850 megawatts of power, 1,680 megawatt-hours of energy, sitting on a former coal ash site at Munmorah on the NSW Central Coast, and for most of its working life it won’t discharge a single megawatt-hour to the market at all. That’s the detail about the Waratah Super Battery that tends to get lost whenever someone calls it the world’s biggest battery, which, by nameplate capacity, it currently is. I drove up the Pacific Highway past Doyalson earlier this year to have a look at the site from the road. You can’t get close, it’s fenced like the substation it effectively is, and the thing that struck me wasn’t the scale, it was how unremarkable it looks for something doing such a strange job.
Most big batteries in the NEM are built to trade. They buy cheap, sell dear, chase the arbitrage spread, maybe pick up some frequency control ancillary services revenue on the side. Waratah isn’t primarily that. Its main function is to sit in reserve as what AEMO and the project’s backers call a System Integrity Protection Scheme, or SIPS: a shock absorber that can inject or absorb enormous amounts of power in milliseconds if something goes wrong on the transmission network south of the Hunter. Think of a major transmission line tripping unexpectedly. Without something fast enough to respond, that fault can cascade, forcing other lines to shed load or trip in sympathy. Waratah’s job is to catch that shock before it propagates.
Who owns what here, and why it matters
The project sits in an ownership structure that’s worth untangling because it explains a lot about how it got built. Transgrid, the NSW transmission network operator, holds the contract to provide the SIPS-related network service and effectively underwrites that function through a regulated revenue stream. Akaysha Energy, the Melbourne-headquartered battery developer backed by global investment manager BlackRock, built and operates the asset and captures the merchant upside: the arbitrage and FCAS revenue available in the hours it isn’t needed for grid security. I’ve written before about Akaysha’s broader project pipeline and about BlackRock’s wider battery bet on the NEM, and Waratah is the project that put the company on the map nationally, even though most households in NSW still couldn’t tell you who Akaysha is.
That split (network-funded security function, merchant-funded trading function) is genuinely novel for the NEM. It’s not quite the Capacity Investment Scheme model I’ve covered in how the Capacity Investment Scheme actually works, and it’s not a pure merchant battery either. It’s closer to a hybrid where the network benefit justifies part of the capital stack and the market exposure justifies the rest. Whether that model gets replicated elsewhere depends a lot on how the cost recovery for the Transgrid piece holds up under AER scrutiny over the coming regulatory period.
Power versus energy, again
Let’s be careful with the numbers here, because 850MW and 1,680MWh get conflated constantly in coverage of this project, including some of my own early reporting on it. The 850MW figure is how fast the battery can push power onto or pull it off the network – instantaneous capacity, like the peak output of a very large gas turbine. The 1,680MWh figure is how much total energy it can store and deliver, which at full 850MW discharge works out to almost exactly two hours of sustained output. For the SIPS function, the power rating is what matters. You need the fast, large injection to arrest a frequency or voltage excursion in the seconds after a fault, not hours of sustained energy. For the merchant trading function layered on top, the duration matters more, because that’s what determines how many peak-price windows you can actually capture in an evening.
A two-hour duration battery at this scale is still a two-hour duration battery. It won’t solve a multi-day wind lull on its own, and nobody serious claims it will. What it solves is a narrower, more technical problem: the stability of the transmission corridor feeding Sydney as coal plant retires behind it.
Why the location is the point
Munmorah sits close to the transmission corridor that used to be anchored by Vales Point and Eraring, and not far from where Liddell used to sit before it closed in 2023. As those coal units retire – Eraring’s own exit has already been pushed out once, which I covered in detail in Eraring power station: how 2025 became 2027 – the system loses not just energy but also the physical inertia and fault-current support those big spinning turbines provided almost as a byproduct of generating electricity. A sudden loss of a major transmission element in that corridor used to be buffered by that inertia. Increasingly, it has to be buffered by something else.
That’s the gap Waratah is built to fill, at least partially. It allows Transgrid to operate parts of the network closer to their thermal limits without the same margin for contingency events, because the battery can respond faster than any mechanical protection scheme ever could. AEMO’s own material on system security, including the operating incident reports it publishes after major network disturbances, has repeatedly flagged exactly this kind of fast-acting intervention as a tool for managing the transition. I’d point readers to AEMO’s Integrated System Plan documentation for the system-wide framing, and the AER’s regulatory determinations for how projects like this get their network revenue approved.
The build and the commissioning path
Construction ran through 2023 and 2024, with the project reaching commercial operation in stages: the full 850MW capacity energised and available for use rather than flicking on overnight. That staged approach is standard for a project of this size; you don’t want to discover a control system fault with the whole fleet live at once. Akaysha’s own project updates and Transgrid’s public materials have tracked the commissioning milestones, and the project has been framed consistently as delivering the SIPS function first, with the merchant trading capability layered in as commissioning progressed.
It’s worth noting this wasn’t a cheap build, though I’ll be straightforward that neither company has published a granular capital cost breakdown I’d stake a specific figure on publicly, so I won’t invent one here. What’s publicly known is that it’s a multi-hundred-million-dollar asset at a scale well past anything previously built in the NEM for grid security purposes specifically, as distinct from pure arbitrage plays like the Hornsdale Power Reserve in South Australia, which I’ve touched on in pieces about South Australia’s renewable energy record.
Where I think the sceptics have a point, and where they don’t
There’s a strand of criticism around big batteries generally that I’ve aired before in are big batteries being built for the wrong job? – the argument that two-hour assets are being asked to do four-hour or eight-hour jobs, propped up by capacity payments that don’t reflect their actual duration limitations. I think that criticism is fair when applied to batteries being built purely to firm evening peak demand over long periods. I don’t think it applies cleanly to Waratah, because the SIPS function it was principally built for doesn’t need duration. It needs speed and peak power, which is exactly what a two-hour lithium-ion battery is good at. If anything, Waratah is a better advertisement for where big batteries make sense than most of the merchant-only projects getting built right now, precisely because its core job matches its physical characteristics instead of straining against them.
Where I’d push back on the project’s own marketing is the “world’s biggest battery” framing, which gets repeated uncritically in a lot of coverage. It’s the biggest by nameplate MW in Australia and among the largest globally at time of writing, but that league table shifts constantly as projects in Texas, California and China come online, and “biggest” by power rating isn’t the same claim as “biggest” by stored energy. A battery project twice its duration at half its power rating could hold more total energy and lose the MW crown. Worth keeping straight.
What it means for the transition more broadly
The bigger story here, I reckon, is less about this one asset and more about what it signals for how transmission businesses fund grid security in a system losing synchronous generation fast. If the Transgrid-Akaysha split proves durable under regulatory review, expect to see similar structures proposed for other critical corridors, particularly around the New England REZ transmission build and the Central-West Orana zone, both of which will eventually face the same inertia and fault-level questions as more coal retires behind them. AEMO’s own Engineering Framework work has flagged system strength and inertia shortfalls as a live, multi-year problem across several NEM regions, not just NSW. It’s not a one-project solution, and nobody involved claims otherwise.
The quieter stress-test will come the first time there’s a genuine, serious network contingency event in that corridor after coal retirement accelerates further, and we get to see the SIPS function actually called upon rather than just contracted and tested. That’s the moment this asset’s value becomes something other than a specification sheet.
– Anjali Rao, Grid & Storage Correspondent
Photo by Anja van de Gronde on Unsplash