Development of a Visual 

Inspection Data Collection Tool 

for Evaluation of Fielded PV 

Module Condition 

Corinne E. Packard 

National Center for Photovoltaics 

National Renewable Energy Laboratory 

Department of Metallurgical and Materials Engineering, 

Colorado School of Mines 

John H. Wohlgemuth and Sarah R. Kurtz 

National Center for Photovoltaics 

National Renewable Energy Laboratory 

NREL is a national laboratory of the U.S. Department of Energy, Office of Energy 

Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC. 

Technical Report 

NREL/TP-5200-56154 

August 2012 

Contract No. DE-AC36-08GO28308 
 

 

 

 

National Renewable Energy Laboratory 

15013 Denver West Parkway 

Golden, Colorado 80401 

303-275-3000 • www.nrel.gov 

Development of a Visual 

Inspection Data Collection 

Tool for Evaluation of Fielded 

PV Module Condition 

Corinne E. Packard 

National Center for Photovoltaics 

National Renewable Energy Laboratory 

Department of Metallurgical and Materials 

Engineering, Colorado School of Mines 

John H. Wohlgemuth and Sarah R. Kurtz 

National Center for Photovoltaics 

National Renewable Energy Laboratory 

Prepared under Task No. SS12.2560 

NREL is a national laboratory of the U.S. Department of Energy, Office of Energy 

Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC. 

Technical Report 

NREL/TP-5200-56154 

August 2012 

Contract No. DE-AC36-08GO28308 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

NOTICE 

This report was prepared as an account of work sponsored by an agency of the United States government. 

Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, 

express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of 

any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately 

owned rights. Reference herein to any specific commercial product, process, or service by trade name, 

trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, 

or favoring by the United States government or any agency thereof. The views and opinions of authors 

expressed herein do not necessarily state or reflect those of the United States government or any agency thereof. 

Available electronically at http://www.osti.gov/bridge 

Available for a processing fee to U.S. Department of Energy 

and its contractors, in paper, from: 

U.S. Department of Energy 

Office of Scientific and Technical Information 

P.O. Box 62 

Oak Ridge, TN 37831-0062 

phone: 865.576.8401 

fax: 865.576.5728 

email: mailto:reports@adonis.osti.gov 

Available for sale to the public, in paper, from: 

U.S. Department of Commerce 

National Technical Information Service 

5285 Port Royal Road 

Springfield, VA 22161 

phone: 800.553.6847 

fax: 703.605.6900 

email: orders@ntis.fedworld.gov 

online ordering: http://www.ntis.gov/help/ordermethods.aspx 

Cover Photos: (left to right) PIX 16416, PIX 17423, PIX 16560, PIX 17613, PIX 17436, PIX 17721 

Printed on paper containing at least 50% wastepaper, including 10% post consumer waste. 
1 

Abstract 

A visual inspection data collection tool for the evaluation of fielded photovoltaic (PV) modules 

has been developed to facilitate describing the condition of PV modules with regard to field 

performance. The proposed data collection tool consists of 14 sections, each documenting the 

appearance or properties of a part of the module. This report instructs on how to use the 

collection tool and defines each attribute to ensure reliable and valid data collection. This tool 

has been evaluated through the inspection of over 60 PV modules produced by more than 20 

manufacturers and fielded at two different sites for varying periods of time. Aggregated data 

from such a single data collection tool has the potential to enable longitudinal studies of module 

condition over time, technology evolution, and field location for the enhancement of module 

reliability models.

Keywords 

PV module, degradation, field data, materials 

1 Introduction and Overview

Understanding how photovoltaic (PV) modules age is crucial for predicting lifetimes, 

particularly in varied climate zones that experience different environmental stressors. Achieving 

a climate zone-dependent reliability assessment requires a combination of weather models, 

accelerated testing results, and decades worth of field data. For new module designs and 

materials, however, a long history of performance in the field is not available. Even for existing 

materials and designs, data regarding observations of degradation are variable in detail, 

consistency, and statistical significance [1-5]. Here we attempt to regularize the collection of this 

data by developing a tool for the evaluation of visually observable defects in fielded PV 

modules. The key goal in this project is to deliver a data collection tool for the comprehensive 

evaluation of visual defects that appear over time in PV modules. This work supports the 

International Energy Agency Photovoltaic Power Systems (IEA PVPS) Programme’s Task 13: 

Performance and Reliability of PV Systems, Subtask 3.2: Collecting Failures and Adapting 

Testing Methods to Failure Mechanism for PV Modules by providing a tool for the collection of 

consistent field data on module degradation and failure. 

Based on the previous experience of our team, a draft data collection tool was developed, briefly 

tested on locally fielded modules, and then applied to a series of modules at Site 1 (the Sites are 

described in detail in Section 2 of this report). Following that site visit and discussions with 

participants on the IEA task force (listed in the Acknowledgements), modifications were made to 

the collection tool to improve comprehensiveness, clarity, and form usability. Data from modules 

from Site 2 were used to further improve the form, particularly the aspects pertaining to thin film 

modules, to generate the current version of the tool. In this report, the development of the 

collection tool is described, the types of visual defects are distinguished, and suggested analysis 

are presented. 

In total, the data collection tool was developed through the evaluation of more than 60 PV 

modules that represent a broad range of technologies, vintages, and field exposure times from 

three distinct field sites. The visual evaluation focuses largely on “symptoms” such as 
2 

discoloration, haziness, and texture changes rather than “diagnoses” (e.g., hot-spots, 

electrochemical migration, etc.) to facilitate the collection of data for a larger number of modules 

than is feasible for in-depth laboratory studies, though these are recognized to be very important 

and may supplement the data collected with the tool. The collection tool consists of 14 sections 

based on module component, with inspection beginning at the rear side of the module, and then 

continuing on to the front. Every attempt was made to adhere to IEC/UL standard terminology. 

Additionally, we have attempted to balance the collection of sufficient detail for failure mode 

evaluation against desires to minimize recording time per module. Cataloging visually 

observable defects and correlating this data with electrical performance metrics will provide 

statistics that determine whether a particular visual defect is benign or will lead to efficiency

loss. It is hoped that, by the large-scale collection of data from modules currently in the field 

around the world, lessons regarding material and system degradation may be accumulated and 

that this information can ultimately be used in the prediction of module lifetime and the 

development of improved PV modules. 

2 Description of Test Facilities

Photovoltaic modules from 2 sites served as the principle testbeds for the development of the 

data collection tool, supplemented with the experience and knowledge of other professionals 

(identified in the Acknowledgements). Modules from Site 1 were inspected on location at the 

APS STAR Center (Arizona Public Services Solar Test and Research Center) in Tempe, Arizona 

USA. Modules from Site 2 were shipped from the field site at the Solar Energy Center (SEC) in 

New Delhi, India [6] to NREL for evaluation. 

Figure 1. Composition of module sets at Site 1 and Site 2 used for early testing of the data 

collection tool. 
3 

In all, 49 modules from Site 1 and 14 modules from Site 2 were inspected, representing 20 and 7 

different manufacturers, respectively. The composition of the sets of modules from the two sites 

varied significantly. As can be seen in Figure 1, the majority of modules from Site 1 were 

crystalline silicon (either monocrystalline or polycrystalline), while the majority of modules 

derived from Site 2 were based on thin film technologies. In addition to covering a broad range 

of technologies and manufacturers, these modules experienced different exposure times in the 

field: modules were fielded between 1 and 12+ years at Site 1 and 1 and 10 years at Site 2 [6]. 

Modules from Site 2 were unmounted at the time of inspection, while modules from Site 1 were 

mounted on open racks that permitted inspection from both the front and the back. 

