Posted by Paul McArdleThursday 12^th March 2026  2:31 PM   Topic: 2026-01-27
Yesterday we wrote ‘Three time-ranges of interest, with respect to aggregate ‘Dispatch Error’ by Fuel Type on Tuesday 27th January 2026’.
As noted in that article, what jumped out at me straight away was:
 
I thought that, from that starting point, it would be better (and clearer for readers) to separate out the two separate VRE legs and analyse and report on each separately.
So this is the 1st of two articles today … this one specifically focused on Large Solar (i.e. the Semi-Scheduled units only, and in aggregate).
 
Taking the ‘Trends Engine’ within ez2view, I took the analysis presented in the prior article and did two things:
This is what we then see:

Note that
With respect to the results above:
1)  We can clearly see that the morning excursion:
(a)  Is an almost contiguous block starting at 09:25 (NEM time) and running through to 12:35;
(b)  And is dominated by large collective under-performance in NSW
(i)  the other regions almost don’t factor at all.
(ii)  which makes me immediately think about Allan’s earlier article ‘Semi-dispatch caps are loading the deviation dice’.
2)  Whereas the afternoon/evening period:
(a)  Is not as contiguous, or large
(b)  And has more contributions from QLD and VIC (as well as NSW)
(c)  So has me wondering if it’s more than just a single cause
… with one of those being the potentially increased (relative) difficulty in forecasting solar yield with a waning sun.
 
With the results above I thought I’d start first in the morning period and (because of its dominant effect) focus just on the NSW (Semi-Scheduled) Large Solar units.
Selecting unit-level data from the ‘Trends Engine’ within ez2view and extracting to do more complex combinations, I produced the following:

In this trend, what we’ve done is:
Step 1)  Calculated Dispatch Error for each NSW Semi-Scheduled Solar Farm discretely, and then
Step 2)  Apportioned to bucketed aggregates:
(a)  The red bucket for units for which (in that dispatch interval) the Semi-Dispatch Cap flag was ON:
… i.e. they were subject to some form of ‘follow dispatch target’ instructions
i.  Either being network constrained or economically curtailed
ii.  And remembering the one-sided nature of ‘follow dispatch target’ for Semi-Scheduled units!
(b)  The green bucket for units for which (in that dispatch interval) the Semi-Dispatch Cap flag was OFF:
… which (as clarified in the AER Rule Change) means to go where the VRE energy resource allowed.
(c)  Noting that the red and green logic above are not the same as the red and green logic Allan used here!
Step 3)  We then stacked* the two bars and trended
* yep, they are stacked, not that the stacking is very visible/necessary given the way the results panned out.
 
We’ll have to come back to that, at some future point in a separate article.
 
 
So at the end of the day we see that, in the majority of cases (especially in the contiguous block in the morning):
1)  the large collective under-performances almost entirely came from units under Semi-Dispatch Cap restrictions.
2)  which:
(a)  as Allan explained here is entirely understandable, given the one-way dimensionality of the SDC arrangements.
(b)  but, at the same time, is one of the things making us question if the Semi-Scheduled category is scalable and sustainable, in its present form.
 
 
Paul McArdle Wed 30^th September 2020 
Following the consultation process conducted by the AER (stemming from their Issues Paper 3 months ago) the AER has today submitted a rule change request to the AEMC relating to Semi-Scheduled generation.
Paul McArdle Thu 7^th August 2025 
Yesterday’s release of the draft report of the Nelson Review has prompted me to re-frame a question I’ve asked before about the Semi-Scheduled category.
Paul McArdle Thu 20^th September 2018 
A detailed look at two specific trading periods in the day (Tuesday 24th July 2018) that saw negative dispatch prices occur at the start of trading periods – hence provided a case study for how existing Semi-Scheduled plant respond (especially in combination with transmission constraints and the Semi-Dispatch Cap).
Paul McArdle Wed 24^th May 2023 
A quick article to capture volatility in QLD and NSW on Wednesday evening 24th May 2023.
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