.3.4 Acceleration factor determination—coulomb basis ......................................... 36

6 Test report ..................................................................................................................... 37

Annex A (normative) Evaluation for moisture ingress sensitivity ........................................... 40

A.1 General ................................................................................................................. 40

A.2 Procedure ............................................................................................................. 40

A.3 Evaluation ............................................................................................................. 41

Annex B (informative) Dew point and required chamber relative humidity (RH)

setpoints depending on temperature difference between module and the chamber air ......... 43

Bibliography .......................................................................................................................... 44

Figure 1 – Circuit suitable for electrical loading, application of system voltage bias and

evaluation of leakage current from the module on the ground return-side .............................. 14

Figure 2 – Module mounting configuration for isolation and measurement of current

transfer to ground ................................................................................................................. 15

Figure 3 – Circuit suitable for electrical loading, application of system voltage bias and

evaluation of leakage current from the module ...................................................................... 15

Figure 4 – Test flow for performing PID tests in the field associated with procedures

described in 5.2.2 to 5.2.5 for evaluation of coulombic transfer from the cell circuit of

the module to earth ............................................................................................................... 17

Figure 5 – PID test flow for performing voltage stress test with module dark and

unpowered ............................................................................................................................ 23

Figure 6 – Apparatus for applying system voltage bias (Vsys) to a PV module in an

environmental chamber ......................................................................................................... 25

Figure 7 – Example test time-temperature-humidity-voltage profile for application of

stress in an environmental chamber ...................................................................................... 27

Figure 8 – Schematic for isolated power supply for application of forward bias voltage

(V ) ..................................................................................................................................... 30

fwd
---------------------- Page: 4 ----------------------
IEC TS 62804-2:2022  IEC 2022 – 3 –

Figure 9 – Schematic for application of system voltage (Vsys) bias on test module on

normally grounded parts ....................................................................................................... 31

Figure 10 – Apparatus for applying system voltage bias (Vsys) to a PV module in an

environmental chamber under light bias ................................................................................ 32

Figure 11 – PID test flow for modules placed under voltage stress and with light bias

or dark forward bias voltage .................................................................................................. 33

Figure A.1 – Test flow for modules to detect and evaluate moisture ingress on PID

rate ....................................................................................................................................... 41

Table 1 – General schema of test procedures ....................................................................... 12

Table 2 – PID chamber test report table (example) (Variables are given in 5.3.2.3.3.7

and 5.3.4.1) .......................................................................................................................... 38

Table 3 – PID chamber recovery test report table (example) (Variables are given in

5.3.3.4) ................................................................................................................................. 38

Table B.1 – Dew point and required chamber relative humidity (RH) setpoints

depending on temperature difference between module and the chamber air ......................... 43

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– 4 – IEC TS 62804-2:2022  IEC 2022
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
PHOTOVOLTAIC (PV) MODULES – TEST METHODS FOR
THE DETECTION OF POTENTIAL-INDUCED DEGRADATION –
Part 2: Thin-film
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

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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 TS 62804-2 has been prepared by IEC technical committee 82: Solar photovoltaic energy

systems. It is a Technical Specification.
The text of this Technical Specification is based on the following documents:
Draft Report on voting
82/1958/DTS 82/2001A/RVDTS

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 Technical Specification is English.

A list of all parts in the IEC 62804 series, published under the general title Photovoltaic (PV)

modules – Test methods for the detection of potential-induced degradation, can be found on

the IEC website.
---------------------- Page: 6 ----------------------
IEC TS 62804-2:2022  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/publications.

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.

IMPORTANT – The "colour inside" logo on the cover page of this document indicates that it

contains colours which are considered to be useful for the correct understanding of its

contents. Users should therefore print this document using a colour printer.
---------------------- Page: 7 ----------------------
– 6 – IEC TS 62804-2:2022  IEC 2022
INTRODUCTION

Potential-induced degradation (PID) refers to any PV module degradation that is caused by the

stress of an electric potential between the active cell circuit and the external surfaces or parts

of the PV module.

The applied stresses, with system voltage being the principal factor in IEC 62804 series

documents, manifest themselves in different degradation modes that depend in part on the

module technology. Therefore, a series of technical specifications is being developed to define

PID tests for different PV module technologies and differing PID modes.

IEC TS 62804-1:2015, Photovoltaic (PV) modules – Test methods for the detection of potential-

induced degradation – Part 1: Crystalline silicon defines test methods for evaluating power loss

by PID in crystalline silicon PV modules.

IEC TS 62804-1-1:2020, Photovoltaic (PV) modules – Test methods for the detection of potential-

induced degradation – Part 1-1: Crystalline silicon – Delamination defines a test method for

evaluating delamination by PID associated with electrochemical processes in crystalline silicon

PV modules.

This part of IEC 62804 defines test methods for evaluating power loss by PID in thin-film PV

modules with moisture sensitive components and those which use moisture barrier
encapsulation because of such sensitivity.

