Spain
Hydrogen-assisted Fatigue Crack Growth: Pre-charging vs In-situ Testing in Gaseous Environments
Mar 2023
Publication
We investigate the implications of conducting hydrogen-assisted fatigue crack growth experiments in a hydrogen gas environment (in-situ hydrogen charging) or in air (following exposure to hydrogen gas). The study is conducted on welded 42CrMo4 steel a primary candidate for the future hydrogen transport infrastructure allowing us to additionally gain insight into the differences in behavior between the base steel and the coarse grain heat affected zone. The results reveal significant differences between the two testing approaches and the two weld regions. The differences are particularly remarkable for the comparison of testing methodologies with fatigue crack growth rates being more than one order of magnitude higher over relevant loading regimes when the samples are tested in a hydrogen-containing environment relative to the pre-charged samples. Aided by finite element modelling and microscopy analysis these differences are discussed and rationalized. Independent of the testing approach the heat affected zone showed a higher susceptibility to hydrogen embrittlement. Similar microstructural behavior is observed for both testing approaches with the base metal exhibiting martensite lath decohesion while the heat affected zone experienced both martensite lath decohesion and intergranular fracture.
Integration of a Multi-Stack Fuel Cell System in Microgrids: A Solution Based on Model Predictive Control
Sep 2020
Publication
This paper proposes a multi-objective model predictive control (MPC) designed for the power management of a multi-stack fuel cell (FC) system integrated into a renewable sources-based microgrid. The main advantage of MPC is the fact that it allows the current timeslot to be optimized while taking future timeslots into account. The multi-objective function solves the problem related to the power dispatch at time that includes criteria to reduce the multi-stack FC degradation operating and maintenance costs as well as hydrogen consumption. Regarding the scientific literature the novelty of this paper lies in the proposal of a generalized MPC controller for a multi-stack FC that can be used independently of the number of stacks that make it up. Although all the stacks that make up the modular FC system are identical their levels of degradation in general will not be. Thus over time each stack can present a different behavior. Therefore the power control strategy cannot be based on an equal distribution according to the nominal power of each stack. On the contrary the control algorithm should take advantage of the characteristics of the multi-stack FC concept distributing operation across all the stacks regarding their capacity to produce power/energy and optimizing the overall performance.
Comparative Analysis of Energy and Exergy Performance of Hydrogen Production Methods
Nov 2020
Publication
The study of the viability of hydrogen production as a sustainable energy source is a current challenge to satisfy the great world energy demand. There are several techniques to produce hydrogen either mature or under development. The election of the hydrogen production method will have a high impact on practical sustainability of the hydrogen economy. An important profile for the viability of a process is the calculation of energy and exergy efficiencies as well as their overall integration into the circular economy. To carry out theoretical energy and exergy analyses we have estimated proposed hydrogen production using different software (DWSIM and MATLAB) and reference conditions. The analysis consolidates methane reforming or auto-thermal reforming as the viable technologies at the present state of the art with reasonable energy and exergy efficiencies but pending on the impact of environmental constraints as CO2 emission countermeasures. However natural gas or electrolysis show very promising results and should be advanced in their technological and maturity scaling. Electrolysis shows a very good exergy efficiency due to the fact that electricity itself is a high exergy source. Pyrolysis exergy loses are mostly in the form of solid carbon material which has a very high integration potential into the hydrogen economy.
New Combustion Modelling Approach for Methane-Hydrogen Fueled Engines Using Machine Learning and Engine Virtualization
Oct 2021
Publication
The achievement of a carbon-free emissions economy is one of the main goals to reduce climate change and its negative effects. Scientists and technological improvements have followed this trend improving efficiency and reducing carbon and other compounds that foment climate change. Since the main contributor of these emissions is transportation detaching this sector from fossil fuels is a necessary step towards an environmentally friendly future. Therefore an evaluation of alternative fuels will be needed to find a suitable replacement for traditional fossil-based fuels. In this scenario hydrogen appears as a possible solution. However the existence of the drawbacks associated with the application of H2 -ICE redirects the solution to dual-fuel strategies which consist of mixing different fuels to reduce negative aspects of their separate use while enhancing the benefits. In this work a new combustion modelling approach based on machine learning (ML) modeling is proposed for predicting the burning rate of different mixtures of methane (CH4 ) and hydrogen (H2). Laminar flame speed calculations have been performed to train the ML model finding a faster way to obtain good results in comparison with actual models applied to SI engines in the virtual engine model framework.
