Carl Wang

Degradation pathway models for photovoltaics module lifetime performance

Previously published accelerated testing data from Underwriter Labs, featuring measurements taken on 18 identical photovoltaic (PV) modules exposed to two stress conditions, were used to develop an analytical methodology. The results provide insight into active degradation mechanisms and pathways present in PV modules under accelerated testing conditions as indicated by statistically significant relationships between variables. Observed experimental results coincide with a domain knowledge based theoretical degradation pathway model informed by literature, and provide a basis for beginning to investigate the degradation modes and pathways truly present in modules and their effects on module performance over lifetime.

Accelerated aging tests on PV grounding connections

As many contemporary Photovoltaic (PV) Power systems being installed are designed to produce significant amount of electricity and claimed to operate for 25 years or more, appropriate grounding on PV modules to reduce or eliminate shock and fire hazards becomes a critical issue under high electricity output and long-term use. Although some PV manufacturers have provided technical bulletins to suggest grounding products and methods, not all of them have been carefully evaluated and reviewed by the certification/listing laboratories. In this paper, different types of PV grounding connectors were collected, installed and put into accelerated environmental test chambers. The effects of current cycling, assembly force, anti-oxidation coating application on grounding reliability were evaluated. The grounding failure modes and mechanisms are also discussed in this paper.

Simulation of internal short circuits in lithium ion cells

Understanding the root causes and mitigating the safety hazards associated with internal short circuits in lithium ion cells is an active area of research and a needed update for battery safety standards. For battery safety standards, there is a need for a practical, safe and reliable test method for battery safety standards that can assess the safety performance of lithium ion cells under the conditions of an internal short circuit. In this paper, we provide details of proposed test method which relies on external, localized indentation of cell casing to induce an internal fault that might simulate some field failures.

Failure mechanism due to aging effects in lithium-ion batteries

In view of the emerging demand for longer-term industrial or second life of lithium-ion batteries, aging effect(s) should be seriously considered to understand all potential safety risks behind those applications. In this study, four categories of critical aging effect(s), including degradation of construction integrity, self-heating effect, decay of thermal stability and failure in key components, were systematically identified based on the considerations of safety and reliability use for lithium-ion batteries. Some case studies in each category were also demonstrated to further explore the impact of those aging effects on the safety behaviors of a real commercial battery product. The key outcome of the study is that we have provided scientific insights into the failure mechanism(s) caused by aging and the correlations between the root causes to each aging effect have also been logistically identified.

Optimization of Temperature Precision for Double-Shell Oven by Lean Six Sigma Method

A relatively inexpensive and highly effective design for high precision oven was developed but the control theory and optimized parameters were totally different from traditional methodologies. Among all kinds of quality programs, lean six sigma LSS is the most famous and widely-used method by manufacturing and service industries. The DMAIC Define, Measure, Analyze, Improve and Control methodology was used to figure out the key factors relative to high precision of temperature and improve the control parameters to meet the target. At the start, the baseline of Z bench was -1.99 and standard deviation was 0.255229. After lean six sigma project implemented, Z bench was up to 3.66 and standard deviation was down to 0.12822. This paper will address the critical process and analysis method for lean six sigma project, especially those for precise temperature control.