Prospects and impediments for hydrogen fuel cell buses

The number of demonstration projects with fuel cell buses has been increasing worldwide. The goal of this paper is to analyse prospects and barriers for fuel cell buses focusing on their economic, technical, and environmental performance. Our results show that the prices of fuel cell buses, although decreasing over time, are still about 40% higher than those of diesel buses. With the looming ban of diesel vehicles, and current limitations of battery electric vehicles, fuel cell buses could become a viable alternative in the mid-to long-term. With the requirements for a better integration of renewable energy sources in the transport system, interest in hydrogen is rising. Hydrogen produced from renewables used in fuel cell buses has the potential to save about 93% of CO 2 emissions in comparison to diesel buses. Yet, from environmental point-of-view it has to be ensured that hydrogen is produced from renewables. Currently, the major barrier, for a faster penetration of fuel cell buses are their high purchase prices, which could be signi ﬁ cantly reduced with the increasing number of buses through technological learning. The ﬁ nal conclusion is that a tougher transport policy framework is needed which fully re ﬂ ects the environmental impact of different buses used.


Introduction
Due to the increasing greenhouse gas (GHG) emissions from the transport sector, as well as rapid urbanization, there is on-going requirement for emission and pollution reductions.To improve life quality in urban areas it is very important to reduce noise level and consumption of fossil fuels, which pose significant risks to the health.There is an urgent need to increase use of alternative fuels and alternative automotive powertrains in mobility applications [1,2].Moreover, it is important to switch from car-oriented mobility toward more energy efficient transport practices, such as public transport.
Mass public transport is the backbone of urban mobility, especially in large cities with high population density.The average number of annual journeys per capita in countries with more than 30 million urban residents is in the range between approximately 40 (in the USA) and 250 (in Japan) [3].This mobility need is covered by different transport modes.However, as shown in Fig. 1, bus is dominant transport mode with a 63% share.Almost 68% of bus fleets are standard buses (12-m buses) with a capacity between 75 (comfort capacity) and 100 (max.capacity) passengers, see Fig. 1.
Currently, diesel buses are the most popular and they represent 50% of all bus fleets.In addition, 22% of the buses use diesel in combination with biodiesel or some other additives.Different types of electric busses account together for about 18% of all buses, as shown in Fig. 2.
In the EU, buses are the mostly used form of public transport due to high cost-efficiency and flexibility.Buses make about 56% of all public transport journeys.They are suitable for urban, as well as for suburban and rural areas.Moreover, they have the lowest carbon footprint per passenger.Currently, there are about 900,000 buses in circulation on Europe's roads [5].
Since the evidence of climate change and local pollution is becoming more and more evident, many cities worldwide have enforced the development of city buses using alternative propulsion systems.Many of the EU's larger cities have set out ambitious targets and policy measures to stimulate a shift in the powertrain technology used in their bus fleets.Some of the measures are set on the national level (e.g. in the Netherlands all new buses procured from 2025 have to be zero-emission buses), and some on the city level (e.g.Paris, Madrid, Athens and Copenhagen committed to remove all diesel vehicles from city by 2025) [6].In the EU, public authorities and operators of public transport services are obliged to follow the Clean Vehicles Directive (2009/33/EC) regarding energy consumption, CO 2 emissions, and other harmful emissions (NOx, NMHC and particulates) when purchasing new buses.Moreover, all new bus models sold on the market after January 1, 2014 must meet the Euro VI standards for harmful emissions [7].Although some improvements have been already reached with Euro VI diesel engines, currently largest expectations for the future are in the transition towards zero-emissions city buses, such as battery electric buses (BEBs) and fuel cells buses (FCBs).
