One of the tantalizing promises of electrified cars, including hybrids, plug-in hybrids and battery vehicles, is that they can not only take in power from the grid but also give it back. Electric cars plug in to charge, but in times of grid stress, their powerful batteries can also act as stabilizers to prevent transformer meltdown. My colleague Erica Gies calls this “the cash-back car.”

I actually saw vehicle-to-grid (V2G) demonstrated by Google in California — the electric meter spun backwards, as a connected Toyota Prius returned electricity to the power company. And I’ve also talked to people who’ve wired those same Priuses to act as backup power generators during blackouts.

But V2G has always seemed like future tech. Google pulled back, but now the longtime champion of the technology, Professor Willet Kempton at the University of Delaware, is pushing it forward in promising ways.

Kempton has been working at V2G since 1997, but he’s finding ways to make it practical and net consumers an extra $440 a year. According to Gies, he contacted the regional transmission organization (RTO) that manages wholesale electricity in 13 states, and persuaded it to allow car owners to get paid for putting electricity back in the grid. And, since 2008, he’s had a pilot project operating that has seven electric cars plugging in and getting monthly payments from their utilities, which grab the available electricity during peak times.

The Federal Energy Regulatory Commission (FERC) is working on a rule that would allow car owners to get paid at a higher rate than those currently handed out to peak plants that perform that load-leveling function now. It could become law within months. And "virtual energy storage" companies like Nuvve in San Diego are signing licensing deals with Kempton and getting ready to make V2G practical. Nuvve is also pushing hard in Europe, where the regulatory climate is friendlier.

One thing V2G can do is help make wind power practical. As Gies writes, “Cars batteries are a good match with wind power because they mostly charge at night, when people are sleeping, and wind tends to peak at night. Right now, because demand plunges at night, wind generated at night is lower value or sometimes even dumped.”

It’s too soon to expect that electric cars will be routinely getting cash back from their utilities, but this is an interesting practical start for V2G. There are still plenty of challenges for V2G, and they're nicely summarized in this video:

Jim Motavalli ( @jmotavalli ) writes about cars, technology and the environmental world to anyone curious enough to ask.

Cars that give back: Connect your electric vehicle to the grid, and make $440 a year
In a process called vehicle-to-grid, or V2G, cars can return electricity to the grid at peak times — and earn money doing it.