IEEE Power & Energy Magazine - July/August 2021 - 47

of the trial period events to evaluate
the performance of NAC compared
to alternative approaches
and hypotheticals.
Of the 34 battery systems, only
31 were available for a majority of
the trials due to outages and installation
delays. The diesel generator
was operated manually both before
and during the trial. It was not an
active part of the NAC optimization
(although it was modeled in it). The
diesel generator was started based
on an alarm in the utility control
room that triggered when the current
in the cable exceeded operational
limits and then was manually
turned off by an operator based on
operational experience.
Figure 5 shows an example of
Battery
100
-100
-200
Diesel
Time
(a)
100
75
50
25
the aggregate battery dispatch the
NAC algorithm achieved over two
days' worth of peak events. Figure
5(b) shows the current under
the sea, which would be overloaded
in the mornings on both
days and the evening on the first
day without battery and diesel intervention. The batteries
charge in anticipation of an upcoming peak based on island
load forecasts and then delay and offset the diesel requirements
until they either run out of charge or the peak ends.
Over the 16 peaks in the trial, the combined operation
Red Phase
White Phase
Blue Phase
Time
(b)
figure 5. The (a) time series of the aggregate battery and diesel generator response
and (b) resulting undersea cable current per phase over two days.
of the batteries and NAC algorithm reduced diesel usage
by around 33%, which provided around AU$1,000 of diesel
savings. There were too few batteries to eliminate all diesel
usage due to the scale and duration of the load peaks, so
achieving a practical 33% reduction in diesel with batteries
capable of meeting only 10% of the peak island demand was
a significant achievement. With more DERs, an additional
value could be unlocked if the diesel generator could be
removed from the island, as a significant cost is maintenance
and depreciation.
On their own, diesel savings are not enough to justify the
initial subsidies provided to customers, but from the outset,
that was not expected, given the proof-of-concept nature of
the trial for this emerging technology. Over time, as battery
costs decline and come within reach of more consumers,
subsidies will not be required. As the following section
shows, customers can gain a lot of additional value from PVs
and batteries, such as self-consuming solar and load shifting.
DNSPs would not have access to these benefits if they
owned and operated the DERs themselves due to regulatory
constraints. Consumers get this value daily and then receive
additional payments on the small number of peak days
throughout the year that require network support.
july/august 2021
As shown in Figure 6, about half of the diesel savings
could be attributed to the natural (uncoordinated) presence
of the new solar and batteries (the PVs + batteries case).
The network peaks occur in the morning and evening, outside
the hours where solar, on its own, would have a large
impact. The conventional EMS battery control, which
responds to any time-of-use pricing and feed-in tariffs, tends
to help the evening peaks but has little impact on those in
100
60
80
20
40
No Trial
PVs
PVs
+ Batteries
PVs
+ Batteries
+ NAC
figure 6. The diesel generation requirements as more
components of the solution are added.
ieee power & energy magazine
47
Cable Current (A)
Load (kW)
Diesel Generation (%)
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IEEE Power & Energy Magazine - July/August 2021

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