AN EVALUATION OF THE ENVIRONMENTAL IMPACT OF THE INTERNAL
COMBUSTION ENGINE VEHICLE VERSUS THE HYBRID-ELECTRIC VEHICLE
by
Sean A. Elliott
An Engineering Project Submitted to the Graduate
Faculty of Rensselaer Polytechnic Institute
in Partial Fulfillment of the
Requirements for the degree of
MASTER OF MECHANICAL ENGINEERING
Approved:
_________________________________________
Dr. Sudhangshu Bose, Project Adviser
Rensselaer Polytechnic Institute
Hartford, Connecticut
April, 2012
© Copyright 2012
by
Sean A. Elliott
All Rights Reserved
ii
Contents
List of Tables ..................................................................................................................... v
List of Figures .................................................................................................................. vii
Abstract ........................................................................................................................... viii
1. Introduction.................................................................................................................. 1
1.1
Background ........................................................................................................ 1
1.2
Previous Studies ................................................................................................. 2
1.3
Project Scope ...................................................................................................... 5
2. Methodology ................................................................................................................ 6
2.1
Life Cycle Assessment Approach ...................................................................... 6
2.2
LCA Scope ......................................................................................................... 6
2.3
List of Key Assumptions.................................................................................... 7
3. Discussion .................................................................................................................. 10
3.1
Selection of Vehicles........................................................................................ 10
3.2
Material Procurement and Vehicle Production ................................................ 12
3.3
3.4
3.2.1
Procurement and Production of Materials............................................ 13
3.2.2
Vehicle Assembly Estimate ................................................................. 16
3.2.3
Batteries................................................................................................ 17
Use Cases ......................................................................................................... 19
3.3.1
Use Case Emissions Totals .................................................................. 19
3.3.2
Use Case Fuel Cost Totals ................................................................... 20
3.3.3
Replacement of Fluids.......................................................................... 21
3.3.4
Battery Replacement ............................................................................ 21
End of Life/Recycle ......................................................................................... 21
4. Results........................................................................................................................ 23
4.1
Energy Totals ................................................................................................... 23
iii
4.2
Emissions Totals .............................................................................................. 23
4.3
Cost Totals ....................................................................................................... 24
5. Conclusions................................................................................................................ 26
References........................................................................................................................ 28
iv
List of Tables
Table 1. Specifications of Vehicles Used for Study [11], [12] ........................................ 11
Table 2. Specifications of Vehicles Considered but not Chosen for Study [13], [14] .... 11
Table 3. Material Estimates by Weight [4] ...................................................................... 13
Table 4. Greenhouse Gas Emission Totals Per Vehicle due to Materials (kg/vehicle) [4]
......................................................................................................................................... 16
Table 5. Vehicle Assembly Information [15] .................................................................. 17
Table 6. Battery Material Compositions [4] .................................................................... 17
Table 7. Production Energies for Raw Battery Materials [4] .......................................... 18
Table 8. Battery Material Production Energies per Vehicle ............................................ 18
Table 9. Battery Assembly and Test Energies [4] ........................................................... 19
Table 10. Vehicle Scenario Parameters [11], [12] ........................................................... 19
Table 11. Emissions Values for Life of Vehicles Used [5] ............................................. 20
Table 12. Lifetime Vehicle Fuel Costs at $3.92/gal ........................................................ 20
Table 13. Lifetime Vehicle Fuel Costs at $5.50/gal ........................................................ 20
Table 14. Vehicle Fluid Weights (lb) [4]......................................................................... 21
Table 15. Material Recycling Estimates by Weight [10] ................................................ 22
Table 16. Energy Totals per Vehicle (in Million Btu)..................................................... 23
Table 17. Net Energy per Vehicle for Case Studies (in Million Btu).............................. 23
Table 18. Greenhouse Gas (GHG) Emission per Vehicle Totals (units of kg CO2e) ...... 24
v
Table 19. Net GHG Emissions per Vehicle for Use Cases (units of kg CO2e) ............... 24
Table 20. Cost per Vehicle (in Dollars) ........................................................................... 25
Table 21. Net Cost per Vehicle (in Dollars) .................................................................... 25
vi
List of Figures
Figure 1. 2012 Toyota Prius Picture [11] ........................................................................ 12
Figure 2. 2012 Toyota Corolla S Picture [12] ................................................................. 12
Figure 3. Total Energy Use Per Vehicle during Production [4] ...................................... 14
Figure 4. Greenhouse Gas Emissions per Vehicle during Production [4] ....................... 15
vii
Abstract
Hybrid-electric vehicles (HEVs) have increased in popularity significantly in recent
years. The principal advertised advantage of these types of vehicles is superior fuel
economy when compared to a class-equivalent internal combustion engine vehicle
(ICEV). Benefits of the superior fuel economy are twofold: 1) cost savings to the
consumer, purchasing less fuel for a given distance traveled, and 2) less environmental
impact due to lower vehicle emissions. Both of these benefits are well publicized by
hybrid-electric vehicle manufacturers and advocates. Other factors must be considered,
however, before an HEV can be proclaimed “better for the environment” or "cheaper to
own" than an ICEV. Materials, manufacturing, reliability of technology, length of useful
life and ease of recycling or disposal all must be considered in this argument. This study
performs a comprehensive analysis focusing on the “cradle to grave” environmental
impact of each of these types of vehicles. A supplementary total cost of ownership
analysis is also included. Results indicate that, as expected, the HEV produces
considerably less emissions than the ICEV. The results of the cost analysis do not show
a clear winner, although the HEV proves to be the better choice if gasoline prices
continue their upward trend.
viii
1. Introduction
1.1 Background
In recent years as the global population has continued to rise, so has the amount of
pollution produced by humans. More than ever, individuals, businesses, and
organizations have embraced the “go green” movement in hopes of preserving our
planet’s natural resources. While air pollution and hazardous wastes produced by
construction, manufacturing, mining, and agriculture industries are very large
contributors to the overall world pollution, none of these are as tangible to the average
individual as motor vehicle emissions, another leading cause of air pollution [1]. More
stringent environmental regulations and individual's desires to do their part in the green
movement have created a strong market for a new wave of green vehicles, motor
vehicles that produce lower emissions.
