An updated tabular list of instances of large AggROT across Semi-Scheduled units

2025

(to 30th June 2025)

Special mention goes to …

19th Aug 2025 …  which saw a massive collective over-performance across Semi-Scheduled units, that drove mainland frequency to 50.2Hz for a sustained (~20 minute) period of time.

In terms of the 6-month period to 30th June 2025, there were 23 discrete instances of large (>+600MW) collective under-performance, and 1 instance of similarly large over-performance. You can see below that some were much larger than 600MW.

23rd June 2025 …  at the 14:55 dispatch interval, the AggROT = +657MW

… there’s already a number of articles collated here for Monday 23rd June 2025:

(a)  Including a note about a ‘New all-time record for NEM-wide wind, on Monday 23rd June 2025’;

(b)  But none highlighting any frequency wobble or large AggROT.

16th June 2025 …  at the 15:40 dispatch interval, the AggROT = +600 MW

… there’s already a number of articles collated here for Monday 16th June 2025, including two relevant articles:

(a)  Starting with ‘Drop in mainland frequency on 16 June 2025’ (in which Linton noted that ‘The low-point was 49.832 Hz, at 15:40:19’; and

(b)  Then ‘Which units show large positive Dispatch Error for 15:40 on Monday 16th June 2025’ … remembering that ‘Dispatch Error’ is a slightly simpler calculation to ‘Aggregate Raw Off-Target’ (but quite related).

9th June 2025 …  at the 15:00 dispatch interval, the AggROT = +688 MW

… there’s already a number of articles collated here for Monday 9th June 2025, but none appear (on quick scan) to be related to this large AggROT, or any potential frequency disturbance.

26th May 2025 …  at the 16:15 dispatch interval, the AggROT = +695 MW

… for this day there are already a large number of articles collated for Monday 26th May 2025, including a number related to the frequency drop (outside of the NOFB) that was triggered by this large instance of AggROT.

24th May 2025 …  at the 16:35 dispatch interval, the AggROT = +616 MW

21st April 2025 …  at the 16:20 dispatch interval, the AggROT = +618 MW

19th April 2025 …  saw two occurrences:

(a)  These were:

i.  at the 14:20 dispatch interval, the AggROT = +685 MW

i.  at the 14:05 dispatch interval, the AggROT = +834 MW

(b)  For this day we already noted ‘Drop in NEM Mainland Frequency appearing to coincide with trips at New England Solar Farm, on Saturday 19th April 2025’, but have not yet followed any further.

31st March 2025 …  was a special day, with 4 discrete instances of large under-performance in the afternoon.

(a)  These were as follows:

i.  at the 16:50 dispatch interval, the AggROT = +851 MW, which was immediately after

ii.  at the 16:45 dispatch interval, the AggROT = +633 MW, which was 3 dispatch intervals after

iii.  at the 16:30 dispatch interval, the AggROT = +613 MW

iv.  at the 13:45 dispatch interval, the AggROT = +686 MW

(b)  At this point we have only posted ‘Frequency excursion on Monday 31st March 2025’ with the time-range on that chart seeming to line up with the 3 x large instances of under-performance after 16:00.

19th March 2025 …  at the 10:50 dispatch interval, the AggROT = +647 MW

22nd Feb 2025 …  saw two discrete instances of collective under-performance:

(a)  These were:

i.  at the 16:55 dispatch interval, the AggROT = +606 MW

ii.  at the 16:35 dispatch interval, the AggROT = +620 MW

(b)  There are a couple articles already collated for Saturday 22nd February 2025, but none looking directly at frequency performance.

21st Feb 2025 …  at the 15:40 dispatch interval, the AggROT = +602 MW

15th Feb 2025 …  was a special day, with 4 discrete instances of large under-performance in the afternoon.

(a)  These were as follows:

i.  at the 16:55 dispatch interval, the AggROT = +742 MW

ii.  at the 16:35 dispatch interval, the AggROT = +752 MW

iii.  at the 16:10 dispatch interval, the AggROT = +849 MW

iv.  at the 15:35 dispatch interval, the AggROT = +626 MW

(b)  Surprisingly, there have been no articles already written and collated with respect to these large instances on 15th February 2025.

14th Feb 2025 …  at the 17:25 dispatch interval, the AggROT = +708 MW

13th Feb 2025 …  at the 13:30 dispatch interval, the AggROT = +686 MW

… noting that the exceedances on Friday 14th and Saturday 15th February 2025 were larger than this instance, it’s interesting to note two articles collated for Thursday 13th February 2025 as follows:

(a)  Firstly ‘NEM Mainland Frequency wandering (somewhat more than ‘normal’) on Thursday afternoon 13th February 2025’; and then

(b)  Followed by ‘A closer look at NEM Mainland Frequency (at 100ms cadence) on Thursday afternoon 13th February 2025 (i.e. Part 2)’ … noting that ‘the lowest point was actually below the NOFB briefly … that was 49.832Hz at 13:31:23.4‘

17th Jan 2025 …  at the 18:05 dispatch interval, the AggROT = +661 MW

2024

With respect to the full calendar 2024 there were 19 discrete dispatch intervals seeing exceedance of greater than 600MW (2 being over-performance, but 17 being under-performance), as follows:

27th Dec 2024 …  at the 17:20 dispatch interval, the AggROT = +692 MW

16th Dec 2024 …  was a special day, with 4 discrete instances of collective under-performance greater than 600MW:

