Effect of Coefficient of Thermal Expansion (CTE) Mismatch of Solder Joint Materials in Photovoltaic (PV) Modules Operating in Elevated Temperature Climate on the Joint's Damage

With failure of solder joints (SJs) in photovoltaic (PV) modules constituting over 40% of the total module failures, investigation of SJ's reliability factors is critical. This study employs the Garofalo creep model in ANSYS Finite Element Modelling (FEM) to simulate solder joint damage. Accumulated creep strain energy density is used to quantify damage. PV modules consisting of interconnections formed from different material combinations (silver, copper, aluminum, zinc, tin and brass) are subjected to induced temperature cycles ranging from -40 °C to +85 °C. Results show that zinc-solder-silver joint having the highest CTE mismatch of 19.6 ppm exhibits the greatest damage while silver-solder-silver with no mismatch possesses the least damage

Generating temperature cycle profiles of different solar photovoltaic module technologies from in-situ conditions for accurate prediction of thermomechanical degradation

The IEC61215 TC200 is a rigorous approval thermal cycling test process that assesses the reliability of solar photovoltaic modules and offers a 25-year lifetime guarantee. However, previous research has shown that installed solar photovoltaic modules experience different rates of degradation depending on the location and climate with most research focused on crystalline silicon. In this study, outdoor weathering data obtained from a rig set up in Kumasi, Ghana for the year 2014, is used to generate thermal cycles for 5 different technologies including monocrystalline, polycrystalline, and amorphous silicon, Copper Indium Gallium Selenide (CIGS) and Heterojunction-With-Intrinsic-Thin-Layer (HIT). From the results, the highest yearly average of the maximum and minimum temperatures, and ramp rates of 54.8oC, 26.1oC, and 6.05oC/h respectively are recorded in CIGS. Polycrystalline recorded the least temperatures of 45.2°C and 23.9°C while HIT recorded the least ramp rate of 4.45°C /h. A comparison between the 2014 and the IEC61215 thermal cycles show extremely wide differences which could explain the higher degradation rates and shorter life of installed solar photovoltaic modules. The procedure adopted in this research can be repeated at different locations to obtain technology-specific thermal cycling profiles to evaluate the thermomechanical damage and predict the life of different solar photovoltaic modules

THE EFFECTS OF THE TRANSIENT AND PERFORMANCE LOSS RATES ON PV OUTPUT PERFORMANCE

Solar photovoltaic (PV) panels experience long-term performance degradation as compared to their initial performance, resulting in lower like-per-like efficiencies and performance ratios. Manufacturers of solar photovoltaic modules normally guarantee a lifespan of more than 20 years. To meet such commitments, it is important to monitor and mitigate PV module degradation during this period, as well as beyond, to recognize maintenance and repair needs. Solar PV modules degrade over time, becoming less effective, less reliable, and eventually unusable. The effects of transient and performance loss rates on the output performance of polycrystalline silicon (p-Si) solar PV modules are the focus of this study. PV modules\u27 electrical performance and solar energy conversion efficiency change as solar irradiance and ambient temperature change. A rise in ambient temperature or a decrease in solar irradiance, for example, all result in a reduction in performance. Large variations in operating conditions due to uncontrollable external parameters such as cloud movement and wind velocity, as well as changes in factors external to PV systems such as unexpected shading, inverter problems, and control failures, may trigger transient performance changes on PV modules output. The data used in this analysis were from the Warrenpoint site location of the Electric Supply Board (ESB) for the years 2016-2020. Clear days in winter, spring, summer, and autumn were caused by a rise in daily sunshine hours in February, May, June, and September, according to the output performance. Due to the highest amount of solar irradiation at the site location, these days saw an increase in PV output generation. According to the performance loss rates, the median degradation rates in 2016 (4.5%/year to 14%/year) and 2017 (0.1%/year to 5.2%/year) are 8.40%/year and 3.87%/year, respectively. This means that the degradation rate is greater than 1%/year, the hazardous probability is between 90% and 100%, and severity of 10 is given (With an associated failure of corrosion in solder bonds). 2018 (-7.5%/year to 2.5%/year), 2019 (-16%/year to -23%/year), and 2020 (-5.1%/year to -10% /year) had median degradation rates of -2.75%/year, -18.23%/year, and -5.2%/year, respectively. This shows that the degradation rates are less than 1% per year, and their hazardous probabilities range from severity rank 9 to 1, or 80% to 70% to 0% safety risk. All of these factors have a negative impact on PV output performance

