Numerical analysis on thermal crack initiation due to non-homogeneous solder coating on the round strip interconnection of photo-voltaic modules

Solar energy is one of the most widely used renewable energy sources, with photo-voltaic (PV) solar cells/panels now utilized as an important energy source. The strip interconnection between solar cells (used for collecting current from solar cells) is a key PV module component; as poor interconnection reliability can lead to PV module failure. Multi-Busbar is a new type of interconnection which incorporates several round copper wires to help increase the energy conversion and transmission efficiency of PV modules and also to reduce the material costs. The non-homogeneity of the solder coating on the wires (resulting from manufacturing process faults), is one of the main factors that is responsible for the poor connections between the wire and the silver pads; which adversely impacts on the interconnection strength and long term reliability. This paper concerns an investigation of the effect of solder coating non-homogeneity on the thermo-mechanical response of round wires used for PV module interconnections. The study evaluates the two main parameters of non-homogeneity (out of centre value and direction), and also investigates the effect of geometrical parameters. The Extended Finite Element Method in ABAQUS software was used to determine the micro-crack initiation temperature and location for a given joint design. The results show that the cracking temperature is most affected by the direction of solder coating non-homogeneity and the downward vertical direction of out of centre positioning of copper in the solder coating leads to the most reduction in cracking temperature (up to 21%)

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

Electrical and mechanical analysis of different TSV geometries

Through-silicon via (TSV) is an important component for implementing 3-D packages and 3-D integrated circuits as the TSV technology allows stacked silicon chips to interconnect through direct contact to help facilitate high-speed signal processing. By facilitating the stacking of silicon chips, the TSV technology also helps to meet the increasing demand for high density and high performance miniaturized electronic products. Our review of the literature shows that very few studies have reported on the impact of TSV bump geometry on the electrical and mechanical characteristics of the TSV. This paper reports on the investigation of different TSV geometries with the focus on identifying the ideal shapes for improved electrical signal transmission as well as for improved mechanical reliability. The cylindrical, quadrangular (square), elliptical, and triangular shapes were investigated in our study and our results showed that the quadrangular shape had the best electrical performance due to good characteristic impedance. Our results also showed that the quadrangular and cylindrical shapes provided improved mechanical reliability as these two shapes lead to high Cu protrusion of TSV after the annealing process

Evaluation of thermo-mechanical damage and fatigue life of solar cell solder interconnections

The soldering process of interconnecting crystalline silicon solar cells to form photovoltaic (PV) module is a key manufacturing process. However, during the soldering process, stress is induced in the solar cell solder joints and remains in the joint as residual stress after soldering. Furthermore, during the module service life time, thermo-mechanical degradation of the solder joints occurs due to thermal cycling of the joints which induce stress, creep strain and strain energy. The resultant effect of damage on the solder joint is premature failure, hence shortened fatigue life. This study seeks to determine accumulated thermo-mechanical damage and fatigue life of solder interconnection in solar cell assembly under thermo-mechanical cycling conditions. In this investigation, finite element modelling (FEM) and simulations are carried out in order to determine nonlinear degradation of SnAgCu solder joints. The degradation of the solder material is simulated using Garofalo-Arrhenius creep model. A three dimensional (3D) geometric model is subjected to six accelerated thermal cycles (ATCs) utilising IEC 61215 standard for photovoltaic panels. The results demonstrate that induced stress, strain and strain energy impacts the solder joints during operations. Furthermore, the larger the accumulated creep strain and creep strain energy in the joints, the shorter the fatigue life. This indicates that creep strain and creep strain energy in the solder joints significantly impacts the thermo-mechanical reliability of the assembly joints. Regions of solder joint with critical stress, strain and strain energy values including their distribution are determined. Analysis of results demonstrates that creep energy density is a better parameter than creep strain in predicting interconnection fatigue life. The use of six ATCs yields significant data which enable better understanding of the response of the solder joints to the induced loads. Moreover, information obtained from this study can be used for improved design and better-quality fabrication of solder interconnections in solar cell assembly for enhanced thermo-mechanical reliability

Optimization of thermo-mechanical reliability of solder joints in crystalline silicon solar cell assembly

