Exergetic life cycle assessment of hydrogen production from renewables

Life cycle assessment is extended to exergetic life cycle assessment and used to evaluate the exergy efficiency, economic effectiveness and environmental impact of producing hydrogen using wind and solar energy in place of fossil fuels. The product hydrogen is considered a fuel for fuel cell vehicles and a substitute for gasoline. Fossil fuel technologies for producing hydrogen from natural gas and gasoline from crude oil are contrasted with options using renewable energy.     

Exergetic life cycle assessment of a hydrogen production process

Exergetic life cycle assessment (ExLCA) is applied with life cycle assessment (LCA) to a hydrogen production process. This comparative environmental study examines a nuclear-based hydrogen production via thermochemical water splitting using a copper–chlorine cycle. LCA, which is an analytical tool to identify, quantify and decrease the overall environmental impact of a system or a product, is extended to ExLCA. Exergy efficiencies and air pollution emissions are evaluated for all process steps, including the uranium processing, nuclear and hydrogen production plants. LCA results are presented in four categories: acidification potential, eutrophication potential, global warming potential and ozone depletion potential. A parametric study is performed for various plant lifetimes. The ExLCA results indicate that the greatest irreversibility is caused by uranium processing. The primary contributor of the life cycle irreversibility of the nuclear-based hydrogen production process is fuel (uranium) processing, for which the exergy efficiency is 26.7% and the exergy destruction is 2916.3 MJ. The lowest global warming potential per megajoule exergy of hydrogen is 5.65 g CO₂-eq achieved a plant capacity of 125,000 kg H₂/day. The corresponding value for a plant capacity of 62,500 kg H₂/day is 5.75 g CO₂-eq.     

Exergy, exergoeconomic and environmental analyses and evolutionary algorithm based multi-objective optimization of combined cycle power plants

A comprehensive exergy, exergoeconomic and environmental impact analysis and optimization is reported of several combined cycle power plants (CCPPs). In the first part, thermodynamic analyses based on energy and exergy of the CCPPs are performed, and the effect of supplementary firing on the natural gas-fired CCPP is investigated. The latter step includes the effect of supplementary firing on the performance of bottoming cycle and CO₂ emissions, and utilizes the first and second laws of thermodynamics. In the second part, a multi-objective optimization is performed to determine the “best” design parameters, accounting for exergetic, economic and environmental factors. The optimization considers three objective functions: CCPP exergy efficiency, total cost rate of the system products and CO₂ emissions of the overall plant. The environmental impact in terms of CO₂ emissions is integrated with the exergoeconomic objective function as a new objective function. The results of both exergy and exergoeconomic analyses show that the largest exergy destructions occur in the CCPP combustion chamber, and that increasing the gas turbine inlet temperature decreases the CCPP cost of exergy destruction. The optimization results demonstrates that CO₂ emissions are reduced by selecting the best components and using a low fuel injection rate into the combustion chamber.     

Clean fuel options with hydrogen for sea transportation: A life cycle approach

In this study, two potential fuels, namely hydrogen and ammonia, are alternatively proposed to replace heavy fuel oils in the engines of sea transportation vehicles. A comparative life cycle assessments of different types of sea transportation vehicles are performed to investigate the impacts of fuel switching on the environment. The entire transport life cycle is considered in the life cycle analyses consisting of production of freight ship and tanker; operation of freight ship and tanker; construction and land use of port; operation, maintenance and disposal of port; production and transportation of these clean fuels. Various environmental impact categories, such as global warming, marine sediment ecotoxicity, marine aquatic ecotoxicity, acidification and ozone layer depletion are selected in order to examine the diverse effects of switching to clean fuels in maritime transportation. As a carbon-free fuel for marine vehicle engines, ammonia and hydrogen, yield considerably lower global warming impact during the operation. Furthermore, numerous production methods of alternative fuels are evaluated to comparatively show environmentally benign options. The results of this study demonstrate that if ammonia is even partially utilized in the engines of ocean tankers as dual fuel (with heavy fuel oils), overall life cycle greenhouse gas emissions per tonne-kilometer can be decreased about 27% whereas it can be decreased by about 40% when hydrogen is used as dual fuel.     