3 Visual Inspection Data Collection Tool

A long form data collection tool is composed of 14 sections and is included in the Appendix A1 

of this report. A short form data collection tool is also presented for use in certain situations. This 

short form is discussed in Section 4 of this report. With regard to the long form, Sections 1–3 

collect information about the field site, system configuration, and module identification. Sections 

4–13 focus on individual module components, starting from the back and ending at the front of 

the module. Section 14 documents locations of electronic records (I-V curves, infrared images, 

etc.). A complementary presentation providing photographic examples of many defects is found 

in the Appendix (A2). In the sections that follow, detailed instructions are given for each part of 

the collection tool to reduce ambiguity and variation in survey responses. If a new type of defect 

is found that cannot be adequately described by the options available in the tool, a section title 

“Other” is available for recording anomalous observations at the end of the collection tool. For 

data collection requiring numerical input (e.g., altitude, length), metric units are assumed 

throughout the collection tool. In order to complete the inspection, the following tools are 

required: a tape measure with centimeter and millimeter gradations, a pen or other recording 

implement, and any personal protective equipment required by the facility. A digital camera is 

recommended. If electronic records will be taken, the following equipment is recommended: an

I-V curve tracer, and an infrared camera. In the data collection tool’s current form, it takes a pair 

of two experienced inspectors approximately 8 minutes to conduct a full visual evaluation of a 

single module. This process could be significantly streamlined for data sets consisting of a large 

number of similar modules, since several entire sections could be filled out in advance and/or 

removed from the active inspection. We estimate that a set of modules with the same model 

number and from the same manufacturer could be visually evaluated by two experienced 

individuals in a period of 4–5 minutes per module. 

3.0 Site Information

The first section of the collection tool records data regarding the date, location, and the module 

inspector. The Location field should include the site name (where applicable), city, state or 

province, and country. The Latitude and Longitude fields should be recorded to the nearest 

hundredth of a degree and should indicate the direction from the equator (+ for North, - for 

South) or from the Prime Meridian (+ for East, - for West). For example, the location of NREL 

would be recorded as Latitude: +39.74, Longitude: -105.18. Altitude should be recorded to the 

nearest meter.
4 

3.1 System Data

Section 1 focuses on collecting relevant data for the design of the PV system. For systems in 

which multiple modules are wired together in an array, details contained in the “Multiple 

module system” sub-section will provide the level of information needed to differentiate defects 

that occur only under certain system conditions that may not occur in single module researchtype installations (i.e., only in a module at the end of a string). Under System bias, one of five 

options should be selected: open circuit, resistive load (for situations where a constant resistive 

load is applied), maximum power tracked, short circuit, or unknown (for systems where the bias 

condition is not known or has been varied among different configurations throughout the history 

of the installation). The System grounding should be recorded as “grounded,” “not grounded,” 

or unknown (for systems where the grounding condition is not known or has been varied among 

different configurations throughout the history of installation). It should be noted that this section 

does not refer to the module frame grounding, which is handled in Section 7. For grounded 

systems, indicate whether the system is grounded on the positive side, negative side, or center of 

the string. If the module is not wired as part of a multiple module system, “single module” 

should be selected under System design, and the questions regarding system bias and grounding 

should be answered based on how the individual module is biased and grounded. 

3.2 Module Data

First, the module technology type should be recorded by selecting one of the following options: 

mono Si (for modules made up of single crystal silicon wafers), multi Si (for modules made 

using polycrystalline silicon cells), a-Si (amorphous silicon), CdTe (cadmium telluride), 

CIGS/CIS (copper indium gallium selenide/copper indium selenide), or other. If “other” is 

selected, the technology type should be entered into the provided blank space, avoiding 

proprietary technology names. Following recording of the system data and module technology 

type, the inspection begins at the rear side of the module. Any certifications listed on the module 

nameplate (also referred to as the label) should be indicated by checking one or more options 

listed in the Certification section and/or listing any other certifications in the space provided. If 

the nameplate does not indicate any IEC, UL, or other certifications, this category should be 

recorded as “unknown.” The estimated deployment date should be recorded as the nearest known 

date or date range in which installation occurred. If electronic records will be collected from 

multiple modules, we have found it prudent to take a photo of the module nameplate at this point 

in the inspection to mark the start of the photo set for the particular module at hand. Information 

indicated on the nameplate regarding manufacturer name, model number, and module serial 

number should be recorded in the spaces provided. If the installation site or facility marks each 

module with a serial number internal to the site, space is provided for recording this information, 

which may be left blank otherwise. The width and length of the module, measured to the outside 

edge of the module frame, should be recorded to the nearest centimeter. For modules that are 

rectangular in shape, the width is considered to be the shorter of the two measured dimensions, 

regardless of module installation orientation. The electrical performance characteristics listed on 

the module nameplate should be recorded under the Nameplate section, where Pmax is the 

maximum power, VOC is the open circuit voltage, Isc is the short circuit current, Sys Volt is the 

rated system voltage, Vmax is the maximum voltage, Imax is the maximum current, If is the fuse 

current rating for the bypass diode, and Series fuse corresponds to the current rating for the series 

fuse. If any of the previously listed specifications are not indicated on the nameplate, the 

corresponding space(s) should be left blank. 
 

 

 

 

 

 

 

3.3 Rear-Side Glass 

Section 3 corresponds to the evaluation of glass on the backside of the module. If the module 

construction simply has a backsheet and no rear-side glass, the section should be marked as “not 

applicable” and the inspector should proceed to Section 4. For modules with rear-side glass, the 

extent of damage should be evaluated. If the rear-side glass is in like-new condition, “no 

damage” should be marked and the inspector should proceed to Section 4. For modules with 

some type of damage, the damage should be categorized as “small, localized” if the damage is 

restricted to isolated areas totaling less than 10% of glass area, while damage that affects 

substantial area (> 10% of area) and/or appears to be associated with module failure should be 

marked as “extensive.” For modules that exhibit either small, localized damage or extensive 

damage, the inspector should mark all applicable damage types, consisting of “crazing or other 

non-crack damage,” “shattered (tempered),” “shattered (non-tempered),” “cracked,” and 

“chipped.” Differentiating between tempered or non-tempered glass is accomplished by 

observing the size and shape of the shattered glass fragments; glass that has been tempered 

exhibits many small fragments, whereas non-tempered glass tends towards larger, sharp shards. 

For modules that have cracked or chipped, further information regarding the number of 

cracks/chips and their locations should be cataloged by filling in the additional information in 

(a.) for cracked modules and (b.) for chipped modules. Regarding cracking, it has been observed 

that cracks may occur due to features intrinsic to a module design or its behavior in the field (hot 

spots, etc.) or due to extrinsic occurrences such as impact by hail, rocks, or other foreign bodies. 

As such, the inspector is asked to provide the location of the crack origin by choosing among the 

options: module corner, module edge, cell, junction box, and foreign body impact location. 

3.4 Backsheet 

Section 4 describes the backsheet in modules that exhibit this type of construction. If the module 

does not have a backsheet (for example, a module with rear-side glass instead), the section 

should be marked as “not applicable” and the inspector should proceed to Section 5. Modules 

having a backsheet are evaluated based on their appearance, texture, material quality, and 

evidence of damage. The backsheet generally consists of a white plastic sheet or laminate that 

covers the back of the module. The appearance of the backsheet should be categorized as “like 

new,” “minor discoloration,” or “major discoloration.” Discoloration that is considered minor 

refers to an observed color that is most easily described as a tone of the original color (for 

example, a backsheet that was originally white shows off-white or yellowish-white coloring), 

while major discoloration is reserved for cases where the discolored area is better described as a 

different color (e.g., yellow, brown, or black). Given options for evaluating the defects in the 

texture of the backsheet include the following: like new, wavy (not delaminated), wavy 

(delaminated), and dented. “Wavy (delaminated)” should be selected for cases where bumps, 

bubbles, or ripples in the backsheet have an air gap between the backsheet and the rest of the 

module or between layers of a multilayered backsheet. The Material quality section is evaluated 

by passing a finger across the backsheet. Evidence of white powder transfer to the finger 

indicates a chalking quality which should be categorized as either “slight” or “substantial,” 

depending on the amount transferred. 

