Towards a new mobility concept for regional trains and hydrogen infrastructure

Highlights

• The hydrogen train shows high-energy performance and reduced hydrogen consumption.

• The integrated infrastructure operates with an energy efficiency of over 50%.

• Simulation of daily operation and refueling schedule.

• Interesting financial results for the analyzed business case.

Abstract

In this paper, an integrated system, refueling infrastructure-hydrogen hybrid fuel cell train, is deeply investigated as an advanced mobility application. The proposed system is analyzed in terms of energy performance and economic aspects. Detailed numerical modeling is performed, to size and simulate the main components of the hydrogen facility and fuel cell hybrid train, on a 140-km regional line located in Southern Italy. For the hybrid railways, two 180-kW fuel cells, in parallel, are used both for passenger and freight locomotives. To size the hydrogen fueling station, 1-day operations are considered, with a hydrogen consumption of approximately 250 kg. The station resulted to be mainly composed of a 670 kW-PEM electrolyzer, producing 260 kg of daily hydrogen, stored at 350 bar. A sensitive analysis is proposed, focusing on the main system parameters, varying the passenger number and freight weight of ± 20%. Promising results are reached, demonstrating the feasibility and benefits of the system, in terms of energy performance, with a fuel cell efficiency higher than 47% and a facility efficiency over 50%, maintaining high values even in the most demanding scenarios.

Via the financial analysis, attractive financial indicators have been reached, e.g. levelized cost of hydrogen and total cost of ownership respectively of about 8 €/kg and 12 €/km, and return on the investment of almost 19%, confirming the huge potentiality of hydrogen technology applied to heavy-duty transport.

Introduction

Energy efficiency-related actions could play an important role in achieving climate mitigation goals and sustainable development targets [1]. Among the United Nations Sustainable Development Goals (SDGs), energy and climate actions are treated as key targets [2].

In particular, the SDG 13 promotes efforts toward climate actions, in accordance with the Paris Agreement. Improvements in energy efficiency and sustainable infrastructures are the core of the SDG 7, dealing with the “promotion of affordable and clean energy” (SDG 7). The SDG 9 targets aim to develop resilient infrastructures and sustainable industrialization, employing innovation. Nowadays, these actions have been also considered as potential key factors to tackle the energy issues raised during the COVID-19 emergency [3].

Considering this context, hydrogen treated as an energy vector has a tremendous potentiality in several sectors, tackling various critical energy challenges [4]. Its applications contribute to decarbonizing different sectors [5], guaranteeing an effective process with flexibility and high efficiency [6] and serving as long-term energy storage [7].

With particular reference to the mobility sector, hydrogen refueling stations are the key infrastructures related to hydrogen storage and delivery.

Apostolou and Xydis [8] offered a comprehensive literature review on the hydrogen station's actual state of the art, including future perspective and expected outcome. In their review, it is outlined the increasing trend of hydrogen station installations, identifying two main axes to be ensured: development of infrastructures to support the mobility, and increasing in the spreading of the fuel cell electric vehicles (FCEV). Research actions are indeed needed since these infrastructures still have critical points. They could be compared to industrial facilities that have to operate with aggressive conditions of pressure and temperature [9]. The refueling process itself is the most critical operation, requiring pressurized hydrogen, up to 800 bar, and low temperature, down to −40 °C, to guarantee a safe and fast fill for fuel cell hydrogen vehicles. Mayyas and Mann [10] offered a deep overview of this infrastructure maturity and market readiness, focusing on their manufacturing competitiveness. As the main result of their analysis, the components related to the dispensing process (storage tanks, the balance of the plant system related to the compressors, and dispenser) resulted to be the most important contributors to a station overall cost. In this regard, niche research actions aimed to investigate the operation of hydrogen compressors [11]. Ligen et al. [12] investigated the performance of mechanical hydrogen compressors via a series of experimental activities, obtaining a comprehensive set of data identifying the performance of the compressors as a function of several operating parameters, while Genovese et al. [13] analyzed the minimum number of buffer tanks needed during a directly pressurized refueling process via booster compressors, to avoid pulsation-related phenomena.

