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:

• Long contiguous periods of collective under-performance (i.e. positive aggregate Dispatch Error from the VRE fleet)
  • with aggregates for both (Semi-Scheduled) Wind and Solar:
    • sometimes overlapping in time;
    • so putting more of a collective drag on frequency (as we’ve already explored on many occasions, some of which are tagged and collated here).
  • though perhaps caused due to different factors
• With the Scheduled units (primarily BESS and Coal units) doing what they can, via PFR and Regulation FCAS arrest the frequency drag.
• On Tuesday 27th January 2026:
  • Which was a day of particular interest for other reasons
  • This seemed to break down into three discrete blocks of time

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).

Breaking the NEM-wide data down to region specifics

Taking the ‘Trends Engine’ within ez2view, I took the analysis presented in the prior article and did two things:

• Dropped the other Fuel Types; and
• Ran the same query for aggregate Dispatch Error, but down at a region level in addition to a NEM-wide level:
  • Adding 4 more data series
  • Noting no Large Solar farms in TAS (yet).

This is what we then see:

Note that

• I’ve kept the axes the same, so that we can easily compare between a few charts in terms of relative size
• Per usual, click on the image for a larger-resolution view
• For those with a licence to the ez2view software, you can access your own copy of this trend query here.

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.

Looking at NSW Solar Farms, particularly in the morning

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.

What about QLD and VIC in the afternoon/evening?

We’ll have to come back to that, at some future point in a separate article.

Headline

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.