The Early U. S. Market for PHEVs:
Anticipating Consumer Awareness, Recharge
Potential, Design Priorities and Energy Impacts
Jonn Axsen
jaxsen@ ucdavis. edu
Ken Kurani
knkurani@ ucdavis. edu
Institute of Transportation Studies
University of California
Davis, CA
UCD- ITS- RR- 08- 22
August 2008
- i-
Abstract
Vehicles that can run on both electricity and gasoline— so- called plug- in hybrid electric
vehicles ( PHEVs)— are proposed as both a near- term technology to achieve energy and
environmental goals and a transitional step toward viable all- electric vehicles addressing
many of the same goals. Whether PHEVs meet any of their goals depends not only on
their design and performance on standardized drive cycles, but also on drivers’ travel and
refueling/ recharging behaviors. To replace assumptions with observations of potential
PHEV drivers’ behavior in market and impact analyses, we conducted an internet- based
survey of 2,373 new car- buying households in the United States. The instrument was
implemented in three separate pieces, requiring multiple days for households to answer
questions, conduct a review of their own driving and parking patterns, and then complete
a sequence of PHEV design exercises. In this paper, we draw five conclusions from the
resulting data. First, most new vehicle buyers are unaware of PHEVs in particular and are
confused about electric- drive terminology commonly used by experts. Second, at least
half of our target population is already equipped for at- home vehicle recharging, but
currently have little opportunity for recharging at their workplace or other locations.
Third, we observed widely varied interests in four possible PHEV attributes— fuel
economy in both charge- depleting ( CD) and charge sustaining ( CS) operation, blended
vs. all- electric operation, the distance over which the vehicle is in CD mode, and
recharging speed. Still, the appeal of increased fuel economy appears to be highest and
that of faster recharging to be lowest. Further, there is little interest in all- electric
operation. Fourth, given the previous two points, we estimate that about a third of the
target population has both the infrastructure to recharge a PHEV and interest in a vehicle
with plug- in capabilities. Fifth, our recharge scenarios demonstrate that although
widespread PHEV use could halve gasoline use, impacts to the electricity grid could
highly depend on the time- of- day and location recharge management strategy. While
unconstrained recharging among PHEV buyers may exacerbate current peak electricity
demand, pushing vehicle recharging to off- peak hours through charging controls, time of
day tariffs or other means could reduce overall electricity used by vehicles. Overall,
policy, technology, and energy providers may use this information to understand whether
their plans, designs, and goals align with these present understandings, or whether it
would be collectively beneficial to foster new understandings of PHEVs among U. S. car-buyers.
- ii-
Executive Summary
The dual fuel potential of plug- in hybrid electric vehicles ( PHEVs) presents inherent
uncertainty to policymakers, automakers, electric utilities, researchers, and other interest
groups. Predictions of gasoline and electricity use, as well as the associated emissions,
depend on PHEV design, e. g., power and energy capacity, as well as driving and
recharging behavior, e. g., location and timing of recharge. Due to lack of direct data,
previous impact and market analyses have heavily relied on assumptions about such
behavior, which are often drawn by proxy from databases of travel patterns and housing
stocks. This study seeks to reduce some of these uncertainties for the potential early U. S.
PHEV market. Four questions are addressed:
1. How aware are consumers regarding electric- drive vehicles?
2. How many households have regular access to vehicle recharging opportunities?
3. What PHEV design( s) currently appeal to consumers?
4. What energy impacts ( gasoline and electricity) can we anticipate with significant
PHEV sales?
Methods: Data were drawn from a web- based survey of 2,373 new vehicle buying
households in the U. S— what we judge to be a representative sample ( Fig. E- 1). The
survey was implemented in three separate pieces, requiring multiple days for households
to answer questions, conduct a review of their own driving and parking patterns, and then
complete a sequence of PHEV design exercises. First, awareness was assessed with
questions eliciting respondents’ familiarity and understanding regarding electric- drive
vehicle technologies. Second, recharge potential data were collected with a Plug- in
Potential diary of driving and parking for one of the household’s vehicle. Third, PHEV
design priority data were collected in two versions of priority- evaluator games: the
Development Priority game, and the Purchase Design game ( Appendix C).
Fig. E- 1: Geographic distribution of PHEV sample across the U. S.
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Results:
1) Consumer Awareness: Responses to this survey suggests the majority of new
vehicle buyers have little or no familiarity with the idea of a PHEV, and may erroneously
believe that existing hybrid- electric vehicles can perform the same basic function as a
PHEV, i. e., have the ability to be refueled by gasoline and to be plugged into an electrical
outlet. This lack of awareness and understanding is both a constraint and opportunity. As
a constraint, unaware consumers may simply fail to recognize or identify compelling
benefits of owning and operating a PHEV, serving as a soft constraint to limit the market.
On the other hand, the early PHEV market in the U. S. may be viewed as a blank slate,
with little preexisting understanding of what a PHEV is or expectations of what it should
be. Thus, the early actions of automakers, governments, electric utilities and other
stakeholders could play an important role in establishing perceptions in the market.
Similarly, the first commercially available PHEV incarnations could set an early bar for
consumer understanding and set expectations of performance levels.
2) Recharge Access: We conclude that just more than half the population of U. S.
households that buy new cars has the potential to recharge a vehicle at home with at least
110- volt service ( Fig. E- 2). This proportion is one- and- a- half to three times larger than
previous estimates. Few respondents located non- home recharge opportunities, such as at
their workplace, friend’s and family’s homes, restaurants, etc. Recharge potential, that is,
the spatial- temporal correspondence between a parked vehicle and a 110- volt electrical
outlet, peaks between 12am and 6am when most vehicles are parked at home and reaches
a broad minimum from 10am to 4pm when most vehicles are parked at work or other
locations or are being driven.
Fig. E- 2: Access to recharge spot by location and outlet distance ( all
respondents, n = 2,373)
0%
10%
20%
30%
40%
50%
60%
70%
80%
Any Home Work Other's
Home
Store All
" Other"
50 ft. 25 ft. 15 ft. 10 ft.
% Finding an Outlet
Location Type
Higher Home
Recharge Potential:
Home recharge outlet
within 25 feet of vehicle
( 52.4% of Respondents)
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3) PHEV Designs and Values: Given access to recharging and the distribution
of PHEV designs from the games, we estimate that about one third of U. S. new vehicle
buying households have both the required infrastructure and interest to purchase a vehicle
with plug- in capabilities. Within this early market potential sub- sample, we observed a
wide diversity of consumer interests in PHEV design options ( Fig. E- 3). Starting with a
base PHEV design offering long recharge times, short CD range, no all- electric
operation, but non- trivial reductions in both CD and CS gasoline consumption, the most
popular upgrade category was improved fuel economy in CS mode. Respondents also
exhibited interest in increasing vehicle range in CD mode, and improving CD fuel
economy. Fewer respondents were willing to devote resources to reduce recharge time.
We found little evidence of inherent demand for all- electric operation in CD mode, even
following the one- day diary, the tutorial on electric- drive vehicles ( Appendix B), and
PHEV design games. This difference suggests that while all- electric CD operation may
be particularly attractive to a small subset of consumers, including those who are already
knowledgeable and experienced with electric vehicles, at this point in time most
households who buy new vehicles are more interested in high fuel economy.
Also, about one- third of the potential early market respondents who constructed a PHEV
variant of their likely next new car ( that they selected rather than a conventional version
of that car) chose no upgrades above the proffered base PHEV design. Overall, there may
be substantial potential for market success with less ambitious PHEV designs, i. e.
blended operation with shorter CD range but high CS fuel economy. This wide variety of
PHEV design selections supports the notion of a “ blank slate” early PHEV market, where
early buyers may have little in the way of performance expectations.
Fig. E- 3: Attribute selection in design exercises ( early market potential
respondents only, n = 827)
0%
20%
40%
60%
80%
100%
Recharge
CD Type
CD Range
CS MPG
Recharge
CD Type
CD Range
CS MPG
Recharge
CD Type
CD Range
CS MPG
Recharge
CD Type
CD Range
CS MPG
Recharge
CD Type
CD Range
CS MPG
Recharge
CD Type
CD Range
CS MPG
Base Model
Recharge
CD Type
CD Range
CS MPG
Base Model
% Choosing Upgrade
Base Model
3rd Level Upgrade
2nd Level Upgrade
1st Level Upgrade
Game 1: Development Priority ( Points) Game 2: Purchase Design ($)
Round 1
( 1pt)
Round 2
( 2pt)
Round 3
( 4pt)
Round 4
( 6pt)
Round 5
( 8pt)
“ High”
Price
“ Low”
Price
- v-
4) PHEV Energy Use Scenarios: The final analysis in this report combined all
the available information from each respondent— driving, recharge potential, and PHEV
design priorities— to estimate the energy impacts of the respondents existing travel and
understandings of PHEVs under a variety of recharging scenarios. Results suggest that
the use of PHEV vehicles could halve gasoline use relative to conventional vehicles— the
majority of this reduction being due to increases in CS fuel economy. Using three
scenarios to represent potential boundary conditions on PHEV driver recharge patterns
( unconstrained, universal workplace recharging, and off- peak only charging), we estimate
tradeoffs between the magnitude and timing of PHEV electricity use ( Fig. E- 4). In the
unconstrained “ Plug and Play” recharge scenario, recharging peaks at 6: 00pm, following
a far more dispersed pattern throughout the earlier part of the day than anticipated by
previous research. PHEV electricity use could be increased through policies increasing
non- home recharge opportunities ( e. g., the “ Enhanced Worker Recharge Access”
scenario), but most of this increase occurs during daytime hours and could contribute to
peak demand ( depending on a given region’s definition of “ peak”). We also demonstrate
how deferring all recharging to off- peak hours ( 8pm to 6am) could eliminate all additions
to daytime electricity demand from PHEVs. However, in such a scenario less electricity
is used due to the elimination of daytime recharge opportunities and less gasoline is
displaced.
Fig. E- 4: Comparing PHEV recharge scenarios, scaled for one million
PHEVs ( weekdays only, early market potential respondents only, n= 590)
0
100
200
300
400
500
600
700
12am 4am 8am 12pm 4pm 8pm 12am
Time of Day
Conclusions: In this paper, we draw five conclusions from the resulting data:
1. Most new vehicle buyers are unaware of PHEVs in particular and are confused
about electric- drive terminology commonly used by experts.
MW per Million PHEVs
“ Off Peak Only”
( 3.6 GWh)
“ Enhanced
Worker Access”
( 5.8 GWh)
“ Plug and Play”
( 4.4 GWh)
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2. At least half of our target population is already equipped for at- home vehicle
recharging, but currently have little opportunity for recharging at their workplace
or other locations.
3. We observed widely varied interests in four possible PHEV attributes— fuel
economy in both charge- depleting ( CD) and charge sustaining ( CS) operation,
blended vs. all- electric operation, the distance over which the vehicle is in CD
mode, and recharging speed. Still, the appeal of increased fuel economy appears
to be highest and that of faster recharging to be lowest. Further, there is little
interest in all- electric operation.
4. Given the previous two points, we estimate that about a third of the target
population has both the infrastructure to recharge a PHEV and interest in a
vehicle with plug- in capabilities.
5. Our recharge scenarios demonstrate that although widespread PHEV use could
halve gasoline use, impacts to the electricity grid highly depend on recharge
management strategy. While unconstrained recharging among PHEV buyers may
exacerbate current peak electricity demand, pushing recharging to off- peak hours
through smart charging, time of day tariffs or other means could reduce overall
electricity used by PHEVs.
Overall, this analysis provides a baseline measure of market potential— one that could be
highly subject to influence. Recharge infrastructure could expand to a higher percentage
of households with changes in building codes, as well as increased employer and publicly
installed vehicle recharge outlets. Recharge behavior may also shift with PHEV purchase;
owners might adjust driving patterns to maximize electricity use or adjust recharge
locations if additional infrastructure is provided away from homes. Desired PHEV
designs and capabilities may be even more subject to change. Survey respondents had
little pre- existing understanding of PHEVs and the elicited responses could be sensitive
to the PHEV information we provided. As information about PHEV technology diffuses
throughout the economy, along with corresponding developments in PHEV values and
meaning, interest in particular attributes could shift. For example, all- electric charge-depleting
operation could become more meaningful to car buyers as they gain experience
and as they participate in the process of identifying just what all- electric operation means
to people. In the meantime, this analysis illustrates how the messages and actions of
policymakers, automakers, electric utilities and other interest groups could have
significant influence over future development of awareness, recharge potential, design
interests, and energy impacts of the PHEV market.