Even these critical points, research efforts, industry interest, and governmental actions are strongly supporting the installations of hydrogen infrastructures, as outlined by Kurtz et al. [14], and the number of stations is rapidly increasing.

Safety and hydrogen-related risks are already the subject of international research, including unintended hydrogen releases during a hydrogen station operation [15], its risk assessment [16], or in alternative hydrogen production methods [17]. Ustolin et al. [18] investigated the potential loss of integrity and reliability of hydrogen infrastructures, identifying materials and hydrogen equipment as the critical topics and issues that research has to address. Kurtz et al. [19] offered a comprehensive overview of the open-to-public hydrogen stations, called retail stations, and their reliability, by analyzing around 180,000 fueling events and thousands of maintenance-related operation events. The authors identified how around 67% of the overall downtime and maintenance events are related to actions and issues related to the dispenser and the compressors. Safety issues are mostly related to the station supply chain, if hydrogen is delivered and supplied in trailers in gaseous or liquid form [20], [21]. Gye et al. [22] performed a risk analysis for a hydrogen station meant to be installed in an urban area, putting in evidence how hydrogen leaks from the dispensing units and trailers are the main critical ones. A complete database with similar hydrogen associated accidents is offered by Hydrogen Tool Portal [23].

To lower safety risks, a smart option towards the hydrogen economic system transition is a hydrogen station configuration characterized by an on-site production via water electrolysis. This station layout can reduce the frequent need for external trailers, offering reliability and avoiding potential accidents in the supply chain, trailer failures, and energy inefficiencies throughout the transport.

Hydrogen station configuration with an on-site electrolysis unit could also enable a better logistic, a lower environmental impact, and a potential match with local renewable energy sources.

Concerning these topics, Gu et al. [24] performed a technical and economic assessment of several production processes and hydrogen supply pathways, by considering solar energy in different Chinese areas. Among the options, the authors considered liquid hydrogen, gas trailers, methanol as an energy carrier, and water electrolysis. All of them were compared to coal-hydrogen production in terms of economics, distance, and carbon taxes. On-site production via water electrolysis showed itself as the best option in terms of environmental impact, and also in terms of energy efficiency. Kiaee et al. [25] analyzed the performance of an existing hydrogen station in Norway, focusing on the operation of an alkaline water electrolyzer, with a working pressure of 1.2 MPa, coupled with two renewable energy power plants: wind and solar. The authors investigated the response of the electrolyzer to the supplied intermittent renewable power. Among the analyzed parameters, the stack power the gas impurities were reported, as well as the operation of the electrolyzer rectifier, providing useful guidelines for the electrolyzer technology installation and operation. Lee et al. [26] investigated the performance of a PEM electrolyzer operating at high-pressure and the potential economic benefits related to its installations. A sensitivity analysis was performed, considering variations up to ± 30% of the nominal capacity, 700 m³/hr, finding how the electricity price, the equipment cost, and the construction share the highest rate and contribution to the overall cost. Ismail et al. [27] proposed a mathematical model to analyze the combination of a solar power plant coupled with a PEM water electrolyzer. The model was implemented in Matlab, in order to directly couple the photovoltaic panels and the electrolyzer, minimizing the losses and guaranteeing a high hydrogen production. The integrated system showed a combined efficiency of almost 15%.

Based on the benefits and potentialities of this technology, several authors analyzed the research issues and the performance of different hydrogen systems and infrastructures based on the process of water electrolysis, both via numerical simulation and experimental activities, adopting different approaches.