This is an accepted manuscript of an article published by Elsevier in Microelectronics Reliability on 28/12/2015, available online: https://doi.org/10.1016/j.microrel.2015.12.031 The accepted version of the publication may differ from the final published version.© 2015 Elsevier Ltd All rights reserved. A robust solder joint in crystalline silicon solar cell assembly is necessary to ensure its thermo-mechanical reliability. The solder joint formed using optimal parameter setting accumulates minimal creep strain energy density which leads to longer fatigue life. In this study, thermo-mechanical reliability of solder joint in crystalline silicon solar cell assembly is evaluated using finite element modelling (FEM) and Taguchi method. Geometric models of the crystalline silicon solar cell assembly are built and subjected to accelerated thermal cycling utilizing IEC 61215 standard for photovoltaic panels. In order to obtain the model with minimum accumulated creep strain energy density, the L9 (33) orthogonal array was applied to Taguchi design of experiments (DOE) to investigate the effects of IMC thickness (IMCT), solder joint width (SJW) and solder joint thickness (SJT) on the thermo-mechanical reliability of solder joints. The solder material used in this study is Sn3.8Ag0.7Cu and its non-linear creep deformation is simulated using Garofalo-Arrhenius creep model. The results obtained indicate that solder joint thickness has the most significant effect on the thermo-mechanical reliability of solder joints. Analysis of results selected towards thermo-mechanical reliability improvement shows the design with optimal parameter setting to be: solder joint thickness - 20 μm, solder joint width - 1000 μm, and IMC thickness - 2.5 μm. Furthermore, the optimized model has the least damage in the solder joint and shows a reduction of 47.96% in accumulated creep strain energy density per cycle compared to the worst case original model. Moreover, the optimized model has 16,264 cycles to failure compared with the expected 13,688 cycles to failure of a PV module designed to last for 25 years.The authors acknowledge funding provided by the Petroleum Technology Development Fund (PTDF, PTDF/E/OSS/PHD/ZMT/623/12), Nigeria used in carrying out this study.Published versio

Cu Protrusion of Different through-Silicon via Shapes under Annealing Process

The through-silicon via (TSV) 3D integration method has become one of the most widely used techniques for achieving system-level integration for applications that require smaller package sizes, higher interconnection density and high performance. This is because the TSV fabrication technology provides the mechanism for facilitating communications between various layers of the 3D integration system and for interconnecting stacked devices at wafer-level. Although there are several reported studies on TSV 3D integration R&D, with most of these studies focused on the improvement of TSV fabrication process, there are very limited in-depth studies associated with the TSV reliability issues and challenges. In this paper, we investigate the effect of TSV geometries on the associated TSV reliability factors. Different TSV geometries including I-type, tapered, elliptical, triangular, quadrangular and circular shapes (with same volume) are investigated to find the most reliable structure under annealing process. The results show that the tapered TSV shape releases thermo-mechanical stress more uniformly than other shapes and larger top surface shows better reliability

Creep-fatigue lifetime estimation of efficient photovoltaic module ribbon interconnections

As the solar PV harvesting energy system are becoming more important sector of renewable energy day to day, improving the efficiency of the solar PV module and reducing the cost of modules are receiving more attentions of PV module manufacturers. Design of the PV module interconnection ribbons is one of the main focus for developing the efficiency of the PV modules and improving the reliability of the modules. In the last decade, new designs for the PV module interconnection ribbon have been introduced, however, there is still a need to optimize their configuration and geometry to achieve higher reliability without dropping the efficiency of the PV modules. Indeed, solely using the wider interconnection ribbons (to provide more joint length) may increase the reliability of the module, but it directly reduces the efficiency of module due to more shading effect. This study provides the results for determining the optimal design for long-term reliability of PV module interconnections. Three main PV module ribbon interconnection designs including Conventional Ribbon (CR), Light-Capturing Ribbon (LCR), and Multi-Busbar (MBB) interconnections are compared in terms of number of cycles to creep-fatigue failure. This study uses the FEM simulation and creep-fatigue reliability formulations to find the effect of the main geometrical parameters on the failure of different PV module ribbon interconnection designs. The finding showed that the MBB interconnections has up to 15 % higher creep-fatigue lifetime compared to the LCR and the CR interconnections

