Energy and the New Reality, Volume 1:
Energy Efficiency and the
Demand for Energy Services
Chapter 5: Transportation Energy Use
L. D. Danny Harvey
harvey@geog.utoronto.ca
Publisher: Earthscan, UK
Homepage: www.earthscan.co.uk/?tabid=101807
This material is intended for use in lectures, presentations and as
handouts to students, and is provided in Powerpoint format so as to allow
customization for the individual needs of course instructors. Permission
of the author and publisher is required for any other usage. Please see
www.earthscan.co.uk for contact details.
Transportation Energy Use, Outline
•
•
•
•
•
Trends in movement of people and goods
Energy use by different modes of transport
Role of urban form and infrastructure
Role of vehicle choice today
Technical options for reducing energy use in
- Cars and light trucks
- Inter-city rail and buses
- Passenger aircraft
- Freight transport
Technical options for cars & light trucks
• Downsizing
• Drive-train efficiency (thermal, mechanical,
transmission)
• Reduced loads (requiring the engine to do less
work)
• Hybrid electric vehicles (HEVs)
• Plug-in hybrid electric vehicles (FCVs)
• Fuel cell vehicles (FCVs)
Issue with fuel cell vehicles
• Cost and performance of fuel cells
• Constraints on supply of precious-metal
catalysts
• Difficulties with on-board processing of
hydrocarbon fuels
• Difficulties with on-board storage of hydrogen
and development of H2 supply infrastructure
Figure 5.1 Proportion of different fuels used
for world transportation
Heavy fuel oil
7%
Other
6%
Jet fuel
10%
Gasoline
44%
Diesel
33%
Source: Gilbert and Pearl (2007, Transport Revolutions:
Moving People and Freight Without Oil, Earthscan, London)
Figure 5.2a Breakdown of transportation energy use
in OECD countries in 2005
2- & 3wheelers
0.9%
People
38.8 EJ
72%
Buses
3.3%
Rail
0.4%
Medium Trucks
5.5%
Air
13.9%
Heavy Trucks
15.1%
Ships
5.7%
Rail 1.3%
Cars & Light
Trucks
54.1%
OECD, Total = 53.5 EJ
Freight
14.8 EJ
28%
Figure 5.2b Break down of transportation energy use
in non-OECD countries in 2005
Rail
Air 10.4% 1.7%
People
15.2 EJ
54%
2- & 3wheelers
3.8%
Medium Trucks
14.6%
Heavy
Trucks
18.7%
Buses
11.0%
Cars & Light
Trucks
27.5%
Ships 8.3%
Rail 3.9%
non-OECD, Total = 27.9 EJ
Freight
12.7 EJ
46%
Figure 5.3a Variation in world passenger-km
movement of people
30
Trillion person-km/year
25
Road
Air
Rail
20
Total movement up 2.50%/yr, 1990-2003
15
10
5
0
1990
1995
2000
2005
Year
Source: Gilbert and Pearl (2007, Transport Revolutions: Moving People and Freight Without Oil, Earthscan, London)
Figure 5.3b Variation in world tonne-km
movement of freight
45
Trillion tonne-km/year
40
Water
Road
Rail
35
30
25
Total movement up 3.67%/yr, 1990-2003
20
15
10
5
0
1990
1995
2000
2005
Year
Source: Gilbert and Pearl (2007, Transport Revolutions:
Moving People and Freight Without Oil, Earthscan, London)
Figure 5.4 Historical variation in world passenger-km
transport by aircraft
5.0
4.5
Projected, 2006-2008
Trillion person-km/year
4.0
3.5
Actual, 1990-2005
3.0
2.5
2.0
Estimate, if no
low-cost carriers
1.5
1.0
Average Growth: 4.44%/yr, 1990-2005
0.5
0.0
1990
1995
2000
2005
2010
Year
Source: Gilbert and Pearl (2007, Transport Revolutions: Moving People and Freight Without Oil, Earthscan, London)
Figure 5.5 Growth in the number of passenger and
commercial vehicles worldwide
800
Millions of Vehicles
700
600
Passenger Vehicles
3.0%/yr growth, 1990-2002
500
400
300
200
Commercial Vehicles
3.1%/yr growth, 1990-2002
100
0
1980
1985
1990
1995
Year
2000
2005
Figure 5.6 Historical variation in the number of
cars per 1000 people
800
Cars per 1000 People
700
600
USA
500
400
W Europe
300
E Europe
200
100
China
0
1950
1970
1990
2010
Year
Source: Gilbert and Pearl (2007, Transport Revolutions: Moving People and Freight Without Oil, Earthscan, London)
Figure 5.7 Breakdown of total travel in USA
Other long
distance
18%
To/from work
19%
Work related
3%
Tourism
10%
Education
3%
Personal
business
18%
Shopping
11%
Leisure
18%
Source: Gilbert and Pearl (2007, Transport Revolutions: Moving People and Freight Without Oil, Earthscan, London)
From Table 5.1, energy intensities of
different modes of travel within cities
• Gas guzzling car (20 litres/100 km), one person:
6.5 MJ/person-km (7.8 MJ/p-km primary energy)
• Energy efficient car (8 litres/100 km), 4 persons:
0.65 MJ/person-km (0.78 MJ/p-km primary energy)
• Diesel bus, typical US loading: 1-2 MJ/person-km
• Light rail: 0.8 MJ/person-km of electricity, 2 MJ/personkm primary energy
• Heavy rail: 0.4 MJ/person-km electricity, 1.0 MJ/personkm primary energy
• Walking: 0.13 MJ/person-km food energy
• Bicycling: 0.1 MJ/person-km food energy
From Table 5.3, primary-energy intensities
of different modes of travel between cities
• Gas guzzling car (12 litres/100 km, 4 people)
1.16 MJ/person-km
• Fuel efficient car (6 litres/100 km, 4 people)
0.58 MJ/person-km
• Intercity bus: 0.28 MJ/person-km
• Diesel train: 0.2-0.5 MJ/person-km
• High speed electric train: 0.2-0.4 MJ/person-km
• Air: 0.6-1.5 MJ/person-km
From Table 5.4: The complete energy
picture for transportation involves
• On-site fuel or electricity use
• Upstream energy use in producing and supplying
the fuel or electricity (this and on-site energy give
primary energy use for the operation of the vehicle,
which is what is given in the preceding two slides)
• The energy used to make the vehicle (embodied
energy), averaged over the total distance travelled
during the lifetime of the vehicle
