How Plug-in Hybrids Will Save the Grid

The use of vehicles that run on electricity could be a boon to the ailing electrical grid.

Major automakers and the Department of Energy are pouring money into research on plug-in hybrid vehicles. These cars promise to cut petroleum consumption by allowing commuters to drive to work using primarily electricity--stored on board in batteries--rather than gas. Although critics have warned that the vehicles could put too much pressure on an already strained electrical grid, experts are now arguing that rather than being a strain on the grid, plug-in hybrids may actually help prevent brownouts, cut the cost of electricity, and increase the use of renewable energy.

Small companies are already making kits that allow drivers to commute using electricity from the grid (stored in extra batteries shown here). When major automakers start making the kits, will charging these cars be too much for the grid to handle? Credit: Technology Review

Plug-in hybrids, like today's hybrid cars, can run on either an electric motor or an internal combustion engine. But plug-ins have much larger battery packs and can be recharged by being plugged into the wall, making it possible to rely much more on the electric motor. Although a handful of companies sell conversion kits to change conventional hybrids into plug-ins, the kits add thousands of dollars to the cost of the car (see "Plug-In Hybrids Are on the Way"). This additional cost, which is primarily from the batteries, is one of the reasons the major automakers haven't yet mass produced such vehicles, although they are now developing them. GM, for example, recently committed to making a plug-in version of a Saturn SUV (see "GM's Plug-In Hybrid").

The concern is that plug-ins are not a good way to reduce gasoline consumption, because if they become popular, and millions of car owners recharged their cars at three in the afternoon on a hot day, it would crash the grid. But plug-in hybrids could actually help stabilize the grid if owners charged their cars at times of low demand, and if the vehicles could return excess energy to the grid when it's needed--say while parked in the company lot at work during peak demand.

Since utilities have built enough power plants to provide electricity when people are operating their air conditioners at full blast, they have excess generating capacity during off-peak hours. As a result, according to an upcoming report from the Pacific Northwestern National Laboratory (PNNL), a Department of Energy lab, there is enough excess generating capacity during the night and morning to allow more than 80 percent of today's vehicles to make the average daily commute solely using this electricity. If plug-in-hybrid or all-electric-car owners charge their vehicles at these times, the power needed for about 180 million cars could be provided simply by running these plants at full capacity.

This could be a boon to utilities, because they'd be able to sell more power without the added cost of building more plants. Ideally, this will translate into lower electricity prices, says Robert Pratt, a scientist at PNNL. It might also help utilities justify the added capital costs of building cleaner coal-burning plants, because they'll be able to recover their investment faster by "selling more electricity with the same set of iron, steel, and concrete," Pratt says.

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Such a system could be further optimized by using smart chargers and other electronics. This system would include a charger that runs on a timer, charging cars only during off-peak hours. Researchers at PNNL are taking this a step further with smart chargers that use the Internet to gather information about electricity demand. Utilities could then temporarily turn off chargers in thousands of homes or businesses to keep the grid from crashing after a spike in demand.

The next step would be to add smart meters that would track electricity use in real time and allow utilities to charge more for power used during times of peak demand, and less at off-peak hours. Coupled with such a system, the PNNL smart charger could ensure that the plug-in batteries are charged only when the electricity is at its cheapest, saving consumers money.