Spain

At present energy demands are mainly covered by the use of fossil fuels. The process of fossil fuel production increases pollution from oil extraction transport to processing centers treatment to obtain lighter fractions and delivery and use by the final consumers. Such polluting circumstances are aggravated in the case of accidents involving fossil fuels. They are also linked to speculative markets. As a result the trend is towards the decarbonization of lifestyles in advanced societies. The present paper addresses the problem of the optimal sizing of a hybrid renewable energy system for scheduling green hydrogen production. A local system fully powered by renewable energies is designed to obtain hydrogen from seawater. In order to monetize excess energy the grid connection of the system is considered under realistic energy market constraints designing an hourly purchasing strategy. This crucial problem which has not been taken into account in the literature is solved by the specific dispatch strategy designed. Several optimization methods have been used to solve this problem; however the scatter search method has not previously been employed. In this paper the problem is faced with a novel implementation of this method. The implementation is competitive in terms of performance when compared to on the one hand the genetic algorithm and differential evolution methods which are well-known state-of-the-art evolutionary algorithms and on the other hand the optimal foraging algorithm (OFA) a more recent algorithm. Furthermore scatter search outperformed all other methods in terms of computational cost. This is promising for real-world applications that require quick responses.

Multi-energy microgrids (MEMGs) with green hydrogen have attracted significant research attention for their benefits such as energy efficiency improvement carbon emission reduction as well as line congestion alleviation. However the complexities of multi-energy networks coupled with diverse uncertainties may threaten MEMG’s operation. In this paper a data-driven methodology is proposed to achieve effective MEMG operation considering the green hydrogen technique and congestion management. First a detailed MEMG modelling approach is developed coupling with electricity green hydrogen natural gas and thermal flows. Different from conventional MEMG models hydrogen-enriched compressed natural gas (HCNG) models and weatherdependent power flow are thoroughly considered in the modelling. Meanwhile the power flow congestion problem is also formulated in the MEMG operation which could be mitigated through HCNG integration. Based on the proposed MEMG model a reinforcement learning-based method is designed to obtain the optimal solution of MEMG operation. To ensure the solution’s safety a soft actor-critic (SAC) algorithm is applied and modified by leveraging the Lagrangian relaxation and safety layer scheme. In the end case studies are conducted and presented to validate the effectiveness of the proposed method.

Microbial electrolysis cells (MECs) have garnered significant attention as a promising solution for industrial wastewater treatment enabling the simultaneous degradation of organic compounds and biohydrogen production. Developing efficient and cost-effective cathodes to drive the hydrogen evolution reaction is central to the success of MECs as a sustainable technology. While numerous lab-scale experiments have been conducted to investigate different cathode materials the transition to pilot-scale applications remains limited leaving the actual performance of these scaled-up cathodes largely unknown. In this study nickel-foam and stainless-steel wool cathodes were employed as catalysts to critically assess hydrogen production in a 150 L MEC pilot plant treating sugar-based industrial wastewater. Continuous hydrogen production was achieved in the reactor for more than 80 days with a maximum COD removal efficiency of 40 %. Nickel-foam cathodes significantly enhanced hydrogen production and energy efficiency at non-limiting substrate concentration yielding the maximum hydrogen production ever reported at pilot-scale (19.07 ± 0.46 L H2 m− 2 d− 1 and 0.21 ± 0.01 m3 m− 3 d− 1 ). This is a 3.0-fold improve in hydrogen production compared to the previous stainless-steel wool cathode. On the other hand the higher price of Ni-foam compared to stainless-steel should also be considered which may constrain its use in real applications. By carefully analysing the energy balance of the system this study demonstrates that MECs have the potential to be net energy producers in addition to effectively oxidize organic matter in wastewater. While higher applied potentials led to increased energy requirements they also resulted in enhanced hydrogen production. For our system a conservative applied potential range from 0.9 to 1.0 V was found to be optimal. Finally the microbial community established on the anode was found to be a syntrophic consortium of exoelectrogenic and fermentative bacteria predominantly Geobacter and Bacteroides which appeared to be well-suited to transform complex organic matter into hydrogen.