A future document will be required for evaluating corrosion and delamination associated with

electrochemical processes in thin-film PV modules and modules with moisture sensitive

components with moisture barrier packaging. Further documents in the series may be

introduced in the future for emerging module technologies, mechanisms, or evaluation methods.

In addition to the IEC 62804 series, IEC 61215-2:2021 contains a PID test (MQT 21) with

methods and severities from IEC TS 62804-1: 2015 method (a) with modifications to avoid some

recognized test-specific degradation and polarization for application to various flat plate module

types. The PID test method in IEC 61215-2:2021 is shorter and simpler than those given in this

document.

Voltage potential that exists between the active circuit and the module surfaces directly or

indirectly connected to earth can lead to module degradation by multiple mechanisms including

ionic transport in the encapsulant, superstrate or substrate; hot carriers in the cell, redistribution

of charges that degrade the active layer of the cell or its surfaces, failure of adhesion at

interfaces, and corrosion of module components. Along with the factor of system voltage, these

processes are most active in wet or damp environments, and in environments prone to soiling

of modules with conductive, acidic, caustic, or ionic species that lead to increased conduction

on the module surfaces. Certain failure mechanisms may only be active with the module

electrically biased in one polarity depending on the cell construction, module materials, and

design. The testing in this document therefore specifies the evaluation of the effects of voltage

stress in both polarities for modules that may be operated in either polarity, or when applicable,

uniquely in the polarity defined by the manufacturer’s documented specifications and

installation instructions.

Considering this document is applicable to modules with a functional moisture barrier packaging,

a procedure is provided in Annex A to evaluate the functionality of the moisture barrier for the

purposes of PID evaluation. If the moisture barrier is not sufficiently functional, the moisture

ingress is likely to affect (usually increase) PID rate during accelerated testing in the

environmental chamber and largely invalidate projections that this document provides about

PID rate in the field.

There are many module designs, which span crystalline silicon, compound semiconductor, thin-

film and tandem technologies. These can exhibit differing sensitivities of the absorber layer,

differing laminate constructions and interfaces, and different mounting types with differing

ability to resist charge transfer between the laminate and ground. Based on the great variability

in acceleration factor between use condition and test, which has been measured in one instance

involving a thin-film module technology to vary between one and two orders of magnitude with

---------------------- Page: 8 ----------------------
IEC TS 62804-2:2022  IEC 2022 – 7 –

the singular change of the edge clip material holding the module [1] , a unique stress level for

accelerated testing of all module types covered by this document is not given at this time.

Instead, a protocol for evaluating the acceleration factor for PID degradation of thin film modules

with respect to climate zones is provided. Use of the acceleration factor method is therefore

motivated because considerable variability in acceleration factor has been found depending on

the thin film product and mounting [1]. Whether the phenomenon is specific to thin film products

has not been clarified.

To overcome the significant variability, this document offers procedures for evaluating the

relative rate (or acceleration) of current transfer and degradation in the chamber versus the

field, which has been found useful for evaluating thin-film technologies in the absence of the

variable of moisture ingress into the module [2-6]. The user may therefore calculate the relative

PID resistance in the chamber condition versus the field condition which to better forecast the

power degradation rate by PID in the use. Using of rate of coulomb transfer in the field and

chamber as a basis provides a platform for comparison of test results. With the understanding

of how many coulombs are transferred in the use environment per year, one can project power

loss by PID for the desired number of years in the use environment based on the measured

coulombs transferred and any observed power loss by PID in the environmental chamber, in

the absence of moisture ingress and significant power recovery if the factor of system voltage

bias is removed.

Differing module constructions transfer PID-inducing current between the cells and ground

differently as a function of extent of moisture on the surfaces and temperature. The charge

density profile of transferred coulombs across the module will vary as a function of temperature

and humidity on the module surfaces as well. To maintain representative temperatures and

humilities for the PID testing, an option to accelerate the PID testing with the factor of elevated

system voltage in the field is additionally offered in this document.

Thin-film modules may exhibit metastability and other effects, whereby the history of exposure

to factors including light and heat may influence power performance either reversibly or

irreversibly. Without attention to this, such effects can hinder the quantification of the PID

incurred in the PID stress test. To normalize for such extraneous power changes exhibited by

modules in this PID test, the power performance after a PID chamber stress test is examined

relative to any change in power of in-chamber control modules undergoing the same stress

regime excluding the factor of system voltage stress.

This document also includes options to mitigate power changes due other test-specific effects

resulting from the unrepresentative conditions of heat and darkness that IEC 61215-2 MQT 19,

Stabilization, alone will not correct. These options include application of light or forward bias

voltage before and during the PID stress test. This document additionally contains a light and

heat exposure sequence that may be optionally applied to the modules after the PID stress test

to obtain the power performance of the module after such recovery procedure. During

IEC 61215-2 MQT 19, Stabilization, the factor of system voltage is not applied, a condition that

does not normally occur in the field.

