Exergy Analysis Research Articles

Simulation and optimization of DMC synthesis process based on conventional and advanced exergy analyses

Dimethyl carbonate has received more and more attentions as an organic solvent in electrolytes. Aiming at the problem of high energy consumption in the process of dimethyl carbonate (DMC) production, the root of the problem was analyzed by using exergy analysis, which provides a theoretical basis for the construction of energy-saving process. Firstly, the overall process of DMC production was constructed, including propylene carbonate (PC) synthesis, DMC synthesis, azeotrope separation and propylene glycol (PG) purification processes. Secondly, the conventional and advanced exergy analyses of the four proposed processes were carried out. The distributions of exergy and exergy destruction were obtained through conventional exergy analysis. The exergy destructions were further divided through advanced exergy analysis, and the avoidable parts were focused on. Based on the above analyses, the corresponding heat integration processes were proposed. Finally, the conventional processes and the heat integration processes were evaluated with the performance indicators of the exergy destruction, total annual cost (TAC), total energy consumption (TEC) and CO2 emissions.

Performance optimization for solar photovoltaic thermal system with spiral rectangular absorber using Taguchi method

Solar collector systems efficiently transform sunlight into energy that may be used to meet various needs. This research aimed to use the Taguchi method to determine the ideal operating parameters for a solar thermal collector with a rectangular spiral absorber. Controllable parameters including mass flow rate, solar radiation, and absorber design were manipulated during the energy recovery process, and features like PV temperature and outlet water temperature were used to assess the system’s effectiveness. The findings indicate that certain criteria significantly affect response indicators. The observed percentage contribution of absorber design, solar radiation, and the mass flow rate was 69.19%, 27.99%, and 2.83% in PV surface temperature. In comparison, the individual percentage contributions were 73.63%, 13.51%, and 10.57% for absorber design, solar radiation and mass flow rate for water output temperatures. The present model’s R2 values for PV and outlet water temperatures are 97.24% and 99.67%, respectively. The Predictive regression model was found in fine harmony and the maximum percentage error is limited to 0.68%. The maximum analytical electrical efficiency was observed with a spiral rectangular absorber of 14.57% at the lowest mass flow rate of 0.04 kg/s at the lowest radiation level of 600 W/m2. In comparison, maximum analytical thermal efficiency was observed with a spiral rectangular thermal absorber of 63.56% at the highest flow rate of 0.06 kg/s and the highest solar radiation level of 1000 W/m2. The analytical and experiment findings were in better agreement in this study, with the highest relative error of 7.52%. According to the study’s findings, the rectangular absorber-based PVT system is at its best at a higher mass flow rate to lower PV temperature and boost thermal energy recovery via water. The present research work can be extended for exergy, environmental, and economic feasibility analysis.

Performance improvement and multi-objective optimization of a two-stage and dual-temperature ejector auto-cascade refrigeration cycle driven by the waste heat

This paper presents a two-stage and dual-temperature ejector auto-cascade refrigeration cycle (TEARC) driven by the waste hot water and low-pressure exhaust steam in chemical plants. In this cycle, a throttle valve is provided between the condenser outlet and separator inlet to regulate the composition and mass flow ratio of mixture refrigerant in the two evaporators. The specific enthalpies of refrigerant at the low-temperature (LT) evaporator and medium-temperature (MT) evaporator inlet are respectively reduced via the evaporative condenser and separator, leading to an enhancement in cooling capacity. Energy, exergy, and economic (3E) analyses are conducted to compare the performance between the TEARC and the basic two-stage and dual-temperature ejector refrigeration cycle (BTERC). At the basic operating condition, the TEARC has enhancements of 9.13 % and 9.95 % in COP and exergy efficiency than those of the BTERC. According to the multi-objective optimization results, it indicates that the TEARC's COP, exergy efficiency, and levelized cost of cooling are respectively improved by 8.93 % and 5.67 % and reduced by 1.22 % compared to the BTERC at optimum operating conditions. The simulation results of the proposed cycle reveal a significant performance improvement and the potential for application in waste heat-driven refrigeration.

