The efficiency of light duty vehicles is an interesting reference, but the use of these technolo- gies in heavy duty vehicles such as buses might yield a very different efficiency comparison. The efficiency of the 27 buses that made up the CUTE program is reported in the CUTE final report [91]. Fuel efficiency ratios can be drawn from controlled tests that compared the FC Citaro with a standard Diesel Euro 3 Citaro, on the same route with the same load. Stockholm found the ratio of FC Bus efficiency to Diesel bus efficiency to be 0.67 [124], and Porto found a ratio of 0.76 [125].
Controlled tests were also conducted in Stuttgart resulting in a fuel efficiency ratio of 0.69 for the fuel cell bus, and they also measured the efficiency ratio of a CNG EEV bus to the Diesel Euro 3 of 0.71 [92]. The NEBUS was an earlier prototype developed by DaimlerChrysler in the late 1990’s to demonstrate a concept fuel cell vehicle, and achieved an efficiency ratio of 1.16. Data from the Perth trial shows a ratio of 0.79 in comparison to the Diesel Euro 2 buses operated by Transperth14.
Overall one can conclude that there is wide range of experiences with the fuel economy of fuel cell vehicles, and great potential for improvements in the energy efficiency of the FC bus engine as it approaches the theoretical estimates.
Focusing on hydrogen bus efficiency, and incorporating data from hydrogen hybrid bus trials, a map of fuel efficiencies can be derived. This collection of data from various literature sources covers the hybrid and non-hybrid vehicle configurations that are to be considered, and constitutes the data range for sensitivity analysis of fuel economy in the life cycle models.
The FC Citaro buses delivered to Perth were designed to demonstrate reliability, and design tradeoffs were made to improve the reliability at the expense of energy efficiency. One of the objectives of the HyFLEET:CUTE trials was to prove that fuel cell buses are sufficiently re- liable to be competitive with CNG buses, and once this had been established the technology would advance by maintaining that reliability standard while optimising energy efficiency in the next-generation bus design.
In researching hydrogen fuel cell bus life cycle studies, one invariably finds that both the NREL and HYFLEET:CUTE evaluation studies are the two most comprehensive hydrogen bus evaluation programs in the world. These two programs encompass the vast majority of hydrogen bus fleets, operating in a wide range of cities, with strong evaluation programs conducted by independent academic institutions.
The field of study has grown and research has been published by other organisations, such as McKenzie et al. [127] which developed an Input-Output LCA and LCC model of tran- sit buses with alternative fuel technologies. Unlike traditional process-based LCA which models all processes within the system boundary using discrete processes, the Input-Output approach expresses the requirements for the product system in terms of demand for eco- 14Calculated using actual data from the STEP FC buses; and Diesel bus consumption of 43 L/100km [126].
2.7. Hydrogen fuel cell bus performance 53
nomic sectors in monetary terms, which in turn allows the computation of the amount of economic activity and the related environmental impacts to deliver the product system to be calculated.
McKenzie et al. find that the additional capital costs to convert from diesel to CNG or Hydrogen buses, including the cost of fuel infrastructure, could be recovered in 5 years15. Importantly, McKenzie et al. also conducted a sensitivity analysis which concluded that hydrogen fuel cell buses were by far the least sensitive to changes in fuel price or passen- ger loading, which translates to greater certainty of year-to-year operating costs, and which would be particularly true in the Australian context where the lack of indigenous oil sources results in acute energy insecurity.
A recent study in the United States compared LCA models and modelling techniques from several studies, including an early publication from the present thesis, to compile an LCA model for alternative fuel buses in the US [128]. The findings include a quantification of the significance of geographical terrain, duty cycle and energy mix factors which can vary the results of such an LCA enough to change the results of a comparative analysis of fleet design options.
The LCA study of alternative transport fuels for heavy vehicles conducted by Beer et al. [85] in 2000 concluded that biofuels would be the lowest greenhouse gas emitters. Hydrogen fuel cell buses had not yet been demonstrated to be an operational technology, nor had any hydrogen vehicle fuelling infrastructure been built in Australia when that study was conducted, and this was acknowledged by Beer et al. in the final report [98].
