The densities and fluxes of concentrated solar radiation in the focal plane of large solar furnaces (LSFs) are studied, taking into account the overall parameters, inaccuracies in the facets of the concentrator and heliostats, and shading and blocking the sun’s rays by the fields of heliostats. It was found that LSFs can work effectively for 8 h a day throughout the year. It is shown that when the irradiance in the focus of the LSF is 0.6 from the limit, the root mean square error (RMS) of angular inaccuracies σ can be about 7 ang. min, and, if they are equal, each flat component (there are eight of them) can have deviations up to ±4.2 ang. min, which if within σ, can be redistributed. The negative constant component of the inaccuracies of the curvature radius (integral inaccuracy) of the facet concentrator has a strong influence on the irradiance in the focus of the LSF, it should not be less than –0.2.

This study reports experimental test results on a solar-pumped laser that utilizes composite YAG/Ce:Nd:YAG/YAG/rod with a diameter of 3 mm. We measured an output power of 8.5 W with optical-to-optical conversion efficiency of 1.43% in multimode operation when the laser was exposed to an incoming solar power of 593 W at an irradiance of 900 W/m2. The YAG/Ce:Nd:YAG/YAG composite laser rod withstood the severe conditions of solar end-pumping for several hours of testing without any negative effects or degradation of laser output over time. To interpret and comprehensively analyze the experimental results, we developed a simulation model based on our experimental setup and conducted calculations with taking into account thermal population of lower laser levels. Simulation calculations show that a small deviation from a straight line in the experimental input–output dependence is a consequence of the weak influence of thermal population of the lower laser levels. To compare with recent achievements with conventional laser rods of comparable sizes and to formulate some useful recommendations when using composite crystals in future studies, we carried out additional numerical experiments taking into account possible optimizations, which do not affect in any way the thermal load on the front part of the laser rod considered in this experiment. The numerical studies demonstrate that solar-to-laser power conversion efficiency of 4.0% is achievable with a 3 mm laser rod when the solar input power is about 600 W. We also discuss the influence of rod size and thermal effects on conversion efficiency. Based on the findings of this study, we conclude that employing laser media composed of a single or multirod system with a composite structure could potentially offer an optimal solution to the thermal challenges inherent in solar-pumped solid-state lasers.

Исследованы дневные тепловые потери и температуры теплоносителя на выходе плоских солнечных коллекторов (СК) с учетом переменности плотности падающего солнечного излучения на СК. Исследования проводили на основе разработанной одномерной трехслойной распределенной нестационарной тепловой модели плоской одноканальной CK с неселективным приемником, учитывающей изменение температур по длине СК. Показано, что основные теплопотери в СК в летнее время – это излучения с прозрачного ограждения (ПО) до 78% и с теплоизоляции днища 15%, конвективные теплопотери составляют около 7%, из них в ПО около 5.5% и 1.5% в изоляции. Эти показатели и температуры теплоносителя на выходе из CK существенно переменны в течение дня, что необходимо учитывать при определении кпд СК. Показано, что улучшение тепловых характеристик CK, в первую очередь, зависит от возможности уменьшения потерь излучением с ПО. Уменьшение тепловых потерь CK за счет увеличения толщины теплоизоляции ограничено из-за малых тепловых эффектов.

The problem of deposition of dust particles with sizes of large wavelengths of the photoactive part of solar radiation on solar batteries (SBs) is considered. Under the assumption that dust particles in the air do not collide and are deposited on the SB in one layer, formulas are obtained to determine the area of shading of the SB by dust particles in time. These dependences also take into account the size of dust particles, their concentration in air, the angle of incidence of sunlight and the angle of inclination of the SB to the horizon. It is shown that the shading area changes in time mainly linearly, but also has a nonlinear daytime component, which depends on the angle of incidence of sunlight on the SB. The influence of the angle of incidence of the rays on the shading is already noticeable at angles of more than 200. The formulas obtained make it possible to estimate the dynamics of shading of the SB by solid particles of dust and to estimate the frequency of its cleaning from dust (at a given power loss). So, even with standard levels of concentration of dust particles with dimensions of 2.5 and 10 microns and an admissible drop in power of the SB by 5%, the frequency of the SBs cleaning is only about 30 days. The results of the study show that when determining the optimal angle of inclination of the SB, it is necessary to take into account the dust factor. The obtained dependences can also be used to assess the dustiness of flat transparent enclosures of solar installations.