The voltage levels applied in testing are the modules’ nameplate-rated system voltage. This

results in a voltage level that is typically above that experienced in the field because:

a) voltage levels are reduced due to their elevated operating temperature under sunlight,

b) they are operated at maximum power and therefore a lower maximum power voltage than

system voltage that is associated with the open-circuit voltage of the modules,
c) most of the modules are not at the extremes of the series string, and

d) due to safety factors or other design criteria, modules may be in strings below the module

rated system voltage.
Numbers in square brackets refer to the Bibliography.
---------------------- Page: 9 ----------------------
– 8 – IEC TS 62804-2:2022  IEC 2022

However, modules connected in series strings that are in open circuit and uncontrolled by a

maximum power tracker, for reasons including being disconnected from their load, may

experience uncontrolled and significantly higher voltages than experienced by the modules

maintained at the maximum power point even though system installation standards require

voltage levels to be below system voltage. The voltage levels applied in testing is thus the

modules’ nameplate-rated system voltage. This provides a small element of acceleration over

typical use conditions, while maintaining a system voltage level that modules may actually

experience in the field.

It is known that variability in manufacturing processes can affect the susceptibility of modules

to system voltage stress. Periodic retesting of modules by the test protocols contained herein

with internal quality assurance programs such as given in IEC 62941, and with external audits,

will aid in verifying not only the durability of the design of the module to system voltage stress,

but also the effects of any variability of the materials and manufacturing processes. Due to the

extended length of time required to perform the tests contained herein, it is anticipated that

module manufacturers themselves will apply them.
---------------------- Page: 10 ----------------------
IEC TS 62804-2:2022  IEC 2022 – 9 –
PHOTOVOLTAIC (PV) MODULES – TEST METHODS FOR
THE DETECTION OF POTENTIAL-INDUCED DEGRADATION –
Part 2: Thin-film
1 Scope

This part of IEC 62804 defines apparatus and procedures to test and evaluate the durability of

photovoltaic (PV) modules to power loss by the effects of high voltage stress in a damp heat

environment, referred to as potential-induced degradation (PID). This document defines a test

method that compares the coulomb transfer between the active cell circuit and ground through

the module packaging under voltage stress during accelerated stress testing with the coulomb

transfer during outdoor testing to determine an acceleration factor for the PID. It is designed

for thin-film PV modules and modules containing moisture sensitive films protected by vapour

barrier packaging, principally with one or two glass surfaces. This document tests for the

degradation mechanisms involving mobile ions influencing the electric field over the

semiconductor absorber layer or electronically interacting with the films such that module power

is affected. This document does not specifically test for electrochemical corrosion or

delamination associated with application of system voltage. This document does not contain

pass or fail criteria and it is not intended for design qualification.

The procedures contained herein, with testing in chamber in combination with in the field or

testing in the field alone are intended for use when it is desired to quantify the acceleration

provided by the applied stress levels over regular use conditions in the natural environment

using coulombs transferred between the module and ground as the index for damage incurred

by PID. The procedures for quantifying the acceleration are not recommended when coulombs

transferred are not an indicator of damage by PID to the module. The procedures are not directly

applicable when moisture ingress into the module laminate occurs affecting PID rate, and to the

extent that there is power recovery when the factor of system voltage bias is removed after

correctly applying the procedures herein, within the period of testing.

The protocols given herein give results according to the chamber stress levels applied and the

module grounding configuration used in the test. Because the stress method of testing in an

environmental chamber employs a non-condensing humidity level to serve as a conductive

pathway to electrical ground, it frequently applies relatively less stress toward the centre of the

module face. Also, the method can evaluate the effectiveness of some construction methods to

mitigate PID; for example, the use of rear rail mounts, edge clips, and insulating frames. The

test, however, does not include all the factors existing in the natural environment that can affect

the PID rate. The actual durability of modules to system voltage stress depends on the actual

environmental conditions under which they are operated.
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 60068-2-78:2012, Environmental testing – Part 2-78: Tests – Test Cab: Damp heat, steady

state
IEC 60529, Degrees of protection provided by enclosures (IP Code)

IEC 60721-2-1:2013, Classification of environmental conditions – Part 2-1: Environmental

conditions appearing in nature – Temperature and humidity

IEC 60904-1, Photovoltaic devices – Part 1: Measurement of photovoltaic current-voltage

characteristics
---------------------- Page: 11 ----------------------
– 10 – IEC TS 62804-2:2022  IEC 2022

IEC 60904-3, Photovoltaic devices – Part 3: Measurement principles for terrestrial photovoltaic

(PV) solar devices with reference spectral irradiance data

IEC TS 60904-13, Photovoltaic devices – Part 13: Electroluminescence of photovoltaic modules

IEC 61215-1, Terrestrial photovoltaic (PV) modules – Design qualification and type approval –

Part 1: Test requirements
IEC 61215-2:2021, Terrestrial photovoltaic (
...

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