This manuscript presents a comprehensive technical review of low-temperature proton exchange membrane fuel cells (LT-PEMFCs) focusing on their performance applications and current challenges within commercial contexts. LT-PEMFCs have reached commercial deployment in light-duty vehicles buses trains heavy-duty trucks stationary combined heat and power units and early maritime platforms. This review consolidates datasheetbased specifications and reconstructed performance parameters from leading manufacturers complemented by qualitative evidence from large-scale deployments in Japan and China to provide the first cross-sectoral benchmarking of LT-PEMFC systems. The analysis is structured around the key performance indicators (KPIs) of the Clean Hydrogen Joint Undertaking and the U.S. Department of Energy which define quantitative targets for 2024 and 2030. Results show that while several light-duty and bus platforms already meet or approach KPI compliance for hydrogen consumption and efficiency other sectors such as heavy-duty stationary and maritime remain below target ranges due to integration constraints and limited transparency in datasheet reporting. The study further highlights divergences between laboratory-reported stack metrics and commercial module specifications demonstrating the need for harmonized definitions of volumetric power density efficiency at rated power and durability. By situating catalogue-only and prototype systems within the technological pipeline the review clarifies how near-term developments may close performance gaps and reduce platinum dependency while also acknowledging the economic and infrastructural dimensions that condition future adoption. This includes recent advances in PGM-free catalysts alloyed and core–shell architectures and ionomer-free electrodes which complement low-PGM approaches in reducing material cost and supply risk. The contribution lies in delivering a transparent and replicable framework that not only maps the current state of LT-PEMFC commercialization but also provides directionality for research policy and industrial innovation on the pathway to 2030 deployment objectives. This represents the first systematic cross-sectoral benchmarking of LTPEMFCs that integrates datasheet-derived and reconstructed specifications with DOE and CHJU KPI frameworks providing both quantitative visualizations and a replicable methodology that clarifies current achievements while indicating where targeted innovation is needed to reach 2030 objectives.

Chemical hydrogen storage is a key step for establishing hydrogen as a main energy vector. For this purpose liquid organic hydrogen carriers (LOHCs) present the outstanding advantage of allowing a safe efficient and high-density hydrogen storage being also highly compatible with existing transport infrastructures. Typical LOHCs are organic compounds able to be hydrogenated and dehydrogenated at mild conditions enabling the hydrogen storage and release respectively. In addition the physical properties of these chemicals are also critical for practical implementation. In this work key properties of potential LOHCs of three different chemical families (homoaromatics and Nand O-heteroaromatics) are estimated using molecular simulations. Thus density viscosity vapour pressure octanol-water coefficient melting point flash point dehydrogenation enthalpy and hydrogen content are estimated using the programs COSMO-RS and HYSYS. In addition we have also evaluated the performance of several binary mixtures as LOHCs using these methodologies. Considering the hydrogen content characteristic temperatures and previous experimental results of the cyclic process; our simulation results suggest that 1-methylnaphthalene/1-methyldecahydronaftalene and methylbenzylpyridine/perhydromethylbenzylpyridine pairs are appropriate candidates for chemical hydrogen storage. Binary mixtures of LOHCs are also relevant alternatives since substances with a great potential can be used as LOHCS when dissolved. That is the case of naphthalene and 1-methyl-naphthalene mixtures or indoles dissolved in benzene or benzylbenzene. Concerning O-compounds although several pairs could be used as LOHCs thermodynamic and kinetic feasibility of the hydrogenation/dehydrogenation cycles must be better studied.

The road-transport is one of the major contributors to greenhouse global gas (GHG) emissions where hydrogen (H2) combustion engines can play a crucial role in the path towards the sector’s decarbonization goal. This study focuses on comparing the performance and emissions of port-fuel injection (PFI) and direct injection (DI) in a spark ignited combustion engine when is fuelled by hydrogen and other noteworthy fuels like methane and coke oven gas (COG). Computational fluid dynamic simulations are performed at optimal spark advance and air-fuel ratio (λ) for engine speeds between 2000 and 5000 rpm. Analysis reveals that brake power increases by 40% for DI attributed to 30.6% enhanced volumetric efficiency while the sNOx are reduced by 36% compared to PFI at optimal λ = 1.5 for hydrogen. Additionally H2 results in 71.8% and 67.2% reduction in fuel consumption compared to methane and COG respectively since the H2 lower heating value per unit of mass is higher.

