South Australia’s June price spike asks how long batteries can keep supplying power

South Australia’s electricity price spikes on 21–22 June 2026 offer a concrete case study of storage under successive periods of supply pressure. The Australian Energy Regulator’s second-quarter report, released on 31 August, identifies a combination of cold weather, exceptionally low wind output, falling battery charge and interstate transmission constraints behind the surge in wholesale prices. It also explicitly states that no actual reserve shortfalls occurred during the periods concerned.¹

AI-generated illustration of battery cabinets, a wind turbine and an hourglass, exploring the duration of energy storage.

What reaching the price cap means

Across the two days, South Australia recorded five 30-minute prices above AUD3,000 per megawatt-hour, ranging from AUD3,836 to AUD20,300. The highest came on the morning of 22 June. AUD20,300 was also the market price cap applicable from 1 July 2025 to 30 June 2026. These are wholesale prices, not household retail tariffs.¹²

The 30-minute figure is an aggregation used in the report’s analysis. The National Electricity Market moved to five-minute settlement on 1 October 2021, aligning settlement with dispatch. The report’s half-hourly figures should therefore not be read as evidence that the market still settles every 30 minutes.³

Pressure built on both sides of the supply-demand balance. The report records temperatures of 4–15°C across the two days and demand of 2,188 MW on the morning of 22 June. Against registered wind capacity of 2,766 MW, output averaged just 85 MW over the two days and reached a low of 3 MW on the afternoon of 21 June. That 3 MW reading was a minimum, not the wind output throughout the high-price periods.¹

Discharge came first, with limited opportunities to recharge

Batteries had already supplied substantial electricity during the evening peak on 21 June. Operators subsequently reduced offered capacity as their expectations of remaining charge changed. The wind lull continued overnight, leaving little opportunity to recharge from renewable generation. As high prices emerged the next morning, total battery offers fell sharply from 326 MW to 1 MW, then to zero in two subsequent five-minute intervals.¹

The 326 MW and zero figures describe capacity offered to the market. They do not mean installed batteries disappeared, nor are they a direct, uniform measurement of every battery’s physical charge. The AER identifies declining charge as an important cause, while also documenting rebids prompted by technical capability, price forecasts and other factors. Describing the whole sequence as all batteries failing would obscure essential market and operating conditions.¹

Transmission and bidding also shaped the outcome

South Australia remained predominantly a net importer of electricity from Victoria. However, imports over Heywood were constrained, while constraints on Murraylink forced counter-price flows from higher-priced South Australia into lower-priced Victoria. Reduced access to cheaper imports made expensive local generation more likely to be necessary to meet demand. Rebidding by gas generators and batteries further affected prices.¹

The episode is therefore best understood as the interaction of low wind, demand, stored energy, transmission and offers. It reveals supply constraints in the configuration operating at the time. On its own, it does not establish that all battery storage is incapable of supporting reliable supply, or that nominal transmission capacity can always be counted on.

Planning must consider power, duration and recharging together

A storage system’s megawatt rating describes instantaneous power; megawatt-hours describe the amount of energy that can be stored and released. AEMO’s guidance on bids by bidirectional units also distinguishes the two: dispatch power can be constrained so that stored energy at the end of an interval remains within specified minimum and maximum limits.⁴ Evaluating storage therefore requires more than asking how many megawatts have been installed. It also requires knowing the charge available when a peak begins, how long supply is needed and where recharging energy can come from between successive peaks.

Extreme intervals should also be distinguished from the quarter as a whole. The AER estimates that prices above AUD5,000/MWh on these two days added AUD13/MWh to South Australia’s quarterly volume-weighted average. That average was AUD95/MWh, below AUD166/MWh a year earlier. Price-spike risk and a decline in overall prices can coexist.¹

The practical lesson is to test prolonged low wind, limited overnight charging and constrained interstate transfers together, while assessing combinations of longer-duration storage, dispatchable generation and demand response. The question is whether supply can be maintained at an acceptable cost through successive tight periods, rather than simply how much capacity exists at a single moment.

Source notes

1. 31 August 2026 · Significant electricity prices for April to June 2026 · Australian Energy Regulator (AER), pp. 17–23; release date confirmed on the report publication page. Source report © Commonwealth of Australia 2026, licensed under CC BY 4.0. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷

2. 27 February 2025 · Schedule of reliability settings – 2025-26 financial year · Australian Energy Market Commission (AEMC). ↩

3. 1 October 2021 · Energy market’s time to shine · Australian Energy Market Operator (AEMO). ↩

4. Accessed 5 October 2026; publication date not stated · Energy Limit in BDU Bids · AEMO. ↩