• The energy used to make and maintain the
infrastructure for the vehicles (roads, rail lines,
airports), averaged over the total distance travelled
during the lifetime of the vehicle
Some prominent results from Table 5.4:
• Vehicle+infrastructure embodied energy for
urban light and heavy rail, interurban car and
interurban rail is about ½ the direct+upstream
operating energy use
• Embodied energy for short air travel (trips of 390
km) exceeds the operating energy
• For international air travel (average distance of
7500 km), the aircraft embodied energy is
important (about 40% of the operating energy)
Figure 5.8 Relationship between private transportation
energy use and urban density
70000
P riv ate Tran sp o rt En erg y U se p er C ap ita (M J /yr)
S a cr a m e n to
H o u s to n
2
R = 0 .85 9 4
S a n D ie g o
60000
P o rtla n d
P h o e n ix
S a n F ra n c is c o
Denver
L o s A n g ele s
D e tro it
B o sto n
W a s h in g to n
50000
C h ic a g o
N e w Yo rk
C a n b e rra
4 0 0 00
C a lg a ry
P e rth
M e lb o u r n e
W in n ip eg
E d m o n to n
To ro n to
Va n c o u v e r
S ydney
M o n tre a l
O ttaw a
F r an k fu rt
A d ela id e
B r is b a n e
3 0 0 00
B r u s s els
Ham burg
Z u ric h
S to c k h o lm
M u n ic h
Vie n n a
P a ris
20000
Lo ndon
10000
A m s te rd a m
S in g a p o r e
K u ala L u m p u r
To ky o
Bang kok
S eoul
J a ka r ta
S u ra b ay a
0
0
25
50
75
100
125
150
175
Ho ng Kong
M a n ila
200
U rb a n D e n s ity (p e rs o n /h a )
Source: Newman and Kenworthy (1999, Sustainability and Cities: Overcoming
Automobile Dependence, Island Press, Washington)
225
250
275
300
325
Compact urban form with different land uses
(residential, retail, offices, schools and daycare
centres, medical) intermixed reduces
transportation energy requirements by:
• Reducing the distances that need to be travelled
• Making is more practical and economical to
serve the reduced travel demand with highquality (i.e., rail-based) public transit
• Increasing the viability of walking and bicycling
Once people start using transit, there is a further
reduction in travel demand (in the distances
travelled) because people start planning their trips
to be more efficient (i.e., combining errands in one
trip)
Bicycling+walking share (in terms of number
of trips taken) in selected cities in 2001:
•
•
•
•
•
•
•
Amsterdam, 52%
Copenhagen, 39%
Hong Kong, 38% (another 46% by public transit)
Sao Paulo, 37%
Berlin, 36%
New York, 9%
Atlanta, 0%
Importance of Choice of Car/Truck
(fuel use is given for city driving)
•
•
•
•
•
•
•
•
Pickup truck, 16 to 26 litres/100 km
SUV, 8 to 26 litres/100 km
Minivan, 11 to 21 litres/100 km
Large car, 11 to 26 litres/ 100 km
Mid-size car, 9 to 24 liters/100 km
Subcompact car, 8 to 21 litres/100 km
Subcompact hybrid, 6 litres/100 km
2-seater, 7 to 29 liters/100 km
Figure 5.9a Mix of vehicles purchased in the US in 1975
P ic k u p
13%
Va n
4%
SUV
2%
L a rg e C a r
17%
S m a ll C a r
45%
M id s ize C a r
19%
Source: Friedman et al (2001, Drilling in Detroit: Tapping Automaker Ingenuity to Build Safe and
Efficient Automobile, Union of Concerned Scientists)
Figure 5.9b Mix of vehicle purchased in the US in 2000
SUV
2 0%
S m all C ar
2 5%
Va n
9%
M id s ize C a r
1 9%
P ic k u p
1 7%
L a rg e C a r
1 0%
Source: Friedman et al (2001, Drilling in Detroit: Tapping Automaker Ingenuity to Build Safe and
Efficient Automobile, Union of Concerned Scientists)
Figure 5.10 Risks posed by different cars
150
M in iv a n s
R is k to D riv e rs o f O th e r Ve h ic le s
P ic k u p Tru c ks
D od g e R am
SUVs
1 25
S u b c o m p a c t C a rs
F o rd F -S e rie s
C o m p ac t C a rs
M id s ize C a r s
100
C h e v y C /K
L arg e C a rs
G M C C /K
75
R an g er
Ta h o e
C h e v y S -1 0
B la z e r
C h e v y S u b u rb a n
50
C h e ro k e e s
E x p lo re r
A s tro v a n
C a ra v a n , Vo y a g e r
& W in d s ta r
25
A ltim a
L u m in a
Ta u ru s /S a b le
J e tta
B o n n e v ille
A c c o rd
G ra n d A m
C a v a lie r/S u n fire
M a rq u is
C o n to u r/M y s tiq u e
L e S a b re
S e n tra
C a m ry
M a x im a
N eo n s
4Ru n ner
C iv ic
C o ro lla
E s c o rt/Tra c e r
C h e v y P rizm
S a tu rn & S tra tu s
A v a lo n
In tre p id & M a zd a 6 2 6
0
0
25
50
75
100
125
150
175
R is k to D riv e rs
Source: Ross and Wenzel (2002, An Analysis of Traffic Deaths by Vehicle Type and Model, ACEEE)
Types of automobiles
• Spark ignition (SI) – runs on gasoline, with power
output reduced by reducing the flow of fuel and
throttling (partially blocking) the airflow, causing a
major loss of efficiency at part load (which is the
typical driving condition)
• Compression ignition (CI) – runs on diesel fuel,
which is ignited by compression without the need
for spark plugs. More efficient than SI engines due
to absence of throttling, high compression ratio
and lean fuel mixture (high air:fuel ratio)
• Internal combustion engine (ICE) – refers to
engines where combustion occurs in cylinders.
Both SI and CI engines are ICEs
Pollution controls
• SI engines use 3-way catalytic converters to
oxidize (add oxygen to) CO and hydrocarbons in
the exhaust while reducing (removing oxygen
from) NOx
• This requires a stoichiometric air:fuel ratio
• Until recently, 3-way catalytic converters could
not reduce NOx in diesel exhaust because of the
excess oxygen
• Recent advances that entail the use of ammonia
have solved this problem
• Much stricter (and comparable) emission
standards can be expected for both gasoline
and diesel vehicles in the future.