Many of the new-wave of green vehicles utilize alternative energies rather than gasoline
but often are limited in range, speed, or power because these technologies are still in
their infancy. One of the most popular green vehicles which utilizes reasonably mature
technology is the hybrid-electric vehicle (HEV). This vehicle augments an internal
combustion gasoline engine with an electric motor and large battery. By using the
electric motor to store unused energy into the battery, this vehicle can operate without
using the gasoline engine all the time. Many environmental advocates overstate the
benefits of the hybrid car, however. The popular educational website “HowStuffWorks”
contains an article on hybrid cars titled “Do Hybrid Cars Cause Pollution?” [2] To those
familiar with the technology, of course the answer is yes since some amount of gasoline
is still being combusted. A common misconception is that the hybrid car is “good” for
the environment when the reality is that it is “less bad” than a vehicle which burns more
fuel over the same distance traveled.
Another aspect of the hybrid vehicle often overlooked is the energy during the
manufacturing of a hybrid car, as this can be related to the amount of pollutants
generated. Because of the advanced technologies and additional components used in a
hybrid car, it often takes additional energy to manufacture when compared to the internal
1
combustion engine vehicle (ICEV). Hybrid car manufacturers claim that the additional
energy required to manufacture the hybrid is easily outweighed by the energy saved
during the vehicle’s lifetime of use. Studies have both disputed and confirmed this
assertion depending on the assumptions made for the length and extent of use considered
to make up the lifetime of the vehicle.
Like the preconceived notion that a hybrid car is better for the environment than a
comparable internal combustion engine vehicle, hybrid cars are marketed claiming that
the lower amount of energy that they use will equate to a financial savings to the
consumer. Again, the realization of this savings is dependent upon the number of miles
driven over the life of the car because the initial capital investment of the more
expensive hybrid vehicle must be offset by the savings in energy costs.
1.2 Previous Studies
As stated in the previous section, various studies have been performed that make
comparisons between the HEV and the ICEV. The scope of these studies differs and the
results lead to a wide range of conclusions. These conclusions must be accepted with
caution, however, as many people or organizations have agendas that lead to biased
results. For example, possibly the most discussed report on this subject matter claims
that a Hummer H2 (an ICEV) is more cost efficient per mile (and by extension, is more
environmentally friendly) than the Toyota Prius (an HEV). This report, titled "Dust to
Dust" [3] was published by a marketing firm and was not peer reviewed by subject
matter experts in either academia or the automotive industry. Digging deeper reveals that
the assumed life expectancy of the Hummer was over 300,000 miles compared to just
109,000 for the Prius. This report was widely publicized prior to the public being made
aware of the questionable route to which the conclusions were made. The lesson here is
that by taking liberties with the assumptions, the results can be skewed significantly in a
given direction.
So as not to fall into a similar trap of trusting distorted results, the literature review
conducted for the findings reported for this project was limited to studies performed in
academia or those supported by United States Government organizations. One study
2
relevant to this report was conducted by Argonne National Laboratory for the US
Department of Energy [4]. This study developed a vehicle-cycle model for the
greenhouse gases, regulated emissions, and energy use in transportation (the GREET
model). This model evaluates energy and emission effects associated with vehicle
material
recovery
and
production,
component
fabrication,
assembly
and
disposal/recycling. When the vehicle-cycle model is combined with the fuel-cycle
model, the GREET model provides a comprehensive life cycle approach to compare
energy use and emissions of conventional (i.e., ICEVs) and advanced vehicle
technologies (i.e., HEVs).
The GREET model was used to estimate total energy cycle results for six mid-size
passenger vehicles, among them an internal combustion engine and an internal
combustion engine with hybrid configuration. Among the relevant conclusions of the
GREET model study to this report are that the lifetime energy use of the HEV is less
than that of the conventional ICEV (an average of about 4200 BTU/mi versus 6400
BTU/mi). Most of the difference in these two figures is due to the vehicle operation (or
use) phase.
A 2001 study comparing the second generation Toyota Prius (an HEV) with a Toyota
Corolla (an ICEV) determined that the Prius is not the most sensible choice from either
an economic or environmental standpoint [5]. This study focused on the cost
effectiveness of the fuel economy and the emissions of the two vehicles. It concluded
that at the 2001 price of gasoline, the Corolla is more cost effective from a fuel economy
standpoint than the Prius, even though the fuel economy of the Prius is superior. This
conclusion is based on the fact that the Prius is more expensive than the Corolla and the
difference in purchase price is not recovered by the fuel savings. In fact, according to the
study, the price of gas would have to increase threefold to make the Prius the more
economical decision. This study did not factor in the potential increase in repair costs for
the more complicated Prius, including the possibility of replacing the expensive hybridelectric battery. In addition, the study also suggests that society may be better suited
devoting resources to other environmental projects
technology.
3
rather than hybrid vehicle
From an environmental standpoint, the study conducted in [5] only takes into account
the emissions from producing and burning the fuel. Even considering this limitation, one
would question whether the conclusion is still valid ten years after its initial publication.
The national average price for gasoline in 2001, the year the study was published, was
$1.46 (Note: the study uses $1.50) [6]. In 2011, the cost per gallon was approximately
$3.56. This is not the threefold increase called out by the survey but nonetheless there is
more of a financial incentive to buy a car with better fuel economy now than in 2001.
