Search Results (717)

Photovoltaic–thermal (PVT) collectors coupled to thermochemical energy storage (TCES) can turn intermittent low-grade solar heat into a dispatchable service, but solar intermittency poses a closed-loop control problem. A companion study established the feedback-only lower bound: a 937 kJ accumulated exergy-delivery-deficit benchmark under optimally tuned proportional–integral–derivative (PID) flow control. The corresponding upper bound is quantified here by means of a deliberately idealised search-based predictive controller that, at each 10 s step, enumerates 51 candidate pump rates, predicts the reactor-inlet temperature by a single forward-Euler step, and is granted perfect future irradiance. On the experimentally validated shared plant (matched to the companion baseline), against an optimally tuned PID, the perfect-foresight advantage is marginal: +0.96% daily exergy on synthetic days and +0.07–0.24% on two measured Walailak University monsoon days, all controllers tracking within 6–13 K on the measured days. Under tropical-monsoon irradiance, the 95 °C desorption setpoint is rarely sustained, so the delivered exergy is nearly controller-independent: the perfect-foresight upper bound lies just above the feedback-only lower bound, and together the two results bracket the exergy envelope available to any flow-rate controller of this system. A horizon sweep localises the bottleneck to internal-model fidelity, not anticipation depth. The eight-node plant is validated against measured module temperature (root-mean-square error 3.5 °C, coefficient of determination R² = 0.89) and a copper-tube PVT prototype (1.5 °C; peak hot water up to 79 °C). The central contribution is therefore a rigorously defined, experimentally grounded upper bound showing that, at this scale and latitude, deployability rather than anticipation is the effective design lever. Full article

Liquid Air Energy Storage (LAES) is a promising large-scale storage technology for supporting the sustainable integration of intermittent renewable electricity into power grids, particularly when electricity storage is combined with waste-heat valorization, cryogenic cold recovery, and reduced exergy degradation. In this thermodynamic sense, the present study proposes a sustainability-oriented framework for the comparative and parametric exergetic analysis of LAES systems, integrating the liquefaction and discharge stages within a unified analysis. The assessment focuses on thermodynamic resource efficiency and exergy performance rather than on a complete economic, environmental, or life-cycle evaluation. The objective is to identify the components and operating parameters that most strongly influence performance and to quantify the reductions in exergy destruction and losses achieved through configuration changes and parameter variation. Three Linde–Hampson-based liquefaction configurations are compared, including arrangements with external and intermediate auxiliary pre-cooling. Improved heat-exchanger integration and temperature matching increase the structural liquefaction exergetic indicator from 7.95% in the baseline configuration to 19.28% in the two-RHX configuration. The discharge stage is assessed parametrically with respect to cryogenic pumping pressure, turbine inlet temperature, and expansion architecture. Single-stage and two-stage adiabatic expansions are compared with an ideal isothermal benchmark. The adiabatic configurations provide mechanical-work recovery together with recoverable cooling potential, whereas the isothermal case gives the highest work-recovery benchmark. Under the reference conditions, using the aggregated compressor representation adopted for the main parametric analysis, the two-stage adiabatic configuration reaches a global exergetic efficiency of 15.92% for the improved Linde–Hampson-based chain and 24.87% for the selected Claude–Heylandt reference block. Full article

