Stanford Engineering
Dauskardt Group

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, supported with characterization techniques and multiscale modeling. This includes significant participation from national labs and industry collaborators, who provide us with the most modern and relevant solar technologies.

Group Members:

Past Group Members

Predicting Encapsulant Delamination in Photovoltaic Modules Bridging Photochemical Reaction Kinetics and Fracture Mechanics

 

Background:

  • PV modules are expected to last upwards of 30 years in the field.
  • Modules are made of 5 layers: glass / encapsulant / cell / encapsulant / backsheet
  • Modules are subjected to harsh operating conditions and undergo degradation due to UV exposure, temperature cycling, and humidity.
  • Delamination (debonding of the encapsulant from the cell and/or the encapsulant from the glass) is a major concern, the second most common cause of module failure.
  • The critical fracture energy, Gc, is the delamination resistance of the module (higher the Gc, the more resistance to debonding).

What has been done:

In this program, we have developed a novel predictive model for simulating the change in the PV module’s Gc over field aging times by bridging the degradation reactions with a rigorous fracture mechanics framework (see above Figure). We have further 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.

Current efforts:

  • Our current focus is on probing the degradation kinetics as a function of UV intensity, temperature, moisture, and oxygen. This is to inform the degradation model, which could then predict the Gc as a function of field aging time at different locations (climate variation).
  • We are aging 3 different types of encapsulants (EVA, POE, EPE) and laminated coupons (cell/encapulant/glass samples) in weathering chambers at different conditions, then utilizing characterization techniques to examine the degradation kinetics.
  • Experimental techniques: adhesion testing, DSC, FTIR, GPC, Soxhlet extraction, DMA

Project Members (currently seeking help):

Interested undergraduates, M.S., and Ph.D. students should contact Alan by email ( aliu1997@stanford.edu ) to inquire about collaborating on the project!

 

Characterization of Adhesion Reliability in Photovoltaic Modules (Past Work)

​Scott Isaacson_5

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

Past Research Projects