Additionally, the hybrid technology has improved in the last ten years, making hybrids
both more efficient and reliable. The rated fuel economy of the 2012 Prius is more than 6
mpg better than that of the 2000 Prius quoted in the study [6],[7]. The improvement in
fuel economy and the increase in gasoline prices make the Prius much more desirable
than this study had forecast. However, the improvement in efficiency comes at the cost
of a Prius that is more expensive to buy relative to the Corolla. Whether the increased
initial cost can be offset by the savings in gasoline will be determined based on longevity
and driving conditions presented later in this report. The utilization of resources to best
help the environment is more difficult to quantify. However, if it can be shown that
hybrid electric vehicles are economically beneficial, the fact that they produce less
emissions than a comparable internal combustion engine vehicle means by default some
amount of environmental benefit is realized.
A Life Cycle Assessment (LCA) was conducted in 2000 that compared the energy
consumed and the byproducts emitted during the use phase of the hybrid and internal
combustion engine vehicle, as well as a diesel engine and an electric vehicle [8]. This
simplified assessment was conducted under the assumption that all vehicle types had
nearly similar production and end of life phases. For emissions, this study tabulated
values for all four vehicle types for greenhouse gases (carbon dioxide, methane and
nitrous oxide) as well as pollutants such as carbon monoxide, nitrogen oxide and others.
Based on the use phase alone, the hybrid car emits about half as much greenhouse gases
as the internal combustion engine vehicle and produces significantly lower amounts of
pollutants. Using a weighted ranking system the emission data collected was compared
for all four vehicles, which showed that the hybrid vehicle was found to have about half
of the environmental impact of the internal combustion engine vehicle. The hybrid car
4
was matched only by the electric vehicle, though much of that vehicle's power was
assumed to be generated by electric currents via nuclear power plants which do not
produce greenhouse gases or pollutants in the same way as combustion-based power
production. This study performs a similar analysis of the use phase and also includes
production and end of life phases that were assumed to be similar and not included in
[8].
1.3 Project Scope
The objective of this study is to conduct an independent analysis of the comprehensive
environmental impact of both HEV and the ICEV. This study is intended to confirm or
challenge the commonly held notion that HEVs are better for the environment than their
ICEV counterparts. The expected outcome will be a quantifiable environmental impact
for each of these vehicles. Multiple scenarios will be explored that attempt to predict the
number of miles and type of driving (city, highway, etc.) for a couple of common types
of drivers. Also included for each of these scenarios is a basic total ownership cost
analysis. The environmental impact and total ownership cost together will allow an
environmentally and economically conscious consumer to make an informed decision
about which of these types of vehicle would best suit their needs and desires.
5
2. Methodology
2.1 Life Cycle Assessment Approach
The Life Cycle Assessment approach can be summarized by four major steps [9]. The
first step in the scope of the project is to determine which environmental concerns are to
be taken into account for the study. The second step involves collecting an inventory of
all environmental inputs (materials, energy, chemicals) and outputs (emissions, solid
waste) of the product system. The data collected in the inventory are then used in the
impact assessment to determine a representative effect of the system on the environment.
The final step of the LCA is interpretation of the results. In this study, the results of the
HEV and the ICEV are compared directly.
2.2 LCA Scope
The goal of this study is to perform a cradle to grave comparison of the HEV and ICEV.
Many prior studies narrow their focus to one portion of the life cycle, such as the use
phase, and draw conclusions based on those results and overarching assumptions made
for other phases. This study combines data extracted from prior works as well as original
calculations to determine a result for the full life cycle. The scope is limited to two
specific make and model vehicles, one hybrid electric and one containing a standard
internal combustion engine. Minor assumptions are made as noted within each phase
rather than leaving out entire phases by considering that the differences between the two
vehicle types are negligible in that particular phase. This way, a reasonable total
approximation of the environmental impact is achieved for each vehicle rather than a
relative answer based solely on the phases analyzed.
The scope of the material procurement and vehicle production phase tabulates the energy
required to produce each major material used in the vehicle and estimates the energy
required and emissions produced for each vehicle during assembly based on vehicle
weight and location of assembly using published numbers. It is noted in [10] that the
energy required for assembly of the vehicle is considered insignificant in relation to the
energy required to produce all of the parts. This study still includes an estimate for this
figure, however insignificant it may seem. The infrastructure of the production and
6
assembly facilities or the transportation of raw materials, parts, and assembled vehicles
are not included as part of the assessment.
The scope of the use phase of the vehicle includes three scenarios designed to simulate
various types of driving conditions experienced over the life of the vehicle. These
scenarios are a low mileage estimate where much of the driving is concentrated in urban
areas, a moderate mileage estimate where city and highway driving are more balanced
and a high mileage estimate where most of the driving is done on the highway. Using the
EPA rated fuel economies for each vehicle, the amount of gas (and in turn the amount of
emissions) consumed by each of the vehicles over their lifetime is determined. Also, use
of fluids, tires, batteries, etc. are assumed for each vehicle and included in the total
environmental impact analysis. The scenarios chosen are not meant to cover extreme
cases but rather average representations of the life of a vehicle of this type.
The end of life phase accounts for the disposal of materials at the end of the life of the
vehicle. Since the energy and emissions associated with extracting and/or producing
each material have already been accounted for, the main purpose of this phase is to give
credit for the energy retrieved during recycling. The energy retrieved is determined by
the energy savings that comes from secondary production using recycled materials
versus primary production using virgin materials. Some energy is expended, however, in
order to extract the materials to be recycled. This study will assume that the car is
shredded (90% of all vehicles that are scrapped are shredded according to [10]). A
nominal energy per unit weight is used to estimate the energy expended by the shredder.
2.3 List of Key Assumptions

Energy and emissions for assembly and production scale with the numbers published
in [15] are based on the location of manufacture and the mass of the vehicle in kg.
These numbers do not differentiate between HEVs and ICEVs.

All major metals used in batteries are considered recyclable. It is indicated in [4] that
the metals from the Ni-MH battery can be recovered and used as alloying metals in
the production of stainless steel.