However ....
• Stricter pollution controls require ultra-low S
concentrations in the fuel (~ 10 ppm, vs 10-250
today in gasoline and 10-500 ppm today in
diesel fuel)
• Achieving the very low S content in fuels
increases refinery energy use by about 1.5%,
and the stricter pollution controls for diesel
trucks (at least) would increase fuel use by 410%
Figure 5.11a Fuel Economy Trend
Fuel Economy (mpg)
30
25
20
15
Cars
Light trucks
Composite
10
5
0
1975
1980
1985
1990
1995
2000
2005
Year
Source: Zachariadis, T. (2006, Energy Policy 34, 1773–1785, http://www.sciencedirect.com/science/journal/03014215)
Fuel Consumption (litres/100 km)
Figure 5.11b Car/light truck fuel economy trend
20
US composite
18
EU composite
16
Japanese average
14
12
10
8
6
4
2
0
1975
1980
1985
1990
1995
2000
2005
Year
Source: Zachariadis, T. (2006, Energy Policy 34, 1773–1785, http://www.sciencedirect.com/science/journal/03014215)
Figure 5.12a Trends in automobile mass
2000
1800
Vehicle Mass (kg)
1600
1400
1200
1000
800
US
EU
Japan
600
400
200
0
1975
1985
1995
2005
Year
Source: Zachariadis, T. (2006, Energy Policy 34, 1773–1785, http://www.sciencedirect.com/science/journal/03014215)
16
160
14
140
12
120
10
100
8
80
6
US Acceleration Time
60
US Top Speed
4
40
2
20
0
1975
1985
1995
Top Speed (mph)
0-60 mph Acceleration time (seconds)
Figure 5.12b Trends in automobile acceleration and top speed
0
2005
Year
Source: Zachariadis, T. (2006, Energy Policy 34, 1773–1785, http://www.sciencedirect.com/science/journal/03014215)
60
150
50
Engine Power (kW)
180
120
40
90
30
60
20
US Engine Power
EU Engine Power
US Power/Displacement
30
0
1975
1980
1985
1990
1995
2000
10
0
2005
Engine Power/Displacement (kW/litre)
Figure 5.12c Trends in engine power and power/displacement
Year
Source: Zachariadis, T. (2006, Energy Policy 34, 1773–1785, http://www.sciencedirect.com/science/journal/03014215)
Figure 5.13 Auto Loads vs. Speed
Velocity (miles/hour)
0
50
100
Required Engine Power (kW)
100
Climbing a 6% grade
Aerodynamic resistance
80
Rolling resistance
60
40
20
0
0
40
80
Velocity (km/hour)
120
160
Figure 5.14 Fuel Use vs Speed
Fuel Energy Use (MJ/km)
7
Total
Engine friction
Tires and accessories
Air drag
6
5
4
3
2
1
0
0
40
80
Speed (kph)
120
160
Figs 5.15-5.16 Energy flow in a typical present day car (8.9 litres/100 km,
26.4 mpg) (left) and advanced vehicle (4.0 litres/100 km, 58.4 mpg) (right)
Options to Improve the Fuel Economy
of Cars and Light Trucks, Part 1
• Improve engine thermal efficiency (fraction of
fuel energy supplied to the pistons, through
combustion)
• Improve engine mechanical efficiency (fraction
of piston energy transferred to the drive shaft)
• Improve the transmission efficiency (fraction of
drive shaft energy transferred to the wheels)
Methods to improve engine thermal efficiency
• Leaner fuel:air mixture (but worsens NOx emissions)
• Variable compression ratio (currently fixed) – saves
10-15% if combined with supercharged downsized
engine
• Direct injection gasoline – fuel sprayed directly into
cylinders at high pressure – saves 4-6%
• Variable stroke (switch between 2-stroke operation
during acceleration and 4-stroke operation at high
speeds) – saves 25%
• Resultant fuel use would be 0.85 x 0.95 x 0.75 =
0.60, a savings of 40% (best case)
Methods to improve engine mechanical efficiency
• Aggressive transmission management – running at
optimal gear ratio at all times, which makes the
engine operate at the torque-rpm combination that
maximizes the engine efficiency for any given
driving condition.
• Smaller engines (most of the time the engine
operates at a small fraction of its peak power). 10%
smaller saves 6.6% in fuel because the engine on
average will operate more efficiently
• Variable valve control instead of throttling of air flow
in gasoline engines – saves up to 10%
• Reduced friction through better lubricants and other
measures – 1-5% savings
• Automatic idle-off when stopped – saves 1-2%
Increasing the transmission efficiency
• As noted above, the way in which the transmission is
operated affects the engine mechanical efficiency
• The transmission itself is another source of energy loss,
which can be reduced
• Typical transmission efficiencies today:
- automatic, 70-80%
- manual, 94%
• Future automatic: 88% with continuously variable
transmission
• Energy use if we go from 70% to 88% is multiplied by
70/88 = 0.795, a savings of about 20%
Combining the savings from different steps:
• Certainly do not add the savings, because the savings
from each successive step applies only to the remaining
energy use, not to the original energy use
• Instead, multiply the individual factors representing the
reduction in fuel use in each step
• Thus, if improved engine thermal efficiency, engine
mechanical efficiency and improved transmission
efficiency save 40%, 10% and 20%, respectively, then
multiply 0.6 x 0.9 x 0.8 to get the overall fuel requirement
• In the above example, this would be 0.432 – a savings of
56.8%
• The factor of 0.432 would be multiplied by a further
factor to represent the effect of reduced loads, giving an
even larger potential savings
Options to Improve the Fuel Economy
of Cars and Light Trucks, Part 2
• Reduced tire rolling resistance through higherpressure tires
• Reduced aerodynamic resistance through
changes in car shape
• Reduced vehicle weight (affects energy use
during acceleration and when climbing hills)
• Reduced vehicle accessory loads
Comparing Figures 5.15 and 5.16
• The energy flow to the wheels increases from 14.8%
to 22.7% of the fuel input
• Thus, for the same energy flow, we need only
14.8/22.7 = 0.652 as much fuel (a savings of 34.8%)
• The loads on the wheels (due to reduced rolling and
aerodynamic resistance and reduced vehicle weight)
drop from 429.9 kJ/km to 298.0 kJ/km, so the fuel
requirement from this alone would be multiplied by
298.0/429.9 = 0.693 (a savings of 30.7%)
• The overall fuel requirement is multiplied by 0.652 x
