Titolo della tesi: Decarbonization of transport sector: a comprehensive technical, economic and operational analysis on hydrogen refuelling stations
Transport is one of the energy segments belonging to the so-called hard-to-abate sectors. Due to the continued rise in road freight activity and the reliance on low-efficiency internal combustion engines powered by fossil fuels, wheel transport is one of the few economic sectors to still record increasing emissions. Achieving the EU's ambitious yet essential 2030 and 2050 decarbonisation goals necessitates the decarbonisation of this sector. However, numerous challenges associated with the chicken-and-egg problem must still be addressed. At present, hydrogen and electricity are widely recognised as the primary sustainable energy sources. Nevertheless, these technologies must overcome the obstacles associated with the fleet and refuelling renewals, as well as the charging infrastructure. Such issues are burdened by a lack of economy of scale, which leave these technologies as expensive nice solutions. Consequently, a key role in the transitional phase of transport decarbonisation may be ascribed to bridging technologies, such as plug-in hybrid vehicles, and bridging fuels, including hydrogen-enriched compressed natural gas (HCNG) blends.
In this framework the aim of this dissertation is to provide a comprehensive analysis regarding the transport sector greening with a specific focus on hydrogen refuelling stations. Hence, the strengths, weaknesses, opportunities and threats associated with the HRSs have been widely disclosed in technical, economic and legislative terms.
In order to address the issue, the thesis commences with the presentation of a solution to the so-called chicken and egg problem that is associated with hydrogen transport. This solution is centred on the potential and versatility of HCNG as a fuel for existing compressed natural gas vehicles and stations.
In the ensuing discussion, the application of hydrogen to heavy-duty vehicles has been thoroughly examined. This examination encompasses an innovative comprehensive evaluation of the various types of on-site and off-site HRSs, an assessment of the total cost of ownership (TCO), and a final investigation into the potential costs of HRSs' infrastructures in Europe by the year 2050. Moreover, a techno-economic comparison between the HRS and fast-charging stations has been conducted, to delineate a tool for defining the most competitive choice. Such techno-economic comparison has been implemented by including the total cost of ownership of the battery electric trucks and fuel cell electric trucks. The economic comparison has been completed by including the megawatt charging stations infrastructure costs. Thus, a complete cost comparison between levelized cost of hydrogen and levelized cost of charging electricity has been undertaken by using a novel indicator: the levelized cost of kilometre.
Hence, this essay addresses a variety of novel concepts from technical, economic and normative perspectives, with a particular focus on hydrogen refuelling stations.
The opportunities offered by the hydrogen enriched compressed natural gas blend as a bridging fuel for the immediate decarbonisation of the transport sector have been comprehensively assessed. This analysis raises from the doubts regarding the HCNG safety, vehicles’ states of charge and resulting driving ranges. Hence, the thermodynamic analysis of HCNG refuelling processes has been addressed to determine the impact on gas temperature due to the Joule-Thomson effect, heat transfer through the cylinder wall, the kinetic energy conversion in internal energy, and compression contribution during the fast fill-up. Specifically, the vehicle tank initial conditions and the refuelling parameters have been analysed, evaluating how they affect the final refuelling temperatures, filled mass, relative states of charge, and refuelling times.
One of the main results of the thermodynamic analysis define that hydrogen volumetric rates up to 30%vol. do not enhance significantly the vehicle tank temperature during the HCNG refuelling process. Consequently, it can be stated that pre-cooling is not necessary, unlike 70MPa-hydrogen refuelling for light-duty vehicles. This aspect is crucial for the HCNG refuelling stations. Indeed, those facilities do not need to be built from scratch; rather, they can be obtained by retrofitting existing CNG stations. Therefore, a techno economic analysis has been carried out in order to optimise the sizing process of a HCNG refuelling station. This analysis incorporated green hydrogen production, storage, compression technologies, and a mixer for on-site blend production.
The present studies corroborate the standpoint of HCNG, which anticipates its pivotal function in expediting the decarbonisation of transport and thereby nurturing the hydrogen economy. Nevertheless, the HCNG partially decarbonizes the transport segment, by substituting part of CNG with hydrogen.