In contrary to very broad portfolio of analysis related to battery electric vehicles and fuel cell passenger cars [8e11], the number of available literatures on BEBs and FCBs is limited.The interest in hydrogen-powered buses is increasing starting from the beginning of this century.Santarelli et al. [12] conducted one of the first studies on fuel cell buses already in 2003.This study evaluated emissions and economics of the FCBs.However, the capital costs used in this study were projected costs, which are below currently experienced costs of FCBs [13].First studies on the social aspects of hydrogen FCBs have focused on general acceptance of hydrogen use as a fuel [2,14] as well as on the corresponding willingness to pay [15,16].Later, these analyses have been extended by examining the view of FCB-implementers and users, indicating that no "showstopper" is identified that would prevent future generations from the use of FCBs [2].Doyle et al. [17] investigated suitability of FCB and BEB from the operator's perspective in different case studies, indicating the environmental and societal benefits of alternative buses in reduction of local pollutants and energy security concerns.In early studies, focus was at first on modification of diesel buses [18] as well as on non-hybridized FCBs in combination with hydrogen produced by steam reforming [19].Moreover, also different sizing configurations were studied [20,21].Ally and Pryor [22,23] conducted a life cycle assessment of FCBs assuming that hydrogen is a by-product from a crude oil refinery.Lee et al. [24] also performed the life-cycle environmental assessment of fuel cell electric school/transit buses in the United States, showing that results can vary significantly depending on duty cycles, geographical factors, hydrogen production pathways, and regional electric grids.Lajunen and Lipman [25] have evaluated the lifecycle costs and carbon dioxide emissions of different transit buses including FCBs.A well-to-wheel analysis is used by Correa et al. [26] to compare performance of different urban buses.
The value chain of green hydrogen for FCBs, considering different hydrogen delivery options, is analysed by Coleman et al. [27] based on field data derived from the 6 MW power-to-gas plant "Energiepark Mainz" and the bus demonstration project "H 2 -Bus Rhein-Main".In 2010, Bonilla and Merino [28] conducted economic assessment of FCB considering carbon credits and subsidies under rather optimistic capital cost assumptions.Cockroft and Owen [29] have accomplished cost-benefit analysis of FCBs in comparison to diesel and CNG buses in the Perth bus fleet assuming, that buses are produced under conditions of economies of scale and fully developed fuel infrastructure.A comparative energy and environmental analysis of different urban buses is conducted by Correa et al. [30] with the focus on Argentina, Brazil and Chile.Meishner and Sauer [31] have conducted technical and economic comparison of different electric bus concepts based on demonstration projects in European cities, however not considering FCBs.A comprehensive review paper on fuel cell applications in the automotive industry is conducted by Olabi et al. [32].They have discussed the challenges related to the use of fuel cells in the transport sector considering different transport modes.
Since in various European countries, such as Austria, some of the bus fleet operators are planning to replace old diesel buses with FCBs, in the scope of this paper we have at first done a comprehensive documentation of the current demonstration projects, as well as fuel cell bus types and characteristics.
The major goal of this paper is to analyse prospects and key barriers for the increasing use of hydrogen fuel cell buses using recent data with a special focus on their economic and technical performance, as well as their environmental impact.In existing literature capital costs used are frequently assumed future costs, which are often below or above currently experienced costs of FCBs.In our analysis, total transport costs of the bus use are calculated per kilometre driven.In addition, a sensitivity analysis is conducted showing the impact of major parameters, such as travel activity, lifetime and hydrogen price.Finally, the future prospects are analysed by developing scenarios based on technological learning.This paper combines comprehensive economic and environmental analysis over the full lifecycle of bus operation, as well as static sensitivity investigations and dynamic future scenario analyses using the most recent data available.In opposite to some of the previous studies that have analysed hydrogen powered internal combustion engine buses or non-hybridized FCBs, in this paper our  major focus is on hybrid fuel cell buses, which are today mostly used configuration.The results of this work are divided in three major categories: (i) documentation of the state of the art of FCBs as a background for the selection of the input parameters for further analysis, (ii) economic assessment and (iii) environmental assessment.
In the section below, we have documented at first state of the art of fuel cell buses with the special focus on demonstrations projects.In Section 3, methods used for economic and environmental assessments are described.Corresponding results of our analysis are presented and discussed in Section 4. Major conclusions are drawn at the end of the paper.