Opportunities for Low-carbon Generation and Storage Technologies to Decarbonise the Future Power System
Feb 2023
Publication
Alternatives to cope with the challenges of high shares of renewable electricity in power systems have been addressed from different approaches such as energy storage and low-carbon technologies. However no model has previously considered integrating these technologies under stability requirements and different climate conditions. In this study we include this approach to analyse the role of new technologies to decarbonise the power system. The Spanish power system is modelled to provide insights for future applications in other regions. After including storage and low-carbon technologies (currently available and under development) batteries and hydrogen fuel cells have low penetration and the derived emission reduction is negligible in all scenarios. Compressed air storage would have a limited role in the short term but its performance improves in the long term. Flexible generation technologies based on hydrogen turbines and long-duration storage would allow the greatest decarbonisation providing stability and covering up to 11–14 % of demand in the short and long term. The hydrogen storage requirement is equivalent to 18 days of average demand (well below the theoretical storage potential in the region). When these solutions are considered decarbonising the electricity system (achieving Paris targets) is possible without a significant increase in system costs (< € 114/MWh).
Optimal Energy Management in a Standalone Microgrid, with Photovoltaic Generation, Short-Term Storage, and Hydrogen Production
Mar 2020
Publication
This paper addresses the energy management of a standalone renewable energy system. The system is configured as a microgrid including photovoltaic generation a lead-acid battery as a short term energy storage system hydrogen production and several loads. In this microgrid an energy management strategy has been incorporated that pursues several objectives. On the one hand it aims to minimize the amount of energy cycled in the battery in order to reduce the associated losses and battery size. On the other hand it seeks to take advantage of the long-term surplus energy producing hydrogen and extracting it from the system to be used in a fuel cell hybrid electric vehicle. A crucial factor in this approach is to accommodate the energy consumption to the energy demand and to achieve this a model predictive control (MPC) scheme is proposed. In this context proper models for solar estimation hydrogen production and battery energy storage will be presented. Moreover the controller is capable of advancing or delaying the deferrable loads from its prescheduled time. As a result a stable and efficient supply with a relatively small battery is obtained. Finally the proposed control scheme has been validated on a real case scenario.
Going Offshore or Not: Where to Generate Hydrogen in Future Integrated Energy Systems?
Jan 2023
Publication
Hydrogen can be key in the energy system transition. We investigate the role of offshore hydrogen generation in a future integrated energy system. By performing energy system optimisation in a model application of the Northern-central European energy system and the North Sea offshore grid towards 2050 we find that offshore hydrogen generation may likely only play a limited role and that offshore wind energy has higher value when sent to shore in the form of electricity. Forcing all hydrogen generation offshore would lead to increased energy system costs. Under the assumed scenario conditions which result in deep decarbonisation of the energy system towards 2050 hydrogen generation – both onshore and offshore – follows solar PV generation patterns. Combined with hydrogen storage this is the most cost-effective solution to satisfy future hydrogen demand. Overall we find that the role of future offshore hydrogen generation should not simply be derived from minimising costs for the offshore sub-system but by also considering the economic value that such generation would create for the whole integrated energy system. We find as a no-regret option to enable and promote the integration of offshore wind in onshore energy markets via electrical connections.
