a new standard for holistic quality assurance - Q-Cells

Preprint to be published in the proceedings of the 

26 th European Photovoltaic Solar Energy Conference, 5–9 September 2011, Hamburg, Germany 

A NEW STANDARD FOR HOLISTIC QUALITY ASSURANCE 

B. Jaeckel 1 , A. Krtschil 1 , D. Cunningham 2 , N. Forney 2 , C. LaMothe 2 , A. Nguyen 2 , M. Disser 3 and A. Roth 3 

1 Q-Cells SE, Bitterfeld-Wolfen, Germany 

2 BP Solar International Inc., Frederick, Maryland, USA 

3 VDE Testing and Certification Institute, Offenbach, Germany 

ABSTRACT: In this paper we present a new standard for product quality validation with special emphasis 

on reliability and mass production monitoring to implement a better level of product quality and of better 

customer and investor confidence in the products. This new quality standard will be expressed by a new 

quality label: VDE Quality-Tested. The seal and the related criteria set a much higher technical quality 

standard as it is currently found in industry. It contains three major improvements compared to standard 

product certification and surveillance. First, we defined harder product qualification criteria, e.g. longer 

testing times combined with stricter pass/fail criteria to provide longer reliability of the modules in the field. 

Second, several inline tests like wet-leakage and high-pot-tests were implemented in mass production as 

well as a 100% product control by electroluminescence. Most of these tests are not required by standard 

module qualification and production surveillance, but appearing fails are suspected to have significant 

impact on module safety and system performance. In consequence, these additional tests will directly 

increase the confidence level of investors and costumers. Third pillar of the Quality-Tested seal is a 

quarterly monitoring of modules reliability by means of regular climate chamber tests with focus on thermomechanical 

and humidity-temperature-induced stresses. 

In summary, Q-Cells, BP Solar and VDE Testing and Certification Institute present a new quality standard 

on base of harder criteria within initial module qualification and permanent production monitoring, which 

gives direct value-add for customers in terms of better module reliability, safety and bankability for PV 

investments. 

Keywords: Qualification and Testing, Stability, PV Module, Crystalline Silicon, c-Si, Safety, Quality 

insurance, Reliability, Durability 

1 INTRODUCTION 

In recent years a systematic change in PV could be 

observed. Started decades ago when “green 

alternatives” to produce electrical power, due to the 

feed-in- tariffs PV is more and more regarded as 

pure investment. Therefore it has been getting more 

important to prove the reliability of a PV product. 

Investors, banks and consultants are asking for 

certificates and other documents to demonstrate the 

quality, durability and reliability of a PV product, and 

in consequence to minimize investment risk. 

In photovoltaics one of the major parts regarding 

reliability is usually the PV module itself. Very often 

failures occur on system level e.g. failing of the 

inverter or fuses. But the quality of the PV modules 

is a crucial factor for systems performance and 

long-term reliability. To further improve the modules 

quality it is very important to develop testing 

procedures that are adequate for today’s products 

evaluations. With this approach in mind Q-Cells, BP 

Solar and VDE started in 2010 to develop the new 

VDE Quality-Tested sequence. Herein the focus is 

set on a high confidence level in the initial 

certification of the product as well as on monitoring 

approaches for the mass production to provide more 

confidence to consumers and investors that they 

only get modules with very high quality, low power 

degradation and high safety standards. 

2 BACKGROUND OF VDE-QUALITY-TESTED 

SEAL 

The background of the VDE-Quality-Tested seal is 

best described on the VDE-webpage: 

(http://www.vde.com/en/Institute/Portfolio/Usability% 

20Test/Pages/VDEQualityTested.aspx). 

“The details for this usability-seal are as following: 

Products enjoy a high degree of acceptance among 

consumers and obviously offer substantial benefits 

to manufacturers and retailers. It is a well-known 

fact that consumers prefer products bearing a 

reliable quality label. 

VDE tested products are safe and greatly trusted by 

consumers. Moreover, consumers expect the 

products they buy to be suitable for use and 

manufactured to a high standard of quality. The 

VDE institute has responded to these demands and 

added test for suitability of use to its range of 

services offered… 

Quality Tested is the VDE Certification Mark for the 

suitability of electro technical products for use… We 

tested the quality characteristics of each product 

based on the relevant rules, laws, norms and 

special standards. In addition to the legally 

stipulated requirements (safety, EMV, health 

protection), our evaluation also takes into 

consideration the technical findings of the VDE 

experts and the expertise of the VDE Institute 

gathered from surveys, which are ultimately 

reflected in the setting of the standards, as well as 

any predictable abnormal use. 

