General Motors unveiled the Chevrolet Volt concept car at the Detroit Auto Show in January 2007, it rocked the green-car world. Its technology—still a lab experiment, then—instantly leapfrogged standard hybrids (like the Toyota Prius) and even hybrids that had been adapted to recharge their battery packs from the power grid, known as “plug-ins”.GM calls the Volt an “extended-range electric vehicle” (or E-REV.) This underlines its crucial point of separation from other hybrids: It operates entirely as an electric car for its first 40 miles after a full charge. It burns no gasoline during those miles, drawing energy from a 400-pound lithium ion battery pack containing 16 kilowatt-hours (kWh). Current from that pack powers a 150-hp electric motor that drives the Volt’s front wheels.
But a 40-mile range isn’t enough to make a car practical, so the Volt also carries a 1.4-liter flex-fuel engine. Crucially, that engine doesn’t drive the wheels—it only kicks in to power a generator that sustains the battery charge enough to give the car another 300 miles of range. And that only happens once the battery is exhausted.
