The theoretically achievable efficiency of the PEC for the single-cell solar cells (SC) is 30%. However, the cost of electricity generated by means of the solar cells has already become equal to that of natural gas. At the same time, the maximum confirmed efficiency for the solar cell is 26.3%. Thus, a certain lag behind the theoretically possible value is still observed. Analysis of the losses of modern photoelectric converters shows that at least 10% of them are related to the reflectivity of the SC surface. Therefore, along with intensive studies on heterojunction, thin-film constructive solutions, much attention is paid to other ones that allow for more than double the conversion efficiency. The paper deals with the formation of antireflective coatings on the surface of the PEC. One of the promising antireflection materials, which is widely studied at the present time, is porous silicon, called black silicon (black silicon b-Si) in the literature. The development of chemical and anodic silicon etching technologies, as well as the low cost and simplicity of the forming process, allow producing b-Si structures with controlled parameters of the antireflection layers. This paper presents the comparative results of the investigation of the reflection coefficients of various porous films obtained by anodic etching of the surface of silicon wafers with orientations (100) and (111). Experimental data indicate a significant decrease in the reflection coefficient in the visible light range from 400 to 1200 nm for all samples with porous layers compared to samples without porous layers. Especially noticeable is the decrease in the degree of reflection for the variational gradient-porous (GPSi-var) structures with a nano-porous outer layer. The magnitude of the reflection coefficient for such structures falls to the level of 0.1% in the range of the investigated frequencies of light radiation. For all porous layers, the tendency of decreasing the degree of reflection is typical as the wavelength of light decreases to less than 10% (compared to the reflection coefficient of the surface of silicon wafer at 30%).

The paper deals with the solar power installations widely used in Moscow and highlights the following power plants on photovoltaic converters: bicycle rental stations, parking systems, traffic lights at pedestrian crossings, street lights, Wi-Fi stations; solar power systems for yard lanterns and lighting in the porches, installed on the roofs of residential buildings. This study was conducted for a group of the bicycle parks and parking lots. The paper presents a method for research, including: 1. Panoramic digital photography from the point of supposed placement of the receiving surface of the photoelectric converter; 2. Analysis of each photograph by imposing on it a horizon line and the diagrams reflecting the trajectory of the Sun's course during the year (analemma); 3. Processing of the resulting complex image and compilation of an illumination matrix; 4. Calculation of the proportion of direct solar radiation which reaches the receiving surface during the year and a fraction of the time during the year when the point (surface) is not shaded; these values allow us to assess the possibilities for the effective use of a solar installation in individual months or for a year as a whole and make a preliminary selection of the optimal site. This method makes it possible to calculate the mean values for the year and ranges of the change in the proportion of direct solar radiation coming to the photoelectric panel, taking into account the shading of the receiving surface. The paper shows that about 10-20% of solar energy is lost due to shading for the year in the case of bicycle parks; more than 70% per year and 90% in the certain months in the case of parking lots. Thus, the study shows that part of the Moscow's solar power plants have been installed extremely unsuccessfully, which demonstrates the need for preliminary assessment of the shading in the residential density conditions.

The paper estimates the seasonal and interannual variability of the wave energy flow for the Barents Sea, where the autonomous power supply of objects on the coast, in the shelf zone and in the open ocean can be most in demand. Numerical calculations of the wind wave parameters were carried out using the wind wave spectral model WaveWatch-III developed at the National Oceanic and Atmospheric Administration (NOAA), and wind data at an altitude of 10 m from NCEP / CFSR reanalysis, which covers the period 1979-2010. The model takes into account the influence of ice, as well as the dissipation of wave energy when approaching the shore, which is of considerable importance in connection with the choice of the object of research (open and coastal areas of the Barents Sea). The calculations were carried out on an original non-structural grid, the spatial resolution of which varies from 15 km in open water areas to 500 m in the coastal zone. The primary results of the simulation are the heights of significant waves and the transfer of wave energy for each node of grid (the time step is 3 hours, the coverage period is 30 years).The results are presented in the form of diagrams of the interannual and intra-annual variability of the wave energy flow, as well as the distribution maps of the flow probability of occurrence. The paper estimates that the flow of wave energy varies in the open part of the sea from 2-5 kW / m in the summer months to 60-100 kW / m in winter; near the coast of the Kola Peninsula, the maximum values of the wave energy flux in the winter months are 20 kW / m; the average multi-year probability of occurrence of wave energy flow (more than 1 kW / m) in the open part of the Barents Sea exceeds 80-90% in all seasons of the year; in the coastal part of the sea, its intra-annual variability is high, in the summer the probability is reduced to 60%.

