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In this study, various multi-channel absorbers with different cross-sections and identical internal surface areas were studied, and a numerical model was used for this purpose. The numerical thermal model extracted from previous studies, covers all the heat transfer mechanisms including convection, radiation, and conduction. In order to solve the numerical equations, the Newton-Raphson algorithm was used. The analysis of the absorbed heat flux inside the channel was carried out by the available ray-tracing method in the commercial CFD softwares. In addition, the thermal performance of the absorbers including efficiency and effectiveness, the impact of air mass flow rate on the temperature profile, the thermal effectiveness, and the efficiency of the channels were evaluated. The main effective parameters for evaluation consist the POM (average heat flux and input mass flow rate), the total (air and wall) cross-section area, the internal hydraulic diameter, and the specific surface area of the channels. For the channel, the effect of increasing or decreasing of POM was investigated on the air and wall temperature distribution, efficiency and effectiveness. [ABSTRACT FROM AUTHOR]

In calculating the total solar energy input into a salt gradient solar pond, the current method is insufficient mainly caused by two problems. Firstly, the existing equations of solar pond energy analysis can be only used for momentary calculations but it is very time-consuming for long time periods. Secondly, the shading effect inside the pond affects significantly the energy storage performance of the pond, especially in small ones. To solve the first problem, the mean values of variable parameters during the concerned time period is proposed in this work and the ‘first mean value theorem for definite integrals’ is used to derive the average values. For the second problem, a rectangular pond with vertical walls is investigated as an example, and the exact sunny areas in different depths of the pond are calculated at different time conditions. The experimental data of a published study is used for the validation. The energy efficiency of the low convective zone of the experimental pond is calculated theoretically, which shows a good agreement with the experimental value. The experimental data and theoretical results for the energy efficiency are 9.68% and 11.38% for January, 17.54% and 18.92% for May, and 28.11% and 30.94% for August, respectively. The modified equations can be used to predict a pond performance before its construction. [ABSTRACT FROM AUTHOR]

Simultaneous production of electricity, heat, and water is a global challenge for rural residential areas. In the present study, techno-economic optimization of a system including PV, wind turbine, generator, battery, and CHP system alongside brackish water reverse osmosis desalination system is investigated. The proposed polygeneration hybrid system provides the required loads of a village and health clinic in a rural area with a warm climate. This study aims to find the optimum energy cost of essential rural needs, including required electricity, heat, and water demands to improve remote areas' life quality. While previous studies often considered only one or two of these needs. Several sensitivity analyses based on the different economic and climate conditions are carried out. The grid breakeven distance, environmental aspects, and the developed hybrid energy system's technical performance are analyzed. The results demonstrate that the optimum system, including PV/WT/DG/CHP/Bat and reverse osmosis desalination unit has COE and NPC equal to 0.236 $/kWh and 428,246 $, respectively. Also, the CHP unit decreased the annual fuel consumption by about 224 m3/yr. Furthermore, the proposed hybrid system has a 58.4% lower CO 2 emission than conventional natural gas-fired plants and less than 27 km of grid breakeven distance. • A polygeneration hybrid system for supplying electricity, heat and water is proposed. • Diesel based CHP and BWRO desalination units are applied in the hybrid system. • The optimum system has 0.236 $/kWh energy cost and 45.4% renewable fraction. • The CHP unit effectively reduces fuel dependency by supplying 33% of thermal demand. • Annual CO 2 emission decreases up to 66.2% compared to the conventional power plants. [ABSTRACT FROM AUTHOR]

A novel integrated structure is introduced in order to produce power and heat through biomass fuel simultaneously. This cycle has different sections including the gasification process, solid oxide fuel cell, gas turbine cycle, Rankine cycle, ORC, and hot air and water line. The heat required for the gasifier agent and the air is supplied through heat recovery in this system. In this article, wood chips are employed to supply the required fuel for a solid oxide fuel cell by gasification process. Also, the heat of the SOFC outlet stream is employed for heating the inlet streams of the Rankine cycle, gas turbine, and ORC. Both energetic and exergetic analyses are considered in order to evaluate the performance of the proposed cycle. A sensitivity analysis is performed for observing the effects of the operational parameters on the output power and overall efficiency of the system. The results illustrate that the output power of the cycle is 152.8 MW, and the electrical and overall efficiencies are 51.43% and 81.13%, respectively. Also, the highest portion of exergy destruction is allocated to the fuel cell, which is about 65 MW. [ABSTRACT FROM AUTHOR]