Exergy analysis of waste emissions

Recently, significant attention has been directed towards the use of exergy analysis in the assessment of thermal and other industrial processes and their environmental impacts since exergy analysis is an effective tool both for achieving efficient energy utilization with minimum (or zero) environmental impact and for understanding environmental issues. In this study, the concepts of exergy analysis and the linkages between exergy and environmental impact are discussed, and several issues regarding the exergies of waste emissions are addressed. Exergy is a measure of the degree of disequilibrium between a substance and its environment. The relations between several measures of environmental impact potential and exergy are investigated by comparing current methods used to assess the environmental impact potential of waste emissions and the exergy associated with those emissions. A case study is presented, to highlight the information revealed using exergy, in which the measures of environmental impact potential considered are the Ontario Ministry of Environment's schedule of industrial air emission limits, and two methods of assessing the environmental costs for air emissions resulting from the combustion of three common fossil fuels: coal, oil and natural gas. Copyright © 1999 John Wiley & Sons, Ltd.     

Influence of driving patterns on life cycle cost and emissions of hybrid and plug-in electric vehicle powertrains

We compare the potential of hybrid, extended-range plug-in hybrid, and battery electric vehicles to reduce lifetime cost and life cycle greenhouse gas emissions under various scenarios and simulated driving conditions. We find that driving conditions affect economic and environmental benefits of electrified vehicles substantially: Under the urban NYC driving cycle, hybrid and plug-in vehicles can cut life cycle emissions by 60% and reduce costs up to 20% relative to conventional vehicles (CVs). In contrast, under highway test conditions (HWFET) electrified vehicles offer marginal emissions reductions at higher costs. NYC conditions with frequent stops triple life cycle emissions and increase costs of conventional vehicles by 30%, while aggressive driving (US06) reduces the all-electric range of plug-in vehicles by up to 45% compared to milder test cycles (like HWFET). Vehicle window stickers, fuel economy standards, and life cycle studies using average lab-test vehicle efficiency estimates are therefore incomplete: (1) driver heterogeneity matters, and efforts to encourage adoption of hybrid and plug-in vehicles will have greater impact if targeted to urban drivers vs. highway drivers; and (2) electrified vehicles perform better on some drive cycles than others, so non-representative tests can bias consumer perception and regulation of alternative technologies. We discuss policy implications.     

Exergy analysis of hydrogen/diesel combustion in a dual fuel engine using three-dimensional model

In the present study, the energy and exergy analysis were carried out for a Deutz dual fuel (diesel + hydrogen) engine at different gas fuel-air ratios (ø_H2 = 0.3, 0.4, 0.5, 0.6, 0.7, and 0.8) and constant diesel fuel amount (6.48 mg/cycle). The energy analysis was performed during a closed cycle by using a three-dimensional CFD code and combustion modeling was carried out by Extend Coherent Flame Model- Three Zone model (ECFM-3Z). For the exergy analysis, an in-house computational code is developed, which uses the results of the energy analysis at different fuel-air ratios. The cylinder pressure results for natural gas/diesel fuelled engine are verified with the experimental data in the literature, which shows a good agreement. This verification gives confidence in the model prediction for hydrogen- fuelled case. With crank position at different gas fuel-air ratios, various rate and cumulative exergy components are identified and calculated separately. It is found that as gas fuel-air ratio increases from 0.3 to 0.8, the exergy efficiency decreases from 43.7% to 34.5%. Furthermore, the value of irreversibility decreases from 29.8% to 26.6% of the mixture fuels chemical exergies. These values are in good agreement with data in the literature for dual fuel engines.     

Exergy-based assessment for waste gas emissions from Chinese transportation

As an effective measure for environmental impact associated with the waste emissions, exergy is used to unify the assessment of the waste gases of CO, NO_x, and SO₂ emitted from fossil fuel consumption by the transportation system in China. An index of emission exergy intensity defined as the ratio of the total chemical exergy of the emissions and the total converted turnover of the transportation is proposed to quantify the environmental impact per unit of traffic service. Time series analyses are presented for the emission exergy and emission exergy intensity of the whole Chinese transportation as well as for its four sectors of highways, railways, waterways and civil aviation from 1978 to 2004. For the increasing emission exergy with CO taking the largest share, the highways sector was the major contributor, while the railways sector initially standing as the second main contributor developed into the least after 1995. The temporal and structural variations of the emissions are illustrated against the transition of the transportation system in a socio-economic perspective, with emphasis on policy-making implications.     

