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Comparative life cycle assessment of hydrogen, methanol and electric vehicles from well to wheel
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e1 1
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Comparative life cycle assessment of hydrogen, methanol and electric vehicles from well to wheel Yusuf Bicer a,*, Ibrahim Dincer a,b a
Clean Energy Research Laboratory (CERL), Faculty of Engineering and Applied Science, University of Ontario Institute of Technology, 2000 Simcoe Street North, Oshawa, Ontario, L1H 7K4, Canada b Mechanical Engineering Department, KFUPM, Dhahran, 31261, Saudi Arabia
article info
abstract
Article history:
A comparative life cycle assessment of methanol, hydrogen and electric vehicles is con-
Received 28 March 2016
ducted to investigate the impacts of alternative vehicles on the environment and human
Received in revised form
health. For each case, the processes are analyzed from extraction of raw materials for
24 July 2016
hydrogen, methanol and electricity to disposal of the vehicles. Three different environ-
Accepted 28 July 2016
mental impact categories are selected in order to understand the diverse effects of vehi-
Available online xxx
cles, namely: global warming, human toxicity and ozone layer depletion. As an alternative fuel for internal combustion engines, hydrogen and methanol, are directly utilized in in-
Keywords:
ternal combustion engine vehicles. The results of this study show that electric vehicles
Hydrogen
yield higher human toxicity values due to the respective manufacturing and maintenance
Methanol
stages. Since the energy density of hydrogen is quite higher than methanol, hydrogen
Electric vehicle
driven vehicles result in a more environmentally-benign option with respect to global
Life cycle assessment
warming and ozone layer depletion potentials.
Transportation
© 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction Since the industrial revolution energy consumption has been increasing throughout the world, where the transportation has been one of the crucial sectors that contributes significantly to greenhouse gas (GHG) emissions and hence to local and global climate change concerns because of being about 95% dependent on fossil fuels. It is noted that the transportation sector consumes 61.2% of world oil reserves, subsidizing 28% of the total final energy supply [1] and 23% of CO2 emissions in the world [2]. For this reason, further research is conducted for sustainable transport systems to decrease the use of fossil fuels and promote the use of alternative fuels such as hydrogen and methanol together with electric
vehicles. The productions of electricity and heat are heavily dependent on coal which is carbon-intensive fossil fuel. The electricity consumption in electric vehicles (EV), if the electricity comes from fossil fuel sources, will continue damaging the environment and human health. Thus, there is a strong need to look for environmentally-benign electricity generation technologies and supply to EVs. Hydrogen can be generated from various resources to subsidize the development of alternative fueled vehicles and can provide long-term option based on renewable resources. At the same time, it can be used as a storage medium of electricity from intermittent renewables such as solar and wind energy [3]. Since the enhancement potential of renewable energy technologies are most likely more than fossil fuels, it is important to realize the production capacity of
* Corresponding author. E-mail addresses: [email protected] (Y. Bicer), [email protected] (I. Dincer). http://dx.doi.org/10.1016/j.ijhydene.2016.07.252 0360-3199/© 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Bicer Y, Dincer I, Comparative life cycle assessment of hydrogen, methanol and electric vehicles from well to wheel, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.07.252
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alternative renewable fuels from an environmental point of view. Haputhanthri et al. [4] studied the feasibility of developing ammonia gasoline liquid fuel blends and the use of ethanol as an emulsifier to enhance the solubility of ammonia in gasoline. They used a small thermostated vapor liquid equilibrium high-pressure cell and resulted in that engine dynamometer shows ammonia rich fuels yield an improved torque and power output especially at higher engine speeds. Zamfirescu and Dincer [5] reported a few potential opportunities and advantages of using ammonia as a sustainable fuel in transportation vehicles. They have compared ammonia with other conventional fuels in different aspects. Additionally, using ammonia both as a refrigerant and a fuel, they calculated refrigeration effect with respect to refrigeration power vs engine's power ending up with that ammonia is the cheapest fuel on $/GJ basis. Methanol is ideal fuel for transporting largely because of combustion efficiency and low cost. If burned, reformulated gasoline produces many harmful and toxic by-products which can be reduced or eliminated when exchanged with methanol. The emissions of unburned carbon and carbon monoxide at a much lower fuel consumption for methanol and it can significantly reduce emissions of NOx. Methanol also burns almost no solid particles - which can lead to breathing problems such as asthma. The operation of life cycle assessment is principally used as a cradle to grave analysis method to examine environmental impacts of a system or process or product. A life cycle is the set of phases of a product or service system, from the extraction of natural resources to last removal. A comprehensive LCA comprises inventory, impact, and improvement studies that quantity material and energy flows, assess the environmental impacts, and suggest improvement options of the processes. Several studies have been conducted in the literature assessing the environmental and combustion performance of alternative transportation methods through the use of LCA [6e9]. Granovskii et al. [10] studied life cycle assessment of hydrogen and gasoline vehicles by containing fuel production and utilization in vehicles powered by fuel cells and internal combustion engines. They evaluated and compared the efficiencies and environmental impacts by resulting that wind electrolysis based hydrogen and PEM fuel cell vehicle is the most environmentally benign method. Hacatoglu et al. [11] reported life cycle assessment of a nuclear-based copper-chlorine hydrogen generation method, containing approximations of fossil fuel energy use and greenhouse gas (GHG) emissions. They compared also other paths indicating that the performance of the method is similar to hydrogen produced by wind-based water electrolysis. Ma et al. [12] defined the key factors affecting the LCA studies of transportation vehicles. They implied that uncertainty, vehicle yearly mileage, driving pattern and material recycling rate have important impacts on the quality of the LCA results. Bartolozzi et al. [13] carried out LCA for vehicles equipped with either fuel cell or internal combustion engine to evaluate and compare the environmental impacts of the alternative scenarios for various hydrogen production options ranging from biomass to hydropower. They chose the pathway of renewable wind and biomass energy sources for hydrogen production either by electrolysis or direct
separation from biomass gasification syngas. Suleman et al. [14] analyzed the environmental impacts of steam methane reforming a membrane, diaphragm and mercury cell based electrolysis options for hydrogen production. According to their results, hydrogen production using mercury cell bring more ozone depletion values after SMR. Ahmadi et al. [15] presented an LCA study of hydrogen passenger cars where hydrogen is produced via three alternative methods, namely electrolysis, thermochemical water splitting, and steam methane reforming, and compared with conventional gasoline vehicles. Their results showed noteworthy decreases in GHG and air contaminant emissions from all three hydrogen production systems in four different provinces of Canada, except for electrolysis in Alberta where most electricity is produced from fossil fuels. Some researchers have examined on-board fuel production resulting in significant and flexible advance in the development of efficient and ecologically benign vehicles [5,16e18]. Li et al. [19] undertook a study for well-to-wheel analyses of battery electrical vehicles and fuel cell vehicles using different sources of energy and technologies in China. The results were compared based on the electricity and hydrogen source in terms of fossil energy use, total energy use and greenhouse gas emissions. Rose et al. [20] performed an LCA for diesel and CNG fueled heavy-duty refuse collection vehicles. The results implied that CNG vehicle is preferable in terms of decreased climate change impact and having lower cost compared to conventional diesel vehicle. Archsmith et al. [21] investigated the electricity fuel source and performance under real-world conditions are the determinants of life cycle GHG emissions. They presented an integrated model of life cycle emissions for both the manufacture and use of ICEs and EVs which additionally takes into account the impacts of climate conditions on vehicle efficiency and non-fossil power sources used for marginal electricity. Zhao and Tatari [22] performed an economic based hybrid LCA to evaluate the potential GHG emissions savings from the use of the electric vehicle as well as the possible emission impacts caused by battery degradation. In this study, both fuel and vehicle cycles for each of the options of hydrogen, electric and methanol driven vehicles are comparatively evaluated via LCA methodology. In terms of environmental impact categories, human toxicity, global warming and stratospheric ozone depletion are considered. The selected methanol and hydrogen vehicles operate with internal combustion engine while, electric cars operate with pure electricity from grid. In the scope of this study, a comprehensive environmental impact assessment for various fueled vehicles is carried out using LCA methodology, the fuel and vehicle cycle of selected vehicles are comparatively evaluated and uncertainty analyses for LCA results are identified in order to determine the reliability of the results.
