Solar cells are photovoltaic devices that convert sun energy directly into the electrical energy. Solar panel is composed of multiple solar cells that are combined together. Depending on the power demand, solar panels are connected to each other in series or parallel. Thus, electrical energy from the solar array systems is created to meet the needs. Solar panels are used on roof and wall systems in buildings and power plants. In solar array design, radiance, temperature, shading, surface angle and effect of series-parallel connection, which are factors affecting the operation of solar panels, should be considered. Shading significantly reduces the efficiency of a solar array system. Shading can occur entirely or partially due to dynamic or static obstacles. The effect of shading varies by location at which the solar panel is formed. In this work, design and optimization of solar arrays, positioned over a large area, having different time constant shading effects, was performed in order to minimize shading effect.
In this paper, dye sensitized solar cells were prepared using titanium dioxide (TiO₂) and natural dye extracted from purple carrot. The performance of dye sensitized solar cells was significantly improved through the pre- and post-treatments of the fluorinated tin oxide (FTO) glass substrate and the TiO₂ film using hydrochloric (HCl), phosphoric (H₃PO₄), and nitric (HNO₃) acids. The results showed that the pre-treatment of the FTO with H₃PO₄ and the post-treatment of TiO₂ with HNO₃ resulted in improved efficiencies of 130% and 250%, respectively.
In this paper, we present an appropriate method of decoupling surface and bulk recombination processes in silicon wafers. The study was carried out using the surface passivation of multicrystalline silicon wafers by ethanolic solution of iodine at different molarities varying between 0.01 M and 0.1 M. The effect of the concentration of ethanolic iodine solution on surface passivation effectiveness was investigated by using quasi steady state photo-conductance technique. Reproducible experiments have shown that the best passivation is reached for a molarity of around 0.02 M. The carrier lifetime after passivation at 0.02 M has been improved by more than one order of magnitude, compared to that of the same wafer before the passivation. Using an adequate modeling of minority carrier lifetime curves τ (Δ n), based on Hornbeck-Haynes model, surface recombination velocity was calculated. The minimum values of surface recombination velocity have been found to be approximately 120 cm/s for 0.02 M. The modeling results indicate that the minority carrier lifetime improvement can be easily correlated with the decrease of the surface recombination velocity for a fixed bulk lifetime τ_{b}=115 μs.
The geometries, electronic structures, polarizabilities, and hyperpolarizabilities of natural dye sensitizer alizarin from madder fruit was studied based on density functional theory using the hybrid functional B3LYP. Features of the electronic absorption spectra in the visible and near-UV regions were assigned based on time-dependent density function theory calculations. The calculated results suggest three excited states with the lowest excited energies in 1,2-dihydroxy-9,10-anthraquinone and it was due to photoinduced electron transfer processes. The interfacial electron transfer between semiconductor TiO_2 electrode and dye sensitizer 1,2-dihydroxy-9,10-anthraquinone is due to an electron injection process from excited dye to the semiconductor conduction band. The importance of hydroxyl group in geometries, electronic structures and spectral properties were reported.
The impact of illuminance on changes of the solar cell electromotive force is analyzed. A mathematical model for a solar cell electromotive force dependence on illuminance is presented. For this purpose, a selection of experimental data trend function was carried out, and the Pearson correlation coefficients were established. The most optimal results were obtained in case of an exponential function with the strongest correlation (R^2=0.983). The analysis has shown that at 100 W/m^2 illuminance the electromotive force saturation is obtained (the electromotive force changes insignificantly and fluctuates at around 2 V), which indicates that upon reaching such an illuminance a solar cell operates at maximum efficiency. A first-order differential equation satisfied by the trend function has been compiled. When interpreting illuminance as an evolution variable, the proposed mathematical model can be interpreted as a dynamical system. The deviation frequency spectrum of the measurement values with respect to the theoretical prediction is analyzed.