Environmental impact categories of hydrogen and ammonia driven transoceanic maritime vehicles: A comparative evaluation

In this study, carbon-free fuels -ammonia and hydrogen-are proposed to replace heavy fuel oils in the engines of maritime transportation vehicles. Also, it is proposed to use hydrogen and ammonia as dual fuels to quantify the reduction potential of greenhouse gas emissions. An environmental impact assessment of transoceanic tanker and transoceanic freight ship is implemented to explore the impacts of fuel substituting on the environment. In the life cycle analyses, the complete transport life cycle is taken into account from manufacture of transoceanic freight ship and tanker to production, transportation and utilization of hydrogen and ammonia in the maritime vehicles. Several hydrogen and ammonia production routes ranging from municipal waste to geothermal options are considered to comparatively evaluate environmentally benign methods. Besides global warming potential, environmental impact categories of marine sediment ecotoxicity and marine aquatic ecotoxicity are also selected in order to examine the diverse effects on marine environment. Being carbon-neutral fuels, ammonia and hydrogen, yield significantly minor global warming impacts during operation. The ecotoxicity impacts on maritime environment vary based on the production route of hydrogen and ammonia. The results imply that even hydrogen and ammonia are utilized as dual fuels in the engines, the global warming potential is quite lower in comparison with heavy fuel oil driven transoceanic tankers. Geothermal energy sourced hydrogen and ammonia fuelled transoceanic tankers release about 0.98 g and 1.65 g CO₂ eq. per tonne-kilometer, respectively whereas current conventional heavy fuel oil tanker releases about 5.33 g/tonne-kilometer CO₂ eq. greenhouse gas emissions.     

Dynamic simulation and lifecycle assessment of hydrogen fuel cell electric vehicles considering various hydrogen production methods

In this research study, a real model of a hydrogen fuel cell vehicle is simulated using Simcenter Amesim software. The software used for vehicle simulation enabled dynamic simulation, resulting in more precise simulation. Furthermore, considering that fuel cell degradation is one of the significant challenges confronting fuel cell vehicle manufacturers, we examined the impact of fuel cell degradation on the performance of hydrogen vehicles. According to the findings, a hydrogen vehicle with a degraded fuel cell consumes 14.3% more fuel than a fresh fuel cell hydrogen vehicle. A comprehensive life cycle assessment (LCA) is also performed for the designed hydrogen vehicle. The results of the hydrogen vehicle life cycle assessment are compared with a gasoline vehicle to fully understand the effect of hydrogen vehicles in reducing air emissions. The methods considered for hydrogen production included natural gas reforming, electrolysis, and thermochemical water splitting method. Furthermore, because the source of electricity used for electrolysis has a significant impact on the life cycle emission of a hydrogen vehicle, three different power sources were considered in this assessment. Finally, while a hydrogen vehicle with a degraded fuel cell emits lower carbon dioxide (CO₂) than a gasoline vehicle, the emitted CO₂ from this vehicle using hydrogen from electrolysis is approximately 25% higher than that of a new hydrogen vehicle.     

Future fuel cell and internal combustion engine automobile technologies: A 25-year life cycle and fleet impact assessment

Hydrogen fuel cell (FC) vehicles are receiving increasing attention as a potential powerful technology to reduce the transportation sector's dependence on petroleum and substantially decrease emissions of greenhouse gases (GHGs) at the same time. This paper projects energy use and GHG emissions from different FC vehicle configurations and compares these values to the projected characteristics of similarly sized and performing gasoline and diesel fueled automobiles on a life cycle, well to wheels and cradle to grave basis. Our analysis suggests that for the next 20 or more years, new internal combustion engine (ICE) hybrid drive train vehicles can achieve similar levels of reduction in energy use and GHG emissions compared to hydrogen FC vehicles, if the hydrogen is derived from natural gas. The fleet impact of more fuel-efficient vehicles depends on the time it takes for new technology to (i) become competitive, (ii) increase its share of the new vehicles produced, and finally (iii) penetrate significantly into the vehicle fleet. Since the lead times for bringing improved ICE vehicle technology into production are the shortest, its impact on vehicle fleet energy use and emissions could be significant in 20–30 years, about half the time required for hydrogen FC vehicles to have a similar impact. Full emission reduction potential of FC vehicles can only be achieved when hydrogen is derived from zero or very low-carbon releasing production processes on a large scale—an option that further increases the impact leadtime. Thus, a comprehensive short- and long-term strategy for reducing automobile energy use and emissions should include both the continuous improvement of ICE vehicles and simultaneous research and development of hydrogen FC cars.     

