Publications

Hydrogen energy represents an ideal medium for energy storage. By integrating hydrogen power conversion utilization and storage technologies with distributed wind and photovoltaic power generation techniques it is possible to achieve complementary utilization and synergistic operation of multiple energy sources in the form of microgrids. However the diverse operational mechanisms varying capacities and distinct forms of distributed energy sources within hydrogen-coupled microgrids complicate their operational conditions making fine-tuned scheduling management and economic operation challenging. In response this paper proposes an energy management method for hydrogen-coupled microgrids based on the deep deterministic policy gradient (DDPG). This method leverages predictive information on photovoltaic power generation load power and other factors to simulate energy management strategies for hydrogen-coupled microgrids using deep neural networks and obtains the optimal strategy through reinforcement learning ultimately achieving optimized operation of hydrogen-coupled microgrids under complex conditions and uncertainties. The paper includes analysis using typical case studies and compares the optimization effects of the deep deterministic policy gradient and deep Q networks validating the effectiveness and robustness of the proposed method.

The MultHyFuel project notably aims to produce the data missing for usable risk analysis and mitigation activity for Hydrogen Refuelling Stations (HRS) in a multi-fuel context. In this framework realistic releases of hydrogen that could occur in representative multi-fuel forecourts were studied. These releases can occur inside or outside fuel dispensers and they can interact with a complex environment notably made of parked cars and trucks. This paper is focused on the most critical scenarios that were addressed by a sub-group through the use of Computational Fluid Dynamics (CFD) modelling. Once the corresponding source terms for hydrogen releases were known two stages are followed:<br/>♦ Model Validation – to evaluate the CFD models selected by the task partners and to evaluate their performance through comparison to experimental data.<br/>♦ Realistic Release Modelling – to perform demonstration simulations of a range of critical scenarios.<br/>The CFD models selected for the Model Validation have been tested against measured data for a set of experiments involving hydrogen releases. Each experiment accounts for physical features that are encountered in the realistic cases. The selected experiments include an under-expanded hydrogen jet discharging into the open atmosphere with no obstacles or through an array of obstacles. Additionally a very different set-up was studied with buoyancy-driven releases inside a naturally ventilated enclosure. The results of the Model Validation exercise show that the models produce acceptable solutions when compared to measured data and give confidence in the ability of the models and the modellers to capture the behaviour of the realistic releases adequately. The Realistic Release Modelling phase will provide estimation of the flammable gas cloud volume for a set of critical scenarios and will be described at the second stage.

The growing demand for energy and the need to reduce the carbon footprint has made green hydrogen a promising alternative to traditional fossil fuels. Green hydrogen is produced using renewable energy sources making it a sustainable and environmentally friendly energy source. Solid-state hydrogen storage aims to store hydrogen in a solid matrix offering potential advantages such as higher safety and improved energy density compared to traditional storage methods such as compressed gas or liquid hydrogen. However the development of efficient and economically viable solid-state storage materials is still a challenge and research continues in this field. Borophene is a two-dimensional material that offers potential as an intermediate hydrogen storage material due to its moderate binding energy and reversible behavior. Its unique geometry and electronic properties also allow for higher hydrogen adsorption capacity than metal-based complex hydrides surpassing the goals set by the U.S. Department of Energy. Borophene has shown great potential for hydrogen storage but it is still not practical for commercial use. In this review borophene nanomaterials chemical and physical properties are discussed related to hydrogen storage and binding energy. The importance of borophene for hydrogen storage the challenges it faces and its future prospects are also being discussed.

