abstract: The popularity of solar photovoltaic (PV) energy is growing across the globe with more than 500 GW installed in 2018 with a capacity of 640 GW in 2019. Improved PV module reliability minimizes the levelized cost of energy. Studying and accelerating encapsulant browning and solder bond degradation—two of the most commonly observed degradation modes in the field—in a lab requires replicating the stress conditions that induce the same field degradation modes in a controlled accelerated environment to reduce testing time. Accelerated testing is vital in learning about the reliability of solar PV modules. The unique streamlined approach taken saves time and resources with a statistically significant number of samples being tested in one chamber under multiple experimental stress conditions that closely mirror field conditions that induce encapsulant browning and solder bond degradation. With short circuit current (Isc) and series resistance (Rs) degradation data sets at multiple temperatures, the activation energies (Ea) for encapsulant browning and solder bond degradation was calculated. Regular degradation was replaced by the wear-out stages of encapsulant browning and solder bond degradation by subjecting two types of field-aged modules to further accelerated testing. For browning, the Ea calculated through the Arrhenius model was 0.37 ± 0.17 eV and 0.71 ± 0.07 eV. For solder bond degradation, the Arrhenius model was used to calculate an Ea of 0.12 ± 0.05 eV for solder with 2wt% Ag and 0.35 ± 0.04 eV for Sn60Pb40 solder. To study the effect of types of encapsulant, backsheet, and solder on encapsulant browning and solder bond degradation, 9-cut-cell samples maximizing available data points while minimizing resources underwent accelerated tests described for modules. A ring-like browning feature was observed in samples with UV pass EVA above and UV cut EVA below the cells. The backsheet permeability influences the extent of oxygen photo-bleaching. In samples with solder bond degradation, increased bright spots and cell darkening resulted in increased Rs. Combining image processing with fluorescence imaging and electroluminescence imaging would yield great insight into the two degradation modes. / Dissertation/Thesis / Doctoral Dissertation Systems Engineering 2020

Cantilevered reinforced concrete columns with a lap splice of the longitudinal reinforcement near the base can induce high moment demands on the splice region when lateral loads are present on the structure. Code design specifications typically require a conservative splice length to account for these high moment demands and their consequences of bond failure. The required splice length is calculated as a function of required development length, which is a function of the bond between the reinforcement and the surrounding concrete, and a factor depending on the section detailing. However, the effects of concrete deterioration due to alkali silica reaction (ASR) and/or delayed ettringite formation (DEF) may weaken the bond of the splice region enough to overcome the conservative splice length, potentially resulting in brittle failure of the column during lateral loading. This thesis presents the following results obtained from an experimental and analytical program. * Fabrication of large-scale specimens of typical column splice regions with concrete that is susceptible to ASR/DEF deterioration * Measurement of the large-scale specimen deterioration due to ASR/DEF accelerated deterioration * Analytical model of the column splice region based on flexure theory as a function of the development length of the reinforcement and a factor to account for deterioration of the bond due to ASR/DEF * Experimental behavior of two large-scale specimens that are not influenced by premature concrete deterioration due to ASR/DEF (control specimens). This experimental data is also used to calibrate the analytical model. The conclusions of the research are that the analytical model correlates well with the experimental behavior of the large-scale control specimens not influenced by ASR/DEF. The lap splice region behaved as expected and an over-strength in the splice region is evident. To account for ASR/DEF damage, the analytical model proposes a reduction factor to decrease the bond strength of the splice region to predict ultimate performance of the region with different levels of premature concrete deterioration.