Exergy based yearly performance analysis of a poly-generation system for a small-town application

The current study conducts a comprehensive year-round exergy analysis of an integrated system centered around a reversible solid oxide cell (RSOC), aimed at fulfilling the power and fresh water requirements of a small town, equivalent to 2.7 MW and 2000 m³/day, respectively. The integrated system encompasses four subsystems: the solar field, RSOC, organic Rankine cycle coupled with ejector cooling (ORC), and zero liquid discharge multi-effect desalination (MED-ZLD). The proposed system is analyzed using MATLAB. The annual exergy efficiency for each subsystem is examined, yielding average values of 11.9 %, 48.11 %, and 56.22 % for the solar field, ORC cycle, and MED-ZLD, respectively. Notably, the exergy efficiency of the Rankine cycle is higher in colder months compared to warmer ones. This phenomenon is attributed to the cycle's greater heat generation relative to the cooling it produces during the cold season. The RSOC exhibits noteworthy average exergy efficiencies of 93 % in electrolysis mode, 69.87 % in fuel cell mode, and an overall average exergy efficiency of 79.62 % throughout the year. The average exergy efficiency of the overall system is evaluated throughout the day, nighst, and the entire operational period. The results are values of 10.74 %, 34.31 %, and 23.34 %, respectively. This discrepancy is due to the primary energy supply source, which is solar energy during the day and input hydrogen during the night. The highest exergy efficiency is observed in December, while the lowest is in June. Furthermore, the study examines the distribution of exergy destruction and identifies cycles with significant impacts by analyzing the exergy destruction ratio across various months. The solar field is the primary contributor to daytime exergy destruction, peaking at 94.9 %. At night, the MED-SET cycle leads in exergy destruction, followed closely by the RSOC cycle operating as a fuel cell. The research also delves into exploring key contributors to exergy destruction in various cycles, shedding light on crucial insights into the intricate dynamics of the integrated system's performance.

Thermodynamic and advanced exergy analysis of Rankine Carnot battery with cascaded latent heat storage

Cascaded latent heat storage offers significant advantages in Rankine Carnot battery systems by minimizing exergy destruction during heat transfer processes. However, the system performance and the sources of exergy destruction remain unclear, and the configuration of multiple phase change materials remains ambiguous. This paper investigates a Rankine Carnot battery system integrated with cascaded latent heat storage using energy, conventional exergy, and advanced exergy analysis methods. First, a novel phase change material partitioning configuration scheme is proposed, considering the phase change of the working fluid, significantly improving temperature matching within the storage. The number of stages in heat storage devices significantly affects system performance, with roundtrip and exergy efficiencies increasing by 32.2 % and 15.2 % as the number of stages rises from 1 to 4, though further increases have minimal impact. Advanced exergy analysis on a 4-stage system indicates that the endogenous avoidable exergy destruction of the expander, compressor, evaporator, and condenser constitutes 12.4 %, 12.0 %, 10.5 %, and 7.0 % of the total system exergy destruction, respectively, highlighting the priority components for system improvement. Furthermore, raising the heat storage temperature by 45 °C reduces roundtrip efficiency by 26.5 % while increasing power output by 63.2 %. Increasing the heat pump’s evaporation temperature by 30 °C improves roundtrip efficiency by 151.1 % but reduces power output by 33.7 %. Reducing the amount of waste heat and surplus electricity results in a significant decrease in the roundtrip efficiency and exergy efficiency, which is mainly caused by the reduction in the isentropic efficiencies of compressor and expander under partial load conditions. The findings on the priority components for system improvement and the configuration of cascaded latent heat storage provide an effective approach for enhancing Rankine Carnot batteries.