Analysis and assessment The life cycle characteristics of vehicle technologies can be divided into two main steps, namely, fuel cycle and vehicle cycle. The fuel cycle considers processes for the production of raw materials and fuel consumption of the vehicle. This phase takes into account the associated energy intake and extracted
Please cite this article in press as: Bicer Y, Dincer I, Comparative life cycle assessment of hydrogen, methanol and electric vehicles from well to wheel, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.07.252
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gas emissions in mining. The emissions related to energy use and refueling of transport include the supply of fuel. A notable part of the analysis of the life cycle is collecting reliable data. Argonne National Laboratory has developed a full life cycle model so-called GREET (greenhouse gases and regulated emissions and energy delivery) which is useful to evaluate various vehicle and fuel combinations, based on the total fuel cycle or cycle of the vehicle [23]. The functional unit can be arranged but in the current study person km is taken as the base unit. In this assessment, the emissions during the operation of vehicles are taken from GREET 2015. Once these operation data are obtained, they are used in SimaPro LCA tool for full life cycle processes. Therefore, the analyses constitute from well to wheel (WTW) which contain the life cycle of equipment production, manufacturing, maintenance and infrastructure at the end of a vehicle's life. Ecoinvent LCA database v2.2 is utilized as data sources which is in the background of SimaPro software [24]. Life cycle analysis can be conducted at three different levels: product, service, or economy. In the current study, a process based LCA is conducted. In a process-based LCA, one lists the inputs as materials and energy sources and the outputs as emissions and wastes to the environment for a given step in producing a product. A few standards from the International Organization for Standards (ISO) govern the exact requirements necessary to manage LCA studies. There are several assessment methods developed over the time to classify and characterize the environmental effects of the system however in the current study, CML 2001 method is utilized. It defines the process to be realized for studying LCA project agreeing to the ISO standards. In the impact assessment phase of LCA, a group of impact classes and the characterization methods and factors for a wide list of materials are suggested. For applying the structures in the ecoinvent life cycle inventory database, it is essential to allocate the characterization factors to the fundamental source streams and pollutant streams described in the database. The categories considered in this study are briefly described in the following sections: Human Toxicity: Toxic substances on the human environment are the main concerns for this category. 1,4dichlorobenzene equivalents/kg emissions is used to express each toxic substance. Reliant on the material, the geographical scale varies between local and global indicator. Global Warming: The greenhouse gases to air are related with the climate change. Adverse effects upon ecosystem health, human health and material welfare can result from climate change. A kg carbon dioxide/kg emission is used to express the Global Warming Potential for time horizon 500 years (GWP500). It has a global scale. Stratospheric Ozone depletion: For the reason of stratospheric ozone depletion, a superior portion of UV-B radiation spreads the earth surface. This may yield damaging impacts on human and animal health, terrestrial and aquatic ecosystems, bioechemical cycles and on substances. Ozone depletion potential of several gasses are specified in kg CFC-11 equivalent/kg emission where the time span is infinity.
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Uncertainty analysis In the Monte Carlo analysis for the take-back system, the absolute uncertainty needs to be calculated. In the Monte Carlo method, the processer proceeds a random variable for each value within the uncertainty limits stated and recalculates the results. The outcome is stored and the calculation is redone by compelling diverse samples within the uncertainty limit, and also this result is stored. After the process is repeated 1000 times, 1000 different answers are found and the answers yield an uncertainty distribution. Mean is the average score of all results. It is the most useful parameter to use when we want to report the best guess value. Median value is the middle value which is useful if outliers are significantly influencing the mean value. Standard error of mean is the stop measure that is the quantity by which the final calculation influenced the mean. CV (coefficient of variability) is the ratio between the standard deviation and the mean which is a useful parameter if sorting of data in a table by the relative magnitude of the uncertainty is required. In order to capture the characteristic variability of data in the process or production systems, Monte Carlo analysis can be used embedded in SimaPro software. In the current study, uncertainty analyses for the selected environmental impact categories are carried out.
Description of the processes On average, lifetime performance of a passenger car is assumed to be 239,000 person km. Generally, the average utilization factor is expected to be 1.59e1.6 passengers per car. Henceforth, the lifetime of the selected vehicles is approximately 150,000 km. The functional unit in the life cycle assessment of the vehicles is chosen as the driving range of 1 km traveled. The results of GHG emissions and other environmental impact categories for each vehicle type are expressed per km distance. Here, the life cycle assessment comprises the following life cycle phases, as illustrated in Fig. 1: (i) manufacturing of the vehicle, (ii) operation of the vehicle, (iii) maintenance of the vehicle, (iv) disposal of the vehicle.
Vehicle manufacturing and maintenance The inventory contains processes of energy, water and material usage in passenger car manufacturing. Rail and road transport of materials is accounted for. The groundwork of plant is involved together with the issues such as land use, building, road and parking structure. The material consumption reflect a modern vehicle. The data for vehicle production are representative for manufacturing sites with an environmental management system. Thus, the resulting data may be an underestimation of environmental impacts of an average vehicle fleet. The electricity comes from a mixture of UCTE (Union for the Co-ordination of Transmission of Electricity) countries. The UCTE is the association of transmission system operators in continental Europe in which about 450 million people are supplied electricity. In the electricity usage process, electricity production in UCTE, the transmission network and direct SF6-emissions to air are included. The conversion of
Please cite this article in press as: Bicer Y, Dincer I, Comparative life cycle assessment of hydrogen, methanol and electric vehicles from well to wheel, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.07.252
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Energy
produc on
Vehicle Disposal
transmission
consump on
Vehicle OperaƟon
Vehicle Manufacturing
Vehicle Maintenance
Fig. 1 e Scope of LCA analyses including fuel and vehicle cycles in this study.
high-medium voltage as well as the transmission of electricity at medium voltage are taken into account. The operation of EV varies from the conventional vehicles in some characteristics as the first difference is the energy source for operation where electricity is utilized despite of petrol or diesel. Henceforth, there are no tail-pipe emissions. It is therefore assumed that emissions are restricted to tire and brake wear and abrasion from the surface of road. For electric vehicles, the required amount of steel is lower compared to conventional cars since there is no ICE in the car. Production of electric motor and lithium ion batteries are included in EVs. Currently available EV batteries are in the range of 100 kg and 400 kg based on vehicle size and range [25]. The average masses of electric motor for and lithium ion battery are assumed to be 104 kg and 312 kg, respectively for this study [26]. The inventory data for battery production and disposal is utilized from GREET model and Ref. [27]. The inventory for maintenance of vehicles contains resources used for alteration parts and energy consumption of garages. Rail and road transportation of supplies is accounted for. For EVs, during the lifetime of the car, one battery change is assumed. Henceforth, lithium ion battery replacement and disposal processes are also taken into account in the maintenance phase.
Vehicle disposal The inventory of vehicle disposal contains disposal processes for bulk materials. For the disposal of tires, a cut off allocation is applied. In addition, the transportation of tires to the cement works is taken into account. For the disposal of steel, aluminum, copper and tires, a cut off allocation is applied. Waste specific water together with air emissions from incineration and supplementary supply depletion for flue gas scrubbing are accounted for. Short term releases to river water and long term emissions to ground water from slag section and remaining material landfill are considered with process energy loads for municipal waste incineration plant (MSWI). The processes included in the disposal of a vehicle include; (i) disposal of plastics in mixture with 15.3% water to municipal incineration (65 kg), (ii) disposal of glass to municipal incineration (30.1 kg), (iii) disposal of emulsion paint leftovers to HWI (100 kg), and (iv) disposal of zinc in car shredder remains to MSWI (5.89 kg).
Lithium ion batteries are recycled for numerous aims. The most noticeable one is the retrieval of valued materials and to follow to ecological laws. Numerous methods are present for recycling lithium ion batteries with diverse environmental consequences. Usually, battery recycling procedures can be expressed in three main categories: mechanical, pyrometallurgical and hydrometallurgical processes. Hydrometallurgical processes are evaluated to require considerably lesser energy desires compared to pyrometallurgical processes. In this study, hydrometallurgical process for disposal of batteries are selected with an average efficiency of 57.5% and energy use of 140 kWh/tonne [27]. The inventory data for the disposal of batteries are taken from Ref. [27]. For ammonia and hydrogen fueled vehicles, the required amount of steel and electrical energy is a little higher than other cars because of storage tank infrastructure.