In response to rising global energy demand and sustainability targets, assessing the energy-related efficiency of agricultural products has become a critical issue. Sweet sorghum is widely recognized as a promising energy crop for sustainable biofuel production, thanks to its low water requirements and high biomass productivity. To the best of the authors’ knowledge, this study provides the first comprehensive cumulative exergy-based evaluation of sweet sorghum production by simultaneously assessing its energy, exergy, and environmental performance using five key indicators: Cumulative Energy Consumption (CEnC, 718.48 MJ/ton), Cumulative Exergy Consumption (CExC, 2031.42 MJ/ton), Cumulative CO₂ Emission (CCO₂E, 124.01 kg CO₂/ton), Cumulative Degree of Perfection (CDP, 2.8) and Renewability Index (RI, 0.64), based on field level data for the production of one ton of sweet sorghum. Input-based analysis revealed that electricity consumption accounted for the largest share of both energy and exergy use, amounting to 334.85 MJ/ton and 1396.32 MJ/ton, respectively. At the same time, irrigation water was identified as a major contributor to carbon emissions. The integration of renewable electricity sources substantially improved system performance, increasing the CDP to 6.32 and the RI to 0.84, corresponding to more than a twofold increase in exergy efficiency and a shift toward a predominantly renewable production system. Overall, the findings highlight the strong potential of sweet sorghum as a sustainable biofuel feedstock and underline the importance of integrated policy and management approaches that simultaneously address energy quality, exergy losses, and carbon emissions in agricultural energy systems. Full article

The potato production process in Konya, Türkiye, was evaluated through a cumulative and system-oriented approach. A functional unit of one ton of potatoes produced was used for all analyses, using region-specific agricultural input data. In this study, the cumulative energy consumption (CEnC), exergy consumption (CExC), and CO₂ emissions (CCO₂E) of the agricultural production process were determined. Specifically, the sustainability performance of the potato production process was examined through thermodynamic indicators. The results indicate that nitrogen fertilizer accounts for the highest CEnC, reaching 368.94 MJ per ton of potato produced, followed by diesel fuel at 179.64 MJ/ton and electricity at 91.79 MJ/ton. However, the CExC assessment revealed a different pattern, with electricity emerging as the dominant source of exergy depletion. Electricity consumption accounted for 382.75 MJ/ton, representing the largest exergy burden among all inputs, while diesel (166.21 MJ/ton) and nitrogen (154.28 MJ/ton) followed as secondary contributors. A similar trend was observed in the carbon emission analysis. Electricity use resulted in the highest CCO₂E value at 12.85 kg CO₂/ton, whereas diesel contributed 2.94 kg CO₂/ton. Emissions from chemical fertilizers remained notably low, with nitrogen, phosphorus and potassium generating only 0.42, 0.22 and 0.75 kg CO₂/ton, respectively. The sustainability indicators further highlighted the system’s performance. The cumulative degree of perfection (CDP) was calculated as 7.34, while the renewability indicator (RI) reached 0.86, suggesting that potato production in Konya demonstrates relatively high thermodynamic efficiency and a strong potential for renewable energy integration. Under a scenario in which agrivoltaic systems (AVS) and fully electric agricultural machinery replace conventional energy inputs, the CDP increased markedly to 21.61 and the RI to 0.95. To the authors’ knowledge, this study is the first thermodynamic analysis of potato production in Türkiye that integrates sustainability indicators with an AVS integration scenario. The proposed framework provides a practical decision support approach for evaluating the integration of renewable energy into agricultural production systems. Full article

Under the carbon neutrality context, underground coal gasification combined cycle (UGCC) power generation with carbon capture and storage (CCS) technology can effectively mitigate climate change and reduce pollutant emissions. However, due to the complexity of the UCG process and significant fluctuations in syngas composition, the overall power generation efficiency of the plant may be affected to some extent. Existing studies have predominantly focused on single-link energy efficiency analysis, with a lack of full life-cycle resource–environment synergistic evaluation based on the extended exergy analysis framework, and comparative sustainability research between UGCC and integrated gasification combined cycle (IGCC) systems remains inadequate. Accordingly, this study establishes an exergy Life-Cycle Assessment model for UGCC power plants based on Aspen Plus, systematically evaluates the resource utilization rate and environmental sustainability index, identifies key influencing factors, and conducts a comparative analysis with IGCC power plants. The results indicate that the comprehensive sustainability performance of UGCC power plants is significantly enhanced after CCS retrofitting, with exergy efficiency reaching 37.56% at an oxygen-to-coal ratio of 0.6 and a water-to-coal ratio of 0.1; compared with IGCC, UGCC demonstrates a superior resource utilization rate but relatively weaker environmental sustainability; and the underground gasification unit is the critical link affecting exergy efficiency. This study offers a new perspective for sustainability assessment of energy systems and provides theoretical support and technical reference for the construction of a low-carbon reliable supply system in the power industry, thereby facilitating the implementation and refinement of a novel sustainable energy system. Full article

