SA1 experienced sustained negative pricing over three consecutive 5-minute intervals (03:50–04:00 on 18 September 2026), with prices settling at −$18/MWh, following an earlier spike to −$42.11/MWh. The event occurred during a period of high wind generation (197.69 MW) combined with modest solar and gas output, in an overnight low-demand window.
Negative pricing in SA1 reflects an oversupply condition typical of high renewable generation during low-demand periods, compounded by binding constraint F_T+LREG_0050 which carried marginal values of 27.58–104.90 $/MWh across the event window. The constraint's high marginal value indicates it was a significant cost driver; the negative prices suggest that managing this binding constraint required the dispatch stack to include low-margin or negative-priced generation, likely due to ramp-rate or minimum-stable-generation requirements that prevented rapid wind backing-off during the early-morning trough.
Causal analysis generated by gridIQ's synthesis model from live AEMO market data: dispatch prices, generation mix, interconnector flows and market notices in the interval surrounding the event.