Opportunities and Barriers of Hydrogen–Electric Hybrid Powertrain Vans: A Systematic Literature Review

: The environmental impact of the road transport sector, together with urban freight transport growth, has a notable repercussions in global warming, health and economy. The need to reduce emissions caused by fossil fuel dependence and to foster the use of renewable energy sources has driven the development of zero-emissions powertrains. These clean transportation technologies are not only necessary to move people but to transport the increasing demand for goods and services that is currently taking place in the larger cities. Full electric battery-powered vans seem to be the best-placed solution to the problem. However, despite the progress in driving range and recharge options, those and other market barriers remain unsolved and the current market share of battery electric vehicles (BEVs) is not signiﬁcant. Based on the development of hydrogen fuel cell stacks, this work explains an emerging powertrain architecture concept for N1 class type vans, that combines a battery-electric conﬁguration with a fuel cell stack powered by hydrogen that works as a range extender (FC-EREV). A literature review is conducted, with the aim to shed light on the possibilities of this hybrid light-duty commercial van for metropolitan delivery tasks, providing insights into the key factors and issues for sizing the powertrain components and fuel management strategies to meet metropolitan freight ﬂeet needs. vehicle performances (payload), environmental e ﬃ ciency (pollutant emissions), fuel production and supply characteristics (cost) and refueling features (time and infrastructure).


Introduction
Nowadays, energy efficiency and sustainability are critical objectives in the value chain of business activities. Manufacturing and logistics are key links in this chain. According to International Energy Agency (IEA) and European Environment Agency (EEA) data, at the end of the year 2017, the world-level energy consumption for the industry and transport sectors were almost the same, around 12.6 ZJ, nevertheless, CO 2 emissions for industry and transport were around 6.2 Mt of CO 2 and 8 Mt of CO 2 respectively. However, what is more interesting, observe the trend curves of energy consumption and CO 2 emissions, which, for industry, has been similar since 2011, however, in the transport sector, it is continuously growing. In particular, if we focus on road transport share of greenhouse gas emissions in the EU28 zone, according to EEA data, is observed that this means of transport has the most important impact with 71.7%.The environmental impact of road transport takes on special relevance in metropolitan areas [1], mainly due to the high rate of economic activities and population concentrated in these areas. The segment of road freight transport whose activities are focused on pick-up and delivery activities in metropolitan areas is known as Urban Freight Transport

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The growth of the city areas and urban population [2]. It is a fact that this phenomenon has been growing continuously since 1950. Over 50% of the global population has lived in in urban areas [3] since 2007, and the trend evolution projects that 60% of the global population will live in cities by 2030. The number of mega-cities (cities with a population of over ten million people) expected by 2030 could reach 41 [4]. One of the consequences, among others, is the inevitable impact in greenhouse gas and pollutant emissions, opening the discussion about the measures that have to be taken to achieve the abatement of the emissions caused by the road transport.

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The new business opportunities offered by e-commerce. The European business-to-consumer (B2C) ecommerce turnover has practically doubled from 2013 to 2018. Not much is certain today, but the buying behavior after COVID-19 will rely heavily on e-commerce.
From the authors' point of view, an increasing and uncontrolled volume of UFT services may cause environmental, health and economic consequences, such as traffic congestion, pollutant emissions (both emissions and noises), energy inefficiencies, road accidents, infrastructure degradation and parking and land space for transport facilities instead of other purposes. On the other hand, greenhouse gas emissions linked to road transport in light commercial vehicles are continuously rising. As an illustrative example, the EU27 greenhouse gas emissions (GHG) caused by road transport in 2018 were 26.8% higher than the 1990s and, particularly, taking as a reference the latest EEA data in light-duty trucks, the growth reached 56.5% This worrying situation has spurred EU governments to engage with road transport environmental policies, such as forecasting low emissions areas and emission tolls, among others, aiming to reduce carbon dioxide emissions by 60% relative to 1990 levels by 2050 [5]. All these reasons lead to a transition towards lower emission vehicle technologies, aiming to reach a sustainable urban freight transport model with efficient energy consumption and at the same time achieving low environmental impacts.
Environmental policies combined with the permanent and unwavering objective of reduction in costs, because of the high cost shareof last-mile delivery in the transport process [6], are pushing the logistic companies to search for solutions for improving their overall efficiency and, at the same time, to minimize the environmental impact caused as a consequence of these activities. Currently, delivery management software (DMS) is widely used to enhance the logistic activities through tracking deliveries, delivery task management, route optimization and collecting data for the evaluation of delivery activity performances. The other face of the solution to address these challenges is based on the progressive substitution of internal combustion vehicles (ICVs) by electric vehicles (EVs) when replacing units of their urban freight delivery fleets. Electric vans could be a good option for a van fleet with a large number of vehicles, high annual mileage per vehicle, route planning and low speed profiles. These working conditions would lead to low running costs and facilitate the introduction of electric powertrains. Despite the advantageous conditions for using EVs in UFT and several governmental actions boosting their market spread, such as subsidies for the purchase of these vehicles, tax exemptions and other non-financial policies (as preferential parking zones, free access to low emissions restricted urban areas, among others), market sale evolution of electric light commercial vehicles has not been fast enough. In accordance with 2019 European Automobile Manufacturers Association (ACEA) data statistics, almost 93% of new registrations in light commercial vehicles across the European Community have a diesel powertrain and the future outlook is not very encouraging [7]. However, there is significant literature and demonstrative projects that further explore and analyze the feasibility of employing different EV technologies in passengers and commercial vehicles (Table 1). In light-duty vehicle class, battery electric vehicles (BEVs) attract all the attention, nevertheless, little attention has been paid to other available electric powertrain configurations that would be of possible interest for UFT activities. This is the case of electricity/hydrogen hybridization and specifically the use of hydrogen, in combination with electricity, in a range extender powertrain (FC-EREV) with an energy-managing strategy designed to overcome the main operational limitations: the range and the recharging time in the case of battery electric vehicles, and the lack of refueling infrastructure in the case of hydrogen. Taking into account European Alternative Fuels Observatory (EAFO) data, there are near 195,000 public charging stations across EU-33 countries, mostly concentrated in five countries, and approximately 90% are power chargers with less than 22 kW of output power. The case of hydrogen filling stations are even worse, there are only 124 filling stations in EU-33, most of them concentrated in Germany. There are other particular barriers related to technological, economic and environmental issues affecting BEV and FCEV technologies to a greater or lesser extent that affect their market success and could be solved with a fuel cell range extender powertrain (FC-EREV). Table 1. Summary of literature reviews of electric vehicle (EV) market feasibility in urban transport over the last years. Type of vehicle powertrains showed: alternative fuel vehicles (AFV), battery electric vehicles (BEV) and fuel cell electric vehicles (FCEV).

