Yet another data point raising questions about whether Eraring will be able to close in 2027, as per current plan

In the print version of the AFR this morning, and posted online late yesterday (Thursday 25th September 2025) was the article ‘Race against time for giant machines that will keep NSW’s lights on’ by Angela Macdonald-Smith:

The article is well worth a read, for those who have access as it speaks about the roll-out of synchronous condensers in NSW that are required before enough other sources of system strength are in place to enable Eraring Power Station to retire.

Directions for System Strength in NSW

In Angela’s article, she writes:

‘The Australian Energy Market Operator flagged last month that gaps in system strength services for the grid – such as provided by syncons – had become a bigger problem for Eraring’s closure than the availability of replacement electrons.’

… (which I presume is referencing the note in the 2025 ESOO, which some might have overlooked) … and also

‘AEMO chief executive Daniel Westerman said this week that in the last week of August outages at coal plants in NSW caused a shortage of synchronous machines, posing a risk to the grid. He said AEMO was forced to direct a hydro plant to connect to the grid and spin – without generating electricity – to keep the lights on.’

Directions for System Strength in NSW

Angela writes, and Daniel spoke, about what happened back on Thursday 28th August 2025 (when Directions were given to Snowy Hydro for TUMUT3)

… but it’s also worth noting that this also nearly was required yesterday (Thursday 25th September 2025).

So readers should be aware that these emerging circumstances are not a one-off:

1) and will increase in frequency in the weeks and months ahead;

2) especially with step changes with each closure of coal units.

Indeed, if we look at number of Eraring units running in each dispatch interval over the past year, readers will see the clear challenge:

… note that it’s whether a unit is running or not, not specifically what output level they are at, that is the prime determinant of whether the unit is providing System Strength (and Inertia)

In this trend we clearly see a minimum of 2 units operational at any time through 2025, with most common being either 3 or 4 units.  That’s a sign of the scale of the System Strength (and Inertia) capability to be replaced, before they can close.

What about the claims that Grid Forming Inverters can substitute for supply of System Strength?

Related to the provision of System Strength, worth also noting that yesterday Giles Parkinson wrote ‘Tesla says its battery inverters are smart enough to keep the lights on: AEMO is not yet convinced’ in RenewEconomy – which contrasts between:

1)  Tesla’s White Paper ‘The Role of Grid-Forming Inverters in Providing Inertia’ published August 2025; and

… with me noting the title speaks to Inertia and not System Strength (though they are somewhat related)

2)  AEMO’s current position – which Giles highlights as follows in his article:

‘But in a speech to a conference hosted by Rupert Murdoch’s The Australian newspaper on Wednesday, AEMO boss Daniel Westerman appeared emphatic – battery inverters can do some but not all of what’s required.

“Batteries can provide some services to keep voltage and frequency stable, but they can’t yet provide sufficient fault current to keep the power system safe,” Westerman said.’

Given the clear divergence of views, I thought I’d skim through the White Paper from Tesla Energy to see what it covered, and find that:

1)  Much of the content relates to Inertia and not System Strength (as, indeed, the title suggests)

2)  But there is this diagram as Figure 3 on p11/35 that does list System Strength as a capability of the Tesla units:

Now:

(a)  that Tesla White Paper notes that this table is copied out of an AEMO document from August 2021 (four years previous) that states that ‘synchronous machines can usually contribute to system strength much more than IBR due to their higher overload capacity’. … which is essentially aligned with what Giles quotes Daniel Westerman as saying, 4 years later (i.e. this week)

(b)  Reading through the White Paper from Tesla Energy, most of the content relates to provision of inertia (as the title suggests), but it does say the following on p30/35:

… with the key part seeming to be:

‘Because fault current and system strength came from the same source, one was used to infer the other. However, this relationship no longer holds with grid-forming batteries, which can provide system strength without needing to produce high fault currents. As a result, fault current is no longer a necessary metric for providing network support services. Tesla’s position is that new technologies should aim to replace the functional outcomes of legacy systems, not replicate their underlying characteristics.’

Now, let readers be clear that I’m not an electrical engineer (and my poor mechanical engineering brain is over-stretched in trying to understand this stuff):

1)   so I certainly can’t tell which is correct.

2)  but this seems to be the point of the disagreement – between what Tesla Energy wrote in August 2025 and which Daniel Westerman spoke about only a month later.

… and it seems a pretty important question, in terms of the pace of the energy transition.