By Janet Raloff, for Science News' Science & the Public Blog
SAN DIEGO — Most people, on average, drive their cars only an hour or two a day. The rest of the time, those pricey vehicles sit parked on the street or in some garage. But if those cars had a big bank of batteries – typical of today’s gasoline hybrids or soon-to-hit-the-road plug-in hybrids – they could be earning their owners money while sitting parked. Maybe $5 to $10 a day, just by serving as a back-up energy-storage system for the electric-utility grid.
Or at least that’s the idea behind the V2G – vehicle-to-grid – movement. A panel of experts described the promise (and hinted at some of the pitfalls) of this power-sharing arrangement, where people agree to effectively lease their cars’ batteries, when they’re not in use, to the power company. It was part of a preview for reporters of a symposium to take place early tomorrow, here at the American Association for the Advancement of Science annual meeting.
To reinforce that V2G is not just a theoretical construct, Tom Gage, president of AC Propulsion in San Dimas, Calif., drove his personally customized V2G-hybrid car from Los Angeles yesterday and into the San Diego Convention Center. It was a big show-and-tell element, parked just a few feet away from the V2G panelists in a second floor meeting room. Hooked up to a meter, it communicated with PJM Interconnection of Valley Forge, Pa., throughout the press conference. PJM, which is responsible for coordinating the movement of wholesale electricity throughout the grid in all or parts of 13 states and the District of Columbia, has been participating in three V2G projects. They included the Mid-Atlantic Grid Interactive Car Consortium, better known as MAGICC.
From time to time, as power demand rose a little, PJM would ask Gage’s car to share some of the power stored in its batteries. Later, when the grid had a little too much generation feeding into it, the company would instruct the grid to dump a trickle of that excess back into the car’s batteries. Real-time details of this computer-controlled power sharing between the grid and Gage’s car (along with two others) were displayed on a screen at the front of the room.
At least initially, the dozens of reporters listening to today’s five speakers had trouble understanding why owners would want to put their cars’ batteries on the line to help out the power company. The problem was that Ken Huber of PJM and his fellow panelists kept emphasizing the public good of sharing our batteries with the grid – without explaining the benefits and putative protections for the owner and vehicle.
Indeed, the speakers initially conveyed the impression that the grid could and would draw down a car’s battery, for a fee, and then let the owner replenish the charge on his or her dime.
Once Huber understood the confusion, he pointedly emphasize that “We are not discharging or charging the vehicles.” Rather, he said, “the regulation signal that we’re sending out varies around zero” – taking and then replacing, over and over again, small quantities of electricity. “So over the course of a day,” Huber said, the batteries “will have charged and discharged just the same amount.” Meaning there should be no net loss of charge on the vehicle. While parked, the vehicle probably will be charging. And owing to the power sharing arrangement, he acknowledged, “we’re varying that charge rate a little bit. But just a little bit – a small percentage.”
For the privilege of adding and withdrawing tiny increments of charge throughout the day, a car’s owner would receive a fee. Not a huge one, Huber says. “But we’ve paid, in the past year, somewhere around $40 a megawatt-hour.” (This year, with fuel costs somewhat lower, he said utilities will probably be paying closer to $28 per megawatt-hour.) “So if you have a megawatt of [hybrid-car] batteries charging, and we do in our grid, they’d make somewhere between $800 and $1,000 a day,” Huber says.
PJM and other utility power brokers are not interested in writing contracts with the occasional car owner here or there. They will want a minimum of a half-megawatt or more in back-up batteries. So it’s likely that companies will develop to sign up willing parties to a compact, where members sign on to collectively lease their batteries.