As in Section 3, the inspector is asked to evaluate Damage to the backsheet by indicating the 

types of damage present and providing additional detail for each according to the 

correspondingly lettered follow-up questions. The fraction of area exhibiting a particular damage 

type should be estimated by eye to the closest available option among <5%, 5–25%, 50%, or 75– 

5 
 

 

 

 

 

 

100% (consistent overall). Photographs of damage to module backsheets including burn marks, 

bubbles, and delamination can be found in Slides 6 and 7 of A2. 

3.5 Wires/Connectors 

Section 5 pertains to the wires protruding from the junction box and the connectors on those 

wires. If there are no wires and/or there are no connectors, the corresponding section should be 

marked as “not applicable” and the inspector should proceed to Section 6. For modules that have 

wires, their coating should first be evaluated as “like new,” “pliable, but degraded,” or 

“embrittled” by light, manual manipulation. If the wires exhibit damage, such as 

cracked/disintegrated insulation, burn marks, corrosion, or animal bites/marks, all types of 

damage present should be marked. The condition of the connectors should also be cataloged, as 

well as connector type and any observed damage. Photographs of damaged wires and connectors 

and common connector types are found in Slides 8 and 9 of A2. 

3.6 Junction Box 

Section 6 focuses more closely on the junction box itself. For modules where the junction box is 

incorporated inside the frame of the module, the inspector should mark the section as “not 

applicable/observable” and proceed to the next section. The physical state of the junction box is 

evaluated first. If the component is damaged in a way that alters its shape or is in a state that 

manipulation would be expected to result in fragmentation, the physical state should be marked 

as “unsound structure.” The damage to the junction box should be further classified by selecting 

all applicable damage types among the following options: weathered, cracked, burnt, and/or 

warped. “Weathered” refers to damage due to environmental exposure such as UV damage, 

abrasion, or leaching and is manifested as a color or texture change. The condition of the 

junction box lid is to be classified as “intact/potted” (intended for undamaged lids and for 

junction boxes that are encapsulated or filled with silicone sealant or other potting compound 

during manufacture), “loose,” “fell off” (if it is no longer present), or “cracked.” 

Following inspection of the junction box itself, the inspector should direct attention to the 

adhesive that secures the junction box to the back of the module. For modules in which a bead of 

adhesive is visibly protruding from underneath the junction box, the inspector should mark 

“applicable” and should evaluate the attachment of the junction box and the adhesive pliability 

by light, manual manipulation. For a module where the junction box’s adhesive is not visible (for 

instance, it may be attached by double-sided tape that does not protrude), “not 

applicable/observable” should be marked and the inspector should advance to the evaluation of 

the junction box wire attachments. For modules with attached wires, the inspector should 

evaluate how well attached the wires are to the junction box, the quality of the seal between the 

wires and the junction box (if there is no seal or the seal is compromised in a way which would 

allow liquid water to flow into the junction box, “seal will leak” should be chosen), and whether 

there is evidence of prior arcing. 

3.7 Frame Grounding 

Section 7 evaluates the presence and condition of frame grounding. If the module design is 

frameless or the module frame is non-conductive, check “not applicable” and move to the next 

section. For module designs that lack a proper frame grounding clip or connection and/or for 

modules that have such a fixture, but has not been connected, the inspector should mark the 

Original state as “no ground.” Wired or resistive grounds should be marked accordingly. 

6 
 

 

 

 

“Unknown” is provided as an option for situations where the frame grounding has been varied 

over time or is unknown, as is common in cases where the modules have been taken from the 

field site for evaluation elsewhere. Evaluation of the Appearance provides the options of “not 

applicable” (for cases where no frame grounding mechanism is evident), “like new,” “some 

corrosion,” or “major corrosion.” Finally, the Function of the frame grounding is visually 

evaluated as “well grounded” or “no connection.” 

3.8 Frame 

Beginning with Section 8, the inspection is conducted on the front side of the module. For glassglass laminate modules that do not have a frame, “not applicable” should be selected and the 

inspector should proceed to Section 9. In inspecting the Appearance of the frame, the inspector 

should choose one option from among “like new,” ”damaged,” or “missing.” Any evidence of 

damage including minor corrosion, major corrosion, frame joint separation, frame cracking, a 

bent frame, and/or discoloration should be recorded by selecting as many options as apply. 

Evidence of discoloration or corrosion may occur due to the damage to an anodization layer 

either during manufacture, shipping, installation, or use. A frame joint separation of >0.25 mm 

has been suggested as a threshold separation distance for classification as a defect [7]. Often a 

bead of adhesive is applied between the top surface of the module and the frame. For 

manufacturing purposes, it has been suggested that a proper adhesive application should be 

smooth, consistent, and uniform with a height of not less than 1 mm and not more than 6 mm [7]. 

The inspector should evaluate the presence and uniformity of this adhesive if it is visible. 

3.9 Frameless Edge Seal 

Frameless modules may employ an edge seal, which is the subject of inspection in Section 9. An 

edge seal is a seam of polymeric material that is intended to create a moisture barrier between 

plates of glass. It is usually white or gray in color and is not to be confused with a bead of 

silicone sometimes placed between plates of glass in frameless modules (Examples of each are 

shown on Slide 13 of A2). The inspector should evaluate the appearance of the edge seal, giving 

further information about the fraction of area affected if the material is discolored. All applicable 

damage types should be selected, with the fraction of area affected indicated if delamination has 

occurred. Photographs of damaged edge seals are provided on Slide 14 of A2. 

3.10 Glass/Polymer (Front) 

Section 10 focuses on the condition of the front panel of the module. The front panel material 

should be chosen from among the following options: glass, polymer, glass/polymer composite, 

or unknown. The features of the front panel, such as whether it is smooth (has a flat surface with 

no intended texture), slightly textured (raised features << 1 mm in size), has a pyramid/wave 

texture (textured features ~1 mm in size), and/or has an antireflection coating, should be noted. 

The Appearance field documents the presence, location, and degree of soiling on the glass. 

Soiling refers to any foreign matter deposited on the front panel or degradation caused by 

sedimentation of rainwater, ion leaching, or ion exchange, and is more prevalent in framed 

modules [2]. Oftentimes, the composition of soiling consists of an assortment of soot particles, 

soluble salts, and fine and coarse deposited particles, the composition of which is discussed in 

detail in Ref. [8]. For the purposes of this data collection tool, the module is inspected in its 

present condition without washing. As such, we do not differentiate between soiling that may be 

removed by washing and that which is well adhered to the surface. “Lightly soiled” is 

7 
 

 

 

 

differentiated from “heavily soiled” by the likelihood of influencing light transmittance, where 

“heavily soiled” is expected to significantly obscure transmittance in the area which is affected. 

Damage to the front panel should be classified as to its degree (“no damage,” “small, localized,” 

or “extensive”) and the type of damage present. For further detail on differentiating between 

degrees of damage and identifying damage types, the inspector should refer to the guidance 

provided in Section 3.3 of this report. Photographs of damage and soiling are available on Slides 

17 and 18 of A2. 

3.11 Metallization 

Section 11 covers the inspection of cell metallization and electrical interconnect within a module. 

