IEEE Power & Energy Magazine - July/August 2021 - 24

not occur. The demand in the early hours of the morning
(12 a.m. until 4 a.m.) was higher than either trial 1 or 2 but
returned to similar levels after this point.
Figure 8 demonstrates that the combination of financial
incentives and the app deployed by GreenFlux was successful
in encouraging participants to be flexible with their
charging load, thus reducing the increase in peak demand
compared to other periods in the trial. The remainder of this
section describes how this was achieved.
The simulated ToU tariff was based on the Octopus (a
U.K. energy supplier) Agile tariff pricing. The tariff was
applied to only the energy used by the participants' EV charger
and was given in the form of a reward value, which was
converted to a gift card/voucher at the end of the trial. Each
participant began trial 3 with a £10 reward value. Table 4
table 4. Electric Nation's ToU reward tariff.
Period Time Period
Night
Day
Peak
Evening
taper
Electricity Cost
(£) Per Unit
(kWh)
10 p.m.-6:30 a.m.
6:30-4:30 p.m.
4:30-7 p.m.
7-7:30 p.m.
7:30-8 p.m.
8-8:30 p.m.
8:30-9 p.m.
9-10 p.m.
.10
.12
.28
.22
.18
.14
.12
.11
Change in
Reward
Value (£)
Per Unit
(kWh)
Used
+.05
+.03
−.13
−.07
−.03
+.01
+.03
+.04
outlines the tariff and the impact that charging in different
periods had on participants' reward value.
The GreenFlux participants could download a smartphone
app that enabled them to set a charging preference (governing
the times of day when their home charger could operate),
which is linked to the pricing periods in Table 4. A total of
82% of participants downloaded the app by the end of trial 3.
The app was a set-and-forget system, meaning that the preference
applied to all the charging events at the home charger
until the setting was changed. Table 5 details the three preferences
and statistics about the level of usage of each.
By the end of trial 3, 61% of the participants had used the
app at least once to change their charging preference. The key
findings from trial 3 included the following:
✔ There were no statistically significant differences in
the time that the participants plugged in their vehicles
during trial 3 (compared to the rest of the trial). Either
the app or the timers were used to avoid charging during
the peak time.
✔ The participants who used the app achieved the greatest
change in their charging behavior during the evening
peak. Before trial 3, 44% of this group's weekday
charging events began between 4 p.m. and 7:59 p.m.,
reducing to 18% during trial 3.
✔ 77% of participants had a smaller proportion of their
charging events occurring in the weekday evening
peak in trial 3 compared to the rest of the project.
✔ The following groups were significantly more likely
to use the charging preferences offered in the app to
avoid charging in the evening peak compared to the
population as a whole:
* those who bought their vehicle (68% compared to 53%)
* the participants whose motivations for getting an EV
included " lower running costs " (64%), " desire for
the latest technology " (72%), and " easier/smoother
drive " (73%)
* those who also charged their vehicle at work (83%).
table 5. The charging preferences
in GreenFlux trial 3.
Preference
Name
Optimize
time (default
option)
Optimize time
and cost
Impact of
Charging
Preference
No
restrictions
No charging
between
4:30 p.m.
and 7 p.m.
Minimize cost No charging
between
4:30 p.m.
and 10 p.m.
24
ieee power & energy magazine
Percentage
of Trial 3
Charging
Events
on Each
Preference
54
6
Percentage of
Participants
Using This
Option Most
Frequently
47
6
40
47
✔ During a focus group at the end of the trial, the
participants were asked what percentage reduction
in the cost of charging their EV would incentivize
them to continue to allow smart charging. The responses
indicated that approximately 15% would
be acceptable. Using the data on energy consumption
for charging EVs, this is equivalent to between
£21 and £108 per annum (a 15% reduction based on
energy consumption between 970 and 5,000 kWh
because energy consumption varies significantly
depending on the battery capacity). The rewards
offered in trial 3 were more generous than this (an
interquartile range of between £60 and £160 per
annum with an average of £22.41 earned during the
two-month trial). This suggests that even a relatively
modest financial reward could be successful
in encouraging drivers to be flexible in their home
EV charging.
july/august 2021
IEEE Power & Energy Magazine - July/August 2021

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