Origin Energy plans to build a big battery alongside the largest gas-fired power station in Victoria, near an existing high-voltage transmission line.
Located in the state's South West Renewable Energy Zone, the $400 million battery will capture cheap solar power during the day and dispatch renewable energy back into the national electricity grid during peak demand.
Avoiding transmission delays, the battery will be built beside a gas-fired power plant on land Origin already owns and will connect to the 500 kilovolt transmission line that runs adjacent to the site.
The 300 megawatt/650 MWh Mortlake big battery will help to maintain reliable power for customers, Origin said on Monday.
There will be no change to the operation of the Mortlake "peaker" plant, which is powered by gas from the Otway Basin and fires up at short notice to cover times of high demand.
Adding system strength and reliability, the battery project will use "gridstack" energy storage technology and artificial intelligence-driven performance management software from global energy company Fluence.
"Australia is an important market for Fluence," president and chief executive Julian Nebreda said.
"Our local team is now delivering over 1GW energy storage projects within Australia to enhance grid stability and enable the country's clean energy transition."
Origin CEO Frank Calabria said large-scale batteries and other storage technologies would play a vital role in Australia's energy transition.
He said the Mortlake battery would help keep the grid stable and support more renewable energy coming into the system as the market continues to decarbonise.
Site preparation and civil works will start over coming months and the battery is expected to be commissioned in late 2026.
The Victoria announcement follows Origin's $600 million investment decision in NSW last year on stage one of the company's first large-scale battery, at Eraring.
