Okoro_Evaluation of Quality Management in the PV Industry

8/7/2019 Okoro_Evaluation of Quality Management in the PV Industry

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Evaluation of Quality Management Systems and TechnicalStandardization Fundamental to the Solar Photovoltaic Industry

Agatha Christy Sonma Okoro

Electrical and Computer Engineering

Jacobs University Bremen

College Ring 6

28759 Bremen, Germany

Type: Guided Research Thesis

Submitted to the School of Engineering and Sciences in partial fulfillment of the requirements for the

degree of Bachelor of Science in Electrical and Computer Engineering

Date: May 9, 2010Supervisor: Prof. Dr. Werner Bergholz

Executive Summary

As an important renewable energy resource, photovoltaic (PV) solar is rapidly gaining worldwide attention

with increased growth and global expansion. At this stage the industry needs to develop and adopt its own

quality and technical standards. Major industry players have already obtained the ISO 9001 certification for

fulfilling requirements of a quality management system developed by the International Organization forStandardization (ISO)

[1]. However certification alone is not sufficient. Manufacturers need perform a period

audit of their suppliers processes and quality management system, rather than just inspecting incoming

material. In addition to this, carrying out inline-process control will help ensure quality of the final product.

Furthermore, standardization is very critical for the industry as it will facilitate significant improvements

along the whole value chain including important areas such as material qualifications, test methods, process

automation and information technology interfaces. The PV industry hardly uses any standards except those

of the semiconductor industry which is not always suitable. Although the two industries have similar

processes, in some cases the standards for semiconductor manufacturing are beyond what is required for

PV, which contributes to unnecessary costs for manufacturers. This research investigates how quality

management systems (QMS) and standards will help to effectively control quality and manage processes in

the industry. It goes without saying that a global standard for PV companies will help reduce costs,

improve product quality and enhance further market expansion. Moreover, it will foster fair and transparent

competition and increase satisfaction for customers and other stakeholders of the industry.


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Table of Contents

1. Introduction ................................................................................................................................. 22. Statement of Motivation and Research ......................................................................................... 33. Process Management and Operation Procedures ........................................................................... 44. Supplier Quality Management ....................................................................................................... 5

4.1 Material Suppliers and Procurement Specification ......................................................................... 75. Production Processes in Crystalline Silicon Photovoltaic Technology .............................................. 7

5.1 Production of Crystalline Silicon Solar Cells ..................................................................................... 85.2 Module Production and Assembly ................................................................................................. 10

6. Optimizing and Controlling Processes through Statistical Process Control ..................................... 116.1 Control of Variation ....................................................................................................................... 116.2 Continual Improvement ................................................................................................................. 126.3 Elimination of Waste ...................................................................................................................... 136.4 Predictability of Processes ............................................................................................................. 136.5 Product Inspection ......................................................................................................................... 14

7. Process Automation and Information Technology (IT) Interfaces .................................................. 148. Quality Issues / Defects in Solar Photovoltaic Cells and Modules .................................................. 15

8.1 Tests and Measurements to Characterize Cell and Module Performance .................................... 178.2 Quality Data and Reporting ........................................................................................................... 17

9. Analysis of Quality Management Systems and Processes of PV Companies ................................... 189.1 Overview of Processes and Certifications ...................................................................................... 189.2 Comparison of Electrical Conversion Efficiencies .......................................................................... 209.3 Reliability of PV Modules in the Market ........................................................................................ 23

10.Conclusion and Recommendations .............................................................................................. 2311.References .................................................................................................................................. 2512.Appendix .................................................................................................................................... 28


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1 Introduction A photovoltaic system is typically a system that converts sunlight to electricity using cells made of

semiconductor material. The materials currently being used in photovoltaic technology include crystalline

silicon (c-Si), amorphous silicon (a-Si), cadmium telluride (CdTe), copper indium selenide (CIS), and

copper indium gallium (di)selenide (CIGS)[2]

. These materials are used to manufacture photovoltaic cells

and modules but they have different levels of energy conversion efficiency. This research will focus on the

crystalline silicon technology which is currently the most widely used compared to the thin film and hybrid

technologies.

There are three main types of crystalline silicon monocrystalline, polycrystalline (or multicrystalline), and

ribbon sheets[2]

. The essential generic manufacturing process steps are:

Silicon crystal growing or casting, and wafering Solar cell manufacture Module assembly Solar system assembly and installation

Each of these generic steps constitutes several process sequences. The first step involves growing crystals for

monocrystalline silicon or ingot casting for multicrystalline silicon. These processes are relatively energy

intensive and the resulting products are called wafers. In the second step, the wafers are taken through a

high technology semiconductor processing sequence of etching, diffusion and screen printing, to produce

solar cells. This part of the manufacturing chain is highly capital intensive due to the complexity and scale

of solar cell plants. Afterwards, the cells are tested and graded for assembly into modules. This usuallyinvolves soldering the cells together and laminating. Finally in the last step using the modules, the solar

system is assembled and then installed[3]

.

Some PV companies specialize in parts of the manufacturing chain while a few others have an integrated

supply chain. In any case, the processes require quality assurance which ensures that products are

manufactured and tested according to a specific standard, and that the manufacturing processes includes

continuous verification, auditing and improvement. However, quality assurance is not limited to the

production processes; rather it encompasses all organizational functions. Hence the need for PV companies

to adopt a Quality Management System (QMS) along with technical standards which should be tailor-made

for the industry. A QMS provides an organization with important tools to assist in improving its internal

systems for manufacturing products or providing services.

The project looks into the current status of QM and standardization in the PV industry with the objective of

identifying the gaps and recommending possible improvements.


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2 Statement of Motivation and ResearchTodays companies are faced with higher quality expectations than they were a few decades ago, and this

expectation is particularly going to increase for the PV industry. This project seeks to address some

problems in the industry such as:

Insufficient or non-existing process and quality management Insufficient standardization Lack of uniform guidelines for manufacturers on how to produce reliable systems or

components and how to install or service them[7]

Lack of accreditation laboratories, which especially affects small and medium sized companies [7] Sometimes tested and accredited product samples are not a true representation of the rest of the

products which the manufacturers label as same type[7]

.

This will be accomplished through the application of ISO 9001:2008 requirements for a QMS. For anorganization it implies the provision of products that meet customer and applicable statutory and regulatory

requirements, enhancement of customer satisfaction, and including processes for continual improvement of

the system[1]

. In addition, other important tools of total quality management (TQM) such as the Six-Sigma

concept, Demings Cycle, Statistical Process Control (SPC) and Benchmarking will also be applied[4]

.

