‘Sometimes diversity does not help’ … such as on Friday 31st October 2025

Friday 31st October 2025 was another interesting day in the NEM, and we’ve already written three articles about what we saw happening with respect to a weakened performance of VRE that dragged frequency down.

In reverse order of publication – but forward order of causality:

1)  We wrote ‘A quick look at Dispatch Error on Friday afternoon 31st October 2025, with the frequency drop’

(a) in which we noted ‘Aggregate Dispatch Error = +755 MW’ across all solar units

(b)  and with Wind also having a positive Aggregate Dispatch Error (+130MW))

2)  And, with respect to frequency:

(a)  We wrote ‘A second look at the frequency drop on Friday afternoon 31st October 2025’, within which we noted:

i.  The decline of interest begins at ~13:46 (NEM time) … which is i.e. 9 minutes before the lowest point

ii.  With the lowest point being at 49.841Hz at 13:55:28.1

… which was outside of the Normal Operating Frequency Band.

iii.  With recovery beginning from that point, but ‘complete’ at ~14:10 (i.e. by 15 minutes afterwards)

iv.  So, altogether, lasting 5 x 5-minute Dispatch Intervals.

(b)  Which followed on from an initial article ‘Frequency drop on Friday afternoon 31st October 2025’.

On Wednesday 3rd December, the AEMO held its annual Intermittent Generation Forum and discussed a number of different aspects of challenges and opportunities with respect to intermittent generation, including with respect to that day.

Given we’ve already identified that day of interest, I thought it would be of interest to our readers to share the following three slides from the AEMO pack (which have been circulated on the AEMO website here today).

In this first of three slides, the AEMO points to coincidentally large Aggregate Dispatch Error(s) across Solar Farms in QLD, and in NSW:

In the second of three slides, AEMO helps to explain the cause of these two Aggregate Dispatch Error(s):

My paraphrasing of the AEMO explanation delivered in the session about the slightly different causes in QLD and NSW is as follows:

1)  In NSW a thick cloud system was seen, and seen to be moving East (so far so good)

… but the forecast timing of when it encroached on various solar farms was slightly off, causing the Dispatch Error,

2)  While in Queensland the error was due to clouds forming ‘out of the blue’, which is difficult to predict.

In the last of these three slides, AEMO speaks to some considerations of steps that might be taken to improve into the future:

These considerations are of particular interest to us, and will be to some of our readers as well…