Death of baseload: World’s biggest isolated grid is reaching 84 pct wind and solar almost daily
 Cunderdin hybrid solar and battery facility.
Giles Parkinson
Oct 20, 2025
Chart of the day
Western Australia continues to defy conventional wisdom about the running of electricity grids, reaching levels of 84 per cent penetration of wind and solar on almost a daily basis.
Such percentages are not uncommon in other parts of Australia – South Australia, for instance, reaches 100 per cent renewables (as a share of grid demand) on almost a daily basis, and has hit a peak of more than 150 per cent renewables.
But that’s because most state grids are able to export surplus capacity. What makes W.A. unique is that it hosts the world’s biggest isolated electricity grid, with no connections to other states or other countries.
That makes its main grid – known as the South-West Interconnected System (SWIS) – wholly reliant on its own resources to manage the variability of wind and solar, and to prepare for the planned closure of the last of the state’s coal fired power generator by the end of the decade.
The transition has already begun in earnest: The state has commissioned three big batteries in the SWIS, including the country’s biggest at Collie (560 MW and 2,240 MWh) and with another 500 MW, 2,000 MWh battery in the same city also working through grid permissions.
It has also commissioned the country’s first large scale solar-battery hybrid, at Cunderdin in the wheat belt, which is regularly feeding solar power into the grid in the evenings, and occasionally through the night.
Another eight big battery projects are under construction, or have been awarded underwriting agreements through state and federal tenders, although one of them has hit a major road hump and is suing its sacked contractors for missing equipment.
The SWIS – which has maximum demand of more than 4 GW – has other challenges too. It doesn’t have any pumped hydro – the common fall back for both fossil fuel baseload plants and renewables – so it is entirely dependent on battery storage, demand management and flexible gas to fill in the gaps.
Over the past week there has been a lot of discussion on LinkedIn and elsewhere about the consistently high penetration of wind and solar, mostly driven by the influence of rooftop PV in the middle of the day.
Jai Thomas, the co-ordinator energy within the W.A. government, says that any time of running more than 80 per cent renewable energy during the day is significant, given that the SWIS is its own closed system.
“We are down to running about 400 MW of thermal generation only in these periods,” he says.
“Critically, we also charge Australia’s largest battery during those periods for discharge at evening peak. The extremely high renewable periods show what is possible as we continue to build from the average 40 per cent renewables and storage that meet electricity demand in the SWIS currently.”
Ray Wills, an energy expert who helped lead the early development of the Cunderdin solar hybrid, reckoned that the state hit a new peak of 87.5 per cent renewables at 11.30am on Saturday, local time.
Thomas is not so sure about that record, pointing out to the differences in calculating rooftop PV consumption in various data sources. Officially, he says, the record as recognised by the market operator stands at 85.1 per cent..
Still, even if not a record, it still points to the radical transformation of the state’s grid in recent times. Consider this graph below provided by Wills.
 It now highlights power “below the line”. i.e. charging into batteries, with the likes of Collie specifically contracted to soak up excess rooftop solar in the middle of the day and feed it into the grid in the evening.
At times, the share of power fed into the grid from big batteries (marked in red) hits more than 20 per cent. And that will increase over time. Neoen’s Collie battery alone can account for 20 per cent of average grid demand.
Wills says higher levels of renewables penetration are almost certain to occur in November and even December, with excellent conditions for wind and solar and relatively low demand, as least until air-cons are switched on in earnest as the summer heat takes hold.
W.A., however, still has challenges in ensuring enough new wind and solar is built to provide the bulk energy needed to replace coal, and last month rolled out a proposed new transmission plant to provide the grid infrastructure to host new projects.
In Australia’s main grid, known as the National Electricity Market, and covering NSW, Queensland, Victoria, South Australia and Tasmania, the highest penetration of renewables on a 30-minute trading period reached 78.6 per cent on Saturday, October 11, according to AEMO.
On a five-minute trading basis, the n ew peak has been set at 79.8 per cent around the same time, according GPE NEMLog. And, as mentioned above, individual states have reached much higher levels of penetration.
AEMO has said it is looking to accommodate up to 100 per cent instanteneous renewables as early as late 2025, although this timeline looks like to slip as it works on the engineering challenges, which including making sure there is enough essential grid services such as system strength available in the grid at such time.
There have been several occasions when “available” renewables amount to more than total NEM demand, but a combination of economic curtailment (negative wholesale prices), and grid curtailment reduces that number to levels that AEMO is comfortable to handle.
The market operator has been focusing on several technologies to provide these services – synchronous condensers that do not burn fuel, equipping gas generators with a “clutch”, and using grid-forming battery inverters.
reneweconomy.com.au |
