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Abstract The uncertainty of operating conditions such as weather and payload cause variations in the energy demand of electric city buses. Uncertain variation in energy demand is a challenge in the design of charging systems and on-board energy storages. To predict the energy demand, a computationally efficient model is required for real-time applications. We present a novel approach to predict energy demand variation with a wide range of uncertain factors. A factor identification is carried out to recognize the range of variation in the operating conditions. A computationally efficient surrogate model is generated based on a previously developed numerical simulation model. The surrogate model is shown to be 10 000 times faster than the numerical model. The surrogate model output corresponds with the numerical model with less than 1% error. The energy demand of the surrogate model varied from 0.43 to 2.30 kWh/km, which is realistic in comparison to previous studies. Successful sensitivity analysis of the surrogate model revealed the most crucial factors. Uncertainty in temperature, rolling resistance and payload contributed most to the variation in energy demand. Variation in these factors should be taken into account when predicting energy consumption and while planning schedules for a bus network. Highlights • Novel surrogate modeling approach for energy demand prediction. • Uncertainty margins of 14 noise factors are identified. • Performing a sensitivity analysis of electric bus energy demand and regeneration. • Computational efficiency is improved significantly with high prediction accuracy. • Consumption depends mainly on the ambient temperature, rolling resistance and mass. [ABSTRACT FROM AUTHOR]

Abstract In order to evaluate the impact of ambient conditions on the performance of indirect dry cooling system quantitatively, an analytical model was established which combined the numerical simulation of thermo-flow performance of natural draft dry cooling tower and the thermodynamic analysis of water-steam system in a 660 MW thermal power generating unit. The model was verified by experimental results and practical operating data, respectively. Temperature and flow fields of cooling air, as well as the back pressure of turbine were obtained under various natural crosswind and ambient temperature conditions. Standard coal consumption rates were acquired accordingly. The results indicated that the back pressure and standard coal consumption rate increased with the ambient temperature and wind speed. The most additional 27.72 g/kWh of standard coal consumption rate can be caused by the natural crosswind and high ambient temperature for the investigated power generating unit. A sensitivity analysis was conducted and the results showed that the value of the standardized coefficients for natural crosswind speed and ambient temperature were 0.446 and 0.888, respectively. Therefore, though the natural crosswind could deteriorate the flow field of ambient air, the ambient temperature had a greater impact on the standard coal consumption rate. Highlights • Analytical model combined both dry cooling tower and power generating unit is established. • Thermo-fluid performances of cooling tower with variable ambient conditions are investigated. • Off-design performances of indirect dry cooling power generating unit are obtained and analyzed. • Standard coal consumption rate increases with the crosswind speed and ambient temperature. • Ambient temperature has greater impact on standard coal consumption than that of crosswind. [ABSTRACT FROM AUTHOR]

Abstract -- In electricity markets, transmission constraint relaxation is frequently used to ensure the feasibility of the optimal power flow (OPF) problem and avoid the expensive yet ineffective congestion adjustment. However, transmission constraint penalty factors have a considerable impact on the market scheduling and prices. There is still no consensus on how to properly set the penalty factors. In this paper, the impact of transmission constraint penalty factors on the market solution is quantitatively investigated via the sensitivity analysis of the DC OPF model. Parametric programming is performed to determine the change of the market scheduling and prices with respect to the change of penalty factors. In particular, we prove for the very first time that when the objective function of the market model is quadratic, the parametric programming can be conveniently performed without the need of re-optimizing the DC OPF model in most cases. On this basis, an efficient method is proposed for exactly characterizing the mapping between the penalty factors and the market solution. Case studies show that the proposed method could be up to 100 times quicker than re-optimizing the DC OPF model as in the traditional parametric programming process. Highlights • Influence of penalty factors on DC OPF solution is quantitatively studied. • Parametric programming for the market model is performed without re-optimization. • Proposed method for calculating the mapping is accelerated by more than 100 times. [ABSTRACT FROM AUTHOR]

Abstract Electricity is the rising force among worldwide end-uses of energy. To meet the increasing demand, accurate policy decisions should be made considering each country's own dynamics. In fact, the selection of appropriate electricity generation resources necessitates the consideration of different aspects of the problem; hence, multi-attribute evaluation should be used. Topcu and Ulengin (2004) conducted a multi-attribute study to select the appropriate electricity generation resource in Turkey. To analyze the potential changes that may occur in electricity generation policy due to the recent dynamics in Turkey, the electricity generation resource selection problem is revisited in this research. Alternatives to be evaluated as well as the criteria to be used for evaluation are initially determined based on the synthesis of a literature survey and expert opinions. The alternatives are identified as solar photovoltaic (PV), wind, hydro, biomass, natural gas, coal, oil, and nuclear. The alternatives were evaluated using a new multiple-attribute decision making (MADM) approach based on the integration of Monte Carlo simulation, entropy, and Borda count methods. Besides updating data of Topcu and Ulengin, this new approach makes a significant contribution to the analysis stage as well. The results reveal that the primary electricity generation resources for Turkey should be a combination of renewable resources. Highlights • The energy resource selection is revisited to analyze potential changes. • We use MADM approach integrating simulation, entropy, and Borda count for analysis. • Sensitivity analysis is conducted for validating the robustness of the results. • Turkey has to increase the share of indigenous and renewable energy sources. [ABSTRACT FROM AUTHOR]

Abstract Many natural methane hydrate (MH) reservoirs are heterogeneous and are characterized by a layered structure. In this study, we numerically investigate gas production from a multi-layered hydrate reservoir by depressurization through a single vertical and a single horizontal well. This layered MH reservoir is constructed based on field test data at the AT1 site of the Eastern Nankai Trough in Japan, and involves three hydrate-bearing layers (HBLs): Upper HBL-1, middle HBL-2, and lower HBL-3. The simulation results indicate that the horizontal well shows a better gas production performance in comparison to the vertical well. Over a production duration of two years, the average gas production rate by using the horizontal well reached 7.3 × 104 ST m3/d, which is 5.7 times higher than that by using the vertical well. However, the gas-to-water ratio for both the vertical and horizontal well cases is low in absolute terms. Sensitivity analysis of gas production by the horizontal well indicates that both the very higher and lower levels of permeability in HBL-2 and hydrate saturation in HBL-3 are unfavorable for long-term gas production. In addition, decrease of vertical permeability in HBL-1 and HBL-3 can lead to lower gas production efficiency. Highlights • Gas production from layered MH reservoir is investigated numerically. • Horizontal well has a better production performance over vertical well. • Gas-to-water ratio is low in long-term gas production. • Vertical permeability has great effect on gas production efficiency. [ABSTRACT FROM AUTHOR]