Electric and plug-in hybrid vehicles influence on CO2 and water vapour emissions

The main objective of this research is to quantify the impact of introducing electric vehicles and plug-in hybrid vehicles, including fuel cell on conventional fleets. The impact is estimated in terms of local pollutants, HC, CO, NO_x, PM, and in terms of CO₂ and water vapour global emissions. The specific fleet of Portugal, roughly 6 million light-duty vehicles (30% diesel, 70% gasoline) is considered, and the mobility indicator of the fleet, 90 thousand million p × km, is kept constant throughout the analysis. Probability density functions for energy consumption and emissions are derived for conventional, electric and plug-in hybrid vehicles, in charge depleting and charge sustaining modes. The Monte Carlo method is used to obtain average distribution estimates for discounting values of “old vehicles” that are removed from the fleet, and to add average distribution estimates for the “new vehicles” entering the fleet. Considering the actual Portuguese fleet as the reference case, local pollutant emissions decrease by a factor of 10-53%, for 50% fleet replacement. A potential 23% decrease of CO₂ is foreseen, and a potential 31% increase of H₂O emissions is forecasted. Life cycle water vapour emissions tend to rise and are, typically, 2-4 times higher than CO₂ values at the upstream stage, due to its release in the cooling towers of thermal power plants. It is interesting to note that considering 1 MJ of energy required at vehicle wheels, in an overall life cycle context, both fuel cell and electric modes have nearly twice as much H₂O emissions than internal combustion vehicles. CO₂ emissions tend to decrease with electric drive vehicles penetration due to the higher fleet life cycle efficiency.     

Comparative LCA of methanol-fuelled SOFCs as auxiliary power systems on-board ships

Fuel cells own the potential for significant environmental improvements both in terms of air quality and climate protection. Through the use of renewable primary energies, local pollutant and greenhouse gas emissions can be significantly minimized over the full life cycle of the electricity generation process, so that marine industry accounts renewable energy as its future energy source. The aim of this paper is to evaluate the use of methanol in Solid Oxide Fuel Cells (SOFC), as auxiliary power systems for commercial vessels, through Life Cycle Assessment (LCA). The LCA methodology allows the assessment of the potential environmental impact along the whole life cycle of the process. The unit considered is a 20 kWel fuel cell system. In a first part of the study different fuel options have been compared (methanol, bio-methanol, natural gas, hydrogen from cracking, electrolysis and reforming), then the operation of the cell fed with methanol has been compared with the traditional auxiliary power system, i.e. a diesel engine. The environmental benefits of the use of fuel cells have been assessed considering different impact categories. The results of the analysis show that fuel production phase has a strong influence on the life cycle impacts and highlight that feeding with bio-methanol represents a highly attractive solution from a life cycle point of view. The comparison with the conventional auxiliary power system shows extremely lower impacts for SOFCs.     

Life cycle analysis of vehicles powered by a fuel cell and by internal combustion engine for Canada

The transportation sector is responsible for a great percentage of the greenhouse gas emissions as well as the energy consumption in the world. Canada is the second major emitter of carbon dioxide in the world. The need for alternative fuels, other than petroleum, and the need to reduce energy consumption and greenhouse gases emissions are the main reasons behind this study. In this study, a full life cycle analysis of an internal combustion engine vehicle (ICEV) and a fuel cell vehicle (FCV) has been carried out. The impact of the material and fuel used in the vehicle on energy consumption and carbon dioxide emissions is analyzed for Canada. The data collected from the literature shows that the energy consumption for the production of 1 kg of aluminum is five times higher than that of 1 kg of steel, although higher aluminum content makes vehicles lightweight and more energy efficient during the vehicle use stage. Greenhouse gas regulated emissions and energy use in transportation (GREET) software has been used to analyze the fuel life cycle. The life cycle of the fuel consists of obtaining the raw material, extracting the fuel from the raw material, transporting, and storing the fuel as well as using the fuel in the vehicle. Four different methods of obtaining hydrogen were analyzed; using coal and nuclear power to produce electricity and extraction of hydrogen through electrolysis and via steam reforming of natural gas in a natural gas plant and in a hydrogen refueling station. It is found that the use of coal to obtain hydrogen generates the highest emissions and consumes the highest energy. Comparing the overall life cycle of an ICEV and a FCV, the total emissions of an FCV are 49% lower than an ICEV and the energy consumption of FCV is 87% lower than that of ICEV. Further, CO₂ emissions during the hydrogen fuel production in a central plant can be easily captured and sequestrated. The comparison carried out in this study between FCV and ICEV is extended to the use of recycled material. It is found that using 100% recycled material can reduce energy consumption by 45% and carbon dioxide emissions by 42%, mainly due to the reduced use of electricity during the manufacturing of the material.     