Hydrogen and fuel cell buses: state of the art
Hydrogen is a secondary energy carrier, like electricity, that can be produced from a range of primary energy sources, and can be used for different purposes.Currently, the mostly used hydrogen production technology is steam reforming of natural gas, due to relatively cheap hydrogen production costs [33].However, using steam reforming of natural gas per energy kilogram of hydrogen about 10 kg of CO 2 is produced [34].Electrolysis of water has currently minor applications but it is of special interest for the future.Larger use of renewable energy sources (RES) is considered as a pre-condition for heading towards smart and sustainable energy systems.With the increasing use of RES, hydrogen as energy storage could bring benefits to the balancing of the electricity system [35].Using renewable or low carbon energy sources (e.g.nuclear) for electrolysis offers significantly higher emission savings than steam reformation or electrolysis powered by fossil energy carriers.
Fuel cell is best device to be used in combination with hydrogen.Fuel cells convert hydrogen and oxygen directly into electricity.In the transport sector, their major advantages comparing to internal combustion engine are better energy efficiency and significant emission reduction.On-road efficiency of fuel cell vehicles is two or three times higher comparing to internal combustion engine (ICE) vehicles.Regardless of the fuel used, fuel cells largely eliminate emission of particulates and oxides of sulphur and nitrogen, which are pollutants associated with conventional ICE.If hydrogen is produced from renewable energy sources, fuel cell vehicles are considered one of the most promising zero-emission automotive technologies in the long term.
Although hydrogen and fuel cells can be used for a broad portfolio of applications, in the mid-term they are appearing to be a suitable alternative to conventional-and battery electric large size vehicles with the need for longer driving range, such as buses.Since buses return regularly to a depot, in urban areas their use can be realized with minimal refueling infrastructure requirements.Their low or zero emissions increase their competitiveness especially with diesel-powered buses.Moreover, they avoid pollution problems specifically related to diesel buses.Due to the environmental benefits over conventional buses, urban authorities often provide subsidies and support for the demonstration of FCBs.
In the EU broad portfolio of policies and directives are directly or indirectly supporting the use of FCBs.In the next years, due to announced ban of diesel vehicles in many countries (e.g.Norway, the Netherlands, Ireland, Slovenia) as well as introduction of the zero emission zones in urban areas, interest in BEBs and FCBs is increasing.
Hydrogen FCBs have been demonstrated in real-world operations especially over the last twenty years.They can be seen as a complementary technology to BEBs.FCBs offer a zero-emission mobility solution on a wide range of routes and challenging terrains.Hydrogen and fuel cells have a particular advantage when heavier bases are required (e.g.articulated e or double decks buses) with a high daily travel needs.The long range of FCBs is a unique advantage in the zero-emission bus sector.This increase operators' flexibility and productivity.In addition, this is supported by short refueling times.FCBs can be refueled in about 7 min.Fast refueling time in combination with long driving range is very suitable for depot-based refueling.This can significantly decrease need for public refueling infrastructure what is very relevant in the early stage of FCB-deployment.
Since the first FCB was developed in 1993 by Ballard [36], their number is continuously increasing.
Currently, there are more than 2000 FCBs on the roads worldwide but majority of them is in China, see Fig. 3.Most of FCBs are operating in the scope of different demonstration projects.The rapid grow in use of FCBs in China over the last few years can be mainly attributed to a favorable policies launched by Chinese governments at various levels.For 2030 and 2050 many countries have announced ambitious targets for the deployment of fuel cell vehicles and buses, as well as development of refueling infrastructure [33].
There are three major configurations of hydrogen buses: (i) the hydrogen powered internal combustion engine bus, (ii) fuel cell bus, and (iii) the hybrid fuel cell bus.The internal combustion hydrogen bus works similar to a conventional diesel bus and is modified for the combustion of hydrogen.In early FCBconfigurations, a fuel cell generates electricity, which is directly supplied to an electric motor.In this configuration, there is no mechanism to capture the kinetic energy dissipated during braking.In the meantime, all of the main fuel cell bus developers have moved to a fully hybridized mode, with the fuel cell operating in a series hybrid configuration.In these fuel cell buses, developers are still experimenting with the energy storage device, which can be batteries, ultra-capacitors, or a combination of both [1].Currently, the mostly used FCB-configuration is hybrid design with battery.In this configuration, the fuel cell system is considered as a "range extender", which recharges the battery during the drive cycle.The batteries themselves provide the main motive power for the bus [1].
Fig. 4 illustrates three different configurations of hydrogenpowered buses.

Survey on case studies
To support research and development of alternative bus solutions, the EU has funded a series of demonstration projects related to FCBs as well as corresponding infrastructure.The number of FCBs is continuously increasing due to such projects.The most important demonstration projects in Europe are listed in Table 1.
Over the last few years, it can be noticed increasing number of FCBs and hydrogen refueling stations.Moreover, it can be noticed increase in energy efficiency of FCBs [37,42,43], and decrease of their investment cost [44e47].However, the hydrogen price remained on the same level.
The newest European funding project H2BUS EUROPE aims to address also this barrier by establishing a green hydrogen value chain with the goal to reduce hydrogen price to 5e7 V per kilogram [37].
Table 2 shows an overview of the major characteristics of the FCBs currently used in European cities.Most of them are standard fuel cell electric buses.With the European funding projects, more and more manufactures are stimulated to enter the FCB-market.