For the purposes of this collection tool, we have adopted the following definitions with regard to 

individual metallization and interconnect components, comprising up to four levels of 

metallization: 

1.	 Gridlines/Fingers- finest level of metallization, <1mm wide 

2.	 Busbars- connect gridlines/fingers within a single cell; often obscured by cell
 

interconnect ribbon
 

3.	 Cell Interconnect Ribbon- connects multiple cells into a string 

4.	 String Interconnect- connects multiple strings of cells 

A schematic distinguishing these components is presented on Slide 17 of A2. All four levels of 

metallization may not be utilized, depending on the module configuration (particularly for thin 

film modules). If any given level of metallization (as defined above) is not present or is not 

observable (e.g., busbars are obscured by overlapping cell interconnect ribbon, string 

interconnect is covered by module frame, etc.), the inspector should mark the corresponding 

section as “not applicable/not observable.” For metallization that can be visually inspected, the 

inspector should evaluate its appearance and any damage. If a particular metallization component 

shows discoloration, the fraction of metallization area that is affected should be estimated to the 

nearest category (<5%, 5–25%, 50%, 75–100% (consistent overall)). “Light discoloration” is 

taken to mean an apparent luster loss or yellowing of the metallization, while “dark 

discoloration” is reserved for metallization that is brown or black in color. Corrosion is marked 

by the presence of galvanic products that may appear powdery, white, light gray, and/or have a 

yellow, blue, or green tinge. Burn marks are often indicated by the presence of brown or black 

coloration, bubbling or melting of the polymeric encapsulant, and/or glass breakage or local loss 

of backsheet material (c.f. damage caused by hot-spots in resistive solder bonds in Ref. [5]). 

Slides 18 and 19 of A2 illustrate some of these conditions. 

3.12 Silicon (Mono or Multi) Module 

Section 12 pertains to single and polycrystalline silicon modules. Amorphous silicon and other 

thin film modules should not be evaluated under this section, thus “not applicable” should be 

marked and the inspector should proceed to Section 13. For modules where this section is 

applicable, the inspector should first record the total number of cells in the module, the number 

of cells composing each string, and the number of strings wired in parallel. The cell size should 

be measure to the nearest tenth of a centimeter. The minimum distance between the frame and 

8 
 

 

 

 

 

 

 

 

 

 

 

the closest cell, as well as the closest distance between cells in a string, should be recorded using 

the options available on the data collection tool. 

Following inspection of the layout, Discoloration is evaluated. Discoloration mainly refers to the 

darkening and loss in transparency of the encapsulant on top of silicon PV cells [9-13]. Firstly, 

the inspector should classify the predominant discoloration as “none/like new,” “light 

discoloration,” or “dark discoloration.” Here, “light discoloration” is intended to represent the 

development of yellowing or haze, while “dark discoloration” is reserved for orange or brown 

shades. The inspector should record pertinent details about the number of discolored cells, 

degree of discoloration, and all locations where discoloration is present. The area above the 

junction box should be evaluated separately, and compared with any predominant discoloration 

over the rest of the module, as increase temperature in this area may enhance existing or generate 

new degradation mechanisms [2]. Slides 20–22 in A2 illustrate several different common and 

rare discoloration patterns. 

The presence of Damage and Delamination are evaluated in successive sections. In both cases, 

all damage types that are present and delamination locations should be noted, and additional 

detail should be provided if the defect has a lettered cross-reference for further evaluation. 

Additional information regarding delamination in silicon modules and worm marks 

(interchangeably called snail tracks) can be found in Refs. [2] and [14], respectively. Many 

photographic examples are provided on Slides 23 and 24 of A2, which illustrate specific types of 

defects. 

3.13 Thin Film Module 

Section 13 pertains to thin film modules including amorphous silicon, CdTe, CIGS/CIS, and 

emerging technologies that are more similar to these than crystalline silicon wafer technologies. 

It is expected that either Section 12 or Section 13 will be completed in full, but not both. If this 

section is applicable to the module under inspection, the inspector should first describe the 

module layout by providing the total number of cells (with each cell defined by adjacent scribe 

lines, generally resulting in >30 cells per module), the number of cells per string, and the number 

of strings wired in parallel, if applicable. Cell size should be estimated to the nearest tenth of a 

centimeter, with the width and length considered to be the short and long directions, respectively. 

The minimum distance between the frame and cells edges should be categorized as less than or 

greater than 10 mm. 

Following evaluation of the module layout, the Appearance is inspected. Subtle changes from 

the original color or appearance or changes over <10% of the module area should be noted as 

“minor/light discoloration,” while gross changes to the appearance or color or that cover >10% 

of the module should be marked as “major/dark discoloration.” If any discoloration is observed, 

the inspector should provide additional information regarding discoloration type and location, 

marking all applicable options. Damage to the module is then evaluated, using similar 

definitions for the extent of damage as used throughout the collection tool. Any applicable 

damage types should be selected from among the list: “burn mark(s),” “cracking,” “possible 

moisture” (for cases where there is evidence of corrosion or moisture ingress or the potential for 

moisture ingress), and “foreign particle embedded” (which refers to a manufacturing defect that 

occurs during the lamination process, but is cataloged in case its presence precipitates additional 

defects). Lastly, the module should be inspected for evidence of Delamination. The extent of 

9 
 

 

 

 

 

 

delamination should be categorized as “no delamination,” “small, localized,” or “extensive.” 

Any locations where delamination has occurred should be noted, as well as the predominant 

delamination type, which can be categorized as “absorber delamination,” “AR coating 

delamination,” or “other.” Absorber delamination is marked by a silver or sparkling appearance 

that often begins from module edges and follows along the edges of scribe lines to create a 

characteristic appearance referred to as ‘bar-graph’-type delamination [15, 16], whereas AR 

coating delamination has the appearance of bubbles or buckling [17]. Photographs of modules 

demonstrating an assortment of defects are shown in Slides 25 and 26 of A2. 

3.14 Electronic Records 

Section 14 provides a space to record various electronic records. If no electronic records are 

taken, “not applicable” should be marked and the rest of the section should be bypassed. Spaces 

are provided to provide the filenames for electronic records of digital photo files, I-V curve(s) 

[18], and electroluminescence (EL) and infrared (IR) images. Space is also provided for 

recording the measured irradiance and temperature and the sensors used for their respective 

measurements. If I-V response is measured, the inspector should evaluate the connector function 

as one of the provided options: functions, no longer mates, or exposed (connector does not 

properly seal the electrical connection). The inspector may also choose to perform a test of the 

bypass diodes. If this test is performed, the total number of diodes should be recorded, along 

with the number of diodes that are found to be shorted or in open circuit condition, and any 

evidence of damage or overheating of diodes. 

4 Short Form Data Collection Tool 

Though a detailed knowledge of module condition is often necessary to diagnose the cause of 

degradation or failure, it may not be practical to collect all of the detailed data requested in A1. 

In cases where large numbers of modules must be processed quickly (PV recyclers, warrantee 

return, and field inspection of grid-scale installations, for example), collecting a subset of data 

can still provide meaningful, yet less comprehensive, statistics for failure analysis purposes. In 

A3, we have provided a short form collection tool. This tool follows the same structure and 

format as the long form collection tool in A1, while removing much of the detail about damage 

location and quantification of damage extent. As a result, select data fields from A1 and A3 can 

be merged for analyses. 

5 Data Analysis 

Since the purpose of this project was to develop a standardized inspection data collection tool for 

visually observable defects in fielded PV modules that could be related to module degradation 

and failure, analysis of the data collected is premature. Regardless, suggestions can be made on 

how to conduct such future analyses pertaining to climate-zone dependent degradation, 

frequency of defect appearance over time for a given set of modules, or the specific influence of 

certain defect types on electrical performance. Such preliminary analysis of the data collected 

from Sites 1 and 2 are enumerated below in Table 1. As the data collection tool was being 

improved at the time of data collection, there were differences in the tool itself and the 

instructions given to inspectors for evaluation of modules from the two sites. As such, the data 

are presented separately, rather than in aggregate. Differences in commonly observed defects 

between the sites may be partially attributable to (1) differences in data collection procedure (as 

10 
 

 

 

 

 

 

 

 

 

described above), (2) variations in age and composition of the modules between the sites (c.f. 