7

The emissions values associated with the production and assembly of the lead acid
batteries are assumed to be negligible as can be seen in Figure 4.

The total parts and labor cost associated with a Prius Ni-MH battery replacement is
assumed to be $3,000. This estimate was developed through online research although
not one specific, citable source was found.

For simplicity of calculations, the price of gasoline is assumed to be static over the
life of the vehicle in each of the two gas price scenarios chosen ($3.92/gal and
$5.50/gal).

One hundred percent of shredded metals are assumed to be recycled. In reality, only
the small amounts of metal that are not able to be separated from non-metal shredder
residue are not recycled.

The environmental impact of the disposal of non-metal shedder residue is not
considered in this study but this impact is assumed to be small compared to the
overall environmental impact of the vehicle including production and use phases.
Emissions from the shredder are also assumed to be negligible.

A net energy savings for nickel was not listed in [10] so the net energy savings is
assumed to be the same as the energy required to produce nickel via the secondary
production process.

The energy expended by the shredder, 32 Btu/lb from [10], is assumed to be
negligible since it is three orders of magnitude lower than the net energy savings of
the metals being analyzed.

Only greenhouse gases are compared in the emissions totals in Section 4. These are
the only pollutants that can be compared using a common metric (CO2e). Other
pollutants can be compared directly by looking at emissions results in Section 3.
8

Cost/energy associated with replacement parts are not included in the totals. These
values will be variable depending on individual situations and are not likely to
amount to a significant percentage of cost and energy.

Any cost benefit or detriment associated with shredding a vehicle and recycling of
materials is considered negligible.
9
3. Discussion
3.1 Selection of Vehicles
The first step in performing any analysis relating to this project is to select two specific
vehicles for comparison. These vehicles will be the basis of the subsequent research
conducted involving materials, manufacturing, use and recycle. There are two key
decision considerations used in the selection of vehicles. The first is that the vehicles
chosen must be similar in a number of key parameters that allow for the best possible
“apples to apples” comparison. To get an accurate picture of the difference between the
hybrid-electric case and the internal combustion-only case, ideally the remainder of the
vehicle should be the same. In addition, this study is targeting a consumer that is
attempting to decide between two similar vehicles, one hybrid-electric and one internal
combustion engine-only. Comparing a sedan with an SUV would not make for an
appropriate scientific control. The second decision parameter is that the vehicles chosen
must be appropriate for comparison using the information regarding materials and
processes used in manufacturing so that as complete of an analysis as possible can be
performed.
The Toyota Prius hybrid vehicle was chosen as the starting point for this project since it
has set the standard for HEVs since its introduction almost 15 years ago. The Prius is the
most recognizable hybrid, both on the road and in name; so it was a logical decision for
inclusion in this study. Three ICEVs were considered for comparison with the Prius: the
Toyota Corolla, the Toyota Matrix and the Honda Civic. Table 1 and Table 2 provide
key specifications that were used to determine the two vehicles that are used in the
study. The specifications for the vehicles chosen as well as those not chosen for this
study are presented for comparison purposes. The hybrid is unique from all of the other
vehicles in a few particular areas. The first is that the additional components (namely the
electric motor and nickel metal-hydride battery) give it some three hundred pounds of
extra weight. The second is that the hybrid provides a nominal improvement of twenty
miles per gallon in advertised fuel economy. The last major departure between the
hybrid and the other three vehicles is the price, with the hybrid costing an average of
over seven thousand dollars more than the three ICEVs.
10
Table 1. Specifications of Vehicles Used for Study [11], [12]
Vehicle Make and Model
Powertrain
Transmission
Net Horsepower
Torque (ft-lb)
Curb Weight (lb)
Passenger Volume (cu. ft.)
Cargo Volume (cu. ft.)
Fuel Tank Capacity (gal)
MPG City
MPG Highway
MPG Combined
MSRP ($)
Toyota Prius 2 (2012)
Toyota Carolla L (2012)
1.8L 4-cylinder DOHC/Permanent
Magnet AC Motor/Ni-MH battery
1.8L 4-cylinder DOHC
Electronically controlled
Continuously Variable
Transmission
134
105 gasoline/153 electric
3042
93.7
21.6
11.9
51
48
50
24,000
5-speed manual
132
128
2734
92.1
12.3
13.2
27
34
-16,130
Table 2. Specifications of Vehicles Considered but not Chosen for Study [13], [14]
Vehicle Make and Model
Powertrain
Transmission
Net Horsepower
Torque (ft-lb)
Curb Weight (lb)
Passenger Volume (cu. ft.)
Cargo Volume (cu. ft.)
Fuel Tank Capacity (gal)
MPG City
MPG Highway
MPG Combined
MSRP ($)
Toyota Matrix L (2012)
1.8L 4-cylinder DOHC
5-speed manual
132
128
2844
94.2
19.8
13.2
26
32
-18,845
Honda Civic DX (2012)
1.8L 4-cylinder SOHC
5-speed manual
140
128
2608
94.6
12.5
13.2
28
36
31
15,805
The decision on which of the three internal combustion engine vehicles ultimately would
be used in this study was made by choosing the best scientific control. If the internal
combustion engine vehicle is considered the “control group” and the Prius is considered
the “experimental group” (control group plus an electric motor and Ni-MH battery),
which vehicle would be the closest match? As seen when comparing the metrics
provided in Table 1 and Table 2, it is clear that the Toyota Corolla is the best match.
11
Both are compact sedans, both are made by the same manufacturer and many of the nonpower train-related components and metrics are identical. Comparing two vehicles this
similar will mean that any differences in the results can very likely be attributed to the
hybrid-electric system. Figure 1 shows a picture of the 2012 base Prius model. The 2012
Corolla is shown in Figure 2.