This study evaluates, from energy, exergy, exergo-sustainability, and environmental perspectives, two combined-cycle configurations based on a supercritical CO₂ Brayton cycle coupled to an ORC: a simple reheat configuration (S-CO₂-ORC) and a recompression-reheat configuration (SRC-CO₂-ORC). Both were assessed under two thermal sources: concentrated solar power (CSP) and a hybrid biomass-CSP source using oil palm residues. Sizing was based on the cooling demand of a 130-home residential complex in Barranquilla, estimated at 152 kW through hourly simulation. The SRC-CO₂-ORC configuration delivered the best energy performance, reaching 138.38 kW and 55.34% with CSP and up to 157.28 kW and 57.66% under hybrid operation. The highest irreversibilities were concentrated in the solar field and receiver, while the thermal sources contributed more than 85% of the total carbon footprint. The lowest life-cycle impact corresponded to the SRC-CO₂-ORC-Solar configuration, at 0.0117 kg CO₂-eq/kWh, against 0.0194 kg CO₂-eq/kWh for the S-CO₂-ORC-Hybrid case. The results confirm the technical feasibility of these configurations for residential applications and reveal a clear trade-off between thermodynamic performance and minimum carbon footprint. Full article

The sustainability of biomass utilization as a fuel is commonly assessed through thermodynamic and ecological methods—energy, exergy, and emergy analyses—applied in isolation, each with only partial scope. Their integration through multicriteria analysis has been proposed for the sugar industry, but has not yet been formalized as a reproducible, auditable, and generalizable protocol: neither the logical sequence linking balances and decision-making, nor an explicit sustainability rule, nor the treatment of the incommensurability between thermodynamic and ecological accounting has been established. This work formalizes such a protocol in three stages: (i) definition of fuel alternatives and screening of criteria through the Delphi method; (ii) characterization of each alternative through three coupled balances—energy (quantity), exergy (quality), and emergy (environmental cost); and (iii) integration through the Analytic Hierarchy Process (AHP) into a single sustainability ranking with an explicit decision rule, supported by a robustness layer based on Monte Carlo simulation and multi-method comparison. The protocol is demonstrated in the Cuban sugar industry using two steam generators (G.V. VU-40 and Retal-type steam generator) and variants of bagasse, agricultural harvest residues (AHR), and marabou (Dichrostachys cinerea). In the demonstration, AHP weighting ranked the emergy criterion above the exergy and energy criteria (priority vectors 0.539, 0.297, and 0.164, respectively; consistency ratio 0.008), and the bagasse alternative emerged as the most sustainable in both technologies despite not being the most efficient. The robustness analysis confirmed that this verdict is stable: bagasse Pareto-dominates the independent emergy indicators and remains the best alternative in more than 95% of the weight space. The contribution of the work is methodological—the formalization and generalization of the protocol—while the case study illustrates its operation and does not constitute a statistical validation. Full article

Low-grade thermal energy is widely available in industrial waste-heat streams and natural temperature fluctuations, yet its utilization remains limited because of weak thermodynamic driving forces and the complexity of conventional heat-engine technologies. This study presents a physics-based framework for modular thermoelastic energy harvesting using the reversible thermal expansion and contraction of structural materials. Analytical models are established to quantify thermoelastic work, structural constraints, thermodynamic and exergy efficiencies, and long-term energy production. Material selection and thermo-mechanical limitations are evaluated through parametric analysis and finite-element verification. The results indicate that extractable work is fundamentally constrained by yield strength, buckling resistance, temperature swing, and the limited exergy content of low-grade heat. Scaling laws show that annual energy generation scales approximately linearly with active structural mass while remaining strongly dependent on column diameter, thermal-cycle frequency, and material performance indices. Thermodynamic and exergy efficiencies remain well below the Carnot limit, highlighting the inherent limitations of solid-state thermoelastic conversion. A techno-economic assessment further indicates that economic viability depends primarily on multi-cycle operation and low-cost implementation. Although the achievable energy density remains modest compared with conventional renewable technologies, the proposed framework provides quantitative performance limits and practical design guidelines for evaluating thermoelastic energy harvesting from low-grade heat. Full article