- vii-
Table of Contents
Abstract ............................................................................................................................... i
Executive Summary............................................................................................................ ii
1. Introduction................................................................................................................... . 1
2. Methods........................................................................................................................ .. 3
2.1 Survey Design........................................................................................................... 3
2.2 Data Collection ....................................................................................................... 10
3. Results........................................................................................................................ .. 14
3.1 Consumer Awareness.............................................................................................. 14
3.2 Recharge Access ..................................................................................................... 15
3.3 PHEV Design and Value ........................................................................................ 19
3.4 PHEV Energy Use Scenarios.................................................................................. 23
4. Discussion and Conclusions ......................................................................................... 29
4.1 Awareness of Electric Drive Vehicles .................................................................... 30
4.2 Recharge Potential and Timing............................................................................... 30
4.3 Design Priorities...................................................................................................... 31
4.4 Energy Impacts ....................................................................................................... 32
Acknowledgments............................................................................................................. 33
References..................................................................................................................... ... 34
Appendix A: Vehicle Diary Example ............................................................................... 37
Appendix B: Plug- in Vehicle Guide ................................................................................. 38
Appendix C: PHEV Design Games .................................................................................. 46
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1. Introduction
Alternative fuel vehicle technologies will play a significant role in helping the U. S. meet
goals to reduce petroleum use, air pollution and greenhouse gas emissions in the
transportation sector. Electric drive technologies are receiving renewed attention as
potential near- term solutions relative to alternatives such as hydrogen. As hybrid- electric
vehicles ( HEVs), typified by the Toyota Prius, continue to achieve significant
commercial success in the U. S. market, plug- in hybrid vehicles ( PHEVs) are touted as the
next step in electric drive development ( Lemoine et al, 2008).
PHEVs are one step closer to the pure electric vehicle ( EV) initially envisioned by
California’s zero emissions vehicle mandate; users can charge the battery from the
electrical grid and drive limited distances ( less than 40 miles) in charge- depleting ( CD)
mode. Figure 1 illustrates CD mode as a reduction in the battery’s state of charge, where
the vehicle is powered either by electricity only ( all- electric operation) or by electricity
and gasoline ( blended operation). Once the battery is depleted to a minimum state of
charge ( typically set at a value greater than 0 percent to preserve battery life), the PHEV
uses only gasoline in charge sustaining ( CS) mode, achieving the fuel efficiency of
today’s typical HEV. Battery size, degree of hybridization, and drivetrain design can all
substantially influence the overall operation of a given PHEV. 1
Fig. 1: Illustration of typical PHEV discharge cycle
Distance
Battery State of Charge ( SOC)
Charge Sustaining
( CS Mode)
Charge Depleting
( CD Mode)
Gasoline
Only
All Electric or
Blended
Source: Adapted from Kromer and Heywood ( 2007, p31). Used with permission from authors.
Primary PHEV benefits are straightforward: by supplementing or replacing gasoline
combustion with grid electricity, consumers could reduce the costs, petroleum use, air
pollution and greenhouse gas emissions associated with driving— without the range
1 For a more detailed discussion of PHEVdesign concepts, see Axsen et al ( 2008).
- 2-
limitations of pure EVs. Other potential benefits are less obvious: PHEVs could provide
“ mobile energy” services, such as backup electricity for home use or storing excess
electricity produced by utilities for load balancing ( Williams and Kurani, 2006).
However, the dual fuel potential of PHEVs presents inherent uncertainty to policymakers,
automakers, electric utilities, researchers, and other interest groups. Predictions of
gasoline and electricity use, as well as the associated emissions, depend on PHEV design,
e. g., power and energy capacity, as well as driving and recharging behavior, e. g., location
and timing of recharge. Due to lack of direct data, previous impact and market analyses
have heavily relied on assumptions about such behavior ( Winkel et al, 2006; Vyas et al,
2007; Duvall et al, 2007), which are often drawn by proxy from databases of travel
patterns and housing stocks. The choice of assumptions can seriously affect results;
Lemoine et al ( 2008) illustrate how varying time of day recharge assumptions can
substantially influence predictions of electricity grid impacts.
Also, as of the writing of this report, the California Air Resources Board ( 2008) is
deliberating how to define a PHEV and assign air emissions credits to automakers for
producing them. Similarly, automakers like Toyota and General Motors are publicly
disputing the viabilities of vastly different PHEV designs: one with a smaller battery and
relatively low CD range ( the Prius Plug- in) and one designed to operate as a pure electric
vehicle for much longer distances ( the Volt concept). In summary, there is a
demonstrated lack of consensus regarding consumer behavior and demand as well as
subsequent environmental impacts.
This study seeks to reduce some of these uncertainties. Four questions are addressed:
1. How aware are consumers regarding electric- drive vehicles?
2. How many households have regular access to vehicle recharging opportunities?
3. What PHEV design( s) currently appeal to consumers?
4. What energy impacts ( gasoline and electricity) can we anticipate with significant
PHEV adoption?
To empirically answer these questions, data were drawn from a web- based survey of new
vehicle buying households in the U. S. Integrating data for all four of these questions,
possible PHEV market niches within the household light- duty vehicle market are
described. Previous electric vehicle constraints analyses estimated that the proportion of
households with home recharge access to be 28 percent in the U. S. ( Nesbitt et al, 1992)
and 15 to 30 percent in California ( Williams and Kurani, 2006). Data for the present
study was collected with a 24- hour Plug- in Potential diary, improving upon previous
research in several ways: ( 1) instead of creating estimates from census data by proxy we
elicited recharge potential directly from respondents, ( 2) we recorded time of day access
to allow estimates of daily recharge patterns, and ( 3) we limit our focus to U. S. new
vehicle buyers, rather than the entire population of U. S. households.
We also investigated the design priorities of the potential PHEV market using two
innovative games. Previous research has used stated- preference methods to directly ask
survey respondents about purchase intention for a certain PHEV design ( e. g. Graham et
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al, 2001). Such results are typically unreliable due to the hypothetical and shallow nature
of the information provided to respondents. We attempted to overcome this limitation by
providing more in- depth information to respondents, described in previous research as a
reflexive design ( Kurani et al, 1996), such as visually depicting the recharge potential
elicited from the Plug- in Potential diary back to the respondent and providing an
informative PHEV buyers’ guide. Respondents then completed a PHEV Development
Priority game, choosing among several PHEV upgrade possibilities over several
iterations, as well as a Purchase Design game, demonstrating interest in a PHEV as
purchase intention under different price conditions. In addition to investigating general
priority patterns among the sample, we also explored two hypotheses gleaned from
Kurani et al’s ( 2007) interviews of 23 drivers of PHEV conversions: that early PHEV
buyers might be particularly interested in ( 1) all- electric CD operation and ( 2) attracted to
certain levels of high instantaneous fuel economy, such as 100 miles per gallon. Along
these lines, we also explore the potential market for more aggressive PHEV design
proposals, e. g. GM’s Volt concept with 40 miles of all electric range, relative to less
aggressive designs, e. g. Toyota’s Plug- in Prius with less than 10 miles of CD range
designed primarily for blended operation.
Taken together, the collected information regarding driving patterns, recharge potential
and design priorities allow the creation of realistic recharge scenarios. The potential
impacts of pure electric and PHEV use on electricity generation could be important with
widespread adoption ( e. g. Kurani et al, 1997; Lemoine et al, 2008; Hadley and
Tsvetkova, 2008). We simulate grid impacts under three scenarios to investigate potential
tradeoffs between overall gasoline and electricity use and the timing of electricity use.
2. Methods
To answer these questions, we conducted a web- based survey of 2,373 new vehicle-buying
households in the U. S.
2.1 Survey Design
The survey instrument collected three types of data from new car buyers which are
analyzed here: 1) their familiarity with electric- drive vehicle technologies, 2) their access
to vehicle recharge opportunities, i. e., electric outlets located at or near their vehicle
parking locations, and 3) their plug- in hybrid electric vehicle ( PHEV) design priorities.
First, awareness was assessed with questions eliciting the stated familiarity of
respondents with conventional gasoline, hybrid- electric, electric, and plug- in hybrid
electric vehicles. Respondents were then asked to demonstrate their understanding by
choosing how each vehicle type could be fueled: with gasoline, electricity through an
electrical outlet, or either. The implication of this exercise is not that consumers need to
have a deep technological understanding of alternative- drive vehicles in order to make a
purchase. However, we feel that a very basic familiarity is required to ensure an
understanding of the fundamental benefits of a technology, i. e. whether or not the vehicle
can be plugged in.
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Second, recharge potential data were collected with a Plug- in Potential diary of driving
and parking for a new vehicle ( model year 2002 or later) driven several times per week
by the respondent’s household. Respondents were assigned a day of the week and
instructed to record information for a 24 hour period starting with their first trip of the
day. Information included the timing and distance of each trip, parking locations, and the
proximity of those locations to an electrical outlet. Respondents recorded data in a diary
printed from a PDF document and then input the data online using the instrument
depicted in Figure 2 ( example of physical diary in Appendix A). The respondent’s diary
day was immediately depicted to them as a graph as seen in Figure 2, using a technique
similar to that used by Kurani et al ( 1994, 1996) to help respondents better understand
their own driving behavior and how an electric- drive vehicle could fit into their lifestyle.
Third, PHEV design priority data were collected in two versions of priority- evaluator
games. Commonly, researchers will infer preferences for attributes of alternative fuelled
vehicles by presenting respondents with a description of one or several new technologies,
followed with a set of hypothetical choice scenarios in which respondents make several
choices from sets of vehicles of different attributes ( see for example Bunch et al, 1993;
Ewing and Sarigollu, 2000; Potogolou and Kanaroglou, 2007). However, Heffner et al
( 2007) demonstrate that more in- depth research, such as household interviews, can reveal
important information that choice experiments cannot. To improve the quality of data
gathered through a nationwide survey, prior to the PHEV design exercises, respondents
were provided two types of preparatory information: ( 1) the 24- hour diary exercise
described above served the additional role of reflecting to respondents aspects of their
travel patterns and potential access to recharge spots, and ( 2) a PHEV buyers’ guide
describing basic design options for PHEVs ( replicated in full in Appendix B).
Respondents then completed two games ( both replicated in Appendix C). The first was a
PHEV Development Priority game in which respondents chose among PHEV design
possibilities over several iterations. Second was a Purchase Design game, similar to the
first, but with the design possibilities priced in dollars and respondents could reject
buying a PHEV, retaining a conventional vehicle.
One key difference between the games utilized in this study and a typical stated choice
exercise is that the games are design exercises, not choice exercises. Rather than choose
their most preferred vehicle design from a limited set of options ( often repeated several
times) specified by the researchers, respondents in the design games have a design
envelope available to them, and they construct their most favored design from within that
envelope subject to resource constraints. Kurani et al ( 1996) discussed the basis for
regarding consumer evaluations, especially of novel products such as electric- drive
vehicles, as being constructed in the process of choosing ( or not choosing).
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Fig. 2: Screenshots of Plug- in Potential Diary ( for hypothetical respondent)
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Both games focused on four PHEV design attributes: ( 1) hours required for complete
recharge of a depleted battery, ( 2) gasoline use in charge- depleting ( CD) mode, ( 3) miles
of range in CD mode, and ( 4) gasoline use in charge- sustaining ( CS) mode. In each game,
a base PHEV design is offered with capabilities easily achievable by current battery
technology ( Axsen et al, 2008): a PHEV that requires up to 8 hours to completely
recharge, that can be driven for the first 10 miles in CD mode using blended operation
that increases fuel economy to 75 mpg, and that can improve fuel efficiency by 10 mpg
over a conventional vehicle when operating in CS mode. 2 In both games, respondents
were given opportunities to improve each attribute under different resource conditions.