From a worldwide perspective, increasing grid reliability by applying renewable energies is one of the most affordable and environmentally-friendly options available for governments. In this study, the possible numbers of future rural power outages in Iran were predicted using machine learning methods based on nine different prediction models such as PLS Regression, Basian Ridge, and LARS Lasso. Then, the predicted blackouts were imported into the grid tool of HOMER software to analyze a common grid-connected HRES that includes PV, biodiesel generator, and battery bank under three power outage scenarios, including peak-time outages, planned outages, and random outages. The analyzed results until 2040 showed that using renewable sources to electrify possible annual blackouts under a day-hours planned power outage scheme can be an affordable solution with energy costs ranging from 0.066 to 0.070 $/kWh. With less than a 5% increase over the national energy tariff, more than 15% of the supplied electricity was renewable and without any blackouts. Furthermore, the sensitivity analysis showed that the government must keep the power outage's mean repair time to less than 2 h to ensure the effective use of renewables and solve the increasing rural blackouts problem in the hot months of the year. • Nine linear regression machine learning methods are evaluated for outage prediction. • The summer possible outages by 2040 are estimated to be > 90 h per year in Iran. • Day-hours planned outage scenario showed proper compatibility with the hybrid system. • Optimized system has a 0.06 $/kWh energy cost and more than a 15% renewable fraction. • The CO 2 emissions are decreased by an average of 16–28% compared to the pure grid. [ABSTRACT FROM AUTHOR]

In this research, an integrated system of large-scale hydrogen production and liquefaction has been introduced. Conceptual configurations for the hydrogen liquefaction cycle are designed, modeled, simulated, optimized, and analyzed for energy, and the most appropriate ones are selected for use in system. A combination of several units is provided together to produce and then liquefy hydrogen utilizing solar energy. The designed system uses linear Fresnel collectors in combination with a solid oxide electrolyzer set, thermoelectric generator, and Rankine cycle to form the hydrogen production section. The proposed system has a production capacity of 6400 kg of liquid hydrogen each hour. The specific energy consumption and coefficient of performance of the proposed refrigeration cycle were calculated for mass flows rates of 1 kg/s, 1.5 kg/s, and 1.77 kg/s. These values at best were 5.72 K w h / K g L H 2 and 0.1804, respectively. Declared values are significantly better than the corresponding values of similar and reference liquefaction cycles. The energy efficiencies of the electrolyzer, LFR, Rankine cycle, and thermoelectric generator were calculated as 71.18%, 21.42%, 46.64%, and 12.4% respectively. Also, the effect of operational parameters of each subsystem, including temperature and pressure of the input current to the electrolyzer and the total area of the solar reflector on the overall proficiency of the system was researched and the results are presented. The energy efficiency of the hydrogen production sector was 15.98% and the system's total solar fraction was 0.86. [Display omitted] • Process for the production and liquefaction of hydrogen using a solar energy is introduced. • The Rankine cycle and thermoelectric generator are used to generate power. • The system is capable of producing 6400 kg of liquid hydrogen per hour. • The energy efficiency of the hydrogen production section is 16.64%. • The specific energy consumed in the hydrogen liquefaction cycle is 5.72 kWh/kgLH2. [ABSTRACT FROM AUTHOR]

