The problem of finding alternative energy sources has become particularly important over the last few decades. The reasons for this are insufficient extraction of fossil fuels, primarily oil and gas, as well as environmental pollution caused by their use. On the other hand, solar energy is a free, almost everywhere available resource that allows generating environmentally friendly electricity without the least harm to the environment. In view of this, solar power is one of the most promising

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... as of rapidly developing alternative energy. Nowadays, semiconductor devices with p-n-junction, which are called solar cells or photocells, have become widely used in the field of solar power. In such devices, due to the internal photoelectric effect under the influence of solar radiation, there is a redistribution of charges that causes emergence of electromotive force, so that it becomes possible to directly convert solar energy into electric energy. The one-diode mathematical model of the solar cell is analyzed in the paper. The solar cell is characterized by impedance which depends of environmental conditions. The laboratory workbench is designed to measure the impedance of the solar cell. The improved impedance mathematical model of a solar cell is proposed. It consists of: the serial resistance, barrier capacitance, barrier resistance, diffusion resistance and fractional order diffusion capacitance. The experimental Nyquist plot was fitted by using of the improved expression for impedance of the solar cell.