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RENEWABLE ENERGY
One of the main factors affecting the photovoltaic (PV) plant power is the self-shading from adjacent rows of solar panels. Due to the peculiarities of the electric connections of photovoltaic cells in PV modules and the presence of bypass diodes, the partial shading is capable of significantly decreasing the PV plant power at certain times of the day. The partial shading of solar panels effects in different ways on the energy production in cases of the vertical placement of PV modules in the panel’s frame (portrait mounting) and the horizontal placement of PV modules (landscape mounting). This work presents a novel analytical approach for determining of the inter-row shading effect on the large PV plant efficiency which is applicable for any seasonal period of PV operation. The initial data for calculations are the hourly generation of shaded and fully illuminated solar panels. On the base of these data, we have calculated the power factor that describes the dependence of the module's electrical power on the shading degree. The power factor is used to determine the amount of radiation entering the panel’s tilted surface during each day of the operation period. The long-term meteorological data for the main radiation components and one of the known anisotropic radiation model are necessary for these calculations. The main calculations result is the distribution maps for the average daily energy output which first proposed in our work. These maps have the form of contour graphs which build in the coordinates “the ground cover ratio – the tilt angle” as construction parameters. Using this maps one can find the optimal ratios of these parameters for two types of optimization problems: (1) ensure the maximum possible output under given installed PV power and (2) the determination of the most rational use of a land plot for PV plant, i.e. the obtaining of maximum PV production per unit of land area. The advantage of the analytical approach is that it allows scaling to large PV systems without increasing the computation time. As examples, the paper performs the optimization calculations based on the monitoring output data for the commercial PV plant located in Germany and on the experimental partial shading data in Odessa region.
The paper presents the experimental research results for the horizontal-axis wind turbine with coaxial wind rotors. It is assumed that such coaxial layout of the wind turbine can be used for designing of the wind energy systems with relatively low capacity and limited location area since the coaxial systems have advantages in overall dimensions and maximum using of the swept area. Possibility of coaxial horizontal-axis wind turbines usage is determined by positive or negative effect of turbines on each other. Literature review shows that closely spaced wind turbines can generally improve flow characteristics under certain conditions and consequently increase wind energy system efficiency. We have carried out the experiments in T-5 wind tunnel with two coaxial model two-bladed wind turbines which rotate in opposite directions. The generator of the first turbine and first turbine itself are located on the same shaft in the test section of wind tunnel. The second generator is in a lower compartment of the experimental setup and is connected by the transmission. We have measured the dynamic, energy and frequency characteristics of wind energy systems based on created experimental setup. A Pitot tube and automatic metering devises have measured the dynamic parameters and energy performance respectively. A frequency counter has saved all of the data obtained with the laser frequency measurement technique. The experiment has some specific technical features so the data received need to be corrected. The coaxial wind turbine power has decreased in comparison to isolated wind turbine at low wind speed. The return flows reinforce turbulence so wind speed falls. If wind speed increases, the impact of the return flows decreases, the coaxial wind turbine capacity significantly grows and exceeds isolated turbine capacity. The possibility of using wind turbines with coaxial wind rotors for autonomous power supply is shown. Such wind turbines are perspective and require more detailed analysis.
Based on the solution of the problem of non-stationary heat transfer during fluid motion in underground permeable layers, dependence was obtained to determine the operating time of the geothermal circulation system in the regime of constant and falling temperatures. It has been established that for a thickness of the layer H <4 m, the influence of heat influxes at = 0.99 and = 0.5 is practically the same, but for a thickness of the layer H> 5 m, the influence of heat inflows depends significantly on temperature. At a thickness of the permeable formation H> 20 m, the heat transfer at = 0.99 has virtually no effect on the thermal processes in the permeable formation, but at = 0.5 the heat influx, depending on the speed of movement, can be from 50 to 90%. Only at H> 50 m, the effect of heat influx significantly decreases and amounts, depending on the filtration rate, from 50 to 10%. The thermal effect of the rock mass with its thickness of more than 10 m, the distance between the discharge circuit and operation, as well as the speed of the coolant have almost no effect on the determination of the operating time of the GCS in constant temperature mode. During operation of the GCS at a dimensionless coolant temperature = 0.5, the velocity of the coolant is significant. With an increase in the speed of the coolant in two times, the error changes by 1.5 times.
