output power.
1.5 Preview of the Book
This book has been written from a historical perspective to guide the reader through how the PV industry learned what the failure and degradation modes were, how accelerated tests were developed to cause the same failures and degradation in the laboratory and then how these tests were used as tools to guide the design and fabrication of more reliable and longer‐life modules. The following sections will provide a brief description of what will be contained within each of the subsequent chapters.
Chapter 2 begins the story with a survey of PV module failure and degradation modes that have been observed in the field. Pictures are provided for many of these to show what the failures look like and to provide the reader with a guide for their own module inspections. The book starts with failures not because PV modules are unreliable, but because identifying likely failure modes is the first step in avoiding them. For some of the failure modes, there is description of the relatively simple fixes that were used to solve some of the early problems with PV modules and therefore led to more reliable products.
The subject of Chapter 3 is accelerated stress tests (ASTs), describing what they are and how they have been used in PV to improve module reliability and lifetime. In developing ASTs, we must cause degradation. The degradation occurring in the AST must be due to the same failure mechanism we saw outdoors. The work to develop the appropriate AST for the different module failure modes is based on more than 35 years of experience. The Chapter concludes with a discussion of various ASTs that have been found to be useful for testing PV modules.
Chapter 4 introduces the concept of Qualification Tests, which are a set of well‐defined ASTs developed out of a reliability program. The purpose of qualification testing is to rapidly detect the presence of known failure or degradation modes that may occur in the intended operating environment. In these tests, the stress levels and durations are limited so the tests can be completed within a reasonable amount of time and cost. The chapter starts with a history of the development of Qualification Testing for PV. It then provides a summary of the testing performed in IEC 61215; the main qualification test standard used for PV modules. The chapter then discusses how Qualification Tests have been critical to improving the reliability and durability of PV modules as well as some of the limitations of the Qualification Tests. The chapter concludes with a discussion of module safety testing including a summary of IEC 61730, the main safety test standard used for PV modules.
Chapter 5 discusses some of the tools used to better understand what has gone wrong within a failed or degraded module. So, it presents characterization tools that look to define what properties of the module (or cells) have degraded and what may have been the cause of such degradation. Methods presented include, how to analyze the I‐V parameters, measurement of performance at different irradiances, visual inspection, Infrared (IR) Inspection, Electroluminescence (EL) Inspection and evaluation of adhesion.
Chapter 6 is about the use of Quality Management Systems in the manufacture of PV modules. The premise is that to continually build quality modules, the manufacturers should be using a Quality Management System that have been developed specifically for PV module manufacturing. The chapter provides the history behind how Quality Management Systems evolved in PV, indicating how successful this has been but also identifying some of the issues with a “do it yourself” system and the need for further improvements that led to the creation of the International PV Quality Assurance Task Force (PVQAT) discussed in the Chapter 7.
Chapter 7 tells the story of PVQAT including its creation and the establishment of its research goals. The three goals include development of improved accelerated stress testing for PV modules, establishment of a Quality Management System for PV module manufacturing and establishment of a conformity assessment system for PV power plants. The chapter concludes with a summary of the objectives and activities of each of the PVQAT Task groups.
Chapter 8 introduces the concept of Conformity Assessment for PV. The first part of the chapter discusses development of conformity assessment systems for PV products, mostly PV modules though some PV products like PV lanterns have also been covered. The second part discusses the extension of conformity assessment from products to PV systems deployed in the field and how this required the creation of a whole new Conformity Assessment organization at IEC called the IEC System for Certification to Standards Relating to Equipment for Use in Renewable Energy Applications or IECRE for short.
Chapter 9 discusses how to predict service life of PV modules. The chapter starts out by addressing how to determine the acceleration factors for the different ASTs that are typically performed on PV modules. It then discusses the impact of module design and control of the manufacturing process on module failure rates and how that impacts lifetime predictions. The third section explains the impact of the weather at the geographic location where the module is deployed and the type of mounting system used on module degradation and failure rates and how those impact lifetime predictions. The fourth section talks about the efforts to get the PV community to agree on one set of extended ASTs that evaluate modules for wear out. The final section discusses development of a methodology for how a PV module manufacturer could set up a system to predict the lifetime of one of their products.
Chapter 10 shifts the focus to the future. Since PV is a dynamic industry, the technology and the testing standards are constantly evolving. The first section provides an update on the changes already in progress for some of the more important module qualification and safety standards. The second section takes a longer‐range view, discussing how PV module reliability is likely to change in the future and what sort of accelerated stress testing will be necessary to validate the quality of the huge volume of modules that will be produced. The book will end with a brief summary of the status of PV module reliability today.
References
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