Quality Management: Bureaucratic Monster or Key Success Factor?
By Werner Bergholz, QTEAM and Jacobs University Bremen
When it comes to enumerating success factors for an emerging industry such as the PV industry, quality management (QM) is rarely mentioned; on the contrary, frequently stereotypes/misconceptions come up, such as:
- “QM is a bureaucratic monster mostly for documentation purposes only, nobody really needs it”
- “QM and ISO 9001 certification is expected by customers, costs a lot of money but does not really help”
- “QM is not needed for the simple photovoltaics processes (PV)”
- “PV cannot afford the extra cost for QM”
QM is necessary, helps to reduce cost and to improve quality and thus is a key success factor for PV. We will show that PV simply cannot afford any longer to be without a structured and stringent QM System.
Quality cannot be tested, but must be “made” throughout the value adding chain
Photovoltaic modules and other system components constitute a significant investment for the end user, and the investment will only we worthwhile, if the system will perform as planned for at least 20 years. Thus it is not only the initial performance, but more so the reliability and the durability of the components and the system for 20 years or more projected lifetime which are essential.
It is a universal industrial experience that a good product quality, more concretely a low variance in the product performance parameters are a prerequisite for a high reliability and durability, it is simply impossible to achieve this goal by a process with a large variability hoping to sort out the good ones. Even the good ones have a high risk of hidden defects which are not apparent yet at the time of the final product test. In fact the need for binning in PV cell production clearly demonstrates rather poor process uniformity in comparison to what is needed to produce PV modules, in which the cells are connected in series.
A good product quality with a low a variance in the product performance can only be achieved by a good process quality, which means the production processes must be stable and under control. This is true for the complete value adding chain, from materials to the final system assembly, see Fig. 1.
As the word “chain” implies, if only one link in the chain is defective, the whole chain will break. This explicitly includes the interfaces between the different stages of the value chain, since it is a general industrial experience that the interfaces are especially prone to causing quality problems. This must be actively addressed by supplier management.
Fig. 1: PV value adding chain and where quality management needs to act
Therefore, all production and system assembly processes must be subjected to tight process control, i.e. the result of each process must be predictably within the technical specification. Thus it will be ensured that there is never a break in the predictable quality being produced in the value adding chain.
In other words: Product quality is ensured by process quality, the process quality must be continuously monitored by process management and statistical process control (two quality management tools out of the QM tool box). Additionally, the transition of the partially processed product at the interfaces between the stages of the PV value adding chain is controlled by quality gates.
Example for the benefits of Quality Management:
Before a more detailed explanation about the “nuts and bolts” ( = quality tools + QM system) of quality management in the next section, a practical example will be described. As mentioned before, one of the main objectives of QM is to reduce the variability of processes. The technique to do this is one of the most important tools of quality management, statistical process control1).
The following example is taken from reference 2. In one of the first cell production lines of the former PV company Q-cells in Germany, the variability of the five most important process control parameters for a standard silicon-based multicrystalline PV cells was reduced over the course of two years approximately by a factor of 2, as measured by the standard deviations, by the application of SPC principles.
Fig. 2: Reduction of the process variability in a PV cell production line, by the application of SPC principles. The sum of the standard deviations at the start of the process improvement efforts has been normalized to 100%, the reduction in the five standard deviations has been expressed in the reduction of the respective percentages.
The improvement in the process capability is only a prerequisite for being able to significantly improve the process quality. According to the proverbial “the proof of the pudding is the eating”, in Fig. 3 it is demonstrated that the reduction of the variability of the key processes (which impact the conversion efficiency of the PV cells) indeed has a measurable positive impact:
- The efforts to reduce the process variability (i.e. to improve the process quality) have paid dividends in terms of improvements in the cell efficiency, if compared to the results of an almost identical PV cell production line in which there were no focused efforts to reduce the process variability, which serves as the reference.
- In addition, the variability of the cell efficiency has also been reduced, and it can certainly be anticipated that this will have a positive impact on the module production and on the reliability and durability of the products.
Fig. 3: Daily average of the efficiency in 2 cell production lines over time.
- a. Orange symbols and sliding average line: A cell production line without the introduction of process control measures to reduce the process variability.
- b. Blue symbols and sliding average line: The cell production line with practically the same equipment but with systematic reduction of the process variability.
In both lines there were continuous efforts to improve the cell efficiency. It is clearly demonstrated that reduction of the process variability significantly support such performance improvement efforts. It is also noteworthy that the standard deviation of the cell efficiencies is also significantly reduced compared to the “business as usual” cell production line.
The Quality Management Toolbox
In the previous sections the relevance and benefits of process management for the photovoltaics industry has been described. In this section, a very short introduction to how quality management is organized in practice is described. This will only be an overview, and it is planned to explain the details of quality management in a small series of follow up papers.
Successful quality management is composed of various activities which can be described as the application of quality tools. SPC is one of them, Design of Experiment (DOE) a second one, other quality tools are FMEA (failure modes and effects analysis), Change Management, Deviation Management, Supplier Management and Integrations are others, this enumeration is not complete.
Such isolated activities are beneficial in themselves, however sustained success of such investments in time and effort is only ensured if such activities are integrated into a quality management system.
This is not unlike the situation in the manufacturing of any products: The unit processes are managed and coordinated by process integration. Another analogy to demonstrate the importance to implement a QM system is the following: Nobody would try to build and operate a computer without an operating system, such as Windows 8, Android or the Apple operating system. Even the best components and the best operations in a computer would not function properly without the operating system. Fortunately, the challenge to create a QM system is by orders of magnitude less demanding than to create a computer operating system. The well-known ISO 90013) standard is a template which is can be very helpful in setting up such a system, and to check whether the system will function properly. One practical way for the validation of the system is to have the system certified by an external accredited certification organization.
In connection with ISO 9001 certification a word of caution is in order: Certification is by no means a guarantee that the resources spent on the system and the quality management activities in the form of the application of the QM toolset will result in improved technical and/or business results. A study4) has shown that if the QM system and the requirements of ISO 9001 are regarded and used by top management as an integrated part of the overall business strategy for continuous improvement, then the benefits will be there. If, on the other hand, the certification is mainly implemented because customers demand it, then the benefits may not materialize.
A QM System as the only way to ensure 20 years lifetime
As mention in the beginning, PV products and systems are expected to have at least 20 years working life. Paradoxically, to date there is absolutely no lifetime test for PV modules which can prove or demonstrate the guaranteed lifetime of the PV modules! So, for a product for which the lifetime is probably the most important aspect for the end user, the lifetime cannot be measured. The IEC standard IEC 61215 that is commonly used in connection with the qualification of PV modules is NOT lifetime test5).
In other technology fields this is different: CPUs or memory ICs used in computers undergo a lifetime test in which the average lifetime and the failure rate as a function of time can be predicted with a high degree of certainty. Such a study needs a sufficient statistical basis, involving typically thousands of samples in accelerated life tests. Clearly, that kind of procedure cannot be replicated for PV modules, for simple practical reasons. The cost to set up and maintain the necessary huge climate chambers and the cost for thousands of modules tested until failure are prohibitive.
Therefore the ONLY way to ensure a the durability of PV modules and to PV systems is 100% stringent process and quality management to “manufacture” a predictable quality of the product by material and process quality overseen and coordinated in a quality management system.
2) Thomas Dinkel, PhD Thesis: “Integrated Efficiency Engineering in Solar Cell Mass Production”, Jacobs University Bremen, 2010
4) M Terziovski, D Power, AS Sohal - European Journal of Operational Research, 146 2003, pp. 580-595
December 15, 2014