The paper briefly describes the creation of PJSC “Cryogenmash”, which appearance and development is inextricably linked with the origin of the cryogenic engineering industry in the USSR, as well as the development of cosmonautics and rocket engineering. The paper describes the tasks solved by leading specialists to create infrastructure for providing the cryogenic fuel components, bench systems for testing of engines and missile blocks, thermo-vacuum chambers, thermostating systems of compartments and the high-boiling fuel components. It was noted that the domestic basic cryogenic equipment surpassed the ones of foreign firms in many respects and solved the issue of effective and explosion-proof operation technology at all stages of the construction of launch and stand complexes. The organization of effective and safe cooling processes in the flow of liquid hydrogen and oxygen at refueling of rocket tanks, which were used in the BR “Ehergy” systems, is considered in detail. The advantages of this technology are shown in comparison with cooling in the storage tanks by evacuation of the vapor space. The cold of liquid hydrogen leaving the vacuum system was used in the liquid oxygen deep cooling system of the “Buran” spacecraft. The paper deals with the development of thermostating systems for providing temperature and humidity parameters in the rocket sections, under which the stable and trouble-free operation of devices and mechanisms is guaranteed, as well as the thermostating of high-boiling components of the fuel. The emphasis is placed on the development of systems based on air turboexpander units instead of the vapor compression machines. The authors attach the importance to the creation of a number of space simulators, including one of the largest in the world (with a volume of 10,000 m 3 ). The tasks that have been solved for the successful operation of the equipment are considered: the problems of strength and stability of the camera shell, ensuring tightness, selection of powerful means for safe evacuation and other important aspects of creating space simulators. It is noted that the experience of creating cryogenic equipment for launching complexes is fully used in the creation of new cosmodromes and, above all, the “Vostochny” cosmodrome.

The paper analyzes the functioning and launching of the cryogenic propulsion upper stages and the stages of rocket-space systems, which are largely determined by heat and mass exchange processes in the elements of supply systems. This is due to the fact that in ground conditions, there are no possibilities of flight conditions simulation during cooling of feed lines and starting the engine. Therefore, the simulation of the flow of cryogenic components with respect to heat and mass exchange processes in supply systems of the units and the test stand is important. The paper gives data that booster pump aggregates of oxidant and fuel, as a rule, are located in the corresponding fuel tanks. This makes it possible to significantly reduce the costs of the component for carrying out the operations of cooling and filling fuel lines and the tank, and to optimize the process of starting the engine when it is switched on repeatedly. It is also noted that in complex ground tests of upper stages there are usually no possibilities to simulate flight conditions during launching operations in complex ground tests of upper stages, therefore the use of physical and mathematical models for the calculation of nonstationary multiphase processes with intensive phase transformations makes it possible to determine the characteristics and to forecast the parameters of supply systems. The following tasks have been accomplished: the development of open source code based on CFD program OpenFoam for simulation of cryogenic flows in conjunction with heat exchange processes with the wall of the tank; the verification of open source code on a simple two-dimensional model of the tank for determination the main mechanisms that arise in the process of cooling and filling the stand tank; the implementation of open source code for simulation the initial stage of the refilling of the stand fuel tank taking into account the evaporation of the cryogenic liquid and heat exchange with the walls. The paper shows that the processes of flow and evaporation can be modeled in the framework of models with a free surface flow. The results of calculations of basic parameters of two-phase flows in the process of cooling the liquid hydrogen fuel tank are presented. The results of the study are expected to be used in the methodology for estimating the parameters of two-phase flows during testing of the advanced space rocket systems.

