Correlation of Qualification and Accelerated Testing with Field Degradation
- Arizona State Univ., Mesa, AZ (United States)
- National Renewable Energy Lab. (NREL), Golden, CO (United States)
Qualification testing of solar photovoltaic (PV) modules per IEC 61215 standard encompasses a set of well-defined accelerated stress tests (irradiation, environmental, mechanical and electrical) with strict pass/fail criteria based on functionality/performance, electrical and mechanical safety, and visual requirements. The qualification testing does not identify all the possible reliability failures or durability issues witnessed in the actual field. However, it does identify the major/catastrophic design quality issues (infant mortality), which could occur early in a module’s field life. Unfortunately, in the industry, there is no consensus-based standard or protocol available to validate manufacturers’ warranty period claims based on the end-of-life wear-out failure mechanisms. Being able to predict the field degradation rates and lifetime using mode-specific accelerated tests on moderately field-aged modules, for example 10 years, for certain commonly occurring degradation modes would be a powerful contribution to all the stakeholders of the PV industry. There is a need to formulate guidelines to find the correlation of accelerated testing with field degradation for individual degradation modes observed in the field. Potential approaches to fulfill this need were experimented in this project and are presented in this report. Two of the most commonly seen degradation modes – encapsulant browning and solder bond thermomechanical fatigue – are addressed in this report through presenting the accelerated testing methods and physical modelling approaches. Two accelerated test methods (UV and thermal cycling) were designed to induce the wear-out mechanisms in the modules and not infant mortality failures. To focus on the wear-out failure modes, the tests were performed on field-aged modules, instead of fresh modules, with known degradation rates and degradation modes. The degradation rates were measured based on the degradation rates of individual cell parameters (short-circuit current, Isc and series resistance, Rs) instead of the degradation rate of maximum power (Pmax) which cannot be used to study any specific/limited degradation mode as the Pmax degradation could be caused by many different degradation modes. The key characteristic parameter considered for encapsulant discoloration and solder bond degradation is Isc and Rs, respectively. The developed physical models/equations relating the testing degradation data and field weather data were utilized to determine the acceleration factor (AF) and to predict the degradation rate for a specific degradation mode of PV modules installed in two different climates, Arizona (hot) and New York (cold). The predicted degradation rates for encapsulant browning and solder bond degradation have also been validated against the actual measured field degradation rates. UV testing cost reduction: To determine acceleration factor, single UV chamber was used for accelerated UV testing at three different temperatures simultaneously, instead of three chambers for three temperatures (or one chamber sequentially which is an extremely time-consuming approach). A passive heating approach was successfully used to achieve and maintain multiple temperatures in the accelerated UV chamber. Foam insulation boards of varying thicknesses were utilized to obtain three different temperatures for UV testing. However, these foam materials tend to disintegrate in the presence of moisture. To alleviate this problem, silicone heating blankets with temperature controls and humidifier can be used if the UV testing is to be performed under hot-humid conditions instead of conventional hot-dry conditions. Thermal cycling testing cost reduction: Single thermal cycling chamber was used for accelerated thermal cycling testing at three different upper temperatures simultaneously, instead of three chambers for three upper temperatures (or one chamber sequentially which is an extremely time-consuming approach). An active heating approach based on silicone heating blankets was successfully used to achieve and maintain multiple upper temperatures in the accelerated thermal cycling chamber. Such blankets provide stable temperature control and thereby more reliable and repeatable for replicate experiments.
- Research Organization:
- Arizona State Univ., Mesa, AZ (United States)
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Solar Energy Technologies Office
- DOE Contract Number:
- EE0007138
- OSTI ID:
- 1561276
- Report Number(s):
- DOE-ASU-2018PREDICTS2
- Resource Relation:
- Related Information: • A summary of two major databases related to the qualification test results and field degradation results are presented in Appendix I. The detailed databases are posted on our website: https://PVreliability.asu.edu• Two standardized protocols for the acceleration factor correlation of accelerated testing with field degradation of photovoltaic modules for encapsulant browning mode in UV testing and solder bond degradation mode in thermal cycle testing have been developed. The need and objective of these two protocols are presented in Appendices II and III, respectively. The detailed protocols are uploaded on our website: https://PVreliability.asu.eduo H. Gopalakrishna, A. Sinha, K. Dolia, D. Jordan, G. Tamizhmani, “Non-destructive Characterization and Accelerated UV Testing of Browned Field-aged PV Modules,” IEEE Journal of Photovoltaics, Accepted, 2019.
- Country of Publication:
- United States
- Language:
- English
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