VDE Quality Tested: Playing it safe - If you are 

involved in manufacturing or retailing, you can play 

it safe with the mark VDE Quality Tested. The 

outstanding competence of the VDE in the field of 

safety is the firm foundation on which to base the 

combination with suitability for use testing. . . . 

Products bearing the VDE Quality Mark therefore 

guarantee a high level of quality. What is so special



about it: The ID Number: With the help of the ID 

Number assigned to the relevant product you can 

learn more about additional aspects of the product 

characteristics that have 

been tested (see Figure 1). 

This offers two major advantages: 

• Helping the consumer when deciding which 

product to buy 

• Improved transparency when deciding 

which product to buy 

Access to the relevant product data sheet can be 

found at www.vde.com/certificate. Enter the 

number and you will be provided with information 

you seek. Try it out by entering the ID Number 

49000000 in the search box on the relevant web 

page.” 

3 TEST SEQUENCES AND REASONS FOR 

IMPLEMENTING THE SELECTED TESTING 

PROCEDURES 

This new quality label is the result of collaboration 

between Q-Cells, BP Solar and VDE Testing and 

Certification Institute and includes innovative testing 

methods for module design and increased sampling 

of modules for verification of quality during the 

different stages of manufacturing process. It covers 

the entire value chain of module production, 

including a 

• harder module design and safety 

qualification 

• continuous mass production inline quality 

monitoring 

• continuous offline site work monitoring. 

The following paragraphs will present the ideas 

behind the modifications and why an accelerated 

aging test sequence was developed for routine 

testing. 

3.1 Initial certification 

To qualify for the VDE Quality-Tested seal an initial 

certification following Figure 2 must be performed. 

The major differences compared to IEC 61215 [1] 

and 61730-2 [3] are, that the number of testsamples 

were doubled, the testing periods were 

increased to a damp-heat test of 1500h and a 

thermal-cycling test of 400 cycles is performed. The 

increase of testing time was based on scientific 

studies. These have shown that failure modes 

involving a high power loss starting typically to be 

detectable in the range of 1200 to 1500h under 

damp-heat (85°C / 85% relative humidity) 

conditions. There are plenty failure modes which we 

won’t describe in detail, since in here it is more 

important to detect those failures as soon as 

possible and as high efficient as possible. 

As the examples in Figure 3 on the left part show, 

four modules would pass the IEC criteria, but only 

one (sample 4) the new harder criteria after 1500h. 

The right part of Figure 3 shows some example data 

from thermal cycling tests with the corresponding 

IEC and Quality-tested pass/fail requirements. 

Although all modules would pass the tests the 

knowledge of power loss data after 300 to 400 

cycles is helpful to understand the long term 

behavior of the modules. Sample 1 obviously 

stabilizes at around 2% power loss whereas sample 

3 displays a further decrease in power. 

In addition to the increased testing times a 

dynamical load test was inserted into the UV-TC-HF 

sequence. The test is performed after the UV 

preconditioning test with a load of 1000Pa for 1000 

cycles. The aim of the dynamical mechanical load 

test is to show that the module will survive a high 

number of load cycles, typically induced by 

continuous wind blowing and wind gusts. This 

periodical stress on the module will impact the 

failure rate of PV-modules caused, e.g., by broken 

soldering points or cracked cells [4, 5]. To see the 

influence of these induced defects on the long term 

reliability the dynamical load test was inserted 

before the TC-50 and HF-10 tests. 

On top of that the pass/fail criteria for the modules 

performance were tightened up. Instead of the 

usually allowed 8% power loss [1] a VDE Quality- 

Tested module is only allowed to have a total power 

loss of 5%. These changes will dramatically 

increase the confidence that a certain module 

design will fulfill the requirements for the usually 

long warranty periods used in photovoltaics. 

3.2 Inline control: 

The initial certification is only the first step towards 

the new seal. There are several requirements for 

inline and offline testing. For a normal certificate, 

that is a combination of IEC 61215 [1] und IEC 

61730 [2, 3], VDE already specifies several inline 

tests in the PM 434 [6] document in which the 

requirements for 100% power measurement and 

100% high-pot-test are described. On top of that the 

new additional criteria for Quality-Tested modules 

are: 

• 100% Electroluminescence (EL) 

• 1% wet-leakage-test of mass production 

• a reverse-current overload-test per day 

• and a grounding-test per day 

The number of samples per day for the reversecurrent 

overload test and the grounding test are 

normalized to a production capacity of 1 mio. 

modules per year. If more modules are produced 

more samples have to be tested. 

These additional tests will provide a fast way to 

collect data about the produced products related to 

their long term reliability. Electroluminescence is a 

powerful tool to investigate cracks and other defects 

of the module on cell level. For a Quality-Tested 

module only a certain number and kinds of defects 

are allowed. The definition of these defects is part of 

the Quality-Tested definition from VDE and is based 

on internal studies and on literature [7–9]. The 

allowed number of defects depends on the number 

of cells in a module. In the basic document the 

numbers are related to a standard 60-cell module. 