Vehicle operation The operation process of the vehicles is one of the key sections of life cycle analyses. In this phase, fuel consumption is involved. Direct airborne emissions of gaseous materials, particulate matters and heavy metals are accounted for. Particulate emissions cover exhaust- and abrasions emissions. Hydrocarbon emissions contain evaporation. Heavy metal emissions to soil and water produced by tire abrasion are accounted for. The values are based on operation of an average vehicle. The specific conditions for the selected vehicles are presented herein. In the hydrogen vehicle study: Hydrogen is produced using underground coal gasification (UCG). Underground coal gasification is a promising option for the upcoming use of un-worked coal. Despite mining coal area, UCG may eventually create unreached coal reserves available. Since UCG leaves the ash behind in the cavity, it can be evaluated as a clean coal utilization. After the gasification of coal, syngas composes with a combination of gas species such as hydrogen (H2), carbon monoxide (CO), water vapor (H2O), and carbon dioxide (CO2) in addition to nitrogen (N2) in the air. Hydrogen gas is separated using pressure swing absorption process. The energy supply of hydrogen production comes from coal fired power plants since UCG process is utilized. For electric vehicles: Production and transmission of electricity as UCTE Mix is considered. Electricity consumption in
Please cite this article in press as: Bicer Y, Dincer I, Comparative life cycle assessment of hydrogen, methanol and electric vehicles from well to wheel, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.07.252
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Table 1 e Fuel and energy requirements per km for the selected vehicles. Vehicle type
Fuel/Supply
Methanol Vehicle
M90
Hydrogen Vehicle Electric Vehicle
Hydrogen Electricity
Natural gas
Fuel/Energy consumption Methanol (90%) Gasoline (10%)
Steam methane reforming
Methanol synthesis
0.1180535 0.0060664 0.0195508 0.2167432
Distillation
Energy requirement kg/km kg/km kg/km kWh/km
2635.7422 kJ/km 2350.2034 kJ/km 780.7007 kJ/km
Methanol
Raw material extraction and processing
Vehicle Maintenance
Conventional and non-conventional resources
Use Power plant
Transmission
Electricity
Raw material extraction and processing
Vehicle Manufacturing Vehicle Disposal Underground coal gasification Injector Well
Syngas
Hydrogen production plant
Hydrogen
Production Well
Fig. 2 e Fuel production processes and vehicle manufacturing.
and electric vehicles given in Table 1 which are obtained from GREET 2015. The obtained results are given in terms of unit km. The global warming potentials of the selected vehicles are comparatively shown in Fig. 3. The lowest GHG emissions are observed in hydrogen vehicle corresponding to 0.057 kg CO2 eq/km. The highest global warming potential is obtained for methanol vehicle with a value of 0.30 kg CO2 eq/km. EVs yield quite lower GHG emissions compared to methanol vehicles but they are still higher than hydrogen vehicle because of electricity production mix process. If electricity production can be realized by renewable sources, total emissions would decrease for EVs. 0.35 0.3 Global warming (kg CO2 eq/km)
the vehicle is included. Particulate emissions comprise exhaust and abrasions emissions. Heavy metal emissions to soil and water caused by tire abrasion are accounted for. In the electricity usage process, electricity production mix, the transmission network and direct SF6-emissions to air are included. Methanol vehicle fuel consists of 90% methanol and 10% gasoline which is a fuel blend. The fuel blending ratio is taken from GREET 2015 model [23]. The raw materials, processing energy, estimate on catalyst use, and emissions to air and water from process, plant infrastructure are included. The process describes the production of methanol from natural gas via steam reforming process to obtain syngas for the production of methanol. There is no CO2 use and hydrogen is assumed as burned in the furnace. The raw materials, average transportation, emissions to air from tank storage, estimation for storage infrastructure are included for the distribution part where 40% of the methanol is assumed to be transported from overseas. The fuel and energy consumption rates of the vehicles are presented in Table 1. The fuel production processes including the vehicle manufacturing for three different scenarios are shown in Fig. 2.
0.25 0.2 0.15 0.1
0.05
Results and discussion 0
The environmental impacts of hydrogen, methanol and electric vehicles are evaluated using SimaPro LCA software based on the energy consumption and GHG emissions of ICE vehicles
Hydrogen Vehicle
Electric Vehicle
Methanol Vehicle
Fig. 3 e Life cycle comparison of global warming potentials of selected vehicles per km travel.
Please cite this article in press as: Bicer Y, Dincer I, Comparative life cycle assessment of hydrogen, methanol and electric vehicles from well to wheel, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.07.252
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Hydrogen from UCG with CCS Pig iron, at plant
29%
Hydrogen Vehicle - Opera on UCG Natural gas, burned in industrial furnace >100kW
53% 2%
Lignite, burned in power plant Polyethylene, HDPE, granulate, at plant
2% 2% 3%
Hard coal, burned in power plant
4%
5%
Remaining processes
Fig. 4 e Contributions of various processes to global warming potential of hydrogen vehicle.
Fig. 6 e Life cycle comparison of human toxicity values of selected vehicles per km traveled.
For hydrogen vehicle, the contribution of various processes to global warming potential is illustrated in Fig. 4. The operation of hydrogen vehicle is responsible only 4% of total GHG emissions while production of hydrogen using UCG is the highest contributor with 53% share, respectively. On-board storage of hydrogen requires high resistant and strength tanks which leads to higher steel and process requirement. Henceforth, non-operation part of hydrogen vehicle constitute about 22% and 44% of overall hydrogen vehicle life cycle for abiotic depletion and global warming potential. In contrast, as shown in Fig. 5, the operation of methanol vehicle represents 92.6% of overall global warming impact because of higher CO2 emissions during utilization. Fig. 6 shows the comparison of human toxicity values in terms of kg 1,4-DB eq per travel km. EVs yield highest human toxicity values corresponding to 0.39 1,4-DB eq/km. Compared to other vehicles, they yield quite higher values because of mainly production and disposal of batteries as shown in Fig. 7. Copper production and disposal of sulfidic tailings have shares of 47% and 22%, respectively. The shares of main processes for human toxicity category of EV are shown in Fig. 8. The depletion of ozone layer is one of the main contributors to climate change in the world. As seen in Fig. 9, methanol
Copper, primary, at refinery
12%
Disposal, sulfidic tailings, off-site
2% 2%
Disposal, spoil from lignite mining, in surface landfill
4%
Aluminium, primary, liquid, at plant
4% 47%
Anode, aluminium electrolysis
7%
Ferrochromium, high-carbon, 68% Cr, at plant Disposal, uranium tailings, nonradioac ve emissions
22%
Remaining processes
Fig. 7 e Contributions of various processes to human toxicity of electric vehicle.
vehicle has the maximum ozone depletion potential since it is produced by fossil based methods which have enormous amount of carbon substance. The values are equal to 2.14 10 8 kg CFC-11 eq. and 8.63 10 9 kg CFC-11 eq per km for methanol and electric vehicles, respectively. The highest contributions are from transportation of natural gas via
1p Methanol Vehicle
100%
4.17E-6 p Vehicle Manufacturing
6.31%
1 personkm Methanol Vehicle Operation
92.6%
4.17E-6 p Maintenance, passenger car/RER/I U
1.05%
Fig. 5 e Shares of main processes for global warming potential of methanol vehicle. Please cite this article in press as: Bicer Y, Dincer I, Comparative life cycle assessment of hydrogen, methanol and electric vehicles from well to wheel, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.07.252
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7
1p Electric Vehicle
100%
4.17E-6 p Electric Vehicle Manufacturing
38.2%
1 personkm Electric Vehicle Operation - UCTE
8.7%
4.17E-6 p Electric Vehicle Maintenance
53.1%
Fig. 8 e The shares of main processes for human toxicity of electric vehicles.
pipelines corresponding more than 70% and production of crude oil with 10% as shown in Fig. 10. The contributions of fundamental processes to ozone layer depletion value are illustrated in Fig. 11 for hydrogen vehicle. Production of vehicle is responsible for about 72.6% of the total environmental impact for this category. For an electric vehicle, the sub-process contributions are accordingly illustrated in Fig. 12 where transportation of natural gas via pipelines is the main contributor. The Monte Carlo uncertainty analysis is performed with 1000 runs and 95% interval of confidence. The standard deviation, coefficient of performance and standard mean of error values are tabulated in Tables 2e4. The mean standard errors for the hydrogen vehicle are 0.00113, 0.00773 and 0.0096 for global warming, human toxicity and ozone layer depletion categories, respectively. The mean standard errors for the methanol vehicle are 0.00112, 0.00674 and 0.00756 for global warming, human toxicity and ozone layer depletion categories, respectively. The mean standard errors for the electric vehicle are 0.00419, 0.0151 and 0.00666 for global warming,
Ozone layer deple on steady state (kg CFC-11 eq/km)
4.00E-08 3.50E-08
human toxicity and ozone layer depletion categories, respectively. Based on the uncertainty analyses results, it is seen that global warming potential values have the lowest uncertainty range compared to others as the coefficient of variation value is 3.55% for hydrogen vehicle which is stated in Table 3. The maximum coefficient of variance is calculated for the human toxicity category in electric vehicle corresponding to 47.70% as shown in Table 4. The uncertainty values of human toxicity and ozone layer depletion potential categories are higher compared to global warming which cause higher CV values. This is due to the accuracy of the available inventory data in SimaPro LCA database for some specific materials or processes. The comparative simulation results for hydrogen and electric vehicles are shown in Fig. 13. The green bars on the left represent the number of times electric vehicle had a lower environmental impact than hydrogen vehicle for given categories. For instance, it shows that in 100% of the cases the global warming, human toxicity and ozone layer depletion values are lower for hydrogen vehicle. In about 70% of the cases, the photochemical oxidation value is lower for electric vehicles. The comparative simulation results for hydrogen and methanol vehicle are presented in Fig. 14. For 100% of the cases the global warming, human toxicity and ozone layer
3.00E-08 2.50E-08 2.00E-08
1.50E-08 1.00E-08 5.00E-09 0.00E+00 Methanol Vehicle
Electric Vehicle
Hydrogen Vehicle
Fig. 9 e Life cycle comparison of ozone layer depletion potentials of selected vehicles per km traveled.
