Origin has lodged plans for a 500 MW, eight-hour battery at Eraring. On its own timetable it would arrive after the coal units close

Origin Energy wants to build a third grid battery on its Eraring Power Station site in Lake Macquarie, and the formal process has started. The NSW Major Projects portal lists it as Eraring North Battery Energy Storage System, State Significant Development application SSD-146467238, with a current status of Prepare SEARs as at 5 October 2026. That is the first of eight stages the portal shows, ending in a determination. Filed beside it is a scoping report prepared by GHD for Origin and dated 28 September 2026. Origin’s project page had said it planned to lodge that report in September 2026, and describes the whole thing plainly: The proposal is in the early stages of the development approval process.

This is the expansion we flagged on 5 October in a note on our account of the battery’s four approved stages. The scoping report adds the detail the project page does not have, and it also adds a second set of storage figures, which we come to below.

How big it is, against what is already there

The existing Eraring battery is two batteries built in four stages. Battery 1 is 460 MW with 1,770 MWh of storage, and Origin’s FY26 annual report records that it began commercial operation on 24 December 2025. Battery 2 is 240 MW with 1,390 MWh, in the final stages of construction and, on the project page, on track for early 2027. Together they are 700 MW / 3,160 MWh, the same figures Origin gave investors in its FY26 results presentation on 13 August 2026. AEMO’s Generation Information for July 2026 lists the same units: 460 MW in service, a further 700 MWh of in-service storage added to it, and 240 MW / 1,390 MWh committed with full commercial use on 31 March 2027.

The proposal adds around 500 MW. The project page says that would bring the site to a combined maximum registered capacity of 1,200 MW. The coal plant beside it is four 720 MW units, 2,880 MW in all, which AEMO lists as an announced withdrawal with a closure date of 30 April 2029. So the batteries already built or being built equal about a quarter of the coal units’ capacity (700 of 2,880 MW, 24 per cent), and with the expansion that would rise to about two-fifths (1,200 of 2,880 MW, 42 per cent). That is a comparison of power, not of what each can supply over a day: a coal unit can run around the clock, while a battery runs for hours and then has to recharge.

On the ground, the scoping report puts the project at about 22 hectares: 11 hectares of new disturbance north of the existing battery, which is the 11 hectares Origin’s page mentions, and another 11 inside the existing battery’s approved area.

Solid: operating. Outlined: under construction. Hatched: proposed, not approved. The lighter solid bar is the approved site total; the grey bar is the coal units. Battery figures are from Origin’s project page and FY26 results presentation; the two proposed storage figures are from Origin’s project page and the 28 September 2026 scoping report; coal capacity and closure date are from AEMO’s July 2026 Generation Information. No combined storage figure is drawn, for the reason set out below.

What eight hours does that the existing batteries do not

A battery’s megawatts say how hard it can push; its megawatt hours say for how long. Divide one by the other and you get its duration at full output. Battery 1 is about four hours (1,770 divided by 460 is 3.8) and Battery 2 about 5.8 hours. The proposal is eight.

AEMO sorts storage by exactly this measure. In its 2026 Integrated System Plan, shallow storage dispatches for less than four hours, and Medium storage can dispatch electricity for four to 12 hours, the kind that can shift large amounts of electricity to meet evening or morning peaks. Deep storage, more than 12 hours, is mostly hydro. On that scale Battery 1, at about four hours, sits on the line between shallow and medium; Battery 2 and the proposal are medium, and the proposal would sit well inside the band rather than at its edge.

In plain terms: run flat out from 5pm, a four-hour battery is empty by 9pm, while an eight-hour battery lasts until 1am. It can also run at part power for longer. The scoping report says the new battery could discharge at full capacity for up to eight hours, or at partial capacity for a longer duration, and Origin’s project page describes it as providing longer-duration supply to cover the evening peak. Origin’s own results presentation (slide 18) draws the line the other way: it describes batteries as well suited to short, sharp evening peaks and its gas fleet as better suited to longer volatility events. An eight-hour battery reaches further into the territory Origin gives to gas.