A Review on Cooling Systems for Portable Energy Storage Units

Achieving the global electricity demand and meeting the United Nations sustainable development target on reliable and sustainable energy supply by 2050 are crucial. Portable energy storage (PES) units, powered by solid-state battery cells, can offer a sustainable and cost-effective solution for regions with limited power-grid access. However, operating in high-dust and high-temperature environments presents challenges that require effective thermal management solutions. This paper is a comprehensive review of thermal management systems for PES units, with a specific focus on addressing the challenge of overheating in airtight designs. The review of various active and passive cooling systems is conducted through extensive study of the relevant literature, which is significant in providing insights into the operation, performance parameters, and design options for different cooling system technologies. The findings from this review show heat pipe (HP) technologies as key cooling-system solutions for airtight PES units. Specifically, loop and oscillating HPs, as well as the vapour chamber, offer desirable features such as compactness, low cost, and high thermal conductivity that make them superior to other alternatives for the cooling systems in PES. The insights and knowledge generated via this review will help facilitate the design and development of innovative, efficient, and reliable PES units, thereby contributing to the advancement of off-grid renewable energy applications and enabling sustainable power solutions worldwide. Furthermore, an appropriate design of PES units can help in reducing capital and maintenance costs

Wind Flow and Its Interaction with a Mobile Solar PV System Mounted on a Trailer

Efficient implementation of clean energy technologies is paramount, with mobile solar PV systems on trailers (MSPTs) emerging as pivotal solutions, particularly in regions with limited power grid access. This endeavour is vital for meeting escalating electricity demands and aligning with the UN Sustainable Development Goal (SDG), aimed at ensuring dependable and sustainable energy provision in developing countries. This study investigates the aerodynamic behaviour of a designed MSPT using numerical simulation and experimental methods, thereby offering optimization potential for MSPT design and enhancing overall performance and reliability. Specifically, the study focuses on the effects of wind velocity and tilt angles on the drag and lift forces, as well as drag and lift coefficients on the panel used in the MSPT system. The overall wind force on the entire MSPT, including nine large solar PV panels, is scrutinised, considering combined wind flow and system geometry effects. The numerical investigations were conducted using ANSYS-Fluent software (version 2022/R2) and experimental testing was performed within the C15-10 Wind Tunnel, utilizing scaled-down models to validate the accuracy of the simulation. The findings from the numerical investigations showed an increased turbulence caused by gaps between panels, resulting in almost 62% higher suction flow velocity and 22% higher suction pressure compared to a single panel. Drag and lift forces on the entire MSPT were approximately 6.7 and 7.8 times greater than those on a single panel with the same 30-degree tilt angle, respectively. The findings revealed that scaling forces on a single panel is insufficient for accurately predicting the aerodynamic forces on the entire MSPT. The insights and the knowledge from this study pave the way for further improvements in mobile solar PV technology

Critical skills needs and challenges for STEM/STEAM graduates increased employability and entrepreneurship in the solar energy sector

Energy produced by photovoltaic module (PVM) is poised to deliver the UN Sustainable Development Goal 7 (SDG-7) by 2030 and Net-Zero by 2050 but not until ample graduates with adequate Solar Energy Technology (SET) skills are produced by Higher education institutions (HEIs). Although PVM has witnessed significant penetration globally, the sustainability of the growth of the sector is challenged by attendant monotonic skilled labour shortages. The evolving growth imbalance is critical in the European Union (EU), limits her global competitiveness and necessitates the need to create wider awareness on the green technology to stimulate more production of solar energy sector (SES) specific skills graduates. Discussing the mismatch between the skills Europe needs and has in the SES, the study outlines key critical skills Science, Technology, Engineering and Mathematics (STEM) cum Arts (STEAM) graduates ought to possess to secure sector employment and the challenges limiting them from acquiring the competencies. The review is conducted via extensive study of relevant literature, analysis of interviews and observations. Academic, industrial, and entrepreneurial skills are identified as critical SES needs. Designing and running educational modules/curricula that embed the identified solar technology specialist skills on students and learners are proposed as vehicle to increase their employability and entrepreneurship. This study profiles trends and developments in the SES for stakeholders’ increased awareness while presenting the specialist skills in-demand for employment in the sector. The adoption of SET Training (SETechTra) curricula/modules by the EIs will substantially increase the production of industry-ready graduates whilst decreasing the SES skills gap