Life cycle evaluation of hydrogen and other potential fuels for aircrafts

In the present study, hydrogen and some other alternative fuels (such as ammonia, methanol, ethanol, liquefied natural gas) are considered for aviation applications under a comprehensive life cycle assessment study and are evaluated comparatively with the conventional kerosene based jet fuel for various impact categories. Therefore, this study is performed with a well-to-wake approach to evaluate the overall life cycle of an aircraft running on these conventional and alternative fuels. Both conventional and renewable fuel routes are considered for the production of ammonia and hydrogen fuels. Although there are modifications required to fulfill the aviation fuel specifications for such alternative fuels, the long term viability and environmental sustainability make them attractive solutions for the future of aviation industry. This study uses a life cycle assessment of an average aircraft utilizing various alternative aviation fuels to determine the relative environmental impact of each life cycle phase. The life cycle phases included in the analyses are as follows: (i) production, operation and maintenance of the aircraft, (ii) construction, maintenance and disposal of the airport, (iii) production, transportation and utilization of the aviation fuel in the aircraft. The results show that hydrogen and liquefied natural gas represent more environmentally benign alternatives although fuel costs are higher compared to ammonia, jet fuel and methanol. The total GHG emissions from hydropower based ammonia and hydrogen are calculated to be about 0.24 kg CO₂ eq. per traveled tonne-km and 0.03 kg CO₂ eq. per traveled tonne-km, respectively. Renewable based ammonia and hydrogen fueled aircrafts can further decrease the overall environmental impact in many categories allowing a brighter future for aviation industry.     

Plug-in hybrid fuel cell vehicles market penetration scenarios

The main objective of this research is to analyze the impact of the market share increase of hydrogen based road vehicles in terms of energy consumption and CO₂, on today's Portuguese light-duty fleet. Actual yearly values of energy consumption and emissions were estimated using COPERT software: 167112 TJ of fossil fuel energy, 12213 kton of CO₂ emission and 141 kton of CO, 20 kton of HC, 46 kton of NO_x and 3 kton of PM. These values represent 20–40% of countries total emissions. Additionally to base fleet, three scenarios of introduction of 10–30% fuel cell vehicles including plug-in hybrids configurations were analysed. Considering the scenarios of increasing hydrogen based vehicles penetration, up to 10% life cycle energy consumption reduction can be obtained if hydrogen from centralized natural gas reforming is considered. Full life cycle CO₂ emissions can also be reduced up to 20% in these scenarios, while local pollutants reach up to 85% reductions. For the purpose of estimating road vehicle technologies energy consumption and CO₂ emissions in a full life cycle perspective, fuel cell, conventional full hybrids and hybrid plug-in technologies were considered with diesel, gasoline, hydrogen and biofuel blends. Energy consumption values were estimated in a real road driving cycle and with ADVISOR software. Materials cradle-to-grave life cycle was estimated using GREET database adapted to Europe electric mix. The main conclusions on CO₂ full life cycle analysis is that light-duty vehicles using fuel cell propulsion technology are highly dependent on hydrogen production pathway. The worst scenario for the current Portuguese and European electric mix is hydrogen produced from on-site electrolysis (in the refuelling stations). In this case full life cycle CO₂ is 270 g/km against 190 g/km for conventional Diesel vehicle, for a typical 150,000 km useful life.     