Abstract A combined Brayton/Brayton power cycle has been investigated using the advanced exergy analysis. The combustion chamber was shown to be the component with the largest exergy destruction. However, the analysis revealed that most of the irreversibility generation at the combustion chamber was endogenous and unavoidable. In contrast, the irreversibility generation at both turbines and both compressors was largely endogenous and avoidable. The total exergy destruction, endogenous unavoidable and exogenous avoidable exergy destruction at the combustion chamber monotonically decreased, while the endogenous avoidable and exogenous unavoidable exergy destruction at the same component initially decreased, reached a minimum, and then increased when the topping cycle pressure ratio was increased. On the other hand, when the bottoming cycle pressure ratio was increased, the endogenous and exogenous unavoidable exergy destruction at the combustion chamber decreased, reached a minimum, and then increased. All four terms of the exergy destruction of the topping cycle turbine and compressor consistently increased with the topping cycle pressure ratio, while their sensitivity to the bottoming cycle pressure ratio was relatively small. Finally, varying the combustion temperature from 1000 K to 1600 K has resulted in a reduction of the total exergy destruction, as well as the endogenous unavoidable, endogenous avoidable, exogenous unavoidable and exogenous avoidable exergy destruction at the least efficient components of the power plant. Highlights • Avoidable, unavoidable, endogenous and exogenous irreversibility is calculated. • The exergy destruction at the combustor is large and essentially unavoidable. • The recovery heat exchanger irreversibility is half endogenous and half exogenous. • The compressors and turbines have the largest endogenous avoidable irreversibility. • The sensitivity of the different parts of the irreversibility generation is discussed. [ABSTRACT FROM AUTHOR]

Abstract Demand-side management has the potential to reduce the cost of solar based community micro-grids and solar home systems for electricity access. This paper presents a methodology for optimal least-cost sizing of generation assets while meeting explicit reliability constraints in micro-grids that are capable of active demand management. The battery management model considers kinetic constraints on battery operation and represents dispatch in the field to regulate the depth of discharge. The model allows consideration of the trade-off between depth of discharge, cycle life, and calendar lifetime in lead-acid batteries. Separate reliability targets for disaggregated, residential load profiles at hourly timesteps are considered to evaluate the performance and cost reduction potential of demand-side management capabilities — with economic results and sensitivity analyses around key input assumptions subsequently presented. We find that demand-side management can reduce the number and cost of requisite solar panels and batteries with the integration of real-time management and controls – a key result for justifying next generation micro-grids for electricity access. Highlights • Techno-economic model evaluates value of demand-side management in micro-grids. • Optimal solar and battery capacities identified for varying levels of reliability. • Kinetic and MDOD dispatch constraints illustrate operation of lead-acid batteries. • Sensitivity analyses show LCOE increases if battery depth of discharge exceeds 40%. [ABSTRACT FROM AUTHOR]

Abstract This study presents a theoretical model for multi-objective optimization of marine diesel charge air cooler by firefly algorithm. By considering the overall cost and exergy destruction minimization as objective functions, energy and exergy analysis is carried out for multi-objective optimization design of a heat exchanger. Sensitivity analysis is performed to find out the effect of design parameters on the objective functions. Firefly algorithm is used to generate a set of Pareto optimum points and a normalized form of the Pareto front is applied as a decision-making approach to finding out optimum solutions. The theoretical model in the present study is verified by an experimental data and shows a good agreement between the current results and the experimental data. Also, the Pareto front shows that irreversible losses decrease while total cost increases and vice versa. Multi-objective optimization results reveal that overall cost and exergy destructions are reduced by 4.03% and 7.66%, respectively. Water pressure drop is decreased by 12.41% and air pressure drop is reduced by 2.95%. Highlights • A multi-objective optimization of charge air cooler is studied by a firefly algorithm. • Total cost and exergy destruction are considered as the objective functions. • The effects of decision variables are studied on the objective functions. • Optimal working points of the charge air cooler are obtained from the Pareto front. [ABSTRACT FROM AUTHOR]

Abstract This study proposes two incentive policies consisting of the feed-in tariff and carbon emission trading. The effects of the policies on the performance (economic, energy, and environmental) of CCHP systems running in office and residential buildings under five different operation strategies (following the electric load (FEL), following the thermal load (FTL), two types of following the hybrid electric-thermal load (FHL1 and FHL2), and following the maximum efficiency of power generation unit) were compared and analyzed. The results showed that the best operation strategies were changed before and after the above two incentive policies carrying out. When the policies are not carried out, the FEL and FHL1 strategies are most suitable for the CCHP system in office and residential buildings. Since the policies implement, the FHL2 and FTL strategies are the best. Incentive policies have a greater positive impact on the CCHP system in residential building than that in office. For promoting the development of the CCHP system in residential buildings, the incentive coefficient can be set higher than that in office buildings. Finally, sensitivity analysis was conducted for CCHP systems and the results were presented in terms of feed-in tariff, incentive coefficient, and gas price. Highlights • The coupling of feed in tariff and carbon emission trading policy was analyzed. • The effect of policies on system in office and residential buildings were analyzed. • Policies have a greater impact on the system in residential building than in office. • The cost of CCHP system under FTL is most sensitive to the incentive coefficient. • A high incentive coefficient brings excess carbon emission in residential buildings. [ABSTRACT FROM AUTHOR]

Abstract Existing hot dry rock geothermal projects are commonly confronted with some technical issues, such as corrosion and scaling, and water loss. To resolve these issues, the present work proposes a novel system for mining hot dry rock geothermal energy, in which a reservoir is combined with a heat pipe system. The new system encompasses a heat pipe placed in a single-well to extract hot dry rock geothermal energy, while an artificial reservoir is built around the main endothermic region of the well, which is permeable and saturated with carbon dioxide (CO 2). This wellbore structure design may stimulate a stronger natural convection in the reservoir, resulting in a higher thermal power production. To evaluate the proposed system, an extensive numerical investigation was conducted. The comparison of the proposed system with the conventional downhole heat exchanger (DHE) system in terms of heat extraction performance indicates clear superiority of the proposed system primarily due to the associated thermosyphon effect of CO 2 fluid in the reservoir. To better understand how operating and design variables affect the heat extraction performance of the system, a detailed sensitivity analysis was conducted taking into consideration a wide range of possible configurations and working conditions. The eventually obtained knowledge will guide the design of the system in practice. Highlights • We propose a novel downhole heat exchanger system for mining geothermal energy. • The system encompasses a closed-cycle downhole heat exchanger with a heat pipe. • An artificial reservoir saturated with CO 2 is around the main endothermic region. • Numerical study indicates clear superiority of the proposed system. • A detailed sensitivity analysis obtains knowledge for the design of this system. [ABSTRACT FROM AUTHOR]

Abstract State of charge estimation is one of the most critical factors to solve the key issues of monitoring and safety concerns of an electric vehicle power battery. In this paper, a state of charge estimation approach using subtractive clustering based neuro-fuzzy system is presented and evaluated by the simulation experiments using advanced vehicle simulator in comparison with back propagation neural network and Elman neural networks. Input parameters to model the state of charge estimation approach using subtractive clustering based neuro-fuzzy system are current, temperature, actual power loss, available and requested power, cooling air temperature and battery thermal factor. Data collected from 10 different drive cycles are utilized for the training and testing stages of the state of charge estimation model. Experimental results illustrated that the proposed model exhibits sufficient accuracy and outperforms both neural network and Elman neural network based models. Thus, the proposed model under different drive cycles show remarkable advancement in state of charge estimation with high potential to overcome the drawbacks in traditional methods and therefore provides an alternative approach in state of charge estimation. In addition, a sensitivity analysis is also performed to determine the importance of each input parameter on output i.e. state of charge. Highlights • An SC-ANFIS model to estimate the battery state of charge is developed. • The proposed model exhibits sufficient accuracy and outperforms other advanced models. • The model requires a simple training procedure and is evaluated using 10 diversified unseen driving cycles. • Different statistical metrics are adopted for the model state of charge estimation performance evaluation. • Sensitivity analysis is performed to determine the influence and importance of input variables on battery state of charge. [ABSTRACT FROM AUTHOR]