Many studies, as numerical and experimental, regarding the applications of solar dish concentrators have been performed. Most researchers focused on the maximum thermal efficiency, the minimum heat loss, and their relations to the solar receiver geometries. This paper presents and discusses the previous studies investigating different cavity receiver geometries and their optimization methods with parabolic dish collectors. More specifically, cylindrical, hemispherical, conical, and flat sides cavity receivers are investigated in this manuscript. For an inlet operating temperature of 200 °C, the conical cavity shape has shown a thermal efficiency of around 70%, exergy efficiency of 30%, and optical efficiency of around 87%. The working fluid temperature is often around 650 °C–750 °C in the solar dish collectors. Due to high working temperature and cavity shape, heat losses such as radiation, conduction, and convection losses are highlighted that could provide adverse effects upon the system thermal efficiency. Besides, the diameter aspect ratio, the cavity inclination angle, type of tube, and the tube shape can be impressive on the cavity heat losses value. Therefore, the optimized geometry of the cavity receiver is a vital subject. Based on the analyzed issues, some suggestions and concluding remarks are presented. • Cylindrical, hemispherical, flat side and conical cavity geometries were studied. • Focus is on performance assessment for different geometries of cavity receivers.. • The advantages and disadvantages of different geometries are mentioned. • Specific designs and innovative cavity receivers are discussed separately. • Diameter aspect ratio, inclination angle and tube shape affect the cavity heat loss. [ABSTRACT FROM AUTHOR]

High technology energy systems have generated a lot of interest due to their significant contribution to efficient and environmentally friendly energy production. Among them there are hybrid cycles which usually have higher energy efficiencies and can provide different forms of energy at the same time. The present research poses a question concerning thermodynamic performance of a molten carbonate fuel cell (MCFC)-Braysson heat engine, conducting a multi-objective optimization study, to give a general description of this hybrid cycle. For this purpose, energy efficiency, power density and exergy destruction rate density are considered as the objective functions in conjunction with ecological function density. First, a parametric evaluation is conducted in order to study the effect of the decision variables on the targets separately. These variables include current density of the fuel cell, turbine inlet temperature, effectiveness of the hot side of the heat exchanger which recovers the waste heat of the fuel cell to run the Braysson cycle, and ratio of heat capacity to heat conductance of the cold side of the heat exchanger which rejects the extra low-temperature heat of the Braysson cycle to the environment. Afterwards, due to the great conflict between the objective functions, three case scenarios of triple multi-objective optimization are defined, considering different combinations of the objective functions; and a Pareto front is obtained for each. Multi-objective evolutionary algorithm joined with non-dominated sorting genetic algorithm approach is employed to this aim. In order to ascertain final solutions between Pareto fronts, three fast and robust decision making methods are employed including LINMAP, TOPSIS and Fuzzy. Finally, the relationship between the objective functions is studied. Examining the outcomes of each decision making method in each case scenario raises some interesting points in addition to the fact that any potential improvement in one objective function is always confined to a certain amount of sacrifice in the other ones. The present research clearly demonstrates to what extent these compromises have to be made in each case scenario, based on the results of each decision making method. Furthermore, a sensitivity analysis of the final optimal solutions is carried out to critically examine these parameters in the design process of the MCFC-Braysson hybrid cycle. [ABSTRACT FROM AUTHOR]

The motivation behind this work is to explore a nanoscale irreversible Stirling refrigerator with respect to size impacts and shows two novel thermo-ecological criteria. Two distinct strategies were suggested in the optimization process and the consequences of every strategy were examined independently. In the primary strategy, with the purpose of maximizing the energetic sustainability index and modified the ecological coefficient of performance (MECOP) and minimizing the dimensionless Ecological function, a multi-objective optimization algorithm (MOEA) was used. In the second strategy, with the purpose of maximizing the ECOP and MECOP and minimizing the dimensionless Ecological function, a MOEA was used. To conclude the final solution from each strategy, three proficient decision makers were utilized. Additionally, to quantify the deviation of the results gained from each decision makers, two different statistical error indexes were employed. Finally, based on the comparison between the results achieved from proposed scenarios reveals that by maximizing the MECOP the maximum values of ESI , ECOP, and a minimum of ecf are achieved. [ABSTRACT FROM AUTHOR]