We chose these four attributes due to their importance in determining driving patterns as
well as reflecting technological capabilities. First, the time to replenish a large depleted
battery would take 6- 8 hours, but technology exists to allow “ fast” charging in less than
one hour— allowing for significantly different recharge patterns. Second, currently
available PHEV conversions are designed for blended CD operation. We specified
upgrades to account for several levels of gasoline only fuel economy in blended
operation: 75- 125 mpg. This range includes the 100 mpg “ magic” number identified as
important among some early PHEV conversion owners ( Kurani et al, 2007). Because
automakers such as General Motors have announced plans to release PHEVs designed for
all- electric operation, we also include an all- electric upgrade option. Third, CD range
depends on battery energy capacity, and proposed designs typically range from 10 to 40
miles ( Pesaren et al, 2007; Kromer and Heywood, 2007). The fourth category, fuel
consumption in charge sustaining ( CS) mode, is comparable to the operation of today’s
hybrid electric vehicles; the battery and electric motor are used to improve the efficiency
of the gasoline engine, not to use grid electricity. Most hybridized drivetrains can
increase fuel economy by 10 to 30 miles per gallon ( mpg) relative to a similar size,
weight, and performance vehicle.
The first exercise was the Development Priority game presenting respondents with a
hypothetical scenario: the household vehicle for which they kept their Plug- in Potential
diary would be upgraded to a PHEV at no cost. The performance and appearance of their
vehicle would remain the same, except for the additional capabilities of a plug- in hybrid:
a battery that can be plugged in to any electrical outlet in order to power the vehicle for
short distances, as well as a drivetrain that reduces gasoline consumption even after the
CD range is exceeded. Respondents were presented with a base PHEV model and given
points they must allocate among various potential upgrades. Over five rounds of the
Development Priority game, respondents were provided progressively more points ( Table
1). For the first three rounds of the game higher levels of upgrades of the four attributes
and more combinations of upgrades were also offered, expanding the PHEV design
2 Note that these PHEV design games are meant to represent designs that are technologically feasible, but
not necessarily with exact specifications. For instance, the battery required for our base PHEV design
would likely require only 2 to 3 hours to fully recharge with a 110 to 120 volt circuit. However, with
careful pre- testing, we consciously chose to simplify attribute levels and ignore potential interactions
among attributes to create exercises that are more likely to be understood by our respondents than to adhere
to experts’ knowledge.
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envelope to observe respondents’ allocation of resources. A screenshot of the game,
along with the language used for respondents, is portrayed in Figure 3.
Table 1: Upgrades for PHEV Development Priority game
Attribute
( base value)
Round One:
( 1 point)
Round Two:
( 2 points)
Rounds Three, Four
and Five:
( 4, 6 and 8 points)
Recharge time:
( 8 hours)
4 hours ( 1pt) 4 hours ( 1pt)
2 hours ( 2pt)
4 hours ( 1pt)
2 hours ( 2pt)
1 hour ( 3pt)
Charge depleting ( CD)
mpg and type :
( 75 mpg)
100 mpg ( 1pt) 100 mpg ( 1pt)
125 mpg ( 2pt)
100 mpg ( 1pt)
125 mpg ( 2pt)
All- electric ( 4pt)
CD range:
( 10 miles)
20 miles ( 1pt) 20 miles ( 1pt)
40 miles ( 2pt)
20 miles ( 1pt)
40 miles ( 2pt)
Charge sustaining ( CS)
mpg:
( Current mpg* + 10)
Current mpg
+ 20 ( 1pt)
Current mpg
+ 20 ( 1pt)
Current mpg
+ 30 ( 2pt)
Current mpg
+ 20 ( 1pt)
Current mpg
+ 30 ( 2pt)
The second exercise was the Purchase Design game which framed the PHEV design
exercise in the context of a future vehicle purchase. The questionnaire first elicited
information about the anticipated price, make and model of the next new vehicle the
respondent’s household would likely buy. The respondent then completed two PHEV
purchase exercises, each comparing their anticipated conventional vehicle with a PHEV
version of the same. Respondents were presented with a “ high” price and “ low” price
PHEV purchase conditions, where prices in both conditions also depended on whether
the vehicle was a car or truck ( Table 2). As in the Development Priority game, each
exercise started with the same base PHEV model, with additional upgrades available for
added price. In each exercise, the respondent could choose either their anticipated
conventional vehicle, the offered ( base) PHEV, or to upgrade the PHEV. Figure 4
portrays a screenshot of this exercise.
- 8-
Fig. 3: Screenshot of Development Priority game ( Round Four)
Because battery and drivetrain costs are highly uncertain, upgrade prices in Table 2 are
largely hypothetical. That is, we are less concerned with whether the prices we now
present to respondents will be right in a future ( if and) when PHEVs are marketed, and
more concerned with how respondents pick and choose from different energy sources,
energy efficiencies, and distinct operating modes within different price contexts. Still, the
price contexts we present are not wholly imaginary. Overall prices are based on short
term ( high price) and long term ( low price) estimates from previous studies: Markel
( 2006) estimates incremental costs for PHEVs with all- electric capabilities ( 7 to 19 kWh)
at $ 6,000 to $ 22,000, while Kalhammer et al ( 2007) provide cost estimates for PHEVs
with slightly lower capacity batteries ( 4 to 14 kWh) in the range of $ 2,000 to $ 8,000. For
comparison, PHEV designs in our survey ranged from $ 3,000 to $ 13,500 for cars in the
“ high” price condition, and from $ 2,000 to $ 7,250 in the “ low” price condition. For
trucks, base model prices are increased and upgrades doubled due Duvall et al’s ( 2002)
estimates of a full size SUV PHEV requiring 75 percent more energy capacity and 190
percent more battery power to achieve the same CD performance as a compact car
PHEV.
- 9-
Fig. 4: Screenshot of Purchase Design game (“ high” price, vehicle model
customized for respondent)
- 10-
Table 2: Price of upgrades for Purchase Design game
“ High” price “ Low” price
Attributes
( base level)
Attribute level Car Truck Car Truck
Base premium $ 3,000 $ 4,000 $ 2,000 $ 3,000
Recharge time
( 8 hours)
4 hours
2 hours
1 hour
+$ 500
+$ 1,000
+$ 1,500
+$ 1,000
+$ 2,000
+$ 3,000
+$ 250
+$ 500
+$ 750
+$ 500
+$ 1,000
+$ 1,500
CD mpg and type
( 75 mpg)
100 mpg
125 mpg
All- electric
+$ 1,000
+$ 2,000
+$ 4,000
+$ 2,000
+$ 4,000
+$ 8,000
+$ 500
+$ 1,000
+$ 2,000
+$ 1,000
+$ 2,000
+$ 4,000
CD range
( 10 miles)
20 miles
40 miles
+$ 2,000
+$ 4,000
+$ 4,000
+$ 8,000
+$ 1,000
+$ 2,000
+$ 2,000
+$ 4,000
CS mpg
( Current mpg + 10)
Current mpg + 20
Current mpg + 30
+$ 500
+$ 1,000
+$ 1,000
+$ 2,000
+$ 250
+$ 500
+$ 500
+$ 1,000
2.2 Data Collection
Our target population is new vehicle buying households in the U. S. To qualify,
respondents had to own a new gasoline vehicle that they purchased in 2002 or later,
which they personally drove at least 3 times per week. The respondent also must have
played a significant role in the household’s decision to purchase this vehicle. In limiting
our study to this population, we imply that the early market for PHEVs is limited to
households that tend to buy new vehicles in general. In total, 2,664 respondents
completed the entire survey in December of 2007. We removed 291 respondents with
incomplete diary data, leaving 2,373 used in this study.
Figure 5 portrays the geographic distribution of the sample, which corresponds to
population density. Two regions, California and a particular area in Northern California,
were intentionally oversampled to permit separate analyses. Because the present study
focuses on the overall U. S. vehicle market, all data has been weighted to be
representative of the whole U. S. including California.
Data were collected with a web- based survey. Relative to mail and telephone methods,
the major strength of internet surveys is the high degree of design flexibility.
Administrators can interactively adapt questions to previous responses as well as more
effectively screen respondents, sequence questions, and avoid item non- response ( Rhodes
et al, 2003). Internet survey techniques can also enhance response accuracy, particularly
- 11-
for travel diaries ( Adler et al, 2002). Lastly, a well- programmed survey will automate
data entry to minimize data administration time and cost ( Couper, 2000).
Fig. 5: Geographic distribution of PHEV sample across the U. S. ( Alaska not
shown)
However, web- based surveys are susceptible to non- coverage error, where a significant
portion of the target population, in this case new car buyers, may be excluded if they
don’t have internet access. This concern is declining in the U. S. as internet usage rates
have grown from 44% in 2000 to over 70% in 2007 ( Internet World Stats, 2007). Also,
we suspect there is a positive correlation between internet access and likeliness to buy
new vehicles, implying an even higher usage rate among our target population. However,
non- response bias is still an important concern because those without internet access tend
to be disproportionally old, with low income and low education ( Rhodes et al, 2003;
Couper et al, 2007).
Respondents for this survey were recruited by Harris Interactive from their internet panel.
To counteract concerns of non- coverage and non- response error, Harris estimates weights
to better match the realized sample to the target population. Weights are based on
geographic, demographic and attitudinal data, and matched to existing databases
collected through multiple survey modes ( including mail and telephone). All results
presented in this study use these weights to match our sample to the U. S. population of
new vehicle buyers.
To assess the external validity of our sample, as well as the impact of Harris’ weights, we
compare sample distributions according to five socio- demographic variables in Table 3:
respondent gender, education and age, and household income and housing type. General
population estimates are available from the 2000 Census, as well as the Current
Population Survey ( CPS) and the American Household Survey ( AHS). However, because
our target population ( new vehicle buyers) is likely to be of higher socioeconomic status
than the general population, we also drew a sub- sample of over 10,000 households
- 12-
owning new vehicles from the 2001 National Household Travel Survey ( NHTS).
Comparing our weighted sample to the NHTS, we find that the income levels of both
samples are about 42 percent higher than general population estimates from similar years
( 2007 and 2000 respectively). Also, gender, age, and housing type follow similar
distributions between the two samples of new vehicle buying households. Education
levels are slightly higher in the present study, with 56 percent having a college degree of
higher compared to 48 percent in the NHTS sample, but this difference is not substantial.
Table 3 also shows that applying the Harris weights has little effect on gender, income
and housing type, but does influence education and age distributions in the same
directions as the NHTS sample. We conclude that our sample matches well with other
samples of new car owners on these socio- demographic measures, strengthening claims
that our results can be extended to the population of new- car owning ( and therefore, new
car- buying) households.
- 13-
Table 3: Comparing demographic distributions of present and previous
samples
Target New vehicle buyers General population
Year 2007 2007 2001 2007 2000
Survey Type
PHEV
unweighted a
PHEV
weighted b
NHTS c
Sample size 2,373 2,373 10,188
Pop. Est. g Census h
Gender d Male 49.3% 52.2% 43.5% 49.3% 49.1%
Female 50.7% 47.8% 56.5% 50.7% 50.9%
CPS i Census h
Education d Highschool or lower 9.3% 19.4% 31.2% 46.6% 48.2%
Some college 25.3% 24.7% 20.7% 19.0% 21.0%
College degree 38.0% 36.7% 32.8% 25.7% 21.9%
Graduate degree 27.4% 19.2% 15.2% 8.7% 8.9%
Pop. Est. g Census h
Age d 15 to 24 2.5% 3.3% 4.5% 17.7% 17.8%
25 to 34 12.6% 17.8% 16.2% 16.9% 18.0%
35 to 44 18.2% 21.7% 22.8% 17.9% 20.4%
45 to 54 25.9% 24.3% 25.5% 18.2% 17.1%
55 to 64 26.2% 21.6% 15.7% 13.6% 11.0%
> 64 14.6% 11.3% 15.4% 15.7% 15.8%
CPS i Census h
Income e < 30 k 5.5% 6.3% 12.2% 31.0% 35.1%
30 k to 60 k 28.2% 26.0% 32.7% 28.6% 31.9%
> 60k to 100k 33.7% 32.5% 32.4% 21.3% 20.7%
> 100k 32.7% 35.3% 22.7% 19.1% 12.3%
Mean income f $ 86,243 $ 87,911 $ 72,478 $ 61,870 $ 50,864
Ratio of new vehicle
buyer mean income
to general population
mean income
1.39 1.42 1.42
AHS j AHS j
Housing type e Detached house 78.4% 78.0% 80.7% 64.3% 62.8%
Attached house 8.9% 8.3% 7.6% 5.7% 6.8%
Apartment 9.5% 10.2% 8.9% 23.7% 23.9%
Mobile home 3.1% 3.5% 2.8% 6.4% 6.6%
a Without using weights provided by Harris Interactive; data only weighted to correct for California oversample.
b Data used for this study: using U. S. weights provided by Harris Interactive.
c NHTS sample limited to responding households that had purchased a vehicle of model year 2001 or 2002.
d Data reported for respondent only.
e Data reported for respondent’s household.
f Mean approximated from the product of middle values assigned to each income category and the proportion of
the sample in that category.
g 2007 Annual estimates of the population by the Population Division of the U. S. Census Bureau.
h 2000 Census by the U. S. Census Bureau.
i 2007 Current Population Survey by the U. S. Census Bureau.
j 2005 and 1999 American Household Surveys by the U. S. Department of Housing and Urban Development.