Abstract Recently, Chinese government has determined to guide the energy structure adjustment. The rapid development of hydropower is still important for the low-carbon transition. Therefore, we established a scenario-based system dynamics model considering emission trade scheme (ETS) and government policy. 4 scenarios (No ETS & policy; Only ETS; Only policy; Both ETS & policy) were established to investigate the development path of hydropower in China. In 2030, the installed-capacity of conventional hydropower will reach 364.2, 416.1, 428.7 and 470.5 million kW under four scenarios; and the installed-capacity of pumped-storage power will be 75.8, 85.6, 95.5 and 100.8 million kW under four scenarios. Note that, the development paths of installed-capacity and power generation of pumped-storage power and conventional hydropower are characterized by oblate “S-shaped” curves. By analyzing the differences between scenario 2 (Only ETS) and scenario 3 (Only policy), we can conclude that the effect of policy support on the development of hydropower is larger than the ETS. The conclusions derived from sensitivity analysis show that the changes in policy intensity have greater impact than changes in ETS price. In brief, all the results and discussions can help Chinese government shape a development plan for hydropower generation. Highlights • This paper systematically investigated current situation of hydropower in China and sorted out related policies. • A scenario-based system dynamics model is used to analyze the development path of hydropower under policy incentives. • The development paths of conventional hydropower and pumped-storage power are characterized by oblate shape like “S”. • We carried out a comprehensive scenario analysis to investigate the effects of government support and ETS policies. [ABSTRACT FROM AUTHOR]

A solar-powered cascade system is proposed for dehumidification, cooling and heating in hot summer and cold winter areas of China. To evaluate the energy, environmental and economic sustainability of the system, the emergy evaluation of the proposed system is analyzed and compared with different energy sources. The effects of solar radiation intensity, air temperature and relative humidity on the emergy performance of the system are discussed. The results show that the input total emergy and transformity of the proposed system are 9.88 × 1016 sej/y and 4.75 × 105 sej/J, which are lower than that of the systems powered by other energy. The environmental load ratio and emergy sustainability index are the highest when the system is powered by solar energy, with the value reaching 1.33 and 1.66, respectively. According to parameter sensitivity analysis, the total emergy input decreases by 6.31% and the emergy saving ratio increases by 29.09% as the increase of solar radiation intensity. The system has the best emergy performance at air temperature of 26.18 °C. The system has lower environmental load and higher sustainability in lower relative humidity climate. This work proves the viability and sustainability of the novel cascade system. • A solar-powered system is proposed for dehumidification, cooling and heating. • Emergy analysis method is conducted to evaluate the sustainability of the system. • The environmental loading ratio and emergy sustainability index are 1.33 and 1.66. • The system has the optimal emergy performance at air temperature of 26.18 °C. • This work proves the viability of the system in HSCWA of China. [ABSTRACT FROM AUTHOR]

The early design stage provides the greatest opportunities to achieve energy-efficient buildings; however, designers require relevant performance data to manage interdisciplinary and conflicting objectives. Thus, for the first time an integrated multi-stage sensitivity analysis and multi-objective optimization approach was developed for four different zones of arid climate in PCM integrated residential buildings. A multi-stage sensitivity analysis is proposed to identify the relative importance of early design stage parameters, which covers envelope thermophysics, building layout and energy-efficiency measures, considering energy and economic indicators. Three global sensitivity analysis approaches (Standardized rank regression coefficient, Partial rank correlation coefficient and Morris method) were employed in the first stage, while the local sensitivity analysis was employed in the second stage. A multi-objective optimization using the genetic algorithm was performed to obtain the Pareto frontier, and two sets of solutions were proposed: the most energy-efficient and the most cost-effective. Finally, multi-criteria decision making was carried out. It was found that sensitivity analysis results showed different rankings of parameters. For each climatic zone, a different set of optimal solutions existed. Compared to reference building, the best solutions reduced total energy consumption by 11.1–34.6%, while the payback period reduced by 17.6–48.5 years. • Multi-stage SA was used to select the most sensitive parameters. • Early design stage parameters were optimized in four arid climate zones. • Multi-objective optimization approach was performed to find optimal solution. • The most energy-efficient and most cost-effective solutions were determined. • Total energy consumption reduced by 11.1–34.6% in all locations. [ABSTRACT FROM AUTHOR]

The present work investigates the effect of wall thermal conditions on the NO emission in the different inlet temperatures and oxidant dilution levels. The studies are performed for the CH 4 -air, oxygen-enriched, and oxy-CH 4 combustion under the HTC and MILD regimes by numerical simulation of the non-premixed furnace and chemical calculations of the WSR reactor. It is found that higher heat loss from the wall and more replacement of CO 2 with N 2 facilitate the establishment of the MILD regime and significant reduction of NO production. The results show an optimum point for achieving the minimum heat loss and NO emission. Under the MILD regime, dominant mechanisms in the NO emission are prompt through reaction CH + N 2 ⇌HCN + N and thermal routes for the CH 4 -air condition and N 2 O-intermediate by reactions N 2 O + O⇌2NO and N 2 O + H⇌N 2 +OH and thermal mechanisms for oxy-CH 4 combustion. In both atmospheres, the thermal route plays the main role in the low heat loss from walls, while other routes are more active in the low maximum flame temperature. Reaction N + NO⇌N 2 +O by supplying O radical from reactions O + CO + M⇌CO 2 +M and H + O 2 +M⇌HO 2 +M is activated by increasing O 2 level, while reactions N + NO⇌N 2 +O and N + OH⇌NO + H show the main contribution in the sensitivity analysis of NO. • Effect of wall thermal conditions in the different T in and X O2 is studied. • There is observed an optimum point between low heat loss from the wall and NO emission. • In high T in or X O2 , thermal route emitted high values of NO and MILD or HTC regimes. • N 2 O-intermediate is responsible for NO emission in oxy-CH 4 MILD combustion. • Prompt mechanism plays the first role in NO production under CH 4 -air MILD regime. [ABSTRACT FROM AUTHOR]

The optimal operation of short-term cascade hydropower systems, with dozens of hydropower stations, multistage calculation periods and complex hydraulic constraints, faces a serious "curse of dimensionality" problem, and it is difficult to solve this problem directly or obtain a precise optimal hydropower dispatching plan in an acceptable time. This study presents an efficient solution framework based on the load decomposition strategy to alleviate the dimensionality problem. First, the load decomposition strategy is exploited by reducing the number of optimization stages to reduce the dimensionality of the original complicated optimization problem. By continuously adjusting the number of time periods and load of each stage, the load decomposition strategy can divide the original optimization problem into two subproblems with different optimization periods, namely, the segmented load process and burr load process. Second, a hydropower station classification method is proposed, in which all stations are divided into balanced power stations for the burr load and main dispatching stations for the base load, significantly reducing the participation of most hydropower stations in the frequent dispatch process. Finally, according to the transformation of the water balance relationship, a mathematical expression that accurately describes the complex hydraulic connection problem between the two subproblems is constructed to obtain more refined solution results. Practical project cases involving a large-scale hydropower system with 7 stations on the Wu River of China are used to test the sensitivity and efficiency of the proposed method. The sensitivity analysis indicates that the different optimization stages in this method can quickly obtain a globally optimal result and improved computational efficiency. Moreover, compared with the 24-point and 96-point traditional optimization scheduling methods, the water discharge of the presented method is reduced by 6.6% and 7.8% in the dry season and 4.0% and 4.9% in the flood season in a limited time, respectively, which suggests that the solving difficulties caused by the "curse of dimensionality" can be effectively alleviated and the solution efficiency can be greatly improved. The simulation calculations for different seasons and scales also indicate that the proposed method is an effective tool for the optimal operation of large-scale hydropower systems. • A solution framework for short-term cascade hydropower system is proposed. • The load decomposition strategy alleviates the dimensionality challenge. • The balanced power station bears frequently fluctuating load process. • Short-term hydropower optimal dispatching plan can be obtained quickly. [ABSTRACT FROM AUTHOR]

