Том 55, № 2 (2019)

This paper presents the results of experimental studies of spectral, dark current–voltage and light load characteristics of the selenide–copper–gallium–indium (Cu(In, Ga)Se₂) solar cell. Тhe main fundamental parameters of the photoactive semiconductor layer Cu(In, Ga)Se_2, such as the band gap, the resistivity of the layer, the equilibrium majority–carrier concentration, the lifetime and the product μ_nτ_n of nonequilibrium minority carriers from the spectral, photoelectric and dark current–voltage characteristics are determined. Based on an analysis of the light-load current–voltage characteristics at various solar radiation powers (50–1000 W/m²), the main parameters of the p–n junction were determined, as well as the nonideality factor and the magnitude of the reverse diode saturation current; a photogeneration mechanism was established in the studied solar radiation range, which had the character of a diffusion mechanism, where carrier recombination in the photoactive layer did not have a significant effect. We found that in conditions of real solar lighting (Р_rad = 50–1000 W/m²), the output parameters of the solar cell – short-circuit current, open circuit voltage, the maximum output power increases with Р_rad. The fill factor (FF) of the light-current–voltage characteristics has a maximum at Р_rad ≈ 200 W/m², and an efficiency has a maximum value at Р_rad ≈ 600 W/m². The observed dependences of FF and efficiency are explained by the dependence of the series (R_ser) and shunt (R_sh) resistance of a solar cell on P_rad. To maintain the efficiency of a solar cell based on thin-film layers Cu(In, Ga)Se₂, equally high in conditions of increased radiation, as well as in conditions of low solar radiation, it is necessary that R_ser decreases and R_sh does not change with P_rad.

The main reserves for increasing the efficiency of solar energy utilization in heat supply systems are considered in this paper. This is of particular relevance under the conditions of market stagnation of modern solar collectors with parameters close to their limiting values, and forcing out traditional solar water heating plants with photovoltaic systems, whose cost becomes commensurate with thermal ones. The research objective is revealing and estimating the main reserves and determining promising directions and rational ways of improving the efficiency of the solar heat supply systems, based on minimizing the loss of temperature voltage during the transfer of thermal energy from solar collector to heat accumulator and further to consumer. It is shown that the main reserves of improvement of efficiency of solar heat supply systems is the improvement of their schematics, auxiliary equipment and operating parameters using the simplest self-regulating active elements, that can significantly influence the hydrodynamics of non-isothermal fluid flow in the system and its thermal efficiency when low specific flow rates of heat carrier through solar collector. The main ways of implementing the assigned task are revealed, which are: decreasing the heating temperature of heat carrier in the solar collector by 5–10°C, due to exclusion of the intermediate heat exchanger between the solar collector and accumulator and replacement of a multi-contour system with antifreeze to a single-contour self-draining unit; increasing the energy efficiency of known self-draining plants up to 65–80% by mutual transformation of potential and kinetic energy of a fluid in the Venturi tube and thereby eliminating the loss of hydrostatic pressure due to jet rupture; decreasing the temperature difference by 5—10°С when charging and discharging the heat accumulator using high-efficient temperature stratification of water; reducing the loss of temperature voltage and stabilization of water heating temperature in thermosiphon solar hot water supply systems due to its single heating in solar collectors; reducing the average operating temperature by 5–10°C of the solar collector and of the helio field of solar collectors by increasing the uniformity of fluid flow distribution by individual collector channels and the helio field as a whole.

The driving motive of this work is to enhance the tolerability of a flat Fresnel-lens concentrator to tracking errors, without the use of secondary optics or sophisticated, and normally costly, meticulous tracking equipment. This is achieved by optimizing the prismatic geometry of the Fresnel lens through a statistical approach that incorporates laws of light refraction and trigonometry. The proposed design produces high focal heat flux that is more suitable for thermal applications. A comparative simulation analysis was conducted for two case studies from literature, each with a different design method for the Fresnel lens. On basis of equivalent geometric concentration ratio and f-number, the flat-spot lenses, designed by this study, returned higher values of the concentration acceptance product (\(CAP\)). In case #1 of a 212× cylindrical lens with an f-number of unity, an equivalent flat lens by this work almost doubled the \(CAP\) from 0.165 to 0.34. For the design case #2 of a 559× aspheric Fresnel lens made by simple geometrical optics, a 60.7% enhanced \(CAP\) was achieved by this work’s lens, from 0.206 to 0.331, at an f-number of 0.83.

The Republic of Uzbekistan currently has an urgent need to provide drinking water to the population of remote rural areas. The water sources in these areas are usually heavily polluted by pathogenic bacteria and the water must be sterilized before use. Due to the remote nature of settlements in these areas, it is impossible to perform this task using traditional methods suitable for urban areas, due to economic challenges. The problem is the lack of a developed infrastructure (electricity, communications) because of the economic situation and the remote location of these villages. In view of this, the scale of infectious diseases of people caused by poor-quality water in rural areas of the republic is quite high. In this regard, the development of compact and efficient water purification devices, which should be affordable for the rural population, is of particular relevance. Unlike most disinfectants, ultraviolet (UV) radiation does not inactivate microorganisms by chemical interaction. UV irradiation inactivates organisms by absorbing light, which causes a photochemical reaction that changes the molecular basis of the components to the function of the cell. As UV rays penetrate the cell wall of a microorganism, energy reacts with nucleic acids and its other vital components, leading to the injury or death of exposed cells. Ultraviolet lamps work in almost the same way as fluorescent lamps. The difference between the two lamps is that the fluorescent bulb of the lamp is coated with a phosphorous compound that converts ultraviolet radiation into visible light. The UV lamp is not covered, so it transmits the ultraviolet radiation produced by the arc. This study confirms the efficiency of the developed scheme of an autonomous device for disinfecting water when it is exposed by the radiation of an ultraviolet lamp with electricity supply from photovoltaic systems.

With the development of small business in Uzbekistan’s rural areas, there is a shortage of electric power, as well as power outages for these consumers. The use of renewable energy sources is one way to solve this problem, and this has been little studied in Bukhara oblast. A preliminary study of this problem shows that the region has the necessary capacity of renewable energy sources. This paper presents the results of a study of wind speed and wind energy potential in Bukhara oblast located in southwestern Uzbekistan. The data of wind speed and direction measured at the weather station at Bukhara’s international airport, taken at an altitude of 10 meters, were analyzed on the basis of the two-parameter Weibull distribution function. The main parameters k and c of the Weibull distribution function were determined using the empirical method. Wind speed and direction were statistically analyzed in MatLab and a graph (wind rose) was plotted. Wind energy potentials at different altitudes were also evaluated.

This paper describes methods to develop the use of the renewable energy sources, particularly solar energy. It considers the key mechanisms to stimulate accelerated development of renewable energy sources, using the Republic of Uzbekistan as an example.