John H. Wohlgemuth’s research while affiliated with National Renewable Energy Laboratory and other places

If the only way to assess the impact of a product change is to deploy it in the field and wait to see what happens, improvements to the technology will take a long time. In order to speed up this process, accelerated stress tests (ASTs) are necessary that cause the same failures to occur in the modules that have been observed in the field, but of course in much shorter times. This chapter discusses various ASTs routinely used for photovoltaic (PV) modules: thermal cycling, damp heat, humidity freeze, ultraviolet light exposure, static mechanical load, cyclic (dynamic) mechanical load, reverse bias hot spot test, bypass diode thermal test, and hail test. It describes each of these ASTs indicating what weather and stress phenomena they accelerate and what failure modes they are best at exposing in PV modules.

Qualification tests, a set of well‐defined accelerated stress tests developed out of a reliability program, incorporate strict pass/fail criteria. The initial development of a Qualification test sequence for photovoltaic (PV) modules occurred during the Jet Propulsion Laboratory's (JPL) Block Buy Program in the late 1970s and early 1980s. This chapter begins with a description of the JPL program and discussions of the lessons learned during that program. Next, it explains how PV‐module Qualification testing transitioned from JPL to IEEE to Solar Energy Research Institute and finally to IEC, where it remains today. Then, the chapter describes the details of the latest version of the IEC Qualification Test Sequence, IEC 61215. It discusses how use of the Qualification tests has improved the reliability of PV modules, and discusses the limitations of Qualification testing and identifies some of the additional steps that are being taken to further improve module reliability and lifetime.

This chapter addresses how to go about determining the acceleration factors for the different accelerated stress tests that are typically performed on photovoltaic (PV) modules. It begins with a statement that finding one set of accelerated stress tests that could be used to predict a module's service life was unlikely, that doesn't mean that it is impossible to predict service life. The earlier parts of this chapter explain why a single test sequence is not likely to be valid for all module types. However, it should be possible for a manufacturer to predict the service life for each of their module types. This requires knowledge of the manufacturing process and its controls, feedback from field deployment and extensive accelerated stress testing. The chapter discusses how a PV‐module manufacturer could set up a system to predict the lifetime of one of their products.

In order to continuously build quality modules, the manufacturers should be using Quality Management Systems (QMS) that have been developed specifically for photovoltaic (PV)‐module manufacturing. This chapter relates some of the history behind how QMS evolved in PV, indicating how successful this has been as well as identifying some of the issues with the system and the need for further improvements. A QMS is usually implemented as a framework of organizational structures, methods, procedures, techniques, policies, processes, and resource allocations established to provide the necessary control over all aspects of the company's operation. The Quality norm in PV became a PV module qualified to IEC 61215 produced in an International Organization for Standardization 9000 certified factory. If a manufacturer is going to make a change to their quality assurance system it should be based on assessing the system they have in place against recommendations provided by an expert group familiar with multiple PV module QMS.

Photovoltaic Quality Assurance Task (PVQAT) helps guide worldwide research to answer important questions related to testing of PV products that predict outdoor performance of PV modules. The objectives of this work are to develop International Electrotechnical Commission standards that can be used for testing PV modules that can then be deployed in any terrestrial environment. To implement this work, PVQAT has established 13 working groups. Each of these groups has been active during at least part of the time since PVQAT's formation in 2011. The chapter discusses the work of each of these task groups. The task groups include PV QA Guidelines for Module Manufacturing; Testing for thermal and mechanical fatigue; Testing for humidity, temperature and voltage; Testing for diodes, shading and reverse bias; Testing for UV, temperature and humidity; Communications of rating information; Testing for snow and wind load; and Testing for thin film modules.

This chapter discusses development of conformity assessment systems for photovoltaics (PV) products mostly PV modules although some PV products like PV lanterns. It also discusses the extension of conformity assessment from the product to the PV system deployed in the field and how this required the creation of a whole new conformity assessment organization at International Electrotechnical Commission (IEC). To help serve the PV industry, European solar test installation obtained third‐party accredited to perform PV‐module measurements and calibration as well as for testing to IEC 61215. IECRE assessments should be done to International Standards, so one of the first steps in establishing the system for PV was to decide what standards to use. Standards are necessary for products, quality management systems, PV system design, PV system installation and commissioning and PV system operation and maintenance. The jury is certainly out on the IECRE PV power plant certification system.

This chapter discusses the each of the failure modes, with emphasis on what causes the failure, what construction or material selections make it worse or better and how the industry eventually modified their products to improve reliability and lifetime. It addresses failure modes specific to thin‐film modules. The improvements made in module design and the improved properties of the materials used for interconnect ribbons has reduced the instances of interconnect breakage in modern photovoltaic (PV) modules. Snail trails are a relatively new phenomenon that occurs as a result of broken or cracked cells. While the accelerated exposures did reduce the measured strength and adhesion of ethylene vinyl acetate (EVA) to glass by more than 50%, they remained at levels that are adequate to prevent delamination. The way to prevent corrosion of the cell metallization is to prevent encapsulant delamination. Discoloration of EVA encapsulant has been observed as a major cause of PV module power degradation.

Photovoltaics (PV) is a dynamic industry so the technology and the testing standards are constantly evolving. This chapter focuses on the future of PV module reliability and the accelerated stress testing associated with it. It provides an update on the changes already in progress for some of the more important module qualification and safety standards. This includes a discussion on the IEC TS 63126: Guidelines for qualifying PV modules, components and materials for operation at high temperatures. Next, the chapter switches to 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 produced. It also presents a brief summary of the status of PV module reliability today.

Regardless of whether a module has degraded from field exposure or accelerated stress testing, it is important to understand what has actually changed within the module that led to lost peak power. This chapter explores some of the methods used to better understand what has gone wrong within the module. Methods reviewed include, analysis of the I‐V parameters, measurement of performance at different irradiances, visual inspection, infrared inspection, electroluminescence and evaluation of adhesion. By analyzing the data from the light I–V curve we can often get a better idea of what has degraded. Another way to see the impacts of series and shunt resistance is to plot the dark I–V curve of the module. Some of the failure modes that occur in modules have no (or minimal) impact on how the modules appear. For visual inspection to be a useful tool, it should be guided by experience.