IEEE Power & Energy Magazine - September/October 2021 - 19

T
september/october 2021
THE NATIONAL ELECTRICITY MARKET (NEM) POWER SYSTEM INTERCONNECTS
five regions in eastern and southern Australia and delivers around 80% of the national electricity
consumption. The NEM and its electrical regions exhibit unique characteristics compared to most
other power systems. It has no interconnection to neighboring countries, covers large geographical
distances, and contains world-class wind and solar resources.
World-leading levels of distributed energy resources have also increased the complexity of
operating this power system. To provide context and a visual comparison, Figure 1 is taken from
the Australian Energy Market Operator's (AEMO's) international review of power systems with
high (>50%) instantaneous penetrations of wind and solar. It compares the geographical size of
the NEM power system with those of some other power systems.
The NEM, like other power systems worldwide, is being transformed from a system with large thermal
power stations connected to a high-voltage transmission network to a decentralized one with an increasing
amount of variable inverter-based renewable resources (IBRs). According to AEMO, the NEM power system
demand ranges from 16 to 35 GW, and it already had 22.2 GW of wind and solar capacity installed
by the end of 2020. Subregions of the NEM such as South Australia have one of the highest penetrations
of wind and solar in the world operating with a maximum instantaneous penetration of over
140%. South Australia also has one of the highest penetrations of rooftop solar PV anywhere in
the world and operated with over 60% instantaneous penetration in 2019 (see Table 1).
By 2025, the NEM is expected to have transformed even further. AEMO's 2020 Integrated
System Plan (ISP) forecasts a total installed capacity of wind and solar (including residential)
of 27 and 36 GW for the studied " Central " or medium scenario and the " Step Change " or high
scenario, respectively.
As outlined on AEMO's website, Figure 2 from its Renewable Integration Study (RIS) Stage 1
Report shows actual data of wind and solar penetration in 2019 in the NEM. The penetration represents
NEM half-hourly wind and solar generation divided by the total electricity demand in the same period.
The 2025 projections indicate the potential instantaneous penetration by 2025 under the ISP's medium
and high scenarios. The fi gure highlights signifi cant forecast growth in the maximum potential instantaneous
penetration of wind and solar from just under 50% in 2019 to more than 75% in the medium and
100% in the high scenario in 2025.
Many of the insights presented in this article are based on the fi ndings of AEMO's 2020 RIS
to identify limits that affect the maximum instantaneous penetration of wind and solar and also to
determine how close the NEM is to these limits now and is expected to be by 2025. In addition, we
will discuss actions that can overcome these barriers so the system can operate securely with higher
penetrations of wind and solar generation in the future.
The article focuses on the RIS report's four core study areas:
✔ power system frequency stability
✔ system strength adequacy
✔ variability and uncertainty in the supply-demand balance
✔ managing of increasing volumes of distributed solar PVs (DPVs).
Power System
Frequency Stability
Synchronous generation provides vital system services to the grid, one of which is synchronous
inertia. Inertia provides a rapid and automatic injection of energy to limit the rate of change in
grid frequency. It is required to stabilize the grid frequency when sudden imbalances between
supply and demand occur. This inertial response was historically abundant in a grid dominated
by synchronous generation.
However, inertia is declining as synchronous generators are being displaced during periods of high
wind and solar penetration. This makes it more challenging to manage frequency stability at these times.
Figure 3 shows the historic decline in the NEM mainland synchronous inertia levels and the 2025
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IEEE Power & Energy Magazine - September/October 2021

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