• Optimised solder interconnections in crystalline silicon (c-Si) photovoltaic modules for improved performance in elevated temperature climate

      Ekere, Nduka Nnamdi; Amalu, Emeka H.; Ogbomo, Osarumen O. (University of Wolverhampton, 2020-02)
      The operations of c-Si PV modules in elevated temperature climates like Africa and the Middle East are plagued with poor thermo-mechanical reliability and short fatigue lives. There is the need to improve the performance of the system operating in such regions to solve the grave energy poverty and power shortages. Solder interconnection failure due to accelerated thermo-mechanical degradation is identified as the most dominant degradation mode and responsible for over 40% of c-Si PV module failures. Hence the optimisation of c-Si PV module solder interconnections for improved performance in elevated temperature climate is the focus of this research. The effects of relevant reliability influencing factors (RIFs) on the performance (thermo-mechanical degradation and fatigue life) of c-Si PV module solder interconnections are investigated utilising a combination of ANSYS finite element modelling (FEM), Taguchi L25 orthogonal array and analytical techniques. The investigated RIFs are operating temperature, material combination and interconnection geometry. Garofalo creep relations and temperature dependent Young’s Modulus of Elasticity are used to model solder properties, EVA layer is modelled as viscoelastic while the other component layers are modelled using appropriate constitutive material models. Results show that fatigue life decays with increases in ambient temperature loads. A power function model 𝐿=721.48𝑇−1.343, was derived to predict the fatigue life (years) of c-Si PV modules in any climatic region. Of the various ribbon-contact material combination models investigated, Silver-Silver, Aluminium-Aluminium, Silver-Aluminium and Aluminium-Silver are the top four best performing solder interconnection models with low deformation ratios, 𝛿𝑅, normalised degradation values, 𝑁𝑑𝑖<1, and normalised fatigue life 𝑁𝑓𝑖>1. Further findings indicate that only the solder layer demonstrates good miniaturisation properties while the standard dimensions for ribbon and contact layers remain the best performing geometry settings. Additionally, from the Taguchi robust optimisation, the Aluminium-Silver ribbon-contact material combination model (ribbon = 180μm, solder = 56μm, contact = 50μm) demonstrated the best performance in elevated temperature climate, reduced solder degradation by 95.1% and is the most suitable substitute to the conventional c-Si PV module solder interconnection in elevated temperature climate conditions – in terms of thermo-mechanical degradation. These findings presented provide more insight into the design and development of c-Si PV modules operating in elevated temperature climates by providing a fatigue life prediction model in various ambient conditions, identifying material combinations and geometry which demonstrate improved thermo-mechanical reliability and elongated fatigue life.