In an effort to encourage industries to switch from fossil fuels to renewable energy resources for supplying their energy demands the exergy and financial aspects of a thermodynamic energy generation system were studied. The suggested system was modeled by MATLAB commercial software to assess the decision-making parameters affecting power generation cooling capacity and to produce hydrogen. The objective functions of this study were exergy efficiency and cost rate while the temperatures at the inlet of the turbine and the evaporator irradiated solar energy mass flow rate and surface area of the collector were the decision-making variables. The model was optimized via MOPSO and its results were compared with two widely utilized algorithms namely NSGA-II and SPEA-II. The comparison results indicated that MOPSO surpassed other two optimization algorithm resulting in exergy efficiency and cost rate of 2.11 % and 21.14 $/h respectively. According to this method the optimum generated power was equal to 21.01 kW. Eventually this system was utilized and evaluated in the city of Semnan Iran. The performance results of the system in Semnan showed that the annual power output taking into account the changes in radiation and ambient temperature is between 316667.4 and 428080.5 kW. Also the amount of hydrogen production is between 1503.66 and 1534.997 kg.

Renewable hydrogen production has an important role in global decarbonization. However when coupled with intermittent and variable sources such as wind or PV electrolyzers are subjected to part-load and dynamic operation. This can lead to low utilization factors and faster degradation of the electrolyzers and affect the specific hydrogen cost. The design and sizing of such electrolysis systems are fundamental to minimize costs. In this study several configurations of an electrolysis system producing green hydrogen from a 39 MWwind farm are compared. The effects of both the size of the plant and the number of separated groups into which it is divided are investigated. Dividing the plant into two separated groups resulted to be enough to increase hydrogen production; a further increase in the number of groups didn't produce significant differences. The most profitable configurations resulted that with one or two groups depending on the hydrogen selling price.

The continued use of energy sources based on fossil fuels has various repercussions for the environment. These repercussions are being minimized through the use of renewable energy supplies and new techniques to decarbonize the global energy matrix. For many years hydrogen has been one of the most used gases in all kinds of industry and now it is possible to produce it efficiently on a large scale and in a non-polluting way. This gas is mainly used in the chemical industry and in the oil refining industry but the constant growth of its applications has generated the interest of all the countries of the world. Its use in transportation petrochemical industries heating equipment etc. will result in a decrease in the production of greenhouse gases which are harmful to the environment. This means hydrogen is widely used and needed by countries creating great opportunities for hydrogen export business. This paper details concepts about the production of green hydrogen its associated technologies and demand projections. In addition the current situation of several countries regarding the use of this new fuel their national strategy and advances in research carried out in different parts of the world for various hydrogen generation projects are discussed. Additionally the great opportunities that Chile has for this new hydrogen export business thanks to the renewable energy production capacities in the north and south of the country are discussed. The latter is key for countries that require large amounts of hydrogen to meet the demand from various industrial energy and transportation sectors. Therefore it is of global importance to determine the real capacities that this country has in the face of this new green fuel. For this modeling was carried out through mathematical representations showing the behavior of the technologies involved in the production of hydrogen for a system composed of an on-grid photovoltaic plant an electrolyser and compressor together with a storage system. The program optimized the capacities of the equipment in such a way as to reduce the costs of hydrogen production and thereby demonstrate Chile’s capacity for the production of this fuel. From this it was found that the LCOH for the case study was equivalent to 3.5 USD/kg which is not yet considered a profitable value for the long term. Due to this five case studies were analyzed to see what factors influence the LCOH and thereby reduce it as much as possible.

Green hydrogen is the term used to reflect the fact that hydrogen is generated from renewable energies. This process is commonly performed by means of water electrolysis decomposing water molecules into oxygen and hydrogen in a zero emissions process. Proton exchange membrane (PEM) electrolyzers are applied for such a purpose. These devices are complex systems with nonlinear behavior which impose the measurement and control of several magnitudes for an effective and safe operation. In this context the modern paradigm of Digital Twin (DT) is applied to represent and even predict the electrolyzer behavior under different operating conditions. To build this cyber replica a paramount previous stage consists of characterizing the device by means of the curves that relate current voltage and hydrogen flow. To this aim this paper presents a processes supervision system focused on the characterization of a experimental PEM electrolyzer. This device is integrated in a microgrid for production of green hydrogen using photovoltaic energy. Three main functions must be performed by the supervision system: measurement of the process magnitudes data acquisition and storage and real-time visualization. To accomplish these tasks firstly a set of sensors measure the process variables. In second place a programmable logic controller is responsible of acquiring the signals provided by the sensors. Finally LabVIEW implements the user interface as well as data storage functions. The process evolution is observed in real-time through the user interface composed by graphical charts and numeric indicators. The deployed process supervision system is reported together with experimental results to prove its suitability.