Figure 1. 2012 Toyota Prius Picture [11]
Figure 2. 2012 Toyota Corolla S Picture [12]
3.2 Material Procurement and Vehicle Production
Information regarding the energy required to produce a vehicle and the emissions
produced on a per vehicle basis based on manufacturing location is reported in [15]. The
emissions discussed are greenhouse gases (GHGs) and are cumulatively expressed in kgCO2 equivalent. The study separately specifies the energy required and emissions
12
produced in the material production and vehicle assembly for a number of
manufacturing locations around the world. This analysis will use a scaled version of the
assembly energy but will independently tally the energy and emissions from the
individual materials. A rough average of all data presented in [15] shows that 25 % of
the energy required to produce a vehicle comes from the assembly portion and 75%
comes from material production. This study will detail the production of materials and
compare this with the assembly energy based on information published in [15].
3.2.1
Procurement and Production of Materials
The materials used to manufacture a vehicle reasonably overlap between the HEV and
the ICEV, with the exception of the electric motor and the battery of the hybrid. Using
the listed curb weights of each vehicle, the amount of each major material used in
production is calculated in Table 3 using percent weight estimates for the HEV and
ICEV from [4]. These materials cover all major components and subsystems for a new
vehicle straight from the assembly line. Not listed in Table 3 are the batteries for each of
the vehicles (lead acid for the Corolla, lead acid and nickel-metal hydride for the Prius)
which will be discussed separately.
Table 3. Material Estimates by Weight [4]
Material
Steel
Cast Iron
Wrought Al
Cast Al
Copper/brass
Magnesium
Glass
Average Plastic
Rubber
Nickel
Platinum
Other
Corolla
Prius
% Weight Weight (lb) % Weight Weight (lb)
61.7
1687
65.2
1983
11.1
303
6
183
2.2
60
1.8
55
4.7
128
5.1
155
1.9
52
4.3
131
0.02
1
0.02
1
2.9
79
2.9
88
11.2
306
10.6
322
2.4
66
1.9
58
0
0
0.1
3
0.0005
0
0.0003
0
1.9
52
2.2
67
Taking into account the fossil fuel energy required to produce the quantity of the
materials listed above, Figure 3, taken from [4] shows an approximation of the energy
13
required to produce an HEV and an ICEV. Note that the values for fluids, batteries, and
ADR (assembly, disposal and recycling) will be discussed later in this report.
Figure 3. Total Energy Use Per Vehicle during Production [4]
The greenhouse gas emissions per vehicle generated during the material production
process are presented in Figure 4, from [4], in units of kg/vehicle. The following
greenhouse gases were included in this tabulation: methane (CH4), nitrous oxide (N2O),
carbon dioxide (CO2), particulate matter (PM10), sulfur oxide (SOx), volatile organic
compounds (VOC), nitrogen oxide (NOx), and carbon monoxide (CO).
14
Figure 4. Greenhouse Gas Emissions per Vehicle during Production [4]
Values of individual greenhouse gases are listed in table format in Table 4. Many of
these greenhouses gases contribute significantly to global warming, most notably
methane, nitrous oxide and carbon dioxide. Also listed in Table 4 are the CO2e values
for the gases which contribute to global warming and the corresponding values of kg
CO2e for each vehicle. In addition to the GHG effect on global warming, sulfur and
nitrogen oxides are acidification gases that contribute to acid rain. Carbon monoxide,
VOCs and particulate matter are all considered pollutants and have adverse effects on
human health.
15
Table 4. Greenhouse Gas Emission Totals Per Vehicle due to Materials (kg/vehicle) [4]
3.2.2
Vehicle
GHG
CO2e
Total
CH4
21
ICEV
kg
kg CO2e
6300
10.3
216.3
HEV
kg
kg CO2e
5400
8.8
184.8
N2O
CO2
0.075
6000
0.062
5100
310
1
23.25
6000
PM10
11.5
9.2
SOX
VOC
NOX
CO
16
2
7.9
39
18
2
6.5
34
19.22
5100
Vehicle Assembly Estimate
The top part of Table 5 presents values quoted in [15] for the energy in MJ and GHG
emissions in kg CO2e for a given vehicle mass in kg, for vehicles produced in the United
States and Japan. This study is being conducted from an American’s perspective so it
will be assumed that the Corolla is assembled in the United States (Toyota has a Corolla
production plant in Blue Springs, Mississippi) and that the Prius is assembled in Japan
(as of 2012, all Prius’ are built and assembled in Japan). Presuming that the energy and
emissions from vehicle assembly are directly proportional to the weight of the vehicle
produced, the scaled values for energy and GHG emissions based on the listed curb
weights of the Corolla and Prius are also presented in Table 5. It is noted that these
values for vehicle assembly should be considered approximate since the specific vehicle
type being assembled was not included with the original data from [15]. The purpose for
using these approximate numbers, scaled by weight, was to try to account for the energy
costs and associated emissions for vehicle assembly based on the location of the plant.
For example, a vehicle produced in Europe might have fewer GHG emissions because of
the use of nuclear power based electricity.
16
Table 5. Vehicle Assembly Information [15]
Vehicle Assembly Values from Yan
Country
US
Japan
Vehicle Mass (kg)
1322
1214
Energy (MJ)
25,779
20,200
GHG Emissions (kg CO2-eq)
1793
1038
Scaled Vehicle Assembly Values
Prius Mass (kg)
-1380
Corolla Mass (kg)
1240
-Energy (MJ)
24,180
22,962
GHG Emissions (kg CO2-eq)
1682
1180
3.2.3
Batteries
One of the most significant fundamental differences between an HEV and an ICEV are
the batteries used to store energy. Both vehicles have the typical lead-acid (Pb-Ac)
batteries that are used to start the vehicle’s engine. In the case of the Prius, the hybrid
also has a larger nickel metal-hydride (Ni-MH) battery that, along with an electric motor,
uses stored energy to supplement the gasoline powered engine. The material
compositions of these two types of batteries are listed in Table 6, as reported in [4]. The
material weights calculated for each vehicle are based on overall battery weights of 16
kg for the internal combustion engine lead acid battery, 10 kg for the hybrid lead acid
battery and 38 kg for the hybrid Ni-MH battery.