To estimate the hazard of explosion during hydrogen/methane gas transportation, the experiments were conducted in a small-scale duct. It studied the effect of hydrogen fraction and equivalent ratio distribution on flame propagation characteristics and pressure characteristics. It showed that the flame propagation process can be divided into steady-state and broken-state. During the steady-state, the addition of hydrogen will accelerate the evolution of the flame structure, leading to a reduction in the observed flame structure patterns. And the pressure transferred from bimodal to unimodal distribution. When entering the broken-state, a secondary explosion occurred. Then the flame propagation velocity started to increase dramatically and emitted a dazzling white light. This secondary explosion is more dangerous and significantly influenced by the equivalence ratio of duct A (φ A) where the ignition source is located. Therefore, it was calculated the parameters of laminar combustion of φ A , and the variation of key radicals was analyzed. Finally, the fitted equations of the maximum flame propagation speed (V max) and the maximum explosion pressure (P max) with laminar burning velocity (S L) were obtained. It was found that the growth rate of V max gradually decreased with increasing S L , while the growth rate of P max gradually increased. • The effect of hydrogen fraction on the non-uniform field explosion was studied. • The flame propagation process can be divided into steady-state and broken-state. • The premixed gas can be divided into rich-methane and poor-methane. • Discuss the evolution regularities of the elementary reactions and radical particles. • Analysis the relation between fuel fundamental parameters and explosion parameters. [ABSTRACT FROM AUTHOR]

Clean-energy vehicles are conducive to reducing greenhouse gas emissions and environmental pollution. The environmental assessment of hydrogen fuel cell vehicles (FCV) and natural gas vehicles (NGV) under different fuel production paths can achieve efficient utilization of renewable energy and reduce environmental pollution. This study conducted a life cycle assessment on hydrogen FCV and NGV under different fuel production paths. The results indicated that compared with NGV, hydrogen FCV exhibit better environmental performance. Among the fuel production methods, wind-power-assisted electrolysis of water for hydrogen production exhibits superior environmental performance. The acidification potential, global warming potential, eutrophication potential, and photochemical ozone creation potential indicators of the wind-powered fuel cell vehicles process were 91.44, 73.33, 96.47, and 93.39% lower than those of the coal synthetic natural gas vehicles process, respectively. Subsequently, the environmental impact of the internal structure in the manufacturing process of hydrogen FCV and NGV was investigated. The results showed that the power system accounted for nearly 50% of the environmental impact in the manufacturing process of hydrogen FCV. Furthermore, the influence of the six methods used for fuel production on environmental performance was evaluated through sensitivity analysis. This study provides a reference for the sustainable development of such vehicles. • Life cycle environmental performance is compared for new energy vehicles. • Environmental performance was analyzed for both vehicle powertrains. • Sensitivity analysis of fuel production efficiency was performed. • Improvement strategies are proposed to reduce environmental impact. [ABSTRACT FROM AUTHOR]

The temperature of the converter gas at the outlet of the converter is as high as 1600 °C, and the output is about 120–150 Nm3/tons steel. In order to improve the utilization efficiency of heat energy, and the recovery rate and calorific value of the converter gas, medical waste (MW) gasification of by the converter gas was proposed. At the same time, the technical feasibility and sensitivity analysis of MW gasification were conducted by Aspen Plus soft on the basis of Gibbs free energy minimization. The simulated results were successfully validated with the experimental data from MW gasification in a bench scale gasifier. Moreover, the influence of the gasification temperature, steam/MW ratio and MW/converter gas ratio on the composition, the low heating value (LHV), gas yield (GY), and carbon conversion efficiency (CCE) were evaluated. During the simulation, the mixed gas (CO: CO 2 : N 2 = 40: 20: 40) was used as the simulated converter. The simulated results demonstrated that the optimum parameters were 1050 °C gasification temperature, 0.8 steam/MW ratio, and 0.08 kg/m3 MW/converter gas ratio, CO, H 2 , and CO 2 reached to 46.54%, 38.09%, and 0.10% due to Boudouard reaction and water-gas shift reaction. After MW gasification, CO 2 content in the converter gas was decreased from 20% to 0.10%, and LHV was increased from 5480 to 10,021 kJ/Nm3. • No additional heat was need for MW gasification by the converter gas. • 1050 °C, 0.8 steam/WM ratio, and 0.08 kg/m3 MW/converter gas were the optimum parameters. • CO 2 content of the converter gas was decreased from 20% to 0.10% by MW gasification. • LHV was increased from 5480 to 10,125 kJ/Nm3 by MW gasification. [ABSTRACT FROM AUTHOR]

The spatial configuration of fracture structures controls the efficiency of heat production in enhanced geothermal systems. However, it is still impossible to fully characterize complex fracture structures, because in practice limited information is available in deep geothermal reservoirs. A simplified representation of fracture structures is necessary, but requires insight into the major parameter(s) controlling the flow and heat transport. In this study, we examine fracture structures at macroscopic and microscopic scales; the fracture orientation is used to characterize the macroscopic fracture structure, and the mean, standard deviation and correlation length of apertures are used to represent the microscopic fracture structure. Effects of these parameters on flow and heat transport and subsequently on heat production are systematically analyzed and compared. It is found that the effect of macroscopic structure on heat production is dependent on the density-driven flow induced by temperature contrast in geothermal systems, and the effect of microscopic structure is related to perturbations in flow paths, cross-sectional flow area and density-driven flow. A sensitivity analysis clarifies that in enhanced geothermal systems, priority should be given to characterize the macroscopic structure of the fracture network, followed by the estimation of the mean and correlation length of fracture apertures. • Effects of macroscopic and microscopic fracture structures on heat production are compared. • Heat production is controlled by macroscopic structure, affected by microscopic structure. • Priority should be given to characterize macroscopic structure with limited reservoir information. [ABSTRACT FROM AUTHOR]

In this paper, an integrated liquefied natural gas (LNG) production process, carbon dioxide separation and liquefaction, and fresh water production is proposed and analyzed. The hybrid system consists of three sections: power and heat generation by the process of combustion with pure oxygen, natural gas liquefaction with a two-stage refrigeration cycle (absorption refrigeration cycle and multi-component refrigerant), and multiple-effect distillation (MED) desalination. This integrated process produce 593.3 ton/h LNG, 84.62 ton/h carbon dioxide, and 74.58 ton/h fresh water. Exergy analysis shows that the highest exergy destruction is related to the shell and tube heat exchangers, which is about 38.8% and the lowest exergy destruction is related to the air coolers, 0.84%. Integrated process has an overall electrical efficiency (LHV Base) of 36.3%, a specific power of 0.179 kWh/kg LNG. Also the amount of energy consumed for producing carbon dioxide is 0.005 kWh/kg CO 2 , and gained output ratio (GOR) of 2.87 is achieved by three-stage MED desalination. A sensitivity analysis is done to investigate and identify the important parameters affecting the integrated process performance. [ABSTRACT FROM AUTHOR]

