WASHINGTON -- The nation's existing electric power grid could fuel as many as 180 million electric cars, a Department of Energy study estimates. The study, being released today by the department's Pacific Northwest National Laboratory, is the federal government's first look at the grid's capacity to handle the demands of so-called plug-in hybrids, which can be operated as an all-electric car for most daily commutes. Until now, there have been few detailed studies of the effect of plug-ins, which are championed by environmental groups and the utility industry. Currently there are only a few hundred plug-ins on the road, most...