Smart and Smarter: Synchronizing the Smart Grid with Electric Cars and Hybrids

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Coupled with a growing fleet of hybrid electric, and eventually fully electric, vehicles, the smart grid could save massive amounts of power, enable alternative energy and be a potent weapon in the fight against climate change. But the question of how best to integrate alternative energy options is tricky. Wind and solar are intermittent. Electric cars rely on an expensive battery and need time to power up. Maximizing alternative energy requires a new kind of intelligence and flexibility.

Fortunately, that dynamic mix should soon be available in the form of a smart grid that's able to deliver electricity with pinpoint efficiency. Electric vehicles will take in electricity when the rates are lowest. Even better is the possibility that such vehicles will then return electricity to the grid when it's most needed. A smart grid would essentially "let the grid reach down and optimize delivery," says Allen Hefner, a scientist on the Smart Grid Team at the National Institute of Standards and Technology.

Charge by Night

In one likely scenario, plug-in vehicles would power their batteries late at night when demand is low. Then, when demand is high, hundreds of thousands of vehicles would return energy to the grid as needed. Institute of Electrical and Electronics Engineer Fellow Alan Mantooth describes "a nine-story garage full of electric vehicles" that he says will function "as one big battery."

Storage has long been a problem for alternative energy, given that solar power can be disrupted by clouds and is unavailable at night, and wind might die down when most needed. The use of plug-in vehicles as storage units, regulated by a smart grid, would thus provide tremendous flexibility, squeezing more out of alternative energy.

Such a scenario "demands a certain level of study," says Mantooth, "to come up with charging/discharge algorithms." Because a battery pack for an electric car costs upwards of $10,000, the possibility that recurrent charging and discharging would wear out the battery remains a problem. The hope is for a resilient battery capable of performing long-term under a variety of conditions. While studies are not complete, anecdotal data on the hybrid electric Toyota Prius shows that "batteries have been holding up nicely," says Mantooth. Another factor is how slowly or quickly batteries charge and discharge energy, with a quick-charge battery the most flexible option to date.

Smart grid users would have control over when their car takes in energy, for instance setting it to charge only at times of minimum costs, if they know their vehicle is to be parked for a long time, or to charge quickly despite cost if they'll need it soon. "If everyone plugs in their vehicles at 5 p.m., the grid can't take it," says Hefner. Instead, charging can be "staggered over a long period of time."

The Plug-Ins

Two kinds of plug-in vehicles are now or will shortly be available. Hybrid electric cars that depend on a gasoline engine for extended range will include the Fisker Karma, the Chevy Volt and a new version of the Toyota Prius. Fully electric cars include the already-available Tesla Roadster and the Nissan Leaf.

Hybrid and electric cars are only a real environmental step up if coupled with greater use of alternative energy. Mantooth points out that the possibility of switching to 100 million electric cars in the U.S., if tied to an electric system based largely on coal, as we have today, would be "trading one problem for another." Renewable energy dispatched through a smart grid, conversely, would be "a big net plus for electrical efficiency and reduction of greenhouse gases."

Two experimental projects are already combining electric vehicles and the smart grid. Toyota, in partnership with Xcel Energy, is supplying about 20 hybrid electric Priuses to SmartGridCity, a working prototype of the future located in Boulder, Colorado (see "A City Gone Smart," page 26). …