http://hdl.handle.net/10366/138606 Fri, 24 Apr 2026 13:18:25 GMT 2026-04-24T13:18:25Z http://hdl.handle.net/10366/169838 [EN]Adiabatic compressed air energy storage is a promising, in-development technology for storing renewable energy, for instance, from wind parks or photovoltaic installations. This work presents a multi-objective thermoeconomic optimization analysis. It is based on a dynamic model of the plant’s thermodynamic performance, in which the dynamics of the thermal energy storage (packed-bed type) and the charge and discharge processes of the air reservoir are solved in detail. A plant configuration, as determined from previous work in our group, with a priori good round-trip efficiencies (around 0.76–0.78), is considered the starting point. It encompasses two-stage compression and expansion trains, along with two radial packedbeds (utilizing either sensible or phase-change materials) to capitalize on the cooling between compression steps. In the developed optimization procedure, the levelized cost of storage (LCoS) and the total capital expenditure (CAPEX) are taken as key performance indicators. The decision variables include, among others, mass flows, thermal energy storage dimensions, maximum and minimum cavern pressures, and the symmetry of the pressure ratios between compressors and turbines. The optimization procedure uses an NSGA-II genetic algorithm. One of the main novelties of the work is that accurate dynamic simulations have been used to obtain Pareto fronts. They are analyzed from different perspectives: the size, geometry, and materials of the packedbeds; the type of compressor (axial or centrifugal); energetic factors such as input and output energy and power; the maximum pressures in the cavern; and the mass flows in the charge and discharge processes. Values of LCoS are calculated with precision using realistic input data, resulting in approximately 80 e/MWh for a plant capable of storing 600 MWh (reference power of 200 MW for charge periods of 3 h) and electricity prices during charge of 50 e/MWh. The specific parameters and configurations that lead to those LCoS levels are made explicit. Furthermore, the influence of cavern costs, charging electricity prices, and idle time is analyzed in detail. Thu, 01 Jan 2026 00:00:00 GMT http://hdl.handle.net/10366/169838 2026-01-01T00:00:00Z http://hdl.handle.net/10366/168406 [EN]Parabolic dish collectors (PDCs) focus solar radiation onto a small area, minimizing the heat-loss area of the solar receiver and improving the heating of the working fluid. This fluid usually drives a Stirling-like or micro-gas turbine (Brayton-like) power generator. PDCs, initially intended for small-capacity applications, are well-suited for electricity and heat generation in remote rural areas, working alone and/or as parabolic dish arrays. PDCs have received considerable attention among solar thermal collectors due to their high concentration ratios and the high temperatures they achieve. However, nowadays, they are the least developed and least commissioned among concentrated solar power configurations, lacking a well-established technology. This review aims to compile the evolution of research on PDCs over recent years from a global perspective and is mainly focused on the subsystems constituting a PDC plant, their integration, and overall system optimisation, thereby addressing a gap in the current literature. Methodological tools used in the field are comprehensively revised, and recent related projects are summarized. Some innovative and promising applications are also highlighted. Mon, 01 Dec 2025 00:00:00 GMT http://hdl.handle.net/10366/168406 2025-12-01T00:00:00Z http://hdl.handle.net/10366/167887 [EN]This work analyzes several adiabatic compressed air energy systems (ACAES) configurations with a thermodynamic time-dependent model. ACAES systems allow for large-scale energy storage, with fast response times and high output power. However, despite being a promising technology, few works have been done in systematically modeling the unsteady dynamic operation and integrating all components in ACAES plants. The developed model in this work can simulate the thermodynamic behavior of the plant components individually and their integration into an ACAES plant as a whole. The influence of an additional organic Rankine cycle on the round-trip efficiency of the plant is also studied. A comparison of the performance of several plant arrangements is obtained under a unified framework, filling an observed gap in the reported literature. Particular results include the centrifugal compression train working along the peak-line efficiency, the analysis and comparison of pressure drops in packed-bed subsystems used as thermal energy storage: axial or radial, and the optimization of the inlet pressure in the Rankine evaporator. As a conclusion, pressure drops in the radial packed-beds