Service Life Prediction of Polymeric Components for Reliable Power Systems

Summary

Aging polymeric components in energy generation and transmission systems, such as those in cables, connectors, encapsulants and backsheets, can lead to lower power performance, higher energy cost, and increased risks of public safety. Due to intensified pricing pressure, low-cost materials are being used increasingly in photovoltaic (PV) power systems, with little knowledge on their long-term performance and reliability in their service conditions. However, standards for quantitatively characterizing the long-term performance and predicting the service lives of polymers in PV systems are still lacking. To address this problem, the project will develop, implement, and deliver measurement science for accurate and timely assessment of the long-term performance and lifetime of polymeric components used in power systems, with focus on emerging PV encapsulants and backsheets. This project involves four major thrusts: (1) advance analytical tools capable of providing crucial data for understanding degradation mechanisms and the failure modes of emerging polymeric components and retrieved field modules, (2) validate a novel accelerated laboratory testing chamber that can apply cyclic mechanical loading with simultaneous UV, temperature and humidity, (3) develop lifetime prediction models and finite element cracking analysis for polymeric films under different environmental conditions, and (4) develop standards for testing, characterizing, and predicting the service life of polymeric components used in power systems. The developed methodology will contribute to safety, reliability and resilience of the power systems.

Description

Objective 
To develop and implement measurement science for accurately testing, characterizing, predicting, and validating lifetime of polymeric components, such as cables, connectors, encapsulants and backsheets, in their service conditions, for reliable and resilient power systems.

Technical Idea
The rapid growth in solar installations can lead to new challenges regarding module reliability, because 1) over 90 % of global PV installations are less than 10 years old, and 2) there has been over a 90% reduction in module price in the past decade, mainly due to the use of new, lower-cost materials and new technologies. These statistics mean that there is a lack of long-term historical data about module reliability, and even if such data were available, it may not be useful because new materials and components may perform differently than their more expensive predecessors. It has been reported that, although overall module quality has improved in recent years, the percentage of industries that experienced failure(s) has increased. Almost one-third of the materials in modules tested suffered at least one failure during testing [1]. However, current industry-consensus standardized test methods used for qualifying PV components and modules are only useful for detecting premature failures, and not for predicting service life or ensuring long-term reliability of products. Additionally, these tests do not apply relevant environmental stressors simultaneously, therefore, the degradation modes from those tests may not be realistic.

The technical idea of this project is to develop measurement science for accurately evaluating and validating the service life of polymeric components in PV emerging systems, with focus on emerging PV encapsulants, backsheets and connectors. This project consists of four major thrusts in FY26: (1) advance analytical tools capable of providing crucial data for understanding degradation mechanisms and the root of failure for emerging polymeric components and retrieved field modules, with the collaborations of PV industry, (2) validate a novel accelerated laboratory testing chamber that can apply cyclic mechanical loadings to polymers with simultaneous UV, temperature and humidity stressors, (3) develop lifetime prediction models and finite element cracking analysis for polymer films under different environmental conditions (including potential disaster conditions), and (4) develop standards for testing, characterizing, and predicting the service life of polymeric components used in power systems by working with standard organizations (ASTM, IEC, etc.) 

Research Plan 
In FY26, this project will continue to identify, measure, model, and integrate scientific knowledge of degradation and failure into the development of reliability-based accelerated test methods and service life prediction tools for emerging polymeric components used in power systems. The research plan consists of the following tasks:

• Engage industry partners to advance and transfer measurement science to stakeholders in an effective, timely manner. We will complete the failure analysis of retrieved modules with inner-layer cracking of backsheets and provide the power industry with a better understanding on the root causes of failures and the mitigation plan by working with Southern Company, NREL and UL. A publication is planned on inner layer cracking in PV backsheets.

• Validate and deploy a novel accelerated laboratory testing chamber that can apply cyclic mechanical loading with simultaneous UV, temperature, and humidity, for long-term durability testing of polymeric components used in power systems. Currently, no commercial accelerated laboratory device can offer such a capability. In FY25, we re-designed the device and substantially improved its capability for aging testing. In FY26, we will test its robustness and complete an evaluation of the impact of cyclic mechanical loading on the degradation and cracking of multilayered polymer sheets during accelerated laboratory aging tests.

• Complete a reciprocity study and submit a paper on degradation of a model polymer used in power systems using NIST high irradiance 6-port SPHERE. The generated dataset will be critical to the development of accelerated laboratory testing with a metal halide light source.

• Continue to develop a micro-focused synchrotron X-ray scattering technique for depth-dependent degradation study of aged multilayered systems. Preliminary data obtained in FY24 and FY25 indicate that this advanced method is promising for providing unique spatially resolved structural information for multilayer degradation.

• Complete 4.5-year outdoor exposure tests for transparent backsheets, coupons, and other emerging backsheet materials in Florida, Arizona, and NIST Gaithersburg. The chemical, optical, and mechanical measurements of exposed backsheets and glass/encapsulant/backsheet laminates will be monitored to better understand real-world backsheet degradation. The dataset will be used to develop the linkage between indoor and outdoor exposures for service life prediction of multilayered polymeric materials.

• Complete a field survey for backsheet performance of the NIST PV arrays. This will be the last field survey on the PV modules in NIST Gaithersburg campus using non-destructive techniques, including color, gloss, portable ATR-FTIR. A paper on the degradation of polymeric backsheets based on multi-year field surveys is planned.

• Complete a feasibility study on a new test method measuring long-term interfacial adhesion strength and mode mixity for multilayered polymer films such as double side coated PV backsheets.

• Further develop standardized test methods for improving materials testing, accelerated laboratory testing and service life prediction of PV polymers and components. In FY26, we will continue to work on the revision of the ASTM G03 work item, “Standard Practice for Operating High Ultraviolet Irradiance Metal Halide Lamp Apparatus for Exposure of Materials”, which addresses the light sources such as those used by the NIST SPHERE, for the re-ballot. In addition, we will continuously provide SPHERE-based data for the development of IEC 62788-1-6 and IEC 62788-7-2.