18 December 2020 Three years after the original Tesla big battery, officially known as the Hornsdale Power Reserve, came into service in South Australia, and Australia’s rule makers and regulators are still trying to figure out the market rules for a technology that wasn’t imagined when the rule-book was drawn up more than two decades ago. The Hornsdale battery succeeds in causing the Australian and international energy markets – from market operators through to developers and big utilities – to re-imagine the future of the grid thanks to its success in keeping the lights on, saving money for consumers, and delivering handsome returns for its investors.