Due to fossil fuel depletion and global warming, biomass plays a significant role in supplying the required energy in the industrial and residential sectors. In order to develop clean and efficient conversion technology, an innovative combined cooling, heating and power (CCHP) system based on biomass is introduced in this paper. The proposed system comprises a gasification process, solid oxide fuel cell, gas turbine cycle, Rankine and organic Rankine cycles, absorption chiller, and multi-effect desalination unit simulated in ASPEN. In this system, a new configuration is proposed in order to regenerate the waste heat efficiently at every level of temperature and increase energy and exergy efficiencies. Also, thermodynamics, economic, and sensitivity analyses are performed in order to investigate the energy and exergy efficiencies, the overall cost of the system, and effective parameters. The novel optimization approach (RSM-GA-TOPSIS) is introduced by combining the response surface methodology, genetic algorithm, and Shannon entropy and TOPSIS in order to model and optimize the objective functions in DESIGN EXPERT and MATLAB software, respectively. The objectives of the optimization are maximizing energy and exergy efficiencies and minimizing the overall cost of the system. As a result, based on the initial conditions, the electricity production, overall energy and exergy efficiencies, overall cost of the system, and overall exergy destruction can be acquired at 25.235 MW, 76.69%, 57.07%, 6.1063 × 106 $, and 26.03 MW, respectively. After performing the optimization method, the optimum solution (point 3) is obtained through the TOPSIS approach. In terms of thermodynamics analysis, the electricity production, energy and exergy efficiencies are acquired at 31 MW, 88.15%, and 67.30%, which are increased by 22.85%, 14.94%, and 17.93%, respectively, compared with the initial conditions of the proposed system. In terms of economic analysis of the optimum solution, the annualized total cost, COE, and COTP can be obtained at 6.594 × 106 $, 7.3857 $/GJ, and 6.7624 $/GJ, respectively. By comparing this point to the initial conditions, although the annualized total cost at this point is increased by 7.99%, the COE and COTP are decreased by 12.1% and 10.4% due to a further increase in electricity production. Therefore, for producing energy with high efficiency and low COE, the system should be operated according to the working conditions of this point (point 3). • The integration of biomass gasification, SOFC, gas turbine, Rankine cycle, ORC, absorption chiller, and MED is introduced. • This system is designed to produce electricity, heating and cooling power, as well as desalinated water. • Novel configuration and optimization method (RSM-GA-TOPSIS) are performed to optimize the system's efficiency and cost. • The energy and exergy efficiencies and the annualized cost of the system are 0.76, 0.57, and 6.10 × 106 $, respectively. • Dou to the optimization, the overall energy and exergy efficiencies are improved by 14.94% and 17.93%, respectively. [ABSTRACT FROM AUTHOR]

In the present work, a solar direct absorption parabolic trough collector is prepared for studying the efficiency enhancement methods. The trough collector was manufactured with a width of 0.7 m and the height of 2 m steel mirror reflector. The main issue in this collector is its absorber tube which is made of borosilicate glass. The glass-glass tube has high transmissivity for longwave radiation and increasing the performance of the collector. The outlet temperature and the thermal efficiency were compared by using of various nanofluids. ASHRAE Standard 93-2010 was used for the operating conditions. The volume fractions of 0.1%, 0.2%, and 0.3% MWCNT/ethylene glycol (EG) and nanosilica/EG were used as various working fluids. The results showed that the temperature difference for 0.1% nanosilica/EG was 2.2 K, for 0.2% nanosilica/EG was 5.3 K, and 7.7 K was obtained for 0.3% nanosilica/EG. while this parameter for 0.1% and 0.2% MWCNT/EG were 5.8 K and 9.3 K. Also, the outlet temperature for 0.3% MWCNT/EG was 15.7 K more than the base fluid. The thermal efficiency of 0.3% carbon nanotube/EG has the highest value, and it is averagely 17% higher than the base fluid. In addition, the optical efficiency of this collector is 71.4%, and the time constant is 8.31 min. [ABSTRACT FROM AUTHOR]