The paper takes into account the fact that today, as a material for the electrolyte of solid oxide fuel cells, the compounds with a perovskite-like structure characterized by oxygen-ion conductivity in the dry air and proton conductivity in the air atmosphere are actively studied. The possibility of proton defects in these compounds is due to the presence of oxygen vacancies. The presence of vacant positions in the oxygen sublattice promotes reversible dissociative absorption of water from the gas phase and the appearance of proton conductivity. An example of a phase characterized by a perovskite structure and having an oxygen deficiency in the anion sublattice is barium-calcium niobate Ba₂CaNbO_5,5 described in the literature as an oxygen-ion and proton conductor. Isovalent and heterovalent doping of cationic sublattices is the one of methods of modification of this type structure and optimization of physicochemical properties of complex oxide materials. However, the development of anionic doping can be an alternative for the obtaining of new materials with improved properties. It was established that the anionic substitution F ⁻→O ²⁻ leads to increase in oxygen and proton conductivities under small fluorine concentration (a mixed anion effect). The present research is an extension of the study of the effect of heterovalent anionic doping on oxygen-ion and proton transport. In this paper, the fluorine-doped complex oxides based on barium-calcium niobate Ba_2-0,5xCaNbO₅,_5-xF_x were obtained, X-ray analysis was performed. The phases were made by the anionic doping of oxygen sublattice of niobate barium-calcium Ba₂CaNbO_5,5  by fluorine ions. The synthesis was carried out by a solidphase method, the maximum annealing temperature was 1300^оС. All the samples (0 < х ≤ 0,4) were single-phase and characterized by the cubic structure of a double perovskite. It has been established that the introduction of ions with a smaller radius (F^- ) leads to a decrease of the lattice parameter of the fluorine-substituted compositions compared with the undoped barium-calcium niobate Ba₂CaNbO_{5,5 .}

 

The paper presents the scheme of mini CHP with methane reformer and planar solid oxide fuel cells (SOFC) stack. The mini CHP produces electricity, superheated steam, hot air and methane for the reformer and it also preheats cathode air used in the SOFC stack as an oxidant. Moreover, the scheme’s mathematical model is constructed. The thermochemical reactor with impeded fluidized bed for autothermal steam reforming of methane (reformer) studied experimentally is the key element in producing synthesis gas – fuel for the SOFC stack. The research indicates that synthesis gas containing 55% of hydrogen can be derived using the reactor. Through mathematical modeling, the entire reactor’s principal dimensions as well as flow rates of air, water and methane were adjusted to the methane reforming for the mini CHP studied. The paper includes the heat balances of the reformer, SOFC stack and waste heat boiler that produces the superheated steam, hot air and methane for the reformer as well as preheated cathode air. These balances were instrumental for calculating the useful product fraction in the reformer, fraction of hydrogen oxidized in the SOFC anode channel, electric gross efficiency, anode temperature, exothermic effect of synthesis gas hydrogen oxidation by air oxygen, excess entropy and Gibbs free energy change at standard conditions, SOFC electromotive force (EMF), specific flow rate of standard fuel for heat, and power generation. The simulation study has shown that the hydrogen oxidation products temperature in the SOFC anode channel is 850ºС, electric gross efficiency 61.0%, single fuel cell EMF 0.985 V, fraction of hydrogen oxidized in the SOFC anode channel 64.6%, specific flow rate of standard fuel for power generation 0.16 kg/(kW·h), for heat generation 44.7 kg/GJ. All the specific parameters are in good agreement with other publications results.

