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.

Proposals for “Qualification Plus” Tests and 

Comparative Rating System

Sarah Kurtz, John 

Wohlgemuth, Mike 

Kempe, Nick Bosco, 

Peter Hacke, Dirk Jordan, 

David Miller, and MANY 

from the community

SPIE Solar Energy + 

Technology Conference

Bankability Workshop, 

Chicago, IL

October 21, 2013

NREL/PR-5200-60718
 NATIONAL RENEWABLE ENERGY LABORATORY

Outline

•Challenge: Creating useful standards quickly

• Qualification – What we’ve been using

• “Qualification plus” – Tests that are being discussed

• Comparative – Climate-specific rating system

• Quantitative – Goal of Service Life Prediction

2
 NATIONAL RENEWABLE ENERGY LABORATORY

Challenge: Create Useful Standards

3

We’ve heard:

• It takes too long to make standards

• Requiring more tests adds cost and delays products

Our goals:

• Strive for sooner

• Identify useful tests (that align with field performance)

• Unify the testing approaches

We ask:

• If we didn’t get it “right,” help us fix it
Some Levels of Accelerated Testing

Qualification Qualification

“Plus” Comparative Service Life

Purpose

Minimum 

design 

qualification

Enhanced

design 

qualification

Comparison of 

products

Substantiation 

of warranty

Quantification Pass/fail Pass/fail Relative Absolute

Climate or 

application

(mounting)

Not 

differentiated

Not 

differentiated Differentiated Differentiated

Specificity Silicon, thinfilm, CPV

For today, 

discuss Si only

Package 

specific?

Product 

specific

Chamber test 

times

Modules: < 2 

months

Modules: ~ 3 

months

Materials: ~ 6 

months

TBD 3 years ?
Some Levels of Accelerated Testing

Qualification Qualification

Plus Comparative Service Life

Purpose

Minimum 

design 

qualification

Enhanced

design 

qualification

Comparison of 

products

Substantiation 

of warranty

Quantification Pass/fail Pass/fail Relative Absolute

Climate or 

application

(mounting)

Not 

differentiated

Not 

differentiated Differentiated Differentiated

Specificity Silicon, thinfilm, CPV

For today, 

discuss Si only

Package 

specific?

Product 

specific

Chamber test 

times

Modules: < 2 

months

Modules: ~ 3 

months

Materials: ~ 6 

months

TBD 3 years ?
Testing beyond current IEC tests

• Ed. 3 of IEC 61215 will have multiple 

revisions/additions

– These will become available to the public 

over the next two years

– Can we adopt improvements sooner?

• CEC has given us the opportunity to 

propose an optional “plus” version of 

their Eligibility Requirements

• Next slides describe “plus” requirements
 NATIONAL RENEWABLE ENERGY LABORATORY

Proposal to test “beyond” the standard

7

• Despite PV’s excellent success, some failures are seen 

in the field.

• Propose 9 new tests

• Low prices motivate manufacturers to cut corners –

might the corner be cut too short?

• Propose more frequent/extensive testing

• Propose oversight of quality management system
 NATIONAL RENEWABLE ENERGY LABORATORY

Proposal to test “beyond” the standard

8

• Despite PV’s excellent success, some failures are seen 

in the field.

• Propose 9 new tests

•Low prices motivate manufacturers to cut corners –

might the corner be cut too short?

• Propose more frequent/extensive testing

• Propose oversight of quality management system
 NATIONAL RENEWABLE ENERGY LABORATORY

#1 Proposed testing “beyond” IEC 61215

9

Failure type: Potential-induced degradation (module 

failure is caused by system voltage)

Proposed change: Apply system voltage during damp 

heat or similar condition.

Benefit: For systems that float (active circuit ungrounded), 

the degradation can be dramatic (tens of % in first year). 

New inverter designs have enabled this style of system 

design. 

Comment: Test has been proposed to IEC.

Modules at negative end of 

string show degradation 

(indicated by black) http://www.nrel.gov/docs/fy12osti/54581.pdf

Mani will discuss
 NATIONAL RENEWABLE ENERGY LABORATORY

#2 Proposed testing “beyond” IEC 61215

10

Failure type: Failure of connections within electrical circuit

Proposed change: Increase thermal cycling from 200 

cycles (~ 6 weeks) to 500 cycles (~ 15 weeks). 

Benefit: This type of failure can lead to fires and/or 

catastrophic module failure. 

Comment: There is evidence that 200 cycles gives 

confidence for ~ 10 y in the field; 500 cycles 

may give confidence closer to 25 y.

