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Contract No. DE-AC36-08GO28308

A Framework for a Comparative 

Accelerated Testing Standard for 

PV Modules

Preprint

Sarah Kurtz1, John Wohlgemuth1, Masaaki Yamamichi2, 

Tony Sample3

, David Miller1, David Meakin4, 

Christos Monokroussos5

, Mani TamizhMani6, 

Michael Kempe1

, Dirk Jordan1, Nick Bosco1, 

Peter Hacke1

, Veronica Bermudez7, and Michio Kondo2

1

National Renewable Energy Laboratory

2

National Institute of Advanced Industrial Science and 

Technology (AIST)

3

European Commission, DG Joint Research Centre IET, 

Renewable Energies Unit

4

Fraunhofer Center for Sustainable Energy Systems CSE

5

TUV Rheinland, Shanghai, China

6

TUV Rheinland PTL, Tempe, Arizona

7

NEXCIS Photovoltaic Technology

Presented at the 39th IEEE Photovoltaic Specialists Conference

Tampa, Florida

June 16–20, 2013

Conference Paper

NREL/CP-5200-57838

August 2013
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A Framework for a Comparative Accelerated Testing Standard for PV 

Modules

Sarah Kurtz1, John Wohlgemuth1, Masaaki Yamamichi2, Tony Sample3, David Miller1, David Meakin4, 

Christos Monokroussos5

, Mani TamizhMani6, Michael Kempe1, Dirk Jordan1, Nick Bosco1, Peter Hacke1, 

Veronica Bermudez7

, Michio Kondo2

1

National Renewable Energy Laboratory, Golden, CO, USA

2

National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan

3

European Commission, DG Joint Research Centre IET, Renewable Energies Unit, Ispra, Italy

4

Fraunhofer Center for Sustainable Energy Systems CSE, Albuquerque, NM, USA

5

TUV Rheinland, Shanghai, China

6

TUV Rheinland PTL, Tempe, Arizona, USA

7

NEXCIS Photovoltaic Technology, Rousset, France

Abstract — As the photovoltaic industry has grown, the interest 

in comparative accelerated testing has also grown. Private test 

labs offer testing services that apply greater stress than the 

standard qualification tests as tools for differentiating products 

and for gaining increased confidence in long-term PV 

investments. While the value of a single international standard 

for comparative accelerated testing is widely acknowledged, the 

development of a consensus is difficult. This paper strives to 

identify a technical basis for a comparative standard. 

Index Terms — photovoltaic modules, accelerated testing, 

service lifetime, wear-out mechanisms, field failures.

I. INTRODUCTION

Since 2009, the prices of photovoltaic modules have fallen 

by almost a factor of three [1], putting pressure on 

manufacturers to develop lower cost products or to justify a 

higher selling price. As customers wish to gain confidence in 

the long-term performance of PV modules and to differentiate 

those products that will last longer, the interest in 

differentiation of products through more thorough, accelerated 

testing has increased. Building on the definition proposed by 

TamizhMani and Kuitche [2], we define “comparative” tests 

as accelerated tests that differentiate products according to 

their long-term durability in the field for a specific use 

environment (Table I). In contrast, qualification tests identify 

design flaws that lead to early failures; lifetime tests predict 

service life in the desired location and application. While 

lifetime prediction is desired, we do not currently have enough 

information about PV module reliability to define a servicelife prediction test.

Many test laboratories now offer comparative accelerated 

testing, as summarized in Table II. These test programs 

generally apply the same tests as the qualification tests, but 

apply them for a longer duration or combine existing tests in a 

test sequence. The primary themes we observed in a review of 

this collection of tests include 1) extended-duration, 2)

sequential tests, 3) quantification of module condition after 

each test, 4) additional measurements (e.g., electroluminescence), and 5) addition of voltage bias during damp heat.

TABLE I. THREE TYPES OF ACCELERATED TESTS [2] 

Qualification Comparative Lifetime

Purpose 

Minimum 

design 

requirement

Comparison 

of products 

Substantiation 

of warranty

Quantification Pass/fail Relative Absolute

Climate or 

Application 

(Mounting)

Not 

differentiated Differentiated Differentiated 

TABLE II. ACCELERATED TEST PROGRAMS

DH: Damp heat, TC: Thermal cycling, DML: Dynamic mechanical load, 

DHWB: Damp heat with bias, HF: Humidity freeze, HS: Hot spot. 

