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For evaluating the heat transfer correlations from literature in designing helical coil evaporators for low-temperature organic Rankine cycles (ORC), an inverse evaporator design methodology is used. This is done by taking four already performed measurements with different working fluid mass flow rates (0.21–0.23 kg/s) and saturation pressures (1.93–3.05 MPa, reduced pressures of 0.51–0.82) at the helical coil evaporator (66 m long) in an already operational experimental solar/thermal ORC system as real-case references for the evaporator inverse design's boundary conditions. R-404A is considered as the working fluid. The heating water inlet temperature is changed between 353 K and 373 K. The total length is inversely calculated via 15 helical coil two-phase heat transfer correlations for each case. Their end designs are compared with the actual length. Results show that the correlations can be used interchangeably for designing helical coil evaporators for low-temperature ORCs since the heat transfer resistance is dominant on the shell-side. For evaluating the sensitivity of these results, a secondary analysis was made by means of changing the shell-side correlation's accuracy from its initial value of 10% to more accurate 7%. Predictions with several correlations design shorter heat exchangers at reduced pressures less than 0.7. [ABSTRACT FROM AUTHOR]

A major drawback of Reverse Osmosis (RO) desalination units is their poor performance at off-design conditions. On the other hand, they can operate with low specific energy consumption and produce high-quality fresh water when they are supplied with almost constant power, according to their design and nominal operating conditions. This aspect brings additional effort when there is the need to desalinate seawater or even brackish water using unsteady power sources, such as renewable energy systems powered by, for example, solar or wind energy. In order to overcome this issue, an alternative small-scale RO unit is investigated here, whose major advantage is that it can operate with almost constant specific energy consumption and produce high-quality fresh water with low Total Dissolved Solids (TDS) for a wide range of power input. Such unit is suitable to be combined with small-scale energy systems, which can have a very high variety on their power output, such as PV, wind turbines, or even solar Organic Rankine Cycle, for power production. The developed RO unit includes three identical sub-units, each placed on its own skid and with a fresh water capacity of 0.7 m3/h. An energy recovery unit of axial piston motor type is equipped at each sub-unit for decreasing its power consumption. These sub-units are switched on/off, according to the power availability, in order to operate them within a range, thus with high efficiency and acceptable fresh water quality. Such small-scale RO unit, capable of producing 2.1 m3/h of fresh water in total, is examined here, focusing on its operation, performance, and fresh water production. The main parameter adjusted is the power availability, ranging from almost zero up to the maximum value of 12 kW. The analysis first focuses on a single sub-unit, exploring its performance for variable power input, while afterwards all three sub-units are synthesized, in order to form the complete RO unit, concluding to the dependence of the fresh water production and specific energy consumption from the power supply. For the single RO sub-unit at low power input, the TDS level is very high, whereas the specific energy consumption is low, since the membrane pressure is much lower than the designed one and slightly above the osmotic pressure. For available power, more than around 1 kW, the TDS level holds acceptable values lower than 400–500 mg/l, which is achieved with the high pressurizing of the feed seawater, with specific energy consumption up to 4–5 kWh/m3. For power input higher than 3 kW, the second and third sub-units are successively switched on. In this case, the specific energy consumption is almost constant and equal to 4.5 kWh/m3, including the required power of the feed pump, while the produced fresh water TDS has small variations and is approximately equal to 200–250 mg/l. [ABSTRACT FROM AUTHOR]

Photovoltaics are methods used to generate electricity by using solar cells, which convert natural energy from the sun. This generation makes use of unlimited natural energy. However, this generation is irregular because they depend on weather occurrences. For this reason, there is a need to improve their economic efficiency through accurate predictions and reducing their uncertainty. Most researches were conducted to predict photovoltaic generation with various machine learning and deep learning methods that have complicated structures and over-fitted performances. As improving the performance, this paper explores the probabilistic approach to improve the prediction of the photovoltaic rate of power output per hour. This research conducted a variable correlation analysis with output values and a specific EM algorithm (expectation and maximization) made from 6054 observations. A comparison was made between the performance of the EM algorithm with five different machine learning algorithms. The EM algorithm exhibited the best performance compared to other algorithms with an average of 0.75 accuracies. Notably, there is the benefit of performance, stability, the goodness of fit, lightness, and avoiding overfitting issues using the EM algorithm. According to the results, the EM algorithm improves photovoltaic power output prediction with simple weather forecasting services. [ABSTRACT FROM AUTHOR]

A power system can be defined as flexible if it can within economic and technological boundaries respond quickly and adequately to variations in supply and demand. The ongoing penetration of variable and intermittent renewable energy sources (RES) like wind and solar imposes additional and more critical requirement on power system flexibility. In this paper we propose a method to quantify these requirements based on the comparison of seven demand side parameters describing the statistical properties of the net load and the residual load of the referred power system. Each one of these parameters reflects a separate requirement on the available conventional generation in hourly and daily time scales—ramp up and ramp-down capabilities, technological minimum of generation, daily variation of generation. The proposed approach can be used to predict the requirements for generation flexibility according to the expected scenario of RES penetration in the future development of energy power system. It has been applied and integrated from the Bulgarian Transmission System Operator (TSO) which name is the Bulgarian Electricity System Operator (ESO). [ABSTRACT FROM AUTHOR]