Multi-vector Energy Management System including Scheduling Electrolyser, Electric Vehicle Charging Station and Other Assets in a Real Scenario
Oct 2022
Publication
Today in the field of energy the main goal is to reduce emissions with 7 the aim of maintaining a clean environment. To reduce energy consumption 8 from fossil fuels new tools for micro-grids have been proposed. In the context 9 of multi-vector energy management systems the present work proposes an 10 optimal scheduler based on genetic algorithms to manage flexible assets in the 11 energy system such as energy storage and manageable demand. This tool is 12 applied to a case study for a Spanish technology park (360 kW consumption 13 peak) with photovoltaic and wind generation (735 kW generation peak) 14 hydrogen production (15 kW) and electric and fuel cell charging stations. 15 It provides an hourly day-ahead scheduling for the existing flexible assets: 16 the electrolyser the electric vehicle charging station the hydrogen refuelling 17 station and the heating ventilation and air conditioning system in one 18 building of the park. 19 A set of experiments is carried out over a period of 14 days using real 20 data and performing computations in real time in order to test and validate 21 the tool. The analysis of results show that the solution maximises the use of 22 local renewable energy production (demand is shifted to those hours when 23 there is a surplus of generation) which means a reduction in energy costs 24 whereas the computational cost allows the implementation of the tool in real 25 time.
Light-Driven Hydrogen Evolution Assisted by Covalent Organic Frameworks
Jun 2021
Publication
Covalent organic frameworks (COFs) are crystalline porous organic polymers built from covalent organic blocks that can be photochemically active when incorporating organic semiconducting units such as triazine rings or diacetylene bridges. The bandgap charge separation capacity porosity wettability and chemical stability of COFs can be tuned by properly choosing their constitutive building blocks by extension of conjugation by adjustment of the size and crystallinity of the pores and by synthetic post-functionalization. This review focuses on the recent uses of COFs as photoactive platforms for the hydrogen evolution reaction (HER) in which usually metal nanoparticles (NPs) or metallic compounds (generally Pt-based) act as co-catalysts. The most promising COF-based photocatalytic HER systems will be discussed and special emphasis will be placed on rationalizing their structure and light-harvesting properties in relation to their catalytic activity and stability under turnover conditions. Finally the aspects that need to be improved in the coming years will be discussed such as the degree of dispersibility in water the global photocatalytic efficiency and the robustness and stability of the hybrid systems putting emphasis on both the COF and the metal co-catalyst.
Methane Cracking as a Bridge Technology to the Hydrogen Economy
Nov 2016
Publication
Shifting the fossil fuel dominated energy system to a sustainable hydrogen economy could mitigate climate change through reduction of greenhouse gas emissions. Because it is estimated that fossil fuels will remain a significant part of our energy system until mid-century bridge technologies which use fossil fuels in an environmentally cleaner way offer an opportunity to reduce the warming impact of continued fossil fuel utilization. Methane cracking is a potential bridge technology during the transition to a sustainable hydrogen economy since it produces hydrogen with zero emissions of carbon dioxide. However methane feedstock obtained from natural gas releases fugitive emissions of methane a potent greenhouse gas that may offset methane cracking benefits. In this work a model exploring the impact of methane cracking implementation in a hydrogen economy is presented and the impact on global emissions of carbon dioxide and methane is explored. The results indicate that the hydrogen economy has the potential to reduce global carbon dioxide equivalent emissions between 0 and 27% when methane leakage from natural gas is relatively low methane cracking is employed to produce hydrogen and a hydrogen fuel cell is applied. This wide range is a result of differences between the scenarios and the CH4 leakage rates used in the scenarios. On the other hand when methane leakage from natural gas is relatively high methane steam reforming is employed to produce hydrogen and an internal combustion engine is applied the hydrogen economy leads to a net increase in global carbon dioxide equivalent emissions between 19 and 27%.