The allowed number of defects of a different cell 

combination in a module can be linearly 

extrapolated. By restricting the number of defects 

the reliability of a product will increase. 

In a similar way the reverse-current overload test is 

used. By using an Infra-Red (IR) camera instead of 

a cheese cloth it is possible to observe local hotspots 

(IR-imaging). An example with the



corresponding EL-picture is shown in Figure 4. 

Locally increased cell temperatures might be 

caused by a localized higher resistivity, but possibly 

also by missing soldering points (see circles in 

Figure 4). Those missing soldering points will 

increase the current density on the other ribbon(s). 

This can increase the risk of material failure and 

might lead to e.g. arcing. Therefore IR-imaging can 

be used to look for bad soldering and is 

complementary to electroluminescence. Similar 

images can also be found in literature where the 

method is used in the same way [10, 11]. 

Since grounding is not mandatory in most countries 

there is no need for testing the ground continuity of 

the PV-modules frame. But for recent failures, e.g. 

by potential induced degradation [12, 13], a simple 

solution might be to ground the modules properly. 

To establish a safe grounding path from each part of 

the frame the implementation of the ground 

continuity test will help to increase module safety, 

usability and reliability. 

3.3 Quarterly quality monitoring 

The third part of the VDE-Quality-Tested seal is a 

quarterly monitoring of modules. In this monitoring 

several modules were tested using accelerated 

aging techniques. The full scheme of the quarterly 

testing requirements is shown in Figure 5. 

To ease the process but not to reduce the 

information quality, one shipping container is 

randomly selected from production. Nowadays a 

container typically holds around twenty modules. 

Therefore the start for the inspection is an amount 

of those twenty modules. They are checked 

according to the optical sorting criteria (OSC) 

defined by clause 7 in IEC 61215, followed by a 

power measurement and an EL-check. This data 

can then be compared to the factory values. These 

will allow for checking the calibration of the factory 

flasher and the high-pot-station as well as the 

sorting in accordance with EL-criteria. These 

measurements also help to check the packaging 

and the transport of the modules. 

As it is shown in Figure 5, four modules were 

selected after the initial check for a reliability 

evaluation using accelerated aging techniques. 

These modules are first preconditioned to proof that 

labeling is in accordance with EN-50380 [14]. Then 

the scheme shows two parallel sequences: One is 

focusing on thermo-mechanical stress tests, the 

other on the impact of humidity and temperature. 

Thermo-mechanical stress test sequence: This 

sequence consists of three major tests. The 

sequence starts with a dynamical load test followed 

by a thermal cycling test with 100 cycles. The 

parameters for the dynamical load test are the same 

as for the basic certification. The two tests will 

induce cracks and weaken solder joints in a time 

period as short as possible. The use of 100 cycles is 

based on experience and with the requirement in 

mind, that the testing routine should also provide a 

fast feedback loop for production. The test 

sequence is finalized with a hot-spot test of one 

module as it is defined in IEC 61215. The 

combination of these tests will provide in a as short 

as possible time period the most details about the 

running production related to thermal and 

mechanical issues like cracking of cells or a high 

number of finger interrupts. 

Humidity and temperature stress test sequence: 

The second sequence starts with a reverse currentoverload 

test to check soldering homogeneity as 

well as any risk for hot-spotting, fire and durability of 

a module not to fail if there is something bad with 

the PV generator [15]. The 

test is performed in accordance with IEC 61730-2, 

with the major difference that an IR-camera is used 

to detect temperature differences. After this first test 

both modules were exposed to damp-heat for 250h. 

Infant mortalities like detaching J-boxes or 

delamination due to bad materials will be 

detectable. The relatively short time will bring up the 

possibility to screen and monitor the production. To 

ensure the safety of the modules after any kind of 

aging the two consecutive tests were selected: First, 

the wiring compartment test from UL-1703 [16] to 

check the attachment of the J-Box and second, the 

ground continuity test from IEC 61730-2 to proof 

proper electrical frame connections. 

For all the above discussed tests a total power loss 

pass/fail criteria of 5% is defined. For the safetytests 

the pass/fail values from IEC 61215 and IEC 

61730 apply. 

3.4. Changes on a module the Quality- 

Tested seal - retesting requirements 

To re-qualify a changed module type the retesting 

guidelines from IEC apply with some differences: 

First, the adjusted testing times and sequences 

have to be used as shown in scheme in Fig. 1 and 

second, the harder pass/fail criteria of 5% applies. 

