Monday's overnight session was relatively contained across most NEM regions before the morning demand ramp sharpened prices. NSW1 and QLD1 averaged $94/MWh on the day, with Queensland's evening peak hitting $240/MWh and a spot read of $139.95/MWh at 06:30 AEST as demand climbed to 6,325 MW. Victoria pulled back sharply from its overnight peak of 6,923 MW, sitting at 5,358 MW and $110.50/MWh at the 06:25 AEST interval. South Australia is the standout watch point as the morning session progresses — the Heywood interconnector (V–SA) is running at its binding export limit of 460.1 MW, and SA1 has already printed $257.83/MWh at 06:30 AEST against an overnight floor of $76.44/MWh. Tasmania held a tight $102–$106/MWh band overnight. Expect the morning demand ramp to continue testing interconnector limits into the working day.
Two stories dominate. SA1 recorded the session's widest price swing — from an overnight floor near $76/MWh to $349/MWh intraday, averaging $132/MWh — driven directly by the Heywood interconnector binding at its 460.1 MW export cap. The transmission constraint is the proximate cause of SA's sustained price premium over the rest of the NEM. Separately, TAS1 delivered a notable operational milestone: 100% renewable penetration during the evening of 25 May, with approximately 2,334 MW supplied entirely by hydro and wind. That achievement was complicated by a major binding constraint on the Basslink interconnector (T_BLINK_TV_NGZ), which registered an extraordinary shadow price of $7.308 million, signalling acute transmission congestion limiting power flow to Victoria despite the surplus renewable generation onshore.
The Western Australian wholesale market (WA1) recorded an average price of $96/MWh across the past 24 hours, with an intraday high of $180/MWh. The session was broadly in line with recent trading ranges. No material supply events or constraint notices have been flagged for WA1 at the time of publication.