- 14-
3. Results
3.1 Consumer Awareness
Among respondents, stated familiarity with vehicle technologies corresponded to real-world
experience with automobiles; high levels of familiarity were most common for
conventional gasoline vehicles, followed in order by HEVs, EVs and PHEVs ( Figure 6).
Familiarity with PHEVs was lowest: 69 percent of respondents reported low or no
familiarity. A question eliciting demonstrated understanding of motor vehicles indicates
that the vast majority of respondents understood that conventional gasoline vehicles
could only use gasoline, while electric vehicles can only use electricity ( Figure 7). But
things are a good deal less clear for HEVs and PHEVs: 25 percent of respondents thought
that a PHEV could only use electricity and 68 percent of respondents thought that an
HEV could be refueled either with gasoline or by plugging in to an electric outlet. The
latter is clearly false for the most common expert definitions of an HEV. This last point
demonstrates enormous potential for misunderstanding PHEVs among new vehicle
buyers, the majority of which seem to think that currently available hybrids can be
plugged in to the electricity grid. An alternative explanation is that our choice of wording
(“ hybrid- electric”) may have been too formal relative to commonly used “ hybrid.” In
either case, there is at least widespread confusion regarding electric- drive terminology,
and perhaps widespread misunderstanding of the functions, requirements, and benefits of
different electric- drive technologies.
Fig. 6: Stated familiarity with electric- drive vehicles ( all respondents)
0%
20%
40%
60%
80%
100%
Gasoline Hybrid-
Electric
Electric Plug- in
Hybrid
Electric
Vehicle Type
% of Respondents
High
Moderate
Low
Not Familiar
- 15-
Fig. 7: Demonstrated understanding of how to fuel an electric- drive vehicle
( all respondents)
0%
20%
40%
60%
80%
100%
Gasoline Hybrid-
Electric
Electric Plug- in
Hybrid
Electric
Vehicle Type
% of Respondents
Only with
gasoline
Only by
plugging
in
Either
3.2 Recharge Access
Results from the Plug- in Potential vehicle diary indicate that more new vehicle buyers
may be pre- adapted for vehicle recharging than previously estimated ( Figure 8).
Following Graham et al ( 2001), we consider a parking spot to be viable for recharging if
located within 25 feet of an electrical outlet. Of the 2,373 respondents, 59.5 percent found
at least one viable recharge location during their 24- hour diary day, and 52.4 percent
identified one at their home. For the remainder of this study, we consider these 52.4
percent of our sample to represent the higher home recharge potential segment among
new vehicle buying households, that is, respondents that identified an electrical outlet
within 25 feet of their vehicle parking spot at their home location at some time during
their 24- hour diary.
Fewer respondents found non- home recharge locations: 4.8 percent found outlets at work
( 6.3 percent of employed respondents), 5.4 percent at the home of a friend or family
member, 2.3 percent at a store or restaurant, and 9.7 percent at all other locations. Figure
8 also depicts the sensitivity of estimated recharge access to the assumption of the
maximum distance of the electrical outlet from the vehicle. Home recharge access ranges
from as high as 60.7 percent if we allow 50 feet between the parked vehicle and the
nearest electrical outlet, to a low 35.8 percent if the outlet must be within 10 feet of the
vehicle.
- 16-
Fig. 8: Access to recharge spot by location and outlet distance ( all
respondents, n = 2,373)
0%
10%
20%
30%
40%
50%
60%
70%
80%
Any Home Work Other's
Home
Store All
" Other"
50 ft. 25 ft. 15 ft. 10 ft.
Figure 9 depicts the split of this higher home recharge potential segment by housing
type: detached homes ( single family dwellings), attached homes ( including duplexes and
townhouses), apartments and mobile homes. Most respondents lived in detached homes
( single family dwellings), and most respondents who lived in detached homes parked
their vehicle at home within 25 feet of an electrical outlet. Over the entire sample, 45.9
percent of our new car buyers live in a detached home and park near an outlet. Somewhat
less than half of residents of attached homes and mobile homes park a car at home near
an outlet. Only about one- in- six apartment dwellers parks a vehicle near an outlet.
Overall, residence in a detached home is positively correlated with at- home recharge
potential, but is neither necessary nor sufficient.
Figure 10 shows that the proportion of our sample with higher home recharge potential is
highest for those parking in attached garages ( 71.9 percent) and detached garages ( 61.6
percent). Driveway and carport locations yield lower proportions of 42.4 and 40.3
percent, respectively. The lowest proportions were found for respondents parking on the
street ( 17.4 percent) and in parking lots ( 4.7 percent). Our findings suggest that the use of
home garages supports at- home recharge potential, but as with detached homes this
condition is neither necessary nor sufficient.
% Finding an Outlet
Location Type
Higher Home
Recharge Potential:
Home recharge outlet
within 25 feet of vehicle
( 52.4% of Respondents)
- 17-
Fig. 9: Access to home recharge by housing type ( all respondents, n =
2,373)
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
Detached
House
Attached
House
Apartment Mobile Home
House Type
% of Respondents
Found outlet within 25 feet
Did not find outlet within 25 feet
Fig. 10: Access to home recharge by type of home parking spot ( all
respondents, n = 2,373)
0%
10%
20%
30%
40%
50%
Attach.
Garage
Detach.
Garage
Driveway Carport On the
Street
Parking
Lot
Home Parking Type
% of Respondents
Found outlet within 25 feet
Did not find outlet within 25 feet
- 18-
We also investigated driving and recharge potential over a 24- hour cycle ( in 15 minute
intervals); the sample was proportionally assigned a weekday ( Figure 11) or weekend-day
( Figure 12) on which to complete their diary. On weekdays, the proportion of
respondents’ driving follows an expected daily pattern, peaking during common
commute hours at 7: 30am and 5: 00pm. At a given point in time, total recharge potential
ranges from over 50% of respondents from 9: 00pm to 7: 00am, to under 20% from
10: 00am to 3: 00pm. Throughout the day, home is by far the most frequent location of
recharge opportunities within respondents’ existing travel and recharge potential. Neither
work nor other non- home locations have recharge potential that surpass 4 percent of
respondents for any 15 minute interval during the day. The general pattern in Figure 11 is
consistent with driving patterns; recharge potential drops when many respondents are
driving or parked at work or other locations, and rises when vehicles are parked at home.
Fig. 11: Time of day driving and recharge potential ( weekdays only, n =
1,650)
0%
10%
20%
30%
40%
50%
60%
12am 4am 8am 12pm 4pm 8pm 12am
0%
3%
6%
9%
12%
15%
18%
As seen in Figurve 12, relative to weekdays, driving patterns on weekend days do not
have the two morning and afternoon peaks, but rather a single broad mid- day rise to a
peak at 12: 30pm ( with a lesser peak in the later evening). Weekend recharge potential
during any given 15 minute interval ranges from a high of 50.3 percent to a low of 28.6
percent of all respondents; home also dominates the potential recharge locations.
Driving
Work
Other
Home
% of Respondents with Access
% of Respondents Driving
Time of Day
- 19-
Fig. 12: Time of day driving and recharge potential ( weekend days only, n =
493)
0%
10%
20%
30%
40%
50%
60%
12am 4am 8am 12pm 4pm 8pm 12am
0%
3%
6%
9%
12%
15%
18%
3.3 PHEV Design and Value
We use recharge potential estimates from the previous section to shape the analysis of
respondents’ PHEV design games. We divide the sample into three segments according
to their demonstrated recharge potential:
1. Higher home recharge potential: this segment consists of the 52.4 percent of
respondents that found an at- home electrical outlet within 25 feet of their vehicle
during their diary day, as identified in Figure 8.
2. Lesser recharge potential: this segment includes the 23.7 percent of respondents
that did not identify a home recharging location in their diary day as specified
above, but elsewhere in the survey indicated they could potentially recharge at
one or more locations at least 8 hours over an average week.
3. No recharge potential: the remaining segment ( 23.9 percent) includes all
respondents that did not indicate they could potentially recharge their vehicle at
one or more locations for at least 8 hours in an average week.
Within each recharge segment, we compared interest in PHEVs as measured by whether
the respondent stayed with a conventional vehicle or designed a PHEV to be their next
new vehicle in the Purchase Design games described in Section 2.1 ( Figure 13). Among
respondents with higher home recharge potential, 64.1 percent designed a PHEV for
their next new vehicle in the “ high” price condition. Such “ purchases” of PHEVs are
more frequent across all recharge potential segments in the “ low” price condition than in
the “ high” price condition, by 11 to 16 percentage points. PHEV purchase intentions are
less frequent in segments with less demonstrated recharge potential, i. e., the lesser and no
Time of Day
% of Respondents with Access
% of Respondents Driving
Driving
Work
Other
Home
- 20-
recharge potential segments. Surprisingly, this decrease is only slight; relative to the
higher home recharge potential segment, purchase intention decreases by 3 percentage
points for the lesser recharge potential segment, and by 12 to 17 percentage points for
the no recharge potential segment. Regardless of the degree of demonstrated recharge
potential, the majority of respondents in each segment assigned significant value to a
vehicle with plug- in capabilities they designed.
Fig. 13: PHEV interest among three recharge segments ( all respondents, n
= 2,373)
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Higher Home
Recharge
Potential ( 52.4%)
Lesser Recharge
Potential ( 23.7%)
No Recharge
Potential ( 23.9%)
Segment Based on Recharge Potential
% of With Purchase Intention
" High" Price Game " Low" Price Game
Because recharge opportunities are relatively sparse at work and other non- home
locations, we isolate home recharging as the key criteria to characterize a potential early
PHEV market in this analysis. This constraint is substantiated by the experience of
drivers of PHEV- conversions reported by Kurani et al ( 2007). We feel that the higher
home recharge potential segment identified above provides a conservative yet realistic
sub- sample from which to explore the size of early PHEV markets; we limit further
consideration of the early PHEV market to the higher home recharge potential segment.
We further constrain this segment based on PHEV interest as indicated by purchase
intentions in the “ high” price condition. Thus, we select the 33.5 percent of respondents
that demonstrate both access to sufficient recharge infrastructure and PHEV interest as a
group best representing the early PHEV market. We will refer to this subset as the
potential early market respondents.
Focusing on the interests of these potential early market respondents, results of the two
PHEV design games are summarized in Figure 14. PHEV performance priorities varied
substantially; no single PHEV design emerged as a favorite of the majority. In Round
One of the Development Priority game, respondents were given one point to allocate
- 21-
towards one upgrade to the base PHEV model. As described in Section 2.1, four upgrades
were available: recharge time ( from 8 to 4 hours), gasoline- fuel economy during CD
operation ( from 75 to 100 MPG), CD distance ( from 10 to 20 miles), or CS gasoline- fuel
economy ( from 10 to 20 MPG over the conventional version of the vehicle). Improving
the CS gasoline- fuel economy was the most frequently chosen upgrade ( 41.1 percent). 3
The general ranking of attribute upgrades in Round One continues through later rounds: a
higher percentage of potential early market respondents designed PHEVs with CS MPG
upgrades than faster recharge times.