Program Name Extra Test 

Sequences* Key Features 

Test 

Length 

(Months)**

Holistic QA 

[3,4] DH, TC, DML Extended 61215 ~4

Thresher [5] DHWB, TC, 

HF 

Document 

degradation after 

each test cycle

~6

Reliability 

Demonstration 

[6]

DHWB, HS Comprehensive ~6

Durability 

Initiative [7] 

DHWB, 

Outdoor, UV, 

HS, DML, TC

Durability 

assessment ~6+ 

Test to Failure 

[8,9] DHWB, TC Test to failure >12 

Long-Term 

Sequential [10]

UV, DH, TC, 

HF

Sequential (passfail) ~12+ 

PV+Test [11] DHWB, TC, 

ML Assign rating ~4

Weather 

[12,13] Multiple*** Simulates weather ~12 

 * Beyond IEC 61215 or IEC 61646 test sequences 

 ** A “+” indicates additional testing in the field 

*** Not based on IEC 61215/61646 test sequences 

There are few data directly indicating the value of these 

longer tests for predicting field performance. The comparison 

of accelerated test results with field data is challenging 

because of the different time scales. However, early PV 

systems have now been in the field for > 30 years, and each 

year more data become available from veteran systems [14]. 
2 This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.

The current qualification tests [15-17] have the stated

scopes: to show “that the module is capable of withstanding 

prolonged [or long-term] exposure in...general open-air 

climates.” These standards do not quantify the meaning of the 

terms “long-term” and “prolonged,” but IEC 60721-2-1 

defines the “general” climate, providing a basis for further 

standards. 

This paper briefly summarizes what is known about 

correlations between field and accelerated testing, and uses 

this information to formulate recommendations for a 

comparative accelerated test standard. We start by reviewing

what was learned from a somewhat similar effort more than 30 

years ago, and then review newer field data to provide a basis 

for the types of mechanisms that need to be prioritized. Based 

on this prioritization and on principles the community agrees 

upon, a rating system for a comparative accelerated test 

standard is proposed as a starting point for standards that will 

evolve toward better meeting the needs of the community. The

intent of this paper is to introduce a rating system built on 

objective technical evidence and reasons and input from 

stakeholders. Examples are shown of how the rating system 

can be communicated with differing levels of detail for the 

various stakeholders. 

II. LEARNING FROM HISTORY

In the late 1970s, the Jet Propulsion Lab (JPL) executed a 

series of block buys of PV modules that passed successively 

harsher accelerated tests [18-23]. A dramatic reduction in 

early failures occurred between Block IV and Block V

[18,24]. The primary differences between these tests are 

highlighted in bold in Table III [21-23] and included:

• Increase in the number of thermal cycles

• More stressful humidity freeze test

• Addition of a hot-spot test.

TABLE III. COMPARISON OF JPL BLOCKS IV AND V TESTS

 

Test Block IV Block V

Thermal Cycling 50 cycles 

(-40 to +90°C)

200 cycles 

(-40 to +90°C)

Humidity (Freeze) 

5 cycles 

54°C/90%RH 

to -23°C

10 cycles 85°C/85%RH 

to -40°C

Hot Spots None 3 cells, 100 h

Mechanical Load 10,000 cycles, 

± 2400 Pa

10,000 cycles, 

± 2400 Pa

Hail 9 impacts 20 mm @ 

20 m/s

10 impacts 25 mm @ 

23 m/s

High Pot < 50 μA @ 1500 V < 50 μA @ 2*Vs+1000

Reported Field 

Failures > 50% [24] ~ 1% [24] 

The thermal-cycling test queries mechanical fatigue, which is 

the mechanism that causes failures of interconnect ribbons, 

solder bonds, and multiple other interfaces. A hard freeze after 

exposure to high humidity causes the expansion of water as it 

freezes, stressing interfaces and promoting delamination; the 

Block V version of the Humidity (Freeze) test caused more 

stress than the Block IV version. The hot-spot test motivated

manufacturers to use bypass diodes, which protect the

modules during cell mismatch caused by partial shading or 

cell damage. These three changes helped to avoid important 

design flaws, decreasing failure rates. It is notable that the 

1000-h damp heat test that is viewed as a critical element of 

today’s qualification test was not included in Block V testing.