Fig. 1. For example, encapsulant discoloration is a common defect in the Site 1 modules, which 

are predominantly mono- or multi-crystalline silicon, whereas this defect does not appear in the 

list most frequently observed defects for Site 2, composed of mainly thin film modules), and/or 

(3) differences in environmental stressors in the two locations. Large-scale data collection, 

aggregation, and detailed analysis are needed to distinguish these effects. 

Table 1. Top Five Most Commonly Observed Defects in Module Sets from Site 1 and Site 2 

Site 1 Site 2 

Observation 

% of 

Modules Observation 

% of 

Modules 

Glass (front): Lightly soiled 55% Glass (front): Small, localized 

damage 50% 

Glass (front): Bird droppings 24% Wires: Pliable but degraded 43% 

Connectors: Pliable but degraded 22% Glass (front): Lightly soiled 43% 

Encapsulant: Major discoloration 20% Junction box: seal will leak 36% 

Backsheet: Small, localized damage 20% Thin film module: Distance 

between frame and cells <10 mm 

36% 

If the proposed visual inspection tool becomes widely adopted, a variety of data mining and 

analysis techniques may provide useful for understanding module degradation and failure. Basic 

analyses may include identification of the most frequently observed defects among a set of 

identical modules in a single location. An extension of this type of study might seek to identify 

which defects are more likely to be associated with decreased performance ratio and which 

defects are more likely to be benign, similar to the approach of Ref. [2]. More comprehensive 

studies could compare data from similar module types in a single location over time (c.f. Refs. 

[3, 4]) or over multiple locations for the same amount of field exposure time. Comparison within 

and between these kinds of studies would be greatly simplified if identical types and amounts of 

data are collected and compiled in a similar manner. Degradation issues that arise from 

environmental exposure may be correlated with climate zone through the linkage of defect 

frequency with latitude and longitude data. Statistical analysis of very large sets of data may 

reveal more subtle connections between specific defects or groups of defects and their 

correlation with the electrical performance characteristics of modules. This type of data is 

currently in limited supply, though analytical frameworks for assessing reliability based on field 

degradation studies are in development (c.f. Ref. [1]). If visually observable defects can be 

correlated or conclusively linked with the measured electrical performance degradation rates, 

visual inspection may provide a relatively low impact method for assessing which PV 

installations may be more likely to see accelerated degradation based on the frequency and types 

of defects that develop. 

6 Conclusion 

This report summarizes our attempts to create a documentation aid for global data collection and 

aggregation of long-term PV degradation, especially with regard to climate zone-specific 

weathering. A data collection tool was developed, tested, and improved through the inspection of 

over 60 modules from a variety of technology types from more than 20 manufacturers and 

11 
12 

fielded at three different sites, and the input of professionals with decades of combined 

experience in the field. Details in this report and associated supplementary material are provided 

to aid identification of different defect types. Additionally, a preliminary analysis of data 

collected from two sites identifies the most commonly observed defects and suggests a wide 

assortment of future capabilities in data analysis and reduction if this inspection tool or 

something similar becomes widely adopted. 

Acknowledgements 

This work was supported by the U.S. Department of Energy under Contract No. DE-AC36-08-

GO28308 with the National Renewable Energy Laboratory. We also acknowledge the 

contributions of Ulrike Jahn (TÜV Rheinland Immissionsschutz und Energiesysteme GmbH, 

Germany), Karl Berger (Austrian Institute of Technology), Thomas Friesen (Scuola Universitaria 

Professionale della Svizzera Italiana), and Marc Koentges (Institut fuer Solarenergieforschung 

GmbH Hameln/Emmerthal) (Lead of IEA PVPS Task 13 Subtask 3.2) in developing the format 

and content of the data collection tool. Special thanks are also due to Cassius McChesney of 

Arizona Public Service for providing access to modules that were deployed there.

References 

[1] M. Vazquez and I. Rey-Stolle, "Photovoltaic module reliability model based on field 

degradation studies," Progress in Photovoltaics, vol. 16, pp. 419-433, Aug 2008. 

[2] P. Sanchez-Friera, et al., "Analysis of degradation mechanisms of crystalline silicon PV 

modules after 12 years of operation in Southern Europe," Progress in Photovoltaics, vol. 

19, pp. 658-666, Sep 2011. 

[3] E. D. Dunlop and D. Halton, "The performance of crystalline silicon photovoltaic solar 

modules after 22 years of continuous outdoor exposure," Progress in Photovoltaics, vol. 

14, pp. 53-64, Jan 2006. 

[4] T. Ishii, et al., "Long-term performance degradation of various kinds of photovoltaic 

modules under moderate climatic conditions," Progress in Photovoltaics, vol. 19, pp. 

170-179, Mar 2011. 

[5] J. Munoz, et al., "An Investigation into Hot-Spots in Two Large Grid-Connected PV 

Plants," Progress in Photovoltaics, vol. 16, pp. 693-701, Dec 2008. 

[6] O. S. Sastry, et al., "Degradation in performance ratio and yields of exposed modules 

under arid conditions," in 26th European Photovoltaic Solar Energy Conference and 

Exhibition, Hamburg, Germany, 2011. 

[7] D. Torp, private communication, 2011. 

[8] T. Lombardo, et al., "Soiling of silica-soda-lime float glass in urban environment: 

measurements and modelling," Atmospheric Environment, vol. 39, pp. 989-997, Feb 

2005. 

[9] W. H. Holley, et al., "Investigation into the causes of browning in EVA encapsulated flat 

plate PV modules," 1994 IEEE First World Conference on Photovoltaic Energy 

Conversion/Conference Record of the Twenty Fourth IEEE Photovoltaic Specialists 

Conference-1994, Vols I and II, pp. 893-896, 1994. 
 

 

 

 

[10]	 M. Ezrin, et al., "Discoloration of EVA encapsulant in photovoltaic cells," Antec 95 - the 

Plastics Challenger: A Revolution in Education, Conference Proceedings, Vols I-III, pp. 

3957-3960, 1995. 

[11]	 M. Ezrin, et al., "Further studies of discoloration of EVA encapsulant in photovoltaic 

modules," Antec '96: Plastics - Racing into the Future, Vols I-III, vol. 42, pp. 3260-3264, 

1996. 

[12]	 W. H. Holley, et al., "UV stability and module testing of non-browning experimental PV 

encapsulants," Conference Record of the Twenty Fifth IEEE Photovoltaic Specialists 

Conference - 1996, pp. 1259-1262, 1996. 

[13]	 P. Klemchuk, et al., "Investigation of the degradation and stabilization of EVA-based 

encapsulant in field-aged solar energy modules," Polymer Degradation and Stability, vol. 

55, pp. 347-365, 1997. 

[14]	 I. Rutschmann, "Unlocking the secret of snail trails," Photon International, pp. 114-125, 

2012. 

[15]	 T. J. McMahon, "Accelerated testing and failure of thin-film PV modules," Progress in 

Photovoltaics, vol. 12, pp. 235-248, Mar-May 2004. 

[16]	 D. E. Carlson, et al., "Corrosion effects in thin-film photovoltaic modules," Progress in 

Photovoltaics, vol. 11, pp. 377-386, Sep 2003. 

[17]	 D. DeGraaff, et al., "Degradation Mechanisms in Si Module Technologies Observed in 

the Field; Their Analysis and Statistics." NREL 2011 Photovoltaic Module Reliability 

Workshop, Golden, CO, 2011. 