Front

Back

Degraaff

NREL Reliability 

Workshop, 2011

Wohlgemuth, 23rd EU 

PVSEC, p. 2663, 2008 

Wear-out mechanism
 NATIONAL RENEWABLE ENERGY LABORATORY

#3 Proposed testing “beyond” IEC 61215

11

Failure type: Cracked cells, etc. leading to disconnections

Proposed change: Apply Dynamic Mechanical Load 

before 50 thermal cycles and 10 humidity freeze cycles

Benefit: This type of failure can lead to fires and/or 

catastrophic module failure. 

Comment: Today’s thinner cells sometimes crack during 

shipping or snow/wind loading. At first, there may be no 

power loss, but after further stress, the metal interconnects 

may begin to break.

Note: this may be a faster way to achieve 

the stress of 500 thermal cycles –

uncovers many types of failures

Wohlgemuth, 33rd PVSC, paper 420, 2008

Pingel, 24th European PVSEC, p. 3459, 2009

Koch, 25th European PVSEC, p. 3998, 2010

Geoff Kinsey will discuss
 NATIONAL RENEWABLE ENERGY LABORATORY

#4 Proposed testing “beyond” IEC 61215

12

Failure type: Degradation of encapsulant (yellowing, 

delamination)

Proposed change: Expose materials in “module-like” 

configuration to UV and heat for ~ 6 months (use test that 

was defined by STR ~ 15 y ago)

Benefit: Avoids degradation. Yellowing causes slow power 

decrease. 

Comment: May be done by 

encapsulant manufacturer.

Note: Historically, encapsulant manufacturers 

used this sort of test, so field failures were small. 

Now, newer manufacturers may or may not use 

adequate testing; it’s not required in IEC 61215.

Wohlgemuth, 39th PVSC, 2013 

Reid, SPIE, vol. 8825, 2013

Wear-out mechanism

Charlie Reid will discuss
 NATIONAL RENEWABLE ENERGY LABORATORY

#5-7 Proposed testing “beyond” IEC 61215

13

Failure type: Degradation of backsheet, 

connectors and junction boxes (cracking, 

delamination) leading to losses in safety 

or performance

Proposed change: Expose backsheet, 

cables, and junction boxes to UV

consistent with outdoor exposure

Benefit: Avoids safety and performance 

issues (e.g. if backsheet no longer 

provides adequate protection of the 

electrical circuit leading to shock hazard 

and/or to corrosion). 

Comment: May be completed by 

component manufacturer.

Gambogi, et al, EUPVSEC 2012, 

Gambogi, et al, NREL PVMRW 2013, 

Gambogi, et al, 39 Wear-out mechanism th PVSC 2013

Bill Gambogi will discuss
 NATIONAL RENEWABLE ENERGY LABORATORY

#8 Proposed testing “beyond” IEC 61215

14

Failure type: Hot-spots from local reverse bias during 

partial shading

Proposed change: Use ASTM E2481-06 hot-spot test 

(more cells and longer test)

Benefit: This type of failure can cause fires. 

Comment: Is planned for adoption into IEC 61215. 

ASTM E2481-06

TamizhMani & Sharma, SPIE 7048 (2008) 
 NATIONAL RENEWABLE ENERGY LABORATORY

#9 Proposed testing “beyond” IEC 61215

15

Failure type: Bypass diode

Proposed change: Increase bypass diode thermal test 

from 1 h to 96 h.

Benefit: Some manufacturers used cheaper diodes that 

passed the 1-h test, but failed in the field. 

Comment: Other bypass diode tests are in development. 

Failure of bypass diodes can lead to fires

Testing for Electrostatic Discharge (ESD) should be done in 

the factory

Zhang, et al, PVMRW 2013
 NATIONAL RENEWABLE ENERGY LABORATORY

Proposal to test “beyond” the standard

16

• Despite PV’s excellent success, some failures are seen 

in the field.

• Propose 9 new tests

• Low prices motivate manufacturers to cut corners –

might the corner be cut too short?

• Propose more frequent/extensive testing

• Propose oversight of quality management system
 NATIONAL RENEWABLE ENERGY LABORATORY

Test (sampling) methods

17

• All test samples must be random samples from 

production line (no engineering samples and no cherry 

picking)

• Number of test samples increased from 2 to 5

• Retest at least once per 4 months (small-volume 

manufacturers may have reduced requirement) by 

manufacturer and any failures addressed.
 NATIONAL RENEWABLE ENERGY LABORATORY

Why we need to test “beyond” the standard

18

• Despite PV’s excellent success, some failures are seen 

in the field.

