NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

HISTORY OF IEC QUALIFICATION 

STANDARDS

International PV Module 

QA Forum

John Wohlgemuth

July 15, 2011

NREL/PR-5200-52246
NATIONAL RENEWABLE ENERGY LABORATORY

Introduction

2

• The commercial success of PV is based on long term 

reliability of the PV modules.

• Today most PV modules are warrantied for 25 years.

• These modules are typically qualified to IEC 61215 or 

IEC 61646.

• These qualification tests do an excellent job of 

identifying design, materials and process flaws that 

could lead to premature field failures.

• This talk will provide a summary of how the 

qualification tests were developed and a review of their 

strengths and limitations.
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Evaluating Long Term Performance

3

• To evaluate long term performance outdoors we really 

need outdoor performance data.

• On the other hand we can not wait 25 years to 

determine if a module is going to have a 25 year 

lifetime.

• Therefore, we have to utilize outdoor test data to 

develop accelerated stress tests.

• Qualification Tests IEC 61215 for crystalline Si and 

IEC 61646 for Thin Films were developed this way. 

• Let’s review where the qualification tests came from 

and what they actually do.

• The first step in this process is to identify the various 

field failures that have been observed for PV modules.
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HISTORY OF FIELD FAILURES

4

• Broken interconnects

• Broken cells

• Corrosion 

• Delamination and/or loss of elastomeric properties of 

encapsulant

• Encapsulant discoloration 

• Solder bond failures

• Broken glass

• Hot Spots

• Ground faults

• Junction box and module connection failures

• Structural failures

• Bypass Diode failures

• Open circuiting leading to arcing
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Additional Failure Modes for Thin Film Modules

5

• Electro-chemical corrosion of TCO.

• Light Induced Degradation – Not really a reliability 

issue as long as it is predictable.

• Inadequate Edge Deletion

• Shunts at laser scribes

• Shunts at impurities in films
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Accelerated Stress Tests

6

• So now that we have a list of failures, we can develop tests 

that duplicate the failures in a fairly short time frame (at 

least compared to outdoor exposure).

• Our goals should be:

– To identify accelerated stresses that cause the same 

types of failures as seen in the field.

– To determine approximately how long the accelerated 

stress test must be performed in order to duplicate a 

reasonable amount of field exposure.

• In developing accelerated stress tests we must cause 

degradation in order to verify that our accelerated test is 

duplicating the failure mechanism we saw outdoors.
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Accelerated Stress Tests for PV

7

Accelerated Stress Test Failure Mode

Thermal Cycles Broken interconnect

Broken cell

Solder bond failure

Junction box adhesion

Module open circuit – potential for arcing

Damp Heat Corrosion

Delamination

Encapsulant loss of adhesion & elasticity

Junction box adhesion

Electrochemical corrosion of TCO

Inadequate edge deletion

Humidity Freeze Delamination

Junction box adhesion

Inadequate edge deletion
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Accelerated Stress Tests for PV (cont)

8

Accelerated Stress Test Failure Mode

UV Test Delamination

Encapsulant loss of adhesion & elasticity

Encapsulant & backsheet discoloration

Ground fault due to backsheet degradation

Static Mechanical Load

(Simulation of wind and snow load)

Structural failures

Broken glass

Broken interconnect ribbons

Broken Cells

Solder bond failures

Dynamic Mechanical Load Broken glass

Broken interconnect ribbons

Broken Cells

Solder bond failures
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Accelerated Stress Tests for PV (cont)

9

Accelerated Stress Test Failure Mode

Hot spot test Hot spots

Shunts in cells or at scribe lines

Inadequate by-pass diode protection

Hail Test Broken glass

Broken cells

By-pass Diode Thermal Test By-pass diode failures

Overheating of diode causing degradation 

of encapsulant, backsheet or junction box

Salt Spray Corrosion due to salt water & salt mist

Corrosion due to salt used for snow and 

ice removal

Ammonia Test Exposure to farm waste
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Qualification testing or Certification

10

• Qualification tests are a set of well defined accelerated 

stress tests developed out of a reliability program. 

• They utilize stress tests to duplicate failure modes 

observed in the field.

• They incorporate strict pass/fail criteria.

• The stress levels and durations are limited so the tests can 

be completed within a reasonable amount of time and cost.

• The goal for Qualification testing is that a significant 

number of commercial modules will pass. 

(If not there will be no commercial market.)

• Qualifies the design and helps to eliminate infant mortality
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History of Qualification Testing

11

JPL Block Buys I-V (1975-1981) – all crystalline Si

European Union Specifications 501 to 503 (1981-1991)

SERI IQT (1990) – modifications for thin films (a-Si)

IEEE 1262 (1995-2000) – all technologies

IEC 61215 (Ed 1 - 1993, Ed 2- 2005) – Crystalline Si

IEC 61646 (Ed 1 - 1996, Ed 2- 2007) – Thin Films
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History of JPL Block Buys

12

JPL Block buys incorporated a set of qualification tests in each 

procurement document.