Authors, Year, Ref. (Ref., Year) Vehicle Type Powertrain
Steenberghen et al., 2008 [8] Passenger & commercial vehicles AFV Pelletier et al., 2016 [9] Commercial vehicles BEV Margaritis et al., 2016 [10] Commercial vehicles BEV Quak et al., 2016 [11] Commercial vehicles BEV Christensen et al., 2017 [12] Passenger & commercial vehicles BEV Birky et al., 2017 [13] Commercial vehicles BEV J. Wang et al., 2018 [14] Passenger vehicles FCEV Biresselioglu et al., 2018 [15] Passenger vehicles BEV M. Wang et al., 2018 [16] Commercial vehicles BEV An FC-EREV powertrain is composed of two subsystems, the vehicle propulsion subsystem and the range extender subsystem [17]. The electric propulsion system consists of an electric motor, a power converter and a battery pack. The range extender basic components are the hydrogen tanks, the fuel cell stack and a fuel cell boost converter. The fuel cell is the range extender, it powers the battery, keeping the state of charge (SoC) value according to an energy management strategy. There are two main operating strategies, charge depleting (CD) and charge sustaining (CS) modes. Usually, range extender configurations are designed to work with a blended battery energy management. In this way, the vehicle initially drives in CD mode until the battery SoC is under a certain value, in that moment the fuel cell starts working to slow down the battery discharge. The objective of this energy management strategy is to increase the vehicle range without being externally charged with electricity. Therefore, in this type of EV powertrain configuration, the electricity stored in the battery comes from the electric network (plug-in option) and from the fuel cell, powered by hydrogen (range extender option). A power control unit (PCU) electronic device manages the fuel cell and battery power outputs and at the same time the regenerative brake capability of the vehicle, according to the energy management strategy outlined. Multiple powertrain components sizing configurations are possible, such as battery capacity, volume of hydrogen tanks and fuel cell power, combined with different energy management strategies with the aim to improve the energy efficiency and allow wider ranges.
The ambition of this research work is to conduct an inquiry into the feasibility of combine hydrogen fuel cell and electric battery powertrains for UFT activities considering the fuel cell hybrid extended range electric vehicle configuration. In this powertrain, both fuels (hydrogen and electricity) manage to fulfill the vehicle requirements, such as cost of ownership, range, performance and load capacity (weight and volume). The research work presents a review of the existing literature about the use of these hybrid powertrains in light commercial vehicles in a systematic way. The method selected for the review has been discussed too. We have explored and analyzed the advantages, barriers and opportunities for employing this type of electric powertrain for urban delivery activities. The focus of the study is to identify gaps and limitations around the feasibility of this range extender technology in existing research studies and explore future trends. Consequently, this literature review aims to answer the following questions: (1) is it possible to state the suitability of the hydrogen fuel cell range extender powertrains for operation in light commercial vehicles for urban delivery tasks?, (2) does the literature provide information on the sizing of components of this type of powertrains to meet the requirements of metropolitan freight carriers?
This research work is organized as follows: Section 2 explains the literature review methodology. Section 3 presents a summary of the literature review results and describes how the research studies have addressed the problem. Section 4 presents a discussion to identify feasibility factors for employing a hydrogen fuel cell range extender powertrain as a suitable solution for light-duty commercial vehicles. The final section presents the main findings and the key insights for future research.

Scope
The last mile delivery scenario has a lot of actors, a great variety of products and a complex operations typology [18]. Global parcel services B2C market share in America and Europe is mainly dominated by four parcel and express companies: FedEx, UPS, DHL and TNT. All of them are involved in demonstrative projects or on-road tests to study the techno-economic feasibility of using electric vans in urban delivery activities because this type of vans can allow effective reduction of running costs and help to reach the environmental objectives. The light commercial vehicles in the EU must comply with the CO 2 emission target of 147 g/km specified in regulation 2019/631 and this target will be reduced by 15% for the 2025-2029 period. In Table 2 are summarized a sample of vehicles used during the last five years for testing purpose. Usually, commercial vehicle classifications are based on the gross vehicle mass (GVM) rating factor. Table 3 shows the US and EU classes considered in light and light-medium commercial vehicles category. As can be seen from the table above, almost all the vehicles have a GVM bellow 7.5 t. If we take as a reference the Table 2 data, and according to Table 3, most of the vehicles belong to N1 or 2a-b US commercial vehicle classes, respectively. These two classes seem to be the most interesting van configurations for logistic fleet operators. This type of vehicle covers a large number of applications with different usage profiles. On the other hand, preferred vehicles tested in this category are BEV-powered, with one exception; DHL has recently tested a hydrogen fuel cell range extender.
On the other hand, the availability of BEVs in the market is still growing, despite the limited demand from the market. All the best-selling brands in the EU light commercial vehicle (LCV) market, such as Ford, Renault, VW and PSA group, have battery-electric vans in their portfolio. In the EU market, the N1 category has great importance. According to the ACEA report [19], in 2016 LCV were almost 75% of the total commercial vehicles (including buses) and nearly 11% of the total vehicles. Given ICCT statistics, in 2018, the rate grew up to 12%. In this report, top-selling light commercial vehicle models in EU-28 were most of the N1 class III, such as Ford Transit, Mercedes Sprinter, Fiat Ducato, Volkswagen Transporter and Renault Master.
It seems clear that battery-electric powered vans have been the focus of great interest in urban delivery works, but there is a certain weakness that should be addressed. Particularly, the authors are hardly seeing any steps to use other electric powertrain options to solve these issues. Therefore, in the present work, the authors will perform the study mainly on the suitability of use hydrogen fuel cell range extender powertrains in light-medium commercial vehicles class for UFT tasks. Especially, those who use Li-ion batteries and PEM fuel cell stacks because of its technical characteristics and market availability [20][21][22]. This paper focuses on the literature review analysis of strengths, weakness and opportunities for market potential and feasibility from technical, economic and environmental (air pollution) points of view. Therefore, social and psychological factors, urban spatial issues and policy measures are not taken into account in the study. On the other hand, only local zero-emissions vehicles will be considered.