Hydrogen-based technologies are widely considered promising pathways for decarbonizing power generation and industrial energy systems; however, their overall sustainability depends strongly on both production routes and conversion efficiencies. This study presents a comparative energy and exergy analysis of hydrogen-based decarbonization pathways under a consistent 1 MW net electrical output boundary, including natural gas combustion (S0), grey hydrogen combustion (S1), grey hydrogen fuel cell (S2), green hydrogen combustion (S3), and green hydrogen fuel cell (S4) systems. The results indicate that combustion-based pathways (S0, S1, and S3) exhibit relatively low energy efficiencies of approximately 30–40% and exergy efficiencies of 25–40%, accompanied by high exergy destruction levels generally exceeding 60%. In contrast, fuel cell-based configurations (S2 and S4) demonstrate improved conversion-stage thermodynamic performance, achieving energy efficiencies of 50–60% and exergy efficiencies of 45–65%, while reducing exergy destruction due to electrochemical conversion and lower irreversibilities. A detailed comparison shows that the natural gas reference system reaches an exergy efficiency of 33.7%, whereas the hydrogen fuel cell system achieves 46.5%, corresponding to approximately 42% lower exergy destruction and about 36% reduced fuel input. From an environmental perspective, the simplified carbon assessment indicates that natural gas combustion generates approximately 577 kg CO₂/h. Grey hydrogen pathways remain associated with substantial upstream emissions, generating approximately 857 kg CO₂/h for grey hydrogen combustion and 545 kg CO₂/h for grey hydrogen fuel cell operation under the 1 MW net electrical output basis. In contrast, green hydrogen-based pathways are assumed to have near-zero direct/upstream operational CO₂ emissions under renewable-powered production assumptions. Overall, the findings show that hydrogen use alone does not guarantee decarbonization; rather, both the hydrogen production route and the final conversion technology must be considered to achieve thermodynamically efficient and low-carbon power generation. Full article

Solar stills are considered an effective solution to produce fresh drinking water from saline water. Solar stills utilize solar energy, which is available in abundant quantity for long periods across Middle Eastern countries like Oman. In this study, two single-slope passive solar stills are fabricated with two configurations: a Conventional Solar Still (CSS) and a Modified Solar Still (MSS). The CSS is the basic model, whereas the MSS is a model obtained by incorporating copper tubes that are filled with phase change material (PCM) combined with nano copper oxide particles, which are attached inside the basin. The objective of this study is to compare the performance of the two systems from energy, exergy, and economical aspects. The solar stills were fabricated according to the geometrical conditions of the city Nizwa, Oman, and the standards for the fabrication of each solar still component. The highlights of this research are comparing the performance of the CSS and MSS under the prevailing atmospheric conditions of the city Nizwa, Oman, and investigating the effects of the nano materials and phase change materials used in the MSS on its performance. The results of the study reveal certain important facts; for example, higher thermal conductivity of the copper tubes increases the heat transfer and evaporation of saline water inside the basin. The freshwater production in the MSS was higher than in the CSS, with an average difference of about 79.75%. This difference in freshwater production is due to the accumulated heat storage and release of heat from the PCM material combined with nanoparticles during reduced solar radiation. The nanoparticles contributed to an increase in the heat transfer rate of the PCM. The presence of copper tubes filled with nano-PCM in the MSS influences and increases both energy and exergy efficiencies to around 30 to 35% and 1 to 1.5% compared to those in the CSS. The increased efficiencies in the MSS are due to its improved evaporation and condensation rates, which enhance the energy utilization in the process of converting saline water to freshwater. Full article

