At present, renewable energy sources are considered to ensure energy security and combat climate change. Vietnam has a high potential for solar power development, especially in the central region and the southern region. However, the northeast region has the lowest solar radiation value, so it can cause difficulty for rooftop solar power investment. In this paper, the study results analyze the financial efficiency of the grid-tied rooftop solar power system with battery storage and compared it to the grid-tied rooftop solar power system without battery storage. The experimental data of a grid-tied solar power system with battery storage at an office building in the northeast region of Vietnam is collected to evaluate the system’s operation performance in real conditions. The study results present that the financial efficiency of rooftop grid-tied power project with and without storage is viable since the benefit-cost ratio (B–C) is larger than one, and internal rate of return (IRR) and net present value (NPV) are positive. However, the grid-tied rooftop solar power system with storage is not quite feasible in case of changing the electricity selling price and investment cost even though the grid-tied solar power system using the storage device can operate more flexibly. The payback period of the grid-tied solar power system with storage is 6.2 years longer and the total profit is nearly 1.9 times lower than the solar power system without battery storage due to the difference in the price of the inverters and the battery. In contrast, the grid-tied solar power system without battery storage shows better financial efficiency but strongly depends on the operation of the utility grid.

In order to understand quantitatively plasma phenomena and ionized gases, accurate electron collision cross-sections and electron transport coefficients for not only pure atoms and molecules but also for the binary gas mixtures are necessary. Electron transport coefficients (electron drift velocity, density-normalized longitudinal diffusion coefficient, and density-normalized effective ionization coefficient) in mixture gases of Cl₂ with Ar, Xe and O₂, therefore, were calculated and analyzed by using a two-term approximation of the Boltzmann equation over a wide E/N range (ratio of the electric field E to the neutral number density N). The limiting field strength values of E/N, (E/N)_lim, for these binary gas mixtures were also derived and compared with those of pure SF₆ gas. These binary gas mixtures are being considered for use in many industries, depending on the mixture ratio and the particular application of the gas and the electrical equipment.

Purpose. To build a mathematical and simulation model to evaluate the effect of voltage flicker on leakage current in an underground mine AC power network containing power electronic devices. Methodology. The research methods used in this study include theoretical method to build the equation of leakage current and simulation modeling method on Matlab/Simulink software to determine the leakage current values in each case of voltage flicker. Findings. In addition to the theoretical analysis on the mine power network model, the paper also evaluates the mine power network model containing the converter on Matlab/Simulink with the model parameters U = 1,140 V, C = 0.19 uF/phase, R = 168 k/phase. The research results show that in the case of low voltage flicker with voltage amplitude lower than 50 % of rated voltage in ½ network cycle, the leakage current before the inverter decreases by the largest 19.7 % and the leakage current after the inverter decreases by the largest 5.2 % compared to the leakage current value at normal voltage. In the case of overvoltage flicker with voltage amplitude higher than 150 % of rated voltage in ½ network cycle, the maximum leakage current before the inverter increases by 33.6 %, the maximum leakage current after the inverter increases by 47.4 % compared to the leakage current value at normal voltage. This problem causes the phenomenon of mistaken operation of the leakage protection relay and causes unsafety in mining. Originality. The study includes the introduction of a leakage current model in an underground mine’s AC power network containing power electronic devices and the simulation to find out the influence of voltage flicker on the leakage current in that power network using Matlab/Simulink software. Practical value. The research results indicate the need for measures to minimize voltage flicker, thereby improving the reliability of leakage protection and improving safety in mining.