[18]	 IEC, "Photovoltaic devices- Part 1: Measurement of photovoltaic current-voltage 

characteristics," vol. 60904-1, 2006. 

13 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 


 


 


 


 

Documentation of module condition 

Date _______________________ Name of data recorder______________________________ 

Location ______________________________________________ 

Latitude___________________ Longitude ________________ Altitude ___________________ 

1. System Data 

System design: ! single module ! multiple modules (a.) ! unknown 

(a.) Multiple module system: 

Module location/number in a series string (from negative) _____________ 

# of modules in series (string) _______ # of strings in parallel (array) _________ 

# of bypass diodes___________ # of modules per bypass diode ___________ 

System Bias: ! open circuit ! resistive load ! max. power tracked ! short circuit 

! unknown 

System Grounding: ! grounded (a.) 

(a.) ! negative ! positive 

! not grounded 

! center of string 

! unknown 

! unknown 

BEGIN INSPECTION AT BACK SIDE OF MODULE 

2. Module Data 

Technology: ! mono Si ! multi Si ! a--Si ! CdTe ! CIGS/CIS 

! other: ____________ 

Certification: ! unknown ! UL 1703 ! IEC 61215 ! IEC 61646 ! IEC 61730 

! other: ____________ 

Estimated deployment date _______________________ 

Photo taken of nameplate: ! yes ! no 

Manufacturer _____________________________________
 

Model # ___________________________________________
 

Serial # ____________________________________________
 

Installation Site/Facility Serial # ___________________________________
 

Width _____________cm Length _____________cm
 

Nameplate: ! nameplate missing 

Pmax _____________ Voc ____________ Isc ___________ 

Sys Volt_________ Vmax __________ Imax _________ 

Bypass diode, If ___________________________________ 

Series fuse _________________________________________ 

3. Rear-side Glass: ! not applicable ! applicable 

Damage: ! no damage ! small, localized ! extensive 

14
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

	 

	 

	 

Damage Type (mark all that apply): 

! crazing or other non--crack damage 

! shattered (tempered ) ! shattered (non-tempered ) ! cracked (a.) ! chipped (b.) 

(a.) Cracks (#):! 1 ! 2 ! 3 ! 4--10 ! >10 

Crack(s) start from: ! module corner ! module edge ! cell ! junction box 

! foreign body impact location

 (b.) Chips (#):	 ! 1 ! 2 ! 3 ! 4--10 ! >10 

Chipping location: ! module corner ! module edge 

4. Backsheet: ! not applicable ! applicable 

Appearance: ! like new ! minor discoloration 

Texture: ! like new ! wavy (not delaminated) 

Material quality --chalking: ! none ! slight 

Damage: ! no damage ! small, localized 

Damage Type (mark all that apply): 

! major discoloration 

! wavy (delaminated) ! dented 

! substantial 

! extensive 

! burn marks (a.) ! bubbles (b.) ! delamination (c.) ! cracks/scratches (d.) 

(a.)Burn marks (#):! 1 ! 2 ! 3 ! 4--10 ! >10 

Fraction of area burned: 

! <5% ! 5--25% ! 50% ! 75% --100% (consistent overall) 

(b.) Bubbles(#):	 ! 1 ! 2 ! 3 ! 4--10 ! >10 

Average bubble dimension: ! <5mm ! 5--30mm ! >30mm 

Fraction of area with bubbles > 5 mm: 

! <5% ! 5--25% ! 50% ! 75% --100% (consistent overall) 

(c.) Fraction of area delaminated: 

! <5% ! 5--25% ! 50% ! 75% --100% (consistent overall) 

Fraction of delamination that exposes circuit or cell(s) 

! <5% ! 5--25% ! 50% ! 75% --100% (consistent overall) 

(d.) Cracks/scratches (#):	 ! 1 ! 2 ! 3 ! 4--10 ! >10 

Cracks/scratches location: ! random/no pattern ! over cells ! between cells 

Fraction of area affected by cracks/scratches (approx.): 

! <5% ! 5--25% ! 50% ! 75% --100% (consistent overall) 

Fraction of cracks/scratches that expose circuit (approx.): 

! 0% ! 25% ! 50% ! 75% ! 100% 

5. Wires/Connectors: 

Wires: ! not applicable ! like new ! pliable, but degraded ! embrittled 

(mark all that apply): ! cracked/disintegrated insulation ! burnt 

! corroded ! animal bites/marks 

Connectors: ! not applicable ! like new ! pliable, but degraded ! embrittled 

Type: ! unsure ! MC3 or MC4 ! Tyco Solarlok ! other ________ 

15
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 

(mark all that apply): ! cracked/disintegrated insulation ! burnt ! corroded 

6. Junction Box: 

Junction box itself: ! not applicable/observable ! applicable
 

Physical state: ! intact ! unsound structure
 

(mark all that apply): ! weathered ! cracked ! burnt ! warped
 

Lid: ! intact/potted ! loose ! fell off ! cracked
 

Junction box adhesive: ! not applicable/observable ! applicable
 

Attachment: ! well attached ! loose/brittle ! fell off
 

Pliability: ! like new ! pliable, but degraded ! embrittled
 

Junction box wire attachments: ! not applicable/observable ! applicable
 

Attachment: ! well attached ! loose ! fell off
 

Seal: ! good seal ! seal will leak
 

other: ! arced/started a fire
 

7. Frame Grounding: 

Original state: ! Wired ground ! Resistive ground ! No ground ! unknown 

Appearance: ! Not applicable ! Like new ! Some corrosion ! Major corrosion 

Function: ! Well grounded ! No connection 

Photos taken of ! back, label, and junction box 

CONTINUE INSPECTION ON FRONT SIDE OF MODULE 

8. Frame: ! not applicable ! applicable 

Appearance: ! like new ! damaged (a.) ! missing 

(a.) (mark all that apply): ! minor corrosion ! major corrosion ! frame joint separation 

! frame cracking ! bent frame ! discoloration 

Frame Adhesive: ! like new/not visible ! degraded (a.)
 

(a.) (mark all that apply): ! adhesive oozed out ! adhesive missing in areas
 

9. Frameless Edge Seal: ! not applicable ! applicable 

Appearance: ! like new ! discoloration (a.) ! visibly degraded
 

(a.) Fraction affected by discoloration:
 

! <5% ! 5--25% ! 50% ! 75% --100% (consistent overall) 

Material problems: 

! squeezed/pinched out ! shows signs of moisture penetration 

Delamination: ! none ! area(s) delaminated (a.)
 

(a.) Fraction Delaminated:
 

! <5% ! 5--25% ! 50% ! 75% --100% (consistent overall) 

16
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 


 


 


 

	 
 


 


 


 


 


 


 


 

	 
 


 


 

10. Glass/Polymer (front): 

Material: ! glass ! polymer ! glass/polymer composite ! unknown
 

Features: ! smooth ! slightly textured ! pyramid/wave texture
 

! antireflection coating 

Appearance: ! clean ! lightly soiled ! heavily soiled
 

Location of soiling:
 

! locally soiled near frame: 

! left ! right ! top ! bottom ! all sides 

! locally soiled on glass /bird droppings 

Damage:	 ! no damage ! small, localized ! extensive
 

Damage Type (mark all that apply):
 

! crazing or other non--crack damage 

! shattered (tempered ) ! shattered (non--tempered ) ! Cracked (a.) 

! Chipped (b.) ! milky discoloration (c.) 