Despite several EU directives promote its decarbonisation, heavy-duty mobility still shows increasing emissions, due to the continuous raise in road freight activity and reliance on low-efficiency internal combustion engines powered by fossil fuels. Hydrogen fuel cell electric trucks represent one of the most valuable solutions for the long-haul transport segment greening. However, the current lack of refuelling infrastructure represents a significant hint to the widespread deployment of hydrogen mobility.
A design methodology for converting a diesel depot into an on-site green hydrogen refuelling station dedicated to fuel cell electric trucks has been addressed, highlighting the economic benefits of such an upgrade. To do so, 150 eligible capacities of photovoltaic (PV) plant, electrolyser and low-pressure storage system have been dynamically simulated in the MATLAB/Simulink environment. Thereafter, by means of a multi-objective optimization, based on Pareto Front and Utopia Point, the optimal solutions have been identified. By maximising the hydrogen production and simultaneously minimising the levelized cost of hydrogen (LCOH), PV energy excess and compressor energy utilisation, the components size can be determined.
In regard to the decarbonisation of the sector, the significance of battery electric trucks, in addition to HFCETs, is paramount. Thus, a technical and economic comparison between hydrogen refuelling and fast charging of zero emissions trucks have been included in this thesis. Notably, a techno-economic analysis of compressed (C-H2), cryo-compressed, subcooled hydrogen refuelling stations along with a fast-charging station has been conducted. The LCOH and the levelized cost of charging (LCOC) have been compared on a per-km base and the total cost of ownership associated to BETs and FCETs have been assessed.
A further pivotal element in comprehensively addressing the chicken-and-egg problem associated with zero-emissions trucks is infrastructure costs. However, a thorough comparison of the public infrastructure costs is lacking, particularly in the context of liquid hydrogen refuelling stations (HRS). Consequently, the infrastructure costs for HRS and public megawatt charging system (MCS) stations, as well as depot charging, are analysed. Existing individual MCS and HRS studies have been examined; furthermore, cost estimates for MCS networks, subcooled liquid hydrogen (sLH2) off-site stations have been incorporated to facilitate a comparison of the infrastructure costs.
In the final section of this thesis, two authentic case studies concerning the engineering of HCNG and hydrogen refuelling stations are presented. These case studies offer a comprehensive overview of operational aspects, techno-economic details, safety considerations, and the prevailing Italian national legislation.
The objective is to address the knowledge gaps that, to the best of the author's knowledge, persist in literature concerning hydrogen refuelling stations. In particular, the primary innovations that the author seeks to address in the context of HCNG pertain to the thermodynamic analysis of the blend refuelling process and the development of a practical techno-economic tool for retrofitting a CNG station into an on-site green hydrogen-enriched compressed natural gas refuelling station. Furthermore, a novel approach has been delineated for the conversion of a diesel depot into an on-site green HRS. This approach involves the implementation of a multi-objective optimisation strategy, aiming at ascertaining the optimal combination of green hydrogen production and storage technologies' capacities. Two further significant innovations that are crucial to the decarbonisation of heavy-duty vehicles have been addressed. These innovations are the subcooled liquid hydrogen and the megawatt charging stations. The latter have been incorporated into the comparison between the total cost of ownership analysis for BETs and HFCETs and the infrastructure assessment for hydrogen refuelling and charging infrastructure for trucks in Europe.The central conclusions of this thesis demonstrate that hydrogen plays a pivotal role in the decarbonisation of the transport sector. However, it is important to acknowledge that this transition is still encumbered by certain techno-economic challenges. In this context, the utilisation of HCNG emerges as a pivotal strategy, facilitating immediate partial decarbonisation in the transport sector. This approach ensures reliable safety standards and facilitates the widespread adoption of hydrogen technologies. The economy of scale associated with a greater presence of HRSs or fast charging stations is crucial for the deployment of zero emissions trucks. A mixed infrastructure can represent an opportunity for the transport sector decarbonisation, whereby electric and hydrogen charging are not mutually exclusive. Also, the costs associated with the electric charging and gaseous hydrogen refuelling have been found to be comparable.