The agro-livestock sector produces about one third of global greenhouse gas (GHG) emissions. Since more energy is needed to meet the growing demand for food and the industrial revolution in agriculture renewable energy sources could improve access to energy resources and energy security reduce dependence on fossil fuels and reduce GHG emissions. Hydrogen production is a promising energy technology but its deployment in the global energy system is lagging. Here we analyzed the theoretical and practical application of green hydrogen generated by electrolysis of water powered by renewable energy sources in the agro-livestock sector. Green hydrogen is at an early stage of development in most applications and barriers to its large-scale deployment remain. Appropriate policies and financial incentives could make it a profitable technology for the future.

Europe’s heavy reliance on diesel power for nearly half of its railway lines for both goods and passengers has significant implications for carbon emissions. To address this challenge the European Union advocates for a shift towards hydrogen-based mobility necessitating the development of robust and cost-effective hydrogen supply chains at regional and national levels. Leveraging renewable energy sources such as wind farms and solid biomass could foster the transition to sustainable hydrogen-based transportation. In this study a mixed-integer linear programming approach integrated with an external heavy-duty refueling station analysis model is employed to address the optimal design of a new hydrogen supply chain. Through multi-objective optimization this study aimed to minimize the overall daily costs and emissions of the supply chain. By applying the model to a case study in Sicily different scenarios with varying supply chain configurations and wind curtailment factors were explored. The findings revealed that increasing the wind curtailment factor from 1% to 2% led to reductions of 12% and 15% in the total daily emission costs and network costs respectively. Additionally centralized biomass-based plants dominated hydrogen production accounting for 96% and 94% of the total production under 1% and 2% wind curtailment factors respectively. Furthermore transporting gaseous hydrogen via tube trailers proved more cost effective than using tanker trucks for liquid hydrogen when compressed gaseous hydrogen is required at the dispenser of forecourt refueling stations. Finally the breakdown of the levelized cost for the hydrogen refuelling station strongly depends on the form of hydrogen received at the gate namely liquid or gaseous. Specifically for the former the dispenser accounts for 60% of the total cost whereas for the latter the compressor is responsible for 58% of the total cost. This study highlights the importance of preliminary and quantitative analyses of new hydrogen supply chains through model-based optimization.

Hydrogen substitution in applications fueled by compressed natural gas arises as a potential alternative to fossil fuels and it may be the key to an effective hydrogen economy transition. The reduction of greenhouse gas emissions especially carbon dioxide and unburned methane as hydrogen is used in transport and industry applications makes its use an attractive option for a sustainable future. The purpose of this research is to examine the gradual adoption of hydrogen as a fuel for light-duty transportation. Particularly the study focuses on evaluating the performance and emissions of a single-cylinder port fuel injection spark-ignition engine as hydrogen is progressively increased in the natural gas-based fuel blend. Results identify the optimal conditions for air dilution and engine operation parameters to achieve the best performance. They corroborate that the dilution rate has to be adjusted to control pollutant emissions as the percentage of hydrogen is increased. Moreover the study identifies the threshold for hydrogen substitution below which the reduction of carbon dioxide emissions due to efficiency gains is negligible compared to the reduction of the carbon content in the fuel blend. These findings will help reduce the environmental footprint of light-duty transportation not only in the long term but also in the short and medium terms.