Review Method
To achieve the objectives of this paper, a literature review was conducted. There are different types of literature reviews [23]. Among all of them, the authors have opted for a systematic literature review with a meta-synthesis approach because this type of literature review integrates existing information in studies with diverse methodologies and provides data for rational decision making better if compared to other types of literature review methodologies [24]. The literature review method employed is based on PRISMA guidelines [25] and includes five main stages: scoping, identification, screening, eligibility and inclusion. They are summarized in a flow diagram presented in Figure 1.
For conducting the literature search it is used more representative databases, such as IEEE Explore, Springer Link, WoS and Scopus, but also Google Scholar (GS) search engine, because it is a competitive searching tool in engineering research areas [26].

Results.
In order to identify the relevant studies, we employed a set of keywords including search strings combinations of the fuel cell, hydrogen, range extender, urban freight, urban logistics, city logistics, last-mile delivery, delivery van, light commercial vehicle, light and medium-duty vehicles, sustainable logistics and sustainable supply chain. They were combined using logic operators to configure searching equations. A list of keywords and search strings are provided in Appendix A (see Appendices). The search includes documents from 2006 to 2019, written in English and published in western countries. The identification phase returned a considerable amount of documents (1842 records) with the search terms included. The screening criterion was whether the study has information about the feasibility of using electric powertrain technologies in UFT, taking into account market feasibility analysis, environmental concerns (air pollution and GHG reduction), refueling and charging infrastructure issues, economic aspects or vehicle configuration technical features. The assessment is conducted through the analysis of the title and abstract sections.
The screening phase returned 449 documents, which is why for the selection of relevant articles that follow the purpose of the document, a reading of the introduction, conclusions and reference sections was performed. The eligibility criteria we tried to assess were: (1) if the document reflects discussions about aspects such as market feasibility, environmental concerns, charging infrastructure issues, economic aspects or vehicle technical features in the use of fuel cell hybrid technologies or (2) if it includes comparisons between FC and BEV technologies (light and light/medium duty vehicles) performing urban delivery tasks. Additionally, the analysis of document references makes it possible to find articles related to one that could be interesting for the research purpose and, in this way, expanding the number of documents for the eligibility stage. In

Results
In order to identify the relevant studies, we employed a set of keywords including search strings combinations of the fuel cell, hydrogen, range extender, urban freight, urban logistics, city logistics, last-mile delivery, delivery van, light commercial vehicle, light and medium-duty vehicles, sustainable logistics and sustainable supply chain. They were combined using logic operators to configure searching equations. A list of keywords and search strings are provided in Appendix A (see Table A1). The search includes documents from 2006 to 2019, written in English and published in western countries. The identification phase returned a considerable amount of documents (1842 records) with the search terms included. The screening criterion was whether the study has information about the feasibility of using electric powertrain technologies in UFT, taking into account market feasibility analysis, environmental concerns (air pollution and GHG reduction), refueling and charging infrastructure issues, economic aspects or vehicle configuration technical features. The assessment is conducted through the analysis of the title and abstract sections.
The screening phase returned 449 documents, which is why for the selection of relevant articles that follow the purpose of the document, a reading of the introduction, conclusions and reference sections was performed. The eligibility criteria we tried to assess were: (1) if the document reflects discussions about aspects such as market feasibility, environmental concerns, charging infrastructure issues, economic aspects or vehicle technical features in the use of fuel cell hybrid technologies or (2) if it includes comparisons between FC and BEV technologies (light and light/medium duty vehicles) performing urban delivery tasks. Additionally, the analysis of document references makes it possible to find articles related to one that could be interesting for the research purpose and, in this way, expanding the number of documents for the eligibility stage. In Appendix B (see Table A2), we summarized the dimensions considered as inclusion criteria. The final number of selected studies was 41.
This section is divided into three subsections. In the first subsection, we present an overview of the selected studies and a bibliographic analysis of these documents. In the second subsection, we present a description of the main topics the research studies have focused on and how these studies have addressed the issues. Finally, we analyzed the attributes evaluated in each reference to identify key factors and issues for using FC-EREV commercial vehicles to meet metropolitan freight carrier requirements.

Selected Studies and Bibliographic Analysis
A summary of the selected studies is presented in Table 4, showing the year of publication, the powertrain type studied, the analysis topic and the methodology used. Furthermore, additional information from the studies, such as publication information, SJR index, type of document, country of origin and vehicle type are provided in Appendix C (see Table A3).  The relevant documents found have been classified to carry out further analysis. The basic characteristics used for the classification are: The results included in Figure 2a-g show that most of the documents available were written from 2013 to 2019, in scientific journal article format, principally published in Germany, US and UK, focused on light-duty vehicles (passengers and commercial use) with topics related with economic aspects, market feasibility and environmental perspectives and focused on battery and fuel cell competitiveness or hybrid-electric commercial vehicles using modeling or simulation methodologies. The results included in Figure 2a-g show that most of the documents available were written from 2013 to 2019, in scientific journal article format, principally published in Germany, US and UK, focused on light-duty vehicles (passengers and commercial use) with topics related with economic aspects, market feasibility and environmental perspectives and focused on battery and fuel cell competitiveness or hybrid-electric commercial vehicles using modeling or simulation methodologies.

Summary of Results of the Main Research Topics. Methodology Used to Address the Issues
The thematic description of the reviewed articles involves three main aspects: research topic, powertrain configuration studied and approach or method used. The data analysis reveals that the research topic of the selected documents has focused mainly on five aspects: cost, performance and efficiency analysis, market potential and environmental perspectives. On the other hand, powertrain components sizing and related technical features, and refueling infrastructure topics have been less investigated. The first of these topics focuses on the techno-economic impacts of different powertrain configurations in several attributes, such as the cost of ownership, range, payload and vehicle performances, among others. The second topic focuses on the feasibility of using EVs in UFT based on their business strengths and weakness. The third topic focuses on environmental issues, basically air pollution impacts. In the fourth topic, technical aspects of electric powertrain components are under study, basically energy storage devices and energy management strategies. Finally, the fifth one takes into account charging and refueling infrastructures, which are essential for the day-to-day operation of a logistic vehicle fleet for an urban delivery business. On the other hand, while the selected studies have conducted their research work using mainly model and simulation tool, in contrast, experimental tests are much less used. In Appendix D (see Appendices) we showed the selected documents sorted by methodology and an overview of the research challenges addressed.

Identification of Key Features Evaluated in the Selected Studies
The key topics analyzed are classified into three areas: economic, technical and operational. These techno-economic and operational issues are of particular interest to give an answer to the user requirements. The analysis of the state of the art reported in Appendix D (see Appendices) has led to generate a list of attributes linked to the key topics. Each area shows specific attributes:

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Economic attributes: purchase price and operational costs.

