Rooftop PV pushes grid demand and coal output to new lows as NSW gets ready for solar switch-off

Rooftop solar has pushed operational demand and coal output on Australia’s main grid, and in its biggest state, to new record lows as the spring season continues to refashion the shape of Australia’s electricity system.

The new lows – which were reached over the weekend – were confirmed by the Australian Energy Market Operator on its Twitter/X account late on Monday.

“Another spring Saturday saw new minimum demand records in NSW and the NEM (National Electricity Market),” it wrote.

“In the NEM, the operational demand record fell from 10,305 to 10,073 MW at 11:30am (AEST). While in NSW, operational demand dropped to 3,121MW at 1pm (AEST).”

Rooftop solar was the driving force, as the graph above provided by AEMO illustrates. Data providers GPE NEMLog noted that rooftop solar jumped to a new record 54.6 per cent, up from 53.2 per cent, at around the same time across the NEM, and to a new peak of 58.9 per cent, up from 55.7 per cent, in NSW.

A day later, according to GPE NEMLog, coal output in NSW fell to a new instantaneous low of 1497 MW at 12.15 pm (AEST), and combined black coal from NSW and Queensland fell to a new record low of 4394 MW at the same time.

Operational demand levels are defined by AEMO as the electricity demand of the power system which needs to be met by grid-scale generators such as wind, solar, gas and coal. It is pushed to record lows when household rooftop PV installations generate a lot more than is used by the home owner.

AEMO is concerned that it may go too low, pushing system security at risk, because it will not have enough levers to pull should something go amiss.

And so it has begun issuing alerts for “Minimum System Load” (MSL) that could trigger either orders to switch off some rooftop solar, or to have big batteries on standby to create demand by charging up during those periods.

AEMO issued two low-level MSL1 alerts for Victoria over the weekend, although they were later cancelled, and forecast another MSL1 for Victoria for this coming Sunday, which was also cancelled. Meanwhile, it issued and then rescinded lack of reserve alerts (at the other end of the spectrum) for Queensland.

So far four states have introduced solar management programs – the nice of saying that local networks will be instructed to switch off some rooftop PV – that can be implemented as a last resort. These are South Australia, Western Australia, Victoria and Queensland.

Renew Economy has also learned that NSW – the biggest state, and with the biggest coal fleet in the country – is also preparing to introduce a similar system by September next year, in time for the 2025 spring when more renewable output, rooftop solar and minimum demand records are sure to be set. Tasmania may not need to bother.

The rooftop switch off mechanisms are not popular – for obvious reasons – for both households and politicians. But they are they seen as necessary by AEMO at least as a last resort. So far, the mechanisms have only been used twice in South Australia.

In Western Australia, however, the rollout of a series of new big batteries – including the biggest in the country – with a specific task of soaking up rooftop solar is likely to alleviate minimum demand concerns in that state, and help usher out the last of its ageing coal fired generators.

Spring is usually the season for records because the generating conditions for both wind and solar are good, and because demand is moderate because of the mild temperatures that require little or no heating or air conditioning loads.