Search Results (32)

Achieving energy sustainability is a major challenge across all sectors of an economy. In agri-food systems (AFSs), this challenge is twofold in the context of energy sustainability; one challenge is to reduce fossil fuel dependency, and another challenge is to provide safe and nutritious food for humans and animals. An appropriate aggregate indicator needs to be used for assessing the energy sustainability of AFSs. This study presents a systematic literature review aimed at developing a core indicators framework to support both research and policymaking. It also critically evaluates and updates existing indicators currently used to evaluate energy sustainability in AFSs, considering environmental, economic, social and technical dimensions. Environmental indicators, such as energy use efficiency, net energy balance, carbon footprint, exergy destruction and renewable energy share, measure the ecological impacts of agricultural practices. Economic indicators, including energy cost share, levelized cost of energy, energy return on investment, and productivity per unit of energy input, reflect how energy use influences farm competitiveness and resilience. Social indicators such as equitable access to energy, labor productivity gains, and system resilience to energy shocks highlight the broader human and societal aspects of energy sustainability. Technical indicators, including technology performance, maintenance intensity, technology lifespan, and resource circularity, emphasize the need to minimize resource depletion and environmental harm. Together, these sustainability indicators provide a strong framework for assessing trade-offs and guiding policy decisions that support the transition toward low-carbon, resilient, and resource-efficient AFSs. Their effective development and implementation require interdisciplinary knowledge integration and active engagement with relevant societal stakeholders in a transdisciplinary sustainability context. Full article

Considering the implementation of the circular economy and the concept of sustainable development, there is a growing need to reduce resource consumption and the environmental impact of industrial processes. This is particularly important in the sugar industry, which is characterized by high energy intensity and a complex process structure. The aim of this paper is to conduct a narrative review of the latest research from 2021–2026 on the assessment of technological processes in the sugar industry from an energy and environmental perspective. The analysis includes approaches such as life-cycle assessment, carbon footprint analysis, energy indicators, and methods related to the circular economy. The results of the review indicate that existing research focuses primarily on selected process aspects, such as greenhouse gas emissions, energy consumption, or by-product management. However, approaches integrating environmental, energy, cost, and process analysis are lacking. This paper identifies a significant research gap and proposes a direction for filling it by integrating dynamic life-cycle assessment, exergy analysis, material flow and energy costing (MFCA), and process–energy modeling. This approach provides a comprehensive framework for process evaluation and supports the identification of improvement strategies that minimize energy consumption, environmental burdens, and production costs while preserving process efficiency. Full article

In the context of dual-carbon goals, Park-Level Integrated Energy Systems (PIES) are pivotal for enhancing renewable energy integration and promoting clean, efficient energy use. However, the inherent non-linearity from multi-energy coupling and the high dimensionality of operational data present substantial challenges for conventional scheduling optimization methods. To overcome these obstacles, this paper introduces a novel multi-objective scheduling framework for PIES leveraging deep reinforcement learning. We innovatively formulate the scheduling task as a Markov Decision Process (MDP) and employ the Trust Region Policy Optimization (TRPO) algorithm, which is adept at handling continuous action spaces. The state and action spaces are meticulously designed according to system constraints and user demands. A comprehensive reward function is then established to concurrently pursue three objectives: minimum operating cost, minimum carbon emissions, and maximum exergy efficiency. Through comparative analyses against other AI-based algorithms, our results demonstrate that the proposed method significantly lowers operating costs and carbon footprint while enhancing overall exergy efficiency. This validates the model’s effectiveness and superiority in addressing the complex multi-objective scheduling challenges inherent in modern energy systems. Full article

