Smart-grid company GridPoint said Thursday it has successfully tested a "smart-charging" software platform for plug-in hybrids with utility Duke Energy.

In the test at a garage wall outlet, GridPoint said its platform prevented a plug-in hybrid from charging during the late afternoon, a time of peak demand for energy, instead allowing it to charge in the evening, when demand is lower.

The company also said it raised $15 million in a strategic investment by the Quercus Trust. GridPoint, which closed $48.5 million in a fourth round of funding in October, has raised a total of $102 million in equity capital.

While plug-in hybrids have yet to reach the mainstream, some industry experts wonder whether the aging grid could support the additional demand if this technology were to become more popular.

Advocates say the hybrids would mainly be plugged in at night, when there’s an energy surplus. They often cite a 2006 Department of Energy study, which found there is enough "off-peak" electric energy to power 84 percent of the country’s 220 million vehicles if they were plug-in hybrids that charged at night (see U.S. Could Plug In Most Cars).

But utilities have said ensuring that cars won’t charge during times of peak demand on the aging, already strained electrical grid, is key to supporting the plug-in hybrid and electric cars that vehicle companies hope to bring to the market.

"Smart charging is an essential capability for Duke and all electric utilities as [plug-in hybrids] enter the market," said David Mohler, chief technology officer for Duke Energy, in a written statement. "Through this capability, we’re able to reduce stress on the grid during peak periods and keep rates low."

GridPoint is far from the only company working on connecting plug-in hybrids and the grid. Also on Thursday Ford Motor Co. announced a three-year partnership with the Electric Power Research Institute to develop ways to integrate plug-in hybrids with the grid. In April the Pacific Gas & Electric Co. demonstrated how electric vehicles could be used to supply homes and businesses with electricity.

And, the search giant’s philanthropic arm, plans to invest $10 million in plug-in hybrid and electric car technologies, including technologies to transfer electricity from cars to the grid (see Google Leaves Out Clean Diesel, Hydrogen and Director ’Technology Can Solve Climate Change).

Still, a number of challenges remain for technologies such as GridPoint’s that manage the connection between vehicles and the grid.

For example, GridPoint said its software for controlling charging is contained within an electrical outlet. It’s unclear from the announcement if an outlet would be able to distinguish between a plug-in hybrid and, say, a power tool or a washing machine. A technology that blocks all uses of an outlet during times of peak demand could aggravate consumers; some users might not be willing to install dedicated outlets for their hybrids -- or pay for software that limits the way they use power for other devices.

Advocates hope that instead of being a strain on the grid, the cars could one day help stabilize it by releasing stored energy at times of high demand.

But analysts, such as Neal Dikeman, a founding partner at Jane Capital, have said a number of issues also would need to be resolved before plug-in vehicles could provide backup power for the grid. Such issues include poor battery life, missing links in the monitoring and managing of electric charging and discharging and -- most significantly -- a lack of plug-in cars and sensor-equipped charging stations on the roads.

"There are technology challenges and industry challenges, and they’re a lot more complex than people believe," Dikeman said in an interview in October.