Thermomechanical degradation mechanisms of silicon photovoltaic modules

The durability and lifetime of photovoltaic (PV) modules is one of the chief concerns for an industry which is rapidly approaching maturity. Guaranteeing the economic viability of potential PV installations is paramount to fostering growth of the industry. Whilst certification standards have helped to improve the reliability of modules, with a significant reduction in early failures, long-term performance degradation and overall lifetimes are yet to be addressed in a meaningful way. For this, it is necessary to quantify the effects of use-environment and module design. Long-term degradation of the solder bonds in PV modules causes steady power loss and leads to the generation of more devastating, secondary mechanisms such as hot-spots. Whilst solder bond degradation is well-recognised and even tested for in certification protocols, the potential rate of degradation is not well understood, particularly with respect to different environmental conditions and material selection. The complex nature of a standard silicon PV module construction makes it difficult to observe the stresses experienced by the various components during normal operation. This thesis presents the development of a finite-element model which is used to observe the stresses and strains experienced by module components during normal operating conditions and quantifies the degradation of solder bonds under different environmental conditions. First, module operating temperatures are examined across a range of climates and locations to evaluate the thermal profiles experienced by modules. Using finite-element techniques, the thermomechanical behaviour of modules is then simulated using the same thermal profiles and a quantification of solder bond degradation potential in each location is achieved. It is shown that hot climates are responsible for the highest degradation potential, but further to this, hot environments with many ii clear sky days, allowing for large swings in module temperature, are significantly more damaging. A comparison is drawn between indoor accelerated stress procedures and outdoor exposure, such that an equivalence between test duration and location-dependent outdoor exposure can be determined. It is shown that for the most damaging climate studied, 86 standard thermal cycles is appropriate for one-year of outdoor exposure whereas the least damaging environment would require 11 standard thermal cycles. However, these conclusions may only be applicable to the specific module design which was modelled as the material selection and interaction within a device plays a major role in the thermomechanical behaviour and degradation potential. In addition to a study on the influence of use-environment, a study on the influence of the encapsulating material is conducted with a particular focus on the effects of the viscoelastic properties of the materials. It is shown that the degradation of solder bonds can vary depending on the encapsulating material. Furthermore, the intended use-environment could inform the selection of the encapsulating material. The temperature-dependency of the material properties means that some materials will mitigate thermomechanical degradation mechanisms more than others under certain conditions i.e. hotter or colder climates

Long-Term Durability of Rooftop Grid-Connected Solar Photovoltaic Systems

Compared to their initial performance, solar photovoltaic (PV) arrays show long-term performance degradation, resulting in lower like-for-like efficiencies and performance ratios. The long-term durability of polycrystalline silicon (p-Si) solar PV modules in three roof-top grid-connected arrays has been examined. Electrical output, ambient temperature, cell temperature, solar irradiance, solar irradiation, and wind speed data were collected at hourly intervals from 2017 to 2021 from three 50 kWp PV installations in Northern Ireland. The results show the extent to which higher PV temperatures associated with more intense solar radiation decrease efficiency, fill factor and maximum power output for PV arrays in a temperate climate. Long-term durability trends for grid-connected roof-top solar photovoltaic systems can be obscured by diurnal and seasonal changes in environmental conditions. To reduce the influence of variable conditions, performance ratios (PRcorr) were “corrected” using the measured annual average cell temperature (Tcell_avg). Introduction of this temperature-correction reduced the seasonal variation of the performance ratio. Using temperature-corrected performance ratios, long-term (in this case those seen after fiveyears operation) performance degradation trends become evident with high confidence after six months for one PV array and within three years for the two other arrays. If lower statistical confidence in trends is acceptable, long-term degradation rates can be identified within one year of operation for all PV arrays examined. These results have the important implication that relatively short-duration outdoor PV performance monitoring may be reliably used to estimate long-term degradation and/or to calibrate normally-conducted accelerated testing

Modelling of solder interconnection’s performance in photovoltaic modules for reliability prediction

A thesis submitted in partial fulfilment of the requirements of the University of Wolverhampton for the degree of Doctor of Philosophy.Standard crystalline silicon photovoltaic (PV) modules are designed to continuously convert solar energy into electricity for 25 years. However, the continual generation of electricity by the PV modules throughout their designed service life has been a concern. The key challenge has been the untimely fatigue failure of solder interconnections of solar cells in the modules due to accelerated thermo-mechanical degradation. The goal of this research is to provide adequate information for proper design of solar cell solder joint against fatigue failure through the study of cyclic thermo-mechanical stresses and strains in the joint. This is carried-out through finite element analysis (FEA) using ANSYS software to develop the solar cell assembly geometric models followed by simulations. Appropriate material constitutive model for solder alloy is employed to predict number of cycles to failure of solder joint, hence predicting its fatigue life. The results obtained from this study indicate that intermetallic compound thickness (TIMC); solder joint thickness (TSJ) and width (WSJ) have significant impacts on fatigue life of solder joint. The impacts of TIMC and TSJ are such that as the thicknesses increases solder joint fatigue life decreases. Conversely, as solder joint width (WSJ) increases, fatigue life increases. Furthermore, optimization of the joint is carried-out towards thermo-mechanical reliability improvement. Analysis of results shows the design with optimal parameter setting to be: TIMC -2.5μm, TSJ -20μm and WSJ -1000μm. In addition, the optimized model has 16,264 cycles to failure which is 18.82% more than the expected 13,688 cycles to failure of a PV module designed to last for 25 years