Green hydrogen is expected to be traded globally in future greenhouse gas neutral energy systems. However there is still a lack of temporally- and spatially-explicit cost-potentials for green hydrogen considering the full process chain which are necessary for creating effective global strategies. Therefore this study provides such detailed cost-potentialcurves for 28 selected countries worldwide until 2050 using an optimizing energy systems approach based on open-field photovoltaics (PV) and onshore wind. The results reveal huge hydrogen potentials (>1500 PWhLHV/a) and 79 PWhLHV/a at costs below 2.30 EUR/kg in 2050 dominated by solar-rich countries in Africa and the Middle East. Decentralized PVbased hydrogen production even in wind-rich countries is always preferred. Supplying sustainable water for hydrogen production is needed while having minor impact on hydrogen cost. Additional costs for imports from democratic regions are only total 7% higher. Hence such regions could boost the geostrategic security of supply for greenhouse gas neutral energy systems.

Fuel cell- and electric-powered trucks are promising technologies for zero-emission heavyduty transportation. Recently Fuel Cell Trucks (FCT) have gained wider acceptance as the technology of choice for long-distance trips due to their lighter weight and shorter fueling time than electric-powered trucks. Broader adoption of Fuel Cell Trucks (FCT) requires planning strategies for locating future hydrogen refueling stations (HRS) especially for fleets that transport freight along intercity and inter-country highways. Existing mathematical models of HRS placement often focus on inner-city layouts which make them inadequate when studying the intercity and intercountry FCT operation scale of FCT. Furthermore the same models rarely consider decentralized hydrogen production from renewable energy sources essential for decarbonizing the transportation sector. This paper proposes a mathematical model to guide the planning of the hydrogen infrastructure to support future long-haul FCTs. First the model uses Geographic Information System (GIS) data to determine the HRS’s optimal number and location placement. Then the model categorizes and compares potential hydrogen production sources including off-site delivery and on-site solar-to-hydrogen production. The proposed model is illustrated through a case study of the west coastal area of the United States (from Baja California Mexico to British Columbia Canada). Different geospatial scenarios were tested ranging from the current operational distance of FCEV (250km) and future releases of hydrogen FCT (up to 1500km). Results highlight the capabilities of the model in identifying the number and location of the HRS based on operation distances in addition to determining the optimal hydrogen production technology for each HRS. The findings also confirm the viability of green hydrogen production through solar energy which could play a critical role in a low-carbon transportation future.

The effect of electrode area electrolyte concentration temperature andlight intensity (up to 218 sun) on PV electrolysis of water is studied using a highconcentrated triple-junction (3-J) photovoltaic cell (PV) connected directly to analkaline membrane electrolyzer (EC). For a given current the voltage requirement torun an electrolyzer increases with a decrease in electrode sizes (4.5 2.0 0.5 and 0.25cm2) due to high current densities. The high current density operation leads to highOhmic losses most probably due to the concentration gradient and bubble formation.The EC operating parameters including the electrolyte concentration and temperaturereduce the voltage requirement by improving the thermodynamics kinetics andtransport properties of the overall electrolysis process. For a direct PV−EC coupling themaximum power point of PV (Pmax) is matched using EC I−V (current−voltage) curvesmeasured for different electrode sizes. A shift in the EC I−V curves toward open-circuitvoltage (Voc) reduces the Pop (operating power) to hydrogen efficiencies due to theincreased voltage losses above the equilibrium water-splitting potential. The solar-to-hydrogen (STH) efficiencies remainedcomparable (∼16%) for all electrode sizes when the operating current (Iop) was similar to the short-circuit current (Isc ) irrespectiveof the operating voltage (Vop) electrolyzer temperature and electrolyte concentration.