This study presents a comprehensive sustainability assessment of open field strawberry production in Batman, Türkiye, utilizing thermodynamic-based analyses. The inputs used during the production phase were obtained through survey data collected from local farms over the past few growing seasons. This study is the first to provide an integrated energy, exergy, and environmental assessment of open-field strawberry production in the Batman region, offering novel insights into resource efficiency and sustainability evaluation in agricultural systems. The evaluation was conducted for a functional unit of one ton of strawberries by analysing the cumulative energy consumption (CEnC), cumulative exergy consumption (CExC), and cumulative carbon dioxide emissions (CCO₂E). The total CEnC was calculated to be 1207.8 MJ/ton, with nitrogen fertilizer (390.91 MJ/ton) and diesel fuel (229.67 MJ/ton) being the most significant inputs. The total CExC was 1919.82 MJ/ton, where farmyard manure (1170.19 MJ/ton) was the dominant contributor, accounting for approximately 61% of the total. The total carbon footprint (CCO₂E) was determined to be 41.43 kg/ton, with irrigation water (10.19 kg/ton) and farmyard manure (10.14 kg/ton) being the primary sources. Key sustainability indicators, the Cumulative Degree of Perfection (CDP) and Renewability Indicator (RI), were calculated as 1.34 and 0.26, respectively. The CDP value is notably higher than that of other open field strawberry studies, while the low RI value indicates a heavy reliance on non-renewable resources. The findings highlight that improving sustainability requires a focus on efficient manure management and reducing fossil fuel-based energy consumption. Full article

Geothermal energy has been recognized as a promising renewable resource for sustainable power generation; however, the efficiency of conventional geothermal power plants has remained relatively low, and high investment costs have limited their competitiveness with other renewable technologies. In this context, the present study introduced an innovative geothermal electricity generation system aimed at enhancing energy efficiency, cost-effectiveness, and sustainability. Unlike traditional configurations, the system raised the geothermal source temperature passively by employing advanced heat transfer mechanisms, eliminating the need for additional energy input. Comprehensive energy, exergy, and exergoeconomic analyses were carried out, revealing a net power output of 43,210 kW and an energy efficiency of 30.03%, notably surpassing the conventional Kalina cycle’s typical 10.30–19.48% range. The system’s annual electricity generation was 11,138.53 MWh, with an initial investment of USD 3.04 million and a short payback period of 3.20 years. A comparative assessment confirmed its superior thermoeconomic performance. In addition to its technoeconomic advantages, the environmental performance of the proposed configuration was quantified. A streamlined life cycle assessment (LCA) was performed with a functional unit of 1 MWh of net electricity. The proposed system exhibited a carbon footprint of 20–60 kg CO₂ eq MWh⁻¹ (baseline: 45 kg CO₂ eq MWh⁻¹), corresponding to annual emissions of 0.22–0.67 kt CO₂ eq for the simulated output of 11,138.53 MWh. Compared with coal- and gas-fired plants of the same capacity, avoided emissions of approximately 8.6 kt and 5.0 kt CO₂ eq per year were achieved. The water footprint was determined as ≈0.10 m³ MWh⁻¹ (≈1114 m³ yr⁻¹), which was substantially lower than the values reported for fossil technologies. These findings confirmed that the proposed system offered a sustainable alternative to conventional geothermal and fossil-based electricity generation. Multi-objective optimization using NSGA-II was carried out to maximize energy and exergy efficiencies while minimizing total cost. Key parameters such as turbine inlet temperature (459–460 K) and ammonia concentration were tuned for performance stability. A sensitivity analysis identified the heat exchanger, the first condenser (Condenser 1), and two separators (Separator 1, Separator 2) as influential on both performance and cost. The exergoeconomic results indicated Separator 1, Separator 2, and the turbine as primary locations of exergy destruction. With an LCOE of 0.026 USD/kWh, the system emerged as a cost-effective and scalable solution for sustainable geothermal power production without auxiliary energy demand. Full article

To meet the high standards required for the liquefaction process by the Floating Liquefied Natural Gas System (FLNG), including low power consumption, compact footprint, high safety, resistance to waves, and portability, this paper proposes a novel FLNG liquefaction process which combines the supersonic swirling separation technology with pressurized liquefaction technology. The process is simulated and optimized using Aspen HYSYS V10 software and genetic algorithms. The results indicate that the specific power consumption of this liquefaction process is only 0.208 kWh/m³, with the cooler, expander, and compressor being the main equipment responsible for exergy losses, accounting for 28.85%, 26.48%, and 21.70%, respectively. This liquefaction process is relatively adaptable to changes in feed gas pressure, temperature, and methane content. The specific power consumption slightly increases with the increasing feed gas pressure and temperature, while it exhibits some fluctuations with the increasing methane content. The process requires a low CO₂ removal rate, possesses moisture pretreatment capability, has fewer pieces of equipment, and saves a significant amount of valuable space. It combines low specific power consumption, minimal impact from swaying, and high safety, providing considerable application potential in future offshore natural gas development. Full article