Offshore electricity production mainly by wind turbines and eventually floating PV is expected to increase renewable energy generation and their dispatchability. In this sense a significant part of this offshore electricity would be directly used for hydrogen generation. The integration of offshore energy production into the hydrogen economy is of paramount importance for both the techno-economic viability of offshore energy generation and the hydrogen economy. An analysis of this integration is presented. The analysis includes a discussion about the current state of the art of hydrogen pipelines and subsea cables as well as the storage and bunkering system that is needed on shore to deliver hydrogen and derivatives. This analysis extends the scope of most of the previous works that consider port-to-port transport while we report offshore to port. Such storage and bunkering will allow access to local and continental energy networks as well as to integrate offshore facilities for the delivery of decarbonized fuel for the maritime sector. The results of such state of the art suggest that the main options for the transport of offshore energy for the production of hydrogen and hydrogenated vectors are through direct electricity transport by subsea cables to produce hydrogen onshore or hydrogen transport by subsea pipeline. A parametric analysis of both alternatives focused on cost estimates of each infrastructure (cable/pipeline) and shipping has been carried out versus the total amount of energy to transport and distance to shore. For low capacity (100 GWh/y) an electric subsea cable is the best option. For high-capacity renewable offshore plants (TWh/y) pipelines start to be competitive for distances above approx. 750 km. Cost is highly dependent on the distance to land ranging from 35 to 200 USD/MWh.

The energy efficiency of water electrolysis is limited by the sluggish kinetics of the anodic oxygen evolution reaction (OER) which simultaneously produces a low-value product oxygen. A promising strategy to address this challenge is to replace OER with a more favorable oxidation reaction that yields a valuable co-product. In this study we investigate the electrochemical reforming of glycerol in alkaline media to simultaneously produce hydrogen at a Pt cathode and formate at a NiSe₂ anode. The NiSe₂ electrode achieves a glycerol oxidation reaction (GOR) current density of up to 100 mA cm−2 in a 1 M KOH solution containing 1 M glycerol significantly outperforming a reference elemental Ni electrode. Both electrodes exhibit high Faradaic efficiencies (FE) achieving around 93 % for formate production at an applied potential of 1.6 V vs. RHE. To rationalize this exceptional performance density functional theory (DFT) calculations were conducted revealing that the incorporation of Se into NiSe₂ enhances the glycerol adsorption and modulates the electron density thereby lowering the energy barrier for the initial dehydrogenation step in the formate formation pathway. These findings provide valuable insights for the design of cost-effective high-performance electrocatalysts for organic oxidation-assisted hydrogen production advancing a more sustainable and economically attractive route for hydrogen generation and chemical valorization.

This study investigates the use of hydrogen (H2 ) as a substitute for compressed natural gas (CNG) in a heavyduty (HD) six-cylinder engine focusing on both port fuel injection (PFI) and direct injection (DI) systems. Numerical modeling in a 0D/1D environment was employed simulating engine operation under stationary conditions and during the worldwide harmonized transient cycle (WHTC) and worldwide harmonized vehicle cycle (WHVC) homologation cycles. Results indicated a reduction in torque (7% for direct injection and 21.5% for port fuel injection) and power (32% for direct injection and 35.5% for port fuel injection) when switching from CNG to H2 . Efficiency slightly decreased primarily due to knocking at high engine loads and speeds during H2 operation. The reduced torque and power were mainly attributed to the turbocharger being undersized for H2 given its low density and the lean mixture combustion strategy used. Upgrading the turbocharger or implementing a two-stage compressor could restore or even improve torque and power levels compared to CNG. Heat transfer losses in the H2 engine were lower than with CNG due to the lower incylinder temperature resulting from the lean mixture strategy which also contributed to a significant reduction in nitrogen oxides (NOx ) emissions approximately 2.5 times lower than those with CNG. Despite a notable exhaust energy loss during H2 operation caused by delayed combustion due to knocking the lower NOx emissions and absence of carbon emissions are crucial for reducing pollution. During vehicle cycles selecting an optimal gear-shift strategy is critical to mitigating the performance gap resulting from reduced torque and power with H2 fueling.