(a)  These were:

i.  at the 17:05 dispatch interval, the AggROT = +644 MW

ii.  at the 13:55 dispatch interval, the AggROT = +626 MW

iii.  at the 13:25 dispatch interval, the AggROT = +633 MW

iv. at the 10:50 dispatch interval, the AggROT = +601 MW

(b)  There have already been many articles written about Monday 16th December 2024 (a very hot, stressful, extremely high demand day), but we’d like to particularly flag the following:

i.  Firstly, ‘Where are those Semi-Scheduled Wind Farms in Victoria that were reviewed w.r.t. Monday 16th December 2024’; and

ii.  Then ‘A quick initial review of bids, for Monday 16th December 2024’.

iii.  ‘Further analysis (and more questions) about four VIC Wind Farms on Monday 16th December 2024’

14th Dec 2024 …  at the 14:50 dispatch interval, the AggROT = +662 MW

8th Dec 2024 …  was a special case, with two instances of large over-performance (the only two this size through the year):

(a)  These were:

i.  at the 11:15 dispatch interval, the AggROT = -610 MW

ii.  at the 08:10 dispatch interval, the AggROT = -661 MW

(b)  There have been some articles already published about this day, but (on quick scan) they seem unrelated to these instances.

7th Dec 2024 …  at the 14:40 dispatch interval, the AggROT = +633 MW

16th Nov 2024 …  at the 12:40 dispatch interval, the AggROT = +642 MW

6th Nov 2024 …  at the 14:50 dispatch interval, the AggROT = +629 MW

… on this occasion we posted the article ‘Mainland frequency wobbles, on Wednesday 6th November 2024’ at 16:12, looking back at a frequency dip that occurred in the two hours preceding 16:02 (which might line up with that level of exceedance).

24th Oct 2024 …  at the 15:15 dispatch interval, the AggROT = +612 MW

5th Oct 2024 …  at the 15:45 dispatch interval, the AggROT = +609 MW

… on this occasion we’d noticed a drop in frequency (which lined up with 15:45), and had posted:

(a)  Firstly ‘Drop in System Frequency (approx 15:45 NEM time) on Saturday 5th October 2024’;

(b)  Then followed up by ‘Drop in System Frequency on Saturday 5th October 2024 – Part 2’.

Note no large exceedances (i.e. >600MW) for 7 months (March through September) in that year.

28th Feb 2024 …  at the 14:45 dispatch interval, the AggROT = +605 MW

22nd Feb 2024 …  there were two instance on this day:

(a)  at the 17:05 dispatch interval, the AggROT = +613 MW

(b)  at the 14:15 dispatch interval, the AggROT = +654 MW

13th Feb 2024 …  Very noteworthy was what happened on Tuesday 13th February 2024 from a broader network point of view:

(a)  But also:

i.  with AggROT at +701MW at 13:35 which followed ~2 hours after

ii.  the larger AggROT at +815MW at 11:40

(b)  Which have already been explored in ‘Aggregate Dispatch Error across all Semi-Scheduled units (NEM-wide) throughout Tuesday 13th February 2024’.

4th Feb 2024 …  at the 15:25 dispatch interval, the AggROT = +697 MW

2023

In completing the review of this particular metric for 2023 Q4, we published the start of two Case Studies:

24 Dec 2023 …  where we posted ‘Large instances of collective under-performance across all Semi-Scheduled units on Sunday 24th December 2023’

31st Oct 2023  ‘… sees the only two instances (in Q4, and all year) of AggROT for Semi-Scheduled units < –500MW’

Earlier in the year (with the 2023 Q3 update) we flagged:

18th Aug 2023 … ‘Case Study (part 1) of large collective under-performance for Semi-Scheduled assets on Friday 18th August 2023’.

Earlier in the year (with the 2023 Q1 update) we flagged:

3rd Feb 2023 … ‘Case Study of Friday 3rd February 2023 (Part 1) … two consecutive large instances of collective under-performance for Semi-Scheduled units’ … with the two instances being:

(a)  AggROT = +845MW at 15:35.

(b)  AggROT = +815MW at 15:40.

20th Jan 2023 … ‘Case Study of Friday 20th January 2023 (Part 1) … large instance of collective over-performance for Semi-Scheduled units’ … with AggROT = –497MW at 16:25.

2022

For the 2022 calendar year we’ve previously prepared the following:

27th Oct 2022 with four parts in this evolving Case Study with respect to an instance of AggROT = +866MW at 17:05.

23rd Aug 2022 about ‘… large instance of collective over-performance for Semi-Scheduled units’ for the AggROT = –650MW at 13:15.

2021

For the 2021 calendar year we’ve previously prepared the following:

16th Feb 2021 about ‘… large instance of collective over-performance for Semi-Scheduled units’.

2020

No Case Studies (yet?) prepared for incidences that occurred through 2020.

Covering 2019, and years before that

Worth highlighting the article ‘Extrapolating from the trend of ‘Aggregated Raw Off-Target’ results, to yield some clues to what the future might hold … and one challenge for NEM 2.0’ published in July 2020.

(a)  In that article we included a tabular section (covering 2013 to 2019) of ‘specific dispatch intervals where AggROT > 300MW’, complete with links to many Case Studies from these earlier years.

(b)  Given that that article provided a detailed reference to earlier Case Studies, I’ll just flag some specific ones below.