0.693 = 0.452 (a savings of 54.8%, which is <
34.8+30.7)
• Cross-check: the ratio of fuel inputs at the tops of the
two figures is 1302/2882 = 0.452
Alternative vehicle drive trains
• Hybrid gasoline-electric or diesel-electric
vehicles (HEVs)
• Plug-in hybrid electric vehicles (PHEVs)
• All-electric or battery electric vehicles (BEVs)
• Fuel cell vehicles (FCVs)
Hybrid electric vehicles
• Use the engine to supply average power
requirements and to recharge a battery, with the
battery used to meet peak requirements
(acceleration, hill climbing)
• This allows downsizing of the engine, thereby
reducing friction losses
• It also allows the engine to operate closer to the
torque-rpm combination that maximizes its
mechanical efficiency
Other energy savings in HEVs
occur through:
• Regenerative braking – using vehicle kinetic
energy to recharge the battery
• Elimination of idling when stopped
• Shifting power steering and other accessories to
more efficient electric operation
• However, the Toyota Prius is not much more
fuel-efficient than a 1993 Honda Civic – because
the technology has largely gone into giving
better acceleration rather than improving fuel
economy
Figure 5.17 Gasoline-battery hybrid vehicle
(parallel drive-train option)
92-95 %
M o tor
94 %
Inv erter
90 -95 %
R egen erative
b rak ing th ro ug h
m otor w ired a s
gen erato r
B a ttery
60 -85 %
93 %
G ear
95 -98 %
M o tor
w ired as
gen erato r
5 -speed
E n gin e
au to m atic
L a un ch d evice:
S tartin g clutch
tran sm issio
n
88 %
2 0%
1 7%
PHEVs
• The idea here is to recharge the battery from the
AC power grid (i.e., by plugging it in when
parked) and using the battery until the battery
energy drops, then switching to the gasoline (or
diesel) engine
• This requires batteries with greater storage
capacity than in HEVs, giving 40-60 km driving
range on the battery
• Since most trips are shorter than this, a large
portion of total distance travelled could be
shifted to electricity in this way
PHEVs (continued)
• The key issues are the cost of the battery, the
mass of the battery (cars with heavier batteries
will need more energy for acceleration and
climbing hills), the amount of energy stored
(usually represent in Wh), which determines the
driving range, and the peak power output from
the battery (W), which determines how fast the
vehicle can accelerate
• The key battery performance parameters are
thus: specific energy, Wh/kg, and specific power,
W/kg
Figure 5.18 Specific power and specific energy
of different batteries
2500
Specific Power (W/kg)
Nickel metal hydride
Lithium ion
2000
Lead acid
1500
1000
500
0
0
50
100
Specific Energy (Wh/kg)
150
Figure 5.19 Battery cost vs battery power:energy ratio
1600
Optimistic Future Costs
Battery Cost ($/kWh)
Current Costs
1200
800
400
HEV
BEV-60 PHEV- 60
PHEV-20
0
0
5
10
15
Battery Power/Energy (kW/kWh)
20
Figure 5.20 kWh-fuel trade off
Miles per Gallon
800
40
30
25
20
15
12
6
Gasoline Vehicle AC Wh/km
Diesel vehicle AC Wh/km
AC Electricity Use (Wh/km)
Gasoline Vehicle kWh/litre saved
Diesel vehicle kWh/litre saved
600
5
400
4
200
3
0
2
0
5
10
15
Fuel Consumption (litres/100 km)
20
AC kWhs to save 1 litre of fuel
50
Figure 5.21 Gasoline savings with PHEVs as a
function of electric driving range for US driving patterns
80
All-electric within range
Gasoline Savings (%)
70
60
50% electric over
2 X range
50
40
30
20
10
0
0
20
40
60
80
Electric-Only Range (km)
100
Figure 5.22 Contributions to air conditioning energy requirements
Extra Fuel
HEV
Engine Braking
Highway
Improved Efficiency
NA-SI
HEV
Urban
NA-SI
0.0
0.2
0.4
0.6
0.8
Energy to Run Air Conditioner (MJ/km)
Source: Kromer and Heywood (2007, Electric Powertrains: Opportunities and Challenges in the U.S. Light-Duty
Vehicle Fleet, Laboratory for Energy and the Environment, MIT)
Figure 5.23 AC and non-AC energy Use (with AC energy use
given as a percentage of the driving energy use)
2.0
Driving
Energy Use (MJ/km)
1.5
Air conditioner
1.0
0.5
57%
10%
12%
15%
0.0
NA-SI
HEV
Urban
NA-SI
HEV
Highway
Source: Kromer and Heywood (2007, Electric Powertrains: Opportunities and Challenges in the U.S. Light-Duty
Vehicle Fleet, Laboratory for Energy and the Environment, MIT)
Figure 5.24 Ratio of energy use by hybrid vehicles to energy
use by conventional vehicles, with and without AC
1.0
HEV/NA-SI Energy Use
0.8
0.6
0.4
0.2
0.0
Urban no AC
Urban with AC
Hwy no AC
Hwy with AC
Fuel Cell Vehicles
• A fuel cell is an electrochemical device that
produces electricity, water and heat
• It requires a hydrogen-rich fuel
• There had been some effort to develop systems
to convert gasoline on-board into a hydrogenrich fuel that in turn would be fed to the fuel cell,
but these efforts have largely been abandoned
• Instead, pure hydrogen fuel would be stored on board
the vehicle
• The major issues are:
- How to store the hydrogen
- How to build up a hydrogen-distribution infrastructure
- What energy sources would be used to make hydrogen
- Cost of fuel cells and of hydrogen fuel
Attractions of hydrogen FCVs
• Zero pollution emissions
• Much lower noise
• The hydrogen could be produced by electrolysis
(splitting) of water using electricity supplied from
renewable wind, solar or hydro sources of
energy
• Thus, zero greenhouse gas emissions and
sustainable energy supply
Options for Onboard Storage of H2
• As a gas compressed to 700 atm pressure
– over 3 times the volume and 1.4 times the weight
of gasoline+tank in a gasoline-powered vehicle with
the same driving range
- energy equiv to 10% that of the stored hydrogen
would be needed for compression
• As liquid hydrogen, at 20 K (= -253ºC)
– just over 2 times the volume but half the weight of
the gasoline+tank
- energy equiv to 1/3 that of the stored hydrogen
would be needed for liquefaction (possibly reduced
to 20% in the future)
• As a metal hydride
– almost 4 times the weight but only 80% of the
volume of gasoline+tank. More mining and
processing of metals needed.