The trade-off is filling it. The same project page says Battery 1 takes slightly over four hours to charge fully at its maximum rate and Battery 2 almost seven, while the proposed battery is expected to take around 10 hours to fully charge. That is most of a sunny day.

What has to happen before it exists

As at 5 October 2026 the scoping report is on the portal and, on the report’s account, the Commonwealth referral has been made. Everything else below is still ahead.

1. Assessment requirements. The Planning Secretary issues the Secretary’s Environmental Assessment Requirements (SEARs), the stage the portal shows the project in now.
2. An environmental impact statement. Origin prepares and lodges an EIS against those requirements. The portal’s remaining stages are exhibition, collation of submissions, response to submissions, assessment, recommendation and determination. The scoping report says a cost estimate certified by a quantity surveyor would come with the EIS; it gives none now.
3. A decision. The scoping report (p. 24) says the consent authority is the NSW planning minister or a delegate, unless the Independent Planning Commission is designated. Origin’s page expects the process to take about 18 months to two years, with a determination by mid-2028.
4. Commonwealth approval. The scoping report (p. 25) says a referral under the EPBC Act has been submitted and expects the project to be assessed through the bilateral NSW and Commonwealth process. We did not check the EPBC portal for the referral.
5. A decision to spend. Origin’s project page puts the money conditionally: If the next stage of the Eraring battery progresses, an additional $1 billion will be invested. The FY26 annual report (p. 56) says further development feasibility work is underway for additional battery expansion at Mortlake and Eraring. Origin’s committed battery program in the FY26 presentation (slide 52), 1,760 MW / 6,408 MWh across six projects, does not include it.
6. Construction. The scoping report (p. 21) says Construction and commissioning of the Project is expected to take between two to three years to complete.

AEMO’s July 2026 Generation Information, the latest release on its page as at 5 October 2026, lists no unit for the expansion. Its Eraring Big Battery entry carries the three existing units and a maximum site capacity of 700 MW.

The storage figures do not agree, so we give no total

Origin’s project page gives the expansion as 500 MW / 4,000 MWh (eight hours) and the existing batteries as 700 MW / 3,160 MWh, then gives the combined site as 1,200 MW / 8,600 MWh, subject to detailed design. Its own parts add to 7,160 MWh, not 8,600. The scoping report’s parts do add to 8,600 MWh, but they are different parts: it gives the existing battery as 3,658 MWh and the new one as approximately 4,942 MWh. The portal’s one-line summary gives 4,924 MWh. Until one figure is settled, any total we printed would be a choice between Origin’s own documents.

Our read

This section is opinion, based on the facts and documents above.

The timing makes this a battery for after the closure, not for it. A determination by mid-2028 followed by two to three years of construction and commissioning points to roughly mid-2030 to mid-2031 at the earliest, a year or more after the coal units’ 30 April 2029 closure date. That is our arithmetic from Origin’s own timetable; neither the project page nor the scoping report gives an operating date. The batteries that will actually be standing when the coal stops are the 700 MW already built or under construction. This one is about what the site does in the 2030s.

Eight hours is the number NSW policy is written around. AEMO’s 2026 plan notes that New South Wales has a 2 GW target for storage of at least eight hours duration by 2030, and the scoping report presents the project as a material contribution to the State’s 2 GW long-duration target. A battery sized at exactly eight hours sits on that line. On Origin’s timetable it would arrive after the 2030 date that target names.

The figures should be settled before anyone is asked to comment on them. A project that is 4,000 MWh on its owner’s web page, about 4,942 in its scoping report and 4,924 on the planning portal, beside an existing battery stated as 3,160, 3,300 and 3,658 MWh, is hard for a neighbour or a submission-writer to weigh. The EIS is where one set of numbers, with its basis stated, belongs.

What we will check

Whether the department issues SEARs, when the EIS is lodged and exhibited, whether AEMO’s next Generation Information release adds the expansion, and which storage figure Origin’s page and the EIS settle on.