Tasmania experienced sustained negative pricing across six intervals between 03:50 and 04:25 on 18 September 2026, with prices ranging from −$10.53/MWh to −$17.40/MWh. The negative pricing was punctuated by a sharp spike to $88.20/MWh at 04:20, suggesting a sudden market rebalancing event.
The negative pricing reflects an oversupply condition in TAS1 during low-demand overnight hours, with combined hydro and wind generation totalling approximately 667–680 MW across the affected intervals. A binding constraint (F_T+LREG_0050) with consistently high marginal values (ranging from 99.09 to 107.17) indicates a physical limit restricting outward flows, forcing Tasmania to accept negative prices to clear surplus renewable generation. The subsequent price spike at 04:20 suggests the constraint relaxed or demand response activated, allowing the market to clear at a substantially higher price level.
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.