Table 6. Battery Material Compositions [4]
Pb-Ac
Ni-MH
Material
% Weight ICEV (kg) HEV (kg)
Material
% Weight HEV (kg)
Lead
69
11.3
6.9 Nickel
28.2
10.8
Water
14.1
2.3
1.4 Steel
23.7
9.1
Sulfuric Acid
7.9
1.3
0.8 Plastic
22.5
8.6
Plastic
6.1
1.0
0.6 Iron
12
4.6
Fiberglass
2.1
0.3
0.2 Rare Earth Metals
6.3
2.4
Other
0.8
0.1
0.1 Copper
3.9
1.5
Cobalt
1.8
0.7
Magnesium
1
0.4
Wrought Al
0.5
0.2
Rubber
0.1
0.0
17
The battery materials that are most significant from an energy standpoint are lead, nickel
and the combination of rare earth metals and other metals that make up the negative
electrode of the Ni-MH battery. The consumption energies required for the production of
each of these materials are presented in Table 7, as reported in [4]. The majority of lead
is produced via secondary production (smelting scrap lead). Nickel is produced via the
electrorefining process which dissolves a 70% nickel matte (smelted nickel ore) in
sulfuric acid to separate the nickel from oxygen. The metal hydride electrode is
produced by mining and processing an intermetallic compound. The original source of
the metal-hydride consumption numbers has been questioned but these numbers are used
due to the lack of substitute information. Table 8 presents the energy required per
vehicle for producing major battery materials. Production energies of other components
of the battery are not included because they are considered negligible compared to the
production energy of the vehicle as a whole.
Table 7. Production Energies for Raw Battery Materials [4]
Material
Production Energy (mmBtu/ton)
Lead
9.5
Nickel
64
Metal Hydride
112.3
Table 8. Battery Material Production Energies per Vehicle
Lead (kg)
Energy (Btu)
Nickel (kg)
Energy (Btu)
Metal-Hydride (kg)
Energy (Btu)
Total Energy (Btu)
Corolla
11.3
118,357
----118,357
Prius
6.9
72,271
10.8
762,073
13.5
1,671,499
2,505,843
The energy required for assembly and testing of the batteries is approximated in [4] as
being 35.2 million Btu/ton of battery material for Ni-MH batteries and 27.5 million
Btu/ton of battery material for Pb-Ac batteries. Based on these numbers and the weights
of the batteries, Table 9 shows the total energy required for battery assembly and testing
for each of the vehicles.
18
Table 9. Battery Assembly and Test Energies [4]
Pb-Ac battery (kg)
Energy (Btu)
Ni-MH battery (kg)
Energy (Btu)
Total Energy (Btu)
Corolla
16.4
497,244
--497,244
Prius
10
303,197
38.3
1,486,395
1,789,592
Figure 4 shows that the GHGs from battery production are negligible for the ICEV and
1500 kg per vehicle for the HEV.
3.3 Use Cases
For the life of the vehicles during the use phase, Table 10 details the three test scenarios
chosen for this study. These scenarios are not meant to represent any extremes of driving
conditions but rather to approximate a diverse range of what the vehicles would
experience in what is considered to be normal driving conditions. The first case assumes
100,000 miles over the life of the vehicle driven mainly in an urban environment. The
second case assumes 150,000 miles split relatively equally between urban and highway.
The third case assumes that the life of the vehicle is 200,000 miles driven mainly on the
highway. The table lists the fuel efficiency (based on EPA estimates reported by the
manufacturer) assumed for each vehicle in each case. These fuel efficiencies were
calculated by summing the EPA City estimate times the percentage of urban driving with
the EPA Highway estimate times the percentage of highway driving.
Table 10. Vehicle Scenario Parameters [11], [12]
Miles over Lifetime
Urban Driving (%)
Highway Driving (%)
Estimated Prius MPG
Case 1
Case 2
Case 3
100,000 150,000 200,000
75
55
20
25
45
80
50.3
49.7
48.6
Estimated Corolla MPG
3.3.1
28.8
30.2
32.6
Use Case Emissions Totals
The emissions associated with the Prius and Corolla as reported in [5] in units of grams
per mile are extrapolated out for each use case in Table 11 below. The emissions
19
reported are non-methane organic gases (NMOG, previously referred to as VOCs),
carbon monoxide (CO), nitrogen oxides (NOx), and carbon dioxide (CO2).
Table 11. Emissions Values for Life of Vehicles Used [5]
Pollutant (g/mi)
NMOG
0.003
CO
0.04
NOx
0.001
CO2
3.3.2
180
Prius
Corolla
Case 1 (kg) Case 2 (kg) Case 3 (kg) (g/mi) Case 1 (kg) Case 2 (kg) Case 3 (kg)
0.3
0.45
0.6 0.04
4
6
8
4
6
8
1.3
130
195
260
0.1
0.15
0.2
0.2
20
30
40
18,000
27,000
36,000
253
25,300
37,950
50,600
Use Case Fuel Cost Totals
Using the mileage for each use case presented in Table 10, and assuming the current
national average price of gasoline of $3.92 per gallon (taken from the week of 3/26/2012
from [16]), the total fuel costs for the lifetime of the vehicle are calculated and shown in
Table 12. Assuming that the price of gas will increase as the car ages (due to inflation
and other economic factors), an average estimate of $5.50 per gallon is used in the
calculations shown in Table 13.
