IEEE Power & Energy Magazine - November/December 2019 - 36

As DERs continue to grow in North America and around
the world, it is apparent that the aggregate amount of them is
having an impact on bulk power system planning and operation.
moving forward. The electric industry needs to address these
challenges with innovative solutions earlier rather than later.

DER Impacts on Hawai'i's
Grid Operation
The islands of Hawai'i, Oahu, and Maui have among the
highest penetration levels of DERs in the United States, in
terms of installed capacity relative to system size. Under
favorable policies and the right economic circumstances, the
rapid deployment of DERs can occur in an extremely short
period of time. In only six years, the average distributed solar
photovoltaic (D-PVs) contribution to meeting the gross peak
daytime demand (net peak plus D-PVs) increased from 12
to 37% on Hawai'i island (see Figure 1). The instantaneous
D-PVs penetration can exceed 71% of the daytime demand
today, and it provides approximately 11% of the annual
energy supply. With increasing DER penetration levels come
rapidly rising levels of variability and uncertainty. Hawai'i is
now seeing more D-PVs systems with battery energy storage
systems (BESSs), and it is anticipating the effect that these
combined systems will have on the islanded grid. Needless
to say, the long-term planning studies performed 10 years
ago never anticipated such a major change.
The performance requirements needed for high DER penetration levels on the island grids were not initially supported

160

Active Power (MW)

140
120
100
80
60
40
20
0

2013 2014 2015 2016 2017 2018 2019
Year
Average Daytime Minimum Load (MW)
Maximum Estimated D-PVs (MW)
Average Maximum Estimated D-PVs (MW)

figure 1. The rapid deployment of D-PVs for the island of
Hawai'i.
36

ieee power & energy magazine

by the requirements in IEEE Standards 1547-2003 and
1547a-2014. Hawai'i's DER interconnection standard (Rule
14 H) eventually deviated from IEEE Standard 1547 to support the continued integration of DERs. However, the new
IEEE Standard 1547-2018 includes requirements that are
beyond Rule 14 H and under consideration for inclusion in
a revised Hawai'i standard. Based on Hawai'i's experience,
robust interconnection requirements need to be in place
well in advance of high penetration levels to support BPS
reliability. It is extremely challenging and expensive to meet
changing BPS needs by retroactively enhancing equipment
that was installed with minimal performance requirements
and capabilities.
For the Hawai'i grid, the following aspects of DER integration are top priorities:
✔ balancing solar PV variability with flexible energy resources that are capable of fast ramping and cycling
and ensuring that regulation resources do not fall below minimum allowable dispatch levels
✔ managing frequency stability with sufficient frequency-responsive reserves and checking that newly installed
DERs have active power-frequency controls enabled to
assist the primary frequency response
✔ improving DER estimation techniques since nearly
all DERs are behind-the-meter (BTM), with no visibility or control by the system operator; D-PVs output is estimated using field irradiance measurements
provided to the operator via supervisory control and
data acquisition
✔ ensuring effective system restoration with variable DER
auto-reconnection and possibly adjusting reconnection
criteria (although this will not address situations of high
solar PV periods where DER control is necessary)
✔ studying the adverse impacts of DERs tripping during
BPS faults and working with existing DER installations to modify trip settings and improve ride-through
capability, where possible.
There are also two issues related to frequency stability that are
worth highlighting: the use of fast-responding battery energy
storage to mitigate legacy DER tripping and the development
of an adaptive UFLS program to ensure system security during severe resource-loss events.

Storage to Mitigate DER Loss
Some legacy DERs do not have a robust ride-through capability and, therefore, are subject to aggregate loss during
over/under frequency and voltage excursions. The behavior
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