Energy and exergy analysis of a two-stage cascade vapor compression refrigeration system with modified system configuration

This study proposes a modification to the two-stage cascade vapor compression refrigeration system by adding internal heat exchangers that function as subcoolers and desuperheater. The influence of each internal heat exchanger proposed on the exergy destruction rate, exergy efficiency, compressor power consumption, ECOP, and COP of the system was investigated. Additionally, various refrigerant combinations were considered as working fluids to evaluate which combination is the most suitable for the proposed system. Mathematical models based on the principles of thermodynamics were established in Engineering Equation Solver (EES), a software used for energy and exergy analysis. The results reveal that the addition of specific internal heat exchangers causes either an increase or decrease in overall system performance, depending on the type of refrigerant combination used. Consequently, there exists an optimal system configuration for each refrigerant combination. Compared with the conventional two-stage cascade refrigeration system, the optimal system configurations in the present study exhibited higher overall system performance. A maximum increase in exergy efficiency, ECOP, and COP of 7.31 %, 9.8 %, and 7.3 %, respectively, can be observed with the refrigerant combination R450A/R404A. Additionally, the results of the exergy analysis identify that the HTC compressor, condenser, LTC compressor, and cascade condenser are the primary contributors to the exergy destruction rate within the system.

Energy, exergy and exergoeconomic analyses and ANN-based three-objective optimization of a supercritical CO2 recompression Brayton cycle driven by a high-temperature geothermal reservoir

The use of CO2-based power cycles to harness high-temperature geothermal resources is an interesting application that has been little explored. Therefore, to obtain a more holistic understanding of these systems, in this work, a supercritical CO2 recompression Brayton cycle is assessed. For comparison, the performances of a recuperative cycle and a recompression cycle with intercooling were also computed. Detailed mathematical models were developed and then, artificial neural network-based surrogate models were adopted to conduct multi-objective optimization. Results of the baseline simulations show that, the high temperature recuperator and the turbine are the most important components from both exergy and exergoeconomic approaches. The optimizations reveal that the intercooled cycle is superior to the other layouts in all the cases while the recuperative cycle is not feasible with reinjection temperatures greater or equal to 150 °C. When the reinjection temperature is constrained to 150 °C, the intercooled cycle attains 4472.70 kW, 62.10 % and 14.42 $/GJ for net power, exergy efficiency and product unit cost, respectively, whereas without this constraint, it achieves 5394.09 kW, 61.83 %, 11.79 $/GJ. In conclusion, the adoption of advanced layouts of the CO2 cycle is beneficial for this application from both technical and economic points of view.

Optimizing integrated energy systems at park level: A cooperative game approach with exergy economics

This study presents a comprehensive framework for optimizing energy systems by integrating exergy analysis, energy economics, and game theory. The concept of exergy, which quantifies the usable energy within a system, is employed to evaluate energy efficiency and losses across various energy sources, including thermal, cooling, chemical, and electrical systems. Stoichiometric coefficients, denoted by the factor λ, are utilized to simplify exergy calculations for different energy types and processes. The economic evaluation of energy flows is conducted through energy economics principles, incorporating cost allocation and balance equations. The integration of game theory into the optimization model ensures strategic interactions among energy components, leading to a Nash equilibrium that balances economic performance, efficiency, and environmental sustainability. The model also accounts for emissions and the required proportion of renewable energy. To solve the complex optimization problem, a modified Particle Swarm Optimization (PSO) algorithm is employed, featuring adaptive mechanisms for velocity and inertia updates, enhancing the search process for the optimal solution. The proposed framework is designed to optimize the Integrated Energy System (IES) efficiently, ensuring sustainable and economically viable energy management. The analysis of optimization strategies highlights a trade-off between cost and efficiency. Strategy 1, focused on minimizing cost, achieves the lowest cost at 4069.37 CNY, 25.79 % less than Strategy 2, but with a reduced exergy efficiency of 59.82 %, which is 10.14 % lower than Strategy 2′s 68.47 %. Strategy 3 offers a balanced approach, with a cost of 4970.89 CNY, 9.43 % higher than Strategy 1 but 9.43 % lower than Strategy 2. It achieves an exergy efficiency of 67.87 %, only 0.60 % lower than Strategy 2, thus providing a practical compromise between economic performance and efficiency.