Table 5.18, mass and volume to store 3.9 kg of usable
hydrogen or gasoline equivalent, sufficient for a 610
km driving range
Figure 5.25 Ballard 85-kW fuel cell
for automotive applications
Source: Little (2000, Cost Analysis of Fuel Cell System for Transportation, Baseline System
Cost Estimate, Task 1 and 2 Final Report to Department of Energy, Cambridge)
Figure 5.26 Ballard 85-kW fuel cell
Source: www.ballard.com
Figure 5.27 Fuel cell-battery hybrid vehicle
90 -95 %
60 -85 %
A ncillary
B a ttery
D evices
H2
F u el
C ell
R egen era tive bra kin g
th rou gh m o tor w ired
as genera tor
D C /D C
Inv erter
M o tor
G
e
a
r
94 %
92- 95 %
92 -98 %
5 1%
4 1%
Figure 5.28 Efficiency of fuel cell vs output
100
80
Efficiency (%)
Stack efficiency
60
System efficiency
40
Auxiliary power draw as a
fraction of gross power output
20
0
0
20
40
60
80
100
% of Peak Net Power
Box 5.1, at the end of this file, contains Figures 5.29 and 5.30
Source: Kromer and Heywood (2007, Electric Powertrains: Opportunities and Challenges in the U.S. Light-Duty
Vehicle Fleet, Laboratory for Energy and the Environment, MIT)
Thus,
• A hydrogen FCV would operate at a typical
efficiency of ~ 60%, which is about three times
the efficiency of a typical ICE (internal
combustion engine) vehicle today
• This in turn reduces the amount of energy (as
H2) that needs to be stored on the vehicle for a
given driving range by a factor of 3
• This in turn is critical because any system of
onboard hydrogen storage will be bulky and/or
heavy in relation to the amount of energy stored
• The high efficiency also greatly reduces the
amount of wind or solar power that would need
to be installed in order to produce enough
hydrogen to replace petroleum for transportation
Problems
• Fuel cells suitable for use in cars need to be able to
operate at low temperature (120ºC)
• Low-temperature fuel cells require precious-metal
catalysts (Pt and ruthenium) in order to operate
(these catalysts are also needed in 3-way catalytic
converters, but would not be needed for such in H2
FCVs)
• Supplies of Pt are quite limited – the availability of Pt
could be a significant constraint on the long-term
viability of H2 FCVs
• Hydrogen could instead be used in ICEs (with much
less pollution), but with only a 10-20% efficiency
gain – so the problem of being able to store enough
H2 onboard in order to get a reasonable driving
range would arise
Figure 5.31 Distribution of Exploitable Pt Resources
Canada
1%
Other
Russia
1%
USA
5%
3%
Finland
5%
Zimbabwe
9%
South Africa
76%
Box 5.3: Constructing a scenario
for Pt demand
Figure 5.32a Pt Scenario for future automobile fleets of 1, 2 or 5
billion (compared to about 700 million passenger vehicles
and 100 million commercial vehicles today)
Annual Consumption (Mg/yr)
1000
900
800
5 billion
700
2 billion
600
1 billion
500
400
300
200
100
0
2000
2050
Year
2100
Figure 5.33a Scenario for the growth in vehicle
production rate and vehicle population used for the 5billion-vehicle case in the previous slide
6000
350
300
5000
Production
4000
250
200
3000
150
Population
2000
100
1000
50
0
2000
2020
2040
2060
Year
2080
0
2100
Auto Population (millions)
Production Rate (millions/year)
400
Figure 5.33b Scenario for the growth in the
fraction of new vehicles and of total vehicle
stock as fuel cell vehicles
1.0
Fraction
0.8
Fraction of new
vehicles as FCVs
0.6
0.4
Fraction of vehicle
stock as FCVs
0.2
0.0
2000
2020
2040
2060
Year
2080
2100
Figure 5.32b Cumulative Pt consumption for the 3 fleets,
assuming 90% recycling of Pt from discarded vehicles
Cumulative Consumption (Gg)
70
60
50
40
30
20
10
0
2000
2020
2040
2060
Year
2080
2100
Bottom-line on Pt constraint
• A vehicle fleet reaching 5 billion (which would
result from a human population of 10 billion with
European levels of car ownership) and
consisting entirely of FCVs would have a
cumulative Pt demand by 2100 equal to the
upper limit of the estimated amount of Pt that
could be mined
• This leaves no room for other uses of Pt (such
as in jewelry and electronics)
4 ways of using solar-energy
to power cars
• Using solar electricity to charge batteries
• Using solar electricity to make H2 for use in a
fuel cell
• Using solar energy to grow biomass that is
converted to methanol and used in a fuel cell
• Using solar energy to grow biomass that is
converted into ethanol and used in an ICE
Steps, solar energy to battery
• PV modules, 15% efficiency
• DC to AC conversion, 85%
• Transmission, 96% (say)
• Battery charging, 95%
• Drive train, 87%
Overall sunlight to wheels energy transfer:
10.1%
Steps, solar energy to H2 Fuel cell
• PV modules, 15% efficiency
• PV to electrolyzer coupling, 85%
• Production of hydrogen and compression to 30
atm, 80%
• Transmission 1000 km at 30 atm pressure, 98%
• Compression from 30 to 700 atm pressure, 90%
• Fuel cell, 50%
• Drive train, 87%
Overall sunlight to wheels energy transfer: 3.9%
Steps, solar energy to methanol to fuel cell
(methanol is another candidate as
a fuel for fuel cells)
• Photosynthesis, 1% efficiency
• Biomass to methanol, 67%
• Transport, 98% (say)
• Fuel cell, 45% (less than using H2)
• Drive train, 87%
Overall sunlight to wheels energy transfer:
0.26%
Steps, solar energy to ethanol, used in
an advanced ICE
• Photosynthesis, 1% efficiency
• Biomass to ethanol, 67%
• Transport, 98% (say)
• ICE, 20%
• Drive train, 87%
Overall sunlight to wheels energy transfer:
0.11%
Conclusion:
• Direct use of renewably-based electricity to
recharge batteries makes far better use of the
renewable electricity than using it to make H2 to
for use in a fuel cell (extra steps mean extra
losses)
• The land area required to convert sunlight to H2
and drive a given distance is ~ 20 times less
than growing biomass to make methanol for use
in a fuel cell, or ~ 40 times less than growing
biomass to make ethanol
• This is because the efficiency of PV modules
(~15 % or more) is vastly greater than the
efficiency of photosynthesis (~ 1%)
Thus, the best bet seems to move to plug-in hybrid vehicles
that are recharged with solar- or wind-generated electricity,
with maybe a small amount of hydrogen as a range
extender in order to eventually get completely off of fossil
fuels
Liquid biofuels would be a distant second best as a range
extender, but might be needed if problems with H2 cannot
be resolved
Swapping the battery for a freshly charged battery every
100 km might be another solution
In any case, the underlying vehicle should be as efficient as
possible to minimize the electricity and/or hydrogen or
biofuel requirements.