Groppi et al. [28] performed a techno-economic assessment, flanked with an environmental analysis, of a hybrid energy system, composed also of a 90 kW electrolyzer, serving Favignana Island (Italy) in terms of transportation and energy storage. The system resulted to have important performance, in terms of economic benefits and technical operation, as well as good reliability, studied via sensitivity analysis. Mehrjerdi et al. [29] investigated the feasibility of an integrated hydrogen system for a building, aiming to achieve the performance of a “net-zero energy buildings”. To face the uncertainty and the seasonality of the renewable sources often considered for these applications, the authors proposed hydrogen as the system energy storage, produced via water electrolysis in time of energy surplus, and fed to a fuel cell when power is needed. The system optimal capacity was also investigating, resulting to be about 12 kg of hydrogen, dealing with and facing the intermittency problem, and performing a reliable operation.

Xu et al. [30] proposed a novel approach to the sizing of a hybrid energy system, based on a data-driven approach via a multi-criteria and multi-objective optimization. The authors applied the approach to an energy system composed of wind turbines, solar photovoltaics, and hydrogen technologies, then validated with data coming from an existing power plant located in China. The adopted algorithm showed a system minimum levelized cost of energy and optimal energy performance with an electrolyzer size of 54 kW, a fuel cell system installed power of 20 kW, and a hydrogen storage of 450 m³.

Bhattacharyya et al. [31] analyzed the hydrogen production process coupling alkaline water electrolysis and solar energy via photovoltaic panels. In particular, the authors estimated the solar irradiance for Mumbai, an Indian location, calculating the potential energy production and the corresponding hydrogen generation, for each day of the year and daily sunshine hours. Hydrogen production was also investigated in extreme temperature conditions, by considering the minimum and the maximum temperature values registered in the chosen site. The electrolyzer size resulted to be around 60 kW by producing 10 Nm³/hr at 5 bar and 70 °C, and the economic analysis showed also a payback period of about 12 years. Fragiacomo and Genovese [32] proposed an innovative hydrogen infrastructure concept for hydrogen light mobility (FCEVs) and hydrogen injections in the natural gas grid. The infrastructure was investigated via numerical simulations, with an ad-hoc implemented model, with three different renewable sources: wind, solar, and geothermal energy. The energy performance of each site was investigated, and an economic and environmental analysis was performed, too, including also the benefits offered by these technologies in terms of health and quality of the air.

The presented literature review gives an exhaustive overview of how hydrogen stations are worldwide investigated by the scientific community, and they are analyzed from several and different points of view.

At the same time and with a marked pace, advanced hydrogen mobility is becoming a reality, increasing in popularity and showing high efficient performance [33], manly given by ongoing research on innovative layout and materials for proton exchange membrane fuel cells [34]. Among the several key benefits, the scientific community recognizes hydrogen technologies as virtually zero-emission vehicles [35], noiseless, more efficient than traditional vehicles [36], and as a potential resource for the transport sector de-carbonization, above all in railway applications [37].

Fuel cell-based trains could indeed be a suitable alternative to the Diesel ones; for a specific regional line, as investigated in [38] over the British route Birmingham Moor Street to Stratford-upon-Avon and return, they can achieve an efficiency improvement of 20%, a decrease in energy demand of 55%, and a reduction in carbon emissions of approximately 70% when compared to Diesel locomotives [38]. Besides, fuel cell technology introduction obtains positive results also in support of conventional electrified lines, as a secondary propulsion system, especially in case of electric disruption or discontinuous overhead lines [39]. In line with these topics, a detailed review is proposed by Siddiqui and Dincer [40] who have classified the main research works according to different areas, such as: prototype design/analysis, energy management, feasibility, and economic assessment and environmental performance. Among them, a particular focus is on numerical and experimental model designs and energy management systems, developed through the implementation of innovative methods and high-performing strategies.

