Tesla’s giant battery pack in South Australia, which at the time of its completion in November 2017 was the world’s largest lithium-ion battery, saw surprisingly good returns on the investment. The company built the battery in just 54 days, after CEO Elon Musk made a bet that he could solve the state’s energy woes in under 100 days.

A new series of documents published last week shows just how well the bet has paid off. French energy firm Neoen, which manages the battery, filed for an initial public offering that details the company’s previous successes. Nestled in the details, as spotted by Electrek, is a note that the whole project cost €56 million ($66 million) with a return of €6.7 million ($7.9 million) from selling energy from the nearby Hornsdale wind farm and €8.1 million ($9.5 million) from grid energy sales, meaning that in total the battery is expected to make around $20 million by the end of its first full year of operation.

tesla australia battery
The Tesla battery in South Australia.

See more: Tesla Just Built the World’s Biggest Battery in Record Time

The 100-megawatt battery has helped provide enough power for 30,000 homes, in a state with a large share of renewable energy. Researchers have noted the battery’s fast reaction times: University of Melbourne researcher Dylan McConnell notes that the battery generated 2.42 gigawatt-hours and consumed 3.06 gigawatt-hours in its first month, registering an approximate round-trip efficiency of 80 percent. The battery provided full power on December 14 when Victoria’s Loy Yant power plant failed in just 140 milliseconds.

However, the battery could be too fast for older production methods. The company complained to the Sydney Morning Herald in March that it did not receive compensation for 30 to 40 percent of this extra power as the models are based on fossil fuel generators that ramp up gradually. While the frequency control ancillary services that plug the gaps in service provide vital support, the market operator looks at response times as fast as six seconds for compensation, meaning the battery can react too fast for the compensation to register in the system.

Tesla is now aiding with the rollout of a virtual power plant in the state, which would fit 50,000 homes with solar panels and Powerwall 2 batteries to offer cheaper electricity to people.

The company has already released some exciting teasers for its next projects.