850 megawatts of power, 1,680 megawatt-hours of energy, sitting on a former coal ash site at Munmorah on the NSW Central Coast. That’s the Waratah Super Battery in two numbers, and I’d argue most coverage of this project still gets the relationship between those two figures backwards. The power rating is what matters here. The energy rating almost doesn’t.
I drove past the Munmorah site on the way back from a weekend up near Lake Macquarie a few months back, not expecting to see much beyond a fenced compound and a lot of grey containers. That’s about right, as it happens. There’s no cooling tower, no stack, nothing that announces itself as a two-billion-dollar-plus piece of grid infrastructure. It just hums. But what it’s doing inside that fence line is genuinely unusual among Australian batteries, and it’s worth being precise about why.
What the battery is actually for #
Most big batteries in the NEM are built to arbitrage: charge cheap, discharge dear, chase the five-minute price spread that the NEM’s five-minute dispatch creates. Waratah does some of that. But its primary job, the one written into its connection agreement with Transgrid and baked into its name, is the System Integrity Protection Scheme – SIPS. Think of it as a very large, very fast electrical shock absorber for the southern NSW transmission network.
Here’s the mechanical problem it solves. The transmission corridor feeding Sydney from the south relies heavily on a handful of major lines. If one of those lines trips – a lightning strike, a fault, a falling tree – the remaining lines can be pushed past their safe thermal and stability limits in the seconds before protection systems or operators can react. The conventional fix is to run the network conservatively: keep flows low enough that even a worst-case trip doesn’t overload what’s left. That’s safe, but it caps how much power, and how much renewable generation – can actually flow through the corridor on a normal day.
Waratah’s SIPS function changes that calculus. Within a couple of hundred milliseconds of a line fault being detected, the battery can inject or absorb a large slug of power to rebalance the network, buying the system time without anyone touching a control room dial. Because that backstop exists, Transgrid and AEMO can run the corridor closer to its actual physical limit on a day-to-day basis, rather than the conservative limit dictated by the worst plausible contingency. That’s the entire commercial logic of the asset in one paragraph, and it’s also the bit that gets flattened into “giant battery helps the grid” in a lot of reporting.
Sizing it properly: power versus energy #
Let’s be careful with that number, because 1,680 megawatt-hours sounds like a lot until you do the division. At full 850MW discharge, that battery empties in two hours. For arbitrage trading, two hours of duration is solid but unremarkable – plenty of batteries in the Capacity Investment Scheme pipeline are being built to similar or longer durations.
For the SIPS role, though, duration is almost beside the point. A line fault event that needs this kind of response lasts seconds, not hours. The battery doesn’t need to hold two hours of energy to do its primary job; it needs to be able to slam 850MW onto or off the network almost instantaneously and hold that output long enough for the network to restabilise and operators to take over. The 1,680MWh of energy behind it is there so the asset can also do commercial trading and other grid services in between those contingency events, which is smart balance-sheet design by Akaysha Energy, but it’s not the number that makes Waratah special. The power figure is.
I’ll admit this distinction trips up a lot of commentary on big batteries generally, not just this one. People default to MWh because it’s the number used to compare the asset to “X homes powered for Y hours,” which makes for an easy headline but obscures what the asset is actually contracted to deliver in the seconds that count.
Who built it and who’s behind the money #
Akaysha Energy developed Waratah and continues to operate it, part of the same stable covered in our profile of Akaysha Energy – a battery-only developer, no retail arm, no generation legacy to manage around. Blackstore acquired Akaysha in 2024, giving the project access to deep infrastructure capital, which matters for an asset class where the revenue streams (network support payments, FCAS, wholesale arbitrage, and a state underwriting contract) take years to fully settle into a predictable cash profile.
The NSW government backed the project early through its Transmission Acceleration Facility and a direct contract for the network security services, recognising that a privately financed battery doing a quasi-network job needed some public underwriting to get built on a reasonable timeline. That’s a model worth watching elsewhere. It’s effectively treating a battery as transmission infrastructure rather than a generation asset, which is the more honest way to think about what Waratah does.
Where the build actually stands #
The project has moved through staged commissioning rather than a single flick-the-switch moment, which is normal for an asset this size and this novel in function. Different blocks of the battery have been brought online and tested against AEMO’s technical requirements in phases, with the SIPS functionality itself needing separate validation from the straightforward charge-discharge commissioning any battery goes through. That staged approach is sensible. You don’t want the first live test of a network stability function to be an actual uncontrolled line trip during peak Sydney demand.
AEMO’s own planning documents, including material feeding into the Integrated System Plan, have flagged for several years that southern NSW transmission constraints were a binding limit on how much renewable energy could move north toward Sydney and the Hunter. Waratah was conceived specifically to loosen that limit without waiting years for new transmission build, which, given how VNI West and other transmission projects have struggled through route and cost disputes – covered in our pieces on VNI West’s long argument with a map – tells you something about why batteries-as-network-assets have become attractive to planners generally.
The capacity it’s freeing up #
The practical upshot, according to Transgrid’s own public statements on the project, is additional transfer capability through the constrained corridor, which translates into more renewable generation able to run at any given moment without being curtailed for network security reasons, and less reliance on expensive, slow-starting reserve generation being held in the wings just in case. Precisely how many additional megawatts of transfer capability the SIPS scheme unlocks depends on grid conditions, time of day, and which specific contingency is modelled, so I won’t pretend there’s one clean constant figure: AEMO’s network documents treat it as a dynamic quantity, not a flat number, and that’s the technically honest way to describe it.
What it does mean for someone watching the broader NSW transition, alongside the gap between coal closures and REZ rollout, is that Waratah buys the network some headroom while transmission augmentation and renewable energy zones catch up. It’s not a substitute for the wires-and-poles build-out. It’s a patch that makes the existing wires work harder in the meantime.
The contrarian bit #
Here’s where I’ll part ways slightly with the more enthusiastic framing of this project. Waratah gets described in some circles as evidence that batteries can replace transmission build. I don’t think that holds up. It’s a genuinely clever way to extract more headroom from an existing corridor, and the SIPS model deserves to be replicated on other constrained parts of the grid where a similar high-power, short-duration intervention could do similar work. But it has limits set by the physical capacity of the lines themselves. You can push a constrained corridor closer to its thermal limit with a fast-acting battery, but you can’t push it past a limit that doesn’t exist yet because the wires aren’t there at all. For genuinely new capacity, you still need new transmission, new REZ connections, the unglamorous stuff covered in our explainer on who actually owns the wires. Waratah is a very good answer to one specific problem. It’s not the answer to the bigger one.
What to watch from here #
The next genuinely interesting data point will be how Waratah performs through its first real unplanned contingency event at scale: a line trip during a high-demand, high-renewable-output period where the SIPS response actually gets tested against a live fault rather than a commissioning simulation. AEMO publishes its system event reports after major incidents, and that’s the document I’d be reading closely when it happens, not the press release. Until then, the project’s value is mostly demonstrated through the modelling AEMO and Transgrid have published rather than through a single dramatic save that made the news.
There’s a reasonable chance other transmission-constrained corridors around the NEM – parts of the Victorian network feeding Melbourne, sections of the Queensland grid ahead of the 2032 Olympics build-out – end up with something similar. If Waratah’s SIPS function performs as designed through a genuine stress event over the next year or two, I’d expect to see very similar proposals pitched as “network batteries” rather than generation assets, with underwriting contracts structured the same way NSW structured this one. Worth watching who moves first.
– Anjali Rao, Grid & Storage Correspondent
Photo by dhahi alsaeedi on Unsplash