The world's largest lithium ion battery has begun dispensing power into an electricity grid in South Australia.
The 100-megawatt battery, built by Tesla, was officially activated on Friday. It had in fact provided some power since Thursday due to demand caused by local hot weather.
South Australia has been crippled by electricity problems in recent times.
Tesla boss Elon Musk famously vowed to build the battery within 100 days – a promise that was fulfilled.
"This is history in the making," South Australian Premier Jay Weatherill said on Friday.
The battery would prevent a repeat of a notorious incident last year where the entire state lost power, Mr Weatherill said.
Mr Musk has described it as three times more powerful than the world's next biggest battery.
From Twitter bet to reality
The idea began when Mr Musk was asked on Twitter if he was serious about helping to resolve South Australia's electricity woes.
Mr Musk said he was – adding that if the battery wasn't built within 100 days, the state would receive it for free.
The countdown began on 30 September after a plan was approved by the state government and regulators. Tesla finished the battery in about 60 days.
Located near Jamestown, about 200km (125 miles) north of Adelaide, the battery is connected to a wind farm run by French energy company Neoen.
When fully charged, the battery can power up to 30,000 homes for an hour. However, it will mostly be used to support and stabilise existing electricity supplies.
The battery is comprised of a grid system that runs on the same technology that powers Tesla's cars.
In a statement, the company said the completion of the battery "shows that a sustainable, effective energy solution is possible".
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