Methods
For the mostly used hybrid FCB configuration, we have conducted economic and environmental assessment using most recent input data from already on-going demonstration projects.In our sensitivity analysis, we have also considered some expectations announced for the future cost developments.

Economic assessment
The major barriers for the faster penetration of FCBs are their high costs in comparison to conventional diesel buses.In the following, we have calculated total costs of the use (TCU) of FCBs in Austria in comparison to diesel and battery electric buses, which are already in uses in many Austrian cities.Moreover, in order to understand the impact of different parameters on the total costs we have conducted sensitivity analyses.
The total costs of mobility with buses analysed are calculated considering their investment costs (IC), driven distance per year (d), their energy costs (C E ) and other operating and maintenance cost (C O&M ): The capital recovery factor (a) is calculated depending on the discount rate (r) over the analysed period (n): The energy costs C E are dependent on the average energy consumption of the buses (E i ) and the corresponding energy (diesel, hydrogen and electricity) prices (P Ei ): The labour cost for the drivers, are not included in this calculation, since these costs are the same for all bus types analysed.
In our base case we have calculated with the current Austrian energy price data [52,53].In this case we have calculated with the exemptions of registration-and value add tax.The major bus characteristics, such are energy consumption, costs, etc., are taken from literature [39,54e57].Major input data and assumptions for our calculations are given in Table 3. Results of our economic analysis are documented in Section 4.

Environmental assessment
The major reason to consider replacement of diesel buses with FCBs is due to some environmental advantages.For their use in urban areas, it is huge benefit that they have zero emissions at the point of use.They are also able to reduce noise level up to 60% [57].Moreover, they can significantly contribute to the CO 2 emission reduction depending on the hydrogen production method and primary energy sources used.
In this paper, we are making difference between 'grey' and 'green' hydrogen.The grey hydrogen is hydrogen produced by a central steam methane reformer, stored with 200 bar in gas bottle bundles and then transported on a trailer over a distance of 200 km to the hydrogen refueling station resulting in a CO 2 emission factor of 13.20 kgCO 2eq.per kg H 2 at nozzle [2].The green hydrogen is produced in electrolyser using electricity from renewable energy sources.For this scenario, we calculate with a CO 2 emission factor of 0.7 kgCO 2eq.per kg H 2 at nozzle [2].
The CO 2 emission factor of electricity for BEBs strongly depends on the electricity mix which can be with a high share of fossil -to reduce the investment cost of FCB down to 625,000 V.
H2BUS EUROPE [47] 2019e2023 600 e1000 Denmark, Latvia and UK, (Norway, Sweden, Germany) -to realize the deployment of 1000 FCB and the necessary infrastructure with competitive cost in European cities and to reach significant reduction of the investment costs.energy such as in Germany, or with high share of renewable energy such as in Austria.The average electricity mix of EU-28 has a CO 2 emission factor somewhere in between these two exemplary countries [58].Table 4 gives an overview of CO 2 emission factors used for different fuel types, including well-to-tank (WTT) and tank-towheel (TTW) emissions.Since FCBs and BEBs have zero emissions at the point of use, the TTW emissions are only relevant for diesel buses, see also Fig. 11.
Finally, CO 2 emissions over the lifespan (n) of the buses are dependent on the level of travel activity (d), the energy intensity of the buses (E), and the carbon content (emission factor) of the energy used (f CO2 ).The relationship between these parameters is represented mathematically by following equation: Results of our environmental analysis are documented in the next section.Note that the focus is put on Well-to-Wheels (WTW) emission analyses.This approach differs from a Life Cycle Analysis (LCA), as it does not consider energy and emissions involved in building facilities and the vehicles, or emissions related to the end of life.WTW analysis focuses on lifetime energy use and corresponding GHG emissions.

Results and Discussion
The results of this work are divided in two major categories: (i) economic assessment and (ii) environmental assessment.