Nevertheless, the changes between the Block IV and Block V 

tests dramatically improved the test’s ability to identify infant 

mortality [18,24]. This experience may be useful toward

developing comparative tests. 

III. IDENTIFICATION OF FAILURES OBSERVED TODAY

A. Field Data Summary

Field experience with PV is increasing exponentially with 

the recent corresponding increased production volume.

Although information is often lacking about the testing used to 

qualify a design and about the manufacturing quality control, 

researchers have assembled some statistical data (Table IV) 

indicating an opportunity for improvement: we strive to 

identify tests that will avoid these failures in the future. 

TABLE IV. SUMMARY OF SELECTED FIELD STUDIES

 

Observation Sample Size Reference

Laminate internal electrical circuit 

36% of failures (~2% of modules 

failed after 8 years); glass 33%; 

j-box and cables 12%; cells 10%; 

encapsulant and backsheet 8%

21 

manufacturers; 

~60% of fleet of 

> 1.5 GW 

DeGraaff 

[25] 

16% of systems required 

replacement of some or all 

modules because of a variety of 

failures, with many showing 

breaks in the electrical circuitry

483 systems Kato [26,27] 

3% developed hot spot after < 7

years; 47% had non-working 

diodes

1232-module 

system Kato [26,27] 

External wiring shattered, failed ~70,000 

modules 

Rosenthal 

[24]

Early degradation linked to 

optical transmission losses 

(through glass and encapsulant) 

and light-induced degradation; 

later degradation is more from 

increased series resistance

204 modules 

from 20 

manufacturers 

Skoczek [28] 

Encapsulant discoloration 66%; 

delamination 60%; corrosion 

26%; glass breakage 23%; j-box 

20%; broken cells 15%*

~2000 reports Jordan [29] 

200 thermal cycles corresponded

to ~10 years in the field

> 10 years of 

manufacturing

Wohlgemuth 

[30,31]

* Fraction of papers reported these visual defects 

DeGraaff summarized data from SunPower’s > 1.5 GW of

installations, including PV modules from 21 manufacturers 

[25]. The most common failure type involved failed solder 

bonds or other internal electrical interconnection issues. 

Delamination of the anti-reflective coating on the glass was

the second most common failure. About 12% of the failures 
3 This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.

were related to the junction boxes or cabling, often causing

arcing that could lead to fires. 

Kato [26,27] reported the need for replacement of modules 

after 5-12 years in ~16% of systems studied, with most of 

those cases showing electrical failures (interconnects or 

bypass diode failures). Rosenthal reported on Block IV and V 

modules, some of which were in the field, for a full 10 years 

[24] with minimal (< 1.3%) failures, implying that 200 cycles 

of thermal cycling may be adequate for a 10-year lifetime.

Jordan’s literature review [29] showed that discoloration and 

delamination were most frequently reported; corrosion, glass 

breakage, cell breakage, and many other problems were also 

observed. 

Four themes from the data in Table IV are:

1. Degradation or safety issues caused by failure of cell 

interconnects, solder bonds, or the bypass diodes that 

protect in case of shading. 

2. Early degradation in the short-circuit current related to 

light-induced degradation and changes in transmittance

associated with changes in anti-reflection coatings, 

encapsulation discoloration, and delamination. 

3. Corrosion (often associated with delamination). 

4. Junction-box failures.

Reports of early failures from manufacturing defects and/or 

potential-induced degradation motivate improvements in 

quality control and improved qualification testing. These 

issues are being addressed by Task Group 1 of the 

International Quality Assurance Task Force and the IEC 

Technical Committee 82 (TC82), Working Group 2 (WG2), 

respectively. Glass and cell breakage are also frequently 

reported, meriting prioritization if resources can be found to 

address these. It could be argued that glass breakage should be 

prioritized above corrosion based on Table IV, but as PV 

markets move into more tropical areas, corrosion may become 

more apparent, increasing its priority. 

B. Evidence of Value of Extended Testing

Correlation of field failures reported in historical studies 

with accelerated testing provides a basis for proposing a new 

test standard. According to the studies of Wohlgemuth [30], 

~500 thermal cycles are needed to screen for 25-year lifetime 

in the field for thermal-fatigue type failures, motivating an 

increase in the number of thermal cycles from 200 to 500. The 

value of dynamic mechanical loading before applying thermal 

cycling has also been demonstrated [32]. 

