Study measures which kinds of infrastructure improvements could lead to wider adoption of clean vehicles.
By David L. Chandler, MIT News Office
January 21, 2021 -- A new study from researchers at
MIT uncovers the kinds of infrastructure improvements that would make the
biggest difference in increasing the number of electric cars on the road, a key
step toward reducing greenhouse gas emissions from transportation.
The
researchers found that installing charging stations on residential streets,
rather than just in central locations such as shopping malls, could have an
outsized benefit. They also found that adding on high-speed charging stations
along highways and making supplementary vehicles more easily available to
people who need to travel beyond the single-charge range of their electric
vehicles could greatly increase the vehicle electrification potential.
The findings
are reported today in the journal Nature Energy, in a paper by MIT
associate professor of energy studies Jessika Trancik, graduate student Wei
Wei, postdoc Sankaran Ramakrishnan, and former doctoral student Zachary Needell
SM ’15, PhD ’18.
The
researchers developed a new methodology to identify charging solutions that
would conveniently fit into people’s daily activities. They used data collected
from GPS tracking devices in cars, as well as survey results about people’s
daily driving habits and needs, including detailed data from the Seattle area
and more general data from the U.S. as a whole. Greatly increasing the
penetration of electric cars into the personal vehicle fleet is a central
feature of climate mitigation policies at local, state, and federal levels,
Trancik says. A goal of this study was “to better understand how to make these
plans for rapid vehicle electrification a reality,” she adds.
In deciding
how to prioritize different kinds of improvements in vehicle charging
infrastructure, she says, “the approach that we took methodologically was to
emphasize building a better understanding of people’s detailed energy consuming
behavior, throughout the day and year.”
To do that,
“we examine how different people are moving from location to location
throughout the day, and where they are stopping,” she says. “And from there
we’re able to look at when and where they would be able to charge without
interrupting their daily travel activities.”
The team
looked at both regular daily activities and the variations that occur over the
course of a year. “The longitudinal view is important for capturing the
different kinds of trips that a driver makes over time, so that we can
determine the kinds of charging infrastructure needed to support vehicle
electrification,” Wei says.
While the vast
majority of people’s daily driving needs can be met by the range provided by
existing lower-cost electric cars, as Trancik and her colleagues have reported,
there are typically a few times when people need to drive much farther. Or,
they may need to make more short trips than usual in a day, with little time to
stop and recharge. These “high-energy days,” as the researchers call them, when
drivers are consuming more than the usual amount of energy for their
transportation needs, may only happen a handful of times per year, but they can
be the deciding factor in people’s decision making about whether to go
electric.
Even though
battery technology is steadily improving and extending the maximum range of
electric cars, that alone will not be enough to meet all drivers’ needs and
achieve rapid emissions reductions. So, addressing the range issue through
infrastructure is essential, Trancik says. The highest-capacity batteries tend
to be the most expensive, and are not affordable to many, she points out, so
getting infrastructure right is also important from an equity perspective.
Being
strategic in placing infrastructure where it can be most convenient and effective
— and making drivers aware of it so they can easily envision where and when
they will charge — could make a huge difference, Trancik says.
“There are
various ways to incentivize the expansion of such charging infrastructures,”
she says. “There’s a role for policymakers at the federal level, for example,
for incentives to encourage private sector competition in this space, and
demonstration sites for testing out, through public-private partnerships, the
rapid expansion of the charging infrastructure.” State and local governments
can also play an important part in driving innovation by businesses, she says,
and a number of them have already signaled their support for vehicle
electrification.
Providing easy
access to alternative transportation for those high-energy days could also play
a role, the study found. Vehicle companies may even find it advantageous to
provide or partner with convenient rental services to help drive their electric
car sales.
In their
analysis of driving habits in Seattle, for example, the team found that the
impact of either adding highway fast-charging stations or increasing
availability of supplementary long-range vehicles for up to four days a year
meant that the number of homes that could meet their driving needs with a lower
cost electric vehicle increased from 10 percent to 40 percent. This number rose
to above 90 percent of households when fast-charging stations, workplace
charging, overnight public charging, and up to 10 days of access to
supplementary vehicles were all available. Importantly, charging options at
residential locations (on or off-street) is key across all of these scenarios.
The study’s
findings highlight the importance of making overnight charging capabilities
available to more people. While those who have their own garages or off-street
parking can often already easily charge their cars at home, many people do not
have that option and use public parking. “It’s really important to provide
access — reliable, predictable access — to charging for people, wherever they
park for longer periods of time near home, often overnight,” Trancik says.
That includes
locations such as hotels as well as residential neighborhoods, she says. “I
think it’s so critical to emphasize these high-impact approaches, such as
figuring out ways to do that on public streets, rather than haphazardly putting
a charger at the grocery store or at the mall or any other public location.”
Not that those aren’t also useful, she says, but public planning should be
aiming to expand accessibility to a greater part of the population. Being
strategic about infrastructure expansion will continue to be important even as
fast chargers fall in cost and new designs begin to allow for more rapid
charging, she adds.
The study
should help to provide some guidance to policymakers at all levels who are
looking for ways to facilitate the reduction of greenhouse gas emissions, since
the transportation sector accounts for about a third of those emissions
overall. “If you have limited funds, which you typically always do, then it’s
just really important to prioritize,” Trancik says, noting that this study
could indicate the areas that could provide the greatest return for those
investments. The high-impact charging solutions they identify can be mixed and
matched across different cities, towns, and regions, the reseachers note in
their paper.
The
researchers’ approach to analyzing high-resolution, real-world driving patterns
is “valuable, enabling several opportunities for further research,"
says Lynette Cheah, an associate professor of engineering systems and
design at Singapore University of Technology and Design, who was not
associated with this work. “Real-world driving data can not only guide
infrastructure and policy planning, but also optimal EV charging management and
vehicle purchasing and usage decisions. … This can provide greater confidence
to drivers about the feasibility and operational implications of switching to
EVs.”
The study was
supported by the European Regional Development Fund, the Lisbon Portugal Regional
Development Program, the Portuguese Foundation for Science and Technology, and
the U.S. Department of Energy.
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