Fig. 14: Attribute selection in both design games ( early market potential
respondents only, n = 827)
0%
20%
40%
60%
80%
100%
Recharge
CD Type
CD Range
CS MPG
Recharge
CD Type
CD Range
CS MPG
Recharge
CD Type
CD Range
CS MPG
Recharge
CD Type
CD Range
CS MPG
Recharge
CD Type
CD Range
CS MPG
Recharge
CD Type
CD Range
CS MPG
Base Model
Recharge
CD Type
CD Range
CS MPG
Base Model
% Choosing Upgrade
Base Model
3rd Level Upgrade
2nd Level Upgrade
1st Level Upgrade
Game 1: Development Priority ( Points) Game 2: Purchase Design ($)
Round 1
( 1pt)
Round 2
( 2pt)
Round 3
( 4pt)
Round 4
( 6pt)
Round 5
( 8pt)
“ High”
Price
“ Low”
Price
All- electric operation ( in CD mode) was first offered to respondents in Round Three;
only 3.4 percent made this upgrade, which came at the expense of any other upgrades
available in prior rounds. In Round Four, the proportion of potential early market
respondents designing a PHEV with all- electric operation rose to 12.3 percent. Figure 15
portrays the 23 different possible PHEV designs possible in Round Four. This is the first
round providing a design envelope allowing respondents to choose a PHEV with 40 miles
of all- electric range— a vehicle similar to GM’s Volt concept. Only 4.7 percent of
potential early market respondents chose this specific design. Overall, all- electric
operation, a feature stated by some automakers to be essential to assure market success,
was not a chosen frequently when points were relatively scarce, i. e. in Rounds Three and
Four.
3 Although the percentages add up to 100 across the columns in Round One, they do not in further Rounds
because respondents have enough points to choose multiple upgrades.
- 22-
Fig. 15: Distribution of selected PHEV designs in Round Four of
Development Priority game ( early market potential respondents only, n =
827)
0% 10% 20% 30% 40% 50%
2 Hours_ 75 MPG_ 40 Miles_+ 30 MPG
1 Hours_ 75 MPG_ 40 Miles_+ 20 MPG
1 Hours_ 75 MPG_ 20 Miles_+ 30 MPG
4 Hours_ 100 MPG_ 40 Miles_+ 30 MPG
2 Hours_ 100 MPG_ 40 Miles_+ 20 MPG
2 Hours_ 100 MPG_ 20 Miles_+ 30 MPG
1 Hours_ 100 MPG_ 40 Miles_+ 10 MPG
1 Hours_ 100 MPG_ 20 Miles_+ 20 MPG
1 Hours_ 100 MPG_ 10 Miles_+ 30 MPG
8 Hours_ 125 MPG_ 40 Miles_+ 30 MPG
4 Hours_ 125 MPG_ 40 Miles_+ 20 MPG
4 Hours_ 125 MPG_ 20 Miles_+ 30 MPG
2 Hours_ 125 MPG_ 40 Miles_+ 10 MPG
2 Hours_ 125 MPG_ 20 Miles_+ 20 MPG
2 Hours_ 125 MPG_ 10 Miles_+ 30 MPG
1 Hours_ 125 MPG_ 20 Miles_+ 10 MPG
1 Hours_ 125 MPG_ 10 Miles_+ 20 MPG
8 Hours_ Electric Only_ 20 Miles_+ 20 MPG
8 Hours_ Electric Only_ 10 Miles_+ 30 MPG
4 Hours_ Electric Only_ 20 Miles_+ 10 MPG
4 Hours_ Electric Only_ 10 Miles_+ 20 MPG
2 Hours_ Electric Only_ 10 Miles_+ 10 MPG
8 Hours_ Electric Only_ 40 Miles_+ 10 MPG
As previously noted, results of the Purchase Design game suggest that the majority of
higher home recharge respondents ( 64.1 to 80.2 percent) would value PHEV capabilities
in their next vehicle. Figure 14 depicts the proportion of upgrades chosen in the price
conditions detailed in Section 2.1. A substantial portion of potential early market
respondents chose the base PHEV models with no upgrades— 38.8 percent in the high
price condition, and 26.5 percent in the low price condition. Among those that chose to
pay extra for upgrades, overall patterns are similar to the Development Priority game; CS
fuel economy upgrades were chosen more often than other upgrades, and there is no
evidence of the strong interest in all- electric operation observed among some pioneer
PHEV conversion drivers ( Kurani et al, 2007). All- electric upgrades were chosen by 1.5
and 5.7 percent of respondents in the high and low cost conditions, respectively.
However, unlike the tradeoff game, CD operation and range improvements were chosen
relatively less often, likely due to our representation of the added price of increasing
battery power and energy density.
% of Respondents Choosing Design
PHEV Design Combination:
( Recharge_ CD Type_ CD Range_ CS MPG) " Volt" Design:
Recharge = 8 hours
CD Type = Electric Only
CD Range = 40 miles
CS MPG = + 10 MPG
75 MPG
100
MPG
125
MPG
Electric
Only
- 23-
3.4 PHEV Energy Use Scenarios
To create scenarios of gasoline and electricity use among early PHEV buyers, we
integrate the information presented thus far from respondents in the higher home
recharge potential segment: driving behavior and recharge potential as recorded by their
24- hour diary, and PHEV design choices as demonstrated in the Purchase Design game.
In other words, we create scenarios of gasoline use and recharge patterns for each
potential early market respondent as if they were driving their chosen PHEV design on
their 24- hour vehicle diary day. These scenarios rely on the following assumptions:
• Gasoline use is modeled using the estimated miles per gallon ( MPG) of the
vehicle, without accounting for potential variation in driving patterns. In other
words, if the vehicle is rated at 50 MPG, we assume this constant rate for each
mile driven ( neglecting potential for different drive patterns over a given trip or
across drivers).
• For charge depleting ( CD) operation, electricity use ( kWh/ mile) and available
battery energy capacity ( kWh) is estimated as in Table 4, based on car estimates
from Kromer and Heywood ( 2007), scaled up to truck estimates based on Duvall
et al ( 2002).
• Each vehicle’s assumed battery state of charge at the beginning of the day is a
function of the distance driven the previous day ( assumed to be the same as the
diary day due to lack of multi- day data) and the respondent’s estimated hours of
recharge potential from the previous day ( elicited elsewhere on the survey).
• Following Lemoine et al’s ( 2008) assumptions, the minimum recharge rate for a
PHEV battery using a regular 110- 120 V outlet is 1 kWh per hour. If the
respondent’s chosen PHEV design has a recharge rate higher than that required
for their battery size, we apply the faster of the two recharge times. For example,
if the respondent chose a PHEV requiring 8 hours for complete recharge, yet their
battery size is only 1.9 kWh ( requiring a maximum of 1.9 hours for full recharge),
we apply the 1.9 hour time. In contrast, if the same respondent selected a recharge
time of one hour, we apply the one hour time.
• Following Lemoine et al’s ( 2008) assumptions, vehicle recharging is
approximately 83 percent efficient— increasing the battery’s state of charge by 1
kWh requires 1.2 kWh from the electrical outlet.
• Each scenario is scaled up to represent 1 million vehicles. This value is not
selected in anticipation of a particular sales volume for a particular year, but
instead is a relatively feasible market size that serves to normalize energy use to
allow comparisons across scenarios ( with different sample sizes). 4
• Vehicles are recharged on a daily basis as detailed in the scenario descriptions
below.
4 An alternative approach would be to estimate the effect of each recharge scenario on the size of the
potential PHEV market, such as the addition of potential PHEV buyers resulting from the expansion of
public vehicle recharge infrastructure, e. g. at the workplace. However, we leave such analyses to future
research, and instead focus on a set market size for each scenario.
- 24-
• The PHEVs are used precisely as were their non- PHEV variants; the scenarios are
based on replicating the travel- days as recorded in the diaries and do not allow for
households to change the assignment of vehicles within the household or
otherwise change vehicle use in response to the PHEV.
• We assume for this analysis that one- day cross- sectional data are adequate to
characterize travel and therefore energy impacts. One- day diaries systematically
under- represent longer travel unless the sampling is conducted according to the
frequency distribution of travel- day or trip distances across people and days. By
sampling across all seven days of the week we attempt to reduce the effect on our
analysis, but do not represent that it is immune. It seems plausible that we, and
anyone using one- day travel data, will underestimate total energy use and gasoline
use in particular. We leave the estimation of the size of this potential problem to
future research.
Table 4: Assumed PHEV specifications
CD mpg Car Truck
75 MPG CD electricity use
10 mile capacity
20 mile capacity
40 mile capacity
0.19 kWh/ mile
1.9 kWh
3.8 kWh
7.6 kWh
0.32 kWh/ mile
3.2 kWh
6.4 kWh
12.8 kWh
100 MPG CD electricity use
10 mile capacity
20 mile capacity
40 mile capacity
0.20 kWh/ mile
2.0 kWh
4.0 kWh
8.0 kWh
0.34 kWh/ mile
3.4 kWh
6.8 kWh
13.6 kWh
125 MPG CD electricity use
10 mile capacity
20 mile capacity
40 mile capacity
0.21 kWh/ mile
2.1 kWh
4.2 kWh
8.4 kWh
0.36 kWh/ mile
3.6 kWh
7.2 kWh
14.4 kWh
All electric CD electricity use
10 mile capacity
20 mile capacity
40 mile capacity
0.26 kWh/ mile
2.6 kWh
5.2 kWh
10.4 kWh
0.45 kWh/ mile
4.5 kWh
9.0 kWh
18.0 kWh
Following these assumptions, we created four scenarios using data from the 827 potential
early market respondents:
1. No PHEVs: In this scenario, we estimate and aggregate the gasoline used by the
respondents on their actual diary days.
2. Plug and Play: In this scenario, we simulate the gasoline used for driving and the
electricity used for recharging, allowing that the conventional vehicles are
displaced by a vehicle with the PHEV upgrades chosen in the “ high” or “ low”
price conditions of the Purchase Design game. Drivers are assumed to recharge
- 25-
whenever they are parked within 25 feet of an electrical outlet. In other words,
there are no pricing mechanisms, e. g., time of use electricity tariffs, or
technologies, e. g., smart charging mechanisms, to divert recharging to off- peak.
3. Enhanced Worker Recharging Access: This scenario starts with the conditions in
Plug and Play, but further supposes that all workers can recharge a vehicle at
work.
4. Off- Peak Only Recharging: Finally, using the same recharge potential and PHEV
designs as Plug and Play, in this scenario no PHEV recharging is allowed during
daytime peak hours ( 6am to 8pm). Smart charging technology is used to optimize
the timing of electricity use over this period, represented as a flat line ( the actual
shape of this line would likely vary according to the needs of a particular electric
utility).
Taken together, these scenarios are meant to represent potential boundary conditions, that
is, where the entire market adheres to a selected condition ( no regulation, enhanced
workplace policy, or off- peak charging). Of course, the early PHEV market may include
elements of more than one of these scenarios, as well as other potential conditions we do
not consider here, all of which are likely to change over time. However, the purpose of
this exercise is to present these boundary conditions to frame discussions of the potential
benefits and drawbacks of different recharge strategies and policies.
Figures 16 to 19 portray each scenario for respondents who completed weekday diaries
given the PHEV designs they selected in the “ high” price conditions. Results from
respondents with weekend day diaries, as well as “ low” price conditions PHEV designs,
are detailed in Table 5. Each figure depicts the time of day gasoline use ( gallons per
minute) and electricity use ( MW) per million vehicles over a 24- hour period. The area
under each curve represents the total gallons of gasoline, or MWh of electricity, used
over the day, respectively. In the Plug and Play scenario, most recharging occurs at home
locations, peaking at 6: 00pm at 596 MW ( 705 MW in the “ low” price condition)—
significantly lower than the 1,200 MW peak anticipated by Lemoine et al ( 2008) for 1
million PHEVs. Their higher peak electricity demand estimate is due to their assumptions
about a uniform PHEV design across the market ( 20 miles of all- electric CD range) and
relatively uniform recharging patterns of PHEV drivers. 5 In contrast, the present study
allows for substantial variation in PHEV designs and daily driving.
Time of day gasoline use corresponds with the rush hour periods observed in Figure 11.
These simulations indicate that in the Plug and Play scenario overall gasoline use is
estimated to cut gasoline by half relative to the No PHEV scenario ( Table 5). Notice that
gasoline use is reduced by a larger degree in the morning due to the higher proportion of
miles driven in CD mode earlier in the day. Table 5 also shows that a large portion of this
gasoline reduction ( 76 to 81 percent) is due to upgrades to CS fuel economy with CD
capabilities eliminated. 6 For this reason, overall gasoline savings varies little across the
5 In each recharge scenario presented by Lemoine et al ( 2008), PHEV drivers are assumed to begin
recharging at approximately the same time of day for the same duration.
6 However, simulating only CS fuel economy upgrades may be inappropriate— respondents might not have
chosen the vehicle upgrades without plug- in and CD capabilities.
- 26-
three charging scenarios or the price levels in the design game; in all instances, gasoline
use is cut in about half compared to the No PHEV scenario.