As indicated in Table IV, discoloration and delamination of 

encapsulants are frequently reported to contribute to module 

degradation. The current qualification tests apply only a few 

months equivalent of field UV (less than 3 months in sunny 

locations), which is grossly inadequate for exploring the 

effects of long-term UV exposure. Longer UV exposure has 

been shown to correlate with improved durability [33]. A test 

developed by STR and successfully used as a guide for 

selecting ethylene-vinyl acetate (EVA) formulations would 

provide a rapidly implementable improvement [33]. 

Jordan’s summary of ~2000 studies found that 26% reported

corrosion. To our knowledge, the community has not 

identified an improved corrosion test to be implemented in the 

near term. A number of reports have suggested that extending 

damp-heat testing beyond 1000 h (e.g., to 1250 h) uncovers 

failures that are observed in the field [30,34,35]. 

Thus, based on correlations between accelerated and field 

testing, we conclude that harsher stress tests for thermal 

fatigue, UV exposure, and corrosion can identify designs that 

last longer in the field. In addition, the large number of diode 

failures reported for a few systems [26,27] and the frequent 

reporting of junction-box issues motivate additional testing. 

Using existing publications, it may be possible to quickly 

define new tests for:

• Thermal fatigue (additional cycles or combined tests) 

• Dynamic mechanical load*

• Encapsulant discoloration (e.g., STR test)

• Corrosion 

• Junction box detachment 

• Bypass diode (extended test) 

• Extended hot-spot test

• Potential-induced degradation.* 

* Drafts of these tests have been submitted to WG2 of TC82.

Standardizing test methods that have proven to be useful to 

manufacturers during the product-development phase is a wise 

strategy for quickly bringing benefit to the community and can 

form a starting point for defining comparative test sequences. 

IV. PROPOSAL FOR CREATION OF COMPARATIVE RATING 

SYSTEM

The complexity of relating the results of multiple 

accelerated tests to a multitude of use conditions challenges us 

to construct a comparative rating system that: 1) requires an 

acceptable testing time, 2) is easy to understand and use, and 

3) still retains enough information to correlate with field 

experience as a function of climate/application. We next 

discuss guiding principles that apply to the creation of the tests 

and a rating system, and then propose the system and how to 

communicate it to the various stakeholders. 

A. Guiding Principles

Although defining the test sequences and the rating system 

is highly controversial, the guiding principles for the tests and 

rating system are more generally accepted. They must: 

• Aim to differentiate products according to their durability 

for the desired deployment conditions. 

• Be relevant (give confidence in warranty period). 

• Be carried out within a reasonable timeframe making it 

applicable for industrial and commercial use. 

• Have acceptable cost.

• Be communicated in useful ways (both simple and detailed 

for different audiences). 
4 This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.

TABLE V. CLIMATES PROPOSED FOR RATING SYSTEM

New Tests Will Require Additional Stress Differentiation of Durability

IEC 60721-2-1 

Climate Designation Proposed Changes C B A 

Moderate Tests listed in section III B 

Comparable to 

qualification test 

Better than 

qualification 

test

Most durable 

Warm Damp, 

Equable Tests for delamination & moisture ingress in humid climates 

Comparable to 

qualification test 

Better than 

qualification 

test

Most durable 

Extremely Warm 

Dry Tests for higher temperatures 

Comparable to 

qualification test 

Better than 

qualification 

test

Most durable 

• Include options to accommodate design and material 

differences. 

• Be designed to learn from the results and be 

dynamically updated, when required (its application will 

help to improve the standard). 

• Specify that when there is insufficient information to 

evaluate the usefulness of a proposed test, we will 

estimate and communicate the uncertainty. 

• Define clear responsibility and accountability for 

communicating the ratings to consumers. 

In general, basic qualification tests duration should be ~ 3 

months or less if they are used as a basis for entering the 

market. However, we expect that meaningful comparative

tests may require more than 3 months.

B. Proposal of Rating Categories Related to Climate

We propose a comparative rating system based on three 

climate zones (Table V) according to IEC 60721-2-1: 

• Moderate

• Warm damp, equable

• Extremely warm dry. 

These might also be labeled as temperate, tropical (or hothumid), and desert (or hot-dry). 

Additionally, just as a module is tested according to its

system voltage, the rating is made in the context of a module intended to be deployed in an open-rack or roof-mount

configuration. Depending on the classification of the 

mounting configuration, the test conditions will be adjusted.