To reach the decarbonisation goals a zero CO2 emissions large ship propulsion system is proposed in this work. The ship selected is a large ferry propelled by an internal combustion engine fuelled by an ammonia-hydrogen blend. The only fuel loaded in the vessel will be ammonia. The hydrogen required for the combustion in the engine will be produced onboard employing ammonia decomposition. The heat required for this decomposition section will be supplied by using the hot flue gases of the combustion engine. To address the issues regarding NOx emissions a selective catalytic reduction (SCR) reactor was designed. The main operating variables for all the equipment were computed for engine load values of 25% 50% 75% and 100%. Considering the lowest SCR removal rate (91% at an engine load of 100%) the NOx emissions of the vessel were less than 0.5 g/kWh lower than the IMO requirements. An energy analysis of the system proposed to transform ammonia into energy for shipping was conducted. The global energy and exergy efficiencies were 42.4% and 48.1%. In addition an economic analysis of the system was performed. The total capital cost (CAPEX) for the system can be estimated at 8.66 M€ (784 €/kW) while the operating cost (OPEX) ranges between 210 €/MWh (engine load 100%) and 243 €/MWh (engine load of 25%). Finally a sensitivity analysis for the price of ammonia was performed resulting in the feasibility of reducing the operating cost to below 150 €/MWh in the near horizon.

In the quest for a sustainable future energy-intensive industries (EIIs) stand at the forefront of Europe’s decarbonisation mission. Despite their significant emissions footprint the path to comprehensive decarbonisation remains elusive at EU and national levels. This study scrutinises key sectors such as non-ferrous metals steel cement lime chemicals fertilisers ceramics and glass. It maps out their current environmental impact and potential for mitigation through innovative strategies. The analysis spans across Spain Greece Germany and the Netherlands highlighting sector-specific ecosystems and the technological breakthroughs shaping them. It addresses the urgency for the industry-wide adoption of electrification the utilisation of green hydrogen biomass bio-based or synthetic fuels and the deployment of carbon capture utilisation and storage to ensure a smooth transition. Investment decisions in EIIs will depend on predictable economic and regulatory landscapes. This analysis discusses the risks associated with continued investment in high-emission technologies which may lead to premature decommissioning and significant economic repercussions. It presents a dichotomy: invest in climate-neutral technologies now or face the closure and offshoring of operations later with consequences for employment. This open discussion concludes that while the technology for near-complete climate neutrality in EIIs exists and is rapidly advancing the higher costs compared to conventional methods pose a significant barrier. Without the ability to pass these costs to consumers the adoption of such technologies is stifled. Therefore it calls for decisive political commitment to support the industry’s transition ensuring a greener more resilient future for Europe’s industrial backbone.

Fuel cells (FCs) and hydrogen technologies are emerging renewable energy sources with promising results when applied to wastewater treatment (WWT). These devices serve not only for power generation but some specific FCs can be employed for degradation of pollutants and synthesis of intermediates needed in WWT. Microbial FCs are potent devices for WWT even containing refractory pollutants. Despite being a nascent technology with high capital expenses the use of cost-effective materials reduction of operational cost and increased generation of energy and value-added chemicals such as hydrogen will facilitate the market penetration through selected niches and hybridization with alternative WWT technologies.

Energy systems increasingly rely on the synergistic operations of the electricity and hydrogen markets pursuing decarbonization. In this context it is necessary to develop tools capable of representing the interactions between these two markets to understand the role of hydrogen as an energy vector. This paper introduces a bi-level optimization model that captures the interactions between the electricity and hydrogen markets positioning hydrogen generators as strategic electricity price makers in the power market. The model can be efficiently solved and applied to real-world scenarios by reformulating it as a Mixed Integer Linear Program. The case studies analyze spot market behaviors when hydrogen generators are modeled as price makers in the electricity market. First single-period simulations reveal the effects of price-making and next a year-long simulation assesses broader implications. The findings demonstrate that conventional modeling assumptions such as the price-taker hydrogen generators in the electricity market and constant production cost hypothesis lead to non-optimal hydrogen generation strategies that raise electricity prices while reducing the profit of hydrogen generators and the hydrogen market social welfare. These results highlight the need for models that accurately reflect the interdependencies between these two energy markets.