Model Predictive Control of an Off-sire Green Hydrogen Production and Refuelling Station
Jan 2023
Publication
The expected increase of hydrogen fuel cell vehicles has motivated the emergence of a significant number of studies on Hydrogen Refuelling Stations (HRS). Some of the main HRS topics are sizing location design optimization and optimal operation. On-site green HRS where hydrogen is produced locally from green renewable energy sources have received special attention due to their contribution to decarbonization. This kind of HRS are complex systems whose hydraulic and electric linked topologies include renewable energy sources electrolyzers buffer hydrogen tanks compressors and batteries among other components. This paper develops a linear model of a real on-site green HRS that is set to be built in Zaragoza Spain. This plant can produce hydrogen either from solar energy or from the utility grid and is designed for three different types of services: light-duty and heavy-duty fuel cell vehicles and gas containers. In the literature there is a lack of online control solutions developed for HRS even more in the form of optimal online control. Hence for the HRS operation a Model Predictive Controller (MPC) is designed to solve a weighted multi-objective online optimization problem taking into account the plant dynamics and constraints as well as the disturbances prediction. Performance is analysed throughout 210 individual month-long simulations and the effect of the multi-objective weighting prediction horizon and hydrogen selling price is discussed. With the simulation results this work shows the suitability of MPC for HRS control and its significant economic advantage compared to the rule-based control solution. In all simulations the MPC operation fulfils all required services. Moreover results show that a seven-day prediction horizon can improve profits by 57% relative to a one-day prediction horizon; that the battery is under-sized; or that the MPC operation strategy is more resolutive for low hydrogen selling prices.
Comparative Sustainability Study of Energy Storage Technologies Using Data Envelopment Analysis
Mar 2022
Publication
The transition to energy systems with a high share of renewable energy depends on the availability of technologies that can connect the physical distances or bridge the time differences between the energy supply and demand points. This study focuses on energy storage technologies due to their expected role in liberating the energy sector from fossil fuels and facilitating the penetration of intermittent renewable sources. The performance of 27 energy storage alternatives is compared considering sustainability aspects by means of data envelopment analysis. To this end storage alternatives are first classified into two clusters: fast-response and long-term. The levelized cost of energy energy and water consumption global warming potential and employment are common indicators considered for both clusters while energy density is used only for fast-response technologies where it plays a key role in technology selection. Flywheel reveals the highest efficiency between all the fast-response technologies while green ammonia powered with solar energy ranks first for long-term energy storage. An uncertainty analysis is incorporated to discuss the reliability of the results. Overall results obtained and guidelines provided can be helpful for both decision-making and research and development purposes. For the former we identify the most appealing energy storage options to be promoted while for the latter we report quantitative improvement targets that would make inefficient technologies competitive if attained. This contribution paves the way for more comprehensive studies in the context of energy storage by presenting a powerful framework for comparing options according to multiple sustainability indicators.
Critical Materials in PEMFC Systems and a LCA Analysis for the Potential Reduction of Environmental Impacts with EoL Strategies
Jul 2019
Publication
Commonly used materials constituting the core components of polymer electrolyte membrane fuel cells (PEMFCs) including the balance‐of‐plant were classified according to the EU criticality methodology with an additional assessment of hazardousness and price. A life‐cycle assessment (LCA) of the materials potentially present in PEMFC systems was performed for 1 g of each material. To demonstrate the importance of appropriate actions at the end of life (EoL) for critical materials a LCA study of the whole life cycle for a 1‐kW PEMFC system and 20000 operating hours was performed. In addition to the manufacturing phase four different scenarios of hydrogen production were analyzed. In the EoL phase recycling was used as a primary strategy with energy extraction and landfill as the second and third. The environmental impacts for 1 g of material show that platinum group metals and precious metals have by far the largest environmental impact; therefore it is necessary to pay special attention to these materials in the EoL phase. The LCA results for the 1‐kW PEMFC system show that in the manufacturing phase the major environmental impacts come from the fuel cell stack where the majority of the critical materials are used. Analysis shows that only 0.75 g of platinum in the manufacturing phase contributes on average 60% of the total environmental impacts of the manufacturing phase. In the operating phase environmentally sounder scenarios are the hydrogen production with water electrolysis using hydroelectricity and natural gas reforming. These two scenarios have lower absolute values for the environmental impact indicators on average compared with the manufacturing phase of the 1‐kW PEMFC system. With proper recycling strategies in the EoL phase for each material and by paying a lot of attention to the critical materials the environmental impacts could be reduced on average by 37.3% for the manufacturing phase and 23.7% for the entire life cycle of the 1‐kW PEMFC system.