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Technological attributes: range, environmental efficiency and vehicle performances.

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Operational attributes: refueling infrastructure, refueling time, fuel cost, fuel production, usage intensity and route planning. Table 5 summarizes a description of the attributes evaluated. Finally, Table 6 shows an overview of the attributes evaluated in each reference. As can be seen, financial and technological features are the most studied in the literature. In contrast, operational features have received less attention.

Summary of Results of the Main Research Topics. Methodology Used to Address the Issues
The thematic description of the reviewed articles involves three main aspects: research topic, powertrain configuration studied and approach or method used. The data analysis reveals that the research topic of the selected documents has focused mainly on five aspects: cost, performance and efficiency analysis, market potential and environmental perspectives. On the other hand, powertrain components sizing and related technical features, and refueling infrastructure topics have been less investigated. The first of these topics focuses on the techno-economic impacts of different powertrain configurations in several attributes, such as the cost of ownership, range, payload and vehicle performances, among others. The second topic focuses on the feasibility of using EVs in UFT based on their business strengths and weakness. The third topic focuses on environmental issues, basically air pollution impacts. In the fourth topic, technical aspects of electric powertrain components are under study, basically energy storage devices and energy management strategies. Finally, the fifth one takes into account charging and refueling infrastructures, which are essential for the day-to-day operation of a logistic vehicle fleet for an urban delivery business. On the other hand, while the selected studies have conducted their research work using mainly model and simulation tool, in contrast, experimental tests are much less used. In Appendix D (see Tables A4-A8) we showed the selected documents sorted by methodology and an overview of the research challenges addressed.

Identification of Key Features Evaluated in the Selected Studies
The key topics analyzed are classified into three areas: economic, technical and operational. These techno-economic and operational issues are of particular interest to give an answer to the user requirements. The analysis of the state of the art reported in Appendix D (see Tables A4-A8) has led to generate a list of attributes linked to the key topics. Each area shows specific attributes:

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Economic attributes: purchase price and operational costs.

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Technological attributes: range, environmental efficiency and vehicle performances.

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Operational attributes: refueling infrastructure, refueling time, fuel cost, fuel production, usage intensity and route planning. Table 5 summarizes a description of the attributes evaluated. Finally, Table 6 shows an overview of the attributes evaluated in each reference. As can be seen, financial and technological features are the most studied in the literature. In contrast, operational features have received less attention.

Attributes Description
Purchase price The acquisition cost of the vehicle is an essential part of the whole life of ownership cost and is also affected by the aids for the purchase and legal fees and taxes.

Operational costs
The running costs are mainly dependent of annual mileages, fuel cost, road and parking taxes, maintenance and insurance costs.

Range
Total vehicle range measured in specific conditions, such as NDEC and WLTC driving cycles.
Environmental efficiency Data related to whole life cycle emissions analysis, well-to-wheel (WtW) or tank-to-wheel (TtW) studies.

Vehicle performances
This factor concerns to payload (load and volume capacity), driving speed, acceleration, maximum gradeability and powertrain configuration (energy storage systems, energy management strategies) Refueling infrastructure Recharge and refueling issues. Refueling time Time needed to get full vehicle range.

Fuel cost
Costs associated with the production, transportation, storage and delivery of fuel to the vehicle. Fuel production Facts related to fuel production and supply issues.

Usage intensity
This factor includes duty cycle characteristics, such as daily trips, route profile (slope), nominal load (usually a payload factor of 50% is considered), driving style and ambient conditions (hot or cold temperatures), and reliability and dealer support over the vehicle service life.
Route planning Daily on-road route plan involving several delivery points taking into account several constraints (e.g., time, distance and vehicle characteristics).

Discussion
The literature review shows that most of the research works, reports and demonstration projects for urban delivery transport applications focus mainly on battery commercial electric vehicles, instead of fuel cell electric vehicles, inheriting technology from the electric passenger vehicles. Nevertheless, under the actual conditions of fuel price and political trends the EVs are not competitive [7] and other alternative-fuel vehicles (AFVs), as CNG-powered vans, are preferred [37].
Although the use of BEVs in the light-duty segment (parcel distribution and transportation of goods) has already become a reality, with vehicles showing higher electric ranges and providing better levels of fuel efficiency than diesel vans operating in low speed and several stops-and-go driving conditions [31,34], electric vans are having problems to reach positioning and consolidate recognition on the market [53]. The reviewed papers show that the problem has several techno-economic and operational feasibility issues in the use of these types of powertrains in metropolitan areas for delivery activities focused on three stakeholders: fleet operator prospects, electrical energy system issues and environmental concerns. There is a relationship, shown in Table 7, between the stakeholders and the key attributes generated from the analysis of the selected studies that will be discussed in the following sections.