The use of hydrogen in internal combustion engines is a promising solution for the decarbonisation of the transport sector. The current transition scenario is marked by the unavailability and storage challenges of hydrogen. Dual fuel combustion of hydrogen and gasoline in current spark ignition engines is a feasible solution in the short and medium term as it can improve engine efficiency reduce pollutant emissions and contribute significantly in tank to wheel decarbonisation without major engine modification. However new research is needed to understand how the incorporation of hydrogen affects existing engines to effectively implement gasoline-hydrogen dual fuel option. Understanding the impact of hydrogen on the combustion process (e.g. combustion speed) will guide and optimize the operation of engines under dual fuel combustion conditions. In this work a commercial gasoline direct injection engine has been modified to operate with gasolinehydrogen fuels. The experiments have been carried out at various air–fuel ratios ranging from stoichiometric to lean combustion conditions at constant engine speed and torque. At each one of the 14 experimental points 200-cycle in-cylinder pressure traces were recorded and processed with a quasi-dimensional diagnostic model and a combustion speed analysis was then carried out. It has been understood that hydrogen mainly reduces the duration of the first combustion phase. Hydrogen also enables to increase air excess ratios (lean in fuel combustion) without significantly increasing combustion duration. Furthermore a correlation is proposed to predict combustion speed as a function of the fuel and air mixture properties. This correlation can be incorporated to calculate combustion duration in predictive models of engines operating under different fuel mixtures and different geometries of the combustion chamber with pent-roof cylinder head and flat piston head.

Hydrogen technologies are evolving to decarbonise the transport sector. The present work focuses on the technical design of a Hydrogen Refueling Station to supply hydrogen to five buses in the city of Valencia Spain. The study deals with the technical selection of the components from production to consumption setting an efficient standardisation method. Different calculation are used to size the storage systems for 70.8 kg of hydrogen produced by the elecrolyser daily. For the high-pressure storage system massive and cascade methods are proposed being the last one more efficient (1577.53 Nm3 non usable volume compared to 9948.95 Nm3 of the massive method).

This paper presents an energy management system (EMS) based on a novel approach using model predictive control (MPC) for the optimized operation of power sources in a hybrid charging station for electric vehicles (EVs). The hybrid charging station is composed of a photovoltaic (PV) system a battery a complete hydrogen system based on a fuel cell (FC) electrolyzer (EZ) and tank as an energy storage system (ESS) grid connection and six fast charging units all of which are connected to a common MVDC bus through Z-source converters (ZSC). The MPC-based EMS is designed to control the power flow among the energy sources of the hybrid charging station and reduce the utilization costs of the ESS and the dependency on the grid. The viability of the EMS was proved under a long-term simulation of 25 years in Simulink using real data for the sun irradiance and a European load profile for EVs. Furthermore this EMS is compared with a simpler alternative that is used as a benchmark which pursues the same objectives although using a states-based strategy. The results prove the suitability of the EMS achieving a lower utilization cost (-25.3%) a notable reduction in grid use (-60% approximately) and an improvement in efficiency.

This paper investigates the temperature control problem in hydrogen fuel cells based on the improved sliding mode control method specifically within the context of multirotor drone applications. The study focuses on constructing a control-oriented nonlinear thermal model which serves as a foundation for the subsequent development of a practical temperature regulation approach. Initially a novel sliding mode control strategy is proposed which significantly enhances the precision and stability of temperature control by reducing the impact of sensor errors and environmental disturbances. Subsequently the effectiveness and robustness of this control method under various dynamic loads and environmental conditions are demonstrated. The simulation results demonstrate that the improved sliding mode controller is effective in managing and regulating the fuel cell temperature ensuring optimal performance and stability.

Green hydrogen production is a sustainable energy solution with great potential offering advantages such as adaptability storage capacity and ease of transport. However there are challenges such as high energy consumption production costs demand and regulation which hinder its largescale adoption. This study explores the role of simulation models in optimizing the technical and economic aspects of green hydrogen production. The proposed system which integrates photovoltaic and energy storage technologies significantly reduces the grid dependency of the electrolyzer achieving an energy self-consumption of 64 kWh per kilogram of hydrogen produced. By replacing the high-fidelity model of the electrolyzer with a reduced-order model it is possible to minimize the computational effort and simulation times for different step configurations. These findings offer relevant information to improve the economic viability and energy efficiency in green hydrogen production. This facilitates decision-making at a local level by implementing strategies to achieve a sustainable energy transition.