Establishing a QM system can be a challenging task, especially for smaller companies, but the investment is

well worth it in the long run. The Global Approval Program for Photovoltaics (PV GAP) has developed a

training manual to help PV companies install a QM system easily, and inexpensively[7]

. International

organizations such as the European Photovoltaic Industry Association (EPIA), SEMI PV Group, and the

International Electrotechnical Commission (IEC), have been working to develop existing standards and

establish new ones for the industry[5][6]

. Quality Management extends to environment, health and safety

(EHS) practices for which standards are also available. However this research will mostly look into the

technical aspects of QM in PV manufacturing.

Many experts have commented that PV manufacturing is highly synergistic to the semiconductor industry.

This synergy has the negative effect of high cost in PV production due to the lack of industry-specific

standards [8]. Hence, the thesis will also analyze the degree of standardization currently in the industry and

how further progress will be an essential part of the very much needed cost-reduction in manufacturing.

Existing quality issues in the industry will be investigated and quality management tools applied as a

solution to these and other potential problems a PV company may encounter. Reference will be made to

efforts by SEMI PV, EPIA and other organizations to establish global standards for the PV industry. The

focus as mentioned earlier will be on the technical standards for crystalline silicon technology production

operations.


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3 Process Management and Operation ProceduresThe ISO 9001 standard promotes the process approach of a Quality Management System. The processapproach involves planning, controlling and monitoring the performance of input processes, including the

interactions between these processes, in order to obtain the desired output. The goal is to make

improvements in manufacturing processes in order to reduce costs, increase throughput and satisfy

customer requirements. The customers may also be internal customers at the next stage of the production

process.

Figure 1: Model of a Process-Based Quality Management System [9]

A process-based QMS provides input for management review, assesses the system effectiveness and

efficiency, and provides insight to process owners [9]. Aside from a QMS, there are other tools and

techniques which can be applied with the unifying aim of attaining a companys strategic goals. The SIPOC

diagram below is a tool used to identify all relevant elements of process improvement starting from the

suppliers, through the processes and then to the customers. It helps in defining a complex project that may

otherwise not be well scoped[10]

. An organization must first understand its processes before it can sustain

continuous improvement.


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Figure 2: SIPOC - A Six-Sigma Model for Assessing Work Processes

4 Supplier Quality ManagementThe general increase in average efficiency of solar cells over the years can be attributed partly to a better

understanding of the interaction between the production processes and material quality. For example, it was

discovered that a well-chosen diffusion process enhances the material quality due to strong gettering effects

for impurities. Similarly, the introduction of a suitable silicon nitride (SiN) film as antireflection coating is

an improvement which also enhances material quality[11]

. Due to this correlation between quality of input

materials and the final product, any issues with material supply can lead to major problems at the end of the

value chain. The cell or module manufacturer is responsible for making sure that incoming materialsconform to required quality and specifications. Hence, it should be incorporated into a companys supply

chain management objectives.

Equally important is the mode of operation of the industrys supply chain which affects its efficiency. The

PV industry mainly functions in a static supply chain mode for controlling material cost and securing the

material supply with mid-to long-term contracts (Krause & Kleemann, 2009). Other industries, such as the

automotive, electronics and semiconductor industries have moved to a dynamic and responsive on demand

supply chain. In this dynamic mode, technical as well as quality responsibilities are transferred into the

supply chain [12]. The PV industry needs to adopt this in order to achieve better improvement potentials in

terms of technology, quality, yield and cost. Efficient management of the PV industry supply chain can be a

useful step towards cost reduction, inventory optimization and quality improvement throughout the value

chain. Following innovative solutions such as IBMs smart supply chain, the complexity of todays

marketplace can be managed through integrated transactions (integrating ERPS1

to ERPS of manufacturers

to suppliers and then to customers). The smart supply chain is intelligent and enables the optimization of

the Four Flows: product flow, information flow, people/process or work flow and the cash or financial flow[12]

.

Effective feedstock management is critical to any facilitys operational plans. Improper feedstockmanagement can negatively affect the quality of the finished product. At the interface between finished

products (wafer cell module), incoming materials required for production have to be procured, except

in the case of integrated manufacturers with an internal supply.

1ERPS Enterprise Resource Planning Systems, an integrated computer-based system used to manage internal and

external resources including tangible assets, financial resources, materials, and human resources

[Bidgoli, Hossein, (2004). The Internet Encyclopedia, Volume 1, John Wiley & Sons, Inc. p. 707.]

Supplier Input Process Output Customer


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4.1. Material Suppliers and Procurement SpecificationThe PV silicon which wafer manufacturers use in production comes in a variety of geometries and purities

obtainable from myriad sources - virgin suppliers, recycle houses, brokers, IC crystal manufacturers and

internally recycled re-melt[13]

. Whereas the cell manufacturer purchases materials from suppliers of silicon

wafers, chemicals, gases, silver and aluminium pastes, etc. The quality requirements of these materials are

usually laid down by the manufacturer in a technical purchase specification. The specifications are contained

in a controlled document, with version number and revision history, and signed off between the customer

and supplier[14]

. Such specifications may include requirements such as wafer properties (diameter,

thickness, resistivity, etc.), dopant concentration and chemical purity among others. Changes in material

properties may necessitate an adjustment in the production process; hence this can have a negative effect on

the stability of the process. To maintain a stable process, manufacturers are recommended to have only one

or two suppliers, with more or less constant material properties[14]

.

Many PV module manufacturers depend on third party solar cell manufacturers for their supply of silicon

solar cells. Currently there exists no common, detailed, baseline cell procurement (or supply-chain)

specification for the industry. The standards that exist cover only performance measurement issues but not

issues faced by module manufacturers in the cell procurement stage (TamizhMani, 2009). Arizona State

University Photovoltaic Testing Laboratory (ASU-PTL) conducted a failure-rate analysis which indicated

that a large portion of the accelerated module qualification failures are related to the failure of the cell itself2

[15]. This emphasizes a need for standards in supply chain procurement, since reliability of the cells is a core

factor affecting module reliability and performance. A study report prepared by Govindasamy TamizhMani

of ASU-PTL gives guidelines for PV c-Si supply chain procurement specification, including parking, labeling

and storage requirements, and recommends their adaptation to other standards as in IEC and SEMI [15].

