According to the latest reports from Australia, the Neoen Hornsdale Battery supplied by Tesla takes advantage on both ends when demand exceeds production and when there is surplus of electricity.
Usually, electricity prices varies between AU$30-150 per MWh if you want to buy, but there could be a period when generation exceeds demand. That's not good, because frequency increases and the grid could be affected.
In such circumstances, electricity is negatively priced at up to AU$1000/MWh (around US$800) before generators adjust output or get turned off. Power plants that put into the grid too much electricity are accordingly penalized.
Here is where the Tesla battery quickly enters game and charges for energy that it later will sell for profit.
Because the Tesla battery is so big (100 MW / 129 MWh), in short period of time it is able to earn more than $50,000.