Modules had to pass test sequence before manufacturer could deliver 

production quantities of modules.

So where did tests come from?

Block I tests were based on NASA tests utilized on space arrays.

– Thermal cycles extremes selected as -40 and +90 °C based on 

guesses for worst case conditions in terrestrial environment.

– The humidity test was for a short time because for space arrays 

exposure to humidity was limited to the time they were 

exposed before launch.

– These were really the only accelerated stress tests in Block I
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JPL Block Qualification Tests

13

Test I II III IV V

Thermal 

Cycles

100 

-40 to +90C

50

-40 to +90C

50

-40 to +90C

50

-40 to +90C

200

-40 to + 90C

Humidity 70C,90%

68 hrs

5 cycles

40 to 23C

90%

5 cycles

40 to 23C

90%

5 cycles

54 to 23C

90%

10 cycles

85 to -40C

85%

Hot Spot

(intrusive)

3 cells

100 hrs

Mechanical

Load

100 cycles

± 2400 Pa

100 cycles 

± 2400 Pa

10000 

± 2400 Pa

10000

± 2400 Pa

Hail 9 impacts

3⁄4” –45 mph

10 impacts

1” – 52 mph

High Pot <15 μA

1500 V

< 50 μA

1500 V

< 50 μA

1500 V

< 50 μA

2*Vs+1000
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Block Field Experience

14

The earliest Block modules were typically utilized in small 

remote site systems.

JPL report stated that “the major cause of module failure to 

date was by gun shot”. 

– Black or blue CZ cells on white background are good 

targets

– Squares cells on non-white back sheets reduced problem

Many early failures were due to cracked cells:

– Because of module design one cracked cell resulted in total 

loss of power.

Non glass superstrate modules suffered from significant 

soiling and delaminations usually due to UV. 
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Testing Development

15

Future procurements utilized modified qualification test 

specifications.

Block II 

– Added 100 mechanical load cycles – once again probably from 

space experience based on launch damage,

– Added a High Pot Test to insure electrical isolation 

– Changed the humidity test from a constant to 5 cycles between 23 

and 40C (Still was too mild a humidity test)

– Reduced the number of thermal cycles from 100 to 50

This was clearly a mistake. I don’t know why they reduced the 

requirement except to guess that Block I modules had a lot of 

trouble passing the 100 cycle test.

Block III 

– Changed the High Pot failure level from > 15 μA to > 50 μA as 

modules were getting bigger.

Block II and III modules were utilized in some larger systems and 

started to experience new failure modes.
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Lessons from Blocks II and III

16

Many Block II and III modules were used in desert environments

– Pagago Indian Reservation in AZ

– Tanguze, Upper Volta

– Natural Bridges, Utah

Modules that survived 50 thermal cycles began failing in the 

desert after 3 to 5 years due to broken interconnects and/or 

broken cells that resulted in total loss of module power.

– Module manufacturers started building in redundant interconnects 

and stress relief.

– Most new module types used glass superstrate construction, 

reducing the thermal expansion and contraction.

– In Block V Thermal Cycles increased to 200 to better evaluate 

module performance.

– JPL began recommending paralleling of cells, but modules built 

this way suffered from shunt related power loss and hot spot 

problems.
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Lessons from Blocks II and III (cont)

17

Hail did significant damage to modules built without 

tempered glass superstrates:

– Broken cells

– Broken annealed glass

Hail test added in Block IV.

Large (60 kW), high voltage system at Mt. Laguna, CA

– Part of array built with Solar Power modules (40 – 4” 

diameter CZ in series) with no by-pass diodes.

– Modules began suffering from hot spot failures.

Hot Spot Test Added in Block V
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Block VI

18

JPL was in the process of finalizing a Block VI 

Specification when the program fell victim to 

Reagan budget cuts.

Additions they were planning in 1985:

– Test for bypass diodes

– UV exposure test

– Damp heat (85C/85% RH)
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European PV Community 

19

Through ESTI the European Community worked on a 

PV Qualification Standard at the same time that JPL 

was working on Block Program.

European Standards 501 and 502 had some similarities 

to the Block V document with:

– Addition of UV Exposure Test

– Addition of Outdoor Exposure Test

– Reduction of thermal cycling maximum from 90 to 85

EU 503 was a draft of IEC 61215, utilized to begin 

testing to the new standard before it had completed 

voting by National Committees. 
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IEC 61215

20

International Standard incorporating the best ideas 

from around the world.

Blocks VI was the basis for 61215.

EU 502 provided UV Test, Outdoor Exposure Test and 

lower maximum temperature in thermal cycle.

