Rural houses stand in front of wind turbines at the Hornsdale wind farm, operated by Neoen SAS, near Jamestown, South Australia, on Friday, Sept. 29, 2017. Against a backdrop of wind turbines 150 miles (241 kilometers) north of Adelaide, Musk announced a contract to build the world's largest lithium-ion battery system had been signed with South Australia's power distributor, triggering a 100-day self-imposed deadline to install the electricity storage system. Photographer: Carla Gottgens/Bloomberg via Getty Images