The rapid growth of graphics processing unit (GPU)-accelerated AI workloads has made data centers significant sources of medium-grade waste heat, creating both a sustainability challenge and an urban decarbonization opportunity. This paper presents the Cascaded Exergy-Economic Valorization (CEEV) framework, a three-stage system that converts data-center waste heat through (1) an organic Rankine cycle for GPU liquid-cooling loops at 65–85 °C; (2) a transcritical CO₂ heat pump, upgrading residual heat to 75–90 °C; and (3) thermochemical energy storage using SrBr₂·6H₂O for seasonal heat banking. The framework introduces two metrics: the Exergy Value Index (EVI, $/kJ) and the Levelized Cost of Stored Heat (LCSH, $/kWhth). Results for a 10 MW liquid-cooled data center across three climate zones show cascade exergy utilization of 31.2–38.7%, operational cost reductions of 15–25%, 20-year NPV of $2.2–8.4 million, and payback periods of 5.8–7.8 years. The simpler HP (heat pump) +TCES (thermochemical energy storag) configuration achieves higher deterministic Net Present Value (NPV) because it preserves the full waste-heat temperature for the heat pump; however, the full three-stage cascade becomes preferable when electricity prices exceed approximately $50/MWhe, when revenue diversification is valued, or when real-options flexibility is important. Real-options analysis shows that traditional NPV undervalues cascaded waste-heat recovery investments by 18–32%. Even without carbon credit revenue, NPV remains positive at $1.6–6.1 million, confirming that district-heating sales and electricity revenue alone can support investment. The CEEV framework advances sustainable data-center development by providing quantifiable tools for waste-heat performance assessment, supporting policy instruments such as the EU Energy Efficiency Directive and the German EnEfG, and aligning with SDGs 7, 9, 11, and 13. Full article

Reliable and sustainable access to energy continues to pose a significant challenge for rural farms in African underprivileged areas, where traditional diesel generators are both economically and environmentally unfeasible. This research explores the potential of pumped thermal energy storage (PTES) systems utilizing a Rankine cycle for the preservation of farm produce, analyzing four configurations of reversible heat pump–organic Rankine cycle (HP–ORC) systems that employ R1234ze(E) as the working fluid: hot-storage cooled HP mode, air-cooled HP mode, basic ORC mode, and ORC mode with integrated electrical heaters. Despite the exploration of hybrid HP–ORC and reversible PTES configurations in the existing literature, there remains a significant lack of research focusing on their feasibility for energy services in rural agriculture, and the literature data remains insufficient for comprehensive decision-making on deployment for small-scale applications in rural settings. To bridge this gap, the thermodynamic performance was evaluated for the PTES configurations through exergy analysis, to measure system irreversibility and component losses. Also, an exergoeconomic assessment was conducted using the Specific Exergy Costing (SPECO) method, while environmental impacts were examined with Eco-Indicator 99, aimed primarily at decision-making for real-life application. The results indicate that the ORC mode with electric heater achieved the highest exergy efficiency at 31.7%, surpassing the hot-storage cooled HP mode by approximately 11 percentage points. The air-cooled ORC with electric heaters exhibited a thermal efficiency of 26.6% and reduced economic losses, while also demonstrating significantly lower environmental degradation compared to the hot-storage HP mode (1327 mpts/s). These results suggest that air-cooled HP-ORC configurations provide an optimal balance of technical, economic, and environmental performance, thereby promoting sustainable, localized energy solutions for rural agricultural practices. Full article