are found to be about 20% lower than in axial packed-beds, and global round-trip efficiencies can be improved by about 2%–3% (reaching values of 0.78) by selecting a suitable symmetrical configuration or by coupling a Rankine cycle. This increase in efficiency is due to the notable reduction in destroyed exergy when an optimized organic Rankine is used for heat recovery instead of discharging heat by an intercooler device. Thu, 01 Jan 2026 00:00:00 GMT http://hdl.handle.net/10366/167887 2026-01-01T00:00:00Z http://hdl.handle.net/10366/166836 [EN]In celebration of 50 years of the endoreversible Carnot-like heat engine, this work aims to link the thermodynamic success of the irreversible Carnot-like heat engine with the stability dynamics of the engine. This region of success is defined by two extreme configurations in the interaction between heat reservoirs and the working fluid. The first corresponds to a fully reversible limit, and the second one is the fully dissipative limit; in between both limits, the heat exchange between reservoirs and working fluid produces irreversibilities and entropy generation. The distance between these two extremal configurations is minimized, independently of the chosen metric, in the state where the efficiency is half the Carnot efficiency. This boundary encloses the region where irreversibilities dominate or the reversible behavior dominates (region of success). A general stability dynamics is proposed based on the endoreversible nature of the model and the operation parameter in charge of defining the operation regime. For this purpose, the maximum ecological and maximum Omega regimes are considered. The results show that for single perturbations, the dynamics rapidly directs the system towards the success region, and under random perturbations producing stochastic trajectories, the system remains always in this region. The results are contrasted with the case in which no restitution dynamics exist. It is shown that stability allows the system to depart from the original steady state to other states that enhance the system’s performance, which could favor the evolution and specialization of systems in nature and in artificial devices. Fri, 01 Aug 2025 00:00:00 GMT http://hdl.handle.net/10366/166836 2025-08-01T00:00:00Z http://hdl.handle.net/10366/166442 [EN]This review provides a comprehensive analysis of the critical challenges and recent advancements related to photovoltaic (PV), biomass gasification (BG), and energy storage (ES) technologies, beginning with technology- specific developments and progressing to their integration in hybrid configurations for power generation and multigeneration systems. Major challenges identified include PV intermittency and limited forecasting accuracy, short ES lifespan and scalability constraints, and persistent BG issues such as tar formation, feedstock variability, and high operational costs. Further difficulties arise during hybridization, including poor control synchroniza- tion, high capital costs, and the lack of robust, context-specific sustainability assessments. To address these barriers, this review synthesizes insights into three strategic pillars: (1) technological integration, including modular system design and advanced storage solutions, (2) advanced control strategies featuring AI-enabled energy management and demand-side optimization, and (3) comprehensive sustainability assessment frame- works grounded in life cycle analysis and socio-economic metrics. Original contributions include the develop- ment of three structured conceptual frameworks: one for guiding system-level hybridization, another for step-by- step implementation in multigeneration settings, and a third for enhancing sustainability, policy integration, and innovation pathways. The review concludes with a roadmap connecting theory to practice through smart grids, circular economy principles, and region-specific deployment strategies to support resilient, cost-effective, and environmentally sustainable energy systems. Sat, 01 Nov 2025 00:00:00 GMT http://hdl.handle.net/10366/166442 2025-11-01T00:00:00Z http://hdl.handle.net/10366/165961 [EN]Concentrated Solar Power (CSP) systems are among the most promising renewable energy technologies in the energy transition scenario. Parabolic dish collectors (PDCs) mainly gather solar power and concentrate it onto a receiver located at the focus of a reflecting paraboloid. They reach the highest concentration factor among CSP configurations. Thus, temperatures even above 1000°C can be achieved. Traditionally, these systems were devoted to producing electricity through a thermodynamic cycle running with a fluid heated up at the receiver working either alone or integrated within micro-cogeneration energy systems or smart grids. However, provided the high temperature these systems can achieve, a wide range of innovative applications