• Propose 9 new tests

• Low prices motivate manufacturers to cut corners –

might the corner be cut too short?

• Propose more frequent/extensive testing

• Propose oversight of quality management system
 NATIONAL RENEWABLE ENERGY LABORATORY 19

Quality Management: PV-specific ISO-9001

Organization controls the PV 

module’s design to align the 

expected lifetime with its 

relationship to the 

organization’s warranty 

*Before launching their recent incentive 

program, Japan created: “JIS Q8901-

2012 Terrestrial photovoltaic (PV) 

modules-Requirement for reliability 

assurance system (design, production, 

and product warranty)” 

• Builds on Japanese standard*

• Report at 

http://www.nrel.gov/docs/fy13osti

/58940.pdf
Levels of Accelerated Testing

Qualification Qualification

Plus Comparative Service Life

Purpose

Minimum 

design 

qualification

Enhanced

design 

qualification

Comparison of 

products

Substantiation 

of warranty

Quantification Pass/fail Pass/fail Relative Absolute

Climate or 

application

(mounting)

Not 

differentiated

Not 

differentiated Differentiated Differentiated

Specificity Silicon, thinfilm, CPV

For today, 

discuss Si only

Package 

specific?

Product 

specific

Chamber test 

times

Modules: < 2 

months

Modules: ~ 3 

months

Materials: ~ 6 

months

TBD 3 years ?
 NATIONAL RENEWABLE ENERGY LABORATORY

“Features” versus “Grades”

Acceptable: “Features” 

 (examples)

• Climate:

• Desert

• Tropical

• Temperate

• Mounting

• Open Rack

• Close roof

• Hail test

• 3 cm

• 5 cm

• “Better than qualification test”

• 2X, 3X, 4X

Unacceptable: “Grades”

• A, B, C

• Score of 1 to 10

• Score of 1 to 100

• One to Five stars

21

Customers want to differentiate, but some companies don’t want to be graded
22

Proposed rating system for climate and mounting

IEC 60721-2-1 Climate 

Designation

Mounting classes

Rack mount Close-roof mount

Moderate (Temperate)

Warm Damp, Equable 

(Tropical)

Extremely Warm Dry 

(Desert)
23

• Failures are frequently 

reported in all climates

• Field data and modeling imply 

that 500 thermal cycles would 

be better than 200

• Propose: Increase thermal 

cycles; use faster cycles or 

dynamic mechanical loading 

(DML) to reduce time - details 

TBD

Disconnected

 interconnection

Kato, 2012

http://www1.eere.energy.gov/solar/pdfs/pvmrw12_tuesam_aist_kato.pdf 

A hot point due to

 soldering degradation

Thermal and mechanical fatigue issues seen everywhere
24

Proposed rating system for climate and mounting

IEC 60721-2-1 Climate 

Designation

Mounting classes

Rack mount Close-roof mount

Moderate (Temperate) 500 thermal cycles or DML + 

200 TC

500 thermal cycles or DML + 

200 TC

Warm Damp, Equable 

(Tropical)

500 thermal cycles or DML + 

200 TC

500 thermal cycles or DML + 

200 TC

Extremely Warm Dry 

(Desert)

500 thermal cycles or DML + 

200 TC

500 thermal cycles or DML + 

200 TC

Proposal:

Increase stress to avoid fatigue-related failures commonly reported today.

So far, we do not have clear evidence that this 

failure varies systematically with climate.

Question: Should the details of the test vary with climate?
25

UV effects usually increase in hot environment

• Loss of current linked to 

decrease in performance; 

frequently associated with 

EVA discoloration

• Discoloration is caused by 

UV exposure, especially at 

higher temperatures

• Proposal: Increase UV 

exposure with appropriate 

temperature

-1

0

1

2

3

4

Data

Pmax Rd+ Isc Rd+ Voc Rd+ FF Rd+

Label

476

IV Parameter

Pmax Isc Voc FF

475 473 397

Degradation Rate (%/year)
26

Proposed rating system for climate and mounting

IEC 60721-2-1 

Climate 

Designation

Mounting classes

Rack mount Close-roof mount

Moderate 

(Temperate)

500 thermal cycles or DML + 200 TC

Increased UV exposure at 60°C*

500 thermal cycles or DML + 200 TC

Increased UV exposure at 80°C*

Warm Damp, 

Equable (Tropical)

500 thermal cycles or DML + 200 TC

Increased UV exposure at 80°C*

500 thermal cycles or DML + 200 TC

Increased UV exposure at 100°C*

Extremely Warm Dry 

(Desert)

500 thermal cycles or DML + 200 TC

Increased UV exposure at 80°C*

500 thermal cycles or DML + 200 TC

Increased UV exposure at 100°C*

Proposal:

Increase UV exposure with appropriate temperature & humidity.