It is expected that fossil fuels will be replaced by renewable energy sources to reduce environmental pollution. Multigenerational integrated plants which generate various useful outputs from the same input are required to utilize these sources more efficiently. An innovative multigeneration system based on biomass for useful outputs including district cooling and heating, bioethanol, biogas, and electricity is proposed in this study. The system includes a biomass combustion unit, Rankine cycle, biofuel production unit, and absorption cooling cycle. 15 types of biomass sources are considered for the combined system and a thermodynamic and environmental analyses are carried out to assess the effects of biomass sources on the multigeneration system. According to the modeling results, using cotton stem leads to the highest CO 2 emission (195.3 kg/MWh) while switchgrass produces the lowest (147.0 kg/MWh). The thermodynamic analysis reveals that, for all considered cases, the burner has the maximum exergy destruction rate among all the stages. Moreover, the exergy and energy efficiencies of the plant for different fuels were assessed, and show that the use of rice straw and rice husk exhibit the highest (68.30%) and lowest (62.72%) overall energy efficiencies, respectively. It is also observed that the system using rice straw and larch wood has the highest (45.29%) and lowest (42.86%) overall exergy efficiencies, respectively. The effects of significant input factors are examined on the system performance and emission indicants. • A new multigeneration system fed by various biomass sources was investigated. • Exergy, energy and environmental performances were analyzed for 15 biomass types. • The system fed by rice straw exhibited the highest energy efficiency. • The system fed by rice straw had the highest exergy efficiency. • The system fed by switchgrass had the lowest CO 2 emission. [ABSTRACT FROM AUTHOR]

• Proposing an integrated system of SOFC-GT-ST-ORC for power plant. • Analyzing internal reforming SOFC with anode recirculation. • Using Stirling engine instead of fuel compressor and suppression valve. • Increasing efficiency by generating power while increasing fuel (LNG) temperature. • Eliminating water pump and auxiliary steam generator for SOFC's reforming process. This study presents systematic analysis and optimization of an integrated system consisting of internal reforming solid oxide fuel cell (SOFC) and gas turbine (GT) as a topping system that feeds the waste heat to a bottoming system consists of a steam cycle (ST) and organic Rankine cycle (ORC) with HFE7000 as working fluid. The study includes energy, exergy, exergo-economic, and environmental analysis. We investigate the possibility of adding SOFC to the existing GT-ST combined powerplant and evaluates the improvement in exergy efficiency and levelized cost of electricity. Also, we propose a novel setup to eliminate the necessity of the water pump and auxiliary steam generator for SOFC's fuel reforming process. The system uses the Stirling engine to heat supplied liquid natural gas (LNG) fuel to a usable temperature condition; Using the Stirling engine increases the system's overall efficiency by eliminating the need for the fuel compressor and suppression valve. A mathematical model of the system is developed to evaluate system conditions in Engineering Equation Solver (EES) program and a multi-objective Non-dominated Sorting Genetic Algorithm (NSGA-II) is used in MATLAB to promote the best operating condition in which minimal levelized cost of electricity is achieved while maximizing exergy efficiency is considered. The results show that energetic and exergetic efficiencies reach the value of 72.66% and 69.23%, respectively. The cost of electricity is calculated as 14.46 [cent kWh-1], of which 1.33 [cent kWh-1] is related to environmental taxes due to air pollution and greenhouse gas emissions. This study can be used as a road map to how existing gas-steam hybrid cycle powerplants can be improved by adding additional equipment without the need to replace currently installed equipment. [ABSTRACT FROM AUTHOR]

