Elon Musk looks to have delivered on his promise to build the biggest lithium-ion battery in the world to help South Australia with its crippling energy problems. “100 days from contract signature or it’s free,” Musk tweeted at the time, in a deal initially negotiated over Twitter. Musk is well ahead of schedule (a rarity for Tesla!), with the 100MW battery set to be energized and tested in the coming days, according to a press release from the local state government.

Elon Musk has finished building the world’s biggest battery

Tesla Powerpacks have been installed and connected at Neon’s Hornsdale windfarm, north of Adelaide, and battery tests will be run to ensure local regulatory requirements are met before it begins operating on December 1st. South Australia suffered a statewide blackout last September, which sparked a highly politicized national debate about energy security. The Australian Government blamed the failure of renewable energy to cover usage. Musk’s battery farm stores vast amounts of energy from renewable sources like wind and solar, and funnels it out to the grid when usage is high.

Musk made his promise in March on Twitter, and the 100-day countdown started at the end of September after the company inked a deal with the South Australian government. Musk essentially delivered his promise in about two months, well short of the self-imposed 100-day deadline. The battery is estimated to cost at least $50 million.

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The world’s largest lithium-ion battery will be an important part of our energy mix, and it sends the clearest message that South Australia will be a leader [sic] renewable energy with battery storage,” South Australian Premier Jay Weatherill said in a statement. “An enormous amount of work has gone into delivering this project in such a short time.