Rankine cycle CO₂ pumped thermal energy storage (R-CPTES) offers high-density, emission-free grid storage, but existing designs are limited by modest turbine inlet temperatures and produce electricity only, leaving their thermal potential unused. This paper introduces a Rankine CO₂ storage cycle driven by a high-concentration parabolic dish collector (PDC) and configured solely for combined heat and power, representing a combination of point focus solar energy with CO₂ pumped thermal storage that has received limited attention in the literature. During discharge, the dish superheats the working fluid and raises the high temperature turbine inlet from 456 °C to 500 °C, boosting net power. A heating recovery exchanger placed ahead of the second regenerator then extracts useful heat from the turbine exhaust for district or process supply, without the absorption refrigeration subsystem used in comparable cooling inclusive designs. The aim is to characterise this system through energy, exergy, and parametric analysis. A closed, pinch-consistent model is developed under steady-state assumptions using the Span–Wagner equation of state, with the discharge low pressure, discharge mass flow rate, and PDC outlet temperature varied independently and jointly at a fixed 10 MPa high-pressure boundary. The analysis reveals a power-versus-heat trade-off governed by the discharge pressure and bounded by physical limits rather than interior optima, shows that the solar superheat is a prerequisite for cogeneration, and identifies the system as heat-transfer destruction dominated, with the latent cold storage the largest single source of irreversibility. At the design point the system delivers 16.1 MW of power and 2.5 MW of heat, attaining a storage round-trip efficiency of 73.2% (electricity-only), a solar-inclusive electrical efficiency of 58%, an energy utilization factor of 67%, and an overall exergy efficiency of 61.3%. A preliminary economic assessment gives a levelised cost of storage of 0.10–0.18 $/kWh, competitive with comparable CO₂ storage systems. The proposed system thus provides a simple, fossil-free cogeneration solution for high-DNI regions based on a modular, point focus solar configuration. Full article

This study proposes and evaluates an integrated coal-based hydrogen–electricity cogeneration concept that combines oxygen transport membrane (OTM) technology, coal partial gasification (CPG), and pressurized oxy-fuel combustion (POFC) with inherent CO₂ capture. Six system configurations, comprising a no-capture baseline, a conventional cryogenic air separation route, and four OTM-based variants differing in membrane operating mode (4-end vs. 3-end) and feed air heating strategy, are systematically compared through Aspen Plus process simulation coupled with a 4E (energy, exergy, environmental, and economic) assessment. The two leading CCS configurations, namely, Case 1 (CASU benchmark) and Case 2 (heat-integrated 4-end OTM configuration), show comparable thermodynamic performance, with overall efficiencies of approximately 50.9% and exergy efficiencies of approximately 48.6%. Their small efficiency difference falls within the propagated auxiliary load uncertainty, indicating that they should be regarded as thermodynamically comparable rather than strictly ranked by first-law efficiency. In the techno-economic assessment, Case 2 delivers the lowest credit-based levelized hydrogen cost among the CCS routes, while both allocation-based and credit-based costs are reported in the main text for comparison. Sensitivity analysis confirms that the comparative ranking is robust to single-parameter and combined adverse market perturbations, while the absolute economic viability remains contingent on hydrogen price, CO₂ credit availability, and membrane-related assumptions. Full article

This study presents an integrated diabatic compressed air energy storage (D-CAES)–cascade organic Rankine cycle (ORC)–liquefied natural gas (LNG) polygeneration system that simultaneously delivers electricity, district cooling, and pipeline-grade natural gas. The D-CAES turbine exhaust serves as the primary heat source for a cascade ORC employing a zeotropic working-fluid mixture, while the LNG warming curve provides a cryogenic condensation sink uniquely suited to glide-matched condensation of the zeotropic condenser. A four-criterion (4E) framework is applied at the component level, yielding four global performance metrics: exergy round-trip efficiency (ERTE), total annualized cost rate (Ż_tot), CO₂ emission factor (ζ_CO2), and net discharge power. A surrogate-assisted multi-objective optimization is developed in which 1000 Latin-hypercube-sampled high-fidelity simulations train three independent artificial neural network (ANN) surrogate models, which are then coupled with the optimization algorithm. The TOPSIS-selected compromise solution achieves an ERTE of 47.55%, a total cost rate of 293.75 USD h⁻¹, and a CO₂ emission factor of 166.98 kg MWh⁻¹. Sensitivity analysis demonstrates that turbine inlet temperature and charging pressure are the dominant thermoeconomic drivers. Full article