Economic assessment
The major barriers for the faster penetration of FCBs are their high costs in comparison to conventional diesel buses.In this paper, we have calculated total mobility costs of FCBs in Austria in comparison to diesel and battery electric buses.
For the three bus types analysed, the total cost of the bus use per km driven are depicted in Fig. 5.It is obvious that the investment costs of FCBs are far away from the possible competitiveness with diesel buses, as well as with BEBs.Beside high investment costs, FCBs have also very high fuel costs due to high hydrogen prices.Only operating and maintenance costs of the FCBs are similar to those of diesel buses and BEBs.
To estimate major impact parameters on the total costs of the bus use per km driven, we have conducted sensitivity analysis.By varying different parameters -the distance driven, hydrogen price and the lifetime of the buses -one after the other, their influence on the total cost structure is assessed.
Regarding the range of bus kilometres driven per year, there is a wide range in the literature.For example, Potk any et al. [54] calculate with a driving distance of about 72,000 km per year for the regular bus line Trnavsk e Mýto e Vajnory in Bratislava, Slovakia.Müller et al. [39] report about common bus ranges up to 250 km per day, e.g. in Bolzano.In Berger [57], 250 km per day is used in the minimum range scenario, resulting in about 87,500 km per year.In addition to our base case where we have calculated with 45,000 km per year, for the sensitivity analysis we have calculated with 90,000 km per year, see in Fig. 6 "variation of km".With an increasing number of km driven, the cost difference between buses analysed decreases, especially between diesel and BEBs.With "variation of life-time" a lifetime reduction from 14 years in the base case to 8 years is analysed.It can be seen, that shorter lifetime is especially unfavourable for FCBs and BEBs.Finally, the case of a lower H 2 -price (5 V/kg instead of 7.5 V/kg), Fig. 6 shows that lower hydrogen price has moderate impact on the total cost of FCBs which are largely dominated by capital cost.To reach market competitiveness of FCBs it is essential to reduce their investment cost.
In addition, we have analysed the future costs in a scenario up to 2050.In this scenario it is assumed that with increasing deployment of FCBs and BEBs, their investment costs could become considerably lower due to technological learning.These scenarios for the development of the investment costs of diesel-, electric-and fuel cell buses are shown in Fig. 7.
Moreover, in this scenario, we have also calculated with a reduction in hydrogen price as shown in Fig. 8. Fig. 8 depicts the development of the fuel costs on a yearly base.As can be seen from this figure, by around 2040 the fuel costs of FCBs will be lower than those of diesel buses.
The major reason for the decrease in hydrogen costs is the assumed technological learning effect of the electrolysers.However, electricity prices are slightly increasing because of increasing costs for grid extention and the construction of new power plants.The efficiency of all technologies is increasing, but also additional energy consuming services of vehicles.At least, over the last years, most of the energy efficiency improvements on conventional cars were offset with increasing car power or additional energy services in vehicles.In this paper we have assumed, increasing CO 2 taxes on fossil energy inputs which have a clear impact on diesel and a slight impact on electricity prices.
The results of the analysis for the TCU on a yearly base up to 2050 are illustrated in Fig. 9.As can be seen from this figure already by about 2027 the total costs of BEBs can be lower than those of diesel buses and by 2050 all three bus types end up with total costs in similar ranges.
Finally, Fig. 10 shows the results of this analysis for the breakdown of the total costs into capital, fuel and O&M costs.As can be seen from this figure already by 2030 the total costs of BEBs can be lower than those of diesel busses and by 2050 all three bus types end up with costs in similar ranges.To increase use of alternative power trains in the transport sector many countries have provided different supporting measures.For example, in Austria, alternative solutions in the field of mobility management, fleets and logistics are supported within the #mission 2030 electro mobility campaign of the federal ministries BMNT (Federal Ministry for Sustainability and Tourism) and BMVIT (Federal Ministry of Transport, Innovation and Technology) with an overall budget of 93 million Euro [61].Companies, regional authorities and associations can get the subsidies for FCBs as well as for BEB as shown in Table 5.