The decarbonization of the maritime sector represents a priority in the energy policy agendas of the majority of Countries worldwide and the International Maritime Organization (IMO) has recently revised its strategy aiming for an ambitious zero-emissions scenario by 2050. In these regards there is a broad consensus on hydrogen as one of the most promising clean energy vectors for maritime transport and a key towards that goal. However to date an international regulatory framework for the use of hydrogen on-board of ships is absent this posing a severe limitation to the adoption of hydrogen technologies in this sector. To cope with this issue this paper presents a preliminary gap assessment analysis for the International Code of Safety for Ship Using Gases or other Low-flashpoint Fuels (IGF Code) with relation to hydrogen as a fuel. The analysis is structured according to the IGF Code chapters and a bottom-up approach is followed to review the code content and assess its relevance to hydrogen. The risks related to hydrogen are accounted for in assessing the gaps and providing a first level set of recommendations for IGF Code updates. By this means this work settles the basis for further research over the identified gaps towards the identification of a final set of recommendations for the IGF Code update.

Energy communities led by local citizens are vital for achieving the European energy transition goals. This study examines the design of a regional energy community in a rural area of Spain aiming to address the pressing issue of rural depopulation. Seven villages were selected based on criteria such as size energy demand population and proximity to infrastructure. Three energy valorization scenarios generating eight subscenarios were analyzed: (1) self-consumption including direct sale (1A) net billing (1B) and selling to other consumers (1C); (2) battery storage including storing for self-consumption (2A) battery-to-grid (2B) and electric vehicle recharging points (2C); and (3) advanced options such as hydrogen refueling stations (3A) and hydrogen-based fertilizer production (3B). The findings underscore that designing rural energy communities with a focus on social impact—especially in relation to depopulation—requires an innovative approach to both their design and operation. Although none of the scenarios alone can fully reverse depopulation trends or drive systemic change they can significantly mitigate the issue if social impact is embedded as a core principle. For rural energy communities to effectively tackle depopulation strategies such as acting as an energy retailer or aggregating individual villages into a single unified energy community structure are crucial. These approaches align with the primary objective of revitalizing rural communities through the energy transition.

The use of aluminum-based products is widespread and growing particularly in industries such as automotive food packaging and construction. Obtaining aluminum is expensive and energy-intensive making the recycling of existing products essential for economic and environmental viability. This work explores the potential of using green hydrogen as a replacement for natural gas in the smelting and refining furnaces in aluminum recycling facilities. The adoption of green hydrogen has the potential to curtail approximately 4.54 Ktons/year of CO2 emissions rendering it a sustainable and economically advantageous solution. The work evaluates the economic viability of a case study through assessing the Net Present Value (NPV) and the Internal Rate of Return (IRR). Furthermore it is employed single- and multi-parameter sensitivity analyses to obtain insight on the most relevant conditions to achieve economic viability. Results demonstrate that integrating on-site green hydrogen generation yields a favorable NPV of €57370 an IRR of 9.83% and a 19.63-year payback period. The primary factors influencing NPV are the initial electricity consumption stack and the H2 price.

The global economic growth the increase in thepopulation and advances in technology lead to an increment in theglobal primary energy demand. Considering that most of thisenergy is currently supplied by fossil fuels a considerable amountof greenhouse gases are emitted contributing to climate changewhich is the reason why the next European Union bindingagreement is focused on reducing carbon emissions usinghydrogen. This study reviews different technologies for hydrogenproduction using renewable and non-renewable resources.Furthermore a comparative analysis is performed on renewable-based technologies to evaluate which technologies are economically and energetically more promising. The results show howbiomass-based technologies allow for a similar hydrogen yield compared to those obtained with water-based technologies but withhigher energy efficiencies and lower operational costs. More specifically biomass gasification and steam reforming obtained a properbalance between the studied parameters with gasification being the technique that allows for higher hydrogen yields while steamreforming is more energy-efficient. Nevertheless the application of hydrogen as the energy vector of the future requires both the useof renewable feedstocks with a sustainable energy source. This combination would potentially produce green hydrogen whilereducing carbon dioxide emissions limiting global climate change and thus achieving the so-called hydrogen economy.