related to thermal energy production are emerging. Combined heat and power, water desalination, synthetic fuel, hydrogen production, or thermal energy storage purposes constitute some examples of those new challenging uses. Besides aiming to decentralize electric energy production, parabolic dish collectors can compete or be hybridized with photovoltaic systems to fulfill distributed energy production demand. This work addresses theoretical and practical issues concerning the above novel and challenging applications, filling a gap in the current literature on the prospects for solar parabolic dish collectors. Wed, 01 Jan 2025 00:00:00 GMT http://hdl.handle.net/10366/165961 2025-01-01T00:00:00Z http://hdl.handle.net/10366/165888 [EN]A study of the integration of a supercritical CO2 hybrid Brayton–Organic Rankine Cycle (ORC) with a Concentrated Solar Power (CSP) system using a particle receiver is presented. It focuses on evaluating the energy and exergy performance of the system to improve its efficiency and reduce fuel consumption. The particle receiver uses a mixture of silicon carbide and air as the working fluid, allowing operation at higher temperatures suitable for coupling with the supercritical CO2 Brayton cycle. Detailed thermodynamic models were developed using Mathematica and Engineering Equation Solver (EES) to simulate the behavior of the system under various conditions. The results show that coupling the particle receiver with the hybrid Brayton cycle significantly reduces fuel consumption by 63.2%. The exergy analysis shows that the highest exergy destruction occurs in the heat exchangers of the entire system, indicating potential areas for further efficiency improvements. The study also highlights the critical role in system performance of the ORC working fluid used in the bottoming cycle. Among the fluids tested, R600a was found to be the most effective, providing the highest efficiency under the considered conditions. The results highlight the potential of integrating particle receivers into CSP systems to improve both the energy efficiency and sustainability of power generation, and thus, it represents a promising approach for achieving more effective and sustainable power generation. Wed, 01 Jan 2025 00:00:00 GMT http://hdl.handle.net/10366/165888 2025-01-01T00:00:00Z http://hdl.handle.net/10366/165887 [EN]The integration of solar and gas turbine technologies through hybridization emerges as a promising approach to enhance the sustainability of power generation systems. However, the design process for such hybrid systems is challenging, particularly in terms of optimization and decision-making strategies. In this research, a case study of redesigning of an existing gas power plant by integrating a heliostat field and a central air receiver for preheating purposes has been presented. To accurately adjust the critical parameters of the hybrid solar gas power plant, a tri-objectives optimization approach was employed using two advanced optimization methods: Non-dominated Sorting Genetic Algorithm III and Multi-Objective Grasshopper Optimization Algorithm. Furthermore, the hybrid Fuzzy Analytic Hierarchy Process and The Technique for Order of Preference by Similarity to Ideal Solution decision-making method has been employed to help select the optimal design points from various scenarios and priorities. The chosen design for the hybrid solar-gas power plant showcases an efficient heliostat field footprint, a competitive LCOE of , achieves an annual reduction in natural gas consumption by , and mitigates CO2 emissions by (,).Thus, this study presents a persuasive example of a low-carbon technological solution, offering a promising strategy for the ongoing energy transition in the Middle East and North Africa (MENA) region. Wed, 01 Jan 2025 00:00:00 GMT http://hdl.handle.net/10366/165887 2025-01-01T00:00:00Z http://hdl.handle.net/10366/163948 [EN]The need for large-scale energy storage in the context of renewable electricity production worldwide is evident. Among the various energy storage methods, thermal energy storage stands out. It is independent of geographical location, allows high storage capacities, does not require scarce materials, and is cheaper than its direct competitors. Currently, several technologies are being intensively developed. In some of them, packed-bed systems play a central role: a heat transfer fluid heats up or releases heat from a porous solid that acts as a thermal energy reservoir. This work compiles their application to concepts such as concentrated solar power, pumped thermal energy storage, and compressed or liquid air energy storage. Different physical models with diverse rfinement degrees and the corresponding computational schemes are comprehensively presented. Comparison with previous experimental works includes gas or liquid heat transfer fluids, sensible or latent heat