Environmental assessment
Although the economic analysis shows clearly that currently FCBs are not competitive with conventional diesel buses as well as with BEBs, they have some environmental advantages, which make them interesting for the future mobility system.Fig. 11 shows in comparison CO 2 emissions of standard 12 m buses.It compares diesel ICEB, FCB powered by grey and green hydrogen, and BEB powered with different electricity mixes: the average mix of the EU-28, Austrian-and German-mix.
It can be noticed that CO 2 emissions of the FCBs in combination with grey hydrogen are even higher than those of conventional diesel buses.However, with FCBs driven with green hydrogen significant emission saving can be reached.Table 6 shows an overview of the potential savings in CO 2 emissions that can be achieved by operating the alternative bus solutions instead of conventional diesel ICEB.
In this context, it is important to discuss the issue of "green" hydrogen.Oft FCBs and BEBs are considered as environmentally  friendly technology.However, their environmental impact is very dependent on the primary energy sources used for electricity generation and hydrogen production.The full environmental benefits of these alternative buses could be reached only in combination with energy carriers produced from renewable or low carbon energy sources.Hence, it is obvious that use of FCBs make sense just in combination with hydrogen production from renewable energy sources.In this analysis the emissions caused during for bus manufacturing and maintenance are not included, due to very limited data sources.However, emissions caused during fuel production and bus operation have an overwhelmingly impact on the total emissions of the buses [2].

Conclusions
To cope with the increasing emissions from the transport sector it is necessary to increase use of alternative automotive technologies with zero or low carbon emissions.Zero-emissions alternatives are of special interest for polluted urban areas.
Public bus transport is currently mostly covered with diesel buses.Although theses buses have been significantly improved over time, they should be in the long-term replaced with more environmentally friendly buses such as FCBs and BEBs.However, these alternative solutions are still not economically competitive on the market, especially FCBs.Currently, FCBs are mostly used in different pilot and demonstration projects.Their total number is very low but increasing.
Although, FCBs are still immature technology they have significant potential for the emissions reduction in comparison to diesel buses if they are using green hydrogen up to 93%.From the environmental point of view, it is of absolutely highest priority to ensure by credible measures that the hydrogen is produced from renewable energy sources.Moreover, FCBs can reduce noise level and local pollution.
In the short-and mid-term BEBs are a more suitable alternative to conventional diesel buses in urban areas.However, in the longterm, especially when longer driving range is required, FCBs will be of interest.
The major barriers for their faster penetration are especially high investment costs of FCBs, which are currently about 40% higher than those of diesel buses.In the future, this could be reduced by harvesting technological learning effects.It can be expected that technological learning and economies-of-scale will

Vehicle class Subsidy amount per vehicle
Class M3, up to 39 passengers 40,000 V Class M3, 39 to 120 passengers 60,000 V Class M3, more than 120 passengers 100,000 V bring down the costs of the FCBs, as well as hydrogen costs.Already by about 2027 the total costs of BEBs can be lower than those of diesel buses and by 2050 total costs of all bus technologies analysed could be in a similar range.Currently, due to high purchase prices of the FCBs, impact of hydrogen prices on total mobility costs is relatively low.
For the broader use of FCBs it will be also necessary to make investments in infrastructure including hydrogen production, distribution and refueling stations.To encourage investment in hydrogen and fuel cells it is very important to have clear and stabile policy goals as well as corresponding policy framework.It would be very important to introduce CO 2 based taxes that reflect costs associated environmental damage caused by mobility.

Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Fig. 1 .
Fig.1.Average modal distribution of all public transport journeys and share of bus fleet types (Data source[3,4]).

Fig. 4 .
Fig. 4. Three types of hydrogen buses (M is the electric motor).

Fig. 6 .
Fig. 6.Sensitivity analysis of total cost of bus use with respect to km driven, lifetime and hydrogen price, 2018.

Fig. 7 .
Fig. 7. Scenarios for the development of the investment costs of diesel-, electric-and fuel cell buses up to 2050 due to technological learning.

Fig. 8 .
Fig. 8. Scenarios for the development of the fuel costs of diesel-, electric-and fuel cell buses up to 2050.

Fig. 9 .
Fig. 9. Scenario for the development of the TCU of diesel-, electric-and fuel cell buses up to 2050 due to technological learning and decreasing hydrogen costs.

Fig. 10 .
Fig. 10.Scenario for the breakdown of the total costs of diesel-, electric-and fuel cell buses in 2030 and 2050 due to technological learning and decreasing hydrogen costs.

Fig. 11 .
Fig. 11.WTT and TTW carbon dioxide emissions of different standard 12 m buses with 45,000 km driven per year.

Table 1
Major demonstration projects in Europe.

Table 3
Major input data and assumptions for the TCU calculation (2018).

Table 6
Savings in CO 2 emissions during the operation of FCB and BEB compared to diesel ICEB.