Fig. 10 e Contributions of various processes to ozone layer depletion of methanol vehicle.
Please cite this article in press as: Bicer Y, Dincer I, Comparative life cycle assessment of hydrogen, methanol and electric vehicles from well to wheel, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.07.252
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1p Hydrogen Vehicle UCG
100%
4.17E-6 p Hydrogen Vehicle Manufacturing
1 personkm Hydrogen Vehicle Operation - UCG
72.6%
4.33%
4.17E-6 p Maintenance, passenger car/RER/I U
23%
Fig. 11 e Shares of main processes for ozone layer depletion of hydrogen vehicles.
depletion values are lower for hydrogen vehicle. There is only a small portion of methanol vehicle which has advantages over the hydrogen vehicle for terrestrial ecotoxicity with a value of 2.8%. In Fig. 15, the blue dot bars on the left represent the comparison of hydrogen and methanol vehicle for different environmental categories. According to the results, the methanol vehicle is 100% more environmentally benign in terms of acidification, eutrophication and human toxicity categories. However, hydrogen vehicle yield the cleanest options for abiotic depletion, ozone layer and global warming potential values. Fig. 12 e Contributions of various processes to ozone layer depletion of electric vehicle.
Table 2 e Monte Carlo uncertainty results of methanol vehicle. Impact category Global warming 500a Human toxicity 500a Ozone layer depletion 40a
Unit
Mean
Median
SD
CV (coefficient of variation)
Std. err. of mean
kg CO2 eq kg 1,4-DB eq kg CFC-11 eq
0.294 0.0378 2.78E-08
0.293 0.0359 2.63E-08
0.0105 0.00923 8.46E-09
3.58% 24.40% 30.40%
0.00113 0.00773 0.0096
Table 3 e Monte Carlo uncertainty results of hydrogen vehicle. Impact category Global warming 500a Human toxicity 500a Ozone layer depletion 40a
Unit
Mean
Median
SD
CV (coefficient of variation)
Std. err. of mean
kg CO2 eq kg 1,4-DB eq kg CFC-11 eq
0.0548 0.025 1.55E-09
0.0547 0.0243 1.48E-09
0.00194 0.00532 3.71E-10
3.55% 21.30% 23.90%
0.00112 0.00674 0.00756
Table 4 e Monte Carlo uncertainty results of electric vehicle. Impact category Global warming 500a Human toxicity 500a Ozone layer depletion 40a
Unit
Mean
Median
SD
CV (coefficient of variation)
Std. err. of mean
kg CO2 eq kg 1,4-DB eq kg CFC-11 eq
0.159 0.254 8.70E-09
0.157 0.222 8.46E-09
0.0211 0.121 1.83E-09
13.30% 47.70% 21.10%
0.00419 0.0151 0.00666
Please cite this article in press as: Bicer Y, Dincer I, Comparative life cycle assessment of hydrogen, methanol and electric vehicles from well to wheel, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.07.252
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-57 Max. ozone incremental reac -50 -70
-80
-60
43.3
vity
50.4
Max. incremental reac vity
30.4
Photochemical oxida on (low NOx)
Photochemical oxida on
-2
97.9
Human toxicity infinite
0
100
Ozone layer deple on steady state
0
100
Upper limit of net global warming
0
100
-40
-20
0
20
40
60
80
100
% A
A >= B
Fig. 13 e Monte-Carlo simulation results of LCA comparison between hydrogen and electric vehicle (A: Electric vehicle, B: Hydrogen vehicle).
-99
Photochemical oxida on (low NOx) 0.9
-99
Marine sediment ecotox. 500a 1.4
-97
Terrestrial ecotoxicity 500a 2.8 Marine aqua c ecotox. 100a 0.8
-99 -100
Human toxicity infinite 0
-100
Ozone layer deple on steady state 0
-100
Upper limit of net global warming 0
-100 -95 -90 -85 -80 -75 -70 -65 -60 -55 -50 -45 -40 -35 -30 -25 -20 -15 -10
-5
5
% A
A >= B
Fig. 14 e Monte-Carlo simulation results of LCA comparison between hydrogen and methanol vehicle (A: Hydrogen vehicle, B: Methanol vehicle).
Conclusions In this study, a comparative environmental impact assessment of alternative vehicles, including hydrogen, methanol and electric vehicles, is undertaken to analyze and evaluate the end results of their utilization. In this regard, the life cycle analyses of hydrogen, methanol and electric vehicles are conducted using ozone layer depletion, global warming potential and human toxicity indicators. The analyses are carried out from production of vehicles to disposal process containing maintenance and operation of the vehicles. In order to determine the reliability of the results, the
uncertainty analyses are conducted using Monte Carlo statistical approach. The results obtained from this study indicate that hydrogen vehicle is the most environmentally benign one in all environmental impact categories compared to methanol and electric vehicles. Even though electric vehicles are considered with no direct CO2 emission during operation, in the process of electricity and battery production and disposal of batteries, they end up with some concerns which damage the environment in terms of human toxicity, GHG emissions and ozone layer depletion. Since methanol production is dependent primarily on natural gas, it has highest global warming potential compared to other vehicles. The production process of electricity plays an important role on
Please cite this article in press as: Bicer Y, Dincer I, Comparative life cycle assessment of hydrogen, methanol and electric vehicles from well to wheel, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.07.252
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-100
Photochemical oxida on (low NOx)
-97
Photochemical oxida on
0 2.9
Human toxicity infinite
0
-100
Ozone layer deple on steady state
0
-100
Upper limit of net global warming
0
Eutrophica on
0
100
Acidifica on
0
100
Abio c deple on
0
-100 -100
-80
-60
-40
100
-20
20
40
60
80
100
% A
A >= B
Fig. 15 e Monte-Carlo simulation results of characterized LCA comparison between electric and methanol vehicle (A: Hydrogen vehicle, B: Methanol vehicle).
overall environmental impact of electric vehicles and also on electrolysis based hydrogen production options. Similarly, natural gas dependence of methanol vehicles is one of major drawbacks of methanol fueled vehicles. Having sustainable and clean transportation options are mostly likely to progress with the implementation of clean and renewable resources for both power and fuel generation.
Acknowledgment The authors acknowledge the support provided by the Natural Sciences and Engineering Research Council of Canada.
Nomenclature CML CNG GHG EV GREET HEV ICE ISO LCA LPG MSWI PTW RCV UCTE WTPW WTW
Center of Environmental Science of Leiden University Compressed Natural Gas Greenhouse Gas Electric Vehicle Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation Hybrid Electric Vehicle Internal Combustion Engine International Organization for Standards Life Cycle Assessment Liquefied Petroleum Gas Municipal Waste Incineration Plant Pump to Wheel Refuse Collection Vehicles Union for the Co-ordination of Transmission of Electricity heel to Pump Well to Wheel
references
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[20] Rose L, Hussain M, Ahmed S, Malek K, Costanzo R, Kjeang E. A comparative life cycle assessment of diesel and compressed natural gas powered refuse collection vehicles in a Canadian city. Energy Policy 2013;52:453e61. [21] Archsmith J, Kendall A, Rapson D. From cradle to junkyard: assessing the life cycle greenhouse gas benefits of electric vehicles. Res Transp Econ 2015;52:72e90. [22] Zhao Y, Tatari O. A hybrid life cycle assessment of the vehicle-to-grid application in light duty commercial fleet. Energy 2015;93:1277e86. Part 2. [23] Argonne National Laboratory. GREET model. 2015. http:// greet.es.anl.gov/. [24] Consultants P. SimaPro life cycle analysis database version 7.3 (software). € € ger G, Dettmer T, Althaus HJ, [25] Duce AD, Egede P, Ohlschl a Bu¨tler T, et al. Guidelines for the LCA of electric vehicles. Eur Union Seventh Framew Programme 2013. [26] Leuenberger M, Frischknecht R. Life cycle assessment of battery electric vehicles and concept cars. Report. ESUServices Ltd; 2010. [27] Boyden A. The environmental impacts of recycling portable lithium-ion batteries. Australian National University; 2014. Thesis Dissertations.
