Tesla’s South Australian Powerpack Project, the world’s largest lithium-ion battery, was fired up at the end of last year. Not only is this farm-sized battery already proving to be an incredible piece of tech, it could also be an exceptionally wise investment for Tesla CEO Elon Musk.

Within just a couple of days, the Powerpack Project could have made approximately AUS $1 million (US $810,000) through the electricity wholesale market, according to an estimate by Australian clean energy news site RenewEconomy. Considering that the project cost an estimated US $50 million to set up, that’s a solid few hours' work.

The battery, located on the Hornsdale Power Reserve adjacent to the Hornsdale wind farm in South Australia, can technically earn money by holding excesses of electricity. Typically, supply and demand for electricity have to be matched at all times. During times when supply exceeds demand, electricity is negatively priced, so consumers are paid to take electricity out of the grid. With renewable energy sources, like wind or solar, storage battery programs are even more useful as the flow of electricity might not be reliable or controllable.

Working in collaboration with the South Australian Government and renewable energy company Neoen, Tesla can profit by soaking up excess energy and storing it for later use. Tesla’s contract with the government is not completely clear, but RenewEconomy worked out this estimate based on figures of power input and outputs from the Hornsdale Power Reserve, combined with the wholesale price. Earlier this month, Electrek also estimated that Tesla managed to earn a cool US $790/MWh to absorb excess electricity from the national power grid.

When the idea of the Powerpack was first coming to fruition, Elon Musk placed a bet on Twitter that he could build the world's biggest battery in Southern Australia within 100 days or it would be free. No surprises, they delivered on time. A system of Tesla's Powerpack batteries was also used to restore power to storm-torn Puerto Rico after Hurricane Maria.

By the looks of things, these highly-successful projects are just the first steps in a master plan.

“Tesla is proud to be part of South Australia’s renewable energy future, and we expect this project will provide a model for future deployments around the world that will help significantly accelerate the adoption of sustainable energy,” the company said in an announcement in July 2017.