The paper deals with the influence of a dimension factor on the thermal-expansion coefficient (TEC) of hafnium diboride. Nano-sized and microcrystalline hafnium diboride is investigated by method of X-ray diffraction in the temperature range of 300–1500 K. The size of nanocrystal HfB₂ with coherent scattering is 15 nanometers and remained constant during heating. The analysis of temperature dependence of the nano and microcrystalline HfB₂ parameters shows the non-linear growth of the cell metrics with increase in temperature. For the first time, the TEC of nano and microcrystalline HfB2 in the directions of crystallographic axes a and c are defined. The analytical expressions of temperature dependences of nano and microcrystalline HfB₂ of the cell parameters are received in the form of 2 degree polynomials. At the linear approximation of temperature dependence of the lattice parameters (i.e. at lack of temperature dependence of TEC), the TEC of microcrystalline HfB₂ in the studied temperature range are αa = 7.37 · 10^–6 and αс = 7.48 · 10^–6 K ^–1 for axes 0a and 0c respectively. The TEC of microcrystalline HfB₂ calculated according to X-ray diffraction data corresponds to TEC calculated by a dilatometric technique α = 7.49 · 10^–6 K ^–1 . At linear approximation of temperature dependence of the lattice parameters, the TEC of the nanocrystal HfB₂ are αa = 7.40 · 10^–6 and αс = 9.88 · 10^–6 K ^–1 for axes 0a and 0c respectively. The paper shows that the TEC of HfB₂ in nanocrystalline state is greater than the TEC of microcrystalline one. The difference between the TEC of nano and microcrystalline HfB2 are bound with increase in the surface energy of material with increase in dispersion. The paper finds the anisotropy of thermal expansion both micro and nanocrystal HfB₂. The TEC on the axis 0c is higher than the TEC on the axis 0a. The anisotropy of TEC is explained taking into account the lengths and the nature of interconnections in crystalline structure of HfB₂. The essential anisotropy of TEC in nanodimensional HfB₂ indicates the domination of the atomic fluctuations anharmonicity growth in nanocrystals in the direction of the axis 0c. The results obtained can be employed to create new environmentally friendly materials for the needs of alternative power engineering.

 

The composite materials based on secondary polyethylene and agricultural wastes (straw of various types) as filler were developed. The prospects of modifying the surface of the filler with resinous waste from the production of 5- hydroxymethylfurfural (5-HMF) from a vegetable source were shown, which is a versatile platform for obtaining valuable chemical products, including monomers for the production of polymers from renewable raw materials. At present, 5-HMF is produced quite successfully from various plant raw materials (sugar beet, Jerusalem artichoke, laminaria, etc.) However, the production of 5-HMF by acid catalyzed dehydration of polysaccharides is accompanied up to 10% of by-product resinous humic-like substances (hereinafter called the resin) formation. The ways of its utilization have of great practical interest. The presence of oligomeric chains with a large number of polar groups in the resin composition ensures its uniform distribution over the surface of hydrophilic filler particles, forming a polymer film, which significantly reduces the water absorption of the composite. Present research shows that as the content of the resin increases from 0% to 4%, the water absorption of composites containing 15 % of rice or wheat straw decreases by 3-5 times. On the other hand, the hydrophobic fragments of the oligomeric resin chains interact with the polyethylene matrix. As a result, the adhesion between the straw particles and the polyethylene increase, and the strength properties of the resulting composite materials increase too. The optimal ratio of components is 15% wheat straw, the ratio of straw / resin is 8-15%, 0.5-2% modifier. It should be noted that improvements in the properties of composite materials have been achieved by introduction of relatively small amounts of a modifier (0.5-2%). The resulting composites can be used as construction and waterproof materials.

The article discusses an innovative device for converting wave energy of water into electricity. There are two main classes of transducers – active and passive. The first one includes all devices having moving under the action of fluctuations in the water mass elements; the second device guides the movement of the water to concentrate the wave energy. The article considers the device for wave energy conversion referring to the first class, namely, the device using the periodic rise of a wave surface and changing its inclination. After analysis of the existing technical solutions, the author proposed the solution of the problem. For the first time, the method for the generation of electricity through the use of gyroscopic forces that arise during operation of the device is proposed. The technical solution is implemented using the device converts the gyroscopic forces generated between two rotors (gyroscopes) placed coaxially and rotating in opposite directions. The appearance of gyroscopic periodically forces due to the fact that the proposed device is fixed on the platform (the float) which changes periodically its angular position in space while the wave surface of water. In this case, the transformation of gyroscopic (mechanical) forces arising between the gyros rotating in opposite directions is carried out by the mechano-electrical transducers fixed between the supporting platform and housings of these gyros.