(a.) Cracks (#): ! 1 ! 2 ! 3 ! 4--10 ! >10 

Crack(s) start from: ! module corner ! module edge ! cell ! junction box 

! foreign body impact location

 (b.) Chips (#): ! 1 ! 2 ! 3 ! 4--10 ! >10
 

Chipping location: ! module corner ! module edge
 

(c.) Fraction of area:
 

! <5% ! 5-25% ! 50% ! 75% -- 100% (consistent overall) 

11. Metallization: 

Gridlines/Fingers: ! not applicable/barely observable ! applicable
 

Appearance: ! like new ! light discoloration(a.) ! dark discoloration(a.)
 

(a.) Fraction of discoloration:
 

! <5% ! 5-25% ! 50% ! 75% - 100% (consistent overall) 

Busbars:	 ! not applicable/not observable ! applicable
 

Appearance: ! like new ! light discoloration(a.) ! dark discoloration(a.)
 

(a.) Fraction of discoloration:
 

! <5% ! 5-25% ! 50% ! 75% - 100% (consistent overall) 

(mark all that apply): ! obvious corrosion ! diffuse burn mark(s) ! misaligned

 Cell Interconnect Ribbon: ! not applicable/not observable ! applicable 

Appearance: ! like new ! light discoloration(a.) ! dark discoloration(a.) 

(a.) Fraction of discoloration: 

! <5% ! 5-25% ! 50% ! 75% - 100% (consistent overall) 

(mark all that apply): ! obvious corrosion !burn marks ! breaks 

String Interconnect: ! not applicable/not observable ! applicable 

Appearance: ! like new ! light discoloration(a.) ! dark discoloration(a.) 

(a.) Fraction of discoloration: 

! <5% ! 5-25% ! 50% ! 75% - 100% (consistent overall) 

(mark all that apply): ! obvious corrosion ! burn marks ! breaks 

! arc tracks (thin, small burns) 

17
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 


 


 


 


 


 


 

	 


 


 


 


 


 

12. Silicon (mono or multi) module: ! not applicable ! applicable 

Number of:

 Cells in module ___________

 Cells in series/string _______

 Strings in parallel __________
 

Cell size: Width ____________ cm Length ____________ cm
 

Distance between frame and cell: ! >10 mm ! <10 mm
 

Distance between cells in a string: ! >1 mm ! <1 mm
 

Discoloration: ! none/like new ! light discoloration ! dark discoloration
 

Number of cells with any discoloration:_________________
 

of those, average % discolored area:
 

! <5% ! 5-25% ! 50% ! 75% - 100% (consistent overall) 

Discoloration location(s) (mark all that apply): 

! module center ! module edges ! cell centers ! cell edges 

! over gridlines ! over busbars ! over tabbing ! between cells 

! individual cell(s)darker than others ! partial cell discoloration 

Junction box area: ! same as elsewhere ! more affected ! less affected 

Damage:	 ! none 

(mark all that apply): ! burn mark (a.) ! cracking (b.) ! moisture
 

! worm marks/snail tracks (c.) ! foreign particle embedded 

(a.) Burns (#): ! 1 ! 2 ! 3 ! 4-10 ! >10 

(b.) Number of cells cracked: ________________ 

(c.) Number of cells with worm marks/snail tracks:_____________ 

Delamination: ! none ! from edges ! uniform ! corner(s) ! near junction box 

! between cells (a.) ! over cells (b.) ! near cell or string interconnect 

(a.) Fraction delaminated between cells: 

! <5% ! 5-25% ! 50% ! 75-100% (consistent overall) 

(b.) Fraction delaminated over cells: 

! <5% ! 5-25% ! 50% ! 75-100% (consistent overall) 

Likely interface (choose 2): 

! glass ! semiconductor ! encapsulant ! back sheet ! busbar 

13. Thin film module: ! not applicable ! applicable 

Number of cells:

 Number of cells in module ___________

 Number of cells in series/string _______

 Number of strings in parallel __________
 

Cell size: Width ____________ cm Length ____________ cm
 

Distance between frame and cell: ! >10 mm ! <10 mm
 

Appearance: ! like new ! minor/light discoloration ! major/dark discoloration
 

Discoloration type (mark all that apply): 

! spotted degradation ! haze (encapsulant browning) ! other 

18
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 


 

	 
 


 

	 


 


 


 


 


 


 


 


 


 


 


 


 

Discoloration location (mark all that apply):
 

! overall/no location pattern ! module center ! module edge(s)
 

! cell center ! cell edges ! near crack(s) 

Damage:	 ! no damage ! small, localized ! extensive
 

Damage Type (mark all that apply): ! burn mark(s) ! cracking
 

! possible moisture ! foreign particle embedded

 Delamination:	 ! no delamination ! small, localized ! extensive 

Location: ! from edges ! uniform ! corner(s) ! near junction box ! near busbar 

! along scribe lines 

Delamination Type: ! absorber delamination ! AR coating delamination ! other 

Photos taken of ! front and defects 

14. Electronic Records ! not applicable ! applicable
 

Photographs and I--V curves recorded electronically--list file names in blanks
 

Photo files ____________________________________________________
 

I--V curve ____________________________________________________
 

Connector function: ! functions ! no longer mates ! exposed
 

Irradiance ___________________________Sensor ____________________
 

Temperature _________________________Sensor ____________________
 

EL picture ______________________________
 

IR picture______________________________
 

Bypass Diode Test: ! not applicable ! applicable
 

Number of diodes:
 

In total______________, shorted__________________, open________________
 

OTHER 

19
Cataloging Module Condition by Visual Inspection
 

A2. Photographic Examples 

C.E. Packard 

NREL, Colorado School of Mines 

J. Wohlgemuth, S. Kurtz 

NREL 

4/2012 

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. 

20
Overview of Visual Inspection Checklist 

•Uses IEC/UL standard terminology 

•Attempts to balance collection of sufficient detail for failure 

mode evaluation against minimizing recording time per module 

•Consists of 14 sections- based on module component 

• This presentation provides example photographs for training purposes 

• Additional detail can be found in the full NREL report 

NATIONAL RENEWABLE ENERGY LABORATORY 2 

21
1. System Data 

NATIONAL RENEWABLE ENERGY LABORATORY 3 

22
2. Module Data 

As indicated on nameplate 

NATIONAL RENEWABLE ENERGY LABORATORY 4

23
3. Rear-side Glass 

Chips >10, module edge 

NATIONAL RENEWABLE ENERGY LABORATORY 5

24
4. Backsheet 

Large 

Bubble 

Wavy (Delaminated) Major 

Discoloration 

Peeling Texture 

(record as delamination) 

Areas missing 

(record as delamination) 

NATIONAL RENEWABLE ENERGY LABORATORY 6 

25
4. Backsheet- Detail on Damage Type
 

Burn Marks 

NATIONAL RENEWABLE ENERGY LABORATORY 7 

26
5. Wires/ Connectors 

Animal bites/marks 

h6p://www.gutachten.streib.de/bilder/index.html Cracked/disintegrated insulation 

NATIONAL RENEWABLE ENERGY LABORATORY 8 

27
5. Wires/ Connectors 

MC3 MC4 

Multi-Contact Staubli Group 

Tyco Solarlok 

Tyco Electronics 

NATIONAL RENEWABLE ENERGY LABORATORY 9 

28
6. Junction Box 

NATIONAL RENEWABLE ENERGY LABORATORY 10

29
7. Frame Grounding 

NATIONAL RENEWABLE ENERGY LABORATORY 11

30
8. Frame 

Frame joint separation 

NATIONAL RENEWABLE ENERGY LABORATORY 12 

31
9. Frameless Edge Seal 

Bead of Silicone Around Module Edges 

Not an Edge Seal- NOT Applicable White or Gray Polymeric 

Sealant Around Module 

Edge Seal- Applicable 

NATIONAL RENEWABLE ENERGY LABORATORY 13 

32
9. Frameless Edge Seal 

NATIONAL RENEWABLE ENERGY LABORATORY 14 

33
10. Glass/Polymer (front) 