The paper deals with the waste disposal problem of the alcohol industry caused by the widespread use of alcohol as biofuels. In the technology for the production of alcohol from cereal crops, a distillery spent wash (DSW) is formed (per 1 dm3 of alcohol – 10–20 dm3 DSW), which refers to highly concentrated wastewater, the COD value reaches 40 g O2/dm3. Since the existing physical and chemical methods of its processing are not cost-effective, the researchers develop the processing technologies for its utilization, for example, an anaerobic digestion. Apart from the purification of highly concentrated wastewater, the advantage of this method is the production of biogas and highquality fertilizer. The problems of biotechnology for biogas production from the distillery spent wash are its high acidity–pH 3.7–5.0 (the optimum pH value for the methanogenesis process is 6.8–7.4) and low nitrogen content, the lack of which inhibits the development of the association of microorganisms. In order to solve these problems, additional raw materials of various origins (chemical compounds, spent anaerobic sludge, waste from livestock farms, etc.) are used. The purpose of this work is to determine the appropriate ratio of the fermentable mixture components: cosubstrate, distillery spent wash and wastewater of the plant for co-fermentation to produce an energy carrier (biogas) and effective wastewater treatment of the distillery. In order to ensure the optimal pH for methanogenesis, poultry manure has been used as a co-substrate. The co-fermentation process of DSW with manure has been carried out at dry matter ratios of 1:1, 1:3, 1:5, 1:7 respectively. It is found that when the concentration of manure in the mixture is insufficient (DSW/manure – 1:1, 1:3), the pH value decreases during fermentation which negatively affects methane formation; when the concentration of manure in the mixture is increased (DSW/manure – 1:5, 1:7), the process is characterized by a high yield of biogas and methane content. The maximum output of biogas with a methane concentration of 70 ± 2% is observed at the ratio of components on a dry matter “wastewater: DSW: manure” – 0,2:1:7 respectively. The COD reduction reaches a 70% when using co-fermentation with the combination of components “wastewater: DSW: manure” (0,3:1:5) respectively.
The work refers to the field of thermochemical processes of the biomass conversion into energy, in particular to the creation of gas-generator stoves operating on biomass for cooking. In view of the high energy efficiency and environmental friendliness gas-burning stoves significantly exceed the traditional direct combustion biomass kilns. The theoretical analysis of the processes of gasification and combustion of fuel flowing in the stove is considered. The stove is considered as a reversed microgasifier with an open top. Gasification is carried out in a vertical microgasifier of a dense layer of fuel with fuel ignition from above and air supply from below. The thermal processes taking place in the microgasifier can be divided into three stages: partial gasification of biofuel, complete gasification of the biochar obtained, direct combustion of the biochar. The pilot samples of a number of stoves with a reactor volume of 5.5 to 9.7 liters were made and pilot tests were carried out for the various types of biofuel (pellets from softwood, trimmed pine saw-timbers, wood chips from hardwood, briquettes from straw, sunflower husks, buckwheat husks). As a result of the tests it was found that the efficiency of the stoves is about 30% which is approximately 3 times more than that of traditional direct combustion furnaces, and the average thermal power of the gas-generator stoves was 0.71–1.78 kW which corresponds to the thermal power of household stoves operating on natural gas. The fuel consumption and the specific burning rate of the fuel are determined by the air supply. For approximate calculations, you can take a fuel consumption of 1 kg / hour. The specific intensity of combustion for the tested fuels varied in the range 27.5–60.6 kg / (m2 · h). The use of the thermal insulation of the hull makes it possible not only to reduce significantly heat losses to the environment but also to avoid burns if the person touches the stove accidentally. The stoves have the following advantages: ecological compatibility; the economy; mobility. Prospective consumers of stoves are the residents of non-gasified areas, summer residents, tourists.
Globalization and sustainable development necessitate joint analysis of technological and environmental trends in energy development taking into account current economic and legal provisions. Based on synthesis of the current state of Ukrainian electric power system in general and hydropower in particular, there have been underscored the importance of comprehensive approach in identifying the key tasks of building the pathway of further electric power industry development. The authors provide the characteristics of today’s organizational and technological structure of the electric power system, including the legal provisions regulating its activity. As currently there are significant legislative changes, particular attention was paid to the review of electricity market. Features of the new liberalized electricity market have been determined in comparison with the current market, and also in connection with renewable energy characteristics. Thus, amendments introduced by the new Law “On electricity market” to the green tariff policy have been detailed with the regard to incentive mechanism for development of renewable energy and liability of electricity producers operating under Green Tariff for imbalances. The article focuses on the analysis of the state and growth potential of small hydropower. Еconomic incentives are systematized according to the current legislation. Also, here is presented the potential for possible growth of small hydropower, namely, quantitative result of the exploration of the technical potential of hydropower resources of small rivers. There have been identified a number of barriers and impediments to the construction of small HPPs. Environmental restrictions to the construction of small hydropower stations have been formulated according to the accurate analysis of various branches of national legislation such as the Land Code, the Water Code, the Law “On the Nature Reserve Fund of Ukraine”, etc., as well as valid ratified documents and other key soft-low instruments at the international level. Additionally, provisions of Сustoms and Tax legislation on small hydropower regarding to incentives for technology development have been defined. Consideration of small hydropower projects successfully implemented on the territory of the country confirms the possibility of the future development of small hydropower.