The features of the nucleation and further growth of nanotube of fullerene C-60 (C-60 NTs) obtained by evaporation of an isolated drop of a dispersed solution of C-60 in ethylbenzene/isopropyl alcohol located on a smooth surface of a silicon substrate have been investigated. The morphological and dimensional characteristics of the obtained C-60 NTs have been determined.

The behavior of intermolecular interactions in fresh and aged solutions of fullerene C60 in neat N-methyl-2-pyrrolidone (NMP), as well as in NMP/xylene mixed solvents, were studied by the methods of ultraviolet-visible spectroscopy and dynamic light scattering (DLS). It has been experimentally shown that the aging of the C60/NMP solution leads to the disappearance of the characteristic maximum of molecular absorption at ∼330 nm with smoothing, as well as to an increase in the optical absorption intensity. The latter depend on the formation of “C60- NMP”complexes, as well as on the transition of fullerene molecules to the nanocluster state. Increasing the xylene content in the C60/NMP leads to significant changes in charge transfer between solute and solvent (“C60-NMP”, “C60-C60”) at a fixed concentration of fullerene. The latter leads to the reorganization of nanoparticles, which proceeds with the destruction of molecular complexes. In this case, using the DLS method, it was found that the geometric dimensions of the synthesized C60 nanoclusters decrease.

The behavior of self-assembly of C-60 molecules in solutions of C-60/hexane/xylene were studied by the methods of refractometry, ultraviolet-visible spectroscopy and dynamic light scattering (DLS). It was experimentally shown that with a slight increase in either the concentration of fullerene C-60 or the volume fraction of xylene in a C-60/hexane/xylene solution, the refractive index of the medium increases. Increasing the xylene content of the C-60/hexane/xylene system leads to significant changes in charge transfer between solute and solvent, which, in particular, exhibit both a positive solvatochromic effect and a hypochromic effect in a strong absorption band at similar to 328.8 nm. It was established by the DLS method that with an increase in the concentration of C-60 in the C-60/hexane solution from 20 to 30 mg/dm(3), the maximum radius of the synthesized nanoclusters in solutions changed from similar to 6.25 nm to similar to 17.2 nm, and also with an increase in the mole fraction of xylene in the C-60/hexane/xylene system, the cluster size gradually decreases.

A nonstationary numerical procedure and program for determining the heating temperature through flat “transparent screens” (TSs) of solar power plants have been developed. The developed procedure makes possible to consider volume absorption of incident and self-radiation of TSs. The program is verified according to mean equilibrium heating temperatures for the glass under a stationary mode of operation. We obtained that under a TS thickness up to 10 mm, the difference between mean equilibrium temperatures is lower than 0.1%. We reveal that a temperature drop in TSs of solar power plants even for glass with a thickness up to 5 mm and if the receiver is heated up to 60°С is not higher than 0.5–0.7°С. We obtain the same gradients in the numerical models for TSs with surface absorptance and heat spectrum emission, but the difference between absolute temperatures can run up to 6°C. The procedure and the program with volume absorption and emission in TSs can be used in nonstationary heat models for solar collectors and energy efficient windows and under heating 1D semi-transparent bodies by solar or laser radiation.

To study the heat losses of a three-layer underground cylindrical heat accumulator (HA), a method for numerically solving the problem of calculating a non-stationary temperature field in the layers of such a system under a symmetrical boundary, has been developed, implemented in the form of a program. Studies of thermal losses of an underground cylindrical HA are carried out. It has been confirmed that no additional thermal insulation is required for the daily underground HA. Creation of a heat-insulating layer in underground HA allows us to increase the period of heat storage up to 10 days with heat loss less than 30%. It is shown that the use of elementary time steps different in time in the calculation makes it possible to reduce the time for calculating heat losses and temperatures in the HA layers by 30 times, up to 1 min, counting per 2000 h of storage. For known temperatures of heat supply and removal in HA according to the pipe-in-pipe scheme, the method and program can be used to study the thermal efficiency of the underground HA, taking into account heat losses in the process of charging and discharging the HA.

