Washington (DC) - A Department of Energy report shows that the U.S. energy grid could support up to 185 million electric or hybrid cars. The department believes a switch to the newer vehicles would clean up the environment and could even improve our national security situation by reducing the need for imported oil.

While the 185 million car figure is certainly amazing, there are a few "gotchas" thrown into the mix. First, the cars have to be plug-in hybrid electrics which are not commonly available today. Modern hybrids like the Toyota Prius charge and store electricity on the fly while driving and do not plug into the wall.

The cars also must be plugged in during the night because there is an energy surplus during off-peak hours. In many areas, especially in the Pacific West, daytime electrical supplies are quite low. Indeed, it was just a few years ago that California experienced rolling blackouts from an electricity shortage.

The DOE believes total air pollution would increase in the near term because extra power plants would have to be built to power the charging vehicles. However, urban pollution levels would improve because power plants are usually built far away from cities. In addition, utilities could inexpensively clean pollution from their smokestacks more economically than gas guzzling cars.

Hybrid plug-in vehicles would increase the average home's electrical usage by about 30 to 40 percent, according to the DOE, but this would be offset with lower off-peak prices and the building of more efficient power plants.