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Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/he
Comparative life cycle assessment of hydrogen, methanol and electric vehicles from well to wheel Yusuf Bicer a,*, Ibrahim Dincer a,b a
Clean Energy Research Laboratory (CERL), Faculty of Engineering and Applied Science, University of Ontario Institute of Technology, 2000 Simcoe Street North, Oshawa, Ontario, L1H 7K4, Canada b Mechanical Engineering Department, KFUPM, Dhahran, 31261, Saudi Arabia
article info
abstract
Article history:
A comparative life cycle assessment of methanol, hydrogen and electric vehicles is con-
Received 28 March 2016
ducted to investigate the impacts of alternative vehicles on the environment and human
Received in revised form
health. For each case, the processes are analyzed from extraction of raw materials for
24 July 2016
hydrogen, methanol and electricity to disposal of the vehicles. Three different environ-
Accepted 28 July 2016
mental impact categories are selected in order to understand the diverse effects of vehi-
Available online xxx
cles, namely: global warming, human toxicity and ozone layer depletion. As an alternative fuel for internal combustion engines, hydrogen and methanol, are directly utilized in in-
Keywords:
ternal combustion engine vehicles. The results of this study show that electric vehicles
Hydrogen
yield higher human toxicity values due to the respective manufacturing and maintenance
Methanol
stages. Since the energy density of hydrogen is quite higher than methanol, hydrogen
Electric vehicle
driven vehicles result in a more environmentally-benign option with respect to global
Life cycle assessment
warming and ozone layer depletion potentials.
Transportation
© 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction Since the industrial revolution energy consumption has been increasing throughout the world, where the transportation has been one of the crucial sectors that contributes significantly to greenhouse gas (GHG) emissions and hence to local and global climate change concerns because of being about 95% dependent on fossil fuels. It is noted that the transportation sector consumes 61.2% of world oil reserves, subsidizing 28% of the total final energy supply [1] and 23% of CO2 emissions in the world [2]. For this reason, further research is conducted for sustainable transport systems to decrease the use of fossil fuels and promote the use of alternative fuels such as hydrogen and methanol together with electric
vehicles. The productions of electricity and heat are heavily dependent on coal which is carbon-intensive fossil fuel. The electricity consumption in electric vehicles (EV), if the electricity comes from fossil fuel sources, will continue damaging the environment and human health. Thus, there is a strong need to look for environmentally-benign electricity generation technologies and supply to EVs. Hydrogen can be generated from various resources to subsidize the development of alternative fueled vehicles and can provide long-term option based on renewable resources. At the same time, it can be used as a storage medium of electricity from intermittent renewables such as solar and wind energy [3]. Since the enhancement potential of renewable energy technologies are most likely more than fossil fuels, it is important to realize the production capacity of
* Corresponding author. E-mail addresses: [email protected] (Y. Bicer), [email protected] (I. Dincer). http://dx.doi.org/10.1016/j.ijhydene.2016.07.252 0360-3199/© 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Bicer Y, Dincer I, Comparative life cycle assessment of hydrogen, methanol and electric vehicles from well to wheel, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.07.252
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alternative renewable fuels from an environmental point of view. Haputhanthri et al. [4] studied the feasibility of developing ammonia gasoline liquid fuel blends and the use of ethanol as an emulsifier to enhance the solubility of ammonia in gasoline. They used a small thermostated vapor liquid equilibrium high-pressure cell and resulted in that engine dynamometer shows ammonia rich fuels yield an improved torque and power output especially at higher engine speeds. Zamfirescu and Dincer [5] reported a few potential opportunities and advantages of using ammonia as a sustainable fuel in transportation vehicles. They have compared ammonia with other conventional fuels in different aspects. Additionally, using ammonia both as a refrigerant and a fuel, they calculated refrigeration effect with respect to refrigeration power vs engine's power ending up with that ammonia is the cheapest fuel on $/GJ basis. Methanol is ideal fuel for transporting largely because of combustion efficiency and low cost. If burned, reformulated gasoline produces many harmful and toxic by-products which can be reduced or eliminated when exchanged with methanol. The emissions of unburned carbon and carbon monoxide at a much lower fuel consumption for methanol and it can significantly reduce emissions of NOx. Methanol also burns almost no solid particles - which can lead to breathing problems such as asthma. The operation of life cycle assessment is principally used as a cradle to grave analysis method to examine environmental impacts of a system or process or product. A life cycle is the set of phases of a product or service system, from the extraction of natural resources to last removal. A comprehensive LCA comprises inventory, impact, and improvement studies that quantity material and energy flows, assess the environmental impacts, and suggest improvement options of the processes. Several studies have been conducted in the literature assessing the environmental and combustion performance of alternative transportation methods through the use of LCA [6e9]. Granovskii et al. [10] studied life cycle assessment of hydrogen and gasoline vehicles by containing fuel production and utilization in vehicles powered by fuel cells and internal combustion engines. They evaluated and compared the efficiencies and environmental impacts by resulting that wind electrolysis based hydrogen and PEM fuel cell vehicle is the most environmentally benign method. Hacatoglu et al. [11] reported life cycle assessment of a nuclear-based copper-chlorine hydrogen generation method, containing approximations of fossil fuel energy use and greenhouse gas (GHG) emissions. They compared also other paths indicating that the performance of the method is similar to hydrogen produced by wind-based water electrolysis. Ma et al. [12] defined the key factors affecting the LCA studies of transportation vehicles. They implied that uncertainty, vehicle yearly mileage, driving pattern and material recycling rate have important impacts on the quality of the LCA results. Bartolozzi et al. [13] carried out LCA for vehicles equipped with either fuel cell or internal combustion engine to evaluate and compare the environmental impacts of the alternative scenarios for various hydrogen production options ranging from biomass to hydropower. They chose the pathway of renewable wind and biomass energy sources for hydrogen production either by electrolysis or direct
separation from biomass gasification syngas. Suleman et al. [14] analyzed the environmental impacts of steam methane reforming a membrane, diaphragm and mercury cell based electrolysis options for hydrogen production. According to their results, hydrogen production using mercury cell bring more ozone depletion values after SMR. Ahmadi et al. [15] presented an LCA study of hydrogen passenger cars where hydrogen is produced via three alternative methods, namely electrolysis, thermochemical water splitting, and steam methane reforming, and compared with conventional gasoline vehicles. Their results showed noteworthy decreases in GHG and air contaminant emissions from all three hydrogen production systems in four different provinces of Canada, except for electrolysis in Alberta where most electricity is produced from fossil fuels. Some researchers have examined on-board fuel production resulting in significant and flexible advance in the development of efficient and ecologically benign vehicles [5,16e18]. Li et al. [19] undertook a study for well-to-wheel analyses of battery electrical vehicles and fuel cell vehicles using different sources of energy and technologies in China. The results were compared based on the electricity and hydrogen source in terms of fossil energy use, total energy use and greenhouse gas emissions. Rose et al. [20] performed an LCA for diesel and CNG fueled heavy-duty refuse collection vehicles. The results implied that CNG vehicle is preferable in terms of decreased climate change impact and having lower cost compared to conventional diesel vehicle. Archsmith et al. [21] investigated the electricity fuel source and performance under real-world conditions are the determinants of life cycle GHG emissions. They presented an integrated model of life cycle emissions for both the manufacture and use of ICEs and EVs which additionally takes into account the impacts of climate conditions on vehicle efficiency and non-fossil power sources used for marginal electricity. Zhao and Tatari [22] performed an economic based hybrid LCA to evaluate the potential GHG emissions savings from the use of the electric vehicle as well as the possible emission impacts caused by battery degradation. In this study, both fuel and vehicle cycles for each of the options of hydrogen, electric and methanol driven vehicles are comparatively evaluated via LCA methodology. In terms of environmental impact categories, human toxicity, global warming and stratospheric ozone depletion are considered. The selected methanol and hydrogen vehicles operate with internal combustion engine while, electric cars operate with pure electricity from grid. In the scope of this study, a comprehensive environmental impact assessment for various fueled vehicles is carried out using LCA methodology, the fuel and vehicle cycle of selected vehicles are comparatively evaluated and uncertainty analyses for LCA results are identified in order to determine the reliability of the results.