• A combination of photovoltaic/wind turbine/fuel generators/battery is optimized. • Cycle charging dispatch strategy is more cost-effective, due to less salvage effect. • Salvage effect on short and long-term projects varies from 3% to 30% of the total costs. • Regarding 0.130 $/kWh to 0.167 $/kWh cost of energy, hybrid system can be applicable. • Even in short-term projects, about 12.5% to 21.4% of renewable fraction is achieved. Natural disasters are considered as severe humankind's challenges, which would make a large number of people homeless. Hence, it is vital to provide people with temporary shelters, energy, and freshwater. The purpose of this article is to find the most reliable and economical way to supply energy and water for the residential and health care containers in the different climatic conditions of Iran. Accordingly, a stand-alone hybrid energy system, including solar panels, small wind turbines, fuel generators, and battery banks is taken into consideration. The main objective of this research is to estimate the impact of various parameters such as the project lifetime, dispatch strategies for hybrid system control, and salvage on the optimum system. In addition, a sensitivity analysis regarding the economic and climatic parameters is performed to generalize the results for other areas. The results show that the cycle charging strategy is an appropriate controlling method for a hybrid system, especially for the short-term projects, in which the salvage value causes a high economic uncertainty. In addition, the study indicates that, due to the uniform power generation profile and the affordable cost of energy ranging from 0.130 $/kWh to 0.167 $/kWh, the hybrid system could be practically attainable. For the long-term project, the optimal renewable fraction is between 31.9% and 55.2%; while, for the short-term project, this value is between 12.5% and 21.4%. In the optimum dispatch strategy, for the project lifetime between 4 and 20 years, the impact of salvage on the final cost of the system would vary from 30% to 3%. These results highlight the importance of the salvage parameter in the economic viability of renewable systems. [ABSTRACT FROM AUTHOR]

Off-grid solar/diesel systems have been widely utilized in remote and rural settings. Some of the main challenges for solar-diesel energies are determining the appropriate capacity and location in rural areas. Therefore, an efficient framework is needed for using off-grid solar/diesel systems. For the optimal sizing and location of off-grid photovoltaic (PV)-diesel schemes in rural areas, a new framework is proposed. In this framework, a geographic information system module is utilized to identify the best location based on technical, economic, reliability, social, and environmental criteria. Then, a hybrid optimization algorithm is utilized to determine the appropriate capacity for continuously meeting of the load via total life cycle cost minimization. A real case study in South Khorasan is considered, in order to illustrate the proposed framework and its effectiveness. The effectiveness of the applied approach is investigated by comparing the outcomes with the results obtained by other heuristic methods. Also, the impacts are investigated of fuel cost variations, initial PV and battery costs, and interest rate on the economics of the hybrid scheme. The simulation results demonstrate that the hybrid algorithm obtains results that are more accurate (by 14.1%) than other applied algorithms, and show that the use of solar energy with a diesel generator, compared to the diesel only system, significantly reduces greenhouse gas emissions (by 59.6%) and supply costs (by 22.2%). The results thus demonstrate the benefits of utilizing the proposed framework for the hybrid system. These results are expected to help enhance acceptance and utilization of cleaner production systems. • An efficient strategy for optimal sizing and location is presented for a hybrid energy system. • A stand-alone photovoltaic-battery-diesel scheme for a rural area is examined. • Technical, economic, social, and environmental criteria are applied. • Impacts of variations in fuel and initial costs of the PV and battery of the hybrid system and interest rate are discussed. • A hybrid optimization algorithm based on geographic information systems provides the most accurate results. [ABSTRACT FROM AUTHOR]

Increasing the production of energy in line with industry development, transportation, and life quality improvement is an interesting topic needs to be addressed. Energy policymakers and researchers have aimed at energy management, particularly by improving energy systems performance. This review paper explains the rising interest of thermoelectric technology and applications. Nowadays, thermoelectric technology such as thermoelectric generators (TEGs) and thermoelectric cooling systems (TECs) provide heat loss recovery of thermodynamic units for power production of remote areas. Unlimited solar energy can also be employed for thermoelectric power production. This paper describes the principles of thermoelectricity and presents an explanation of current and upcoming materials. Developed models and various performed optimization of thermoelectric applications by using non-equilibrium thermodynamics and finite time thermodynamics are discussed as well. Additionally, a number of topical applications and energy resources are introduced. The main goal of this study is to give a clear overview of thermoelectric technology and applications. • Explains the rising interest of thermoelectric technology and applications. • Describes thermoelectricity principles and current and upcoming materials. • Developed models and various performed optimization are discussed. • Includes non-equilibrium thermodynamics and finite time thermodynamics. • A number of topical applications and energy resources are introduced. [ABSTRACT FROM AUTHOR]