Table 12. Lifetime Vehicle Fuel Costs at $3.92/gal
Miles over Lifetime
Estimated Prius MPG
Total Prius Fuel Cost ($)
Estimated Corolla MPG
Total Corolla Fuel Cost ($)
Case 1
Case 2
Case 3
100,000 150,000 200,000
50.3
49.7
48.6
$7,801 $11,843 $16,132
28.8
30.2
32.6
$13,635 $19,502 $24,049
Table 13. Lifetime Vehicle Fuel Costs at $5.50/gal
Miles over Lifetime
Estimated Prius MPG
Total Prius Fuel Cost ($)
Estimated Corolla MPG
Total Corolla Fuel Cost ($)
Case 1
Case 2
Case 3
100,000 150,000 200,000
50.3
49.7
48.6
$10,945 $16,616 $22,634
28.8
30.2
32.6
$19,130 $27,363 $33,742
20
3.3.3
Replacement of Fluids
Table 14 below from [4] estimates the amount of fluids (excluding gasoline) that are
used to support vehicle operation. These fluids are assumed to be replaced at various
intervals over the course of the vehicle's life. Figure 3 and Figure 4 show the estimates
for energy use and greenhouse gas emissions from the fluids for the life of each of the
vehicles. The totals for the ICEV are approximately 13 million Btu/vehicle and 7,000 kg
CO2e/vehicle. The totals for the HEV are approximately 12 million Btu/vehicle and
6,000 kg CO2e/vehicle.
Table 14. Vehicle Fluid Weights (lb) [4]
3.3.4
Battery Replacement
The Ni-MH battery is expected to last 150,000 miles based on Toyota laboratory bench
testing [11]. The hybrid-electric battery is typically covered under warranty up to at least
100,000 miles. Battery replacement will be considered for Case 3 only and the parts and
labor cost for this replacement will be assumed to be $3,000 ($2,400 parts, $600 labor).
To account for the energy of the replacement battery, the energy values for the Ni-MH
battery will simply be counted twice in Case 3.
3.4 End of Life/Recycle
The end of life of these vehicles is considered to be the point where they are no longer
road worthy, either because it is cost prohibitive to continue to drive the vehicle or it is
no longer capable of passing a safety or emissions inspection. For the purposes of this
study, the vehicle is assumed to be shredded since the vast majority of scrapped vehicles
in the United States are shredded [10]. This study will assume that 100% of shredded
metals are recycled and that all non-metals will be either incinerated or sent to a landfill.
This assumption is reasonably accurate as the only metal that is wasted in the shedding
21
process is metal that cannot be separated from the automobile shredder residue (ASR).
Table 15 provides values of net energy savings for the metals found in the Corolla and
Prius. These values were obtained from [10] with the exception of the nickel value,
which was assumed to be the same as the secondary production value of nickel discussed
previously in this report. The remainder of these energy savings are estimated by the
savings in energy from using recycled metals versus the energy required for mining and
production of virgin metals. The estimated 32 Btu/lb of recycled metal required for the
shedding process is assumed to be negligible.
Table 15 calculates the estimated total energy savings based on the metal quantities
present in the Corolla and Prius. These values include the metals used in the batteries for
each of the vehicles. The total values compare favorably to the estimated 55 million
Btu/vehicle energy savings for a vehicle that has been shredded quoted in [10].
Table 15. Material Recycling Estimates by Weight [10]
Net Savings
Corolla
Prius
(Btu/lb)
Weight (lb) Savings (Btu) Weight (lb) Savings (Btu)
Aluminum
120,200
188
22,597,600
238
28,607,600
Copper
37,000
52
1,924,000
137
5,069,000
Lead
14,200
25
355,000
15
213,000
Iron
10,700
303
3,242,100
193
2,065,100
Steel
10,700
1,687
18,050,900
2,003
21,432,100
Nickel*
32,000
0
0
24
768,000
Total
46,169,600
58,154,800
Material
22
4. Results
4.1 Energy Totals
The energy figures presented in Section 3 for production, assembly, use and recycling,
converted to the common unit of British thermal unit (Btu), are presented in Table 16 for
the Corolla, the ICEV and the Prius, the HEV. These energy values are summed in Table
17 to determine the net energy usage per vehicle for each use case. Use case energy
values are calculated as the product of the number of gallons of gasoline burned and the
amount of energy that can be extracted from burning one gallon of gasoline (132 MJ)
[17].
Table 16. Energy Totals per Vehicle (in Million Btu)
Energy per Vehicle (mmBtu)
Material Production
Vehicle Assembly
Battery Production
Battery Assembly and Test
Fluids Including Replacement
Gasoline (Case 1)
Gasoline (Case 2)
Gasoline (Case 3)
Battery Replacement (Case 3)
Recycled Metal Savings
Corolla (ICEV) Prius (HEV)
75
64
23
22
0.12
2.5
0.50
1.8
13
12
435
249
623
378
768
515
0
3.9
-46
-58
Table 17. Net Energy per Vehicle for Case Studies (in Million Btu)
Net Energy per Vehicle (mm Btu) Corolla (ICEV) Prius (HEV)
Case 1
500
293
Case 2
688
422
Case 3
833
563
4.2 Emissions Totals
The greenhouse gas emissions from production, assembly, and use of each of the
vehicles are presented in Table 18 in units of kilograms of CO2-equivalent. Only
greenhouse gases are included in this total because the amounts of these gases can be
compared across the various vehicle stages using a single common quantifier (CO2-e).
Note that the production GHG emissions value for the HEV also includes 1,500 kg of
23
GHG from the Ni-MH battery. Information on other pollutants is presented in Section 3,
where available. Table 19 presents the net greenhouse gas emissions per vehicle for each
of the use cases. Note that the net GHG emissions for Case 3 include the production
emissions from two Ni-MH batteries.
