(Prepared on the day; I won’t have a chance to further review this event on Tuesday after bid data is published)
Another day, another isolated 5 minute spike in Queensland, falling in DI 06:50:
The underlying causes are very likely similar to those we saw in last Friday’s spike, although today we didn’t see rapidly increasing generation, reversing interconnector flows and negative settlement residues, because the spike arrived relatively late in the half hour. However we did again see some immediate reduction in demand probably associated with price-responsive loads.
Quickly reviewing 5 minute actual data in ez2view’s Swim Lanes widget, time-travelled a few periods beyond the spike, we can draw some early conclusions on cause:
DI 06:50 was the only period where flows on the interconnectors from NSW hit their limits, allowing the Queensland price to separate from NSW. This likely forced the dispatch of high-price bid bands in Queensland – the thin bidstack effect seen throughout this summer.
There may also have been some generator rebids just prior to the 06:50 dispatch interval, leading to higher interconnector flows and price separation. We can get a hint of this before the next day’s publication of bid data by comparing metered actual generation output levels around the time of the price spike, using ez2view’s Schematic widget time travelled to adjoining dispatch intervals. I’ve highlighted the noticeable changes:
We see output at some coal fired generators reducing despite the higher dispatch price while output increases at a number of gas fired units (we see these changes in the next dispatch interval following the spike – DI 06:55 being the five minute period 06:50-06:55 – as the start time of this interval is when these actual output data are captured and published by AEMO’s systems). It’s therefore likely that the spike was at least partially due to rebids on some of those coal-fired generation units lowering their output and causing high priced generation offers to be dispatched after the interconnectors constrained.
Tuesday’s bid data will show if I was right.