Fleet Operator Prospects
As already seen, a lot of logistics operators have investigated the suitability of use AFVs in their daily operations with hard driving conditions and special vehicle requirements, such us payload and driving range among others [37]. So, if EVs want to gain market share in commercial vehicles fulfilling user transport task requirements efficiently, it is important to assess several techno-economic and operational issues that have an important influence in the purchase decision. These issues are namely payload, duty cycle, refueling infrastructure, vehicle performances, maintenance and reliability concerns, and total cost of ownership.
The payload is significantly reduced in battery-electric vans mainly due to the weight of batteries. While a conventional diesel van has a payload of around 1600 kg, a battery-electric van has a much lower capacity. If we take as a reference the Renault Master L1H2 diesel-powered has 1600 kg of effective load in contrast to 1100 kg of ZE version with the same 9 m 3 of useful volume. This issue cannot be overcome unless the maximum allowed gross vehicle m would be 4250 kg [12]. Nevertheless, the payload in vans for urban delivery activities might be a non-issue from a utility point of view [36,54], but it has effects in the energy consumption, vehicle dynamics and powertrain components sizing. The fuel cell powertrains are the least overweight. In FCEVs, hydrogen is stored onboard in high-pressure fuel tanks (70 MPa). Current energy density for hydrogen power systems is at best 1.5 kW h/kg, in contrast, typical Li-Ion batteries offer at most 0.3 kW h/kg [35]. Typical fuel cell system, including the hydrogen tanks, a high power battery pack for regenerative braking and peak power demand, and the fuel cell stack plus all auxiliary fuel cell system components such as a humidifier, air blowers and control electronics, offer 0.69-1.5 kW h/kg. On the other hand, typical Li-Ion batteries offer (for 100% SoC) 0.2-0.3 kW h/kg and (for 70% SoC) 0.14-0.24 kW h/kg. Therefore, the same range of a battery-electric vehicle can be achieved with a FCEV with less weight, and hence, with less fuel consumption [42].
Another important issue is the duty cycle. There are user requirements, such us route profile (slope), climate conditions, nominal load and driving style that could affect the electric van operational range. The range of the vehicle will limit daily trips [31]. Most of the papers reviewed consider 200 km as a suitable range for a daily route, but this goal is difficult to achieve with available battery-electric vans in the market. The averaged real range of the battery-electric vans should be around the 80-120 km range, but in certain work conditions, such as high load, urban driving with frequent stop-and-go, hot or cold days, road profile (slope) and driver behavior, the range should be significantly lower [27,30,[62][63][64]. So, the real range of electric vans is quite different from the official range [37], and this is one of the main problems of BEVs. Battery packs that increase the range up to 200 km or more could be a solution, but it presents obvious problems of costs and recharging time [24]. An additional problem is the increase in weight and volume, whose impact is noticeable in electric energy consumption and payload [27,30,35]. Nevertheless, the excess weight to gain range in an FCEV is negligible, only larger tanks are needed [42].
Additionally, there are some issues with respect to recharging and refueling infrastructure. The battery-electric vans, due to the limited range, need a suitable recharging infrastructure with high power outlets (more than 20 kW) to reduce the recharging time, while recharging time is a critical factor from the user point of view [31]. According to European Alternative Fuels Observatory (EAFO) data, in the EU zone, the quality of charging public stations is increasing, but less than 9.5% are fast-charging points and the share of electric vehicles per charging point is low on average. Moreover, fast-charging is limited by the onboard vehicle charger capacity, usually around 7 kW, and could origin battery reliability problems reducing the service life. An alternative method to solve the problem is managing delivery routes [28] to avoid idle times needed for recharging. However, firstly it is not a simple matter to determine the most suitable daily delivery path for a vehicle fleet composed of a set of internal combustion, hybrid and full battery electric vehicles. It implies taking into account several, and an interrelated number of parameters, such as constrained driving-range capabilities, traffic jam, weather conditions, driver behavior and route orography, for example. Secondly, there is a recent increase in the frequency of urban deliveries. There has been considerable business development based on urban delivery possibilities and this affects the mileage [30]. Another possible solution is using battery swap stations, but it is difficult to become a reality because of the different battery standards available in the market [31]. The situation is even worse in actual hydrogen refueling stations. Taking into account European Alternative Fuels Observatory (EAFO) data the total number of HRS in the EU-33 zone is 124, but the future hydrogen infrastructures perspectives and costs associated with hydrogen production in an efficient and environmentally-friendly way are important issues too [8]. Nevertheless, the hydrogen refueling time in a fuel cell electric van is equivalent to a diesel-powered van, giving to the users a similar feeling [31,44].
On the other hand, the van required performance parameters, such as efficiency, driving speed and acceleration, maximum gradeability rate and range are dependent on the powertrain components (i.e., battery size, fuel cell power, hydrogen storage system, the energy managing strategy among others) and vehicle dynamics (i.e., curb weight, rolling and, although to a minor extent due to the low-speed urban driving conditions, the aerodynamic resistance). There is an increasing trend in the proportion of larger and powerful vans in the market because these kinds of vehicles are more useful in terms of load capacity [36,54], but these factors have a great influence in the van efficiency and CO 2 emissions. The tank-to-wheel efficiency is a key factor when comparing FCEVs and BEVs powertrain. Typical fuel cell systems efficiencies are around 40-60% due to energy consumption of system components, however, BEVs have higher efficiency, in the 80-90% range [35,40]. It is also important to take into account particular and complementary performance attributes of fuel cell stack and batteries, such as batteries' quick response and high peak power, and higher energy density of hydrogen fuel tanks [41].
Continuing with aspects related to maintenance and reliability concerns. Both of them are related to the dealer support and the powertrain components. The importance of dealer support is concerning to dealer network, the servicing maintenance interval and warranty periods [32,33]. In respect of powertrain components, according to DOE durability targets, the whole fuel cell system applied to automotive applications has to reach a minimum operating life of 5000 h and 17,000 start/stop cycles, but actual technology is far away from these targets [47], also maintenance and repair costs (spare parts and service interval frequency) are more expensive than diesel and pure electric powertrains [39]. On the other hand, current battery technologies have to solve problems of longevity, it is necessary to overcome 4000 full recharge cycles, self-discharge issues and performances in extreme climate conditions [35].
Furthermore, the total cost of ownership (TCO) and payback period have key influences in the AFVs purchase decision in large commercial fleets [7,28]. While the purchase price of a battery-electric van is higher than diesel models, the running costs are already lower thanks to the electricity and maintenance costs, provided that the van covers a minimum annual mileage [54,60]. The annual mileage depends on the transport task, and in the BEV case, it is influenced by the vehicle range and the available refueling infrastructure. In fact, yearly mileage, depreciation period of the van, purchase taxes, fuel price and the second-hand value, which depends on powertrain reliability and infrastructure availability, are key parameters in the TCO calculation [7,32,33,48].
At this point, the reviewed studies differ on the boundary conditions and the parameters used for the calculation of ownership cost. This is the case of the battery replacement cost, usable state of battery charge (SoC), energy prices, powertrain components sizing, and energy consumption. The battery replacement cost is usually omitted because it is considered that it will last the entire household period, which may not be true over certain values of annual mileages and depreciation periods [40]. This is contrary to EVs running costs advantage with the use. On the other hand, reducing the useful percentage of SoC to a real value will reduce the range and increase the operating costs [41]. The energy cost estimation is highly dependent on market conditions and electricity production mix, so its value has variations over time. The powertrain components characteristics, which affect acquisition cost to a large extent, have to fulfill a defined vehicle requirements regard to performances, range and load capacity, and optimized to minimize the operating costs [49]. Finally, the energy consumption considered relies on the duty cycle, the powertrain efficiency and the energy management strategy [25].
At least, the studies analyzed show EV should be cost-effective compared to diesel vans in certain scenario spaces defined by the type of duty cycle and cost of ownership [37,38,45]. The break-even point is different for BEVs and FCEVs, and actually more favorable for BEVs due to operating costs (energy price and maintenance costs), higher resale values and lower purchase price. Another fact detected is that many of techno-economic and operational factors are interrelated.
Nevertheless, from a fleet operator perspective, urban transport services require flexibility, high grade of van service readiness and cost-efficient coverage of delivery tasks [30], hence, the main drawbacks of BEVs such us high purchase cost, limited range, lack of suitable charging infrastructure, long recharge times and limited load capacity have been the key barriers for their market feasibility in urban freight transport activities. Moreover, fuel cell powertrain, notwithstanding its particular drawbacks, seems to be the best choice for heavy-duty vehicles [40,42].