The exploitation of oceans is currently recognized as an abundant, geographically diverse and renewable source of energy which still remains largely untapped. Marine currents are, together with waves, one of the most promising sources of ocean energy thanks to their enormous potential for electricity production and their high predictability. Owing to the fact that the marine current harnessing industry has only just begun to demonstrate full-scale devices and device arrays, most of the research papers related to marine current harnessing technologies have been focused on improving their technical aspects. However, there is limited information as regards other aspects, such as those of an economic nature, that should be studied in detail in order not to compromise the future of these technologies. The objective of this research is to address this gap by providing an economic-financial methodology that will help quantify the profitability and feasibility of these renewable energy projects. The methodology developed considers the following aspects: (i) a definition of the fundamental variables of the economic model. (ii) a definition of its financing structure on the basis of the industry's common stockholder equity that partners must provide and the estimation of bank financing needs; (iii) a definition of the main components required to obtain the forecast balance, the forecast income statement and the forecast sources and application of funds for the entire service life of the project; (iv) a determination of the cost-benefit analysis, carried out using the information provided in the cash-flows of the project and the forecast sources and application of funds; (v) an analysis of the most important economic-financial ratios of the model and; (vi) the realization of a sensitivity analysis, with the aim of detecting business risks when fundamental variables of the model, such as investment, the annual energy production, the price of energy or the percentage of loan requested, among others, oscillate. The proposed model has been applied to a case study, after which it was found to provide a good profitability for the project and the stakeholders. The results also indicate that the variables that most affect the profitability of the project are the interest rate, the price of energy and the annual energy produced. [ABSTRACT FROM AUTHOR]

Two novel integrated cryogenic helium extraction from natural gas processes are introduced and analyzed. Helium recovery efficiency, energy consumption per extracted helium, energy and exergy analyzes are studied for the proposed processes. Multi streams heat exchangers composite curves show that thermal design of the processes has been done with good efficiency. The results show that efficiency of the integrated processes is higher than the flash method. Efficiency of the modified Linde and Exxon mobile integrated processes are 96% and 95% respectively. Based on the results modified Linde process performance is better than the modified Exxon mobile process. Exergy analysis results show that valves have more exergy destruction comparing to the other equipment. Also air coolers have low exergy loss and high exergy efficiency. [ABSTRACT FROM AUTHOR]

The application of the European directives related to the energy consumption of existing buildings leads to the integration of efficient techniques into the refurbishment actions. This procedure allows reaching high energy savings and reducing pollutant emissions. The identification of the energy consumption profile of the building stocks is a necessary step to evaluate the impact of retrofit measures. With this aim, the energy performance of representative dwellings has been analyzed to develop a citizen-oriented platform. This representativeness has been chosen through one parametric matrix that characterizes the residential building stock of Madrid. Different refurbishment strategies have been highlighted to assess the energy savings in comparison with the initial situation. Two building cases and three boundary conditions have been selected to develop six TRNSYS models. The energy impact produced by the implementation of selected refurbishment strategies has been evaluated through a sensitivity analysis. Batteries of simulations have been executed coupling the TRNSYS models with GenOpt. The most influential strategies are the typology of façades, insulation at the roof, variable set point temperatures, better glazing and exterior summer shading over the windows. Building performances to minimize the annual thermal needs and one economic study have been developed. [ABSTRACT FROM AUTHOR]

This research presents technical and cost-minimised design to decarbonise the heating network by using large-scale heat pump and thermal heat storage. In this paper, real hourly heat-consumption and heat-production cost data for the city of Aarhus, Denmark are used for calculating techno-economic feasibility of coupling the heating network with electrical grid. An optimum solution is suggested for the entire network with least amount of backup generation capacity, thermal heat storage capacity, natural gas boiler capacity and levelised cost of energy. Aarhus constitutes 5% of the Denmark's total heat demand and 4% of electrical load demand. This can be fulfilled with 160 MW of rated wind generation capacity, 35 MW of solar PV generation capacity, 45 MW of backup generation capacity, 221 MW of natural gas boiler capacity and 3.4 GWh of thermal heat storage capacity. The levelised cost of energy shows that, the coupling between the electrical grid and heating sector reduces the cost by more than 50% to 45  € /MWh. However, the cost-minimised design is possible with wind/solar mix of 85% and renewable energy penetration of 100%. Sensitivity analysis concedes that, the 100% decarbonisation of heating sector relies heavily upon the cost assumed for wind generation and solar PV generation, instead of the operation and maintenance cost for heat pump. Furthermore, the reduction in cost for wind generation and solar PV generation leads to the decrease in levelised cost of energy. Whereas, the reduction in cost for heat pump, thermal heat storage capacity and natural gas boiler capacity leads to an increase in renewable energy penetration. Sensitivity analysis further reveals that, increasing thermal heat storage capacity and the cost of selling excess renewable energy does not have major impact upon the levelised cost of energy and can be instrumental for the economic viability of fossil-free future. [ABSTRACT FROM AUTHOR]

Based on a benchmark hybrid power system of molten carbonate fuel cell(MCFC) integrated with the steam turbine(ST) bottom cycle system, a new MCFC/ST hybrid power system is proposed in this paper. The detailed thermodynamic models of the overall system are established. The effects of the key parameters on the new system performance are deeply studied. The exergy analysis method is used to reveal the theoretical root of performance advantage of new system. The off-design performance of the new system is analyzed. In order to improve the off-design performance of the new system, two control modes are proposed to make the fuel cell operate at 650 °C. The results indicate that the total exergy loss of the new system is obviously reduced compared with the benchmark system. The net efficiency of the new system reaches the highest when the carbon-to-steam ratio is 2.5, CO 2 utilization rate is 75%, fuel utilization rate is 85% and the current density is 1500 A/m 2 . The fuel cell is more efficient at part load than at the design point and the net hybrid power system efficiency increases in the first control mode and almost remains unchanged in the second control mode with the decrease of the load. [ABSTRACT FROM AUTHOR]

One-dimensional theoretical methods are always utilized for analysis of performances of a steam ejector but they commonly have certain limitations. Numerical simulation and analysis were carried out by means of CFD method to the flow field inside a steam ejector for recovery of waste heat; moreover, the single-factor analysis was performed to see how the ejector was affected by those single-factors such as the diameter of the nozzle outlet, the distance between the nozzle outlet to the inlet of the mixing chamber and diameters of the contraction section of the mixing chamber and the diffuser chamber, respectively, while other conditions are fixed. Multi-factor analysis was then carried out to investigate the performances of the ejector and its structures were optimized by means of the five-factor and four-level orthogonal tests to gain the sensitivity for each factor to performances of the ejector. Results indicate that the optimized ejector has much better performances and the diameter of the nozzle outlet is the most sensitively influencing factor on performances of the ejector. This study may provide a new way of thinking for optimization of structure parameters of any steam ejector and have certain values for design and application of steam ejectors. [ABSTRACT FROM AUTHOR]