However, the peak magnitude and timing of recharging varies significantly across
scenarios. Figure 20 plots all three recharge scenarios. The Enhanced Worker Recharging
Access scenario increases overall electricity use by 34 percent relative to Plug and Play,
with much of the addition occurring in the morning as drivers arrive at work. In contrast,
the Off Peak Only scenario reduces electricity use by 16 percent, largely due to the
elimination of work and other non- home recharge opportunities that occur during peak
hours. Of course, this scenario has the benefit of eliminating all electricity use during
peak hours, with nightly demand balanced at 365 MW. As noted, the specific balancing
strategy used in this scenario would likely vary by electric utilities to flatten out overall
off- peak demand, as seen in Lemoine et al’s ( 2008) “ optimal charging” scenario. Our
scenario merely demonstrates the potential for shifting and minimizing peak demand.
Table 5: Summary of recharge scenarios, scaled to one million PHEVs
( early market potential respondents only, n = 827)
PHEV Design Game 2:
“ High” price
PHEV Design Game 2:
“ Low” price
Scenario Weekday
( n = 590)
Weekend
( n = 168)
Weekday
( n = 590)
Weekend
( n = 168)
No PHEVs Gasoline ( Gal.) 1,678,681 1,383,481 1,678,681 1,383,481
CS upgrade only Gasoline ( Gal.) 1,017,273 803,156 988,387 766,027
% Gas reduced 39.4% 41.9% 41.1% 44.6%
Plug and Play Gasoline ( Gal.) 866,830 660,561 821,488 567,867.3
% Gas reduced 48.4% 52.3% 51.1% 59.0%
Electricity ( MWh) 4,354 4,284 5,353 5,782
Peak ( MW) 596 384 705 520
Peak Time 6: 00pm 1: 45pm 6: 30pm 1: 45pm
Gasoline ( Gal.) 819,174 655,104 774,019 Enhanced 559,107
Worker access % Gas reduced 51.2% 52.6% 53.9% 59.6%
Electricity ( MWh) 5,815 4,488 6,861 6,042
Peak ( MW) 559 384 625 524
Peak Time 6: 00pm 1: 45pm 6: 30pm 1: 45pm
Off peak only Gasoline ( Gal.) 892,361 688,324 844,107 604,952
% Gas reduced 46.8% 50.2% 49.7% 56.3%
Electricity ( MWh) 3,647 3,533 4,633 4,815
Peak ( MW) 365 353 463 482
Peak Time 8pm- 6am 8pm- 6am 8pm- 6am 8pm- 6am
- 27-
Fig. 16: Gasoline use in “ No PHEV” scenario, scaled for one million
vehicles ( weekdays only, early market potential respondents only, n = 590)
12am 4am 8am 12pm 4pm 8pm 12am
0
500
1000
1500
2000
2500
3000
3500
Fig. 17: Energy use in “ Plug and Play” scenario, scaled for one million
PHEVs ( weekdays only, early market potential respondents only, n = 590)
0
100
200
300
400
500
600
700
12am 4am 8am 12pm 4pm 8pm 12am
0
500
1000
1500
2000
2500
3000
3500
Gal./ min per Gal./ min per Million Vehicles Million Vehicles
Time of Day
Time of Day
MW per Million PHEVs
Gas
Work
Other
Home
- 28-
Fig. 18: Energy use in “ Enhanced Worker Recharging Access” scenario,
scaled for one million PHEVs ( weekdays only, early market potential
respondents only, n = 590)
0
100
200
300
400
500
600
700
12am 4am 8am 12pm 4pm 8pm 12am
0
500
1000
1500
2000
2500
3000
3500
Fig. 19: Energy use in “ Off Peak Only” scenario, scaled for one million
PHEVs ( weekdays only, early market potential respondents only, n = 590)
0
100
200
300
400
500
600
700
12am 4am 8am 12pm 4pm 8pm 12am
0
500
1000
1500
2000
2500
3000
3500
Gal./ min per Gal./ min per Million Vehicles Million Vehicles
Time of Day
Time of Day
MW per Million PHEVs MW per Million PHEVs
Other Work
Gas
Work
Other
Gas
Home
Home
- 29-
Fig. 20: Comparing PHEV recharge scenarios, scaled for one million PHEVs
( weekdays only, early market potential respondents only, n = 590)
0
100
200
300
400
500
600
700
12am 4am 8am 12pm 4pm 8pm 12am
4. Discussion and Conclusions
Results from this analysis offer initial answers to our four research questions: anticipating
consumer awareness, recharge potential, design priorities, and energy impacts of the early
PHEV market. In regards to the last three, our simulated world contains far more variety
of PHEV designs than any prior study. This is an intentional difference, allowing
respondents to design the PHEV they would most desire given their current
understanding and valuation of four PHEV performance parameters. We believe this is a
more realistic representation of a plausible near future than the imposition of one or a few
PHEV designs on the entire population of vehicle drivers. Certainly as we analyze “ one-million
PHEV” scenarios— suggesting that we are attempting to analyze a world existing
a few years after the introduction of PHEVs— a world of greater variety is more plausible
than a world of one or a few PHEV designs. Our scenario analyses remain susceptible to
other threats endemic to such efforts. Radically changing travel behavior— in response to
fuel prices, competition from other alternatives, or in response to PHEVs themselves—
could invalidate our use of data on existing real travel. Rapid technology development
and cost reductions— or their delay— may render our design games under-, or over-optimistic.
And as discussed in the description of our recharging scenarios, none of them
likely capture precisely what will happen with workplace recharging, efforts to control
time of day of recharging, or efforts to provide home recharging to the one- third to nearly
one- half of new car- buying households who do not now find that where they park their
cars at home has access to electricity.
“ Off Peak Only”
( 3.6 GWh)
“ Enhanced
Worker Access”
( 5.8 GWh)
“ Plug and Play”
( 4.4 GWh)
MW per Million PHEVs
Time of Day
- 30-
4.1 Awareness of Electric Drive Vehicles
Acknowledging that vehicle buyers generally do not need intimate technological
understanding of a given vehicle to ensure purchase, we do suspect that basic levels of
awareness and understanding can play an important role in the introduction of a vehicle
that operates in a fundamentally new way and provides symbolic meanings not
previously available from motor vehicles. Responses to this survey suggest that presently
the majority of new vehicle buyers have little or no familiarity with the idea of a PHEV,
and may erroneously believe that existing hybrid- electric vehicles can perform the same
basic function of a PHEV, i. e., have the ability to be refueled by gasoline and to be
plugged into an electrical outlet. The latter finding is particularly surprising, given that
HEVs have been available in the U. S. auto market for almost a decade. These perceptions
of HEVs indicate there is both potential for misconceptions and confusion regarding the
availability and purported benefits of PHEVs and that such misconceptions may persist
for years. Potentially related to this is the further finding that respondents did not exhibit
a strong attraction to all- electric operation in CD mode for PHEVs. Given that the vast
majority of respondents have not experienced electric drive vehicles, they may have
limited understanding of potential benefits including functional attributes such as reduced
noise, vibration, emissions, and costs, as well as the personal and shared meanings that
have come to be associated with HEVs ( see Heffner, 2007 and Heffner et al 2007).
This lack of awareness and understanding is both a constraint and opportunity. As a
constraint, unaware consumers may simply fail to recognize or identify compelling
benefits of owning and operating a PHEV, serving as a soft constraint to limit the market.
On the other hand, the early PHEV market in the U. S. may be seen as a “ blank slate”,
with little preexisting understanding of what a PHEV is or expectations of what it should
be. Thus, the early actions of automakers, governments, electric utilities and other
stakeholders could play an important role in establishing perceptions in the market. For
example, despite the initial lack of PHEV awareness among our sample, once
respondents were provided with basic descriptions of the technology ( in the Plug- in
Buyers’ Guide provide to them as part of their survey), the majority expressed interest
during the design exercises. Similarly, the first commercially available PHEV
incarnations could set an early bar for consumer understanding and set expectations of
performance levels.
4.2 Recharge Potential and Timing
Based on the results reported here, we conclude that just more than half the population of
households that buy new cars has the potential to recharge a vehicle at home with at least
110- volt service. This estimate is one- and- a- half to three times larger than previous
estimates of home recharging potential in the entire population of American households
by Nesbitt et al ( 1992) and Williams and Kurani ( 2006). The reasons for this difference
are that the present analysis ( 1) targets new vehicle buying households rather than general
population of American households, and ( 2) draws information directly from the
respondent’s identification of recharge opportunities instead of relying on proxies from
U. S. Census or other data. Given their own observed driving and parking behavior, few
- 31-
drivers perceive an opportunity for non- home recharging opportunities, such as at their
workplace, friend’s and family’s homes, restaurants, etc. Therefore, we selected access to
home recharging as a key constraint for what we call the higher home recharge potential
segment. Within this segment we find that although a higher proportion of respondents
with single- family dwellings found home recharge opportunities than respondents in
other housing types ( attached, apartments or mobile homes), this condition is neither
necessary nor sufficient for recharge potential. We find a similar pattern for respondents
who typically park their vehicle in a private garage at home.
As previously assumed and reported, e. g., by Lemoine et al ( 2008), Duvall et al ( 2007),
Samaras and Meisterling ( 2008), and Hadley and Tsvetkova ( 2008), vehicle access to
recharge infrastructure as identified by diary respondents follows an inverse of the
diurnal pattern of driving activity. Recharge potential, that is, the spatial- temporal
correspondence between a parked vehicle and a 110- volt electrical outlet, peaks between
12am and 6am when most vehicles are parked at home and reaches a broad minimum
from 10am to 4pm when most vehicles are parked at work or other locations or being
driven.
The present analysis is useful in providing a plausible baseline for the early PHEV
market; but a baseline from which consumers, infrastructure and vehicle providers, and
policy makers can create change. Research suggests that with the right incentives,
consumers might locate more recharge locations, modify existing recharge locations, e. g.
clean up the home garage, and adjust driving patterns and adapt vehicle use among the
household fleet to maximize electricity use ( Kurani et al, 1996, 2007). Much adaptation
by consumers may not occur until after they purchase a PHEV, and their perceived
recharge potential that may lead to PHEV purchase may be based on existing driving
patterns, i. e., current perceptions of recharge locations.
Still, it may be possible to lead PHEV purchases by changing perceptions of the
availability of vehicle recharging, by actually increasing the availability of recharging for
those households who do not now find it and by improving the visibility and viability of
existing electrical infrastructure for vehicle recharging. Recharge infrastructure could
expand to a higher percentage of households with changes in building codes, as well as
increased employer and publicly installed vehicle recharge outlets.
4.3 Design Priorities
Among the respondents with at- home vehicle recharging, most constructed more
expensive vehicle designs that added plug- in capability to their next vehicle purchase
than did those without access to recharging. Given access to recharging and the
distribution of PHEV designs from the games, we estimate that about one- third of U. S.
new vehicle buying households have both the required infrastructure and interest to
purchase a vehicle with plug- in capabilities. The variety of PHEV designs created by
respondents suggests there is still ample opportunity for automakers to explore and
develop different PHEV designs.
- 32-
We observed a wide diversity of consumer interests in PHEV design options. Starting
with a base PHEV design offering long recharge times, short CD range, no all- electric
operation, but non- trivial increases in both CD and CS gasoline fuel economy, the most
popular upgrade category was to further improve fuel economy in CS mode. Respondents
also exhibited interest in increasing vehicle range in CD mode, and improving CD fuel
economy. Fewer respondents were willing to devote resources to reduce recharge time;
most potential early market respondents have access to periods of home- based charging
long enough to fully recharge each day even at the slowest offered rate.
We found little evidence of inherent demand for all- electric operation in CD mode, even
following the one- day diary, the tutorial on electric- drive vehicles, and PHEV design
games. An even smaller subset was interested in creating a vehicle with performance
attributes including 40 miles of all electric CD range. These patterns contrast with the
findings of Kurani et al’s ( 2007) interviews with “ pioneer” PHEV conversion drivers
who exhibited strong interest in maximizing CD range in all- electric mode— effectively
to approach the capabilities of pure electric vehicles. This difference suggests that while
all- electric CD operation may be particularly attractive to a small subset of consumers,
including those who are already knowledgeable and experienced with electric vehicles, at
this point in time most households who buy new vehicles are more interested in high fuel
economy.