Exergetic characterization of flat plate solar collector using genetic algorithm

With the rapid advancement of technology, the global demand for energy is increasing exponentially. It is crucial to focus on energy conservation and conversion across all sectors. This study conducted a second law or exergy analysis on a solar water heating system to uncover hidden losses during the process. To optimize exergetic efficiency, a genetic algorithm was employed to control the overall loss coefficient of a solar flat plate collector. Four decision variables were used in the genetic algorithm—heat flux rate, glass cover temperatures at the inlet and exit, and collector plate temperature to minimize the overall loss coefficient. Energy efficiency, entropy generation, and exergy destruction were estimated for various mass flow rates using thermodynamic equilibrium equations. Exergy correlations were developed concerning mass flow rate (0.001–0.009 kg/s), inlet temperature (300 K–360 K), collector plate area (1–10 m²), incident solar energy (400–900 W/m²), optical efficiency (0.4%–1%), and ambient temperature (300–315 K) under a range of initial conditions. It was found that exergy efficiency slightly increased (0.01%–0.08%) over a 12-h period. Although this increase is small, it can significantly contribute to energy conservation over the long term. The genetic algorithm predicted the minimum loss coefficient occurring during peak hours (12–14 p.m.) with respect to four decision variables. The results of this study were compared with existing literature and showed good agreement. In addition to the exergy analysis, an uncertainty error analysis was performed to assess the reliability and accuracy of the experimental measurements and computational predictions. By quantifying these uncertainties, the study ensured that the reported enhancements in exergy efficiency and the optimization results obtained through the genetic algorithm are robust and credible. This rigorous error analysis adds confidence to the findings, highlighting the potential for improved energy conservation in solar water heating systems.

Development of a geothermal-driven multi-output scheme for electricity, cooling, and hydrogen production: Techno-economic assessment and genetic algorithm-based optimization

This study aims to develop an environmentally friendly multi-energy system for sustainable production of electricity, cooling and hydrogen. The study introduces a pioneering geothermal-based system, integrating an ejector refrigeration cycle, a dual-loop organic Rankine cycle, and a hydrogen production unit with proton exchange membrane electrolyzers. The study provides a thorough analysis of the system's energy and exergy performance, as well as its economic feasibility. Through sensitivity and parametric analyses, the research identifies key parameters that significantly influence system performance. The system's innovative design promises minimal environmental impact while delivering multifaceted performance: generating 1.38 MW of electricity, supplying 436 kW of cooling load, and producing 5.39 kg/h of hydrogen. In the exergy analysis, Evaporator1 is identified as the primary contributor to exergy loss, representing 34 % of the total exergy destruction. This is followed by the electrolysis unit, the condenser, and the ejector refrigeration cycle, which contribute 18 %, 14 %, and 12 %, respectively. The system achieves optimal efficiency at an organic Rankine cycle turbine1 inlet temperature of 387 K, yielding a power generation of 885.4 kW and an exergy efficiency of 26.7 %. Beyond this temperature, any further increase leads to a decline in power output due to operational disturbances. A multi-criteria optimization using genetic algorithm is applied, resulting in an optimized system with a cost rate of 18.13 $/h and an exergy efficiency of 38.96 %.

Thermal and exergy analysis of solar air heater enhanced with sodium carbonate decahydrate and Magnesium sulfate heptahydrate PCM: Performance evaluation

The advancement of renewable solar energy is prospective for energy, heat exchanger, and air heater applications. The main objective of the present research is enhancing the solar air heater thermal performance by the modification of a collector absorber-like plain absorber featuring rectangular fine (SAH 2) and sodium carbonate decahydrate (Na2CO3·10H2O) and Magnesium sulfate heptahydrate (MgSO4·7H2O) PCM with rectangular fin (SAH 3). During the experimental evaluation, the airflow varied by 0.042 and 0.059 kg/s. Influences of collector modification on the functional behaviour of solar air heaters (SAH) are evaluated. Its results are compared to the system of conventional setup without modification of the solar collector with a plain absorber (SAH-1). With the excellence of Na2CO3·10H2O/MgSO4·7H2O with fin setup performed with 0.059 kg/s found better heat transfer performance including heat gain, thermal & exergy efficiency, heat loss coefficient, and PCM temperatures like 927.3 W, 78.6 %, 33.6 %, 16.9 W/m2K, and 68.3 ⁰C respectively. Moreover, Increasing the airflow rate leads to improved heat transfer, and the SAH proves to be effective at higher flow rates when equipped with fins and PCM.