C. Additional Stresses Included in Rating System

For a rating system to have predictive value, it must 

encompass all primary failure modes and all associated 

stresses. We propose a comprehensive rating system that

considers all stresses including:

• UV, temperature, and humidity experienced in locations 

associated with the climate definitions in IEC 60721-2-1 

• Temperature variability (thermal cycling)

• Salt spray

• System voltage with specified bias polarity and in 

conjunction with temperature and humidity

• Mechanical damage caused by snow

• Mechanical damage caused by wind

• Hail

• Ammonia. 

D. Differentiation of Durability 

A primary goal of the new rating system is to differentiate 

products according to their durability. Given that we do not 

yet fully understand what differentiation is useful, we 

propose that within each climate rating, an A, B, or C rating 

may be ascribed (as described in Table V). As the 

accelerated test procedures are defined, the A, B, and C 

ratings will be defined either because the tests are 

completed at a higher level of stress or because the module 

retained a higher performance/safety rating after completion 

of the stress test. 

The meanings of other stresses may be defined more 

quantitatively, as in the case of hail testing in which the size 

and velocity of the ice balls are specified. There is a need to 

more effectively communicate the meanings of the snow, 

wind, and other tests, as indicated in Table VI. 

The proposed rating system will provide a means for 

comparing the expected durability of new products and will 

help customers to gain confidence in their upfront 

investments for each use environment. Confidence in longterm investments is becoming increasingly important as 

incentive programs are scaled back [36]. The continued 

growth of the industry relies on confidence that the products 

will last for the full warranty period; a comparative test 

standard is the first step toward assessing durability 

commensurate with the warranty. 

TABLE VI. OTHER STRESSES

Stress Existing test Comment

Snow 

IEC 61215 or 61646, 

10.16 mechanical 

load test

Test is not currently effective 

at identifying some types of 

damage

Wind 

IEC 61215 or 61646, 

10.16 mechanical 

load test

Test does not identify 

problems with uplift 

Hail IEC 61215 or 61646, 

10.17 Hail test

Results could be more 

effectively communicated

Salt IEC 61701 Salt mist Results could be more 

effectively communicated

Ammonia IEC 62715 Ammonia 

test

Results could be more 

effectively communicated
5 This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.

E. Creation of Test Protocols

The test protocols used as the basis for the rating system 

will be developed by careful scientific evaluation of failures 

that have been observed in the field and how these have 

been successfully duplicated in accelerated tests. Whenever 

possible, rate equations and related simulations will 

elucidate the meanings of the tests. We anticipate that the 

test protocols will use combinations of stresses. As more

understanding is gained, the tests will be updated.

F. Three Ways to Communicate Rating System

The ratings proposed using Tables V and VI must be 

communicated to: 

• Customers who want an in-depth analysis for a large 

purchase of modules

• Customers who want to quickly screen a large number 

of modules and/or who desire a high-level summary 

without in-depth analysis (e.g., for a small purchase)

• Future researchers or insurance companies who want to 

correlate the rating tests with field experience for lifetime 

prediction. 

To address the needs of all users, we recommend 

communicating the test results in three ways (Table VII).

TABLE VII. PROPOSED COMMUNICATION OF RATINGS

Communication 

Vehicle Purpose Defined by Standard?

Test Report Provide details for in-depth 

analysis Yes

Nameplate 

Screening of many modules; 

easy to understand; high-level 

summary to correlate with 

field performance

Yes

Maps, Tables, 

or Graphs

Interpret meaning of test for 

each location No 

For customers wishing to do an in-depth analysis, a test 

report should be defined in the standard, including the data 

that were measured at each stage of the testing. 

For customers seeking a high level summary, a rating 

should be derived from the complicated test results using a 

formula constructed by the tests’ authors. For purposes of 

illustration, we suggest that an A, B, or C be assigned, as 

indicated in Table V. To aid future researchers, a high-level 

summary will be required on the name plate for easy 

reference when field results are studied decades from now

(Fig. 1). At the manufacturer’s discretion, test results can

also be included in marketing information (e.g., datasheets).

Finally, the meaning of the rating can be summarized in 

maps, tables, or graphs as research projects outside of the 

test standard, to the extent that the information is available.

These visual aids could indicate the number of years of 

service life expected for a product in a specified use 

environment. More generally, a map could show the 

recommended minimum rating needed for a desired lifetime 

and application (e.g., rack mounting) as shown in Fig. 2 or 

similar information could be presented in a table for every 

location. The multiple stress ratings could be compared with 

the desired ratings for a specific location in a spider graph.