Another necessary action toward ensuring the right quality of materials is for manufacturers to perform a

periodic audit of the suppliers production process and quality management system. A supplier which

implements an effective quality management system is better positioned to supply high quality materials

and products according to specifications, cost and timing. This can be accomplished through appropriate

supplier development and integration program which will increase confidence in quality of suppliers

products. Moreover, manufacturers need to be aware of any significant modifications in suppliers materials

or processes in order to make an appropriate procurement decision.

5 Production Processes in Crystalline Silicon Photovoltaic TechnologyThe value chain of a manufacturing industry consists of value-adding processes from raw material to

finished product for the end customer. In the case of the PV industry, the value chain ranges from raw

2Quantitative information on the correlation of module failures to failure of cells could not be found from the reference


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silicon up to the final installed module at the customers site, including after -sales activities such as

maintenance, upgrades, grid management, etc.[12]

. The solar industry had been known to use material

rejected by the semiconductor industry. This includes seed and end cones of the crystals, and part of the

crystals that does not meet specification. However, this scrap is now in short supply since the PV industry is

growing rapidly. The required starting material is a solar grade polysilicon feedstock produced by the

Siemens process. Afterwards the polysilicon is processed through slightly different methods to obtainmonocrystalline or multicrystalline silicon.

a. Monocrystalline silicon The main technique for producing monocrystalline silicon for solar cellsis the Czochralski (CZ) method. High-purity polycrystalline is melted in a quartz crucible and

single-crystal silicon seed is dipped into this molten mass of polycrystalline. As the seed is pulled

slowly from the melt, a single-crystal ingot is formed. The ingots are then sawed into thin wafers

with 150 micrometers (mm) diameter and about 200 - 400 mm thick[16]

.

b. Multicrystalline silicon The common method of producing multicrystalline silicon is to slice thinwafers from blocks of cast polycrystalline silicon. This material is stronger and can be cut in to onethird of the thickness of monocrystalline wafers. Hence, multicrystalline cells have lower wafer cost

and less strict growth requirements[16]

.

The final wafers are sorted according to thickness and surface quality suitable for manufacturing solar cells,

and damaged wafers discarded or reworked to meet specifications.

5.1. Production of Crystalline Silicon Solar CellsThe first stage in the manufacture of crystalline silicon solar cells is wafer processing. Wafers can be

processed either in batches (vertical) or inline (horizontal). In batch processing, substrates are loaded in

carriers and transported into a process station. On the other hand for inline processing, wafers are processed

in a continuous way in all process stations[17]

. Inline processing is one of the fastest-growing production

processes for crystalline silicon solar cells. The advantages is has over the traditional batch processing is that

it achieves higher overall throughput and an improved manufacturing yield through reduced breakage of

wafers[18]

. This is due to the fact that it eliminates several handling steps unique to batch processing

techniques. The following are unit process steps for solar cell manufacturing:

Wafer Etching and Cleaning: Etching is a process of removing any crystal damage on the wafers. Wet

etching uses chemical reagents like hydrogen fluoride/water solution while dry etching makes use of gases.

Wafers are etched and cleaned to remove all particles, organic and metal impurities adsorbed on the surface

of the silicon. Wet chemical texturing is applied to roughen the surface for higher currents and thus, higher

efficiencies[17]

.


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Diffusion: In this process a P-N junction is created through doping with ions such as phosphorus, boron

and arsenic although the most commonly used is phosphorus. A layer of oxide material is grown or

deposited onto the wafer in a furnace with a flow of gas running over the wafers. Phosphorus is then

diffused into the surface of p-type silicon wafers, forming a P-N junction. Subsequently, the phosphorus

silicate glass that is formed as a by-product of the diffusion process is removed in an etch bath[19]

.

Silicon Nitride Deposition (Passivation): Silicon nitride layer is deposited to protect the wafers from

contamination during assembly. This is done through Chemical Vapor Deposition (CVD) or Plasma

Enhanced Chemical Vapor Deposition (PECVD) process. This layer serves as an antireflection coating and

reduces the losses in the bulk of the silicon and at front surface (bulk and surface passivation)[17]

.

The above processes cause some damages (recombination sites) to the wafers, therefore an additional

heating (annealing) is performed so that the crystal lattice structure of the wafer will repair itself.

Screen Printing and Back Metallization: Metallization is a process usually integrated into automatic

manufacturing lines near the end of the cell fabrication process. Typical solar cells require three screen

printed layers, the grid on the front side and the aluminum plane and silver busbars on the back. The layer

is dried before the next print process begins[20]

. After each layer is printed, the wafer is dried to remove

solvents and fired in a tunnel furnace at high temperatures of about 900 degrees to sinter metal contacts to

the cell wafer. This is followed by a laser edge isolation procedure which should be done correctly to avoid a

linear shunt edge.

Testing and Sorting: In order to increase productivity in the next process step, the solar cells are usually

tested and sorted according to efficiency, short circuit current (ISC), open circuit voltage (VOC), and fill

factor (FF). A solar simulator is used to test each cell under standard testing conditions (STC). The

manufacturer can identify process-induced defects and defect trends, and utilize this data for yield control,

process management and improvement of the preceding steps[21]

.

Process Step ParametersCrystal growth (Ingot quality) Minority carrier lifetime ()

Wire sawing Surface roughness / residue

Incoming wafer quality

Diffusion length (L) /

, defect density Wafer etching and cleaning Etch rate, impurity concentration

Texturing Texture height

Junction depth Sheet resistance

Anti-reflective coating Thickness, refractive index

Metallization Line width

Table 1: Summary ofMajor Process Steps and Corresponding Quality Parameters [22]


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5.2. Module Production and AssemblySolar cells are usually categorized into different performance bins in order to reduce mismatch power losses

in silicon-wafer based photovoltaic modules. This is a common industrial practice and the method is known

as cell binning. Assembly of the cells into a module involves the following steps: - cell layup, stringing,

mounting and electrical connection of the cells circuit in the module. Afterwards the module is encapsulated

usually with encapsulant sheet of transparent polyvinyl butyrol (PVB) or ethylene vinyl acetate (EVA) and

glass. Back-contact configuration of c-Si PV cells enables assembly using a monolithic module assembly

(MMA) method where all the PV cells can be electrically connected in a module and encapsulated in a

single step.

Figure 3: Illustration of Monolithic Module Assembly[23]Developing cells which have all contacts at the rear and so can be easily interconnected reduces the cost of

module manufacturing because it makes automation more straightforward. The next step involves framing

of the modules, usually with aluminium frames. This is followed by standard module qualification tests and

certification. Finally with the modules and balance of system (BOS)3

components, the photovoltaic solar

system is assembled and then installed at the consumer end.