A study was carried out by means of computer simulation of solar-to-laser-power conversion process using Monte-Carlo ray-tracing methods in solar concentrators with spot sizes exceeding the transverse dimensions of commonly used active media by several or more times. It is shown that, in such cases, the use of one active medium for pumping does not allow achieving high conversion efficiency, and in this connection, a new multi-rod system is proposed, which makes it possible to increase the efficiency by several times.

Fused yttrium-alumoborate glasses doped with ytterbium, silicon, chromium, and sodium were synthesized. The influence of the matrix on the "spectroscopic behavior" of chromium ions and the efficiency of their sensitization of Yb3+ luminescence was established by spectral-luminescence and EPR-studies. It was found that (1) chromium in alkali-free glasses is mainly in the oxidation degree Cr(III) with an appreciable admixture of Cr(IV) and Cr(V), (2) the partial replacement of Al2O3 or B2O3 by SiO2 and Y2O3 by Yb2O3 affects to a different extent the relative concentration of optical centers of chromium ions, (3) the addition of alkali results in the formation of Cr(VI) centers as a result of oxidation of less charged chromium ions and predominantly tetracoordinated Cr4+ and Cr5+, (4) Cr3+ ions make the main contribution to the luminescence sensitization of Yb3+ ions, while Cr4+ ions and to a lesser extent Cr5+ play the role of luminescence quencher and internal filter. Sensitization of Yb3+ luminescence through the charge transfer band in Cr(VI) was found. An alkaline glass doped with Cr and Yb upon excitation through the sensitizer produced a luminescence quantum yield of 32% and the conditions for its enhancement were considered. It is shown that the temperature quenching of luminescence of CrYb-containing glasses is significantly lower than that of Cr-containing glasses.

The article discusses the features of heat losses by convection and radiation of flat solar collectors on the basis of a non-stationary thermal model and program. The connection of heat losses with the generalized heat loss coefficient of solar collectors is shown. The article also deals with the problem of determining the distribution of temperatures and heat losses by convection and radiation of a thermal insulation system – accumulating body (water) for a spherical heat accumulator under symmetric boundary conditions. The problem is solved numerically according to the program developed on the basis of the proposed “gap method.” The method and program for the numerical calculation of heat losses and temperatures in time in a spherical two-layer heat accumulator with symmetric boundary conditions, taking into account both incident and intrinsic radiation, have been developed. The program has been developed for a “long” two-layer cylindrical heat accumulator of solar collectors.

We investigated the luminescence intensity of a Nd 3+ :Y3Al 3 O 12 laser crystal excited by the radiation of a blue LED with λ » 454 нм, simulating the ultraviolet part of the solar spectrum, before and after using of a spectral converter based on the Ce 3+ : Y 3 Al 3 O 12 phosphor. It was found that while we used such a phosphor, the luminescence intensity of Nd 3+ : Y 3 Al 3 O 12 at λ » 1064 nm was approximately three times higher than without it. Thus, yttrium-aluminum garnet crystals doped with cerium ions are promising luminophores for the introduction in quanthrons of solar-pumped neodymium lasers for increasing their efficiency.

A new method for approximate numerical calculation of the temperature field and heat losses by convection and radiation (Q) of a two-layer cylindrical heat accumulator (HA) with symmetrical boundary conditions is presented and its software implementation is given. We estimate the accuracy of an approximate solution with a known analytical solution for the case with convective heat losses only and with a constant heat transfer coefficient and we reveal that the error of the approximate method starts to exceed 1% when Fo > 2 or when the HA temperature is already less than a half of the HA initial temperature (90°C). It is shown that under permissible heat loss of 10% for 10 h for a HA with R = 0.2 m, the thermal insulation thickness should be about of 5 cm, and the relative heat loss depends greatly on the HA volume. It is important to investigate the effect of thermal insulation emissivity under a small insulation thickness: if thermal insulation thickness is higher than 2 cm, its influence is only of about 5–6%.

The luminescence intensity of a Nd3+:Y3Al5O12 laser crystal excited by light from a blue LED with λ ≈ 454 nm, simulating the ultraviolet part of the solar spectrum, is studied before and after use of a special converter based on Ce3+:Y3Al5O12 luminophore. It is found that when this type of luminophore was used, the intensity of the luminosity of the Nd3+:Y3Al5O12 at λ ≈ 1064 nm was ~3 times greater than without it. Thus, cerium–ion doped yttrium–aluminum garnet crystals offer promise as luminophores in the heads of solar-pumped neodymium lasers for raising their efficiency.