Electric Energy System Prospects. Energy Production and Supply Issues
BEVs should overcome the range limitation in the future using advanced battery technologies with higher energy density and supported by a wide fast-charging public infrastructure, but in this case, it will be necessary to take into account those challenges related to electric grid load balancing when a large number of BEVs are recharging at the same time [27]. Intelligent management of charging periods can avoid these problems and allow a right-sizing of the new infrastructure for electricity transportation [40].
As an alternative, if the van uses hydrogen as alternative energy, could be the development of refueling stations with hydrogen produced on-site through electrolyzers and using electricity from renewable energies [29]. In this way, despite the poor efficiency in the electric energy conversion, using less electric power installed compared with a fast-charging electric station, it is possible to supply fuel to more vehicles in much less time [28]. The recharging time and power capacity of recharging stations is an important issue [31].
Another advantage of hydrogen as an energy carrier is the possibility to store peaks of electric power generation from renewable sources (wind and solar) using electrolyzers [8,29,59]. In this way, it is guaranteed the electricity supply when the power generation will be based on renewable energy sources, thanks to seasonal hydrogen storage options [44].
It is necessary to keep in mind that it is more efficient using this electricity to charge batteries because of the electrolysis process loses approximately 25% of the electric energy [42]. This main reason why the electrolysis is only profitable if the electricity used in the process has a very low cost [27]. However, it also possible to obtain hydrogen in a cost-efficient way from natural gas reforming with carbon capture and storage [8,43], meanwhile the green hydrogen production is coming.
The complementary use of electricity and hydrogen have revealed synergies in energy storage and distribution, reducing infrastructure costs [59].
Infrastructure investment for hydrogen refueling stations based on electrolysis technology using electricity from renewable sources will be more expensive than a battery charging infrastructure if the number of electric-powered vehicle fleets are low, but the situation would the reverse if all the light vehicle fleet changes to electric mobility [44].

Environmental Concerns
BEVs and FCEVs are local zero-emissions, they do not produce noises nor pollutant emissions. However, there are upstream emissions during the vehicle manufacturing process, vehicle maintenance and scrapping, and from the energy generation, storage and distribution.
Battery-electric vehicles, due to their high well to wheel efficiency, have better environmental performances (lower global GHG emissions) than FCEV [29,43,45]. Calculating the benefits in emissions of introducing FCEVs is even more uncertain than BEVs, due to the even wider selection of energy pathways available to produce hydrogen than electricity [45,52,65]. Consequently, it is also necessary to keep in mind the electricity production mix and the need for conversion of electrical generation from conventional power plants to renewable energy systems [28,35,43]. The availability of green hydrogen and high turnout of renewable sources in the electricity production mix is decisive in the environmental competitiveness of fuel cell electric vans [35,40,45,47].
In the case of BEVs, they can get the highest energy economy and achieve a GHG emission reduction if it is possible to know in advance the real work conditions of the van, optimizing the timing of the vehicle charge and the charging components (hardware and software). However, FCEVs can provide greenhouse gas reductions in hard duty conditions, such as daily trips over 200 km [42,52].
From the manufacturing processes point of view the extensive use of key raw materials, such as cobalt and lithium for batteries and platinum for fuel cell stacks, might become a problem for the deployment of fuel cell and battery powertrain technologies in the future [28,41].