Optimising Fuel Supply Chains within Planetary Boundaries: A Case Study of Hydrogen for Road Transport in the UK
Jul 2020
Publication
The world-wide sustainability implications of transport technologies remain unclear because their assessment often relies on metrics that are hard to interpret from a global perspective. To contribute to filling this gap here we apply the concept of planetary boundaries (PBs) i.e. a set of biophysical limits critical for operating the planet safely to address the optimal design of sustainable fuel supply chains (SCs) focusing on hydrogen for vehicle use. By incorporating PBs into a mixed-integer linear programming model (MILP) we identify SC configurations that satisfy a given transport demand while minimising the PBs transgression level i.e. while reducing the risk of surpassing the ecological capacity of the Earth. On applying this methodology to the UK we find that the current fossil-based sector is unsustainable as it transgresses the energy imbalance CO2 concentration and ocean acidification PBs heavily i.e. five to 55-fold depending on the downscale principle. The move to hydrogen would help to reduce current transgression levels substantially i.e. reductions of 9–86% depending on the case. However it would be insufficient to operate entirely within all the PBs concurrently. The minimum impact SCs would produce hydrogen via water electrolysis powered by wind and nuclear energy and store it in compressed form followed by distribution via rail which would require as much as 37 TWh of electricity per year. Our work unfolds new avenues for the incorporation of PBs in the assessment and optimisation of energy systems to arrive at sustainable solutions that are entirely consistent with the carrying capacity of the planet.
Waste Aluminum Application as Energy Valorization for Hydrogen Fuel Cells for Mobile Low Power Machines Applications
Nov 2021
Publication
This article proposes a new model of power supply for mobile low power machines applications between 10 W and 30 W such as radio-controlled (RC) electric cars. This power supply is based on general hydrogen from residual aluminum and water with NaOH so it is proposed energy valorization of aluminum waste. In the present research a theoretical model allows us to predict the requested aluminum surface and the required flow of hydrogen has been developed also considering in addition to the geometry and purity of the material two key variables as the temperature and the molarity of the alkaline solution used in the hydrogen production process. Focusing on hydrogen production isopropyl alcohol plays a key role in the reactor’s fuel cell vehicle as it filters out NaOH particles and maintains a constant flow of hydrogen for the operation of the machine keeping the reactor temperature controlled. Finally a comparison of the theoretical and experimental data has been used to validate the developed model using aluminum sheets from ring cans to generate hydrogen which will be used as a source of hydrogen in a power fuel cell of an RC car. Finally the manuscript shows the parts of the vehicle’s powertrain its behavior and mode of operation.
Recent Advances in Alkaline Exchange Membrane Water Electrolysis and Electrode Manufacturing
Oct 2021
Publication
Water electrolysis to obtain hydrogen in combination with intermittent renewable energy resources is an emerging sustainable alternative to fossil fuels. Among the available electrolyzer technologies anion exchange membrane water electrolysis (AEMWE) has been paid much attention because of its advantageous behavior compared to other more traditional approaches such as solid oxide electrolyzer cells and alkaline or proton exchange membrane water electrolyzers. Recently very promising results have been obtained in the AEMWE technology. This review paper is focused on recent advances in membrane electrode assembly components paying particular attention to the preparation methods for catalyst coated on gas diffusion layers which has not been previously reported in the literature for this type of electrolyzers. The most successful methodologies utilized for the preparation of catalysts including co-precipitation electrodeposition sol–gel hydrothermal chemical vapor deposition atomic layer deposition ion beam sputtering and magnetron sputtering deposition techniques have been detailed. Besides a description of these procedures in this review we also present a critical appraisal of the efficiency of the water electrolysis carried out with cells fitted with electrodes prepared with these procedures. Based on this analysis a critical comparison of cell performance is carried out and future prospects and expected developments of the AEMWE are discussed.
