The gigafactory, which will eventually turn out batteries for 500,000 vehicles, should cut their cost by another 30%, according to Tesla (see chart). Mr Musk reckons that two-thirds of that saving will come from scale alone—the new factory will double the world’s lithium-battery output—with the rest down to improved manufacturing technology. If Tesla makes good on its promise, electric motoring could finally take off. Sanford C. Bernstein, a research firm, reckons that when costs drop below $200 a kWh, battery-powered cars start to become competitive with conventional ones without subsidies. The gigafactory could bring Tesla close to that.