IEEE Electrification - September 2020 - 89

2019, there were roughly 1.2 million EVs out of 270 million
registered vehicles in the United States.
The impact of EV charging/discharging has been
documented as amending the net thermal load toward
lowering ramping-flexibility requirements and the
additional services provided by thermal units. Principally, EVs store energy for daily transportation. It is
necessary and expected to have EVs charged before
departure and for them to remain partially charged at
any time during the day for emergency transportation
purposes. Thus, a limited volume of EVs' stored energy
can be counted on for delivering ancillary services.
Furthermore, vehicles are not always connected to the
distribution network, as they are traveling, are on
roads, or are parked at unequipped venues where they
are inaccessible as ancillary service providers to power
distribution systems. In contrast, stationary energy
storage devices could be entirely available to generate/
absorb active/reactive powers as fast as are renewable
energy variations.
Ignoring network losses, stationary energy storage
units are, ideally, more dependable than EVs for providing
energy when it is needed. However, the massive deployment of EVs can reverse these arguments quickly. Customer-site storage units can work with EV storage units
to properly balance the net power of on-site generation
and impede the technical challenges that originate from
reverse power flow occurrences. Otherwise, utilities
might have to convert the electricity grid's operation to
those with two-way flows to support net-metering
requests, which will be an expensive and time-consuming mandate.
Large-scale EV utilization would subside carbon dioxide emissions from both the transportation and electricity-generation sectors. The electrification of
transportation can eliminate carbon emissions in densely
populated urban areas, which is very important for public
health and clear air. This is the major social benefit
achieved through EV deployment, but the monetary
assessment may not be as straightforward because 1) the
health issues caused by air pollution usually arise over a
long period of time, 2) transportation is not the only
source of emissions, and 3) individual societies are faced
with other dynamics in terms of people who are exposed
to air pollution. In this regard, the degree to which EV
adoption can achieve carbon reduction will largely
depend on how the electricity supplied to EVs is generated, how intelligently EV charging is managed, and to
what extent power plant emissions are mitigated and the
power grid is controlled.
The use of renewable energies for charging EVs is a key
consideration for carbon reductions. Coordinating the
transportation and power utility sectors is an effective and
favorable strategy to augment the extensive penetration of
solar PV units and promote the large-scale utilization of
EVs. The decoupling of electricity and transportation

infrastructures from their significant dependence on oil-
the chief cause of greenhouse gas emissions-would
facilitate positive socioeconomic changes in various parts
of the world. Meticulous and inclusive modeling efforts
incorporating various credible scenarios of meteorological
conditions, EV power charging/discharging, and transportation systems are, in essence, applicable to the optimal
planning of both electrical and transportation systems.
However, it is rather unlikely that any advancements solely in EV technology can lead this transformation; rather, a
novel harmonization of the transportation and energy
sectors is needed to realize the practical aspects of smart
EV charging/discharging.
The lack of coordinated charging in a large fleet of EVs
can influence power grid operation, control, and economics
adversely, especially at the distribution level. Because the
driving habits of EV owners in terms of departure and arrival times are similar to some extent, the uncontrolled charging of a large number of EVs could lead to increased feeder
losses, voltage deviations, the overloading of distribution
transformers, and so on. Other studies have shown that the
uncoordinated charging of large-scale EVs can strain distribution grids, requiring the upgrading of, among others, distribution transformers, which are traditionally designed to
be off-loaded at off-peak hours to cool down the cycling oil.
In contrast, sizable numbers of EVs could present a
large potential for demand response in power distribution
networks, which could enhance EV charging-cycle flexibility in coordination with distribution network loading. EVs
can use smart charging strategies to present unique opportunities, offering ancillary services to often-stressed local
distribution grids. EV aggregation and charging/discharging
coordination could go beyond the power distribution level,
where smart grid strategies can support transmission system operations for frequency/voltage control, the judicious
flattening and reshaping of the aggregated load profile, and
contingency management without sacrificing the security
of local distribution power systems.

The Use of Vehicle to Vehicle and Vehicle to Grid
as Transactive Energy in EV Portfolios
The proliferation of EVs could enhance the contributions of
variable rooftop solar both at home and at the grid level.
The EV charging process could be scheduled for the daytime hours, when EV owners are most likely at work, to fill
up the duck curve's belly. In this sense, the peak-to-valley
load difference gets smaller and additional thermal units
will remain online during the daytime hours. More importantly, the late-evening charging hours can be intensified to
partially reduce the tension on the distribution grid during
the daytime hours. The provision of EV alternatives could
lower ramping-flexibility requirements in which less-flexible thermal units have a longer time to ramp up their generations and participate in serving peak-hour demands.
EV chargers converting ac to dc power can be designed
to work in a reverse direction by sending power back to

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IEEE Electrification - September 2020

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