Hydrogen or Hydrogen-derived Methanol for Dual-fuel Compression-ignition Combustion: An Engine Perspective
Oct 2022
Publication
Synthetic fuels or e-fuels produced from captured CO2 and renewable hydrogen are envisaged as a feasible path towards a climate-neutral transportation in medium/heavy-duty and maritime sectors. EU is presently debating energy targets by 2030 for these fuels. As their production involves chemical processing of hydrogen it must be evaluated if the extra cost is worthy at least in applications where hydrogen use is possible. This manuscript focuses on the performance and environmental impact when hydrogen and methanol are fed to a heavy-duty compression-ignition engine working under dual-fuel combustion. The trade-off thermal efficiency-NOx emissions is primary considered in the assessment by combining both variables in an own defined function. During the work engine operating settings were adjusted to exploit the potential of methanol and hydrogen. Compared to conventional combustion methanol required centering the combustion towards TDC and doubling the EGR rate resulting in a low temperature highly premixed combustion almost soot-free and with extremely low NOx emissions. The best settings for hydrogen were in the middle of those for methanol and conventional combustion. Results showed great dependance with the engine load but methanol proved superior to hydrogen for all conditions. At high load 20–60 % methanol even improved the efficiency and reduced the NOx emissions obtained by conventional combustion. However at low load hydrogen could substitute 90 % of the diesel fuel while methanol failed at substitutions higher than 55 %.
Decarbonizing the Spanish Transportation Sector by 2050: Design and Techno-economic Assessment of the Hydrogen Generation and Supply Chain
May 2023
Publication
The transport sector is difficult to decarbonize due to its high reliance on fossil fuels accounting for 37% of global end-use sectors emissions in 2021. Therefore this work proposes an energy model to replace the Spanish vehicle fleet by hydrogen-fueled vehicles by 2050. Thus six regions are defined according to their proximity to regasification plants where hydrogen generation hubs are implemented. Likewise renewables deployment is subject to their land availability. Hydrogen is transported through an overhauled primary natural gas transport network while two distribution methods are compared for levelized cost of hydrogen minimization: gaseous pipeline vs liquid hydrogen supply in trucks. Hence a capacity of 443.1 GW of renewables 214 GW of electrolyzers and 3.45 TWh of hydrogen storage is required nationwide. Additionally gaseous hydrogen distribution is on average 17% cheaper than liquid hydrogen delivery. Finally all the regions present lower prices per km traveled than gasoline or diesel.
From Grey to Green and from West to East: The Geography and Innovation Trajectories of Hydrogen Fuel Technologies
May 2023
Publication
Despite the potential of hydrogen as a sustainable energy carrier existing studies analysing the recent evolution of this technology are scattered typically focusing on a specific type of hydrogen technology within a single country or region. In this paper we adopt a broader perspective providing an overview of the evolution of knowledge generation across different types of hydrogen fuel and the leading countries in developing new technologies in this field. Using data from the European Patent Office we map knowledge generation on hydrogen fuel technologies exploring its geographic distribution and its link with environmental sustainability. While the United States leads the generation of new knowledge other Asian and European countries show greater dynamism in growth and specialisation. Our study shows that although hydrogen fuel is considered environmentally friendly most recent technological developments are still related to fossil energy sources. However a faster growth rate is observed in the knowledge of hydrogen fuel from renewable sources pointing to a promising path towards sustainability. Moreover our analysis of the knowledge interconnection between different hydrogen types suggests that those technologies developed for hydrogen based on fossil energy sources have enabled novel applications based on renewable energies.
Life Cycle Assessment of an Autonomous Underwater Vehicle that Employs Hydrogen Fuel Cell
Aug 2023
Publication
In recent years there has been a significant increase in the adoption of autonomous vehicles for marine and submarine missions. The advancement of emerging imaging navigation and communication technologies has greatly expanded the range of operational capabilities and opportunities available. The ENDURUNS project is a European research endeavor focused on identifying strategies for achieving minimal environmental impact. To measure these facts this article evaluates the product impacts employing the Life Cycle Assessment methodology for the first time following the ISO 14040 standard. In this analysis the quantitative values of Damage and Environmental Impact using the Eco-Indicator 99 methodology in SimaPro software are presented. The results report that the main contributors in environmental impact terms have been placed during the manufacturing phase. Thus one of the challenges is accomplished avoiding the use phase emissions that are the focus to reduce nowadays in the marine industry.
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