In some regions, only one rating might be needed; in other 

regions, multiple requirements might apply, including 

ratings for hail, salt, etc. It may take many years to advance 

the understanding of the tests far enough to be able to create 

these maps, but the vision of how they could be used by the 

community can guide us as we create the rating system.

Fig. 1. Example of how the new rating system could be 

communicated on a nameplate.

Fig. 2. Example map illustrating how the meaning of the ratings 

could be communicated once the information is available. Mod, 

Damp, and Dry refer to the climate zones indicated in Table V.

V. CONCLUSIONS

As a basis for creating comparative test standards, we 

note that there is evidence of benefit in adding harsher tests 

for:

• Thermal-fatigue (e.g., solder bond failures)

• UV-induced degradation

• Corrosion

• Diode and junction-box failures. 

The effects of temperature and humidity can be assessed 

relative to three climate zones defined in IEC 60721-2-1: 

• Moderate

• Extremely warm dry

• Warm damp, equable. 

These should be assessed in the context of classification 

according to the mounting configuration:

• Open rack mounted

• Roof mounted. 
6 This report is available at no cost from the 

National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.

We propose a comprehensive rating system that considers 

stress from wind, snow, salt, and hail in addition to the tests 

related to the temperature and humidity aspects of climate.

When creating these new tests, we must apply stresses in 

combinations to duplicate the types of failures seen in the 

field. The results of the comparative tests may be 

summarized with ratings A to C and communicated by:

• Detailed report

• Nameplate

• Interpretive maps, tables, or graphs. 

In the future, we may correlate long-term performance 

with the comparative test results toward validating a service 

life prediction. In the meantime, this rating system will 

increase confidence in long-term performance and provide 

customers with a tool to differentiate products.

ACKNOWLEDGEMENTS

This work was supported in part by the U.S. Department 

of Energy under Contract No. DE-AC36-08GO28308. 

REFERENCES

[1] D. Feldman, et al., "Photovoltaic (PV) Pricing Trends: 

Historical, Recent, and Near-Term Projections", National 

Renewable Energy Laboratory, DOE/GO-102012-3839, (2012).

[2] G. TamizhMani, and J. Kuitche, "A Literature Review and 

Analysis on: Accelerated Lifetime Testing of Photovoltaic 

Modules", Solar ABCs, (2013).

[3] B. Jaeckel, et al. "A New Standard for Holistic Quality 

Assurance.” 26th European PVSEC, Hamburg, 2011 pp 3484-

3490. 

[4] D. Cunningham, B. Jaeckel, and A. Roth "A New Approach for 

Holistic PV Module Quality Assurance by Extended Stress 

Testing and Production Monitoring.” PV Module Reliability 

Workshop, Golden, CO 2012. 

[5] A. Funcell "'The Thresher Test' Crystalline Silicon Terrestrial 

Photovoltaic Modules Long Term Reliability and Degradation.”

PV Module Reliability Workshop, Golden, CO 2012. 

[6] J. Meydbray "Reliability Demonstration Test.” PV Module 

Reliability Workshop, Golden, CO 2012. 

[7] [1] D.H. Meakin, et al. "Fraunhofer PV Durability Intiative for 

solar modules", Photovoltaics International, 20, 2013, p. 77.

[8] P. Hacke, et al. "Test-to-Failure of Crystalline Silicon Modules.”

35th IEEE PVSC, Honolulu, pp. 244-250, 2010. 

[9] P. Hacke, et al. "Application of the NREL Test-to-Failure 

Protocol for PV Modules", 19th Crystalline Silicon Workshop, 

Vail, CO 2009. 

[10] G. TamizhMani "Long-Term Sequential Testing (LST) of PV 

Modules.” PV Module Reliability Workshop, Golden, CO 2012. 

[11] "Introducing "Best of modules" Quality assurance", PV 

Magazine, 2011, (02), 2011, pp. 92-107. 

[12] K.P. Scott and A. Zielnik "Atlas 25plus - Long Term 

Durability Test for PV Modules.” PV Module Reliability 

Workshop, Golden, CO 2012. 

[13] A. Zielnik ‘PV Durability and Reliability Issues’, 

Photovoltaics World, Nov/Dec pp. 10-14, 2009. 

