Hornsdale Power Reserve, near Jamestown in South Australia, was the world's largest lithium-ion battery when it was switched on on 1 December 2017. Built from Tesla Powerpacks and connected to Neoen's 317 MW Hornsdale Wind Farm, it launched with 100 MW of output and 129 MWh of storage, letting wind power be dispatched to the grid day and night whether or not the wind was blowing. The battery answered a crisis. After a statewide blackout in September 2016, the South Australian Government's Energy Plan called for large-scale storage, and in July 2017 Neoen and Tesla won the contract. Elon Musk promised delivery in 100 days or it would be free; the system was online 63 days after the grid connection agreement was signed, ahead of summer peak demand. Its first year proved the case. An independent Aurecon study found it responded to grid frequency events in under 100 milliseconds, helped keep South Australia supplied when a coal unit tripped and transmission lines failed, cut regulation service prices in the state by around 75% and contributed to savings approaching A$40 million a year. Owned and operated by Neoen, it became the reference project for grid batteries across Australia and beyond.