Assessment of FC-EREV Powertrain Deployment in Vans for Metropolitan Delivery Tasks
Taking into account the strengths and limitations of BEVs and FCEVs for delivery activities in metropolitan areas and the powertrain synergies between both technologies, a good solution could be the FC-EREV powertrain [41]. Figure 3 summarizes FCEVs and BEVs advantages and drawbacks in the use of these technologies for light commercial vehicles compiled from the analyzed papers.
In this range extender concept, one of the major advantages lies in the fact that the power of the fuel cell stack may not be required to move the vehicle, and it can be set to operate at its maximum efficiency. However, the battery and the electric traction system must be powerful enough to move the van in driving conditions [23]. The traction battery can efficiently cover short distances (up to 100 km) and guarantee peak power demands, while the fuel cell stack allows fast refueling and sufficient range for long distances [28,30,34,38,41,46].
As previously mentioned, the total cost of ownership is the key factor in the decision to purchase. The purchase price for an FC-EREV van will be cheaper than an FCEV but more expensive than a BEV, but with less range. An analysis of operational costs [30] shows the benefits for the hybrid electrified powertrains compared with conventional vans, but the running cost is highly affected by the hydrogen cost, maintenance expenses, vehicle lifetime and annual mileage [25,32,48]. Some of these factors rely on the right powertrain component sizing. The cost-efficient component sizing depends on onboard hydrogen storage capacity, fuel cell power and traction battery size, while maintaining the performances [49,61].
On the other hand, and taking into account maintenance and repair aspects, in vehicles equipped with a proton exchange membrane (PEM) fuel cell stack type, short driving distance causes membrane stress reducing the estimated service life. In contrast, a PEM fuel cell stack working in stationary conditions can reach up to 40,000 h of service. Additionally, the Li-ion batteries for vehicles have an operative life of less than 4000 deep discharge cycles and a service life around 10-15 years. However, the battery state of health and lifecycles can vary as a function of the depth of the charge (DoD), discharge process (high or low) and the type of recharge selected (normal or fast). That is why a battery and fuel cell working together in an FC-EREV in urban driving conditions can improve both the reliability and performance, of the commercial vehicles, using the fuel cell working at its maximum efficiency to assist the battery in order to maintain a determined state of charge (SoC) level, improving the range and the overall battery and fuel cell life, and in the The traction battery can efficiently cover short distances (up to 100 km) and guarantee peak power demands, while the fuel cell stack allows fast refueling and sufficient range for long distances [28,30,34,38,41,46].
As previously mentioned, the total cost of ownership is the key factor in the decision to purchase. The purchase price for an FC-EREV van will be cheaper than an FCEV but more expensive than a BEV, but with less range. An analysis of operational costs [30] shows the benefits for the hybrid electrified powertrains compared with conventional vans, but the running cost is highly affected by the hydrogen cost, maintenance expenses, vehicle lifetime and annual mileage [25,32,48]. Some of these factors rely on the right powertrain component sizing. The cost-efficient component sizing depends on onboard hydrogen storage capacity, fuel cell power and traction battery size, while maintaining the performances [49,61].
On the other hand, and taking into account maintenance and repair aspects, in vehicles equipped with a proton exchange membrane (PEM) fuel cell stack type, short driving distance causes membrane stress reducing the estimated service life. In contrast, a PEM fuel cell stack working in stationary conditions can reach up to 40,000 h of service. Additionally, the Li-ion batteries for vehicles have an operative life of less than 4000 deep discharge cycles and a service life around 10-15 years. However, the battery state of health and lifecycles can vary as a function of the depth of the charge (DoD), discharge process (high or low) and the type of recharge selected (normal or fast). That is why a battery and fuel cell working together in an FC-EREV in urban driving conditions can improve both the reliability and performance, of the commercial vehicles, using the fuel cell working at its maximum efficiency to assist the battery in order to maintain a determined state of charge (SoC) level, improving the range and the overall battery and fuel cell life, and in the same way reducing the operating costs [23,34,46]. Consequently, it is important to have adequate energy management combining both power sources [47].
From a performance point of view, the van configuration in terms of useful volume and payload versus range is better for FC-EREV powertrain because the overweight to increase the range depends on hydrogen tanks, while in BEVs, mass increase significantly with the range due to the heavier batteries, chassis stiffness and oversized powertrain components (brakes and traction motor, among others) in order to keep the same performance [34,42]. Current technology states the useful energy density for the FCEV powertrain with 70 MPa pressure storage tanks reaches ranges almost four times higher than an equivalent BEV [42]. In this way, FC-EREV configuration gives the option to optimize the whole system to achieve higher cost-effectiveness than either which FCEV or BEV can offer [35,38]. The estimated lifecycle cost of FC-EREVs and BEVs would be similar, depending on daily mileage and costs estimations for electricity generation and hydrogen fuel. Nevertheless, the low operating cost of BEVs allows them to stay competitive when the driving range is under 100 km, but if overall costs are taken care of, FC-EREV represents a better option [41,48].
The efficiency of FC-EREVs should be similar to those provided by BEVs (over 70%) in short distances or FCEVs on large trips (around 50%) [35]. However, FC-EREV powertrain components sizing becomes complicated, a particular range requirement could be satisfied using several different hardware configurations depending on cost-effectiveness and required performances for the singular transport activity. In electric hybrid powertrains, a blended battery energy management strategy is used, based on different shares of two main operating strategies; charge depleting (CD) and charge sustaining (CS) operation mode [30]. An FC-EREV uses a blended battery energy management where the vehicle drives initially in CD mode and once the battery has reached a predefined SoC threshold, the fuel cell turns on to empower the battery allowing slow down battery discharge. The definition of the share in each mode according to technical, economical or environmental rules determine the right sizing of the powertrain components and energy management strategy, in order to maximize the energy efficiency of the powertrain configuration and minimize costs [32,38,52], maximizing the use of, up to now, inexpensive off-board electricity, while the driving range is limited only by the amount of hydrogen stored in the fuel tanks [24,38,46,48,53]. Nevertheless, determine the degree of hybridization ratio (DOH), it expresses the ratio between the peak power of the battery relative to the whole powertrain power, and the operational strategy in CD or CS mode in an extended range is not an easy matter.
It is important to remark that FC-EREV powertrain technology opens the opportunity to upgrade the existing battery-powered vans with a fuel cell range extender system. In this way, the fleet operators have the option to address delivery activities with large range requirements in metropolitan areas [39]. The lack of public hydrogen infrastructure becomes a minor matter because several delivery trips could be covered with electricity without range anxiety [44]. However, there already exists an electricity net infrastructure and, in the short term, building a recharging infrastructure over the existing power grid is likely to be significantly easier and less expensive than building a hydrogen refueling station [41]. However, this type of powertrain encourages a complementary combination of the electric charging and the hydrogen refueling infrastructure and will help to maximize energy efficiency, optimizing the use of renewable energy sources [44].
Nevertheless, there are several issues for the deployment of FC-EREV powertrains in light-duty commercial vehicles related to market status and refueling infrastructure. Nowdays, there is no flexibility for vehicle selection. Current commercial vehicle availability is limited to custom-made range-extended battery electric vehicles or prototypes. For further market deployment, more development of FC-EREV delivery van prototypes and increase the number of successful demonstration projects will be necessary [39]. On the other hand, the hydrogen refueling infrastructure available is very low, so the best solution should be the use of HRS sited at the logistic operator vehicle depot using stand-alone hydrogen generators.
Everything points to the best choice for the future development of FCEV technology begining with the deployment of FC-EREV [41].

Conclusions
This paper provides an overview of the literature addressing the employment of FC-EREV powertrain for light-duty vehicles in UFT services. It puts the focus firstly on the hydrogen fuel cell stack system that works as a range extender (FC-EREV) for a battery-powered N1 class type van designed for the transportation and delivery of goods. A literature review is conducted to assess the feasibility of using the hydrogen fuel cell range extender technology in commercial electric battery vans and provide insights into the key factors and issues for sizing the powertrain components and power management strategies to meet metropolitan freight fleet needs.
The review has explored and analyzed literature which involves three main aspects: research topic, powertrain configuration and approach or method used. The data analysis reveals that the selected documents have focused mainly on five topics. The five topics are: cost, performance and efficiency analysis, market potential (feasibility), environmental perspectives, powertrain components sizing and related technical features, and refueling infrastructure issues. These topics are classified into three areas: economic, technical and operational. These techno-economic and operational issues are of particular interest to give an answer to main stakeholders involved, such as fleet operators, energy system prospects and environmental concerns. Each issue shows specific attributes:

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Economic attributes: purchase price and operational costs.

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Technological attributes: range, environmental efficiency and vehicle performances.