Greenhouse gas implications of using coal for transportation: Life cycle assessment of coal-to-liquids,plug-in hybrids,and hydrogen pathways

Using coal to produce transportation fuels could improve the energy security of the United States by replacing some of the demand for imported petroleum. Because of concerns regarding climate change and the high greenhouse gas (GHG) emissions associated with conventional coal use, policies to encourage pathways that utilize coal for transportation should seek to reduce GHGs compared to petroleum fuels. This paper compares the GHG emissions of coal-to-liquid (CTL) fuels to the emissions of plug-in hybrid electric vehicles (PHEV) powered with coal-based electricity, and to the emissions of a fuel cell vehicle (FCV) that uses coal-based hydrogen. A life cycle approach is used to account for fuel cycle and use-phase emissions, as well as vehicle cycle and battery manufacturing emissions. This analysis allows policymakers to better identify benefits or disadvantages of an energy future that includes coal as a transportation fuel. We find that PHEVs could reduce vehicle life cycle GHG emissions by up to about one-half when coal with carbon capture and sequestration is used to generate the electricity used by the vehicles. On the other hand, CTL fuels and coal-based hydrogen would likely lead to significantly increased emissions compared to PHEVs and conventional vehicles using petroleum-based fuels.     

Trigeneration: A comprehensive review based on prime movers

In this paper, various aspects of trigeneration power plants including advantages, challenges and criteria for high efficiency operation are discussed. In trigeneration systems, prime movers are treated to be the heart of the plant and thus an appropriate selection is crucial for successful operation. A comparative analysis of potential prime movers, together with a comprehensive literature review used in trigeneration and, their selection criteria are presented. A case study of a trigeneration plant based on solid oxide fuel cells and an organic Rankine cycle is examined using thermodynamic analysis. This thermodynamic analysis includes performance assessment of the system through energy and exergy efficiencies. An environmental impact assessment is also conducted based on CO₂ emissions as a measure. The present study reveals that compared to power cycle efficiency (considering net electrical efficiency), there is a minimum potential of 22% gain in efficiency when trigeneration is used. Also, it is shown that there is more than 200 kg MWh^?1 reduction in CO₂ emissions when trigeneration is used compared to the case where a power cycle is only used. Copyright © 2010 John Wiley & Sons, Ltd.     

Comparative life cycle assessment of hydrogen pathways from fossil sources in China

Emissions of multiple hydrogen production pathways from fossil sources were evaluated and compared with that of fossil fuel production pathways in China by using the life cycle assessment method. The considered hydrogen pathways are gasoline reforming, diesel reforming, natural gas reforming, soybean‐derived biodiesel (s‐biodiesel) reforming, and waste cooking oil‐derived biodiesel reforming. Moreover, emissions and energy consumption of fuel cell vehicles utilizing hydrogen from different fossil sources were presented and compared with those of the electric vehicle, the internal combustion engine vehicle, and the compression ignition engine vehicle. The results indicate both fuel cell vehicles and the electric vehicle have less greenhouse gas emissions and energy consumption compared with the traditional vehicle technologies in China. Based on an overall performance comparison of five different fuel cell vehicles and the electric vehicle in China, fuel cell vehicles operating on hydrogen produced from natural gas and waste cooking oil‐derived biodiesel show the best performance, whereas the electric vehicle has the worse performance than all the fuel cell vehicles because of very high share of coal in the electricity mix of China. The emissions of electric vehicle in China will be in the same level with that of natural gas fuel cell vehicle if the share of coal decreases to around 40% and the share of renewable energy increases to around 20% in the electricity mix of China. Copyright © 2016 John Wiley & Sons, Ltd.     

The impact of fuel cell vehicle deployment on road transport greenhouse gas emissions: The China case

Considerable attention has been paid to energy security and climate problems caused by road vehicle fleets. Fuel cell vehicles provide a new solution for reducing energy consumption and greenhouse gas emissions, especially those from heavy-duty trucks. Although cost may become the key issue in fuel cell vehicle development, with technological improvements and cleaner pathways for hydrogen production, fuel cell vehicles will exhibit great potential of cost reduction. In accordance with the industrial plan in China, this study introduces five scenarios to evaluate the impact of fuel cell vehicles on the road vehicle fleet greenhouse gas emissions in China. Under the most optimistic scenario, greenhouse gas emissions generated by the whole fleet will decrease by 13.9% compared with the emissions in a scenario with no fuel cell vehicles, and heavy-duty truck greenhouse gas emissions will decrease by nearly one-fifth. Greenhouse gas emissions intensity of hydrogen production will play an essential role when fuel cell vehicles' fuel cycle greenhouse gas emissions are calculated; therefore, hydrogen production pathways will be critical in the future.