As mass production in the PV industry grows rapidly, it becomes more and more crucial to implement

process control and monitoring for better productivity and quality. One means of achieving this is through

the use of Statistical Process Control.

3In a photovoltaic system, the term 'balance of system' refers to all of the system components except the PV modules.

The components consist of structures, enclosures, wiring, switch gear, fuses, ground fault detectors, charge controllers,

batteries, and inverters. [Source: http://photovoltaics.sandia.gov/docs/BOS.htm]


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6 Optimizing and Controlling Processes through Statistical Process ControlStatistical Process Control (SPC) is a statistical method of separating variation resulting from special causes

from variation resulting from natural causes, to eliminate the special causes and to establish and maintain

consistency in a process, enabling process improvement (Goetsch & Davis, 2006). A broad view of SPC

includes statistical tools such as Pareto charts, control charts, cause-and-effect diagrams, stratification, check

sheets, histograms, scatter diagrams, and run charts [4]. Control charts, being at the heart of SPC, are used

by both companies and their suppliers for processes where they offer real benefit.

Figure 4: Examples of Processes Without and With SPC (from Infineon training manual) [14]The left graph in the figure above shows a process that, without continuous control, continues to get worse.

On the other hand, the right hand side shows the graph of a process under control, with constant variations

only due to the natural causes.

Five key areas where SPC comes into play are: control of variation, continual improvement, elimination of

waste, predictability of processes, and product inspection[4]

.

6.1. Control of VariationProcess variation is an enemy of quality. SPC uses statistical tools and techniques to control variation in any

process. Special causes of variation may originate for example from the environment and the five Ms -

Machines employed, Materials used, Methods (work instructions) provided, Measurements taken, and

Manpower (people) who operate the process. Natural variation is inherent in any process and is expected to

account for 2,700 out-of-limits parts per million in a 3-sigma process, 63 out-of-limits parts per million in a

4-sigma process and 3.4 out-of-limits parts per million in a 6-sigma process[4]

. Hence, more companies are

moving to a 6-sigma process (see appendix) to achieve better performance.


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Figure 5: Sigma Levels and Equivalent Conformance Rates [24]In figure 5 above, the target value is at the center of the bell-shaped frequency distribution curve and any

variation is to the left or right of the center. A 3-sigma quality level (3 limits) translates to a yield of

99.73% while a 6-sigma quality level (6) implies a success rate of 99.99999998%[4]

. The process

parameters for which variation must be controlled around the target value are the Key Control

Characteristics (KCCs). They include parameters such as temperature, humidity, particle density, etc. The

method of Key Characteristics helps companies focus on those features that have a significant impact on

product conformity[25]

.

6.2. Continual ImprovementThis is a major element of total quality through which the improvement of processes can lead to animprovement of products and services. Improving a process requires understanding the process, identifying

external factors that may generate special causes of variation and eliminating them. However, care must be

taken to avoid tampering with the process and making changes that could yield worse results.

Figure 6:PDCA/Demings Cycle: The Wheel of Continual Improvement

Plan

Do

Check

Act

USL = Upper Specification Limit

LSL = Lower Specification Limit

= Standard Deviation

= Mean


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6.3. Elimination of WasteDuring production, defective products or products that do not meet specification are discarded as scrap.

Therefore, production performance indicators such as rework rate and scrap rate4

have to be monitored and

kept at bare minimum. SPC is a key to eliminating such waste so that a company can reduce cost and

increase the overall quality of process output.

6.4. Predictability of ProcessesSPC facilitates the predictability of processes since they will be under control. Companies that implement

SPC will be better able to know whether or not their process is capable of meeting customers requirements.

The process capability parameters are described below:

Process Capability, Cp: a straightforward indicator of process capability

Figure 7: Natural Distribution Fit within Defined Specification Limits [26]In figure 7 above, processes (a) and (b) have Cp greater than 1, (c) is equal to 1 and (d) is less than 1

[26].

Process Capability Index, Cpk: an adjustment of Cp for the effect of non-centered distribution.

A Cpk value less than 1 indicates that the process is incapable, between 1 and 3 indicates a capable process,

whereas values greater than 3 show that the process is very capable[26]

.

4Rework rate is the percentage of defective products re-processed to meet requirements while scrap rate is the

percentage of defective products that are discarded.


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6.5. Product InspectionInspection is performed on products during manufacturing (in-process inspection) and as finished goods

(final inspection). Inspection costs money, time, equipment and labor. It will be unrealistic to have a 100%

inspection of all products in a large scale manufacturing firm such as in the PV where millions of wafers

and solar cells are produced per year. Therefore products are usually sampled for inspection. The ISO 2859

standard gives detailed sampling procedures for tests and inspections [1].But for sampling to be accepted,

the process must be under control. If a suppliers process is under control and capable of meeting customer

requirements, then the manufacturer can confidently reduce inspection, and focus more on periodic audit of

the process[4]

. This also applies to the companys internal operations where the internal quality assurance

organization can reduce its inspection and process surveillance, relying more on a planned process audit

program[4]

.

SPC is applicable to all process stages in the PV industry, ranging from purity of materials and processes, to

product data analysis and quality reporting. An example is in Siemens Solar Industries where SPC is

implemented in their diffusion and cell printing lines to improve capability and electrical yields [27]. Software

interface solutions enable implementation of SPC in manufacturing equipment and automation, to provide

real-time data.

7 Process Automation and Information Technology (IT) InterfacesProcess automation involves using computer technology and software engineering to help factories operate

more efficiently and safely. Without process automation, plant operators will have to physically monitor

performance values and the quality of outputs to determine the best settings on which to run theproduction equipment

[28]. In PV manufacturing, existing and developing areas of automation include:

Process stages in solar cell manufacturing Automated material handling and transport Automated tests, inspection Cell interconnection Integrated module-edge processing system combining automated edge trimming, edge sealing

and framing processes

Automated junction-box installation system Automated buffer storage system

The SEMI PV Transport Carrier Task Force, led by Q-Cells, is looking at standards needed for PV wafer

and cell carriers, equipment load ports and transport systems within PV production lines. A new SEMI PV

Automation Standards Committee will be formed as well in Europe and Japan to focus on both mechanical


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In Total Quality Management (TQM), quality is to be expected not inspected, which means that quality

should be built into the product right from the beginning of the manufacturing process. A company which

implements a proper quality management system is better equipped to produce very reliable solar cells and

modules with minimum efficiency losses. Examples of quality and reliability problems that have been

known to occur in PV products include:

Physical defects such as bubbles, metallic inclusions, chips or cracks on a cell Misaligned cell connection string, hotspots in cells or interconnections Non-uniform sealant in module frame, delamination, glass fracture Incorrect electrical isolation between module current conductor parts and the frame Slow degradation of the short circuit current Light-Induced degradation (LID) associated with p-type CZ-Si solar cells Failure of BOS components Modules performing below labeled power output

These defects contribute to failures in PV systems and can be avoided from the beginning of the

manufacturing chain through process management and sophisticated quality assurance programs.

