ZigBee Alliance coordinating vehicle-to-grid technology

What will happen when millions of electric vehicles plug into the grid at at the same time? If ZigBee Alliance's blueprints for the smart grid go according to plan, not much.

Liane Yvkoff
Liane Yvkoff is a freelance writer who blogs about cars for CNET Car Tech. E-mail Liane.
Liane Yvkoff
4 min read

What will happen when millions of electric vehicles plug into the grid at at the same time? If ZigBee Alliance's blueprints for the SmartGrid go according to plan, not much.

The ugly specter of mass blackouts caused by hoards of EVs rolling into garages and plugging in at the same time is just one of the many arguments EV detractors use against electric vehicles and plug-ins. But EV adoption is inevitable, and the smart grid should make sure that energy loads will be balanced and shifted as needed to recharge them without causing widespread power failure. And eventually, ZigBee predicts, electric cars and plug-ins will become part of the energy solution supplying power to the grid.

But let's back up.

If you haven't heard of the ZigBee Alliance, you're not alone. Before I started this article, I'd never heard of it until I was forwarded one of its press releases. Named after a little-known Nordic elf that has nothing to do with wireless networks or energy, the ZigBee is a standard for wireless sensor networks on which the Smart Grid operates. "And the domain name was available," says Bob Heile, who is chairman of the curiously named group and one of the founders of 802.11.

More than 300 metering, computer, chip processing, electronics, and automotive companies are members the ZigBee Alliance. By incorporating ZigBee's technology in their products, many of these companies are laying the infrastructure that will enable utility companies, networked homes and buildings, and appliances to communicate wirelessly and automate metering as part of the smart grid. That includes electric vehicles.

Electric and plug-in vehicles will undoubtedly be a significant drain on the smart grid--each plugged-in EV has the equivalent drain of another house for hours at a time. But they're also uniquely designed to be able to give back.

"They are essentially batteries with wheels," says Heile. "Ultimately, long after the EV infrastructure is in place and consumers adopt them, there will be opportunities to load shift."

This means that at peak hours people can sell the energy stored in EV batteries back to utility companies. But don't think you can offset the cost of a new Nissan Leaf or Chevrolet Volt by becoming a homespun energy trader of sorts--that technology is still years away.

The typical EV and smart meter rhetoric goes something like, "You can charge your car overnight when electricity rates are cheaper." But the technology isn't entirely there to support that rational. Right now if you don't own a smart meter (you would know if you do) and you plug an EV into an outlet, it doesn't know what the device is or who it belongs to, or when to charge it other than right now. But in the future, it will know who you are by the car you drive so that when you charge at a friend's house, you'll get the bill. Or so the theory goes.

Specifications for vehicle-to-grid technology are still being developed by the Society of Automotive Engineers as part of the ZigBee Alliance's Smart Grid Interoperability roadmap. Coulomb Technology's ChargePoint Stations, which Heile describes as "first generation or first and a half generation equipment," are able to identify users, but the charging stations aren't yet equipped with ZigBee Alliance's smart meter technology that is required to load shift, says Heile. However, ChargePoint Stations are equipped with the features that would enable vehicle-to-grid technology once the specifications are in place and automotive manufacturers get on board.

For the moment, there's no urgent need. Roughly speaking, the U.S. can handle 2 million electric vehicles before a management system is required. "After that, it's grid crippling," says Heile.

This is not to say that after the 2 millionth vehicle rolls off the factory line that all transformers will break. That number is an estimate--the real breaking point will vary by geographic area and how many additional loads a electric plant can take at peak without busting transformers. A typical plant might be able to handle a 10 percent load increase, but definitely not 50 percent, explains Heile.

Especially since not everyone will recharge their EV only at night--some portion of EV drivers are going to need to recharge at peak hours. Managing those needs will require the cooperation of everyone. Smart grid technology expects that in the future people will program in when and how they want to recharge their car instead of everyone charging at the same time.

"It's going to give priority to the vehicles that need to charge first," says Heile.

It will also price energy according to supply and demand. If you have an important trip and need to be able to leave at 9 p.m., you will have to pay peak power rates just as if you are running low on gas--you will pay whatever the rate is of the nearest station because you don't have the luxury of shopping around.

But ZigBee Alliance's specifications aren't all about making drivers feel the power pinch--the same technology that will enable you to recharge your car according to pricing and scheduling will enable you to decide when to sell the energy back. Another feature of the vehicle-to-home network capability is that you could even run your home appliances off your car. If you decide that energy rates are too expensive midday on a Saturday during a heat wave, you can run your air conditioning off your Volt.

Although ZigBee technology is being installed in 40 million meters in North America, automatic metering infrastructure is still some time away. How quickly it becomes a reality is tied to how popular electric vehicles become.

"California will be an early adopter," says Heile, "but it will be a while before you see consistent infrastructure. It's sort of like the re-electrificaiton of America--it's not going to happen overnight."