Renewable energy based hybrid energy cooling system is an economic and convenient option for rural milk preservation in remote coastal province in southern part of India. In this work, a model is presented for the techno-economic evaluation of hybrid renewable energy operated chilling system to fulfil the preservation requirements of isolated coastal sites where the bio resources and solar energy are plenty available. A milk chilling plant operated by vapour absorption cooling system which obtains thermal energy from various combinations of existing renewable energy sources has been studied and to predict the effect of different energy proportions of existing renewable energy resources on the overall system performance and economical parameters. From the analysis, it can be concluded that the Gobar gas/Biomass/Biogas/Solar (0.5:0.25:0.125:0.125) has been recommended for the suitable combination. The analysis reveals that the proposed hybrid renewable energy based chilling system can show the overall system performance as 0.18–0.19 with lowest Payback period (4 years 6 months to 5 years 3 months), life cycle cost (INR 16.8–19.5 million) and positive net present value. The sensitivity analysis show that the energy conversion efficiency and interest rate significantly influences the overall COP and capital cost, running cost and payback period. [ABSTRACT FROM AUTHOR]

Distribution network expansion planning problem is carried out to supply the forecasted demand of distribution network in a certain time in which optimal size and location of distribution substations and feeders should be determined. In this paper, this problem in the presence of different types of distributed generators is addressed. For this purpose, a new approach is applied to model several practical aspects such as pollution, investment and operation costs of distributed generators, purchased power form the main grid, dynamic planning, and uncertainties of load demand and electricity prices. The uncertainties are modeled using the probability distribution function and Monte-Carlo simulation is applied to insert them into the planning problem. Because the problem involves many variables and constraints and is a non-convex and large-scale one, improved harmony search algorithm is used to solve it. To show the effectiveness of the proposed model and solving approach, it is applied to the 9-node and 69-node standard radial distribution networks and a real system of western part of Iranian national 20 kV distribution grid. The results show that the harmony search algorithm can solve the problem in a better manner in comparison with other methods such as genetic algorithm and particle swarm optimization. [ABSTRACT FROM AUTHOR]

As weather-dependent distributed renewable energy resources (RERs) such as photovoltaic (PV) systems and wind farms have increasingly been connected to distribution networks, energy storage systems able to compensate intermittency in their power generation may be required. Moreover, such RERs can participate in reactive power control upon voltage regulation. Thus, the problem of optimizing the capacity of storage systems for RERs with the capability of reactive power control is necessary for planning, maintaining, or upgrading a distribution network. The objective of this study is to optimize the capacity of storage systems for RERs, particularly PV inverters with the capability of reactive power control in this study. For this purpose, this study proposes the power-flow algorithm able to optimize reactive power amount to be either consumed or injected by PV systems and a hybrid multi-objective sensitivity analysis algorithm that optimizes the capacity of PV and storage systems. The proposed algorithm includes an objective function that minimizes voltage variations and capital costs of PV and storage as well as maximizes energy savings and peak load reduction. Then, it successfully optimizes the capacity of PV and storage systems in the well-known IEEE test feeders. [ABSTRACT FROM AUTHOR]

The paper aims at presenting a methodology to choose the proper sizing of an integrated Photovoltaic unit and a storage architecture starting from the knowledge of the load and solar irradiance time profiles. To do this, first a simple logic to manage the charging/discharging of the storage is proposed, then the function representing the overall cost during the whole life of the system is derived. The computation of the cost function for different photovoltaic and storage sizes allows finding the best sizing of the system. Finally, a thorough economic analysis is conducted to provide criteria to check whether the investment is economically advantageous. This is done considering the impact of the economic variables which are more influential on the investment key assessment parameters. The proposed methodology has been validated in different realistic test cases against the results provided by an energy management system, showing an excellent agreement between the approaches. Moreover, the economic analysis has been applied to four realistic situations in order to tailor the microgrid components ratings on the specific test case. [ABSTRACT FROM AUTHOR]

Advances in computer-based optimization techniques can be used to enhance the efficiency of energy conversions processes, such as by reducing the aerodynamic loss in thermal power plant turbomachines. One viable approach for reducing this flow energy loss is by endwall contouring. This paper implements a design optimization workflow for the casing geometry of a 1.5 stage axial turbine, towards mitigating secondary flows. Two different parametric casing surface definitions are used in the optimization process. The first method is a new nonaxisymmetric casing design using a novel surface definition. The second method is an established diffusion design technique. The designs are tested on a three-dimensional axial turbine RANS model. Computer-based optimization of the surface topology is demonstrated towards automating the design process. This is implemented using Automated Process and Optimization Workbench (APOW) software. Kriging is used to accelerate the optimization process. The optimization and its sensitivity analysis give confidence that a good predictive ability is obtained by the Kriging surrogate model used in the prototype design process tested in this work. A flow analysis confirms the positive impact of the optimized casing groove design on the stage isentropic efficiency compared to the diffusion design and compared to the benchmark axisymmetric design. [ABSTRACT FROM AUTHOR]

This paper presents an analytical methodology of evaluating the economic viability of a CCHP system, over three alternative configurations: (1) boiler and electric chiller, which have been extendedly analyzed in literature, (2) boiler and gas driven absorption chiller and (3) reversible heat pump, which have been slightly investigated in comparison with CCHP systems. An adjusted Levelized Cost of Electricity (LCOE) is defined for those cases and used as a decision-making criterion. A sensitivity analysis is carried out to explore the effect of technical and economic data and load characteristics on the LCOE. The viability of the CCHP system is determined by comparing the LCOE with the electricity market prices. Two different economic viability problems are considered: (1) investing viability for new CCHP systems, and (2) operating viability for existing CCHP systems. The results demonstrate interesting interactions and encouraging perspectives, especially when CCHP system is used in combination with conventional technologies like boilers and chillers. [ABSTRACT FROM AUTHOR]

One of the challenges in electrical grid expansion planning is how to expand the infrastructure while considering fundamental changes in demand and supply, in part due to “game-changing” consumers, such as electric vehicles (EVs), and optional distributed generation (DG) by consumers. This work proposes an optimization model that addresses the generation and transmission expansion of the grid, including the facilities' locations, upgrades, and the network's design decisions. In contrast to some other models, it is not static in time: the model considers time-dependent demand in short-term (hourly) and long-term (yearly) variations. The proposed optimization model considers energy loss, transmission substations upgrades, constraints such as demand, capacities, and more. The model minimizes the long-term costs of infrastructure investments and the operational costs of generation. The work is supplemented by numerical experiments of the model in simulated scenarios. Sensitivity analysis conducted on some of the model features, demonstrates the importance of including them in the model. [ABSTRACT FROM AUTHOR]

Adjoint sensitivity based optimization methodology for a supercritical CO 2 (S-CO 2 ) cycle is developed in this paper. The adjoint sensitivity analysis method (adjoint method) is a way to analyze sensitivity very quickly. By using the developed methodology, the optimal state variation due to the change of cycle parameters is analyzed. The S-CO 2 recompression Brayton cycle is used for an example case for the demonstration of the proposed method. The independence of time consumption for the developed adjoint sensitivity analysis method to the number of optimized variables is demonstrated. For the test case, the developed algorithm shows the ability to make the design parameters converge with a precision of 10 −6 by more than ten times faster for calculating the sensitivity than conventional optimization methods. Validation of the obtained optimal point is also included in the paper. For the validation, a response surface analysis is performed to visualize the pathway during the iteration for optimization. It is very challenging to carry out the optimization having the same precision using a brute force algorithm or a probability-based optimization algorithm since the number of variables to be optimized is substantial for this type of a problem. The smoothness of an optimal cycle efficiency variation is observed in every case. [ABSTRACT FROM AUTHOR]

