No abstract

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

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 L 9 (3 3) orthogonal array was applied to Taguchi design of experiments (DOE) to investigate the effects of IMC thickness (IMC T), solder joint width (SJ W) and solder joint thickness (SJ T) 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 thermomechanical reliability of solder joints. Analysis of results selected towards thermomechanical reliability improvement shows the design with optimal parameter setting to be: solder joint thickness-20µm, solder joint width-1000µm, and IMC thickness-2.5µm. 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 16264 cycles to failure compared with the expected 13688 cycles to failure of a PV module designed to last for 25 years.

This study evaluates the impact of intermetallic compound (IMC) thickness on thermomechanical reliability of lead-free SnAgCu solder joints in crystalline silicon solar cell assembly with regards to fatigue life. Finite element modelling is used to simulate the non-linear thermomechanical deformation of the joints. Five geometric models of solar cell assemblies with different IMC thickness layers in the range of 1 to 4µm are utilized. The models were subjected to accelerated thermal cycling from -40 o C to 85 o C employing IEC 61215 standard for photovoltaic panels. Creep response of each of the assembly's solder joints to the induced thermal load were simulated using Garofalo-Arrhenius creep model. Simulation results indicate that when IMC thickness grows incrementally to 1, 2, 2.5, 3 and 4µm, thermo-mechanical fatigue life of solder joints diminishes to 13,800, 11,800, 10,600, 9400 and 7,800 cycles to failure respectively. Thus, solder joint fatigue life decreases as the IMC thickness increases during service lifetime. Therefore, proper design of solder joint in crystalline silicon solar cell assembly must include consideration of IMC layer thickness to prevent premature failure and to ensure fulfilment of desired functional lifetime of 13,688 cycles to failure (25 years).

No abstract

Physical and chemical composition analyses of Abuja’s municipal solid waste samples have been carried out in this study. Laboratory procedures were employed to determine the higher calorific value, the proximate analysis and ultimate analysis of MSW samples from selected districts of Abuja metropolis. An analytical methodology was therefore employed to determine whether the city’s MSW will be good resource for energy generation as a strategy for effective waste management. Abuja’s MSW has an aggregate higher heating value of 38.13MJ/kg. Moisture content of less than 8% obtained for all the samples compares very well with values for Nigerian coals. Volatile matter was found to be above than 60% for each samples tested while fixed carbon was determined to be less than 26% for each sample. The MSW samples gave excellent results for ash content of less than 4% when compared to most Nigerian coals with minimum ash content of 10.72%. The ultimate analysis shows the MSW samples compares fairly well with Nigerian coal samples in terms of elemental carbon, the least value being 41.80%. The least value for elemental carbon in most coal samples is 53.27%. Also, the sulphur content of the MSW samples is much less (not higher than 0.15%), compared with the least value of 0.58% for the coal samples. All the factors considered above indicate that the Abuja’s MSW will perform very well as a primary solid fuel when incinerated for energy recovery. The economic significance of this study lies in the confirmation that Abuja’s MSW is a good and cheap source of energy for electric power generation, replacing the expensive fossil fuel sources with their attendant hazardous emission to the environment. This will make the study area to be a cleaner and healthier environment.

Electric Power Generation Potential of Municipal Solid Wastes (MSW) in Abuja, the capital city of Nigeria has been studied in this work. A pilot study on  waste generation activities in Galadimawa District of Abuja was carried out and the results were applied to the metropolis as a whole due to the observed  similarities in the demographics of Galadimawa and other Districts in the metropolis. The city of Abuja presently has an annual MSW  generation rate of 973,557 tons with a per capita generation of 0.77 kg/day. Waste fractions for the metropolis were also analysed and discounting  materials that have recycling value, energy bearing fractions of organic and textile wastes were found to be 59.5%. This translates to 579266.42 tons per  annum and with an aggregate higher heating value (HHV) of 15.84 MJ/kg for this fraction, this approximates to about 9.2 x 109 MJ/annum of realisable  energy. Using a typical waste-to-energy (WTE) plant efficiency of 44% it is seen that Abuja’s MSW can support a power generating plant with a capacity of  128 MW. This potential far exceeds the energy being presently delivered to Abuja city from the national grid which is about 80 MW.

Abstract The thermal stability of Abuja’s municipal solid waste has been investigated in this study. Thermogravimetric and differential thermal analyses (TGA and DTA) were carried out on the MSW samples from three selected districts of Abuja metropolis under nitrogen atmosphere. The TG curves for samples from Lugbe and Dutse-Alhaji market are observed to have the same thermal behavioural trends which may be due to the presence of structural similarity of substances contained in the two samples compared to the behaviour of sample from Galadimawa district. It was observed that Galadimawa sample exhibited two stages of decomposition while Lugbe and Dutse-Alhaji samples have three main stages of decomposition. This study reveals that Abuja’s MSW have endothermic temperature peaks of 405.75 oC for sample from Lugbe district, 409.51 oC for Galadimawa district sample and 381.42 oC for sample taken from Dutse-Alhaji market, respectively. These values compare well with corresponding values for Nigerian coals (Enugu with 408 oC), thereby showing good thermal stability, and will be better and more economic fuel for energy generation than coal in addition to being renewable.