Nanofluids are an innovative working medium in solar hot water installations (DHWs), thanks to their increased thermal conductivity and heat transfer coefficient. The aim of this work was to assess the effect of Al₂O₃ nanofluids in a water–ethylene glycol base (40:60%) and with the addition of Tween 80 surfactant (0.2 wt%) on thermal efficiency (ε) and exergy (η_ex) in a plate heat exchanger at DHW flows of 3 and 12 L/min. The numerical NTU–ε model was used with dynamic updating of thermophysical properties of nanofluids and the solution of the ODE system using the ode45 method, and the validation was carried out against the literature data. The results showed that the nanofluids achieved ε ≈ 0.85 (vs. ε ≈ 0.87 for the base fluid) and η_ex ≈ 0.72 (vs. η_ex ≈ 0.74), with higher entropy generation. The addition of Tween 80 reduced the viscosity by about 10–15%, resulting in a slight increase of Re and h-factor; however, the impact on ε and η_ex was marginal. The environmental analysis with an annual demand of Q = 3000 kWh/year and an emission factor of 0.2 kg CO₂/kWh showed that for ε < 0.87 the nanofluids increased the emissions by ≈16 kg CO₂/year, while at ε ≈ 0.92, a reduction of ≈5% was possible. This paper highlights the need to optimize nanofluid viscosity and exchanger geometry to maximize energy and environmental benefits. Nowadays, due to the growing problems of global warming, the analysis of energy efficiency and carbon footprint related to the functioning of a building seems to be crucial. Full article

The amount of municipal solid waste (MSW) produced has increased with population growth and consumption patterns. Currently, most waste goes to dumps, although the Brazilian law requires the final destination to be landfills. The latter does not consider the energy lost by these solutions and the carbon footprint that better destinations could avoid. However, not treating the waste correctly aggravates land availability problems, especially in large cities such as São Paulo. Anaerobic digestion is an alternative to traditional waste management, and in addition to treating residues, it generates energy and recovers the nutrients present in MSW. Thermodynamic analyses are still scarce in the literature despite being a known process. This study performed an exergy analysis of an existing biogas plant at the Institute of Energy and Environment of the University of São Paulo with a processing capacity of 20 tons of MSW per day composed of three reactors (430 m³ each) and one internal combustion engine (ICE) of 75 kW. The plant uses MSW as the substrate for anaerobic digestion and generates electrical energy, biogas, and fertilizer for agriculture (digestate). Additionally, the plant operates in cogeneration, as the anaerobic digestion reactor uses the heat produced to generate electrical energy. The results showed that the exergy present in the substrate is 67,320 MJ/day. The products’ exergy flows and the processes’ efficiencies show that the exergy flow of the biogas (44,488 MJ/day) is significantly higher than the exergy flow of the digestate (1455 MJ/day). When considering the cogeneration process, the exergy flow was similar for heat and electric energy as the final products, with 10,987 MJ/day for electric energy and 5215 MJ/day for electric energy. The exergy efficiency of the digestion process was 68.25%, while that of cogeneration (digestate, heat and electric energy) was 26.23%. These results can help identify inefficiencies and optimize processes in an anaerobic digestion plant. Furthermore, thermodynamic analyses of anaerobic digestion found in the literature are mostly based on theoretical models. Thus, this study fills a gap regarding exergy analysis of actual biogas plants. Full article