Power photovoltaic applications, as photovoltaic power plants or building integrated photovoltaic systems, are mainly built using parallel or serial photovoltaic modules strings. Daily usage of such systems usually produces non-uniform string connected behavior due to partial or total shading. In these conditions, less illuminated cells transform into power receivers, thus producing supplementary losses and local panel heating. This phenomenon, called hot-spot, may evolve into producing zonal or total destruction of the solar modules. For these purposes this paper will submit to your attention simulation and experimental results of the partial and total illumination phenomenon, targeting specific information in the effect evaluation of any photovoltaic panel.
We show that coherence induced by Fano interference can enhance the power produced by photovoltaic devices, e.g. photodetectors and solar cells, as compared to the same system with no coherence. No additional external energy source is necessary to create such induced coherence. In the present model, coherence generated by photocurrent increases (for optically thin cells) the flow of electrons through the load, which reduces radiative recombination and enhances cell power. We discuss two schemes in which coherence is generated between upper or lower energy levels. We also study the influence of decoherence, τa, on cell power and show that one can design a device with Fano enhancement even at relatively large decoherence rates. Finally we investigate the effect of ambient temperature Ta on the cell power in a scheme with no interference and show that for certain parameters power can be increased by increasing Ta.
This paper presents an evaluation of the performance degradation of photovoltaic modules after twelve operation years in a steppe region environment in Algeria. The objective is to understand the different degradation modes of the photovoltaic modules and associated factors and their impact on the electrical properties (V_{oc}, I_{sc}, V_{max}, I_{max}, P_{max} and FF) using the degradation tests of IEC 61215 qualification standard and the electroluminescence test. The experimental results show that yearly degradation rates of the maximum power output P_{max} present the highest possible loss, ranging from 2.08% to 5.2%. Additionally, the results show that the short-circuit current I_{sc} comes second with yearly degradation rates spanning from 2.75% to 2.84%. Finally the open-circuit voltage V_{oc} is the least affected, with yearly degradation occurring from 0.01% to 4.25%.
In the present work, the fabrication and characterization of non-curling, free-standing TiO_2 nanotube membranes and their integration in front-side illuminated dye-sensitized solar cells are reported. Vertically oriented TiO_2 nanotube arrays were fabricated by anodic oxidation of a titanium foil. Nanotube membranes were detached from the metallic foil, transferred and bonded on transparent fluorine-doped tin oxide/glass substrates employing a TiO_2 sol as a binder. Crystalline phase and morphology of the film were investigated, evidencing the formation of a highly ordered 1D nanotubes carpet, with a pure anatase crystalline structure. TiO_2 nanotube-based DSCs were fabricated using reversible microfluidic architecture. The cell performances were studied by I-V electrical characterization, incident-photon-to-electron conversion efficiency, electrochemical impedance spectroscopy and open circuit voltage decay measurements, showing an increase in electron lifetime compared to nanoparticle-based dye-sensitized solar cells.
We propose a 3D branched ZnO nanostructure for the fabrication of highly efficient dye-sensitized solar cell photoanodes. A coral-shaped structured Zn layer was deposited by radio frequency magnetron sputtering at room temperature onto fluorine-doped tin oxide/glass sheets and then thermally oxidized in ambient atmosphere, obtaining a high-density branched ZnO film. The porous structure provides a large surface area, and, as a consequence, a high number of adsorption sites, and the size and spacing of the nanostructures (on the order of the exciton diffusion length) are optimal for good electron collection efficiency. The proposed synthesis technique is simple and scalable and the reproducibility of the growth results was tested. The crystalline phase of the film was investigated, evidencing the complete oxidation and the formation of a pure wurtzite crystalline structure. ZnO-based solar harvesters were fabricated in a microfluidic architecture, using conventional sensitizer and electrolyte. The dependence of the cell efficiency on dye incubation time and film thickness was studied with I-V electrical characterization and electrochemical impedance spectroscopy. The obtained conversion efficiency values, with a maximum value of 4.83%, confirm the highly promising properties of this material for the implementation in dye-sensitized solar cell photoanodes.
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