The key component of the project is a pumped hydro energy storage system (PHES) on land within the current Stratford Mining Complex, which proponents Yancoal Australia say could generate up to 3.6 gigawatt-hours of renewable energy.

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“This energy storage would provide 300 MW for up to 12 hours – equivalent to the daily energy consumption of between 140,000 to 180,000 households,” Yancoal told NOTA in a statement.

A solar farm would also be constructed to supply approximately 320 MW AC of renewable energy to ‘charge’ the PHES by pumping water from the lower reservoir to the upper reservoir.

Energy would also need to be imported from the electricity grid to fully charge the PHES.

“Once operational, the project would avoid 320,000 to 550,000 tonnes of carbon dioxide equivalent per annum if this energy was alternatively produced by gas-fired power generation,” the project website states.

The NSW Government declared the potential project Critical State Significant Infrastructure (CSSI) in July 2024. Yancoal says the site’s natural topography, land holdings, and proximity to existing electricity transmission infrastructure and demand centres makes it an “ideal location” for pumped hydro.

“The project represents a beneficial use of the water that is stored in the mine voids,” Yancoal said.

“Compared to other pumped hydro systems that are required to draw their water from nearby streams and rivers, this is a significant advantage.”

In the 23 October edition of Gloucester District News Of The Area, letter writer Steve Robinson questioned whether pumped hydro was the best use for the site, suggesting a solar farm and batteries as a more effective use of the mine site.

Mr Robinson listed the following as risks of pumped hydro.

“It (the SREH) involves flooding a rainforest gully and other native vegetation (145 hectares) impacting 20 threatened species including koala, sooty owl, stuttering frog etc, the most critically endangered being 217 scrub turpentine for which Yancoal are offering to donate $250,000 to a species recovery organisation,” Mr Robinson wrote.

“The water that is pumped between two dams will be the untreated polluted mine water which is bound to damage the pumps.”

In a statement to NOTA last week, Yancoal stated, “The Stratford PHES system has been designed as a ‘closed system’ to allow the water to be reused, while keeping it on-site.

“The design of the dams will meet stringent requirements of NSW Dams Safety and will be designed and built to the appropriate engineering requirements.

“Testing of the water stored in the Stratford East Dam and other mine voids shows similar water quality to groundwater within the local and regional aquifers.

“Water quality has always been a consideration in the engineering design, including the pump maintenance schedule.”

Yancoal said while batteries are a viable option for fast, short-term energy responses, pumped hydro’s strength lies in its ability to “provide large-scale, long-duration storage” – aligning with the Government’s long-duration storage (LDS) targets.

“Therefore, this makes PHES a more feasible and cost-effective option for supporting grid-scale renewable energy systems over longer periods of time,” Yancoal stated.

The NSW Government has legislated 16 GWh of long-duration storage (LDS) by 2030 under the Electricity Infrastructure Investment Act 2020, with plans to increase the target to 28 GWh by 2034.