Also, about one- third of the potential early market respondents who constructed a PHEV
variant of their likely next new car ( that they selected rather than a conventional version
of that car) chose no upgrades above the proffered base PHEV design. Overall, there may
be substantial potential for market success with less ambitious PHEV designs, i. e.
blended operation with shorter CD range but high CS fuel economy. This wide variety of
PHEV design selections further supports the notion of a “ blank slate” early PHEV
market, where early buyers may have little in the way of performance expectations.
Desired PHEV designs and capabilities may be subject to change. Survey respondents
had little pre- existing understanding of PHEVs and the responses we elicited may be
sensitive to the PHEV information we provided. As information about PHEV technology,
costs, benefits, and meanings are transmitted throughout the population, interest in
particular attributes and performances could shift. For example, all- electric CD operation
could become more meaningful to car buyers as they gain experience and as they
participate in the process of identifying just what all- electric operation means to people.
In the meantime, this analysis provides a baseline of market potential— one that could be
subject to influence. The messages and actions of policymakers, automakers, electric
utilities and other interest groups could have significant influence over future
development of awareness, recharge potential, design interests, and energy impacts of the
PHEV market.
4.4 Energy Impacts
The final analysis in this report combined all the available information from each
respondent— driving, recharge potential, and PHEV design priorities— to estimate the
- 33-
energy impacts of the respondents existing travel and understandings of PHEVs under a
variety of recharging scenarios. Results suggest that the use of PHEV vehicles could
halve gasoline use relative to conventional vehicles— the majority of this reduction being
due to increases in CS fuel economy. Using three scenarios to represent potential
boundary conditions on PHEV driver recharge patterns ( unconstrained, universal
workplace recharging, and off- peak only charging), we estimate tradeoffs between the
magnitude and timing of PHEV electricity use. In the unconstrained “ Plug and Play”
recharge scenario, recharging peaks at 6: 00pm, following a far more dispersed pattern
throughout the earlier part of the day than anticipated by Lemoine et al ( 2008) and
Hadley and Tsvetkova ( 2008). The more dispersed time- of- day recharging pattern in our
work is due to our ability to realistically account for heterogeneity in driving and parking
behavior and to allow for heterogeneity of PHEV designs. PHEV electricity use could be
increased through policies increasing non- home recharge opportunities ( e. g., the
“ Enhanced Worker Recharge Access” scenario), but most of this increase occurs during
daytime hours and could contribute to peak demand ( depending on a given region’s
definition of “ peak”). We also demonstrate how deferring all recharging to off- peak
hours ( 8pm- 6am) could eliminate all additions to daytime electricity demand from
PHEVs, similar to what Lemoine et al ( 2008) call “ optimal charging.” However, as also
found by Kurani et al ( 1997) for EVs, in this scenario less electricity is used due to the
elimination of daytime recharge opportunities and less gasoline is displaced.
This analysis provides one measure of the potential threat and opportunity for electric
utilities. The threat is that without control, the majority of recharging may occur during
peak hours ( 6am- 8pm), with a peak at 6pm during weekdays. This spike coincides with
seasonal peak electricity demand periods in some U. S. states and with a large enough
PHEV market, overall electricity generation requirements may be increased ( Lemoine et
al, 2008). However, the observed 12am- 6am recharge potential in late evening and early
morning presents an opportunity for “ smart charging” strategies in which PHEV
recharging ( as well as any other electrical load) can be shifted to off- peak periods subject
to varying levels of control by electricity users and suppliers.
Our scenarios are limited in that we do not represent recharge scenarios specific to the
various regions and electric utilities across the U. S. Instead we produce an aggregated
nationwide pattern without explicitly representing current electricity demand patterns,
i. e., without PHEVs. Our intention is to represent energy use according to general trends
rather than to provide a specific energy analysis for a given region. Further analysis will
be conducted based on our over- sample of California. Such refinement will be of
relevance to the California Energy Commission and the California Integrated System
Operator, though not for specific utilities even in California.
Acknowledgments
The authors would like to thank the California Energy Commission for funding this
project and the Social Sciences and Humanities Research Council of Canada.
- 34-
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Appendix A: Vehicle Diary Example
- 38-
Appendix B: Plug- in Vehicle Guide
Your Plug- In Vehicle Guide
Why read this guide?
Think of this as a 10 minute shopping guide. Part 3 of the ‘ Household
Vehicle Survey’ will allow you to design your own plug- in hybrid vehicle.
You will determine how this technology might fit into your household’s
lifestyle, if at all. This guide explains the design options you will be given in
Part 3.
This Guide Focuses on Plug in Hybrid Vehicles ONLY
A plug- in hybrid is a combination of an electric vehicle and a hybrid- electric
vehicle. Recall the descriptions you were provided in Part 1 of the survey:
Vehicle Type Description
A) Electric:
An electric vehicle is fueled by electricity only. It is charged by
plugging in to an electric outlet. The electricity is stored in the
vehicle until it is used to power the vehicle. This technology is
not currently produced by any major car companies, but a few
smaller companies do.
B) Hybrid- Electric:
A hybrid- electric vehicle is fueled by gasoline only. It uses a
hybrid- electric technology to use gasoline more efficiently. A
hybrid- electric vehicle can not be plugged in to an electric outlet.
This technology includes the Toyota Prius, which has become
quite popular in the US.
C) Plug- In Hybrid
A plug- in hybrid combines these two technologies. It can be
plugged in to an electric outlet to charge up with electricity, and
it can be filled with gasoline. A plug- in hybrid can run on
electricity only, gasoline only, or a combination of the two.
No car company currently sells this technology, although several
have plans.
(* Note: This guide refers to ‘ gasoline’ as your vehicle fuel, but this term includes whatever fuel your
current vehicle uses, including diesel or ethanol)
Your Plug- In Hybrid Guide:
Lesson 1: Refueling and Recharging …....…. p. 2- 3
Lesson 2: Gasoline Mode ( Driving Without Electricity) ………. p. 4
Lesson 3: Electric Mode ( Driving With Electricity) ………. p. 5- 6
Lesson 4: Upgrading Your Plug- In Vehicle ………. p. 7- 8
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Lesson 1: Refueling and Recharging
The plug- in hybrid is unique because it can be refueled with gasoline and
recharged with electricity. Unlike a basic electric vehicle, the plug- in hybrid
will still drive if it runs out of electricity ( as long as you have gasoline left).
Refueling and recharging your vehicle is simple:
Refuel
At a gas station.
Recharge
Using an electrical outlet.
Gasoline: Refueling
Refuel at any gasoline station. You have the same fuel tank you are used to,
which holds the same amount of gas. If you want, you could use only
gasoline all the time without ever plugging in, just like your current vehicle.
Electricity: Recharging
Recharge your vehicle using any normal electrical outlet ( 110- volt) – just
like you recharge your cell phone or laptop computer. These are the same
types of outlets you use for a TV or toaster. An outlet might be at home,
work, a store or a friend’s house, and would likely be outside or in a garage.
Why plug- in when I could just use gasoline?
Electricity is generally cheaper than gasoline… but it is difficult to say how
much cheaper. Gasoline prices change often, and electricity prices vary by
region, season, and other factors. In most regions today, driving with only
electricity would cost 60- 80% less per mile than driving with only gasoline.
This saving is like reducing your gas cost from $ 3.00/ gallon to around $ 1.00.
Also, driving with electricity usually causes less air pollution and
greenhouse gas emissions than driving with gasoline. The size of these
reductions depends on how your electricity is produced.
AND/ OR
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How long does it take to recharge?
Recharge time depends on the vehicle design you choose. An empty battery
could take 1 to 8 hours to fully recharge. In Part 3 of the survey, you will be
given the following four upgrade options when you design your own plug- in
hybrid vehicles:
1)
8 Hours
2)
4 Hours
3)
2 Hours
4)
1 Hour
Can I interrupt the recharging process?
Yes. For instance, if your vehicle requires 8 hours for a full charge, and you
unplug it after 2 hours, you will get one quarter of a full charge. Similarly,
you could plug it in for only 1 hour, or even 10 minutes.
EXAMPLES: Recharge Upgrades
Think of Paul and Sarah, two different drivers who each designed their own
plug- in hybrid vehicles. Each driver completed a Plug- In Vehicle Diary to
see what opportunities they have to recharge ( access to electrical outlets).
Paul’s family has only one place where they can recharge their vehicle: at
their home garage where they park every night. Because Paul can recharge
for 12 hours a day, he chose not to improve recharge time beyond 8 hours.
Sarah lives in an apartment building, where there are no electric outlets near
her parking spot. She drives around on business frequently during the day
time, where she may occasionally be parked near an electrical outlet for 1- 2
hours at a time. Because she has only brief opportunities to recharge, Sarah
chose to upgrade her plug- in vehicle recharge time to the quickest choice: 1
hour.
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Lesson 2: Gasoline Mode ( Driving Without Electricity)
All plug- in hybrid vehicles can drive without electricity. Once
the battery runs out, the vehicle continues by using gasoline only.
You could drive your plug- in vehicle without ever plugging in.
‘ Gasoline’ Mode: Efficiency Upgrade
A bonus of a plug- in hybrid vehicle is that once the electric charge runs out,
the vehicle switches to ‘ Gasoline’ mode and behaves just like a typical
hybrid electric vehicle ( like a Toyota Prius). This means that even if you
don’t plug- in, a plug- in hybrid vehicle uses less gasoline than a regular
vehicle. At a minimum, ‘ Gasoline’ mode will allow you to drive an extra 10
miles per gallon (+ 10 MPG) over a typical vehicle. If your current vehicle
can travel 27 miles with a gallon of gasoline, the plug- in version could travel
at least 37 miles.
You will have 3 options to improve the efficiency of ‘ Gasoline’ mode:
1) Current Vehicle
+ 10 MPG
2) Current Vehicle
+ 20 MPG
3) Current Vehicle
+ 30 MPG
Each improvement is relative to your current vehicle. If your current vehicle
can drive 30 miles per gallon of fuel, you can upgrade ‘ Gasoline’ mode
efficiency to 40, 50 or 60 miles per gallon.
EXAMPLES: Upgrading Gasoline Mode
Again think of Paul and Sarah, who both vehicles that originally had a fuel
efficiency of 27 miles per gallon ( MPG).
Paul’s family doesn’t drive in ‘ Gasoline’ mode very often because they can
recharge regularly at home. He chose the minimum upgrade of 37 MPG.
Sarah chose the maximum ‘ Gasoline’ mode upgrade of 57 miles per
gallon. She is interested in saving money, and she knows that on many days
she can’t recharge at all. She wants to maximize her fuel savings even when
she can’t use electricity.
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Lesson 3: Electric Mode ( Driving With
Electricity)
If you recharge your plug- in vehicle, you can drive for some
distance using electricity. Depending on your chosen design, electricity
would either reduce gasoline use ( Electric Assist) or replace gasoline use
( All Electric) for this limited distance.
Note: For all upgrades discussed in this guide, the vehicle’s performance
does not change. For instance, improving gasoline efficiency or electricity
use does not reduce acceleration, horsepower, top speed or towing ability.
Electric Assist: Reducing Gasoline Use
When recharged, a vehicle that is ‘ Electric Assist’ capable will use both
electricity and gasoline at the same time. The electricity helps the gasoline
engine, offsetting the gasoline required to drive. For instance, an average car
can travel 27 miles with a gallon of gasoline ( 27 MPG). However, a charged
plug- in hybrid can travel at a rate of at least 75 miles per gallon of gasoline
( 75 MPG), because the electricity is helping. Once the battery runs out, the
vehicle returns to using gasoline only. You will not be stuck!
There are 3 types of ‘ Electric Assist’ plug- in hybrid vehicles. More
advanced types use more electricity and less gasoline ( represented by the
changing size of the battery and gasoline icons in the diagrams below).
Type # 1: Electric Assist ( 75 MPG)
Where electricity helps the gasoline engine,
improving your gas mileage to 75 miles per
gallon ( MPG). Some gasoline is always required
to drive.
75 MPG
Electric Assist
Type # 2: Electric Assist ( 100 MPG)
Same as above, but improving your gas mileage
to 100 miles per gallon ( MPG). Some gasoline is
always required to drive
100 MPG
Electric Assist
Type # 3: Electric Assist ( 125 MPG)
Same as above, but improving your gas mileage
to 125 miles per gallon ( MPG). Some gasoline is
always required to drive
125 MPG
Electric Assist
- 43-
All Electric: Temporarily Replacing Gasoline Use
A fourth type of electric design is ‘ All Electric’ capable. This technology is more
advanced than the ‘ Electric Assist’ options because electricity can fully replace the
use of gasoline for a limited distance. Once the battery has run out, the vehicle
returns to using gasoline only. You will not be stuck!