However, more recent studies of alternative fuel options for bus fleets, such as the very comprehensive report by Nylund and Koponen for VTT Technology in 2012 [129], often still describe hydrogen’s current stage of development as pre-commercial, or research and development. This assumption can be used as a reason to discount hydrogen as a realistic fuel option, and in the case of the Nylund and Koponen study the key finding is that the best way to reduce greenhouse gas emissions is a switch from fossil fuels to biofuels.
An LCA of six alternative fuel bus technologies in China [130]16 concluded that only half of the technologies could realise an energy and GHG savings in relation to conventional technologies, and hydrogen fuel cells was not one of these due to its low market penetration and the embodied emissions of hydrogen derived from natural gas in China.
Other studies which discount hydrogen’s current stage of readiness, such as the multi-criteria analysis of fuel cell buses conducted by Tzeng et al. [16] and the scenario analysis conducted by Wayne and Clark [131], find that retirement of old diesel buses for replacement by hybrid diesel buses is the most effective way to improve emissions within a reasonable cost. A more
15The life cycle cost analysis in this study assumed an emissions price of$100/tCO 2e. 16
Ou et al. published useful input data for well-to-pump and pump-to-wheels LCA calculations, and bus performance data based on actual operational results in China. This data can be referenced for scenario and sensitivity analysis. The six technologies studied by Ou et al. were Liquid Propane Gas ICE, Compressed Nat- ural Gas ICE, Natural Gas Hydrogen Fuel Cell, Methanol Spark Ignition ICE, Direct Methanol Compression Ignition ICE and Electric Buses.
54 Chapter 2. Literature Review
recent study by Ribau et al. [132] used an efficiency and cost optimisation model to minimise life cycle greenhouse gas emissions from fuel cell hybrid and plug-in hybrid buses, and found that a reduction of 58% in primary energy demand and 68% in carbon dioxide equivalent emissions could be achieved by a fuel cell hybrid bus over the conventional diesel baseline.
Many of these studies do not have the zero-emissions objective, and particularly the zero tailpipe emissions objective, which is a key element of hydrogen fuel cell bus development programs. These studies show that even without this target there is still no one clear technol- ogysilver bulletthat is emerging as the clear choice. Therefore, further study is warranted.
The HyFLEET:CUTE and NREL programs remain the most comprehensive data sets, and establish thestate of the art in hydrogen bus life cycle literature. These two programs both merit a more in-depth analysis.
2.7.1 The HyFLEET:CUTE Trial Evaluation
The CUTE project included nine cities in Europe operating a total of 27 fuel cell buses. Each city operated three buses, and had to establish the fuel supply pathway and other infrastruc- ture required to support the hydrogen technology. The CUTE project was associated with ECTOS and STEP, which also operated three buses each [133].
As part of the CUTE trial, an official work package (Work Package 9) was defined to evalu- ate theenvironmental, technical and economicimpacts of fuel cell bus technology, including hydrogen production methods, bus operation, and comparison to conventional bus systems (diesel and CNG). The methodology for this analysis is discussed in the technical reportDe- liverable 36 [77], and is in accordance with the international ISO 14040 standard. The same methodological framework has been adopted for the present study, but in the Australian context and with Australian data and boundary conditions.
When comparing Australian to European data, the hydrogen production, bus operation, and conventional bus technologies are all unique. In addition, the data inventory that the envi- ronmental analysis is based on is different because Australian environmental data sources, such as the National Pollutant Inventory (NPI) and the National Greenhouse and Energy Reporting System (NGERS), have their own reporting policies and emissions factors that are not always common to those used in the EU. Methodology was discussed in Section 2.3, and the application of these standards in the present study is the subject of Chapter 3.
The technical report Deliverable 37 gives a detailed account of the Life Cycle Assessment applied to the fuel cell, CNG and diesel versions of the Citaro bus that are evaluated in the CUTE trial [93]. This document describes the objectives of the LCA and details the modelling of the different bus systems and fuel infrastructures, as well as a general overview of Life Cycle Inventory (LCI) methodology. Much of the data published can be employed for validation purposes in the Perth bus LCA, including descriptions of the diesel and natural gas Citaro construction, the emissions from the bus manufacturing plant in Germany, bus utilisation data, and fuel consumption statistics for the European fleet.
