Tesla switched on the world’s biggest lithium ion battery on Friday in time to feed Australia’s shaky power grid for the first day of summer, meeting a promise by Elon Musk to build it in 100 days or give it free. “South Australia is now leading the world in dispatchable renewable energy,” state Premier Jay Weatherill said at the official launch at the Hornsdale wind farm, owned by private French firm Neoen. Tesla won a bid in July to build the 129-megawatt hour battery for South Australia, which expanded in wind power far quicker than the rest of the country,