DENVER, Feb. 22 Xcel Energy announced Wednesday the results of a study on the impact of plug-in hybrid electric vehicles.The study was done in collaboration with the U.S. Department of Energy's National Renewable Energy Laboratory. PHEVs, the study says, would lower the overall cost of owning a vehicle and cut emissions from vehicles by about 50 percent.Hybrid gas/electric vehicles are already on the market and PHEVs are staged for growth, so we wanted to know how that could affect our business, said Mike Carlson, chief information officer of Xcel Energy. The model in the study measured how much energy it would take to charge the vehicles if they became integrated on a mass level. To cut emissions by half, the battery used was a 9 kilowatt hour battery and using that, owner saved more than $450 in fuel costs annually.Depending on when customers choose to recharge, adding PHEVs to the road may help reduce overall emissions of carbon dioxide without significant increases in utility infrastructure, Carlson said. A smart grid system, for which plans are currently underway, would allow customers to put excess energy from their PHEVs back into the utility grid.Copyright 2007 by UPI