The curious case of the ‘Q^^TR_CLHA_-600’ constraint equation on Monday 3rd February 2025 (Part 1)

I was speaking with a client earlier today showing them some of the ez2view functionality, and we came across the unfolding situation with the ‘Q^^TR_CLHA_-600’ constraint equation.    It prompted some questions that I said we’d look into further, to the extent that time permits.

Given that we’re in the current day (i.e. so we don’t yet have visibility of the larger ‘next day public’ data set) I said I’d post this briefly today (albeit perhaps cryptically for our readers

Setting the scene

Here’s a snapshot of the ‘NEM Map’ widget and the ‘QLD Schematic’ widget time-travelled back to* the 10:00 dispatch interval (NEM Time) earlier today

* note that Time-Travelling within the current day:
(a)  does not provide visibility of the ‘next day public’ data, because it’s not yet ‘next day’ …
(b)  but it does switch the view from InitialMW (in real time) to FinalMW (time-travelled back before ‘now’) in many widgets

Briefly, note that:

1)  The QLD spot price (at $220.42/MWh) is separated from the NSW spot price ($71.63/MWh)

2)  That’s happening because the interconnectors (especially QNI) are bound … although the more interesting point for some is that they are constrained such that they must flow south (i.e. creating a counter-price flow).

3)  Within the QLD Schematic:

(a)  via units with + or – symbols on dots, we see that there are many units subject to one of more bound constraint equations at this point.

(b)  Some solar farms have been ‘constrained down’ to 0MW (or near zero) output in recent dispatch intervals … some have been highlighted.

About the ‘Q^^TR_CLHA_-600’ constraint equation

Whilst there are many constraint equations relevant in this dispatch interval (including several within QLD) we want to specifically focus in on the ‘Q^^TR_CLHA_-600’ constraint equation, which is the focus of this collage of widgets here:

With respect to this image:

1)  On the right we have the ‘Constraint Dashboard’ widget that we have seen before in other articles

2)  Whereas on the right we have a newer ‘in development’ version of the ‘Congestion Map’ widget that:

(a)  we’ve seen before in some articles (i.e. as earlier versions)

(b)  that’s a new widget we started developing late in 2024 and have been workshopping with many clients since that time.

3)  In the map on the left:

(a)  we’ve filtered down the DUIDs (i.e. the dots) to only those on the LHS of the ‘Q^^TR_CLHA_-600’ constraint equation

(b)  they are coloured by the Local Price Adjustment (LPA):

i.  Which is derived by AEMO in NEMDE from the Marginal Value of some of the bound Constraint Equations;

ii.  And is an input into the CPD Price that we’ve seen many times in articles over recent years.

iii.  Because of the form of this constraint (i.e. which is LHS ≤ RHS) we know that a negative LPA will indicate that a supply-side unit will be being penalised (in their CPD Price) by differing levels of severity in relation to their LHS Factor amongst other things

iv.  The CPD Price is then a guide to how they might need to bid, in order to have any chance of dispatching.

4)  In the ‘Constraint Dashboard’ widget on the right, we see that:

(a)  I’ve highlighted three Solar Farms that are amongst those who have their Contribution  (i.e. their Output x LHS Factor) reduced to 0MW as they are ‘constrained down’ as the RHS of this constraint ratchets down over the preceding dispatch intervals.

(b)  We also see that there is a range of CPD Prices applying to different units on the LHS:

i.  A question was asked about why the three coal units are still running … because:

>>  they have the highest LHS factors (contributing to lowest CPD Prices)

>> noting that the CPD Prices (down at –$1,024.90/MWh) are below the Market Price Floor (which also sets the lower bound of what units can output at).

… I said in the conversation that there are several reasons why that might be happening (i.e. its not a conspiracy) and that we’d look at what was happening more later.

ii.  We see that the Solar Farms that appear to be ‘constrained down’ (incl MOUSF1, EMERASF1, MIDDLESF1, CLERMSF1 and LILYSF1) all have CPD Prices below –$1,000/MWh

iii.  We see many other units have CPD Prices at –$1,000/MWh (exactly) and are still producing output.

More to come …. in a Part 2 (time permitting).