The purpose of this paper is to examine several real house cases as renewable energy resources are installed. It is an empirical study, based on first principles applied to measured data. In the first case presented, a PV solar system has been installed and a hybrid vehicle purchased. Battery storage is being considered. Smart Meter data (provided in Victoria, Australia) measures the electrical energy flowing to and from the grid in each half hour. Missing is the story about what the house is generating and what its energy requirements are through each half hour interval. We apply actual (on site) solar PV data to this study, resolving the unknown energy flows. Analysing energy flow has revealed that there are five fundamental quantities which determine performance, namely energy load, energy import, energy harvesting, energy export and energy storage. As a function of PV size these quantities depend on four parameters, easily derivable from the Smart Meter data, namely the house load, the night-time house load (no PV generation), the rating of the solar PV system and the tariffs charged. This reveals most of the information for providing advice on PV array size and whether to install a battery. An important discovery is that a battery, no matter what size, needs a PV system large enough to charge it during the winter months. The analysis is extended to two more houses located within 5 km for which detailed solar data is unavailable. [ABSTRACT FROM AUTHOR]

Photovoltaic water pumping systems (PVWPS) are a promising solution to improve domestic water access in low-income rural areas. It is challenging, however, to make them more affordable for the local communities. We develop here a comparative methodology to assess relevant features of both widely employed PVWPS architecture with water tank storage, and hardly used PVWPS architecture with a battery bank instead of tank storage. The quantitative comparison is carried out through techno-economic optimization, with the goal of minimizing the life cycle cost of PVWPS with constraints on the satisfaction of the water demand of local inhabitants and on the groundwater resource sustainability. It is aimed to support decision-makers in selecting most appropriate storage for domestic water supply projects. We applied the methodology in the rural village of Gogma, Burkina Faso. Results indicate that the life-cycle cost of an optimized PVWPS with batteries is $24.1k while it is $31.1k if a tank is used instead. Moreover, reduced impact on groundwater resources and greater modularity to adapt to evolving water demand is noted if using batteries. However, as batteries must be replaced regularly and recycled adequately, PVWPS' financial accessibility could increase only if sustainable and efficient operation, maintenance, and recycling facilities for batteries were present or developed locally. [ABSTRACT FROM AUTHOR]

A twisted-fin array as an innovative structure for intensifying the charging response of a phase-change material (PCM) within a shell-and-tube storage system is introduced in this work. A three-dimensional model describing the thermal management with charging phase change process in PCM was developed and numerically analyzed by the enthalpy-porosity method using commercial CFD software. Efficacy of the proposed structure of fins for performing better heat communication between the active heating surface and the adjacent layers of PCM was verified via comparing with conventional longitudinal fins within the same design limitations of fin material and volume usage. Optimization of the fin geometric parameters including the pitch, number, thickness, and the height of the twisted fins for superior performance of the proposed fin structure, was also introduced via the Taguchi method. The results show that a faster charging rate, higher storage rate, and better uniformity in temperature distribution could be achieved in the PCMs with Twisted fins. Based on the design of twisted fins, it was found that the energy charging time could be reduced by up to 42%, and the energy storage rate could be enhanced up to 63% compared to the reference case of straight longitudinal fins within the same PCM mass limitations. [ABSTRACT FROM AUTHOR]

Using numerical methods, studies have been carried out to determine the effect of the introduction of the technology of two-stage combustion of high-ash Karaganda coal on the main characteristics of heat and mass transfer processes in the furnace of the BKZ-75 boiler at Shakhtinskaya TPP (Kazakhstan). Various regimes of supplying additional air into the combustion space, the volume of which varied from 0% (traditional basic version) to 30% of the total volume of air required for fuel combustion, have been investigated using 3D computer modeling methods. The performed computational experiments made it possible to obtain the distributions of the total velocity vector, temperature fields, concentration fields of carbon monoxide CO and nitrogen dioxide NO2 over the entire volume of the furnace and at the outlet from it. The introduction of the two-stage combustion technology made it possible to optimize the combustion of high-ash coal, since in this case there is an increase in the temperature in the torch core and a decrease in it at the outlet from the furnace, which has a significant effect on the chemical processes of the formation of combustion products. Based on the results obtained, it can be concluded that an increase in the percentage of air supplied through additional injectors to 18% leads to a decrease in the concentrations of carbon monoxide CO by about 36%, and nitrogen dioxide NO2 by 25% compared to the base case. A further increase in the volume of additional air leads to a deterioration in these indicators. The results obtained will make it possible to optimize the combustion of low-grade fuel in the furnace of the BKZ-75 boiler, increase the efficiency of fuel burnout, reduce harmful emissions into the atmosphere, and introduce a two-stage combustion technology at other coal-fired TPPs. [ABSTRACT FROM AUTHOR]

Because of the unpredictable activity of solar energy sources, photovoltaic (PV) maximum power point tracking (MPPT) is essential to guarantee the continuous operation of electrical energy generation at optimal power levels. Several works have extensively examined the generation of the maximum power from the PV systems under normal and shading conditions. The fuzzy logic control (FLC) method is one of the effective MPPT techniques, but it needs to be adapted to work in partial shading conditions. The current paper presents the FLC-based on dynamic safety margin (DSM) as an MPPT technique for a PV system to overcome the limitations of FLC in shading conditions. The DSM is a performance index that measures the system state deviation from the normal situation. As a performance index, DSM is used to adapt the FLC controller output to rapidly reach the global maxima of the PV system. The ability of the proposed algorithm and its performance are evaluated using simulation and practical implementation results for single phase grid-connected PV system under normal and partial shading operating conditions. [ABSTRACT FROM AUTHOR]

In this article, we describe the case of a 49-year-old male gypsy on hemodialysis that was referred to our center due to high fever, breathlessness, and productive cough with bloody sputum. Forty-five days before hospitalization, he was treated for vasculitis with prednisolone and intravenous cyclophosphamide. Soon after admission he was resuscitated and intubated after a cardiac arrest. A large worm load of Strongyloides stercoralis larvae was identified in the sputum. The patient was treated with thiopental 25 mg/kgBW/12 h through a Levine tube and died 24 h later. [ABSTRACT FROM AUTHOR]