The study of the process of energy transfer in an active medium with a sensitizer based on Ce: Nd: YAG material under pumping by LED at a wavelength of 454 nm and by solar radiation is carried out. Based on the results of experimental studies of the energy transfer process with blue LED excitation, it was determined that the overall efficiency of energy transfer from Ce ions to active Nd ions in a Ce: Nd: YAG laser rod is similar to 76%. The conducted comparative studies of Nd: YAG and Ce: Nd: YAG luminescence with the excitation by solar radiation has shown 1.5 fold increase of Nd luminescence in Ce:Nd:YAG which means that the threshold power of Ce:Nd:YAG solar lasers can be reduced by 1.5 times. At the same time, the pumping efficiency is increased by the same factor compared to Nd:YAG solar laser. Thus, under the same pumping conditions, the output power of Ce:Nd:YAG solar laser can reach two fold increase compared to Nd:YAG solar laser. Our study confirms that Ce: Nd: YAG is one of the best alternatives to Nd: YAG in solar pumped lasers.

The results of experiments on the self-aggregation of C60 fullerene molecules both inside a two-component solvent (xylene/tetrahydrofuran) and in the volume of an evaporating drop of C60 colloidal solution on a flat substrate surface are presented. The investigations of C60 solutions using dynamic light scattering, transmission electron microscopy and UV–Vis absorption spectroscopy methods revealed the possibility of synthesis of fractal nanoaggregates with a diameter of up to ~135 nm at low concentrations of C60 in the solutions. The final geometric dimensions of C60 nanoaggregates were determined by the initial concentration of fullerene in the solvent medium. Using the scanning electron microscopy method, we have shown that in an open dissipative system – in the volume of an evaporating droplet of the colloidal solution of fullerene C60 sessile on the surface of a flat glass substrate, large quasispherical nanoaggregates with an average diameter of ~380–800 nm are formed. The physical features and regularities that characterize the processes of self-aggregation of fullerene particles in the volume of a drying drop were determined.

There are needed energy (heat) accumulators to increase the efficiency of solar installations, including solar collectors (water heaters, air heaters, dryers). One of the tasks of designing heat accumulators is to ensure its minimal heat loss. The article considers the problem of determining the distribution of temperatures and heat losses by convection and radiation of the heat insulation-accumulating body (water) system for a ball heat accumulator under symmetric boundary conditions. The problem is solved numerically according to the program developed on the basis of the proposed «gap method». (Research purpose) The research purpose is in determining heat losses by convection and radiation of a two-layer ball heat accumulator with symmetric boundary conditions. (Materials and methods) Authors used the Fourier heat equation for spherical bodies. The article presents the determined boundary and initial conditions for bodies and their surfaces. (Results and discussion) The thickness of the insulation and the volume of the heat accumulator affect the dynamics and values of heat loss. The effect of increasing the thickness of the thermal insulation decreases with increasing its thickness, starting with a certain volume of the heat accumulator or with R > 0.3 meters, the heat losses change almost linearly over time. The dynamics of heat loss decreases with increasing shelf life, but the losses remain large. (Conclusions) Authors have developed a method and program for numerical calculation of heat loss and temperature over time in a spherical two-layer heat accumulator with symmetric boundary conditions, taking into account both falling and intrinsic radiation. The proposed method allows to unify the boundary conditions between contacting bodies.

The results of experiments on the self-organization of fullerene C60/70 molecules both inside a xylene solution and in the volume of a drying drop of C60/70 solution on a flat substrate surface are presented. The studies of C60/70 solution using transmission electron microscopy and UV–Vis absorption spectroscopy methods revealed the possibility of synthesis of porous fractal quasispherical clusters with a diameter of 300÷800 nm at concentration of C60/70 in xylene ∼2.6·10 mol·L. It has been shown by scanning electron microscopy method that large nanoclusters and nanostructured coatings based on them are formed in the volume of an evaporating droplet of a colloidal solution of fullerene C60/70 sessile on the surface of a flat glass substrate.