Understanding how these problems arise during production is essential to controlling and improving the

process in order to get the desired results. The following are some important quality detractors which need

to be monitored during production.

Detractor OutcomeCrystal defects

Impurities in chemicals, materials

These determine the material quality, and thus the

solar cell conversion efficiency

Particle density

Particles in equipment

Impurities introduced by processes

Contaminants are one of the major causes of

defects; therefore standard level of cleanliness has

to be maintained in all process steps

Improper handling

Poorly carried-out processes

Rough processing

These can affect electrical properties, e.g. low

shunt resistance leading to decrease in conversion

efficiencyFlaws in wafer dimensions

Failed mechanical and electrical properties

These have to be checked to minimize risk of

breakage and deficiencies in cell parameters

Wrong setup in production line

Defective laminating processes

Faulty frame assemblies

Such problems lead to production of modules

with poor quality and reliability

Table 2: Causes of Poor Quality in PV Cells and Modules


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Conversion efficiencies of commercial modules are typically 2% lower than bare cell efficiencies. This has

been attributed to factors such as area-related losses from cell packing density and the module frame,

absorption of the glass, cell mismatch losses and losses in the cell interconnect ribbon. Nevertheless,

developments in module technology are closing this gap[30]

.

8.1. Tests and Measurements to Characterize Cell and Module PerformanceEfficient tests and measurements have to be carried out on all solar cells during production to avoid

assembling defective solar cells in a module. In order to identify the magnitude and sources of defects, the

following parameters are most commonly measured[31]

:

Several varying test and measurement methods exist, but the three broad areas of test technology are [31]:

Spectroscopy Electrical (contact) measurements Infrared (IR) imaging

SEMI, ISO and IEC have developed standards including guidelines for tests and measurements. ISO/IEC

17025:2005 specifies the general requirements for the competence to carry out tests and/or calibrations;

including sampling using standard, non-standard or laboratory-developed methods[1]

. The certification IEC

61215:2005 of PV modules includes 17 tests which determine the thermal and electrical characteristics of themodule. These qualification tests are not expected to identify all possible module reliability issues in the

actual field. However, they cover the major design quality issues and are thus regarded as minimum

requirements for reliability testing[32]

.

8.2. Quality Data and ReportingData records provide a source of information for management to assess the performance of a system and for

quality control. Data can be stored and properly documented either digitally or in written form. For

business operations, typical records contain such things as contracts, purchase orders received, specialrequirements for products, deliveries, and meeting notes. On the other hand manufacturing records contain

data of the quality process, including tests performed to check product operating parameters, records of the

results of these tests, preventive and corrective actions, stock records, shipping, and the disposition of non-

compliant products[7]

. However, it is important to avoid unnecessary data that are not significant to the

quality of the product. The PV GAP Quality Control Training Manual provides a detailed description of

how companies can manage and utilize reports and documentations for quality control[7]

.

- Resistivity

- Current/Voltage (I-V) curves

- Capacitance/Current (C-V) curves

- Optical properties

- Charge carrier characteristics

- Free charge recombination lifetime

- Bulk material lifetime

- Effective lifetime


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9 Analysis of Quality Management Systems and Processes of PV CompaniesThere are three important aspects which can be regarded as the key performance indicators of quality in

organizations:

1. Structure quality how well a companys organizational structure influences its mode of operationfor high performance.

2. Process quality - howthe companys business and manufacturing processes are optimized for highperformance and productivity.

3. Product qualityhow well a companys product satisfies the customers and gains market share.These aspects can be perceived and measured differently, depending on the type of company. In this

section, some PV companies will be analyzed based on information obtained from their websites,

publications and PV news magazines. The aim is to have an idea of what goes on in the PV industry in

terms of quality assurance measures, process stability, automation, efficiency and reliability of cells/modules.

9.1. Overview of Processes and CertificationsTable 1 below shows information gathered from company websites and technical data sheets classified into

different categories (columns A - G):

A. Process steps stated as automated according to description of companys production processes. Somecompanies have fully automated processes while others mentioned specific processes which are

automated.

B. Information on how companies manage their incoming material supply and quality. Companies whichoperate along the whole value chain are vertically integrated and therefore do not rely on external

suppliers for silicon materials. This implies that the quality of those materials depend on their internal

operations and is not affected by damages due to transportation. Other companies indicate type of

relationship or activities with their suppliers.

C. Indicates which companies have a quality management system certified according to ISO 9001standards.

D. Indicates which companies have certification for an environmental management system according toISO 14001 standards.

E. Indicates which companies have the IEC 61215 certification for crystalline silicon terrestrialphotovoltaic (PV) modules: Design qualification and type approval.

F. Judges from the goals, mission statements, etc. found on the company website which companies seem toemphasize commitment to quality.

G. Based on description of the companys processes with regard to quality control, inspection, tests andmeasurements. (Refer to appendix for abbreviations).


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A

B C D E F GCompany/

Products

Process

automation

Supplier Quality

ManagementISO 9001 ISO 14001 IEC 61215

Company

goals show

commitment

to quality

Other quality measures

SUNTECH/

cells, modules?

Developing s upplier

relationship, virtual

integration with upstream and

downstream partners

Yes Yes YES Yes

Team of 700 quali ty control

professionals who work

closely with UL, IEC, CE, TV

Q-CELLS/

cells

Fully automated

(warehousing to

final quality

control)

Handling all product flow

logis tics through to working

on technology with s uppliers

Yes Yes Yes

Detailed documentation of test

criteria , objective and benefit,

quali ty pre-checks on

incoming wafers

YINGLI/

polysili con to

modules

Automated soldering Vertically integrated Yes Yes Yes Yes

Implements at l east 39

separate quality inspection

steps from start to finish,

stric ter ac celerated aging tests

than IEC and UL

JA SOLAR/

cells, modulesAutomated soldering ? Yes ? Yes Yes

Daily SPC, visual and

performance ins pections,

cross l inking and stripping

tests

KYOCERA/

modulesFully automated ? Yes Yes Yes Yes ?