Figure 5.34 Fuel-efficient cars
3.5
3.0
Embodied energy
Energy Use (MJ/km)
Upstream fuel energy
2.5
2.0
1.5
1.0
0.5
0.0
On board fuel energy
Figure 5.35 Drive-train cost components (NPV=net present value)
Energy use
50000
Maintenance
Lightweight body
Drivetrain
NPV of Lifecycle Cost ($)
40000
Vehicle except drivetrain
30000
20000
10000
0
NA-SI
HEV
PHEV
BEV
FCV
Figure 5.36 Lifecycle costs for alternative vehicles
10000
Gasoline at $2/litre
8000
Gasoline at $1.5/litre
Gasoline at $1/litre
Net Savings ($)
6000
4000
2000
0
-2000
-4000
-6000
HEV
PHEV
$20/GJ $40/GJ
$50/kW $100/kW
$20/GJ
$50/kW
$40/GJ
$100/kW
--------------------- FCV --------------------
Inter-City Rail Transport
• French TGV (Train à grand vitesse)
• German ICE (Inter-city express)
• Japanese Shinkansen
Recall:
• Energy use to move people by cars is ~ 2.5
MJ/person km with 1 person per car, and
projected to be ~ 1 MJ/person-km with advanced
future vehicles (~ 0.25 MJ/person-km if you pack
4 people into the car)
• The energy required in today’s high speed trains
is ~ 0.08 to 0.15 MJ/person-km
Figure 5.37 Energy intensity for successive generations of
the German Intercity Express (ICE) high-speed trains
0 .1 4
IC E 1
0 .1 2
IC E 2
k W h/s e at-k m
0 .1 0
0 .0 8
0 .0 6
IC E 3
0 .0 4
0 .0 2
0 .0 0
0
100
200
300
400
S p e e d k m /h
Source: Kemp (2007, T618 – Traction Energy Metrics, Lancaster University, Lancaster, www.rssb.co.uk)
Figure 5.38 Shinkansen energy use
0.14
Energy Use (MJ/seat-km)
0.12
0.10
0.08
0.06
0.04
0.02
0.00
Series 0
(1964)
Series 300
(1992)
Series 700
(1998)
Series N700
(2005)
Caveats:
• The savings are not quite as large as they
appear to be, because high speed trains use
electricity which will typically be generated at an
efficiency of only 35-40%
• So, divide the (electrical) energy use by the train
by (0.35 to 0.4 times the transmission and
transformer efficiencies) to get fuel use at the
powerplant that generates the electricity
• Compare this with the amount of crude oil
needed to produce the gasoline energy that is
saved when people switch to trains. This will be
the saved gasoline divided by the efficiency in
making gasoline from oil, about 0.85
Caveats (continued):
• The energy requirements for high speed trains
increase rapidly with increasing speed beyond
about 300 km per hour
• The absolute time savings over a given distance
gets smaller and smaller for each additional
increment of speed
• Faster trains increase total transportation
demand – so some of the passengers on the
train are people who would not have travelled at
all
• Thus, careful market analysis is required to
determine if the introduction of high-speed trains
really does save energy
Aircraft Energy Use
Major types of aircraft
• Turbojet
• Turbo fan (popularly called “jets”)
• Turbo prop
All three have, as their core, a gas turbine (the gas
turbines now used to generate electricity using
natural gas were derived from aircraft turbines
developed for the military)
In a true “jet”, all of the air thrown behind the
aircraft passes through the turbine, where
combustion of fuel occurs. This is found only in
military fighter jets
V
c
T
Vjet
(b)
Turbojet
In commercial “jet” aircraft, most of the air thrown
behind the jet bypasses the turbine, as it is
accelerated by a big fan attached to the turbine
(this is what you see when you look at a the
engine of a commercial jet)
V
F
A
N
Vjet
c
T
LPT
Core
Bypass
(c)
Bypass jet or turbofan
A third option is for the turbine to drive
a propeller that is in front of the turbine
Fuel
Exhaust
Air
c
T
Wnet
Compressor
Turbine
(a)
Turboprop
The performance of an aircraft is represented by
the specific air range, which is the distance that
can be travelled per MJ of fuel energy used. It
depends on 3 factors:
• The amount of thrust produced by the engines
per kg of fuel used
• The aircraft drag for a given velocity
• The aircraft weight
The thrust generated by the engine is equal to the
product of mass x velocity of the air thrown behind
the engine
Doubling the mass of air thrown and cutting its
speed in half gives the same thrust, but much less
kinetic energy (which varies with v2) needs to be
added in this case
Thus, the engine needs to do less work while
producing the same thrust
This is why turbofan aircraft were developed
• The larger the bypass ratio, the greater the
amount of air that is thrown behind the engine,
but the less it needs to be accelerated
• This tends to make the engine more effective
• However, this requires a larger engine casing,
which increases the drag and weight
• Thus, there is an optimal bypass ratio, which is
where we are now – not much further
improvement can be expected
Figure 5.40a Trends in thrust specific fuel consumption (fuel
consumption per unit of thrust generated – smaller is better)
30
TSFC (mg/Ns)
25
20
15
10
5
Turboprops
Regional Jets
Large Jets
0
1955
1960
1965
1970
1975
1980
1985
1990
1995
Year
Source: Babikian et al (2002, Journal of Air Transport Management 8, 389–400, http://www.sciencedirect.com/science/journal/09696997)
2000
Figure 5.40b Trend in lift/drag ratio (larger is better)
25
20
L/Dmax
15
10
Turboprops
5
Regional Jets
Large Aircraft
0
1955
1960
1965
1970
1975
1980
1985
1990
1995
2000
Year
Source: Babikian et al (2002, Journal of Air Transport Management 8, 389–400, http://www.sciencedirect.com/science/journal/09696997)
Figure 5.40c Trend in ratio of empty weight to maximum
allowed take-off weight (smaller is better).