transfers, and a wide range of temperature levels. It is shown that the continuous 1D solid phase model solved with an implicit Euler method provides satisfactory results with a reasonable computing time for various systems. The ifluence of time step and spatial mesh is surveyed, as well as that of pressure drops. Efficiencies and stored energies are calculated for some particular cases, and sensitivity analysis is presented, including parameters such as fluid velocity in discharge and storage time. Concerning the latter, discharge efficiencies for long-time storage (between 10 and 15 h) are fairly good, between 0.39 and 0.20. Wed, 01 Jan 2025 00:00:00 GMT http://hdl.handle.net/10366/163948 2025-01-01T00:00:00Z http://hdl.handle.net/10366/163947 [EN]Online education due to COVID-19 confinement impacted the use of the Information and Communication Technology (ICT) in Spain, where it was poorly implemented. The aim of this paper was to inspect the methodological changes in Physics and Chemistry teaching during the confinement as well as in the ICT use and the lockdown impact afterwards. For this purpose, an online survey was administered by email to the Physics and Chemistry teachers of three provinces of Spain. Based on the analysis, the most widely used methodology was the traditional one. Still, during the lockdown, its use decreased, and others, such as the flipped classroom, increased significantly. Other adaptations included increasing the use of virtual simulations and self-learning by the student. It can be outlined the incorporation of new tools such as WebQuests, the smartphone, or online education platforms, whose use has continued. The ICT was used for new functionalities such as evaluation or answering student questions. According to the respondents, the lockdown had entailed that they strengthen implementation of ICT. In conclusion, there have been changes that have remained in the Physics and Chemistry didactic and in the ICT use due to the lockdown situation. Sat, 01 Jan 2022 00:00:00 GMT http://hdl.handle.net/10366/163947 2022-01-01T00:00:00Z http://hdl.handle.net/10366/163839 [EN]In this paper, four main configurations of a Rankine-based Pumped Thermal Energy Storage (PTES) system are proposed and compared in terms of achievable electrical and exergy roundtrip efficiency and energy density. The analysis considers a conventional setup employing commercial heat pumps and Organic Rankine Cycle (ORC) systems integrated with a Thermal Energy Storage (TES) unit as reference. The initial findings indicate that offthe- shelf systems result in roundtrip efficiencies lower than 40%, even under optimal high-temperature conditions at the heat pump evaporator inlet. This is primarily due to significant exogenous exergy destructions inherent in the commercial equipment. The study then explores upgraded alternatives to the reference PTES configuration, focusing on optimizing the heat pump layout and selecting non-conventional working fluids. This optimization process includes evaluating various working fluids, where n-hexane is identified as the optimal choice for achieving the highest electrical and exergy roundtrip efficiencies, particularly at evaporator inlet temperatures above 60◦C. For lower temperature ranges, acetone emerges as a more suitable fluid due to its favorable thermodynamic properties. Further enhancements are made by optimizing the ORC layout, specifically through the introduction of an additional thermal storage tank and improved heat exchangers. These modifications are aimed at minimizing heat transfer losses and thereby boosting the overall system performance. With these changes, the PTES system's roundtrip efficiency reaches approximately 70%. The most advanced configuration integrates the heat pump and ORC systems into a single assembly, utilizing the working fluid not only for energy transfer but also as a storage medium. This integration reduces the number of required components and further increases efficiency. As a result, roundtrip efficiencies of about 80% are achieved, representing a significant advancement over current commercial systems. Wed, 01 Jan 2025 00:00:00 GMT http://hdl.handle.net/10366/163839 2025-01-01T00:00:00Z http://hdl.handle.net/10366/163593 [EN]Low-grade thermal energy utilization plays an important role in addressing escalating energy demand and environmental challenges. However, primary low-grade thermal energy harvesting technologies are currently only capable of their own single and fixed energy conversion and transport modes, which limits their further application. To break this bottleneck, we innovatively propose an electrochemical energy converter (EEC(s)) cycle model, which consists of three isothermal processes and three open-circuit heating (or cooling) processes and operates between three heat reservoirs. Notably, the proposed EEC(s) integrates and enables flexible