Managing Minimum System Load (MSL)
Australians continue to invest in distributed photovoltaics (DPV) at world-leading levels. More than one-third of homes across the country now host rooftop solar systems, helping households and business reduce their energy bills and directly contributing to the decarbonisation of the energy system.
Given the growing aggregate contribution of DPV generation, there are increasing periods where the DPV generation is very high relative to underlying demand, resulting in low demand from the grid. Other types of consumer energy resources and behind-the-meter flexibility (including electric vehicles (EVs), storage and demand response) can be harnessed to 'soak up' this excess DPV generation. However, these capabilities are operationally limited at present, and will take time to develop.
AEMO has identified a possible risk of scenarios where the demand for grid-connected generation is so low that power system security violations could emerge, requiring new pre-emptive management actions.
The report below provides stakeholders with a status assessment on some of the new capabilities required to securely operate the National Electricity Market (NEM) in periods with high levels of generation from distributed PV and low demand. To facilitate continuing growth in customer distributed PV, in addition to a broad suite of complementary measures including accelerating efforts to provide customers access to market frameworks, the report recommends urgent action to introduce 'emergency backstop' capabilities for all new distributed PV installations so that the NEM can operate securely in these periods.
To manage these potential security issues in a transparent and coordinated manner, in 2021 AEMO introduced the Minimum System Load (MSL) framework.
The MSL framework
The following fact sheets provide further information on the MSL framework:
MSL incident reporting
The NEM Lack of Reserve Framework Quarterly Reports include reporting on MSL1, 2 and 3 events and can be found here:
Incident reporting on use of emergency backstop mechanisms
The following reports provide further detail on instances where emergency backstop mechanisms have been used to maintain system security:
14 March 2021: South Australia
On 14 March 2021, AEMO issued an instruction that operational demand in South Australia be maintained above the minimum level required to ensure the power system remained in a secure operating state.
This instruction resulted in SA Power Networks activating ‘Smarter Homes’ requirements for the first time, resulting in the registered Relevant Agents curtailing a small amount of distributed photovoltaic (DPV) generation for a short time.
13–19 November 2022: South Australia
At 1639 hrs on 12 November 2022 severe thunderstorm activity led to failure of a double circuit tower, causing the majority of the South Australian region to become synchronously separated from the rest of the NEM. South Australia was operated as an island until temporary structures were erected on 19 November 2022.
During the period 13–19 November 2022, very high levels of DPV generation were forecast in South Australia. To maintain power system security within the SA island, AEMO instructed ElectraNet to maintain operational demand above the necessary thresholds each day. SA Power Networks applied a range of mechanisms to curtail DPV on each day from 13–17 November 2022 and on 19 November 2022, with curtailment lasting between four and nine hours each day and reaching a maximum of approximately 410 MW.
This DPV curtailment successfully reduced the largest credible contingency in the South Australian island to within a secure operating limit.
15 February 2024: South Australia
Due to transmission damage on 13 February 2024, South Australia operated at credible risk of separation until 1833 hrs on 15 February 2024.
On 15 February 2024, a DPVC3 (distributed PV contingency) condition arose, with forecasts of constraint violations on the Heywood interconnector. The maximum DPV generation forecast for South Australia was above the secure DPV generation limit. At the time the only available action to maintain system security was to reduce DPV generation in South Australia.
At 1216 hrs, AEMO issued a NER clause 4.8.9 instruction to ElectraNet to require SA Power Networks (SAPN) maintain operational demand above 301 MW.
SAPN advised that a total of 51 MW of DPV was curtailed, in accordance with their operating procedures. This involved 46 MW of larger DPV (>200kW), curtailed via SCADA control, and 5 MW of small-scale DPV (<200kW), curtailed via Relevant Agents under the CSIP-Aus Smarter Homes framework.
Past reports on the evolution of MSL issues
The following reports outline the evolution of previous analysis on DER integration and maintaining power system security while levels of DER grow:
August 2024: 2024 Electricity Statement of Opportunities
Chapter 7.6
Highlights upcoming periods in all NEM mainland regions where high distributed photovoltaics (PV) relative to underlying demand results in minimum operational demand levels that may require action to maintain power system security.
August 2021: 2021 Electricity Statement of Opportunities
Chapter 6, Appendices A2.5, A3.5, A5.5
Discusses the challenges and opportunities associated with periods of high DER penetration for the mainland NEM. Highlights the imminent nature of these challenges, outlines adaptations to manage reducing minimum demand and implications if no actions are taken.
Nov 2020: 2020 South Australian Electricity Report
Chapter 8
Highlights the challenges and opportunities associated with the high level of renewable energy resources in South Australia. The chapter includes a summary of DER integration issues, including unintended disconnection of distributed PV in disturbances, minimum demand thresholds, impacts of DER on under frequency load shedding, and the requirement for emergency PV curtailment capability.
Aug 2020: 2020 Electricity Statement of Opportunities
Chapter 7
Discusses the challenges arising across the NEM relating to managing voltage, system strength and inertia in low load conditions. It highlights opportunities for managing the power system during low demand periods including active DER management, load shifting, using frequency control services and transmission voltage control services, and actions to take to mitigate risk including introducing emergency back stop mechanisms and improving DER performance.
May 2020: Technical Report: Minimum operational demand threshold in South Australia
Whole report
Investigates operational challenges that could emerge as South Australia moves to lower levels of operational demand due to increasing growth in distributed PV.
April 2020: Renewable Integration Study (RIS)
Appendix A
Case studies on DER integration challenges in South Australia.