Solar energy and biomass offer sustainable alternatives to meet the energy demand and reduce the environmental impact of fossil fuels. In this study, through mass and energy balances, a comparative analysis of energy, exergy, and environmental impact (LCA) was conducted on two renewable thermal sources: solar energy and coconut shell biomass, both coupled to a supercritical CO₂ Brayton cycle (sCO₂) with an organic Rankine cycle (ORC) for waste heat recovery. The sCO₂–ORC–biomass configuration showed higher exergy efficiency (41.1%) and lower exergy destruction (188.88 kW) compared to the sCO₂–ORC–solar system (23.76% and 422.63 kW). Thermal efficiency (50.6%) and net power output (131.73 kW) were similar for both sources. However, the solar system (204,055.57 kg CO₂-equi) had an 85.6% higher environmental impact than the biomass system (109,933.63 kg CO₂-equi). Additionally, the construction phase contributed ~95% of emissions in both systems, followed by decommissioning (~4.5%) and operation (~0.1%). Finally, systems built with aluminum generate a higher carbon footprint than those with copper, with differences of 2% and 3.2% in sCO₂–ORC–solar and sCO₂–ORC–biomass, respectively. This study and an economic analysis make these systems viable thermo-sustainable options for clean energy generation. Full article

The increasing environmental challenges posed by the widespread use of fossil fuels and the fluctuating nature of renewable energy have driven the need for more efficient and sustainable energy solutions. Current research is actively exploring hybrid energy systems as a means to address these issues. One such area of focus is the integration of Organic Rankine Cycles (ORCs) with gas and steam turbines, utilizing both natural gas (NG) and solar parabolic trough collectors (PTCs) as energy sources. This study examines the performance of a hybrid system implemented in Kirkuk, Iraq, a region known for its substantial solar radiation. Previous research has shown that hybrid systems can effectively enhance energy conversion efficiency and reduce environmental impacts, but there is still a need to assess the specific benefits of such systems in different geographical and operational contexts. The analysis reveals a thermal efficiency of 59.32% and an exergy efficiency of 57.28%. The exergoeconomic analysis highlights the optimal energy cost at USD 71.93/MWh when the compressor pressure ratio is set to 8 bar. The environmental assessment demonstrates a significant reduction in ${\mathrm{C}\mathrm{O}}_2$/emissions, with a carbon footprint of 316.3 kg ${\mathrm{C}\mathrm{O}}_2$/MWh at higher compressor pressure ratios. These results suggest that integrating solar energy with natural gas can substantially improve electricity generation while being both cost-effective and environmentally sustainable. Full article

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. Full article

In a conventional automotive manufacturing plant, the paint shop alone can represent 36% of the total energy consumption, making it the most demanding area in terms of electricity and fossil fuel energy consumption. This study explores the possibility of decentralizing the production of electrical power and heat simultaneously, using an Organic Rankine Cycle (ORC) system integrated with a Parabolic Trough Collector (PTC) in a paint shop. To date, no similar system has been explored or implemented by the automotive industry. To increase the efficiency of the integrated system, wasted heat generated during the paint manufacturing process is recovered and used to pre-heat the organic fluid in the ORC system. A 4E analysis (Energy, Exergy, Economic, and Environmental) is conducted to determine the practical viability of the proposed system. When applied to the southern region of the USA, this system’s installed capacity is projected to be 11 times higher than the two unique SORC pieces of equipment currently running in Louisiana and Florida. The goals are to reduce the reliance on external primary energy sources and decrease the carbon emission footprint from production activity. The system is evaluated for a location in Alabama, USA. The designed SORC, using toluene, can produce 712.2 kW_el net and 13,132 kg/h of hot water, with an overall energy efficiency of 31.02%; exergy efficiency of 34.23; and ORC efficiency of 27.70%. This leads to an electrical energy saving of 5.9% for the manufacturing plant. The regenerative thermal oxidizer (RTO) heat exchanger, the secondary heat source of the system, has the highest exergy destruction—3583 kW. The system avoids the emission of 4521 tCO₂ per year. A payback period of 10.16 years for the proposed system is estimated. Considering a planning horizon of 10 years, the investment in the system is also justified by a benefit–cost analysis. Full article