0.7
0.6
OEW / MTOW
0.5
0.4
0.3
0.2
Turboprops
Regional Jets
Large Aircraft
0.1
0.0
1955
1960
1965
1970
1975
1980
1985
1990
1995
2000
Year
Source: Babikian et al (2002, Journal of Air Transport Management 8, 389–400, http://www.sciencedirect.com/science/journal/09696997)
Observations from the previous figures:
• The big improvement has been in thrust specific
fuel consumption (TSFC) – decreasing by about
50% for long-haul aircraft from 1959 to 1998,
achieved in part through development of
engines with larger bypass ratios
• Turboprop aircraft have about 20% smaller
TSFC than turbofan aircraft
• No trend in lift/drag ratio – improvements in
overall aerodynamics have offset the impact of
fatter engines with larger bypass ratios
• A slight upward trend in ratio of empty to full
weight – related in part of extra in-flight
entertainment systems
The energy requirement per passenger-km under
cruising conditions is equal to the reciprocal of the
(specific air range x seating capacity). It is shown
by the coloured (solid) symbols in the next figure
Figure 5.40d Aircraft energy intensity (MJ used per available seat-km)
3.0
EU,CR or EU (MJ/ASK)
2.5
2.0
1.5
1.0
Large aircraft, Eu,cr
Large aircraft, Total Eu
Regional aircraft, Eu,cr
Regional aircraft, Total Eu
0.5
0.0
1955
1960
1965
1970
1975
1980
1985
1990
1995
2000
Year
Source: Babikian et al (2002, Journal of Air Transport Management 8, 389–400, http://www.sciencedirect.com/science/journal/09696997)
Other factors affecting energy use per
km travelled by air travel:
• Distance – the most energy-intensive part of the
flight is the takeoff. On longer flights, this energy
use is spread over more kms, reducing the
average energy use per km
• The airborne efficiency – related to distance
flown (and thus flying time) to the shortest
distance between the starting and ending points
• The ground efficiency – the ratio of flying hours
to total hours (including taxiing)
Figure 5.41a Ground efficiency for different aircraft and
distances travelled
hg (Airborne hours/Block hours)
1.0
0.8
0.6
Turboprop aircraft
0.4
Regional turbofan aircraft
Large aircraft
0.2
0.0
0
2000
4000
6000
8000
Stage Length (km)
Source: Babikian et al (2002, Journal of Air Transport Management 8, 389–400, http://www.sciencedirect.com/science/journal/09696997)
Figure 5.41b Airborne efficiency for different aircraft
and travel distances
ha (Minimum hours/Airborne hours)
1.0
0.8
0.6
0.4
Turboprop aircraft
Regional turbofan aircraft
0.2
Large aircraft
0.0
0
2000
4000
6000
8000
Stage Length (km)
Source: Babikian et al (2002, Journal of Air Transport Management 8, 389–400, http://www.sciencedirect.com/science/journal/09696997)
Figure 5.42 Energy intensity averaged over the entire
flight (including taxiing, waiting to take off, circling
before landing)
3.5
3.0
Turboprop aircraft
Turbofan ("jet") aircraft
Eu (MJ/ASK)
2.5
2.0
1.5
1.0
0.5
0.0
0
2000
4000
6000
8000
Stage Length (km)
Source: Babikian et al (2002, Journal of Air Transport Management 8, 389–400, http://www.sciencedirect.com/science/journal/09696997)
See Figure 5.37d again – note the difference
between energy intensity while cruising (solid
symbols) and overall flight energy intensity (open
symbols)
Prospects for the future
• Weight reductions through increasing use of Cfibre composite materials
• 10-25% further improvement in engine efficiency
• Overall reduction in fleet average energy use
per passenger-km of 20-25% from 1995 to 2030
seems to be quite feasible
• Shifting from turbofan (“jet”) to the latest
turboprop aircraft for distances up to 1000 km
also reduces energy use
• The most efficient aircraft will still be many times
as energy intensive as high-speed trains
Freight Transport
Figure 5.43 Freight transport modes
A ir
W a te r A ir
7 .7 % 0 .4 %
W ater
1 9.2 %
0 .4 %
R a il
4 7.4 %
R oad
3 3 .8%
R ail
5 8 .1%
Road
3 3.0 %
C anada
W a te r
1 2 .6 %
U SA
A ir
A ir
0 .1 %
0 .2 %
R a il
4 .0 %
R a il
2 7 .1 %
W a te r
4 1 .3 %
R oad
5 4 .5 %
R oad
6 0 .2 %
E u ro p e
Japan
Figure 5.44 Variation of freight energy intensity with distance
transported, and difference between modes of transport
1.5
Energy Intensity (MJ/tonne-km)
Truck
Rail
General cargo
Container ship
Bulk cargo
Oil Tanker
1.0
0.5
0.0
0
500
1000
1500
2000
Distance (km)
Source: Skolsvik et al (2000b, Study of Greenhouse Gas Emissions from Ships, Appendices, International Marine
Organization, London)
Figure 5.45 Variation freight energy intensity with capacity factor
Energy Intensity (MJ/tonne-km)
1.5
Truck
Rail
General cargo
Container ship
Bulk cargo
Oil Tanker
1.0
0.5
0.0
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Capacity Factor
Source: Skolsvik et al (2000b, Study of Greenhouse Gas Emissions from Ships, Appendices, International Marine
Organization, London)
Prospects for reducing road freight transport
energy intensity (that, reducing energy use
per tonne-km of transport)
• Improved diesel engine thermal efficiency (from
45% to 55%)
• Hybrid diesel-electric trucks – 25-45% savings
for delivery vehicles in urban settings
• Elimination of idling in heavy trucks (averages
about 2400 hours/year) through use of auxiliary
power units such as fuel cells for air conditioning
and other loads (high-temp fuel cells, not
requiring Pt catalysts, could be used)
Prospects for reducing road freight transport
energy intensity (continued )
• Improved aerodynamics
• Improved loading factor
• Reduced speed
Net result:
A 50% or better reduction in the energy intensity of
