Giga-scale big battery proposal seeks green tick for NSW coal country

Plans to construct a 400 megawatt (MW), four-hour battery in New South Wales coal country have joined the federal government’s environmental approval queue.

The McCullys Gap Battery Energy Storage System (BESS), lodged for assessment under the EPBC Act on January 30, proposes to develop a 400 MW/1,600-megawatt-hour (MWh) BESS near Muswellbrook in the Upper Hunter Region of New South Wales.

The project has been proposed by BW ESS, a global energy storage owner-operator based in Zurich, Switzerland, which currently boasts a global pipeline of about 9.5 gigawatts (GW) across the UK, Australia, Italy, Germany, Spain, and Sweden, including over 500 MWh of energy storage projects in operation and over 2.5 gigawatt-hours in active construction.

If all approvals are secured, BW ESS hopes to begin construction of the project in 2027 at a site adjacent to the existing Muswellbrook substation operated by TransGrid and expects construction to take approximately 18 months to complete.

In its early stages, BW ESS is willing to build the project in one or more stages. The operation of the project, once construction commissioning, testing, and demobilisation are completed, would get underway approximately 18 months later.

The project would then operate for at least 30 years.

BW ESS hopes the project will help provide critical support to the existing and proposed generation infrastructure in the region and provide additional storage to help stabilise the electricity system during times of peak demand. The system would also help manage the variability of generation sources.

Consultation with the local community, First Nation parties, and relevant stakeholders has been ongoing since early 2025.

The project’s addition to the ever-expanding EPBC queue comes less than a month after Australian energy giant AGL submitted their own proposed battery storage system in Muswellbrook for EPBC approval.

AGL’s Muswellbrook Battery, a 150 MW/300 MWh BESS which has already secured state significant development approval, would be located adjacent to AGL’s own Muswellbrook Substation.

AGL is also hoping to build the Muswellbrook Pumped Hydro Energy Storage facility at the site of the former Muswellbrook Coal Mine, which opened in 1907 but was shuttered in 2022. The project is also currently edging its way through the EPCB after being submitted back in March of 2025.

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