At 14:20 (NEM time) on Saturday 11th April 2026, there was a short spike of system frequency outside of the NOFB.
It appears that:
(a) this was related to a glitch affecting the AEMO operational forecasting systems for UIGF for Semi-Scheduled units.
(b) in an event eerily similar to that which occurred the day before.
Given prior analysis we'd written and published about two recent glitches (Fri 10th April and Sat 11th April 2026) it was not really a surprise, though it’s nice to know, that the AEMO declared both Scheduling Errors.
We start with this unbundled listing of 402 discrete stories about the performance of Semi-Scheduled units (115 solar & 86 wind) units on Friday 10th and Saturday 11th April with the frequency spikes.
Presenting this single image which summarises the sequence of events (for a number of Semi-Scheduled units) over three dispatch intervals across the pair of frequency spikes (on Fri 10th and Sat 11th April 2026).
Next layer of the onion, in investigating the eerily similar (and closely related) frequency spikes outside the NOFB on Friday 10th April 2026 and Saturday 11th April 2026.
With the advantage of 'next day public' data we look at 'Dispatch Error' (for all 201 Semi-Scheduled units) at 14:20 on Saturday 11th April 2026 to see what drove the frequency spike outside of the NOFB. There was a big imbalance...
A first look at a frequency spike (outside the NOFB) focused in the 14:20 (excursion) and 14:25 (recovery) dispatch intervals NEM time on Saturday 11th April 2026 (an almost identical event to what happened the day before).
We've already written about the collective over-performance of Semi-Scheduled VRE on Friday 10th April at 10:30 driving frequency high. There was also an incident at 14:20 on Saturday 11th April 2026 worth investigating ...