switching of thermal-to-electricity and thermal-to-refrigeration harvesting strategies. Moreover, the complementary roles of thermal energy and electricity are enabled to meet different levels of cooling demand. Significantly, its extraordinary thermal-to-refrigeration conversion efficiency and great potential as an alternative to conventional thermally driven refrigerators are emphasized. Specifically, when the EEC(s) operates at maximum cooling power density, a thermal-to-refrigeration conversion performance coefficient of 0.498 and a Carnot-relative efficiency of 32.3% are predicted for the given operating temperatures. Additionally, the different roles of the cell parameters in enhancing the EECs performance are specified. This work demonstrates the feasibility of integrating multiple energy conversion and transport modes into a novel electrochemical cycle configuration and provides a promising solution for efficient and comprehensive low-grade thermal energy utilizations. Wed, 01 Jan 2025 00:00:00 GMT http://hdl.handle.net/10366/163593 2025-01-01T00:00:00Z http://hdl.handle.net/10366/160566 [EN]Floating photovoltaic energy is an emerging solution to the need for decarbonization of the current society. It is currently in the early stages of implementation, so there are not many previous experiences to standardize decision-making and the most relevant operating parameters such as, the tilt angle of a fast as in conventional photovoltaics. In addition, the lack of specific design tools and production calculations for floating solar is a barrier to the correct understanding of the real advantages of floating solar versus conventional solar. From the point of view of the investment, the stakeholders do not have a complete analysis of the profitability of their investment. From a technical, environmental and legislative point of view, there is not enough information available to establish standards and criteria for the design and selection of the most suitable water bodies at local, regional or state level. This research aims to fill this gap by proposing a specific framework based on geographic information systems (GIS), multi-criteria analysis (MCDA) and intelligent optimization (Genetic Algorithm). The objective is to select within a set of water bodies those where the investment is most beneficial from a holistic perspective considering technical, economic, social, environmental, and legislative criteria. Once the optimal location is obtained, the framework obtains the tilt angles that minimize the Levelized Cost of Energy (LCOE) by means of intelligent optimization techniques that evaluate the characteristics of each water body, such as location or available surface. The tilt angle obtained in this research achieves LCOE improvements of between 2.1% and 8.4% with respect to the tilt angle obtained by conventional methods applied to ground photovoltaics. Spain has been chosen as a case study as it is a region with a high solar potential and an even distribution of water bodies in which there is still no legislative framework in force. Mon, 01 Jan 2024 00:00:00 GMT http://hdl.handle.net/10366/160566 2024-01-01T00:00:00Z http://hdl.handle.net/10366/158448 [EN]Absorption carbon capture is currently the most commercialized technology and deemed as the vital solution to balance continued use of fossil fuels and carbon emission reduction. Nevertheless, its high energy cost remains the major concern for wide-scale application. Consequently, it is of great significance to address this issue by analyzing the underlying energy conversion mechanism, answering the pivotal question “What characteristics lead to a superior absorbent?”, and developing more efficient absorbent. In this paper, an irreversible decoupling model of absorption carbon capture system, consisting of a heat engine and a chemical pump, is innovatively established. Accordingly, key performance indicators are analytically derived and the optimal operation strategies of the system are explicitly determined. Notably, the matching of two subsystems leads to a novel insight into the heat and mass transfer interaction of absorbent, according to which the simulated results and the question concerning the best absorbent are thermodynamically interpreted and addressed, respectively. Additionally, the comparisons between the calculated optimal energy conversion efficiencies with experimental and simulated results are presented and discussed. Our findings may indicate the efficient pathway for developing advanced absorbent and provide instructing information for the design and operation of practical carbon capture systems. Sun, 01 Sep 2024 00:00:00 GMT http://hdl.handle.net/10366/158448 2024-09-01T00:00:00Z http://hdl.handle.net/10366/157884 [EN]An optimal design for seasonal underground energy storage systems is presented. This study includes the possible use of natural