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.