IEEE Power & Energy Magazine - July/August 2021 - 20

table 1. A summary of the trial stages.
Trial Stage
Outside of
management
Trial 1: blind
Trial 2:
interactive
Trial 3:
incentivized
Was Demand
Management
Active if the
Demand
Exceeded
Capacity?
No
Yes
Yes
Were Participants
Informed
When Demand
Management
was Active?
-
No
No; available
only to GreenFlux
participants in the
app interface
Yes
No; available
only to GreenFlux
participants in the
app interface
Could the
Participants
Interact With
the Smart
Charging
Systems?
-
No
Yes
Financial
Rewards/
Penalties
-
No
No
What Time Does
Charging Occur?
Figure 4 depicts the percentage of
all the charging events that began
in each hour of the day. Trial 3
strongly affected the time when
the charging began and is excluded
from the graph as it does not represent
baseline charging behavior.
Figure 4 shows a peak in chargYes
Yes;
linked
to the time
when the
charging
took place
16
14
12
10
8
6
4
2
Weekday Weekend
ing sessions beginning in the early
evening, particularly on weekdays.
This is likely to arise as drivers
come home from work and plug
in their vehicles. EV charging in
the early evening coincides with
the existing network peak in residential
areas. This indicates that
flexibility may be required to defer
or avoid the need for network reinforcement
to accommodate the
additional load.
0123456789 10 11 12
Starting Hour Number
13 14 15 16 17 18 19 20 21 22 23
figure 4. The distribution of charging start times for weekdays and weekends.
table 2. The median charging frequency by vehicle
type and battery capacity.
Category
All participants
Vehicle type
PHEV
Range
extender EV
BEV
Battery capacity
Fewer than
10 kWh
10-25 kWh
25-35 kWh
35 kWh
and higher
20
ieee power & energy magazine
Median Charging
Frequency (Charge
Sessions Per Day)
0.52
0.76
0.45
0.39
0.73
0.63
0.39
0.31
How Often Do Drivers
Charge Their EVs?
How often EV drivers charge their
vehicle contributes to the diversity
of the charging load. For example,
the distribution in Figure 4 demonstrates
that charging events are
clustered around the evening peak.
If all the drivers plugged in every
day, then the resulting additional
peak time load would be much
higher than if drivers plugged in
less frequently. Table 2 lists the
median charging frequency for
the Electric Nation participants, according to vehicle type
and battery capacity.
This shows that, across the trial population, drivers
charge approximately every other day. Only 15% of the participants
charged their vehicle at least once a day, and this
group was dominated by PHEV drivers (72% of the group).
The data from Electric Nation show that drivers with
lower weekly mileages (fewer than 200 mi) were significantly
more likely to have a lower charging frequency (fewer
than 1.6 times a week) than those with higher mileages. In
2019 in the United Kingdom, the average annual car mileage
was 7,400 mi (National Travel Survey Table NTS0901),
which is equivalent to 20 mi per day or 142 mi per week.
Charging frequency decreases for larger battery capacities
as the distance the participant could drive before needing
to recharge is greater. Newer EVs typically have larger
battery capacities, so the charging frequency is unlikely to
increase in the future.
july/august 2021
Percentage of Charge Events
Starting in Hour Number
IEEE Power & Energy Magazine - July/August 2021

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - July/August 2021
