Porsche AG will build a plug-in hybrid version of the Panamera sedan starting in 2014, sources familiar with the situation said last week. The plug-in hybrid likely will come to the United States, but the timing is unclear, a source said. Volkswagen AG, which owns 49.9 percent of Porsche\'s sports car business, will roll out plug-in hybrid versions of the Audi Q7 crossover and European-sold VW Passat starting in 2014 or 2015, a source said. The next-generation Audi A3 also will get a plug-in hybrid variant in 2014, Audi CEO Rupert Stadler told reporters this month at the Geneva auto show. Rudolf Krebs, VW\'s group chief officer for electric traction, said last week in an interview, \"We are really convinced that the future of hybrids won\'t be pure hybrids, but the plug-in hybrids.\" Hybrids, such as the Toyota Prius, have two propulsion systems, such as a gasoline engine and an electric motor or a diesel engine and an electric motor. They do not plug in. Plug-in hybrids, such as the Chevrolet Volt, are powered by an electric motor and battery pack backed up by a gasoline or diesel engine that extends driving range and recharges the battery. The advantage of plug-in hybrids, Krebs said, is their ability to use electric power for short distances and still get the range of an internal-combustion engine. VW plans to introduce plug-in hybrid versions of its luxury cars first because people who own those cars tend to drive longer distances, Krebs said. The VW brand also plans to produce electric versions of its Up! city car and Golf starting next year.