Solar Reliability

Overview

Our “solar reliability” area focuses on studying and modeling the thermomechanical and photochemical reliability of silicon photovoltaic (PV) module components, primarily on the three layers of glass – encapsulant – PV cell. We employ a fracture mechanics based approach to understand the fundamental degradation mechanisms of module materials and interfaces. This includes significant participation from national labs and industry collaborators, who provide us with the most modern and relevant solar technologies.

Group Members:

Alan Liu

Past Group Members

Predicting Encapsulation Delamination in Photovoltaic Modules Using Photochemical Reaction Kinetics and Fracture Mechanics

PV modules are expected to last upwards of 30 years in the field.
Modules are subjected to harsh operating conditions and undergo degradation due to UV exposure, temperature cycling, and humidity.
The critical fracture energy, GC, is the amount of energy the module can absorb before failure, and characterizes the module’s resistance to delamination.
In this project, we have created a novel predictive model for simulating the change in the PV module’s GC over field aging times by incorporating the degradation reactions in a rigorous fracture mechanics framework, shown in the figure above.
We have also performed delamination and nanoindentation mechanical tests to characterize the change in the fracture energies and mechanical properties of field and lab aged PV modules to corroborate the model results.
Our current work is trying to generalize this model to include modules with a different polymer encapsulant than EVA.

Project Members: Alan Liu

Characterization of Adhesion Reliability in Photovoltaic Modules (Past Work)

Recently, a reliable and repeatable method of characterizing adhesive properties of module interfaces has not existed. However, through collaboration with the Bay Area Photovoltaic Consortium (BAPVC) and the National Renewable Energy Laboratory (NREL), we developed simple metrologies that, for the first time ever, provide direct, quantitative measurements of adhesion in encapsulation and backsheet structures. These techniques have been used to evaluate adhesion in 30-year-old field modules and, ultimately, provide a framework for one-to-one comparisons of modules that have operated in different terrestrial environments. Advanced characterization techniques are frequently utilized, such as WAXS/SAXS with our collaborators at SLAC, to complement and elucidate the mechanical adhesion measurements.

Recent work on modeling the degradation of solar encapsulation has been carried out as part of the Department of Energy’s SunShot Initiative in collaboration with NREL (published cover art shown above). Fundamentally modeling the kinetics and mechanics of solar encapsulant degradation is critical to providing predictive capabilities as solar power generation becomes more widespread globally. Delamination of the encapsulant is preceded by a breakdown of the mechanical integrity of the encapsulant layer. Over time, this degradation diminishes the critical adhesion energy required to induce delamination to levels below empirically determined threshold values, making delamination much more likely through normal usage. Our work in determining the fundamental mechanisms and kinetics that drive this loss in adhesion energy provides the solar community with an essential understanding of the reliability considerations that are vital to expanding the usage of solar modules into additional terrestrial environments and integrating potential new materials as solar encapsulants. As industrial partners seek to avoid premature failures and to increase the guaranteed lifetimes of solar modules, understanding how a critical component of these solar modules degrades and ultimately leads to delamination is elemental.

While so much time is allocated to discussing efficiencies of solar modules, the actual mechanical durability and reliability of the solar modules is often ignored and underappreciated. From optics to encapsulation to the cells themselves, we have developed and employed testing methods to evaluate the reliability of these materials and furthermore, continue to expand on and develop the knowledge and understanding crucial to advancing the goals of the solar community and ensuring future success.

Past Project Members: Patrick Thornton, Jared Tracy, Alan Liu