The world's biggest battery is ready for testing in South Australia, with hopes it can help solve the energy problems plaguing that state.

Tesla's Elon Musk promised back in March to build the 100-megawatt lithium ion battery within 100 days of signing a contract with the South Australia government. Australian software billionaire Mike Cannon-Brookes promised to secure the funds and the approvals if Musk was serious.

South Australia was hit with a state-wide blackout in September 2016 that left 1.7 million residents without power, Australia's legendary summer heat waves brought further power problems this year, prompting a national debate about the country's energy mix. While Prime Minister Malcolm Turnbull has backed coal and other fossil fuel energy sources, some state governments have been pushing for more renewable energy like wind and solar.

In March, South Australia Premier Jay Weatherill announced a wide-reaching energy plan that included $150 million in funding for renewable energy projects, with the massive storage battery to be built by Tesla.

The Powerpack will store energy generated by the Hornsdale Wind Farm and deliver it to the grid when needed. It's an attempt to alleviate the state's unstable grid with a reliable source of backup energy drawn from sustainable sources.

Tesla says the Powerpack will be able to power 30,000 homes. With an energy capacity of 129 megawatt-hours, it could theoretically last about an hour and 20 minutes at 100 MW, before being recharged.

The countdown on Musk's 100-day promise started in September, when a grid-connection agreement was signed with transmission company Electranet — though the facility was half-built by then.

Weatherill announced Wednesday that installation was complete — ahead of schedule — and testing will begin to ensure the Powerpack meets regulatory requirements, with the goal of being fully online by December 1, just in time for summer.

It's estimated the project cost $50 million.