On Tuesday 25 August SA Power Networks had planned to conduct its annual test of its ability to temporarily curtail rooftop solar generation.
A high-level overview of the what, why and how of the test is described the SA Power Networks announcement. It explains that the capability to temporarily curtail rooftop PV is needed to manage electricity grid stability when rooftop solar exports are very high and electricity demand is very low, to avoid an unstable electricity grid.
In the announcement. We note:
The test will check:
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- Solar systems installed after September 2020 are compliant.
- Third parties known as Relevant Agents, who are responsible for disconnecting and reconnecting systems, can respond quickly.
- All systems reconnect smoothly once the emergency is over.
In the leadup to the test, at 10:00 (NEM time) AEMO’s small scale rooftop PV forecast was indicating there would be 1179 MW exporting in SA at peak.
A south to southwesterly airstream was driving thicker morning cloud away from Adelaide. This is seen in the Bureau of Meteorology SatView image below. Patchy cloud cover and temperatures in the low teens followed.
What we saw at the State level
It is likely too early to say how much of an impact the test had on demand or other electricity data inidcators. More data, or more analysis, or both is likely needed to assess the test.
In the Trends chart below we observe an increase in SA demand between 15:00 and 15:30 aligning with a decline in rooftop PV. A return to possibly normal demand levels appears by 16:00 and this aligns with a weakening of the rooftop PV decline.
We know there was cloud cover that would create output variability. Further, demand levels appear to have been well below the forecast 1179 MW peak, reaching 879 MW at 14:30. These aspects indicate that fluctuations in the data might be attributable to many things.
When might rooftop solar be curtailed, for real?
WattClarity compiled a list of three different causes/drivers of distributed PV curtailment. In that article, we say “distributed” to encompass small scale rooftop systems and larger commercial systems found distributed throughout the network. Summarising, for ease of access:
- Distributed PV (DPV) curtailment that happens in DPV Contingency Events is not due to the Minimum System Load (MSL) requirements; as AEMO’s market notices explain it’s to do with managing contingency sizes.
- Distribution System Issues; in some cases, disconnection of solar PV might have been an unintended by-product of challenges within the distribution system.
- Minimum system load; while aggregate DPV output certainly drives this, the issue appears to relate to the total level of system load (grid demand) and the issues that creates for things like voltage control, keeping sufficient synchronous units online etc.
On emergency backstop mechanisms
This ability to curtail rooftop PV export levels is sometimes referred to as an emergency backstop mechanism. In SA, the Smarter Homes regulations set out requirements that support ability to achieve this.
AEMO’s Learnings from industry implementation of emergency backstop mechanisms for distributed resources offers insights into how these mechanisms have been implemented and used (as of 2025). This report includes learnings from SAPN’s experiences.
Nope, not a blip in production yesterday (Tues 25th), Adelaide southern suburbs.
We did haveoutage during 2025 backstop testing.
Thanks Les, for the ‘on the ground’ observation! Is your system equipped for CSIP-AUS communication capability? Thinking perhaps the testing this time was only targeting that protocol, and or that protocol offers greater control over the level of curtailment.