Analysis and assessment The life cycle characteristics of vehicle technologies can be divided into two main steps, namely, fuel cycle and vehicle cycle. The fuel cycle considers processes for the production of raw materials and fuel consumption of the vehicle. This phase takes into account the associated energy intake and extracted
Please cite this article in press as: Bicer Y, Dincer I, Comparative life cycle assessment of hydrogen, methanol and electric vehicles from well to wheel, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.07.252
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gas emissions in mining. The emissions related to energy use and refueling of transport include the supply of fuel. A notable part of the analysis of the life cycle is collecting reliable data. Argonne National Laboratory has developed a full life cycle model so-called GREET (greenhouse gases and regulated emissions and energy delivery) which is useful to evaluate various vehicle and fuel combinations, based on the total fuel cycle or cycle of the vehicle [23]. The functional unit can be arranged but in the current study person km is taken as the base unit. In this assessment, the emissions during the operation of vehicles are taken from GREET 2015. Once these operation data are obtained, they are used in SimaPro LCA tool for full life cycle processes. Therefore, the analyses constitute from well to wheel (WTW) which contain the life cycle of equipment production, manufacturing, maintenance and infrastructure at the end of a vehicle's life. Ecoinvent LCA database v2.2 is utilized as data sources which is in the background of SimaPro software [24]. Life cycle analysis can be conducted at three different levels: product, service, or economy. In the current study, a process based LCA is conducted. In a process-based LCA, one lists the inputs as materials and energy sources and the outputs as emissions and wastes to the environment for a given step in producing a product. A few standards from the International Organization for Standards (ISO) govern the exact requirements necessary to manage LCA studies. There are several assessment methods developed over the time to classify and characterize the environmental effects of the system however in the current study, CML 2001 method is utilized. It defines the process to be realized for studying LCA project agreeing to the ISO standards. In the impact assessment phase of LCA, a group of impact classes and the characterization methods and factors for a wide list of materials are suggested. For applying the structures in the ecoinvent life cycle inventory database, it is essential to allocate the characterization factors to the fundamental source streams and pollutant streams described in the database. The categories considered in this study are briefly described in the following sections: Human Toxicity: Toxic substances on the human environment are the main concerns for this category. 1,4dichlorobenzene equivalents/kg emissions is used to express each toxic substance. Reliant on the material, the geographical scale varies between local and global indicator. Global Warming: The greenhouse gases to air are related with the climate change. Adverse effects upon ecosystem health, human health and material welfare can result from climate change. A kg carbon dioxide/kg emission is used to express the Global Warming Potential for time horizon 500 years (GWP500). It has a global scale. Stratospheric Ozone depletion: For the reason of stratospheric ozone depletion, a superior portion of UV-B radiation spreads the earth surface. This may yield damaging impacts on human and animal health, terrestrial and aquatic ecosystems, bioechemical cycles and on substances. Ozone depletion potential of several gasses are specified in kg CFC-11 equivalent/kg emission where the time span is infinity.
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Uncertainty analysis In the Monte Carlo analysis for the take-back system, the absolute uncertainty needs to be calculated. In the Monte Carlo method, the processer proceeds a random variable for each value within the uncertainty limits stated and recalculates the results. The outcome is stored and the calculation is redone by compelling diverse samples within the uncertainty limit, and also this result is stored. After the process is repeated 1000 times, 1000 different answers are found and the answers yield an uncertainty distribution. Mean is the average score of all results. It is the most useful parameter to use when we want to report the best guess value. Median value is the middle value which is useful if outliers are significantly influencing the mean value. Standard error of mean is the stop measure that is the quantity by which the final calculation influenced the mean. CV (coefficient of variability) is the ratio between the standard deviation and the mean which is a useful parameter if sorting of data in a table by the relative magnitude of the uncertainty is required. In order to capture the characteristic variability of data in the process or production systems, Monte Carlo analysis can be used embedded in SimaPro software. In the current study, uncertainty analyses for the selected environmental impact categories are carried out.
Description of the processes On average, lifetime performance of a passenger car is assumed to be 239,000 person km. Generally, the average utilization factor is expected to be 1.59e1.6 passengers per car. Henceforth, the lifetime of the selected vehicles is approximately 150,000 km. The functional unit in the life cycle assessment of the vehicles is chosen as the driving range of 1 km traveled. The results of GHG emissions and other environmental impact categories for each vehicle type are expressed per km distance. Here, the life cycle assessment comprises the following life cycle phases, as illustrated in Fig. 1: (i) manufacturing of the vehicle, (ii) operation of the vehicle, (iii) maintenance of the vehicle, (iv) disposal of the vehicle.
Vehicle manufacturing and maintenance The inventory contains processes of energy, water and material usage in passenger car manufacturing. Rail and road transport of materials is accounted for. The groundwork of plant is involved together with the issues such as land use, building, road and parking structure. The material consumption reflect a modern vehicle. The data for vehicle production are representative for manufacturing sites with an environmental management system. Thus, the resulting data may be an underestimation of environmental impacts of an average vehicle fleet. The electricity comes from a mixture of UCTE (Union for the Co-ordination of Transmission of Electricity) countries. The UCTE is the association of transmission system operators in continental Europe in which about 450 million people are supplied electricity. In the electricity usage process, electricity production in UCTE, the transmission network and direct SF6-emissions to air are included. The conversion of
Please cite this article in press as: Bicer Y, Dincer I, Comparative life cycle assessment of hydrogen, methanol and electric vehicles from well to wheel, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.07.252
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Energy
produc on
Vehicle Disposal
transmission
consump on
Vehicle OperaƟon
Vehicle Manufacturing
Vehicle Maintenance
Fig. 1 e Scope of LCA analyses including fuel and vehicle cycles in this study.
high-medium voltage as well as the transmission of electricity at medium voltage are taken into account. The operation of EV varies from the conventional vehicles in some characteristics as the first difference is the energy source for operation where electricity is utilized despite of petrol or diesel. Henceforth, there are no tail-pipe emissions. It is therefore assumed that emissions are restricted to tire and brake wear and abrasion from the surface of road. For electric vehicles, the required amount of steel is lower compared to conventional cars since there is no ICE in the car. Production of electric motor and lithium ion batteries are included in EVs. Currently available EV batteries are in the range of 100 kg and 400 kg based on vehicle size and range [25]. The average masses of electric motor for and lithium ion battery are assumed to be 104 kg and 312 kg, respectively for this study [26]. The inventory data for battery production and disposal is utilized from GREET model and Ref. [27]. The inventory for maintenance of vehicles contains resources used for alteration parts and energy consumption of garages. Rail and road transportation of supplies is accounted for. For EVs, during the lifetime of the car, one battery change is assumed. Henceforth, lithium ion battery replacement and disposal processes are also taken into account in the maintenance phase.
Vehicle disposal The inventory of vehicle disposal contains disposal processes for bulk materials. For the disposal of tires, a cut off allocation is applied. In addition, the transportation of tires to the cement works is taken into account. For the disposal of steel, aluminum, copper and tires, a cut off allocation is applied. Waste specific water together with air emissions from incineration and supplementary supply depletion for flue gas scrubbing are accounted for. Short term releases to river water and long term emissions to ground water from slag section and remaining material landfill are considered with process energy loads for municipal waste incineration plant (MSWI). The processes included in the disposal of a vehicle include; (i) disposal of plastics in mixture with 15.3% water to municipal incineration (65 kg), (ii) disposal of glass to municipal incineration (30.1 kg), (iii) disposal of emulsion paint leftovers to HWI (100 kg), and (iv) disposal of zinc in car shredder remains to MSWI (5.89 kg).
Lithium ion batteries are recycled for numerous aims. The most noticeable one is the retrieval of valued materials and to follow to ecological laws. Numerous methods are present for recycling lithium ion batteries with diverse environmental consequences. Usually, battery recycling procedures can be expressed in three main categories: mechanical, pyrometallurgical and hydrometallurgical processes. Hydrometallurgical processes are evaluated to require considerably lesser energy desires compared to pyrometallurgical processes. In this study, hydrometallurgical process for disposal of batteries are selected with an average efficiency of 57.5% and energy use of 140 kWh/tonne [27]. The inventory data for the disposal of batteries are taken from Ref. [27]. For ammonia and hydrogen fueled vehicles, the required amount of steel and electrical energy is a little higher than other cars because of storage tank infrastructure.