structures at a depth of 100 to 500 m depth. For safety reasons the storage fluid considered is water at an initial temperature of 90 °C. A finite element method simulation using collected data on the thermal properties of the soil was performed. As a practical example of this methodology, an analysis with data collected in the region of Avila, Spain is made. A temperature-depth map using data measured in the zone was generated. A 3D model of the underground material composition was obtained by electromagnetic field diffusion techniques carried out from the surface. This allows for an analysis of available solutions in energy storage strategies, tailored to the specific conditions on the site with a sufficient degree of precision for a first evaluation without the need for deep excavations. This study shows alternating regions of sands and clays, with natural structures for potential use within a depth of 500 m. Thermal properties of water depending on temperature and pressure are considered. A variety of size configurations shows that, in a cylindrical geometry, a storage system with a radius beyond 2 m does not offer significant benefits in energy stored per mass unit. The benefits of a clay envelope are noticeable, compared with the scenario of a cavity surrounded by sand and followed by clay even after 6 months of storage. According to the underground temperature and the energy needed to transport the storage fluid, it is shown that the thermal performance does not significantly improve between 50 m and 100 m of depth. However, between 100 m and 200 m a noticeable improvement is achieved, and from there down to 500 m the improvement is negligible. Several materials for containing the storage fluid and for thermal isolation are analyzed. For periods beyond 14 days, the thermal properties of thermoplastics are relevant, as found in the case of the Acrylonitrile-Styrene-Acrylate which exhibited the best performance in the simulation. In the best configuration, it is possible to see that by storing water at 90 °C (obtaining 138.78 kJ/kg from an exchange with a typical system at ambient temperature in the months of January–February) compared to the case where the water is stored at the temperature of the underground, that is 25 °C (obtaining 77.08 kJ/kg), it is possible to store 1.8 times more energy per kg of store water without affecting the surrounding medium. Finally, the efficiency of the storage system is calculated from the thermal energy that can be potentially recovered according to the input energy needed to raise the temperature of the fluid from an ambient temperature, up to the initial storage temperature of 90 °C. Due to the thermal properties of clay in the subsoil, previous efficiencies ( ) reported in aquifer energy thermal energy storages can be obtained with relatively small storages without continuous energy inlets as is the case of the majority of seasonal thermal energy arranges, with a potential to recover 70% of the inlet thermal energy under optimum conditions of the storage Wed, 01 May 2024 00:00:00 GMT http://hdl.handle.net/10366/157884 2024-05-01T00:00:00Z http://hdl.handle.net/10366/157883 [EN]The expected performance of an innovative Pumped Thermal Energy Storage (PTES) system based on a closedloop Brayton-Joule cycle and integrated with a Concentrated Solar Power (CSP) plant are analysed in this study. The integrated PTES–CSP plant includes five machines (two compressors and three turbines), a central receiver tower system, three water coolers and three Thermal Energy Storage (TES) tanks, while argon and granite pebbles are chosen as working fluid and storage media, respectively. A sizing of the main components of the integrated plant has been firstly carried out for the design of an integrated PTES-CSP plant with a nominal net power of 5 MW and a nominal storage capacity of 6 equivalent hours of operation. Specific mathematical models have been developed in MATLAB-Simulink to simulate the PTES and CSP subsystem in different operating conditions, and to evaluate the thermocline profile evolution within the three storage tanks during/charging and discharging processes. A control strategy has finally been developed to determine the operating modes of the plant based on the grid service request, the solar availability, and the TES levels. The performance of the system during a summer and a winter day have been analysed considering the integration of the PTES subsystem in the Italian energy market for arbitrage. Results have demonstrated the technical feasibility of the hybridization of a PTES system with a CSP plant and the ability of the integrated system to participate to energy arbitrage, although a lower exergy roundtrip efficiency (about 54 %) has been observed with respect to the sole PTES system (about 60 %). Fri, 01 Dec 2023 00:00:00 GMT http://hdl.handle.net/10366/157883 2023-12-01T00:00:00Z