Here at the Global-Roam office, we are very much focused on the “here and now” of the NEM. For example, at the front of our office sits four 85-inch monitors with our ez2view software. They act as a faux “trading wall”, allowing us to monitor what’s happening in the market and on the grid as each day unfolds.

Many others in the broader electricity industry aren’t afforded the same opportunity to see and understand the many ebbs and flows of the NEM. In this brief article, I’ll share a four-minute video time-lapse demonstrating four days of market activity.

Market conditions earlier in April

For useful context, between Monday the 7th and Thursday the 10th of April, there was elevated market volatility and other noteworthy outcomes in Queensland and New South Wales.

One underlying driver of this volatility was a sudden clinker incident that started a long forced outage at the 466 MW Callide C3 unit in Queensland that occurred several days earlier. The unexpected nature of this outage meant that the market was marginally shorter on available dispatchable supply than would otherwise have been the case. In a separate article earlier this month, Paul shared an image of other coal outages that were simultaneously occurring, and he has also published another article specifically looking into the bidding behaviour within the fleet of each fuel type during this period.  However, it’s important to state that these were not the only factors in play, as will be discussed further below.

A running view of the NEM

Below is a video I’ve created to illustrate congestion and other market dynamics in QLD and NSW over these four days. The video starts by briefly explaining the different elements of the ez2view layout that I configured to create this time-lapse. It then cycles through 1,152 screenshots of our software—one for each 5-minute dispatch interval—across the four-day period.

I have purposely not annotated any market activity during the time-lapse, so that readers could observe the ebbs and flows of the NEM firsthand. As such, the video sifts through a lot of information very quickly, so I recommend viewers pause the video as needed to understand different bits of market context at each point in time.

The main purpose of this time-lapse is to demonstrate how congestion impacts the market in a very dynamic but consistent manner. Therefore, I’d suggest keeping an eye on the Congestion Map on the right of the screen.

In simple terms, red dots on this map indicate units that are in parts of the network where additional megawatts of generation are being valued lowly by the dispatch engine, and green dots indicate parts of the network where additional megawatts of generation are being valued highly. For those more interested in how this widget works, we’ve published several articles demonstrating past prototypes of this map that can be found under this tag.

I hope this video highlights the highly dynamic nature of network congestion across the NEM, particularly during daylight hours.

Below is a summary of some of the other high-level dynamics that we can observe over this four-day period:

• We note that high prices (near or above $1,000/MWh) eventuated in the early evening of each of these four days in both QLD & NSW. We noted these price spikes in separate WattClarity articles at the time (i.e. for the 7th, 8th, 9th and 10th of April).
• We can observe that a significant amount of VRE curtailment occurred across QLD and NSW during the daylight hours of April 7th, coinciding with negative prices (i.e. economic curtailment) during the day, and active network constraints in the early evening (i.e. network curtailment).
• We can also observe how congestion perennially impacts the areas of NSW that are south and west of Sydney. Of note are several system normal and outage constraints that commonly bound over this four-day period:
  • N>NIL_94T: A thermal constraint to protect the Orange to Molong 132kV transmission line, with the constraint impacting several units in central-west NSW.
  • N::N_03+4_2: A transient stability constraint to protect parts of the 330kV network around Yass, with the constraint impacting several units in the south-western portion of NSW.
  • Multiple system strength constraints in southern NSW, designed to manage voltage stability post a potential contingency event.
  • Multiple hard and soft ramping constraints bind each morning across regions.
• We can also see the effect of interconnector limits, particularly on VNI, and how they lead to a frequent north-south divide. There are also regular daytime counter price flows from NSW to VIC, and several instances of one of the NRM constraints setting the import limit on VNI.

And for those who want to dig a little bit deeper, there are a few interesting intervals over this period that are worth flagging, with the video timestamp stated in parentheses:

• 2025-04-07 12:30 (1 min 25 sec) – Approximately 40% of the large solar fleet across QLD and NSW is being curtailed as (1) negative prices occur in both regions, and (2) a handful of solar farms in NSW are (potentially) impacted by binding constraints. We see that the battery fleet had a net charge/discharge target of 0 MW during this interval—those targets lowered (i.e. to charge) over the following two hours.
• 2025-04-07 17:10 (1 min 34 secs) – We see a material amount of (almost certainly network) curtailment in the wind fleet despite prices in QLD and NSW being above $1,000/MWh. There is a delayed response in battery targets during this initial price spike. We also see an NRM constraint setting the import limit on VNI during this counter-price flow interval. Prices then spike even higher, to above $10,000/MWh in the next interval, and battery targets progressively increase over the ensuing intervals.
• 2025-04-09 07:50 (2 min 48 secs) – The congestion map lights up like a Christmas tree during this interval with 28 mis-pricing constraints binding at once—including many ramping constraints for individual units. There are also several positive adjustments in certain parts of the NSW region during this interval.
• 2025-04-09 17:25 (3 min 07 secs) – Prices spike above $15,000/MWh in both QLD and NSW, with the N::N_4+07_2 transient stability constraint essentially splitting the NSW region into two. During this interval, we also see a 500 MW counter price flow into VIC with the NRM constraint setting the import limit on VNI. This also coincides with lower-than-typical wind production in QLD and NSW.