Proposals for Next-Generation Eco-Friendly Non-Flammable Refrigerants for a −100 °C Semiconductor Etching Chiller Based on 4E (Energy, Exergy, Environmental, and Exergoeconomic) Analysis

Recent advancements in cryogenic etching, characterized by high aspect ratios and etching rates, address the growing demand for enhanced performance and reduced power consumption in electronics. To precisely maintain the temperature under high loads, the cascade mixed-refrigerant cycle (CMRC) is predominantly used. However, most refrigerants currently used in semiconductor cryogenic etching have high global warming potential (GWP). This study introduces a −100 °C chiller using a mixed refrigerant (MR) with a GWP of 150 or less, aiming to comply with stricter environmental standards and contribute to environmental preservation. The optimal configuration for the CMRC was determined based on a previously established methodology for selecting the best MR configuration. Comprehensive analyses—energy, exergy, environmental, and exergoeconomic—were conducted on the data obtained using Matlab simulations to evaluate the feasibility of replacing conventional refrigerants. The results reveal that using eco-friendly MRs increases the coefficient of performance by 52%, enabling a reduction in compressor size due to significantly decreased discharge volumes. The exergy analysis indicated a 16.41% improvement in efficiency and a substantial decrease in exergy destruction. The environmental analysis demonstrated that eco-friendly MRs could reduce carbon emissions by 60%. Economically, the evaporator and condenser accounted for over 70% of the total exergy costs in all cases, with a 52.44% reduction in exergy costs when using eco-friendly MRs. This study highlights the potential for eco-friendly refrigerants to be integrated into semiconductor cryogenic etching processes, responding effectively to environmental regulations in the cryogenic sector.

Determination of the energy efficiency of granulation equipment based on exergy analysis

The object of research is the process of granulation of mineral fertilizers by applying rolling and pouring methods, as well as in fluidized and suspended layers with active hydrodynamics of flows. It is noted that the development of the main technological stages of the production of granulated fertilizers should be aimed at improving the hardware design of granulators, establishing the most rational regime and technological parameters of the process in order to increase its efficiency and reduce energy costs. It is noted that the main indicators of the efficiency of granulation plants using heat are economic costs, exergy losses, as well as reduced costs. The method of exergy analysis for the assessment of energy costs for granulation processes in different types of granulators is presented, which allows to justify the choice of rational parameters of the specified processes, taking into account energy costs and equipment efficiency. Equations are presented for determining the amount of exergy of material flows and exergy losses caused by heat exchange at finite temperature differences of technological flows at the entrance to the device and at the exit from it. The equation for determining the exergy efficiency, which characterizes the energy efficiency of the technical system, is presented. The smaller the temperature difference for the technological flows at the exit from the device, the smaller the exergy losses, the higher the value of the exergy efficiency. and, accordingly, the device will have greater energy efficiency. An exergy analysis of granulation processes in granulation towers without a cooler, in granulation towers with a cooler, fluidized bed devices and multi-stage (shelf) devices was carried out. The analysis showed that the exergy efficiency for the specified granulation plants is equal to: 64 %, 71 %, 32 % and 96 %, respectively. The obtained research results can be applied in production conditions where granulation towers and devices of fluidized or suspended layers are used. Enterprises that plan to reduce energy costs and increase the environmental safety of their technological processes can implement improvements based on the proposed methods and equations. The application of research results will contribute to the selection of more rational indicators of the granule production process, which will increase the productivity and quality of the final product.

Exergy and energy analysis on the performance of high thermal conductivity material in PV/T system: An experimental approach

The energy loss of any system might be affects the performance. This paper focuses on the investigation of 10E: Exergy, Energy, Environmental, Economic, Exergo-Enviro-Economic, Energo-Economic, Energo-Enviro, Exergo Economic, Enviro-Economic and Exergo-Environmental analysis. The energy loss of PV/T can be mitigated by incorporating with the mixture of Aluminium, Copper and Iron as high thermal conductivity material. Energy output per-year for the developed PV is 0.9960 kW-hour. The energy output per-year for the developed solar still is 117.913 kW-hour. The Capacity Utilisation Factor for the developed system increased from 2.77 percent to 2.91 percent compared to the conventional. The Levelized Cost of Electricity for the Conventional-Solar-Still is deemed to be 3.39 $ whereas for the developed work it is 3.46 $. The output exergy per-year for the developed PV system is 140.08 kW-hour and in developed solar-still, it is 12.798 kW-hour. Gross Carbon Reduction is observed as 94 tCO2. The Carbon-Payback-Period for the developed system is 34.72 years. The estimated cost per litre of the developed work is 0.018$, 0.016$ and 0.015$ for considering the period of 15 years, 20 years and 30 years. Overall, the 10E framework of developed PV/T system provides the significant performance.

