While it may take several years of plug-in hybrid sales to capture even a small percentage of the market, some utilities that currently experience power shortfalls would need to quickly implement technology to limit recharging plug-in hybrids during peak times.

As residents of California know, during days of extreme heat demand for electricity can outstrip supply, so the introduction of thousands of plug-in hybrids would further complicate management of the power grid.

If plug-in hybrids were to compose just 10 percent of vehicles in California, there would be several days per year that the grid would not be sufficient to recharge all plug-in hybrid batteries during off-peak hours, according to the PNL report. With 30 percent plug-in penetration, not all vehicles would be able to be recharged on as many as 45 days a year. Would plug-in hybrid owners there accept using only gasoline power during these days?

Plug-in hybrids will be recharged via standard 110-volt outlets and require up to seven hours to fully recharge depleted batteries. To prevent, or at least discourage people from plugging in their cars when the grid is under stress, utilities will need to work with the auto industry to develop technology that would control plug-in hybrids' power consumption. Plug-in vehicles would connect with "smart meters" that relay to the power company when the vehicle is recharged so that they could be denied recharging or pay a higher price at peak times, according to EPRI's Gellings. "If you give consumer the right information, they will make the right choice."

"This (smart metering) is something that has to happen," according to James Lyons, the chief engineer for electrical systems at GE Global Research. "But we have to make a vehicle that works first. Over the next 5 years we can sort this out. "

The auto and power industries would have to jointly create standards for passing information between plug-in vehicles and utilities, Gellings says. The utility industry currently has 152 different communications protocols, so getting power companies from across the nation to agree with automakers "would be a huge challenge," according to Gellings.

Utilities could give discounted rates to individuals who set up separate circuits for plugging in vehicles, according to Dave Alexander, a senior analyst at ABI Research. These circuits can be turned off in the event of a brown out, much like some customers who have set up circuits for their air conditioning systems today, Alexander says.