Hybrid energy system based on solar and wind power coupled with energy storage unit provides a reliable and cost effective energy alternative above the commonly used diesel based standalone power system. Various methodologies are adopted for modeling hybrid energy system component. They are modeled either by deterministic or probabilistic methods. The current study considers the hardware failure of photovoltaic panels while modeling. A probability distribution (PD) represents the various capacity states due to hardware failure of photovoltaic panels and corresponding probabilities. A concept based on random number generation is adopted to calculate the actual hourly available photovoltaic power. Wind turbine power output modeling incorporate force outage rate of the turbine. A new meta-heuristic algorithm called Cuckoo Search is applied for solving the hybrid energy system optimization problem. Photovoltaic-Battery, Wind-Battery and Photovoltaic-Wind-Battery system applicable to a remote area located in Almora district of Uttarakhand, India are considered. The effectiveness of Cuckoo Search in solving hybrid system design problem is investigated and its performance is compared with other well known optimization algorithms like Genetic Algorithm and Particle Swarm Optimization algorithm. Furthermore, this paper investigates the sensitivity of various input parameters like solar, wind resources and capital cost on the cost of energy. [ABSTRACT FROM AUTHOR]

Abstracts While small scale ORCs are currently dominated by volumetric expanders, the use of turbomachines is reconsidered due to their high efficiency and power density. Yet, suitable performance maps, which ensure an accurate starting point for the turbine design, are still missing for small scale turbines. This paper proposes a new non-dimensional performance map tailored for small scale turbines. The map is generated using an experimentally validated 1D code and adapted to small scale ORCs applications. A new polynomial fit is proposed, which accounts for the pressure ratio, since it is suggested to have a strong influence on the shape of the map. Through the analysis of the turbine losses, the underlying phenomena shaping the efficiency map are explained. A sensitivity analysis of the geometrical dependencies on the map shows a strong impact of the shroud to tip radius ratio, and explains why the Ns-Ds surface of the presented map is smaller than the original one. Compared to the experimentally validated 1D model the new map yields prediction errors below 4%. [ABSTRACT FROM AUTHOR]

In this study, a downdraft gasifier model is coupled with a single-particle model to analyze the effects of particle geometries such as slab, cylindrical, and spherical on different parameters. Simulations were performed using particles in a thermally thick regime with larger particle sizes of 0.003–0.05 m, which are generally used in commercial gasifiers. This combination of the downdraft gasifier model and single particle model was implemented using Comsol Multiphysics software program. The results obtained are in good agreement with those of obtained in previous studies. The low thermal conductivity of biomass ( k B ), small particle size ( d p ), high gas temperature ( T g ), higher molar fraction of oxygen in primary air ( X O 2 ), and high mass-transfer coefficient ( k m ) favor the formation of carbon monoxide ( CO ), hydrogen ( H 2 ), high tar conversion, and higher lower heating value. To maximize the CO composition and tar conversion, the initial gas temperature ( T g ) is more crucial. The least sensitive parameter is the thermal conductivity of biomass ( k B ) in relation to product composition of CO , carbon dioxide ( CO 2 ), H 2 , and methane ( CH 4 ). The sensitivity for all the parameters is found to be the highest for the spherical geometry and is least for the slab geometry. [ABSTRACT FROM AUTHOR]

This paper analyzes the energy consumption of buildings considering the uncertainty of structural and environmental parameters. To this end, two-point estimate method (2PEM) is used to model the uncertainties. EnergyPlus software is used in this paper to evaluate the energy consumption, the thermal comfort, and the energy cost of a building. We examine the proposed method in a retail building to show the effectiveness of the method in comparison with the Monte-Carlo Simulation and deterministic methods. The results show that the 2PEM method although may cause a bit accuracy loss, it can considerably reduce the simulation time by more than 97%. In addition, a sensitivity analysis is effectuated in this paper to investigate the impacts of different climate zones on the results of energy consumption analysis. [ABSTRACT FROM AUTHOR]

The energy used for mechanical cooling systems in buildings in hot climate is about 70%–80% of the total energy consumption. It is important to curtail this part of energy consumption by exploring new technologies. The proposed system is a building integrated photovoltaic thermoelectric (BIPVTE) wall system which combines the concept of active PV façade and solar cooling. We present a complex model of BIPVTE consisting of a PV system and thermoelectric radiant wall system. The thermal and electrical performance of BIPVTE under cooling dominant climates was numerically investigated using experimentally validated system model. The performance of BIPVTE is embodied by comparative analysis with a conventional concrete wall. A steady state analysis was designed to explain and explore the system working mechanism. A sensitivity analysis was conducted for model parameters optimization. With the optimized results, the energy saving potential of BIPVTE in Hong Kong and other 6 cities in Hot Summer and Warm Winter zone of China was implemented. The results indicated that in Hong Kong, the energy saving ratio of BIPVTE is nearly 480%, and the installation of BIPVTE in other 6 cities can save energy ranging from 29.19 kWh/m 2 to 62.94 kWh/m 2 annually. [ABSTRACT FROM AUTHOR]

This article describes an analysis of both a binary and a conventional Rankine cycle for a coal-fired power plant. The major question is whether it is possible to compensate the expected higher capital investment associated with additional components by a lower fuel consumption during the operation. By implementing an exergy analysis, the concept of a binary Rankine cycle with potassium and water as working fluids is compared to a conventional coal-fired power plant. Furthermore, an exergoeconomic analysis is carried out in order to understand the formation and flow of costs in the systems. With the help of sensitivity analyses, we show the impact of uncertain economic parameters, such as fuel cost, capacity factor, or capital investment on the levelized cost of electricity. The comparative exergoeconomic analysis shows that the concept of a binary Rankine cycle is suitable for fuel and emission reduction and economically viable. Under certain conditions, such as a sufficient number of annual equivalent full-load hours, an advantage arises over a conventional coal-fired power plant. [ABSTRACT FROM AUTHOR]

A humidified combined gas power cycle has been theoretically investigated in this paper. The topping cycle is a conventional air Brayton cycle, whereas the bottoming cycle has an air humidifier installed between the compressor and the recovery heat exchanger. Using mass and energy balance equations, the performance of the combined power plant has been calculated and its sensitivity to various operation parameters has been discussed. The energy efficiency and specific power generation varied linearly when the air mass flowrate in the bottoming cycle increased. The performance of the plant initially improved, reached a maximum, and then degraded when the topping cycle pressure ratio was increased. The same qualitative behavior was observed upon increasing the bottoming cycle pressure ratio while maintaining the topping cycle pressure ratio constant. The power output increased in a quasi linear fashion and the energy efficiency increased in a logarithmic fashion when the combustion chamber temperature was increased. In all these cases, humidification of the air after the bottoming cycle compressor proved to be a good means of improving the performance of the power plant, especially when the combustion temperature is low or the bottoming cycle pressure ratio is high. [ABSTRACT FROM AUTHOR]