Vehicle operation The operation process of the vehicles is one of the key sections of life cycle analyses. In this phase, fuel consumption is involved. Direct airborne emissions of gaseous materials, particulate matters and heavy metals are accounted for. Particulate emissions cover exhaust- and abrasions emissions. Hydrocarbon emissions contain evaporation. Heavy metal emissions to soil and water produced by tire abrasion are accounted for. The values are based on operation of an average vehicle. The specific conditions for the selected vehicles are presented herein. In the hydrogen vehicle study: Hydrogen is produced using underground coal gasification (UCG). Underground coal gasification is a promising option for the upcoming use of un-worked coal. Despite mining coal area, UCG may eventually create unreached coal reserves available. Since UCG leaves the ash behind in the cavity, it can be evaluated as a clean coal utilization. After the gasification of coal, syngas composes with a combination of gas species such as hydrogen (H2), carbon monoxide (CO), water vapor (H2O), and carbon dioxide (CO2) in addition to nitrogen (N2) in the air. Hydrogen gas is separated using pressure swing absorption process. The energy supply of hydrogen production comes from coal fired power plants since UCG process is utilized. For electric vehicles: Production and transmission of electricity as UCTE Mix is considered. Electricity consumption in
Please cite this article in press as: Bicer Y, Dincer I, Comparative life cycle assessment of hydrogen, methanol and electric vehicles from well to wheel, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.07.252
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Table 1 e Fuel and energy requirements per km for the selected vehicles. Vehicle type
Fuel/Supply
Methanol Vehicle
M90
Hydrogen Vehicle Electric Vehicle
Hydrogen Electricity
Natural gas
Fuel/Energy consumption Methanol (90%) Gasoline (10%)
Steam methane reforming
Methanol synthesis
0.1180535 0.0060664 0.0195508 0.2167432
Distillation
Energy requirement kg/km kg/km kg/km kWh/km
2635.7422 kJ/km 2350.2034 kJ/km 780.7007 kJ/km
Methanol
Raw material extraction and processing
Vehicle Maintenance
Conventional and non-conventional resources
Use Power plant
Transmission
Electricity
Raw material extraction and processing
Vehicle Manufacturing Vehicle Disposal Underground coal gasification Injector Well
Syngas
Hydrogen production plant
Hydrogen
Production Well
Fig. 2 e Fuel production processes and vehicle manufacturing.
and electric vehicles given in Table 1 which are obtained from GREET 2015. The obtained results are given in terms of unit km. The global warming potentials of the selected vehicles are comparatively shown in Fig. 3. The lowest GHG emissions are observed in hydrogen vehicle corresponding to 0.057 kg CO2 eq/km. The highest global warming potential is obtained for methanol vehicle with a value of 0.30 kg CO2 eq/km. EVs yield quite lower GHG emissions compared to methanol vehicles but they are still higher than hydrogen vehicle because of electricity production mix process. If electricity production can be realized by renewable sources, total emissions would decrease for EVs. 0.35 0.3 Global warming (kg CO2 eq/km)
the vehicle is included. Particulate emissions comprise exhaust and abrasions emissions. Heavy metal emissions to soil and water caused by tire abrasion are accounted for. In the electricity usage process, electricity production mix, the transmission network and direct SF6-emissions to air are included. Methanol vehicle fuel consists of 90% methanol and 10% gasoline which is a fuel blend. The fuel blending ratio is taken from GREET 2015 model [23]. The raw materials, processing energy, estimate on catalyst use, and emissions to air and water from process, plant infrastructure are included. The process describes the production of methanol from natural gas via steam reforming process to obtain syngas for the production of methanol. There is no CO2 use and hydrogen is assumed as burned in the furnace. The raw materials, average transportation, emissions to air from tank storage, estimation for storage infrastructure are included for the distribution part where 40% of the methanol is assumed to be transported from overseas. The fuel and energy consumption rates of the vehicles are presented in Table 1. The fuel production processes including the vehicle manufacturing for three different scenarios are shown in Fig. 2.
0.25 0.2 0.15 0.1
0.05
Results and discussion 0
The environmental impacts of hydrogen, methanol and electric vehicles are evaluated using SimaPro LCA software based on the energy consumption and GHG emissions of ICE vehicles
Hydrogen Vehicle
Electric Vehicle
Methanol Vehicle
Fig. 3 e Life cycle comparison of global warming potentials of selected vehicles per km travel.
Please cite this article in press as: Bicer Y, Dincer I, Comparative life cycle assessment of hydrogen, methanol and electric vehicles from well to wheel, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.07.252
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Hydrogen from UCG with CCS Pig iron, at plant
29%
Hydrogen Vehicle - Opera on UCG Natural gas, burned in industrial furnace >100kW
53% 2%
Lignite, burned in power plant Polyethylene, HDPE, granulate, at plant
2% 2% 3%
Hard coal, burned in power plant
4%
5%
Remaining processes
Fig. 4 e Contributions of various processes to global warming potential of hydrogen vehicle.
Fig. 6 e Life cycle comparison of human toxicity values of selected vehicles per km traveled.
For hydrogen vehicle, the contribution of various processes to global warming potential is illustrated in Fig. 4. The operation of hydrogen vehicle is responsible only 4% of total GHG emissions while production of hydrogen using UCG is the highest contributor with 53% share, respectively. On-board storage of hydrogen requires high resistant and strength tanks which leads to higher steel and process requirement. Henceforth, non-operation part of hydrogen vehicle constitute about 22% and 44% of overall hydrogen vehicle life cycle for abiotic depletion and global warming potential. In contrast, as shown in Fig. 5, the operation of methanol vehicle represents 92.6% of overall global warming impact because of higher CO2 emissions during utilization. Fig. 6 shows the comparison of human toxicity values in terms of kg 1,4-DB eq per travel km. EVs yield highest human toxicity values corresponding to 0.39 1,4-DB eq/km. Compared to other vehicles, they yield quite higher values because of mainly production and disposal of batteries as shown in Fig. 7. Copper production and disposal of sulfidic tailings have shares of 47% and 22%, respectively. The shares of main processes for human toxicity category of EV are shown in Fig. 8. The depletion of ozone layer is one of the main contributors to climate change in the world. As seen in Fig. 9, methanol
Copper, primary, at refinery
12%
Disposal, sulfidic tailings, off-site
2% 2%
Disposal, spoil from lignite mining, in surface landfill
4%
Aluminium, primary, liquid, at plant
4% 47%
Anode, aluminium electrolysis
7%
Ferrochromium, high-carbon, 68% Cr, at plant Disposal, uranium tailings, nonradioac ve emissions
22%
Remaining processes
Fig. 7 e Contributions of various processes to human toxicity of electric vehicle.
vehicle has the maximum ozone depletion potential since it is produced by fossil based methods which have enormous amount of carbon substance. The values are equal to 2.14 10 8 kg CFC-11 eq. and 8.63 10 9 kg CFC-11 eq per km for methanol and electric vehicles, respectively. The highest contributions are from transportation of natural gas via
1p Methanol Vehicle
100%
4.17E-6 p Vehicle Manufacturing
6.31%
1 personkm Methanol Vehicle Operation
92.6%
4.17E-6 p Maintenance, passenger car/RER/I U
1.05%
Fig. 5 e Shares of main processes for global warming potential of methanol vehicle. Please cite this article in press as: Bicer Y, Dincer I, Comparative life cycle assessment of hydrogen, methanol and electric vehicles from well to wheel, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.07.252
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e1 1
7
1p Electric Vehicle
100%
4.17E-6 p Electric Vehicle Manufacturing
38.2%
1 personkm Electric Vehicle Operation - UCTE
8.7%
4.17E-6 p Electric Vehicle Maintenance
53.1%
Fig. 8 e The shares of main processes for human toxicity of electric vehicles.