2.7. Hydrogen fuel cell bus performance 55
A number of other publications have emerged from research in partnership with the CUTE project, such as the modelling of a hydrogen refuelling structure for London by Joffe et al. [32], and a study in Stockholm examining the climatic effects on fuel cell bus operation by Haraldsson et al. [124].
An overview of the fuel cell bus and hydrogen production technologies used throughout the CUTE trial can be found in the CUTE Technology Brochure [133], and a final summary of achievements including the final LCA findings was published at the conclusion of the trial [91].
The CUTE trial evolved into a new program entitledHyFLEET:CUTE, which incorporated the CUTE program in an expanded and extended scope that included 33 hydrogen fuel cell buses and 14 H2ICE buses operating in 10 different cities. The final report of the HyFLEET:CUTE project [43] is a valuable reference which includes the operational data derived from the STEP trial, as well as many other useful reference data for the LCA model, including:
• The hydrogen supply chain and infrastructure used in each city that participated in the program;
• operational performance of the buses including kilometres travelled, fuel used and availability;
• design details and specifications for fuel cell buses, fuel cell hybrid buses, and buses using hydrogen internal combustion engines;
• environmental impact results including LCA results from the HyFLEET:CUTE mod- elling; and
• social impacts.
The HyFLEET:CUTE final report provides summary statistics on the operation of 33 hy- drogen fuel cell buses and 14 hydrogen internal combustion engine buses, operated over 2 million kilometres, 140 thousand hours, and transporting over 8.5 million passengers in rev- enue service. The HyFLEET:CUTE project also reports on 10 different hydrogen stations and hydrogen supply chains including in-station water electrolysis, in-station steam reform- ing, and external hydrogen supplies.The LCA of the HyFLEET:CUTE program included several very useful conclusions:
• Fuel economy is, for fuel cell vehicles and conventional vehicles alike, highly depen- dent on traffic conditions, stops per kilometre and topography17.
• Hybridisation of the drivetrain results in an improvement in primary energy demand of between 25%18 and 44%19.
17Summary statistics for the entire duration of the program shows that buses in Madrid achieved a fuel con-
sumption of 29.1 kg/100km, while the same bus make and model in Perth achieved a fuel economy of 19.0 kg/100km, a 34% difference.
18
Calculated for electrolysis hydrogen production systems using electrolysis from renewable energy sources.
56 Chapter 2. Literature Review
• Next generation fuel cell hybrid buses deliver a 10% lower global warming potential than previous non-hybrid generations, mainly due to weight reduction.
Data collected in regular revenue service, as opposed to test data, showed a possible correla- tion between average speed and fuel economy. To illustrate this, the data from the cities that participated in the HyFLEET:CUTE trial, and the fleet average, are presented in Figure 2.4. The graph shows an apparent correlation between fuel economy and average speed. How- ever, a linear regression model registers anR2 value of 0.49 and therefore the correlation is not sufficiently strong to be considered statistically significant.
Figure 2.4:Data from the HyFLEET:CUTE trial, illustrating the apparent correlation between fuel economy and average speed.
The HYFLEET:CUTE trial evolved into the CHIC program, which is still underway as of the time of this writing. The CHIC program also includes an LCA component which will be published following the completion of the program20.
2.7.2 NREL Fuel Cell Bus Evaluations
Other fuel cell bus demonstration projects have also published fuel economy results for the generation of buses which followed those of the STEP program. In February 2014 the Canadian BC Transit Fuel Cell Bus project released its final evaluation results [134]. The fleet of 20 buses running typical transit routes in Whistler, BC, recorded a fuel economy that ranged from 13 kg/100km to 17.8 kg/100km with an average of 15.48 kg/100km. The
20
The CHIC website states that, “CHIC, the Clean Hydrogen in European Cities project, is the essential next step leading the full market commercialization of Fuel Cell Hydrogen powered buses. The project involves integrating 26 FCH buses in daily public transport operations and bus routes in five locations across Europe - Aargau (Switzerland), Blozano/Bolzen (Italy), London (UK), Milan (Italy), and Oslo (Norway). http://chic- project.eu/.