TRINASOLAR/

ignots to

modules

?Long-term partnerships with

leading equipment suppliersYes Yes Yes Yes

Incoming inspections, in-

process qual ity control, output

inspection and test, offers

after-sales technical service

support

SUNPOWER/

modules? ? Yes ? Yes Yes

Use preventive processes and

testing

BOSCH/

wafer, cell ,

module

Automation in al lproduction lines

Suppliers subjected to thesame high quality standards

Yes Yes Yes Yes

Preventive quali ty assura nce,

packaging: suitable for digitalrecording of i ncoming goods

usi ng barcode system

GINTECH/

cells, modules

Automated

Inspection

Forming strategic alliances

with upstream polysilicon and

wafer makers

Yes Yes ? Somewhat

100% inspection for shunt

resis tance and reverse current,

in-line optical inspection on

all products

BP SOLAR/

cells, modules? ? Yes Yes Yes Somewhat

Routine use of special ized

accelerated tests to predict

product li fetime

MOTECH/

cells, modules? ? Yes Yes Yes Yes

Frequent internal monitoring

of LID, color uniformity within

cells are closely monitored

and controlled

MITSUBISHI

ELECTRIC/

cells, modules

Integrated facilities,

automated

processes

? Yes Yes Yes SomewhatAll modules are 100%

inspected

DELSOLAR/cells

Automated wafer

transport s ystem,

automation

equipment

developed in-house

Vertical integration with DeltaElectroincs

Yes Yes Yes Yes ?

SUNWAYS/

modules? ? Yes Underway Yes Somewhat

Meticul ous tolerance and

quality checks

SOLARWORLD/

raw sili con to

complete sola r

electric

systems

Automated wafer

testing a nd sorting,

highly automated

cell and module

production

Fully integrated Yes Yes Yes Yes

Cell position measured and

al igned before screen printing,

quality check on arrival of

pure silicon, continuous batch

tracking, digital data

collection of incoming goods,

internal recycling

PHOTOWATT/

ignot to

modules

? Vertical ly integrated Yes ? Yes YesQuality and relia bili ty

validated at each stage

SOLLAND/

cells

Automated

production

Work cl osely with producers

of solar modules and

suppliers (producers of

wafers, ancil lary materialsand equipment)

Underway ? Yes ?

Every cell individually tested

and sorted, visual inspection

on every si ngle cell for

mechanical and aestheticfaults

SCHOTT SOLAR/

wafers to

modules

Fully automated

wafer i nspection,

highly automated

production

Qualify and test suppliers

regularlyYes Yes Yes Yes

Strict 100% i ncoming goods

ins pection, optimum c ontrol

and monitoring of each step

ALEO SOLAR/

modules? ? Yes Yes Yes Somewhat Very strict quality control

ISOFOTON/

cells, modules? ? Yes Yes Yes Somewhat

Assures proper measurement

through verificati ons and

maintenance of its l aboratory

equipmentsTable 3: Information from Websites of 20 PV Companies around the World? No information found in that category


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As can be observed from the above table, no information was found on some company websites for certain

categories. It may mean that such information either exists in other portions of the website but were not

found, or was not stated at all on the website. Therefore the limitation of this research is that one cannot

come to any conclusions on what the company does or does not do in those areas since no field

survey/audit was involved. Nevertheless the impression is that companies which have highly automated

processes, or carry out stringent quality assurance measures and hold these of significant importance to thecompanies operations, most likely have this stated on their website. In general, all the companies

researched have ISO 9001 certification except for Solland Solar which states that its quality policy will be

certified according to that standard. Not all companies have the ISO 14001 certification but all the module

producers have IEC 61215 certification. Not much information was found from the websites on the use of

SPC in processes. But it seems that for many companies, improvement is needed in the utilization of

equipment automation and in supplier quality management.

9.2. Comparison of Electrical Conversion EfficienciesResearch and development efforts in the PV industry have been largely geared towards increasing the

conversion efficiency of solar cells and modules. Higher efficiency attained through increased productivity

and reduced costs will subsequently result in lower cost per watt peak. However there is still a large gap

between efficiency of cells produced on a large scale at the plants and those obtainable in the laboratory

(about 25% for c-Si). The conversion efficiency of a companys product to a large extent is an indication of

the companys process technology and product quality which also translates to its market performance. The

charts below show the average efficiency of solar cells and modules produced by a few companies between

the years 2004 and 2010.

Figure 9: Average Conversion Efficiency of Monocrystalline Solar Cells [33]In general, companies achieved higher efficiencies over the years for monocrystalline cells. Monocrystalline

silicon produces better efficiency cells than multicrystalline silicon material. However multicrystalline cells

are cheaper to produce, therefore more companies manufacture with this material than with monocrystalline

silicon.


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Figure 10: Average Conversion Efficiency of Multicrystalline Solar Cells [33]From the chart above, it appears that most companies achieved in average, higher efficiencies over the yearswith the exception of Sunways which has a lower average efficiency in 2010 than in 2005. The reason for

this is not clear, but looking at table 1, one may deduce that the companys processes do not reflect as much

quality assurance or quality information as some other companies in that table. However, one may also cite

economic reasons as a possible explanation for the lower average efficiency in 2010.

Figure 11: Average Conversion Efficiency of Monocrystalline Solar Modules [33]From the chart above, it can be seen that ErSol (Bosch) achieved significantly higher average efficiency in its

monocrystalline modules than the other companies. This is a reflection of better production processes and

quality management.


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Figure 12: Average Conversion Efficiency of Multicrystalline Solar Modules [33]In addition to average conversion efficiency, another important factor is the efficiency variation in the same

batch of a companys products.

Figure 13: Probability Density vs. Conversion Efficiencies in PV Cells and Modules of Companies


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The above plots show variations in efficiency of cells and modules from different companies technical

datasheets. Some product series have a narrower efficiency range than others, which is a good sign. In

contrast Photowatts multicrystalline module (bottom right) shows a very wide range of efficiencies

which explains the low average efficiency obtained in 2009 [figure 12]. Such variations may be traced to

variations in materials, processes or environmental parameters. Hence a stable and consistent process

which can be accomplished through process and quality management is essential for reducing this gap.