Table 18. Greenhouse Gas (GHG) Emission per Vehicle Totals (units of kg CO2e)
Emissions per Vehicle (kg CO2e) Corolla (ICEV) Prius (HEV)
Production GHG Emissions
6,250
6,800
Assembly GHG Emissions
1,682
1,180
Use GHG Emissions (Case 1)
25,300
18,000
Use GHG Emissions (Case 2)
37,950
27,000
Use GHG Emissions (Case 3)
50,600
36,000
Table 19. Net GHG Emissions per Vehicle for Use Cases (units of kg CO 2e)
Emissions per Vehicle (kg CO2e) Corolla (ICEV) Prius (HEV)
Net GHG Emissions (Case 1)
33,232
25,980
Net GHG Emissions (Case 2)
45,882
34,980
Net GHG Emissions (Case 3)
58,532
45,480
4.3 Cost Totals
The total costs per vehicle in units of dollars including the manufacturer's suggested
retail price (MSRP) which encompasses production and assembly, the cost of gasoline
for the use phase and the assumed cost of battery replacement for the hybrid Ni-MH
battery (Case 3 only) are presented in Table 20. Costs such as maintenance, replacement
parts and fluids are not included but can be assumed to be roughly similar between the
ICEV and the HEV, on average. Also, no cost is included for vehicle shredding as the
cost of the shredder is assumed to be offset by the sale of the recycled materials. Table
21 presents the net cost per vehicle for each use case ($3.92/gallon and $5.50/gallon
assumptions are both included).
24
Table 20. Cost per Vehicle (in Dollars)
Cost ($)
Corolla (ICEV) Prius (HEV)
Vehicle MSRP
$16,130
$24,000
Gasoline (Case 1, $3.92/gal)
$13,635
$7,801
Gasoline (Case 2, $3.92/gal)
$19,502
$11,843
Gasoline (Case 3, $3.92/gal)
$24,049
$16,132
Gasoline (Case 1, $5.50/gal)
$19,130
$10,945
Gasoline (Case 2, $5.50/gal)
$27,363
$16,616
Gasoline (Case 3, $5.50/gal)
$33,742
$22,634
Battery Replacement (Case 3)
$0
$3,000
Table 21. Net Cost per Vehicle (in Dollars)
Net Cost ($)
Gasoline (Case 1, $3.92/gal)
Gasoline (Case 2, $3.92/gal)
Gasoline (Case 3, $3.92/gal)
Gasoline (Case 1, $5.50/gal)
Gasoline (Case 2, $5.50/gal)
Gasoline (Case 3, $5.50/gal)
25
Corolla (ICEV) Prius (HEV)
$29,765
$31,801
$35,632
$35,843
$40,179
$43,132
$35,260
$34,945
$43,493
$40,616
$49,872
$49,634
5. Conclusions
The net energy per vehicle values listed in Table 17 show that the Prius uses an average
of about 60% of the energy that the Corolla uses over their respective lifetimes. This
study was unable to replicate the scenario where the Prius required more energy to
produce and assemble than the Corolla, likely because general manufacturing
information based on overall vehicle mass was used instead of information specific to
the Prius and Corolla. Although the energy to produce the Prius' battery was included,
the energy intensive processes used to manufacture other components unique to the Prius
were not accounted for. Another reason for the energy difference is that the energy totals
from [15] for vehicle production and assembly were lower in Japan (where the Prius is
manufactured) than in the US (where the Corolla is built) even after considering the fact
that the Prius weighs more than the Corolla. The totals nonetheless show that the
majority of the energy use does in fact occur during the use phase, where the Prius
clearly has the advantage. The Prius also is of more value from a recycled metals
perspective because it contains abundance of metals such as aluminum, copper and
nickel.
The greenhouse gas emissions per vehicle accumulated over a lifetime also favor the
Prius as shown in Table 19. The Prius produces just under 80% of the greenhouse gas
emissions of the Corolla over the vehicle lifetime. As stated in the previous paragraph,
assembly values for the Prius were expected to be higher than the Corolla but this did
not turn out to be the case. However, accounting for the GHG emissions from producing
the battery, the Prius did produce more GHGs during production and assembly than the
Corolla. This difference was more than compensated for during the use phase. Again the
greenhouse gas emission totals from the use phase are 3-5 times those of the production
totals, with the Prius being decidedly better in the use phase. Other pollutants are listed
in Table 4 and Table 11 with the Prius having a large cumulative advantage regarding
total pollution emitted. The amount of pollution and greenhouse gases emitted during the
shredding process is assumed to be comparable for both vehicles and negligible relative
to the production and use phases.
26
As indicated in Table 21, the Corolla is the more economical choice at today's gasoline
price ($3.92/gal) but the Prius proves to be cheaper at a price of $5.50/gal. This result
does not resoundingly support the hybrid manufacturer's claims but the lower gasoline
price scenario agrees with the conclusions reported in [5]. Since some of the additional
cost of the Prius can be attributed to the consideration that the Prius is slightly better
equipped in terms of amenities than the Corolla, the fact that the overall costs between
the two vehicles are close or in favor of the Prius may sway some buyers in the direction
of the HEV. At high mileage and high gasoline prices, the Prius turns out to be less
expensive than the Corolla even including the cost to replace the hybrid Ni-MH battery.
The Prius proved to be considerably better for the environment because of a lower
lifetime energy consumption and fewer emissions but the decision on which vehicle is
less expensive when all costs are considered is not as clear. While these results are not a
significant departure from what was expected based on prior research, it seems that the
Prius is a better choice in a high gas price scenario while the Corolla makes financial
sense only if one assumes that the price of gasoline will be stagnant. While hybrid and
other alternative energy technologies will become a critical part of the future of
transportation given government plans to increase fuel consumption regulations, a
consumer wishing to make a decision based on the products of today could still see a
financial benefit by purchasing a Corolla if they predict a low mileage and/or low gas
price scenario, provided they were not morally opposed to the would-be negative
environmental impact that comes along with such a savings. However, ultimately the
environmental advantage of the Prius is without question and the bottom line cost favors
the Prius if gasoline prices continue their upward trend, making it the most sensible
choice for the majority of consumers.
27
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29