Use measurements and modeling to select temperatures.

*Temperatures are estimates; final values TBD, but should vary with mounting/climate.
27

Humidity can cause corrosion

• Failures are sometimes 

reported 

• Corrosion usually follows 

delamination

• Proposal: Use UV exposure + 

humidity freeze to induce 

any delamination, then 

expose to damp heat to 

cause corrosion
28

Proposed rating system for climate and mounting

IEC 60721-2-1 

Climate Mounting classes

Rack mount Close-roof mount

Moderate 

(Temperate)

500 thermal cycles or DML + 200 TC

Increased UV exposure at 60°C*, 

followed by 10 cycles of humidity freeze 

and short damp heat

500 thermal cycles or DML + 200 TC

Increased UV exposure at 80°C*, 

followed by 10 cycles of humidity freeze 

and short damp heat

Warm Damp, 

Equable 

(Tropical)

500 thermal cycles or DML + 200 TC

Increased UV exposure at 80°C*, 

followed by 10 cycles of humidity freeze 

and 1000 h damp heat

500 thermal cycles or DML + 200 TC

Increased UV exposure at 100°C*, 

followed by 10 cycles of humidity freeze 

and 1000 h damp heat

Extremely 

Warm Dry 

(Desert)

500 thermal cycles or DML + 200 TC

Increased UV exposure at 80°C*, 

followed by 10 cycles of humidity freeze 

and short damp heat

500 thermal cycles or DML + 200 TC

Increased UV exposure at 100°C*, 

followed by 10 cycles of humidity freeze 

and short damp heat

Proposal:

After UV exposure add humidity freeze and damp heat.

Use measurements and modeling to select conditions.

*Temperatures and other details are estimates; final values TBD.
29

Application-specific ratings

• Existing tests:

- Hail

- Mechanical strength 

(snow and wind load; 

moving snow)

- Salt

- Ammonia

- Sand

Proposal:

Document existing tests 

along with climatespecific rating to 

provide complete 

information 
Levels of Accelerated Testing

Qualification Qualification

Plus Comparative Service Life

Purpose

Minimum 

design 

qualification

Enhanced

design 

qualification

Comparison of 

products

Substantiation 

of warranty

Quantification Pass/fail Pass/fail Relative Absolute

Climate or 

application

(mounting)

Not 

differentiated

Not 

differentiated Differentiated Differentiated

Specificity Silicon, thinfilm, CPV

For today, 

discuss Si only

Package 

specific?

Product 

specific

Chamber test 

times

Modules: < 2 

months

Modules: ~ 3 

months

Materials: ~ 6 

months

TBD 3 years ?
Service Life Prediction Standard?

• How would you write a standard for 

making a Service Life Prediction?

• The failure mechanisms that limit the life 

of a product may vary
Service Life Prediction

1. Identify failure/degradation mechanisms that 

determine end of life

2. Quantify reaction rates

3. For given use environment, apply rates in a 

model to estimate expected lifetime

4. Verify model by comparing with field data

This step-by-step procedure is clear, 

but the actual tests are not

This procedure is similar to quality management
 NATIONAL RENEWABLE ENERGY LABORATORY 33

Propose: Implement Service Life Prediction within 

Quality Management System

• The best quality management 

systems assess whether the 

product can meet the warranty –

this is the best place to quantify 

Service Life

• A complete Service Life 

Prediction takes many years to 

create and verify – most aspects 

of the product design must be 

“frozen” first

• Propose to differentiate with 

ratings:

• New product (~6 months)

• Practiced (~2 years)

• Mature (~5 years)
 NATIONAL RENEWABLE ENERGY LABORATORY

Summary

34

• “Qualification Plus” tests improve over IEC 61215

• Nine tests that go “beyond” IEC 61215 (**new**)

• Random product sampling and periodic testing (**new**)

• Robust quality management system (PV-specific version of ISO 

9001) (**new**)

• Propose as optional version of CEC eligible hardware list

• Climate-specific, comparative tests

• Desert, Tropical, Temperate

• Open-rack or Close-roof mounting

• Quality Management System is the pathway to defining a 

standard method for ascribing Service Life

• We look for your feedback and support