freight transport by new trucks is achievable over
the next two decades. More time would be
required to see this improvement over the entire
fleet of trucks
Locomotives for Freight Trains
• Ideal candidate for early application of fuel cells
(on-board fuel storage and start-up time are not
an issue)
• Upfront costs less important than for passenger
vehicles because fuel cost savings over a 20-30
year lifespan are important
Figure 5.46 Locomotive energy flow with a diesel engine used to
generate electricity that in turn drives an electric motor
Diesel
Engine
h=0.423
Fuel
100
Engine
Power
42.3
Exhaust Cooling
30.8
26.9
DC Drive
AC Drive
Traction
Power
39.3
Rectifier
h=0.98
AC or DC
Drive
36.6
Auxiliaries
3.0
DC Traction
Motor , h=0.91
DC-to-AC
Inverter
h=0.98
Alternator
h=0.95
AC Traction
Motor
h=0.95
Gears and
Bearings
h=0.98
Gears and
Bearings
h=0.98
Power to
Rail
32.6
Power to
Rail
33.4
Figure 5.47 Locomotive energy flow using a fuel cell to
generate electricity that in turn drives an electric motor
Fuel
100
PEM
Fuel Cell
h=0.60
Fuel Cell
Power
Exhaust and
Cooling, 32
Drive
Power
60
58.5
Auxiliaries
1.5
DC
Drive
DC-to-DC Converter
(Variable Voltage
output), h=0.97
DC Traction
Motor
h=0.91
AC
Drive
DC-to-AC Inverter
(Variable frequency
and current output)
h=0.98
AC Traction
Motor
h=0.95
Gears and
Bearings
h=0.98
Gears and
Bearings
h=0.98
to
AC or DC
Drive
58.5
Power to
Rail
50.6
Power to
Rail
53.4
Reducing the energy intensity of shipping
• The International Maritime Organization has
identified measures that could be phased in and
which would reduce shipping energy intensity by
37% over 20 years and by 45% over 30 years
• Small wind turbines on a vertical axis (Flettner
rotors) fitted to ships and connected to
propellers could potentially reduce the remaining
energy requirement by 30-40% (already used by
the German wind turbine manufacture Enercon
on the barges used to transport its offshore wind
turbines to where they are installed)
Reducing the need to transport freight
• The previous discussion has focused on the
energy intensity of freight transport – the energy
used to transport a given amount of freight a
given distance
• Globalization and free trade deals have caused
global freight movement to increase much faster
than the growth of the global economy
• This growth has depended on cheap fuel and
unequal wages, worker benefits, and health,
safety and environmental standards in different
countries (and, in some cases, artificial
exchange rates)
• With the inevitable increase in fuel costs and a
reduction in the differences between countries,
the trend toward ever greater trade may very
well be reversed, thereby contributing to
reduced freight transportation energy use
• Conscious effort by consumers to buy locallyproduced products can also contribute to this
Impacts of e-commerce
• Allows greater transport distances and greater
delivery frequencies (tending to increase energy
use), but can also be used to improve the
distribution system
• Can result in greater use of packaging
• Can result in reduced warehouse building area
by facilitating just-in-time delivery, thereby
reducing warehouse energy use
• Can permit electronic grocery shopping and
home delivery services
To maximize the energy savings from e-shopping
and home delivery, a re-organization of the
relationship between suppliers, distribution and
collection centres, and retailers would need to
occur. This might happen spontaneously from the
need for improved logistics
Figure 5.48 Flow of goods from producers to consumers at
present (left) and as might occur with an energy-efficient
e-commerce arrangement
Source: Bratt and Persson (2001, European Council for an Energy Efficient Economy, 2001 Summer Proceedings 3, 480–492)
Box 5.1: Efficiency of a fuel cell
The efficiency of a fuel cell is equal to the product
of three efficiencies:
• The reversible efficiency
• The voltage efficiency (high operating voltage
gives a larger voltage efficiency)
• The Faradic efficiency (almost always = 1.0)
Figure 5.29a Factors contributing to the reduction in the voltage of
a PEM fuel cell compared to the theoretical maximum voltage
1.8
1.4
1.0
Reversible Voltage, ER (=DG/DH x ETN)
1.2
0.8
Region 1: Mixed losses
1.0
Region 2: Activation loss
0.8
Region 3: Resistance loss
0.6
0.6
0.4
0.4
T=70o C, P= 5
0.2
0.2
Region 4: Mass
transport loss
atm
0.0
0.0
0
300
600
900
Current Density (mA/cm2)
1200
1500
Efficiency
1.6
Cell Potential, Volts
1.2
Thermoneutral Voltage, ETN (if DG=DH)
Figure 5.29b Variation of the efficiency and power density of a PEM
fuel cell with current density. A smaller current density means that a
larger and hence more expensive fuel cell is needed for a given power.
1.0
500
0.8
Power Density
400
0.6
300
0.4
200
0.2
Efficiency
100
0
0
300
600
900
1200
Current Density (mA/cm2)
0.0
1500
Efficiency
Power Density (mW/cm2)
600
Figure 5.30a Variation of voltage of a PEM cell with current
density for operation at 50oC and at different pressures.
1.2
Cell Potential, Volts
1.0
0.8
1 atm
0.7
3 atm
0.6
5 atm
0.5
0.6
0.4
0.3
0.4
0.2
0.2
T=50oC
0.1
300
0.0
1500
0.0
0
600
900
1200
Current Density (mA/cm2)
Efficiency
0.8
Figure 5.30b Variation of voltage of a PEM cell with current
density for operation at 70oC and at different pressures.
1.2
Cell Potential, Volts
1.0
0.8
1 atm
0.7
3 atm
0.6
5 atm
0.5
0.6
0.4
0.3
0.4
0.2
0.2
T=70oC
0.1
0.0
0
300
600
900
1200
Current Density (mA/cm2)
0.0
1500
Efficiency
0.8