It took 100,000 construction workers a quarter of a century to bore through the Snowy Mountains to build Australia’s largest hydroelectric scheme. The vast nation-building project links nine power stations and 16 dams via a network of 145km of tunnels and pipelines, providing irrigation water and energy that has helped transform the country’s economy since it began operating in 1974.

Now, almost half a century later, Australia’s newly elected government is placing the state-owned Snowy Hydro plant at the vanguard of another energy transition by transforming it into a massive “water battery” that will help keep the lights on as the country shifts from an electricity grid based mainly on fossil fuels to one built around renewable energy.