pipelines corresponding more than 70% and production of crude oil with 10% as shown in Fig. 10. The contributions of fundamental processes to ozone layer depletion value are illustrated in Fig. 11 for hydrogen vehicle. Production of vehicle is responsible for about 72.6% of the total environmental impact for this category. For an electric vehicle, the sub-process contributions are accordingly illustrated in Fig. 12 where transportation of natural gas via pipelines is the main contributor. The Monte Carlo uncertainty analysis is performed with 1000 runs and 95% interval of confidence. The standard deviation, coefficient of performance and standard mean of error values are tabulated in Tables 2e4. The mean standard errors for the hydrogen vehicle are 0.00113, 0.00773 and 0.0096 for global warming, human toxicity and ozone layer depletion categories, respectively. The mean standard errors for the methanol vehicle are 0.00112, 0.00674 and 0.00756 for global warming, human toxicity and ozone layer depletion categories, respectively. The mean standard errors for the electric vehicle are 0.00419, 0.0151 and 0.00666 for global warming,
Ozone layer deple on steady state (kg CFC-11 eq/km)
4.00E-08 3.50E-08
human toxicity and ozone layer depletion categories, respectively. Based on the uncertainty analyses results, it is seen that global warming potential values have the lowest uncertainty range compared to others as the coefficient of variation value is 3.55% for hydrogen vehicle which is stated in Table 3. The maximum coefficient of variance is calculated for the human toxicity category in electric vehicle corresponding to 47.70% as shown in Table 4. The uncertainty values of human toxicity and ozone layer depletion potential categories are higher compared to global warming which cause higher CV values. This is due to the accuracy of the available inventory data in SimaPro LCA database for some specific materials or processes. The comparative simulation results for hydrogen and electric vehicles are shown in Fig. 13. The green bars on the left represent the number of times electric vehicle had a lower environmental impact than hydrogen vehicle for given categories. For instance, it shows that in 100% of the cases the global warming, human toxicity and ozone layer depletion values are lower for hydrogen vehicle. In about 70% of the cases, the photochemical oxidation value is lower for electric vehicles. The comparative simulation results for hydrogen and methanol vehicle are presented in Fig. 14. For 100% of the cases the global warming, human toxicity and ozone layer
3.00E-08 2.50E-08 2.00E-08
1.50E-08 1.00E-08 5.00E-09 0.00E+00 Methanol Vehicle
Electric Vehicle
Hydrogen Vehicle
Fig. 9 e Life cycle comparison of ozone layer depletion potentials of selected vehicles per km traveled.
Fig. 10 e Contributions of various processes to ozone layer depletion of methanol vehicle.
Please cite this article in press as: Bicer Y, Dincer I, Comparative life cycle assessment of hydrogen, methanol and electric vehicles from well to wheel, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.07.252
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i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e1 1
1p Hydrogen Vehicle UCG
100%
4.17E-6 p Hydrogen Vehicle Manufacturing
1 personkm Hydrogen Vehicle Operation - UCG
72.6%
4.33%
4.17E-6 p Maintenance, passenger car/RER/I U
23%
Fig. 11 e Shares of main processes for ozone layer depletion of hydrogen vehicles.
depletion values are lower for hydrogen vehicle. There is only a small portion of methanol vehicle which has advantages over the hydrogen vehicle for terrestrial ecotoxicity with a value of 2.8%. In Fig. 15, the blue dot bars on the left represent the comparison of hydrogen and methanol vehicle for different environmental categories. According to the results, the methanol vehicle is 100% more environmentally benign in terms of acidification, eutrophication and human toxicity categories. However, hydrogen vehicle yield the cleanest options for abiotic depletion, ozone layer and global warming potential values. Fig. 12 e Contributions of various processes to ozone layer depletion of electric vehicle.
Table 2 e Monte Carlo uncertainty results of methanol vehicle. Impact category Global warming 500a Human toxicity 500a Ozone layer depletion 40a
Unit
Mean
Median
SD
CV (coefficient of variation)
Std. err. of mean
kg CO2 eq kg 1,4-DB eq kg CFC-11 eq
0.294 0.0378 2.78E-08
0.293 0.0359 2.63E-08
0.0105 0.00923 8.46E-09
3.58% 24.40% 30.40%
0.00113 0.00773 0.0096
Table 3 e Monte Carlo uncertainty results of hydrogen vehicle. Impact category Global warming 500a Human toxicity 500a Ozone layer depletion 40a
Unit
Mean
Median
SD
CV (coefficient of variation)
Std. err. of mean
kg CO2 eq kg 1,4-DB eq kg CFC-11 eq
0.0548 0.025 1.55E-09
0.0547 0.0243 1.48E-09
0.00194 0.00532 3.71E-10
3.55% 21.30% 23.90%
0.00112 0.00674 0.00756
Table 4 e Monte Carlo uncertainty results of electric vehicle. Impact category Global warming 500a Human toxicity 500a Ozone layer depletion 40a
Unit
Mean
Median
SD
CV (coefficient of variation)
Std. err. of mean
kg CO2 eq kg 1,4-DB eq kg CFC-11 eq
0.159 0.254 8.70E-09
0.157 0.222 8.46E-09
0.0211 0.121 1.83E-09
13.30% 47.70% 21.10%
0.00419 0.0151 0.00666
Please cite this article in press as: Bicer Y, Dincer I, Comparative life cycle assessment of hydrogen, methanol and electric vehicles from well to wheel, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.07.252
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i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e1 1
-57 Max. ozone incremental reac -50 -70
-80
-60
43.3
vity
50.4
Max. incremental reac vity
30.4
Photochemical oxida on (low NOx)
Photochemical oxida on
-2
97.9
Human toxicity infinite
0
100
Ozone layer deple on steady state
0
100
Upper limit of net global warming
0
100
-40
-20
0
20
40
60
80
100
% A
A >= B
Fig. 13 e Monte-Carlo simulation results of LCA comparison between hydrogen and electric vehicle (A: Electric vehicle, B: Hydrogen vehicle).
-99
Photochemical oxida on (low NOx) 0.9
-99
Marine sediment ecotox. 500a 1.4
-97
Terrestrial ecotoxicity 500a 2.8 Marine aqua c ecotox. 100a 0.8
-99 -100
Human toxicity infinite 0
-100
Ozone layer deple on steady state 0
-100
Upper limit of net global warming 0
-100 -95 -90 -85 -80 -75 -70 -65 -60 -55 -50 -45 -40 -35 -30 -25 -20 -15 -10
-5
5
% A
A >= B
Fig. 14 e Monte-Carlo simulation results of LCA comparison between hydrogen and methanol vehicle (A: Hydrogen vehicle, B: Methanol vehicle).
Conclusions In this study, a comparative environmental impact assessment of alternative vehicles, including hydrogen, methanol and electric vehicles, is undertaken to analyze and evaluate the end results of their utilization. In this regard, the life cycle analyses of hydrogen, methanol and electric vehicles are conducted using ozone layer depletion, global warming potential and human toxicity indicators. The analyses are carried out from production of vehicles to disposal process containing maintenance and operation of the vehicles. In order to determine the reliability of the results, the
uncertainty analyses are conducted using Monte Carlo statistical approach. The results obtained from this study indicate that hydrogen vehicle is the most environmentally benign one in all environmental impact categories compared to methanol and electric vehicles. Even though electric vehicles are considered with no direct CO2 emission during operation, in the process of electricity and battery production and disposal of batteries, they end up with some concerns which damage the environment in terms of human toxicity, GHG emissions and ozone layer depletion. Since methanol production is dependent primarily on natural gas, it has highest global warming potential compared to other vehicles. The production process of electricity plays an important role on
Please cite this article in press as: Bicer Y, Dincer I, Comparative life cycle assessment of hydrogen, methanol and electric vehicles from well to wheel, International Journal of Hydrogen Energy (2016), http://dx.doi.org/10.1016/j.ijhydene.2016.07.252
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i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e1 1
-100
Photochemical oxida on (low NOx)
-97
Photochemical oxida on
0 2.9
Human toxicity infinite
0
-100
Ozone layer deple on steady state
0
-100
Upper limit of net global warming
0
Eutrophica on
0
100
Acidifica on
0
100
Abio c deple on
0
-100 -100
-80
-60
-40
100
-20
20
40
60
80
100
% A
A >= B
Fig. 15 e Monte-Carlo simulation results of characterized LCA comparison between electric and methanol vehicle (A: Hydrogen vehicle, B: Methanol vehicle).
overall environmental impact of electric vehicles and also on electrolysis based hydrogen production options. Similarly, natural gas dependence of methanol vehicles is one of major drawbacks of methanol fueled vehicles. Having sustainable and clean transportation options are mostly likely to progress with the implementation of clean and renewable resources for both power and fuel generation.
Acknowledgment The authors acknowledge the support provided by the Natural Sciences and Engineering Research Council of Canada.
Nomenclature CML CNG GHG EV GREET HEV ICE ISO LCA LPG MSWI PTW RCV UCTE WTPW WTW
Center of Environmental Science of Leiden University Compressed Natural Gas Greenhouse Gas Electric Vehicle Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation Hybrid Electric Vehicle Internal Combustion Engine International Organization for Standards Life Cycle Assessment Liquefied Petroleum Gas Municipal Waste Incineration Plant Pump to Wheel Refuse Collection Vehicles Union for the Co-ordination of Transmission of Electricity heel to Pump Well to Wheel
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