Type # 4: All Electric
Where electricity is temporarily used instead
of gasoline. As long as the vehicle is
charged up, no gasoline is required to drive. All Electric
How long does the Electric Charge last?
You can choose the distance your electric charge will last. This distance does not
change if you choose Type # 1, # 2, # 3 or # 4. You can choose to have a full charge
last for the first 10, 20 or 40 miles of travel. Beyond this distance, your vehicle
returns to ‘ Gasoline’ mode. If you choose 20 miles, your fully charged vehicle will
drive in electric mode for the first 20 miles (‘ Electric Assist’ or ‘ All Electric’).
When Fully Charged
Drive in ‘ Electric Assist’ or ‘ All Electric’ Mode:
1) For the First
10 Miles
2) For the First
20 Miles
3) For the First
40 Miles
EXAMPLES: Upgrading Electric Mode and Electric Distance
Again think of Paul and Sarah, two different plug- in hybrid owners.
Paul likes the idea of driving an electric car in the city, so he chose a ‘ Type # 4: All
Electric’ capable vehicle. He lives 6 miles from work ( 12 miles round trip), so he chose a
vehicle with 10 miles of distance per charge. He can recharge each night, then commute
to work, and most of the way home with only electricity. His vehicle switches to
‘ Gasoline’ mode for the last 2 miles of his commute.
Sarah does not care if she uses gasoline or electricity; she just wants to save money. She
chose the ‘ Electric Assist’ capability, as she doesn’t think ‘ All- Electric’ mode is worth
the extra cost. She chose ‘ Type # 2: Electric Assist ( 100 MPG)’ so she can drive at a rate
of 100 miles per gallon of gasoline ( MPG). She also chose to upgrade to 40 miles of
distance per charge, because she knows she cannot recharge regularly.
- 44-
Lesson 4: Upgrading Your Plug- In Vehicle
Minimum Upgrade Package
In Part 3 of the survey, you will use an interactive diagram to design your ideal plug- in
hybrid vehicle ( given different constraints). The diagram below shows the baseline plug-in
upgrade package you will be shown, with the minimum values shown for each option:
This plug- in hybrid vehicle requires 8 hours to fully recharge. When charged, it can drive
with ‘ Type # 1: Electric Assist ( 75 MPG)’ for the first 10 miles. After 10 miles, the
vehicle switches to gasoline mode, which can travel 10 more miles per gallon ( MPG) of
gasoline than your current vehicle.
Your Plug- In Hybrid
Vehicle
Upgrades
Recharge Time:
8 Hours
Time to Fully Recharge:
● 8 Hours
○ 4 Hours
○ 2 Hours
○ 1 Hour
Electric Capability:
● Type # 1: Electric Assist ( 75 MPG)
○ Type # 2: Electric Assist ( 100 MPG)
○ Type # 3: Electric Assist ( 125 MPG)
○ Type # 4: All Electric
Electric Mode:
75 MPG
Electric Assist
For the First
10 Miles
Distance With Electric Capability:
● First 10 miles
○ First 20 miles
○ First 40 miles
Gasoline Mode:
Your Vehicle + 10 MPG
Gasoline Use:
● + 10 Miles Per Gallon
○ + 20 Miles Per Gallon
○ + 30 Miles Per Gallon
- 45-
EXAMPLES:
Here is a summary of the plug- in upgrades Paul and Sarah chose:
Paul’s family chose a plug- in vehicle that takes 8 hours to fully recharge. When
fully charged, the vehicle can drive without any gasoline ( Type # 4: All Electric)
for the first 10 miles. After 10 miles ( unless recharged), the vehicle runs out of
electricity and uses gasoline only ( 37 MPG), but still saves fuel compared to a
regular vehicle (+ 10 miles per gallon).
Sarah chose a plug- in vehicle that takes only 1 hour to recharge. The fully
charged vehicle can drive with Electric Assist ( Type # 2) for 40 miles, using
electricity to boost fuel economy up to 100 miles per gallon. After 40 miles, the
vehicle switches to gasoline only, where her vehicle can travel an extra 30 miles
per gallon of gasoline ( 57 MPG) compared to a typical vehicle.
Paul’s Upgrades Sarah’s Upgrades
Recharge Time:
8 Hours
Recharge:
● 8 Hours
○ 4 Hours
○ 2 Hours
○ 1 Hour
Recharge Time:
1 Hour
Recharge:
○ 8 Hours
○ 4 Hours
○ 2 Hours
● 1 Hour
Electric:
○ Type # 1
○ Type # 2
○ Type # 3
● Type # 4
Electric:
○ Type # 1
● Type # 2
○ Type # 3
○ Type # 4
Electric Mode:
All Electric
For the First
10 Miles
Distance:
● 10 miles
○ 20 miles
○ 40 miles
Electric Mode:
100 MPG
Electric Assist
For the First
40 Miles
Distance:
○ 10 miles
○ 20 miles
● 40 miles
Gasoline Mode:
37 MPG
Gasoline:
● + 10 MPG
○ + 20 MPG
○ + 30 MPG
Gasoline Mode:
57 MPG
Gasoline:
○ + 10 MPG
○ + 20 MPG
● + 30 MPG
Now think about your household. Which upgrades are
important? Please consult with your family to prioritize these
upgrades.
- 46-
Appendix C: PHEV Design Games
Section 3: Designing Your Plug- In Vehicle
Now, Imagine that... you have a just won a contest to upgrade your MINI COOPER
into a plug- in hybrid vehicle, allowing you to use electricity to drive, using less gasoline.
This upgrade promises that everything else about your vehicle will stay the same
( appearance, performance, safety, warranty, etc.).
Remember, A Plug- in Hybrid is... a vehicle that can be powered by either: electricity
( from an electrical outlet), gasoline ( like a typical vehicle), or a combination of both, as
shown below:
Electricity Only
OR
Gasoline Only
OR
Both Electricity and Gasoline
You Have Choices... because your ' Plug- in Prize' allows you to choose what kind of
battery upgrade you receive. But first...
First We Need to Know...
What is the average fuel economy of your MINI COOPER in miles per gallon ( MPG)?
Choose a value that is the average of city/ highway driving.
( Remember, a higher MPG means you are required less fuel to drive a given distance.)
21 MPG - About average for a new truck
27 MPG - About average for a new car
28 MPG - About average for a basic MINI COOPER
Other - Please Specify: MPG
Next
- 47-
Now you have the opportunity to upgrade your vehicle. You can upgrade your plug- in
vehicle in four different ways, as described in Your Plug- In Vehicle Guide. Please
consult this document for explanations if you need help.
Each upgrade requires a certain number of  points  . We want to know what upgrades
you consider to be most important. You will be shown 5 scenarios. Each scenario will
give you a different number of  points  to make upgrades. Each scenario is
independent, so you can choose different upgrades each time.
Scenario # 1: If you have 1 point to make an upgrade, how would you use
it?
Please be realistic. Consider how your household uses this vehicle, and where you have
access to electrical outlets, if at all ( from your plug- in diary).
Make your selection( s) in the Upgrade column to use your points, then click ' This is My
Choice' when you are finished.
Your choice is visually represented in the left column.
- 48-
Description of Your Choice:
The above vehicle takes 8 hours to recharge. When fully recharged, it can be driven for
the first 10 miles in Type # 1: Electric Assist ( 75 MPG) mode. After this distance, it can
only be driven in gasoline mode until recharged, getting 33 Miles Per Gallon.
This is My Choice
- 49-
Scenario # 2: If you have 2 point to make an upgrade, how would you use
it?
Description of Your Choice:
The above vehicle takes 8 Hours to recharge. When fully recharged, it can be driven for
the First 10 miles in Type # 1: Electric Assist ( 75 MPG) mode. After this distance, it
can only be driven in gasoline mode until recharged, getting 58 Miles Per Gallon
This is My Choice
- 50-
Scenario # 3: If you have 4 point to make an upgrade, how would you use
it?
Description of Your Choice:
The above vehicle takes 8 Hours to recharge. When fully recharged, it can be driven for
the First 10 miles in Type # 4: All Electric mode. After this distance, it can only be
driven in gasoline mode until recharged, getting 38 Miles Per Gallon
This is My Choice
- 51-
Scenario # 4: If you have 6 point to make an upgrade, how would you use
it?
Description of Your Choice:
The above vehicle takes 8 Hours to recharge. When fully recharged, it can be driven for
the First 40 miles in Type # 4: All Electric mode. After this distance, it can only be
driven in gasoline mode until recharged, getting 38 Miles Per Gallon
This is My Choice
- 52-
Scenario # 5: If you have 8 point to make an upgrade, how would you use
it?
Description of Your Choice:
The above vehicle takes 4 Hours to recharge. When fully recharged, it can be driven for
the First 40 miles in Type # 4: All Electric mode. After this distance, it can only be
driven in gasoline mode until recharged, getting 48 Miles Per Gallon
This is My Choice
- 53-
Section 4: Next Vehicle Purchase
This section will present a game to simulate your household's next new vehicle purchase.
First, we ask several questions about your household's intentions.
1) Which of the following statements best summarizes your household's plans to
purchase your next new vehicle?
My household has...
... already picked out our next vehicle
... discussed a few different vehicles models, but has not yet decided on one
... a rough idea of what vehicle to buy next, but has not yet looked around
... not yet thought about our next vehicle
2) How soon do you believe your household will buy or lease its next new vehicle?
Within the next 6 months
Between 6 months and 1 years from now
Between 1 and 2 years from now
Between 2 and 5 years from now
More than 5 years from now
We have no idea.
3) Which of the following best describes your next vehicle purchase?
The next vehicle my household purchases will...
... replace the MINI COOPER
... replace another vehicle
... not replace any vehicle, but will be an addition
We have no idea.
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4) When your household buys or leases its next new vehicle, which of the following
descriptions best describes the vehicle type you will likely choose?
Compact car
Midsize Car
Large Car
Small SUV
Midsize SUV
Large SUV
Minivan
Cargo van
Small pickup truck
Large pickup truck
We have no idea
Next
5) For this last section, we will refer to the type of vehicle your household will likely buy
or lease next. Please select a make and model that best describes your next vehicle. If you
are unsure, you can simply select your current vehicle ( MINI COOPER).
I choose MINI COOPER
I would like to select another vehicle. Please specify Make and Model:
Example:
Make = Honda
Model = Accord
Make:
Make
Model:
Model
Click here if your vehicle isn't listed above.
Next
From here on, we assume that your household's next vehicle purchase will be a new
FORD MUSTANG.
- 55-
6) About how much do you think your household will spend to buy this FORD
MUSTANG?
$ 27000 - About the base cost of a FORD MUSTANG
Another value - Please Specify: Thousand
7) What do you think will be the approximate fuel economy ( Miles Per Gallon - MPG) of
this FORD MUSTANG you will buy?
Choose a value that is the average of city/ highway driving.
( Remember, a higher MPG means you required less fuel to drive a given distance.)
21 MPG - About average for a new truck
27 MPG - About average for a new car
28 MPG - About average for your basic MINI COOPER
25 MPG - About average for brand new 2007 basic FORD MUSTANG
Another value - Please Specify: MPG
Next
You will be shown 3 scenarios. Each scenario you will show you different prices for the
plug- in hybrid options and upgrades. Each scenario is independent, so you can choose
different vehicles or upgrades each time.
You can customize the specific features of the plug- in version, just as you did in the
previous exercise. Again, refer to Your Plug- In Vehicle Guide for help in choosing
upgrades, particularly the summary on pages 7 to 8.
Given the two options below, which would your household likely purchase?
Other than the price, the plug- in feature, and fuel consumption, every other characteristic
of the two vehicles are identical. In other words, the plug- in version of the FORD
MUSTANG has the same body, performance, interior size, etc. as the regular FORD
MUSTANG.
Please be realistic, and consider your expected household budget constraints
- 56-
Price Scenario # 1 ( Low Cost Scenario – Order Randomized)
This is My Choice
- 57-
Price Scenario # 2 ( Medium Cost Scenario – Order Randomized)
This is My Choice
- 58-
Price Scenario # 3 ( High Cost Scenario – Order Randomized)
This is My Choice