9.3. Reliability of PV Modules in the Market

Figure 14: Failure Rate Comparison of c-Si Modules for the 1997-2005 and 2005-2007 Periods [32]The above figure shows the results of the failure rate analysis of crystalline silicon PV modules conducted by

ASU-PTL. It shows that the failure rate dramatically increased in the period 2005-2007 as compared to1997-2005. According to the analysis, this higher percentage of failure was partly due to the market entry of

a large number of new manufacturers[32]

. This implies that the new PV manufacturers did not have as

much stringent quality management as the older companies in the industry. Such a situation poses a risk of

jeopardizing customer and investor confidence in PV products. If not properly addressed, it will curtail

progress at this stage when the industry is in constant need of improvements throughout the whole value

chain. Therefore, it is important that new PV manufacturers establish a quality management system right

from the start of their operations. Better yet, quality assurance should be enforced globally by appropriate

regulatory bodies for all companies entering the PV market. Supplemented by standardization in the

industry, companies can be equipped with uniform guidelines for operation along the manufacturing chain.

10 Conclusion and RecommendationsQuality in the PV industry is a reflection of the structure, process and product quality of PV companies.

Ultimately, such quality has to be bankable in the sense that it is stable enough to ensure profitability and


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hence attract more investors to the industry. Implementing adequate quality and process management is

instrumental to achieving this. Major companies in the industry have the ISO 9001 certification for a QM

system. However some areas still need to be improved such as in:

Supply chain efficiency shifting from a static to a dynamic and efficient supply chain Supplier QM performing periodic audits of suppliers quality system and processes Upgrade of IT structure for the supply network and equipment communication interfaces Implementing proper SPC Control for improved stability in all process stages Increasing in-line product tests to reduce rate of failed products at the end of the line Technical inspections preferably unannounced inspection of production sites to check that

manufacturers processes are continually improved and conform to quality standards

Module Certification - In addition to testing products, performing quality audit of PV processes,before issuing certifications

With new manufacturers entering the supply chain, the continued growth of the PV industry makes the

need for standards more important than ever. Standardization efforts are already underway through SEMI

PV Group in co-operation with EPIA and other technical experts in the industry. Several PV standards

committees have been formed across the globe to handle specific tasks in such areas as tests and

measurements, processes, materials and equipment.

Some PV companies have formed partnerships and strategic alliances with other companies in order to

benefit through resources such as manufacturing capability, distribution channels, equipment, expertise, etc.

This highlights the importance of benchmarking, a tool of total quality used among companies striving to

be more competitive. Benchmarking will help PV companies improve their process or product quality by

learning best practices of other companies in the industry.

Figure 15: Quality Management and Standardization PV Industry Cooperation for Good Results


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11 References[1] International Organization for Standardization (ISO). International Standards for Business,

Government and Society (2010).http://www.iso.org/iso/home.html

[2] PV Technologies: Cells and Modules. European Photovoltaic Industry Association (EPIA). (2010).http://www.epia.org/solar-pv/pv-technologies-cells-and-modules.html

[3] Solar Cell Manufacturing Plants. SolarbuzzTM. (2010). Solarbuzz, LLC. (18 Jan. 2010).http://www.solarbuzz.com/plants.htm

[4] Goetsch L. D., Davis B. S. Quality Management: Introduction to Total Quality Management forProduction, Processing, and Services. New Jersy: Pearson Prentice Hall. (2006).

[5] James Amano, Director, International Standards, SEMI. PV Standards Update. (April 2010).http://www.pvgroup.org/NewsArchive/ctr_036230.

[6] The Global Approval Program for Photovoltaics (PV GAP).http://www.pvgap.org/index.html[7] Varadi, P. F., Dominiguez, R. and Shaeffer, L. Quality Management in Photovoltaics: Manufacturers

Quality Control Training Manual. Quality in Manufacturing: General Concepts. Global Approval

Program for Photovoltaics (PV GAP). Geneva, Switzerland. (Feb. 2002).

[8] George Marsh. PV Manufacture: Synergy Without Dependence. (01 Mar. 2009). Renewable EnergyFocus. 17 Jan. 2010. http://www.renewableenergyfocus.com/view/3187/pv-manufacturesynergy-

without-dependance/

[9] Ron Sedlock. The Process-Based Approach: Going Beyond Auditing to Assessing. American Societyfor Quality (ASQ) San Diego Sect. 703 Meeting. (May 9, 2006). The Quality Catalyst. Melrose,

Florida USA.

[10]Kerri Simon. SIPOC Diagram. iSixSigma: Quality Resources for Achieving Six Sigma Results.http://www.isixsigma.com/index.php?option=com_k2&view=item&id=1013:sipoc-

diagram&Itemid=219

[11]Dietmar Borchert, Markus Rinio. Interaction between Process Technology and Material Qualityduring the Processing of Multicrystalline Silicon Solar Cells. (March 20, 2008). Springer

Science+Business Media, LLC. (2008).[12]Rainer Krause, Udo Kleemann. Supply Chain Management in the PV Industry. IBM Deutschland,

Mainz, Germany. PV-tech. (2009).

[13]Crabtree, G., Jester, T. L., Fredric C., Nickerson J., Meemongkolkiat V. and Rohatgi A. ProductionViability of Gallium Doped Mono-Crystalline Solar Cells. Shell Solar Industries, Camarillo, USA.

School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, USA.
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[14]Prof. Dr. Werner Bergholz. Jacobs University Bremen, Germany. Microelectronics. (Spring 2010).[15]Govindasamy TamizhMani. Crystalline Silicon Terrestrial Photovoltaic Cells Supply Chain

Procurement Specification Guideline. Arizona State University Photovoltaic Reliability Laboratory.

(March 2009). Solar America Board for Codes and Standards (Solar abcs).

[16]Olivia Mah. Fundamentals of Photovoltaic Materials. National Solar Power Research Institute, Inc.(December 21, 1998).

[17]Crystalline Silicon Solar Cell Technology. Energy Research Centre of the Netherlands.http://www.ecn.nl/units/zon/rd-programme/silicon-photovoltaics/crystalline-silicon-solar-cell-

technology/

[18]Johan Hoogboom et al, Mallinckrodt Baker B.V. Surface Modification for Efficiency Improvementof Inline Solar Cell Manufacture. Deventer, The Netherlands. PV-tech.

[19]Cell Production from Inside. Q-Cells AG. www.q-cells.com[20]Sefar Knows Solar. Sefar AG.http://www.sefar.com/htm/609/en/Solar-Industry.htm?Folder=31423[21]Dr. Seth P. Bates. Silicon Wafer Processing. San Jose State University, USA. Applied Materials.

(Summer 2000).

[22]B. Sopori, Y. Zhang, and W. Chen. Process Monitoring in Solar Cell Manufacturing. NationalRenewable Energy Laboratory (NREL). (October 1999).

