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Tesla battery system and wind farm
An artist’s conception shows Tesla’s battery storage system deployed at a wind farm in South Australia. (Tesla Illustration)

One hundred megawatts. That’s how much electrical power the world’s biggest lithium-ion battery system will store when Tesla builds it for the state of South Australia.

And it’ll be built in 100 days, or it’s free.

The agreement, announced today in Adelaide, follows through on a pledge that Tesla CEO Elon Musk made during a Twitter exchange with Australian billionaire Mike Cannon-Brookes about South Australia’s power woes back in March:

The 100-megawatt battery pack, capable of delivering 129 megawatt-hours of energy, is to be built near the small town of Jamestown, north of Adelaide. It’ll address the power problems that South Australia has been facing as it makes the switch from coal-fired plants to wind and solar power.

Last September, storm damage to the state’s electrical grid caused a cascade of failures, leading to a massive blackout that left South Australia’s 1.7 million residents without power for as long as two weeks.

Tesla said its Powerpack system was chosen through a competitive bidding process to beef up the state’s power storage capacity. It’ll be paired with Neoen’s Hornsdale Wind Farm to balance out the supply of electrical power for more than 30,000 homes, Tesla said in a statement.

“This is not a minor foray into the frontier,” RadioWave quoted Musk as saying in Adelaide. “I’m pretty darn impressed with South Australia willing to do a project of this magnitude that is beyond anything else in the world.”

The project is bigger than the 30-megawatt lithium-ion battery system that AES Energy Storage built for San Diego Gas & Electric, and the 20-megawatt system that Tesla built for Southern California Edison. Australia’s will be the biggest lithium-ion system in terms of megawatts, but other types of storage systems that rely on pumped water, compressed air or molten salt can store much more.

Another caveat has to do with megawatt-hours vs. megawatts: The Powerwall system’s 129 megawatt-hours of energy capacity will be only slightly more than the San Diego system’s 120 megawatt-hours.

AES is planning to build a 100-megawatt, 400-Mwh battery system for Southern California Edison, potentially with an option to expand to 300 megawatts. But installation won’t be complete until 2021.

Tesla says its agreement with the South Australian government calls for its system to be complete by December. That’s more than 100 days from now, which suggests some allowances have been made for paperwork and other preparations.

Getting the Powerwall system into operation on time would demonstrate Tesla’s ability to build capacity quickly. But there’s some risk involved: Even Musk has acknowledged he’s not always good about keeping to a schedule.

“There will be a lot of people that will look at this [and say] ‘Did they get it done within 100 days? Did it work?'” Reuters quoted Musk as saying. “We are going to make sure it does.”

Musk estimated that Tesla could be out $50 million or more if it fails to follow through on the timetable.

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