Due to intensified pricing pressure and rapid growth of photovoltaic (PV) technology, low cost and emerging polymeric materials are being used increasingly in module manufacturing. Because of their relatively recent deployment, little is known about their long-term performance and reliability. Furthermore, standards for quantitatively characterizing the performance and predicting the service lives of polymeric components used in PV systems are lacking, hindering innovation, implementation, and assurance of PV technologies. To address this problem, this 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 PV systems. This project involves four major thrusts: (1) Advance analytical tools capable of providing crucial data for understanding degradation mechanisms and failure modes of PV polymeric components, laminates, and mini-modules, (2) Construct a state-of-the-art accelerated weathering laboratory device with multiple applied environmental stresses for testing PV components, laminates and mini-modules, (3) Develop validated reliability-based mathematical models for linking field and laboratory exposure results and predicting service lives of PV components under different environmental conditions, and (4) Develop standards for testing, characterizing, and predicting service life of PV polymeric components.
Objective - To develop and implement measurement science for predicting and validating the lifetime of polymeric components utilized in photovoltaic applications.
What is the new technical idea?
Over the past decade, the PV market has experienced unprecedented growth. [1-2] According to the International Renewable Energy Agency report [3-4], solar energy installation exceeded the combined new capacity of coal, gas and nuclear power in 2017. This rapid deployment has come with new challenges regarding module reliability: 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 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. A literature review from NREL reported that the median rate of degradation for exposure up to 10 years was significantly higher than that of 10 years and longer.  A recent study on degradation rates of PV modules in hot-dry desert climates over a period of 12 years showed that about 50% of PV modules had degradation rates over 1 %/year.  Therefore, it is significantly important to study degradation and failure mechanisms, and develop measurement science to accurately predict the field performance of materials in modules, especially for new materials used in the emerging technologies without any historical field data (e.g., bifacial passivated emitter and rear contact (PERC) modules).
The long-term reliability of a PV module is highly affected by the degradation behavior of the polymeric components within the module, such as the encapsulant and backsheet . For example, corrosion, a major field failure mode leading to loss of power, is strongly accelerated by acetic acid, a product from degradation of encapsulant ethylene vinyl acetate (EVA). The cracking and delamination of the backsheet due to degradation can lead to the dielectric breakdown of PV systems and safety concerns as well as lower reliability of PV modules. However, current 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. This is problematic because degradation of the PV modules can be non-linear through their lifetime . Additionally, these tests do not apply the relevant environmental stressors simultaneously, therefore, the degradation modes from those tests may not be realistic.
To address this problem, the new technical idea of this project is to develop and transfer measurement science to industry for evaluating and validating the lifetime of polymeric components in PV systems. In the previous phase of this project, we developed methods to expose, characterize, and predict the damage of PV materials and components based on the SPHERE technology and the reliability-based damage model. Due to the interdependent multi-stress effect, complex degradation mechanisms, and a high demand on the precise and accurate control of exposure weathering for service life prediction, there is a need to enhance the exposure capability, deepen the understanding, refine the tests, validate the prediction models, and continue developing the standards for service life prediction. This project consists of four major thrusts: (1) to advance analytical tools capable of providing crucial data for understanding degradation mechanisms and failure modes of PV polymeric components, laminates, and mini-modules, (2) to build up a state-of-the-art accelerated weathering laboratory chamber that applies multiple simultaneous environmental stresses for testing PV components, laminates, and mini-modules, (3) to develop reliability-based models for linking field and laboratory exposure results and predicting service lives of PV components under different environmental conditions, and (4) to develop and improve standards for testing, characterizing, and predicting service life of PV polymeric components.
What is the research plan?
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 polymeric components used in PV systems. The research plan consists of the following component tasks:
“PVPS 2019 Snapshot of Global PV Markets”, https://resources.solarbusinesshub.com/images/reports/216.pdf
2 RenewEconomy Daily Newsletter, March 21, 2014 (http://reneweconomy.com.au/2014/global-solar-pv-market-set-to-reach-500…).
5 Jordan and Kurtz, “Photovoltaic Degradation Rates — An Analytical Review”. NREL/JA-5200-51664 (2012) (http://www.nrel.gov/docs/fy12osti/51664.pdf)
6 Tamizh and Mani, “Degradation Rates, Safety Failures and Reliability Failures of Fielded PV
Modules: Lessons Learned in Hot-Dry Desert Climates”, 2nd Atlas/NIST PV Materials
Durability Workshop (2013) (http://www.nist.gov/el/building_materials/upload/tamiznew.pdf)
7 Kohl, et al, “Impact of Permeation Properties and Backsheet-Encapsulant Interactions on the
Reliability of PV Modules”, ISRN Renewable Energy, Vol. 2012, Article ID 459731 (2012)
8 Jordan, D. C., Silverman, T. J., Sekulic, B., and Kurtz, S. R. (2016) PV degradation curves: non-linearities and failure modes. Prog. Photovolt: Res. Appl., doi: 10.1002/pip.2835.