[23]James M. Gee and Ted F. Ciszek. The Crystalline-Silicon Photovoltaic R&D Project at NREL andSNL.http://photovoltaics.sandia.gov/docs/cells5.htm

[24]Thomas Pyzdek, Paul Keller. The Six Sigma Handbook.(Chapter 3). Quality Publishing. (1999).[25]Don J. Lee, Anna C. Thornton. The Identification and Use of Key Characteristics in the Product

Development Process. Department of Mechanical Engineering, Massachusetts Institute of

Technology, USA. (1996).

[26]Process Capability: How to Understand it. Quality Tools: Tools and Techniques for QualityImprovement and Problem Solving.http://syque.com/quality_tools/toolbook/Procap/how.htm

[27]C.E. Witt, R.L. Mitchell, H.P. Thomas, M.L. Symko, R. King, and D.S. Ruby. ManufacturingImprovements in the Photovoltaic Manufacturing Technology (PVMaT) Project. NationalRenewable Energy Laboratory (NREL). (July, 1998).

[28]What is Process Automation? The ABB Group.http://www.abb.com/cawp/db0003db002698/b3913fe3a1296b7bc12571f10040f47f.aspx
http://www.ecn.nl/units/zon/rd-programme/silicon-photovoltaics/crystalline-silicon-solar-cell-technology/http://www.ecn.nl/units/zon/rd-programme/silicon-photovoltaics/crystalline-silicon-solar-cell-technology/http://www.ecn.nl/units/zon/rd-programme/silicon-photovoltaics/crystalline-silicon-solar-cell-technology/http://www.q-cells.com/http://www.q-cells.com/http://www.sefar.com/htm/609/en/Solar-Industry.htm?Folder=31423http://www.sefar.com/htm/609/en/Solar-Industry.htm?Folder=31423http://www.sefar.com/htm/609/en/Solar-Industry.htm?Folder=31423http://photovoltaics.sandia.gov/docs/cells5.htmhttp://photovoltaics.sandia.gov/docs/cells5.htmhttp://photovoltaics.sandia.gov/docs/cells5.htmhttp://syque.com/quality_tools/toolbook/Procap/how.htmhttp://syque.com/quality_tools/toolbook/Procap/how.htmhttp://www.abb.com/cawp/db0003db002698/b3913fe3a1296b7bc12571f10040f47f.aspxhttp://www.abb.com/cawp/db0003db002698/b3913fe3a1296b7bc12571f10040f47f.aspxhttp://www.abb.com/cawp/db0003db002698/b3913fe3a1296b7bc12571f10040f47f.aspxhttp://syque.com/quality_tools/toolbook/Procap/how.htmhttp://photovoltaics.sandia.gov/docs/cells5.htmhttp://www.sefar.com/htm/609/en/Solar-Industry.htm?Folder=31423http://www.q-cells.com/http://www.ecn.nl/units/zon/rd-programme/silicon-photovoltaics/crystalline-silicon-solar-cell-technology/http://www.ecn.nl/units/zon/rd-programme/silicon-photovoltaics/crystalline-silicon-solar-cell-technology/


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[29] Win Baylies, Marty Burkhart, Don Cook, Dick Hockett, Matthias Meier and Bettina Weiss.Structuring Standards for the Photovoltaic Manufacturing Industry. SEMI/PV Group Photovoltaic

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[30]Nigel B. Mason. Industry Developments that Sustain the Growth of Crystalline Silicon PV Output.BP Solar, Proceedings of the Photovoltaic Science, Applications and Technology Conference,

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[31]Marcus Tarin. Lock-in Thermography Enables Solar Cell Development. MoviTHERM; RossOverstreet/FLIR Systems. Photovoltaics World Magazine. New Hampshire, USA (January 11, 2010).

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[32]G. TamizhMani, B. Li, T. Arends, J. Kuitche, B. Raghuraman, W. Shisler, K. Farnsworth, J.Gonzales, & A. Voropayev. Failure Analysis of Design Qualification Testing: 2007 vs. 2005.

Arizona State University Photovoltaic Testing Laboratory (ASU-PTL), Mesa, Arizona, USA.

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[33]Mediha Zeneli. Comparative Analysis of PV Cell and Module Makers Parameters. Bachelor ThesisElectrical and Computer Engineering. Jacobs University Bremen, Germany. (Spring 2010).
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12 Appendix

1. SIX-SIGMAThe Six-Sigma concept is an innovative tool which is used to improve the performance of processes to the

point of 3.4 per million or less defects. It was designed for use in high-volume production settings; therefore

it is well suited to manufacturing systems. It follows a six-step protocol for process movement which is asfollows

[4]:

1. Identify the product characteristics wanted by customers2. Classify the characteristics in terms of their criticality3. Determine if the classified characteristics are controlled by part and/or process4. Determine the maximum allowable tolerance for each classified characteristic5. Determine the process variation for each classified characteristic6. Change the design of the product, process, or both to achieve a Six Sigma process performance

2. DEMINGS CYCLEThe Deming (PDCA) Cycle links production of a product with consumer needs and focuses the resources

of all departments (research, design, production, marketing).

1. Plan plan to improve operations by identifying problems and finding solutions2. Do make changes accordingly on a small or experimental scale, to minimize disruptions3. Check check whether the changes are achieving the desired results or not, including continuous

check of key parameters (e.g. the KCCs) to ensure that any new problems are identified.

4. Act implement changes on a larger scale if successful. Otherwise, plan to make adjustments fordesired results.

3. BENCHMARKINGBenchmarking is part of the total quality process where companies compare processes and performance

metrics to best practices within the industry or from other industries. There are two types:

Competitive benchmarking a competitors operation is studied using publicly available data without

cooperation with the target firm[4]

.

Cooperative or process benchmarking a partner companys key processes are studied through cooperation

efforts by both firms so as to improve the benchmarking firm from a substandard to a world-class level[4]

.


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4. EXAMPLES QUALITY ISSUES IN PV CELLS AND MODULES

Jorge Coello, 23rd European Photovoltaic Solar Energy Conference, 1-5 September 2008, Valencia, Spain

5. ABBREVIATIONS IN TABLE 3UL Underwriters laboratories Inc.; provides product safety certification and compliance solutions.

IEC International Electrotechnical Commission; prepares and publishes standards for electrical, electronic

and related technologies.

CE - Conformit Europenne; conformance to EC (European Commission) directives. The CE mark on a

product indicates that the manufacturer or the importer for the EEA (European Economic Area) has

respected the requirements for safety, health and the environment.

TV - Technischer berwachungs-Verein (Technical Surveillance Association); carries out tests, inspections

and certification of products, services and systems in industries worldwide.

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