Origin Energy’s 650MWh Mortlake BESS begins commercial operations in Australia

Origin Energy has confirmed that its 300MW/650MWh Mortlake battery energy storage system (BESS) in south-west Victoria has commenced commercial operations, following completion of major commissioning works.

Origin Energy is one of Australia’s largest energy companies, operating as both a generator and retailer across electricity, gas and renewable energy.

The Mortlake facility is located at the site of Origin’s existing Mortlake Power Station, around 200km west of Melbourne, and connects directly to AusNet’s 500kV switchyard through a dedicated substation.

The AU$400 million (US$279 million) project was first announced by Origin in January 2024, with construction beginning that August. Fluence served as the main contractor for the build.

The facility uses grid-forming inverter technology, distinguishing it from conventional grid-following battery systems through its ability to set its own internal voltage waveform reference and operate independently of other generation sources when required, allowing it to actively stabilise the grid in a manner similar to synchronous generators.

However, it should be noted that grid-forming inverter-equipped battery storage systems have not yet been confirmed to meet the highest tier of system strength requirements in the NEM, according to the Australian Energy Market Operator (AEMO).

This hasn’t stopped the technology from becoming a core pillar of battery storage systems in Australia, with grid-forming inverters featuring in 74% of Australia’s 33.2GW NEM battery storage pipeline.

From commissioning to commercial operation

The commercial launch follows a formal testing process that began in early 2026. The system, designated MLB01 in the AEMO registry, entered AEMO’s Market Management System in March 2026, marking its transition into low-load injection and consumption testing to verify integration with Victoria’s transmission network.

That step followed Origin’s completion of unconditional connection agreements with AEMO in November 2025, which provided the regulatory certainty needed to proceed through the project’s final construction phases after satisfying the technical assessments and grid-impact studies required for safe integration.

Mortlake’s location also adds to a growing concentration of grid-scale battery storage in western Victoria, sitting roughly 30km northwest of the 100MW/200MWh Terang BESS.

The clustering of large battery storage systems in the region reflects both the availability of established transmission infrastructure at legacy generation sites and the value grid-forming assets provide in areas of the network where synchronous generation is being phased out.

For Origin Energy, Mortlake represents a shift in how the company uses its existing generation assets, pairing battery storage with sites that already have grid connections built for thermal power stations.

The approach reduces the cost and lead time associated with new transmission infrastructure, a factor increasingly shaping where large-scale battery storage projects are sited across the NEM as developers compete for connection capacity in areas with adequate network headroom.

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