Energy and exergy analyses were carried out for a medium-capacity methanol plant based on a low-pressure synthesis process for natural gas. The process comprises a pretreatment of natural gas, a steam-methane reforming unit for generation of synthesis gas, a methanol synthesis, a distillation of crude methanol, and an integrated steam cycle for waste heat recovery. Carbon dioxide from carbon capture is used for gas conditioning by adjusting the syngas module for methanol synthesis through counterbalancing of the excess hydrogen. A sensitivity analysis was performed to identify favorable operation parameters for the tubular steam reformer. The energetic and exergetic efficiencies for the overall system were found to be 35.9% and 37.7%, respectively. The specific energy requirements (energy intensities) are 19.6 GJ th /t CH3OH and 0.8 GJ el /t CH3OH , while the specific methane consumption was calculated to be 0.54 ton CH 4 per ton CH 3 OH. Compared to a stand-alone plant, the utilization of carbon dioxide increases the methanol yield by 22%. The exergy analysis shows that the highest inefficiencies occur in the reforming unit, the steam cycle, and the synthesis unit. In particular, the steam reformer, the synthesis reactor, and several heat exchangers show a high potential for thermodynamic improvement. [ABSTRACT FROM AUTHOR]

The performance of a solid oxide fuel cell (SOFC) is subject to inherent uncertainty in operational and geometrical parameters, which can cause performance variability and affect system reliability. Operating conditions such as current demand, cell temperature and fuel utilization play an important role on the degradation mechanisms, which affect typical SOFCs. In previous work, a deterministic empirical degradation model of a SOFC was developed as a function of such operating conditions. By the nature of experimental data and regression fitting, this model was not deterministic. The aim of this work is to evaluate the impact of the uncertainties in the degradation model through a stochastic analysis. In particular, the Response Sensitivity Analysis (RSA), an approximate stochastic method based on Taylor series expansion, is applied to a standalone SOFC model and a fuel cell hybrid system model both subjected to cell degradation. The attention is principally focused on the impact on the fuel cell lifetime. To provide an indication of degradation effect and resulting lifetime uncertainty on economic performance, a cursory economic analysis is performed. [ABSTRACT FROM AUTHOR]

This study aims to evaluate the feasibility of solid oxide fuel cell based combined cooling heating and power (SOFC-CCHP) applications in public buildings of China from different perspectives. Operations of the natural gas fueled SOFC-CCHP systems for 20 years’ have been simulated for five categories of public buildings in five locations of China. Parallel simulations of combustion based CCHP systems and conventional system have been conducted for comparison. By single criterion assessment, SOFC-CCHP systems demonstrate outstanding performance on energy efficiency as well as reducing carbon emission, air pollution and human health damage cost. The levelized cost of energy (LCOE) turns out to be competitive with commercial electricity price, but a long payback period (SPP) has also been identified. To further assess the overall performance of SOFC-CCHP systems, a multi-criteria assessment model has been developed by combining the gray relational analysis (GRA) approach and the entropy-weighting method. The result indicates that hospital, hotel, and supermarket achieve more benefits than office and school; warmer regions rank slightly higher than colder regions. In addition, sensitivity analysis has been performed on SPP and LCOE. Overall, this paper provides theoretical guidance and evaluation approach for SOFC-CCHP demonstrations in China. [ABSTRACT FROM AUTHOR]

Distributed energy system (DES) has become favorite topic for energy saving, but exposed to a range of technical constrains on the system structure, operation strategy and optimization method with gradually accelerating the penetration. Thus, it is significant to study how to make some improvements from these three aspects. This paper proposes a new DES integrating cogeneration, photovoltaic and ground source heat pump (GSHP), which is modeled from energy balances and flows. Considering the high-dimension of the DES without any capacity assumptions, a multi-objective optimization method is built to analyze the annual energy saving ratio ( AESR ), cost saving ratio ( ACSR ) and emission reduction ratio ( AERR ), based on the differential evolution and particle swarm optimization hybrid algorithm and analytic hierarchy process. Then taking a large office in Beijing as the baseline building, a seasonal operation strategy coupled with seasonal adjustment of the cooling/heating share provided by GSHP is developed. The sensitive analysis of the photovoltaic capacity, energy price and objective weights is also performed to show the variation rules of the benefits under different optimization conditions. Results show that the integrated energy system under seasonal operation strategy outperforms the separate system with the AESR , ACSR , AERR of 17.85%, 55.50% and 34.22%. [ABSTRACT FROM AUTHOR]

This paper studies the sensitivity of heat losses in collective heat distribution systems using a simplified calculation method. The approach is applied to a specific type of heat distribution system where the network distributes heat for both space heating and sanitary hot water. The proposed methodology takes design parameters influencing the thermal performance of the heat distribution system into account. Among other parameters, the recirculation control strategy and the length of service pipes are taken into account. The present study assesses the impact of potential variations in the input parameters on the total heat loss and distribution efficiency. To that aim, a simulation study was conducted with a multilevel factorial design, consisting of the combinations of parameters which were varied from the levels at which they were set. Results show how sensitive the solution is to the different parameter values. Furthermore, the potential of the improved calculation method, which allows combining different design conditions within a single heating distribution system, was demonstrated. [ABSTRACT FROM AUTHOR]

The effects of the above-mentioned parameters on exergy destruction, and CO 2 emission of the power plant are determined for circulating fluidized bed power plant co-firing. The aim of this study is to perform thermodynamic analysis on Çan Circulating Fluidized Bed Power Plant (CFBPP) co-fired with olive pits. The results of this study also show that the total exergy damage of the plant is about 295 MW and the net exergy yield is 31.26%. The majority (252.40 MW) of exergy destruction occurs in the main boiler and accounts for 86.05% of the total exergy breakdown of CFBPP through exergy analysis. The results show that CFBPP has an effective feature of biomass supplement for exergetic performance and CO 2 emissions. [ABSTRACT FROM AUTHOR]

Distinct secondary gas injection modes of a vortexing fluidized-bed combustor (VFBC) affect combustion fraction distribution, resulting in different combustion and pollutant emissions characteristics. To determine the important operational conditions, correlations that consider most of the VFBC parameters were derived to predict the in-bed combustion fraction in VFBC. The predictions obtained using the regression correlation analysis were in good agreement with the results of present experiments and with previously published results. Response surface methodology (RSM) was used to analyze the sensitivity of different coded factors based on established model. A new correlation equation, with a fewer parameters, based on the sensitivity analysis, was also developed and exhibited a positive predictive accuracy. Results demonstrate that the primary gas ratio, particle size, and fuel type significantly affect the combustion fraction. The in-bed combustion fraction increases with increasing particle size, and decreases with increasing primary gas ratio and the ratio of volatile to fixed carbon. [ABSTRACT FROM AUTHOR]

This paper proposes a novel risk assessment method for power network failures considering a uniform-pricing market environment, different from previous risk assessment studies, which mainly emphasize technical consequences of the failures. In this type of market, dispatch infeasibilities caused by line failures are solved using a counter-trading mechanism where costs arise as a result of correcting the power dispatch. The risk index proposed takes into account these correction costs as well as the cost of the energy not served due to the failure, while considering an oligopolistic behavior of the generation companies. A 3-stage model is proposed to simulate the bidding behavior in the market, under different line failures scenarios. The risk index proposed and the method for its calculation are applied on an adapted IEEE 6-bus reliability test system. A sensitivity analysis is performed to investigate the sensitivity of the results with respect to the level of competitiveness of the generation companies, measured by the conjectured-price response parameter which is assumed to be exogenous in our study. [ABSTRACT FROM AUTHOR]