Analysis of the exergy transfers in subcritical and transcritical CO[formula omitted] ejectors and their connection with the performance of the refrigeration cycle

Ejector refrigeration systems (ERSs) operating with carbon dioxide are notoriously challenging from both design and operation perspectives. In particular, the ejector itself gives rise to special attention since it directly affects the performance of the global system. In this study, the connections between local exergy transfers within the ejector and global cycle performance are investigated by using a novel multi-scale numerical approach. Computational Fluid Dynamics (CFD) is used to generate accurate predictions of the ejector operation with access to the local flow and heat transfer features. The exergy tube analysis is applied onto the simulation results, linking local transfers within the ejector to the results at the component- and cycle-scale. A state-of-the-art ejector thermodynamic model is then calibrated onto the CFD results, and employed to determine the physically possible operation of the ERS. In addition, the metastability impact on the exergy transfers and overall system performance is investigated by comparing the CFD results of the classical Homogeneous Equilibrium Model with those obtained with the Homogeneous Relaxation Model. Notably, it is found that at fixed ejector inlet conditions, there exits an outlet pressure that maximizes the exergy transfers from primary to secondary streams. Interestingly, this work shows for the first time that the maximum exergy gain of the secondary stream appears to correlate with the maximum coefficient of performance of the system, independently of the on- or off-design operation of the ejector. Moreover, metastability generally deteriorates the performance at both scales. The results of the present study serve to pave the way towards better ejector design objectives.

Optimizing solarized desalination unit through the implementation of 4-step MED method using energy, exergy, economic and environmental analysis

The consumption of thermal energy in thermal desalination plants leads to a higher price for the fresh water they produce compared to other methods. By utilizing optimization techniques, it is possible to lower both energy consumption and price. The focus of this paper is on optimizing a solarized desalination unit through the implementation of the 4-step MED method with a PTC collector. To achieve this objective, the NSGA II algorithm was implemented in MATLAB using a function for optimization. This algorithm is known for its cost-effectiveness and high energy efficiency. According to the results, there has been an improvement in the fresh water flow rate, desalination efficiency, and GOR, with values reaching 126.87, 53.6%, and 3.66 respectively, compared to the previous values of 116.5, 49.21%, and 3.32. In the ideal condition, the power generated is 6089 kW, priced at 3.28 cents per kilowatt, and the cost of producing fresh water is 8.49 dollars per cubic meter, which decreases as the process lifespan increases. Solar collectors and thermal tanks account for the largest portion (64%) of exergy destruction, as indicated by the exergy analysis. Optimization of the process has led to energy and exergy efficiencies of 59.8% and 58%, respectively, representing a notable enhancement of around 10% in the system's lifespan. The optimal mode also includes the completion of the sensitivity analysis. The process was subjected to LCA analysis, and the results indicated that the largest impact is on human health, with the collectors and thermal storage tanks being responsible for most of the pollution. As a result, the optimized process has delivered outstanding results while also being environmentally conscious.

Thermo-economic investigation and comparative multi-objective optimization of dual-pressure evaporation ORC using binary zeotropic mixtures as working fluids for geothermal energy application