Localized scratches 

(non-crack damage) 

NATIONAL RENEWABLE ENERGY LABORATORY 15 

34
10. Glass/Polymer (front) 

Lightly soiled near frame bottom 

Sanchez-Friera et al. Prog. Photovolt: Res. Appl. 2011 

NATIONAL RENEWABLE ENERGY LABORATORY 16

35
11. Metallization- Clarification of Terminology 

Up to 4 levels of metallization and interconnects considered: 

1.	 Gridlines/Fingers- finest level of metallization, <1mm thick 

2.	 Busbars- connect gridlines/fingers within a single cell; often obscured by cell 

interconnect ribbon 

3.	 Cell Interconnect Ribbon- connects multiple cells into a string 

4.	 String Interconnect- connects multiple strings of cells 

On an individual silicon cell On a silicon module Gridlines 

Busbars Cell Interconnect Ribbons String Interconnect 

Note: The condition of the busbars is often unobservable 

due to the overlap of the cell interconnect ribbon 

For thin film modulesConsider function of metallization; generally will not use all 4 levels 

NATIONAL RENEWABLE ENERGY LABORATORY 17 

36
11. Metallization 

Gridlines 

NATIONAL RENEWABLE ENERGY LABORATORY 18 

37
11. Metallization 

Dark Discoloration on String Interconnect 

Gridline 

Cell 

Interconnect 

Ribbon 

NATIONAL RENEWABLE ENERGY LABORATORY 19 

38
12. Silicon Module: Cells 

NATIONAL RENEWABLE ENERGY LABORATORY 20 

39
12. Silicon Module: Discoloration 

Dark discoloration at cell Light and dark discoloration 

edges, between cells, and with one individual cell Light discoloration over gridlines and busbars darker than others at cell center 

NATIONAL RENEWABLE ENERGY LABORATORY 21

40
12. Silicon Module: Discoloration 

Discoloration 

No discoloration Discoloration over Center Of Cells over whole cell 

NATIONAL RENEWABLE ENERGY LABORATORY 22 

41
 

12. Silicon Module: Damage 

Worm marks (snail tracks) 

M. Kontges, K. Bothe, Elektrolumineszensmessung an Photovoltaik-­‐Modulen.	
  

Photovoltaik Aktuell supplement	
  in Elektro Prak4ker 7/ 2008, p.	
  36-­‐40

NATIONAL RENEWABLE ENERGY LABORATORY 23

42
12. Silicon Module: Delamination 

Semiconductor/Encapsulant delamination Semiconductor/Encapsulant delamination 

near edges near busbar 

Sanchez-Friera et al. Prog. Photovolt: Res. Appl. 2011 

NATIONAL RENEWABLE ENERGY LABORATORY 24 

43
13. Thin Film Module 

Major discoloration/other/module edges 

Minor discoloration/haze 

Major discoloration/spotted degradation/no pattern 

NATIONAL RENEWABLE ENERGY LABORATORY 25 

44
13. Thin Film Module 

Foreign particle embedded 

Small, localized damage/ 

Possible moisture/cracking 

Absorber delamination 

NATIONAL RENEWABLE ENERGY LABORATORY 26 

45
14. Electronic Records 

NATIONAL RENEWABLE ENERGY LABORATORY 27 

46
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Documentation of module condition 

Date _______________________ Name of data recorder______________________________ 

Location ______________________________________________ 

1. System Data 

System design: ! single module ! multiple modules ! unknown 

BEGIN INSPECTION AT BACK SIDE OF MODULE 

2. Module Data 

Technology: ! mono Si ! multi Si ! a--Si ! CdTe ! CIGS/CIS 

! other: ____________ 

Estimated deployment date _______________________ 

Manufacturer _____________________________________ 

Model # ___________________________________________ 

Serial # ____________________________________________ 

3. Rear-side Glass: ! not applicable ! applicable 

Damage: ! no damage ! small, localized ! extensive 

Damage Type (mark all that apply): 

! crazing or other non--crack damage 

! shattered (tempered ) ! shattered (non-tempered ) ! Cracked ! Chipped 

4. Backsheet: ! not applicable ! applicable 

Appearance: ! like new ! minor discoloration 

Texture: ! like new ! wavy (not delaminated) 

Material quality --chalking: ! none ! slight 

Damage: ! no damage ! small, localized 

Damage Type (mark all that apply): 

! burn marks ! bubbles ! delamination 

! major discoloration 

! wavy (delaminated) ! dented 

! substantial 

! extensive 

! cracks/scratches 

5. Wires/Connectors: 

Wires: ! not applicable ! like new ! pliable, but degraded ! embrittled 

(mark all that apply): ! cracked/disintegrated insulation ! burnt 

! corroded ! animal bites/marks 

Connectors: ! not applicable ! like new ! pliable, but degraded ! embrittled 

Type: ! unsure ! MC3 or MC4 ! Tyco Solarlok ! other 

(mark all that apply): ! cracked/disintegrated insulation ! burnt ! corroded 

4747
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 

6. Junction Box: 

Junction box itself: ! not applicable/observable ! applicable
 

Physical state: ! intact ! unsound structure
 

(mark all that apply): ! weathered ! cracked ! burnt ! warped
 

Lid: ! intact/potted ! loose ! fell off ! cracked
 

Junction box adhesive: ! not applicable/observable ! applicable
 

Attachment: ! well attached ! loose/brittle ! fell off
 

Pliability: ! like new ! pliable, but degraded ! embrittled
 

Junction box wire attachments: ! not applicable/observable ! applicable
 

Attachment: ! well attached ! loose ! fell off
 

Seal: ! good seal ! seal will leak
 

other: ! arced/started a fire
 

(7. Frame Grounding: Null) 

CONTINUE INSPECTION ON FRONT SIDE OF MODULE 

8. Frame: ! not applicable ! applicable 

Appearance: ! like new ! damaged ! missing
 

Frame Adhesive: ! like new/not visible ! degraded
 

9. Frameless Edge Seal: ! not applicable ! applicable 

Appearance: ! like new ! discoloration ! visibly degraded
 

Material problems:
 

! squeezed/pinched out ! shows signs of moisture penetration 

Delamination: ! none ! area(s) delaminated 

10. Glass/Polymer (front): 

Material: ! glass ! polymer ! glass/polymer composite ! unknown
 

Appearance: ! clean ! lightly soiled ! heavily soiled
 

Damage: ! no damage ! small, localized ! extensive
 

Damage Type (mark all that apply): 

! crazing or other non--crack damage ! shattered (tempered) 

! shattered (non--tempered) ! Cracked ! Chipped ! milky discoloration 

11. Metallization: 

Appearance: ! like new ! light discoloration ! dark discoloration 

48
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

	 

12. Silicon (mono or multi) module: ! not applicable ! applicable 

Discoloration: ! none/like new ! light discoloration ! dark discoloration 

Damage: ! none 

(mark all that apply): ! burn mark(s) ! cracking ! moisture 

! worm marks/snail tracks ! foreign particle embedded 

Delamination: ! none ! from edges ! uniform ! corner(s) ! near junction box 

! between cells ! over cells ! near cell or string interconnect 

13. Thin film module: ! not applicable ! applicable 

Appearance: ! like new ! minor/light discoloration ! major/dark discoloration 

Damage: ! no damage ! small, localized ! extensive 

Damage Type (mark all that apply): ! burn mark(s) ! cracking 

! possible moisture ! foreign particle embedded

 Delamination:	 ! no delamination ! small, localized ! extensive 

Location: ! from edges ! uniform ! corner(s) ! near junction box ! near busbar 

! along scribe lines 

49