Several tests from Block VI were not included in IEC 

61215 – most notably: – Dynamic Mechanical Load Test, because the test defined in 

Block V was unsuitable for large sized modules. 

– Bypass Diode Thermal Test, because international community 

didn’t think the test was adequately developed.

IEC 61215 rapidly became the qualification test to pass 

in order to participate in the PV marketplace, especially 

in Europe.
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SERI IQT 

21

SERI work on thin film modules (mostly a-Si) led to 

new “interim standard” for these modules

Biggest new issue was the high leakage current 

resulting from inadequate edge isolation of the TCO on 

the glass.

IQT added a Wet Insulation Resistance Test to test for 

this problem.

IQT also added:

– Ground continuity from UL 1703

– Cut Susceptibility Test from UL 1703

– Bypass diode Test from Block VI
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Thin Film PV Testing – IEEE 1262

22

IQT led to IEEE 1262 and then to IEC 61646.

IEEE 1262 

– Was a hybrid having components from IQT and IEC 61215. 

– It used the 61215 backbone of tests but incorporated the 

additions from IQT 

– It introduced annealing steps to address light induced 

degradation in a-Si.

IEEE 1262 served its purpose as the first consensus 

qualification test standard for thin film modules.

Once IEC 61646 was approved there was no reason to 

have 2 standards so IEEE 1262 was withdrawn.
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IEC - 61646

23

Written for the thin film modules available in 1996 –

they were mostly a-Si.

Combined ideas of IEC 61215 and IEEE 1262.

IEC 61646 added new concept of using thermal 

annealing and light soak in an attempt to characterize 

the power loss caused by the different accelerated 

tests.

Changes from IEC 61215

– Added wet leakage current test.

– Added light soak and anneal cycles.

– Added maximum output power at STC after final light soak 

as a pass/fail criteria
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IEC 61215 Edition 2

24

Twist test was eliminated

Wet leakage current test was added from IEC 61646 

Bypass diode thermal test was added from IEEE 1262 

Pass criteria for dielectric withstand and wet leakage 

current tests were made dependent on the test module 

area.

UV test was clearly labeled a preconditioning test

Added the requirement to run peak power current 

through the module during the 200 thermal cycles to 

evaluate a failure of solder bonds observed in the field.
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IEC 61646 Edition 2

25

An attempt to adapt IEC 61646 to different types of thin 

film modules.

Modified the pass/fail criteria – No longer relies on meeting a plus/minus criterion before and after 

each test

– Requires meeting the rated power after all of the tests have been 

completed and the modules have been stabilized

Twist test was eliminated

Pass criteria for dielectric withstand and wet leakage 

current tests were made dependent on the test module 

area.

Rewrote the Hot Spot Test.

Added by-pass diode thermal test

UV test was clearly labeled a preconditioning test
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IEC 61215 Outline

26
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Passing IEC 61215 or IEC 61646

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• So what does it mean if a module type is qualified to IEC 

61215 or IEC 61646?

• Passing the qualification test means the product has met a 

specific set of requirements.

• Those that have passed the qualification test are much 

more likely to survive in the field and not have design flaws 

that lead to infant mortality.

• Most of today’s commercial modules pass the qualification 

sequence with minimum change, meaning that they suffer 

almost no degradation in power output from the test 

sequence. 

• In many markets passing one of these qualification tests is 

a minimum requirement to participate.
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How Successful are the Qualification Tests?

28

• They must be fairly successful because the PV 

industry has been growing rapidly.

• The literature survey on degradation rates reported 

at PVSC by Jordan and Kurtz indicates that the 

Qualification Tests have been quite successful in 

identifying and eliminating module types that suffer 

large degradation rates early in their lifetime.

• There have been many reports of PV modules being 

the most reliable component in PV systems.
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Limitations of Qualification Tests

29

• By design the qualification tests have limitations.

• They do not test for wear out mechanisms.

• Previously reported (23rd EU PVSEC) an experiment 

where 10 crystalline Si module types (all previously 

qualified to IEC 61215) were tested for 500 thermals 

cycles and 1250 hours of damp heat.

 2 out of 10 module types failed 500 TC’s.

 8 out of 10 module types failed 1250 hours of DH

• Just knowing that a module type passed IEC 61215 

doesn’t tell you how well it will do in longer term 

testing or how long it will survive in the field.
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Testing for 25 year Lifetime

30

• What we would really like is to determine what 

accelerated stress levels would represent a 25 year 

lifetime to be consistent with the warranty.

• But we don’t know how to do that today. 

 We don’t know what combined set of stress tests would be 

a good predictor of a 25 year lifetime

 When those stress levels are determined, they are likely to 

depend on the geographic location where the module is 

deployed as well as how it is mounted.

• It was to address this situation that the International 

PV Module QA Forum was organized.