This contribution performs an energy, exergy, and exergoeconomic (3E) analysis of a dual-pressure evaporation organic Rankine cycle system employing twenty different binary zeotropic mixtures as working fluids for power production from a geothermal field. To this end, the designed system is modeled, invoking the mass and energy conservation laws and the exergy and cost balance analyses. Specific Exergy Costing (SPECO) procedure is utilized to provide practical insights into the exergoeconomic aspect of the system. Comparative optimization based on the multi-objective genetic algorithm is accomplished for each mixture in order to simultaneously maximize the exergy efficiency and minimize the total cost rate using the design variables of pressure factor in low-pressure and high-pressure stages, mixture fraction, pinch point temperature differences in low-pressure and high-pressure heat exchangers, and degree of superheat in the high-pressure heat exchanger. In this regard, the Pareto frontiers are drawn for the system with all twenty different binary zeotropic mixtures. The optimal point for each mixture is obtained via the decision-making technique of LINMAP. Subsequently, the LINMAP is re-utilized to find the preferred mixture. The optimization results suggest the R123/C2Butene (96.89/3.11) mixture for this system as the optimum working fluid, considering a trade-off between a low-cost rate of $88.0651 per hr and a high exergy efficiency of 64.07 %. Finally, the exergy flow diagram is plotted to provide the exergy flow rate and the amount of exergy destruction in each segment of the system considering the optimal working fluid. In the proposed system, exergy destruction chiefly occurs within the low-pressure preheater with a value of 1061 kW, followed by the low-pressure turbine and condenser with magnitudes of about 669 kW and 266 kW, respectively.

Performance Assessment and Improvement of Photovoltaic-Thermal System based on Energy, Exergy, Economic and Environment Analysis

Performance Assessment and Improvement of Photovoltaic-Thermal System based on Energy, Exergy, Economic and Environment Analysis

A Thermodynamic Comparison of Exergy Production from Sugarcane and Photovoltaic Modules in the Context of Brazilian Energy Transition

This article applies the exergy analysis to the production and use of sugarcane, considering a model published in the literature. In this way, we compute incident solar irradiation, carbohydrate production, water consumption, and the production of stalks and straws. Following the production estimate, we analyze a biorefinery production cycle, from solar irradiation to the biorefinery products on an exergy basis, from birth to production of sugar, electrical energy, and ethanol. The calculated sugarcane production values are 80.7 tons per hectare for a 52-week cycle. As a result, the average exergy efficiency of sugarcane is 4.99%, reaching peaks of 8.3%. When considering only the useful exergy generated in the production of stalks and straw, an annual yield of 17.86 kWh/m2 represents an overall exergy efficiency of 1.31%. Considering the energy conversion processes in the biorefinery, the exergy efficiency from the radiation to the products from the biorefinery was 0.38%. The photovoltaic modules already have a well-established application in the country, though they need to increase their insertion over time, whereby the panels exhibit an average exergy efficiency of 31.6%, resulting in an annual electrical energy production of 255.84 kWh/m2. The results show that photovoltaic modules are a more efficient alternative than sugarcane regarding exergy land use. In conclusion, this study briefly discusses the use of sugarcane and photovoltaic modules in the context of Brazil’s energy transition towards a reduced dependence on fossil fuels, based on the fact that sugarcane already has a low carbon footprint for transportation using ethanol, with supply from more than 40,000 stations, and a similar or lower carbon footprint than electrical vehicles used across the country.

Enhancing efficiency and economy of hydrogen-based integrated energy system: A green dispatch approach based on exergy analysis

Hydrogen-based integrated energy system holds promise for leveraging the low carbon advantage of hydrogen, but inefficiency of electrolysis hydrogen production leads to significant exergy loss within its operation. Addressing this, this paper focuses on the energy-saving and economic operation of the hydrogen-based integrated energy system, proposes a novel green dispatch approach using loss cost as the objective function and establishes a refined loss cost accounting model based on exergy analysis theory. Firstly, derived from the analogy of exergy loss, the concept and accounting framework of system loss cost are proposed. Secondly, employing exergy analysis and consistent unit exergy cost principle, equipment operation loss cost is calculated through energy, exergy flows analysis and cost allocation. Thirdly, utilizing the total of equipment operation loss cost, wind curtailment penalty cost, and transmission line loss cost as the objective function, a green dispatch model is formulated to minimize overall loss cost while ensuring energy balance and other constraints. Finally, simulations analysis are conducted. The results show that compared to economic dispatch, minimized exergy loss dispatch and multi-objective dispatch methods, proposed approach increases exergy efficiency by 0.54 %, reduces cost by 6.13 % and increases the scale of hydrogen utilization by 3.45 %, respectively.