The component selection for a specific tramway cycle is presented by in [41]; three powertrain configurations are tested (namely fuel cell-battery, fuel cell-supercapacitor, and battery supercapacitor), analyzing the vehicle performance and highlighting the satisfying fuel cell behavior, with efficiency around 49%. Not only the energy sources but also the power electronics devices play a crucial role; Fernandez el at., in their wors [42], [43], a single DC/DC converter and a two DC/DC converter powertrains are tested for a fuel cell-battery tramway; suitable degrees of hybridization are evaluated and good performance is achieved for two control systems tested: state machine and cascade control strategies. Among the innovative power-sharing strategies presented, significant importance is on optimization strategies: Zhang et al. [44] proposed an equivalent consumption minimization strategy, tested on a full-size prototype, achieving satisfying experimental results, with approximately 1.5 kg H2 for a 2.4 km-journey. These strategies have a huge impact also on rail operating costs [45]: a Firefly Algorithm Optimization-Based control is numerically tested, having a daily operating cost of $304.99 per day. The whole powertrain investigation has been performed by Piraino and Fragiacomo [46], by means of a detailed energy efficiency analysis; energy sources, power electronics, and drivetrain components are numerically modeled and tested through a multi-method control strategy, reaching 42.5% overall vehicle efficiency. Among the innovative power-sharing strategies presented, significant importance is on optimization strategies: Zhang et al. [44] proposed an equivalent consumption minimization strategy, tested on a full-size prototype, achieving satisfying experimental results, with approximately 1.5 kg H2 for a 2.4 km-journey. These strategies have a huge impact also on rail operating costs [45]: a Firefly Algorithm Optimization-Based control is numerically tested, having a daily operating cost of $304.99 per day. Along with performance and economic aspects, important considerations should be carried out on safety issues. Crucial attention is focused on hydrogen system locations: Miller et al. [47] and Peng et al. [48] suggest a roof location because of harmless hydrogen dissipations, in case of a leak, and minimum damage possibilities, in the event of rail incidents. For this hydrogen system layout, 350 bar tanks, lighter than 700 bar ones, are strongly recommended in order to maintain the vehicle center of gravity in safety ranges. In addition, especially in railways, 700 bar tank use is not indispensable since different 350 bar tanks can be located on all the car roof, without incurring space issues and guaranteeing a suitable hydrogen amount for the required operations.

To support the spreading out of these innovative vehicles, hydrogen stations are needed for the exploitation and the refueling [49]. Therefore, a research question lays in the interconnection and operation of hydrogen infrastructures and advanced mobility systems. To the best knowledge of the authors, the integration of a hydrogen refueling station with hydrogen trains has not been deeply analyzed yet, as previously investigated by the authors [50]. Moreover, a better understanding and investigations of the involved energy parameters could strongly support the sustainability of these systems, by producing relevant data analysis that can enable better decisions on their operation. As a matter of fact, an energy analysis could lead to produce relevant statistics or to enable data-driven decisions. As a strong and powerful tool, modeling could help to address important global challenges dealing with climate change and clean energy solutions. The fourth industrial revolution is indeed offering a new role to numerical models and tools, which can contribute to the deployment of renewable energy and optimized energy applications and uses, leading to important cost savings.

To address this research gap, and considering also that modeling actions and in-depth assessment are beneficial to support and sustain hydrogen advanced mobility technologies in their rolling-up and execution, thanks to more comprehensive energy analysis, the activity presented in this paper aims to give its contribution to the scientific community by presenting a mathematical model and investigations on the integration of a hydrogen infrastructure connected to a fuel cell (FC) hybrid train as an advanced mobility application.

In particular, the study of the railway and the hydrogen infrastructure performance are presented, considering results achieved for passenger and freight trains that operate on a regional track. After the vehicle performance investigation, a suitable sizing for the hydrogen station is carried out. A dispensing schedule is designed in accordance with the route features and to the operation of both the trains and the hydrogen station.

The performances of the system are indeed simulated and presented for the applied case-study, which includes the estimation of the energy demand, the integration of the associated components, sensitivity analysis of the main system parameters, and a comprehensive financial assessment.