Australia may have hit record levels of renewables during the last quarter of 2025, but the share may have been so much higher were it not for the economy and network curtailment off large scale wind and solar, which also reached record levels.
According to the Australian Energy Market Operator, the total economic “offloading” of wind and grid-scale solar generation averaged 1,312 MW across the December quarter, the highest quarterly average on record and double the previous peak set in the same period a year earlier.
Grid-scale solar was the worst affected, offloading an average 18 per cent of its available output due to economic factors i.e. negative prices. Solar farms in NSW and Queensland suffered big increases in offloading levels, but the biggest victims were in South Australia.
According to AEMO, economic offloading for its handful of solar farms reached a staggering 59 per cent of potential output in the December quarter, a result of the fact that rooftop solar meets much, and sometime all of daytime demand, pushing wholesale prices into negative territory.
When prices go negative, most solar farms are obliged to turn off, depending on the nature of their off-take agreements, because it means they have to pay to produce.
Most coal generators are happy to do this – and are usually the ones responsible for pushing wholesale prices into negative territory, but they reason it is cheaper to pay others to take their power than to switch off and switch on again, although some companies like AGL are experimenting with so-called “two shifting” of coal units.
The solar farms most affected by offloading in South Australia include the biggest, the 220 MW Bungala facility (contracted by Origin Energy), and Tailem Bend (contracted by Snowy Hydro), as well as the Port Augusta Renewable Hub, where 100MW of solar with more than 200 MW of wind.
What to do about economic offloading? More network capacity will help, as it will allow more excess power to be exported to places that need it, as will more home batteries (absorbing the output of rooftop PV), and more big batteries, that like to charge from the grid at low prices.
The growth of offloading is one reason why nearly every new solar project is now presented as a solar-battery hybrid, helped along by changes in connection rules, and the plunging price of battery storage that have enabled those facilities to easily compete in the evening peaks, where they will want to send their output.
The AEMO Quarterly Energy Dynamics report also notes that economic curtailment of wind also more than doubled to an average 695 MW over the quarter, also a record high.
That equated to 15 per cent of average wind availability, up from 10 per cent a year earlier. It was most pronounced in Victoria, where offloading now represents more than 25 per cent of available wind output, an increase blamed on network limits that have restricted wind exports to NSW and Tasmania.
Wind and solar output can also be constrained by network constraints, often imposed by network companies or the market operator itself.
According to AEMO, average curtailment of grid-scale solar generation by network constraints also increased from 176 MW in Q4 2024 to an all-time high of 213 MW in Q4 2025, mostly because of issues in NSW. But it said as a share of potential output, the share of network curtailment actually fell to 6.3 per cent from 6.5 per cent.
Wind curtailment as a result of network constraints remained broadly unchanged at 37 MW, and its percentage of total potential output reduced slightly to 0.8 per cent.
Despite the big increases in economic offloading, the output of both wind and solar hit record highs in the quarter, thanks to the commissioning of new facilities and in some cases better conditions.
Grid-scale solar output across the NEM reached an all-time quarterly high of 2,535 MW, AEMO says, with availability growing by 628 MW – thanks to new solar capacity at the Stubbo, Wollar, Culcairn, Walla Walla and Aldoga soalr farms.
Remarkably, AEMO says Victoria recorded the highest average capacity factor at 34 per cent, probably due to the fact that rooftop solar has a lower impact, as a proportion of the grid, than in other states.
Wind capacity also grew, with additions from the Golden Plains, MacIntyre, Clarke Creek, Goyder South and Ryan Corner wind farms, and output from existing facilities also grew because of better wind conditions.
AEMO says Tasmania recorded the highest average capacity factor at 49%, up 7.7 pp year on year, but in Queensland it fell 2.8 pp to 31%.
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