Dusk was settling over the hills around Jamestown, three hours north of Adelaide, as a column of vehicles that included an unusual number of Tesla electric cars snaked towards a white marquee on the site of the Hornsdale Wind Farm. Nothing in the formal invitation had hinted that the event was to be anything more than a sod-turning to launch the construction of what would be the world's largest lithium battery. Coaches had driven from Adelaide for the occasion. But for the VIPs and press on board, a surprise was in store.

On disembarking it was clear that the first sod had been turned weeks, if not months, before. Laid out beneath the wind turbines was a half-completed bank of Tesla batteries, capable of pumping out about 50 megawatts of power – enough to power 15,000 typical homes and businesses.