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Operational attributes: refueling infrastructure, refueling time, fuel cost, fuel production, usage intensity and route planning.
Besides, by observing the number of articles per attribute, the attention is mainly focused on the cost, range, vehicle performance and efficiency analysis of electric powertrains in the UFT area. According to the research, topic key attributes to ensure the widespread use of using hydrogen-based ECVs in UFT are, in order of importance, the total cost of ownership (purchase prices and operational costs), operational conditions (range and usage intensity), vehicle performances (payload), environmental efficiency (pollutant emissions), fuel production and supply characteristics (cost) and refueling features (time and infrastructure).
On the other hand, several of the studies analyzed focuses on the comparison of BEV and FCEV powertrains for UFT activities and less attention is paid to hybrid electric powertrains in light-duty commercial vehicles, such us FC-EREV or FC-PHEV. Furthermore, the selected studies have conducted research work on the problem, using mainly modeling and simulation techniques with several powertrain configurations and energy managing strategies are used to study fuel efficiency, costs, emissions and charging infrastructure needs.
As a result of the investigation, assessment of the suitability of hydrogen fuel cell range extender powertrain in light-duty commercial vehicles for metropolitan delivery tasks are conducted, taking into account the strengths and limitations of BEVs and FCEVs for delivery activities in metropolitan areas and the powertrain synergies between both technologies. In this sense, the main findings of the study are: • User requirements for light-duty vans are related to the total cost of ownership (purchase and operating costs), autonomy between refueling (range), performance (payload, maximum gradeability rate, top speed, acceleration, etc.), operating time per day, flexibility to assign a delivery route, uptime (reliability and service maintenance intervals) and service life.
• Refueling infrastructure is a key issue for BEV and FCEV technologies. Nowdays, the number of available electric public recharging stations, although fast-growing, are limited. The situation is even worse in actual hydrogen refueling stations. • FC-EREV van purchase price is strongly influenced by the sizing of the powertrain components used and its costs over time. Different hardware configurations and energy management strategies adapted to particular duty conditions (range over 200 km and/or high usage intensity working conditions) could lead to a cost-effectiveness configuration. • FC-EREV van operational costs depend on the distance traveled per year, the number of years of ownership, maintenance expenses, the fuel cost (electricity and hydrogen) and the proportion of each energy used, this last factor is influenced by duty cycle conditions, the degree of hybridization ratio, the energy management strategy and the range available with electricity and hydrogen. The current fuel cost, to a larger extent the hydrogen cost, and the high maintenance expenses, because of greater technical complexity than BEV, could lead to a longer ownership period and it could reduce the final second-hand resale price. • FC-EREV van has clear advantages when the averaged real range needed is more than 200 km and/or high usage intensity conditions that could affect the energy consumption, as route profile (steep slopes), high load, high traffic density, delivery plan with frequent stop-and-go, adverse ambient conditions (hot or cold days) and aggressive driving style. • FC-EREV van powertrain and energy management strategy flexibility configuration allows to fulfill a great variety of user-defined performance parameters, such as range, payload, driving speed and maximum gradeability rate, with fewer effects on fuel consumption and vehicle dynamics in hard-duty conditions. Powertrain configuration and energy management strategies have a strong influence on fuel efficiency.

•
The hydrogen refueling time in an FC-EREV van is equivalent to a diesel-powered van, giving a similar feeling to the users. The electricity recharging time depends on the recharging infrastructure power outlet and the onboard vehicle charger capacity. • FC-EREV van environmental performances are more uncertain than BEVs due to variable powertrain configuration, the wider selection of energy pathways available to produce hydrogen than electricity and the current FC technology readiness, but FC-EREV vans could provide advantageous life cycle GHG reduction in hard duty conditions and/or daily trips over 200 km. In any case, as BEVs, depends on the use of renewable energy sources.
Moreover, key factors for sizing the powertrain components to meet metropolitan freight carrier needs are identified. The degree of hybridization, that is to say, how the powertrain components should be designed to operate in blended or all-electric mode and the energy management strategies are the most significant drivers. These factors influence the sizing of the powertrain components once the vehicle performance requirements have been met.
At present, FC-EREV inherits the most advantages of both technologies overcoming range and vehicle performance limitations, but also some of the weaknesses, such as lack of suitable charging infrastructure, high purchase cost, faces high technical risks and the lack of flexibility for vehicle selection. However, FC-EREV configuration gives the option to optimize the efficiency of the whole system to reach low operational costs, opens the opportunity for fleet operators to upgrade of existing battery-powered vans with a fuel cell range extender, offers an alternative path to GHG reduction and petroleum dependence, give more relaxed requirements for refueling infrastructures, less range anxiety and refueling idle times.
The authors of this literature review work have tried to shed light on the emerging problems that suppose the selection of the more suitable powertrains used in the currently diffuse last-mile delivery scenario trough a better knowledge of hydrogen fuel cell range extender van attributes and the way to satisfactorily match these attributes with end-user preferences in urban delivery tasks. For future research it is worth paying attention to (1) the influence of user requirements on the powertrain and the energy management strategy configuration, (2) how sensitive is the energy consumption and cost to these factors?, (3) which energy management strategy is adequate to maximize the efficiency for FC-EREV powertrains in metropolitan delivery activities and, finally, (4) challenges on refueling infrastructure facilities.       Table A6.
Research challenges and problems addressed of studies focused on environmental perspectives.

Authors
Problem Addressed Research Challenge Bartolozzi et al., 2013 [29] Investigation of the potential of the use of hydrogen produced from renewable sources as automotive fuel conducting a life cycle assessment for evaluating the environmental sustainability applied to a fleet of hydrogen vehicles for urban commercial delivery. A comparison of vehicles equipped with either fuel cell, standard electric and internal combustion engine is done. Evaluation of several alternative vehicle and fuel options to assess the societal benefits (greenhouse gas emissions) of replacing conventional gasoline cars.
Alternative fuelled vehicles; Dynamic simulation; Urban air pollution Thomas, 2009 [43] Comparison of alternative transportation options including hybrid electric vehicles and plug-in hybrids fuelled by gasoline, diesel fuel, natural gas, and ethanol, and all-electric vehicles powered by either batteries or fuel cells from environmental impact point of view (air pollution) and oil consumption. Comparison the use of alternative powertrain technologies on the basis of their overall efficiency and GHG emissions involved in the conversion of the primary energy source to the actual energy required at wheels through a well-to-wheel analysis.
Alternative fuelled vehicle; Greenhouse gas (GHG) emissions; Biofuels; Battery electric vehicle; Fuel cell electric vehicle; Efficiency; Well to wheel analysis; Electricity mix; Life cycle analysis (LCA) Maniatopoulos et al., 2015 [59] Review of the potential reduction of GHG emissions in road transport through the total replacement of petroleum-fuelled vehicles with hydrogen and battery electrical vehicles. Battery electric vehicle; Fuel cell electric vehicle; Hydrogen economy; Road transport; Sustainable energy strategy; GHG emissions Study of an optimal sizing methodology for an Energy Storage System (ESS) composed by a fuel cell and an assistant source to show the benefits of hybridization according to the range in terms of weight, cost and fuel consumption.
Energy Storage System; Fuel cell; Hydrogen consumption; Sizing; Energy management strategy Table A8. Research challenges and problems addressed of studies focused on refueling and charging infrastructures.