4 CONCLUSION 

In order to increase the high quality standard for PV 

modules it is necessary to adopt knowledge from 

field and laboratories in new standards. It is also 

important to regularly prove the quality of a product 

to customers, investors and banks. The concept 

behind the VDE-quality-tested seal for PV combines 

harder qualification criteria as well as continuous 

production and laboratory data to increase trust, 

bankability and investment assurance of a product 

labeled with the new seal. In this paper the ideas 

behind the seal and the selection of the tests are 

described and motivated for a broader 

understanding. In summary the seal consists of 

three major parts: First the initial qualification, 

second the inline testing done on a statistically 

reliable sample size, and third a quarterly testing 

sequence to control the long term reliability of the 

modules. Due to the proven high quality, durability 

and reliability of the product the risk of an 

investment is strongly reduced and projects with 

these products are more bankable. 

5 LITERATURE 

[1] IEC 61215 Ed.2: Crystalline silicon terrestrial 

photovoltaic (PV) modules - Design qualification and 

type approval (2005)



[2] IEC 61730-1 Ed.1: Photovoltaic (PV) module 

safety qualification - Part 1: Requirements for 

construction (2004) 

[16] UL 1703-3 Ed.1, Flat-Plate Photovoltaic 

Modules and Panels (2004) 

[3] IEC 61730-2 Ed.1: Photovoltaic (PV) module 

safety qualification - Part 2: Requirements for 

testing (2004) 

[4] M. Assmus, S. Jack, K.-A.Weiss, M. Koehl: 

Measurement and simulation of vibrations of PVmodules 

induced by dynamic mechanical loads; 

Progress in Photovoltaics: Research and 

Applications (2011) 

[5] S. Koch, J. Kupke, D. Tornow, M. Schoppa, S. 

Krauter, P. Grunow: Dynamic Mechanical Load 

Tests on Crystalline Silicon Modules; 25th European 

Photovoltaic Solar Energy Conference – Valencia 

(2010) 

[6] VDE PM-434: Test instruction for factory 

surveillance of terrestrial photovoltaic modules in 

accordance with VDE 0126-30-1, -30-2, -31, -32 

(2010) 

[7] M. Koentges, K. Bothe: 

Elektrolumineszenzmessung an PV-Modulen, 

Photovoltaik aktuell (2008) 

[8] M. Koentges, I. Kunze, S. Kajari-Schroeder, X. 

Breitenmoser, B. Bjorneklett: Quantifying the risk of 

power loss in PV modules due to micro cracks, 25th 

European Photovoltaic Solar Energy Conference, 

Valencia, Spain (2010) 

[9] U. Hoyer, C. Bürhop, U. Jahn: 

Electroluminescence and Infrared Imaging for 

Quality Improvements of PV Modules, 23rd 

European Photovoltaic Solar Energy Conference 

(2008) 

[10] J. H. Wohlgemuth, D.W. Cunningham, P. 

Monus, J. Miller, A. Nguyen: Long term reliability of 

Photovoltaic modules; Conference Record of the 

2006 IEEE 4th World Conference on Photovoltaic 

Energy Conversion (2006) 

[11] M. Koehl: Schlussbericht - Zuverlässigkeit von 

PV-Modulen; Fraunhofer ISE Reports (2009) 

[12] J. Siemer: Hohes Schadenspotential, Photon 

(12/2010) 

[13] P. Hacke, K. Terwilliger, R. Smith, S. Glick, J. 

Pankow, M. Kempe, S. Kurtz, I. Bennett, M. Kloos: 

System voltage potential-induced degradation 

mechanisms in PV Modules and Methods for Test, 

37st IEEE Photovoltaic Specialists Conference - 

Seattle (2011) 

[14] EN-50380: Datasheet and Label requirements 

for photovoltaic modules (2003) 

[15] P. Futan: Fehlerströme und Schutztechniken in 

Photovoltaikanlagen, 3. Sicherungstag -Würzburg 

(2010)



Figure 1: VDE Quality-Tested seal 

Figure 2: Full scheme for the design qualification process for a VDE-Quality-Tested module.



Figure 3: Results from damp-heat (left) and thermal cycling test (right) that clearly show that critical power loss 

often occurs between 1200 and 1500h of damp-heat. The increased number of cycles from 200 cycles to 400 

cycles in the thermal cycling test will additionally improve confidence to the selected module design. 

Figure 4: Example of EL (left) and IR-pictures (right) to show the effect of soldering problems that can be 

detected by IR-imaging. The correlation is quite obvious.



Figure 5: Scheme for the monthly quality check. All "intermediate measurements" are defined as a 

measurement of power, high-pot, wet-leakage-test and electroluminescence as well as a visual inspection of the 

modules.

a new standard for holistic quality assurance - Q-Cells

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