In the ongoing debate about the feasibility of enforcing a transition to decentralized energy conversion systems, arguments are often presented that lack scientific rigor. Granted, the issue is multi-faceted and fundamentally multi-disciplinary, and possible solutions strongly depend on the selection of location as well as on local climate and demographics. Furthermore, decentralizing the final energy distribution leads to potential socio-economic considerations that involve value judgements. However, the most serious problem is that media have appropriated the topic and are often publishing opinion papers authored by non-specialists and even by representatives of interest groups. The present paper proposes an approach that is innovative on two counts: first, it treats “final energy” as any other commodity and therefore expands the field of investigation to the problems arising from the decentralization of a generic production line or technological chain; second, it argues that a method solidly rooted in Thermodynamics, the Extended Exergy Accounting, may be used to quantify the total amount of primary exergy resources requested by a decentralized strategy (as opposed to a centralized one), so that a comparison can be performed and discussed on a rational, unbiased and scientific basis. This is an introductory paper that reports some theoretical results of the method: realistic applications are perforce excluded because the idea is that the procedure must be drafted in such a way to be applicable to different socio-economic scenarios and locations and to remain valid under a broad range of boundary conditions. Full article

Rising energy demands, the depletion of fossil fuels, and their environmental impact necessitate a shift towards sustainable power generation. Concentrating solar power (CSP) offers a promising solution. This study examines a hybridization of a combined cycle power plant (CCPP) based on solar energy with fossil fuel and energy storage in rock layers to increase Saudi Arabia’s electricity production from renewable energy. The fuel is used to keep the temperature at the inlet of the gas turbine at 1000 °C, ensuring the power produced by the Rankine cycle remains constant. During the summer, the sun is the main source of power generation, whereas in the winter, reliance on fuel increases significantly. The Brayton cycle operates for 10 h during peak solar radiation periods, storing exhaust heat in rock beds. For the remaining 14 h of the day, this stored heat is discharged to operate the Rankine steam cycle. Simulations and optimizations are performed, and the system is evaluated using a comprehensive 4E analysis (energy, exergy, exergoconomic, and environmental) alongside a sustainability assessment. A parametric evaluation examines the effect of key factors on system performance. The rock bed storage system compensates for solar intermittency, enabling power generation even without sunlight. The study reveals that the system generated 12.334 MW in June, achieving an energy efficiency of 37% and an exergy efficiency of 40.35%. The average electricity cost during this period was 0.0303 USD/kWh, and the carbon footprint was 0.108 kg CO₂/kWh. In contrast, during January, the system produced 13.276 MW with an energy efficiency of 37.91% and an exergy efficiency of 44.16%. The average electricity cost in January was 0.045 USD/kWh, and the carbon footprint was 0.1 kg CO₂/kWh. Interestingly, solar energy played a significant role: it contributed 81.42% of the heat in June, while in January, it accounted for 46.77%. The reduced electricity costs during June are primarily attributed to the abundant sunshine, which significantly powered the system. Full article

Even though the hydrodynamic cavitation reactor (HCR) performs better than the mechanical stirring reactor (MSR) at producing biodiesel, and the ethylic process of biodiesel production is entirely bio-based and environmentally friendly, non-homogeneous ethanol with the triglyceride of underutilized oil, despite the many technical advantages, has discouraged the biodiesel industry and stakeholders from producing ethylic biodiesel in HCRs. This study examines the generation of biodiesel from rubber seed oil (RSO) by comparing the ethyl-based HCR and MSR. Despite ethyl’s technical advantages and environmental friendliness, a lack of scalable protocols for various feedstocks hinders its global adoption. The research employs Aspen HYSYS simulations to investigate the ethanolysis process for RSO in both HCRs and MSRs. The HCR proves more productive, converting 99.01% of RSO compared to the MSR’s 94.85%. The HCR’s exergetic efficiency is 89.56% vs. the MSR’s 54.92%, with significantly lower energy usage. Removing catalytic and glycerin purification stages impacts both processes, with HC showing lower exergy destruction. Economic analysis reveals the HCR’s lower investment cost and higher net present value (USD 57.2 million) and return on investment (176%) compared to the MSR’s. The HCR also has a much smaller carbon footprint, emitting 7.2 t CO₂ eq./year, while the MSR emits 172 t CO₂ eq./year. This study provides database information for quickly scaling up the production of ethanolic biodiesel from non-edible and third-generation feedstocks in the HCR and MSR. Full article