The article is devoted to the development of an express method for assessing the potential of hydropower resources of the small rivers in Ukraine, taking into account the requirements of the current regulatory framework in the environmental and energy sectors, which provides objective information for the development of small hydropower stations at the current stage of alternative energy development. The article determines the environmental restrictions of small hydropower based on the provisions of the current regulatory and legal framework of Ukraine, the criteria for the ecological value of the territory and the principles of preserving the diversity of wild fauna of rivers. Restrictions on the use of water for the production of small hydropower plants take into account the sanitary discharge, the continuous operation of fishers, low water, floods, operational measures to regulate the water flow through hydroconstructions, the regulation of hydroelectric power through the watercourse which allows practically no distortion of the natural hydrological regime and biological state of river below the station. Restrictions on the use of the territory for the construction of small hydropower stations take into account the presence of national natural parks, reserves, and natural monuments, places of deposits of minerals and mineral waters, historical and cultural heritage, special purpose land. Restrictions on the permissible bias of river sections have been introduced with regard to environmental restrictions. The article substantiates the significance of the technical potential of the hydropower resources of small rivers in Ukraine, taking into account environmental restrictions, at the level of 1270 million kWh/year (about 375 MW of installed capacity of small HPPs), and its distribution over the hydrological zones of the country. It is established that the volume of technically achievable potential of hydropower resources, even for the main deep-water small rivers of Ukraine, is within 3–15% of their natural potential. The results obtained are essential for the development of a modern concept of regional programs for the development of small hydropower and the Energy Strategy, implementation of the activities of the National Action Plan for Renewable Energy in Ukraine.
ENVIRONMENTAL ASPECTS OF ENERGY
The article considers the role and place of water and water vapor in combustion processes with the purpose of reduction the effluents of nitrogen oxides and carbon oxide. We have carried out the complex of theoretical and computational researches on reduction of harmful nitrogen and carbon oxides by gas fuel combustion in dependence on humidity of atmospheric air by two approaches: CFD modeling with attraction of DRM 19 chemical kinetics mechanism of combustion for 19 components along with Bowman’s mechanism used as “postprocessor” to determine the [NO] concentration; different thermodynamic models of predicting the nitrogen oxides NO formation. The numerical simulation of the transport processes for momentum, mass and heat being solved simultaneously in the united equations’ system with the chemical kinetics equations in frame of GRI methane combustion mechanism and NO formation calculated afterwards as “postprocessor” allow calculating the absolute actual [CO] and [NO] concentrations in dependence on combustion operative conditions and on design of furnace facilities. Prediction in frame of thermodynamic equilibrium state for combustion products ensures only evaluation of the relative value of [NO] concentration by wet combustion the gas with humid air regarding that in case of dry air – oxidant. We have developed the methodology and have revealed the results of numerical simulation of impact of the relative humidity of atmospheric air on harmful gases formation. Range of relative air humidity under calculations of atmospheric air under impact on [NO] and [CO] concentrations at the furnace chamber exit makes φ = 0 – 100%. The results of CFD modeling have been verified both by author’s experimental data and due comparing with the trends stated in world literature. We have carried out the complex of the experimental investigations regarding atmospheric air humidification impact on flame structure and environmental characteristics at natural gas combustion with premixed flame formation in open air. The article also proposes the methodology for evaluation of the nitrogen oxides formation in dependence on moisture content of burning mixture. The results of measurements have been used for verification the calculation data. Coincidence of relative change the NO (NOx) yield due humidification the combustion air revealed by means of CFD prediction has confirmed the qualitative and the quantitative correspondence of physical and chemical kinetics mechanisms and the CFD modeling procedures with the processes to be studied. A sharp, more than an order of reduction in NO emissions and simultaneously approximately a two-fold decrease in the CO concentration during combustion of the methane-air mixture under conditions of humidification of the combustion air to a saturation state at a temperature of 325 K.
