South Australia has the most wind and solar and no baseload: So why is it the only state not fretting about a vulnerable grid?

South Australia has the highest wind and solar share – an average of around 72 per cent over the last 12 months – vastly more than other state in Australia, and higher than any other gigawatt scale grid in the world.

Renewable energy critics, particularly those that don’t understand the way that grids work, instantly assume that this means South Australia’s grid must be weak and unreliable. But that is simply not true, and a new report from Australian Energy Market Operator on “system strength” underlines why this is so.

System strength is an important part of grid security, and – according to AEMO – describes the ability of the power system to maintain and control the voltage waveform at a given location, when the grid is running normally and particularly when it has to deal with a major disturbance.

That disturbance could be a network fault, due to a fire, storm, falling trees or some other issue, or a trip of a generator, an increasingly frequent event given Australia’s ageing coal fleet and soaring summer temperatures.

If there is a shortfall in system strength, then the ability of the grid to recover from the disturbance is impeded, increasing the risk of wider and longer outages.

AEMO’s 2024 System Strength Report, published earlier this week, find that there are potential shortfalls in system strength in all of the states that make up the country’s main grid, known as the National Electricity Market. The one exception is South Australia.

“All regions except South Australia are expected to experience system strength shortfalls over the
next three years unless adequate investment or services are provided,” the report says.

The reason is relatively simple. South Australia closed the last of its coal fired generators in 2016, and despite having a number of gas generators these are largely “peaking plants” that operate rarely, or “intermediate” that operate part time. There is no baseload power left in the state.

That has not affected its energy reliability (despite what some pundits have been claiming), and nor has it affected its energy security. AEMO and the local network owners have already taken action to install four synchronous condensers – spinning machines that do not burn fuel – and which have addressed the issue.

In time, battery storage may also be able to provide that service with their advanced “grid forming” inverters.

Other states, however, are still grappling with the accelerating pace and scale and urgency of the energy transition from centralised fossil fuel generators to distributed wind, solar and storage.

The NSW government decision to pay Origin Energy up to $450 million to keep the country’s biggest coal generator at Eraring open for another two years has effectively deferred its emerging system strength shortfall to 2027. But it will still have to address those issues should Origin close as planned in that year.

The main transmission company in the state is Transgrid, and it is currently assessing options to fill that shortfall – and will likely do so with a mix of syncons and big batteries with advance grid-forming inveters.

Ironically, the decision to keep Eraring open has caused problems for Queensland. That’s because – with Eraring generating – coal plants in Queensland will be operating less often.

“These shortfalls (in Queensland)n are primarily linked with decreased energy exports to New South Wales, with more energy available in that region following the delayed retirement of Eraring Power Station,” AEMO says.

“That change has resulted in fewer thermal units expected to be online economically in Queensland, and lower fault levels than previously projected.” Queensland’s Powerlink is now going through an accelerated process to fill those gaps, much in the same way as Transgrid.

Victoria is also forecast to have a system strength shortfall in 2025/26, largely the result of the expiry of existing contracts. These will be addressed either with new contracts, or at leat partially by a new syncon that has been announced by the state government this week to support its roll out of renewables.

Even Tasmania, which generates most of its power from hydro, faces multiple shortfalls at all four its network nodes, and the local transmission company is also working to provide solutions.

Of course, these are not predictions that the lights will go out – any more than AEMO’s regular lack of reserve notices, or electricity statement of opportunities are. They are simply identifying where gaps are likely to emerge and ensuring that action is take to fill it.

But the work has already been done in South Australia – underlying why it is now regarded as one of the most secure and reliable grids in the country. Just like another renewable energy powerhouse Germany, where the reliability factor is at 99.997 per cent.

Grids that depend on wind and solar may be dealing with variable power supplies, but they are largely predictable. Sudden trips of large centralised generators are not predictable, and that – as AEMO has made clear on repeated occasions – is what it fears most.

See also: Baseload power generators not needed to guarantee supply, say science and engineering academies