[14] D. Jordan and S. Kurtz "Photovoltaic Degradation Rates—an 

Analytical Review", Prog.Photovolt:Res.Appl., 2013; 21 : 12-29. 

[15] IEC 61215: "Crystalline silicon terrestrial photovoltaic (PV) 

modules - Design qualification and type approval," 2005. 

[16] IEC 61646: "Thin film terrestrial photovoltaic (PV) modules - 

Design qualification and type approval," 2008.

[17] IEC 62108: "Concentrator photovoltaic (CPV) modules and 

assemblies - Design qualification and type approval," 2007.

[18] M. Whipple "The Performance of PV Systems", PV Performance and Reliability Workshop, Golden, CO 1993, p. 453.

[19] A. Hoffman and R. Ross "Environmental Qualification 

Testing of Terrestrial Solar Cell Modules.” 13th IEEE PVSC, 

Washington DC, pp. 835-842, 1978. 

[20] M. Smokler, D. Otth, and R. Ross "The Block Program 

Approach to Photovoltaic Module Development.” 18th IEEE 

PVSC, Las Vegas, NV, pp. 1150-1157, 1985. 

[21] R. Ross "FSA Engineering & Reliability Development Methods - Can They be Applied Today?", InterSolar, San Francisco, 

CA http://www2.jpl.nasa.gov/adv_tech/photovol/ppr_86-

90/Ross SEMI-VG_07-08-12.pdf, 2012.

[22] "Block V Solar Cell Module Design and Test Specification 

for Intermediate Load Applications", JPL, (1981).

[23] R. Ross, and M. Smokler, "Flat Plate Solar Array Project 

Final Report, Volume VI", JPL, (1986).

[24] A. Rosenthal, M. Thomas, and S. Durand "A Ten Year 

Review of Performance of Photovoltaic Systems.” 23rd IEEE 

PVSC, pp. 1289-1291, 1993. 

[25] D. Degraaff, R. Lacerda, and Z. Campeau "Degradation 

Mechanisms in Si Module Technologies Observed in the Field; 

Their Analysis and Statistics", PV Module Reliability Workshop, 

Golden, CO 2011. 

[26] K. Kato "PVRessQ!: a research activity on reliability of PV 

systems from a user's viewpoint in Japan.” SPIE, San Diego

2011, 81120K, doi:10.1117/12.896135.

[27] K. Kato "PVRessQ! PV Module Failures Observed in the 

Field", PV Module Reliability Workshop, Golden, CO 2012. 

[28] A. Skoczek, T. Sample, and E. Dunlop "The Results of 

Performance Measurements of Field-aged Crystalline Silicon 

Photovoltaic Modules", Prog.Photovolt:Res.Appl, 17, 2009, pp. 

227-240. 

[29] D. Jordan, J. Wohlgemuth, and S. Kurtz "Technology and 

Climate Trends in PV Module Degradation.” 27th European 

PVSEC, Frankfurt, Germany 2012, pp 3118 – 3124. 

[30] J. Wohlgemuth, et al. "Using Accelerated Tests and Field 

Data to Predict Module Reliability and Lifetime.” 23rd 

European PVSEC, Valencia, Spain, 2008, pp 2663 – 2669. 

[31] J. Wohlgemuth, D. Cunningham, A. Nguyen, and J. Miller 

"Long Term Reliability of PV Modules.” 20th European PVSEC, 

Barcelona, Spain, 2005, pp. 1942-1948. 

[32] J. Wohlgemuth "The effect of cell thickness on module 

reliability", 33rd IEEE PVSC, San Diego, CA, 2008, paper 420. 

[33] J. Wohlgemuth, M. Kempe, and D. Miller "Discoloration of 

PV Encapsulants.” 39th PVSC, Tampa, FL, 2013.

[34] W. Eerenstein, et al. "Climate Chamber Test Results of MWT 

Back Contact Modules.” 25th European PVSEC, Valencia, 

Spain, pp. 3854-3847, 2010. 

[35] D. Degraaff, et al. "Qualification, Manufacturing, and 

Reliability Testing Methodologies for Deploying HighReliability Solar Modules.” 25th European PVSEC, Valencia, 

Spain, pp. 3722-3734, 2010. 

[36] M. Bazilian, et al. "Reconsidering the economics of 

photovoltaic power", Renewable Energy, 53, (May), 2013, pp. 

329-338.