How Low-energy Vehicles Work

Precious Plug-ins

Electric vehicles (we'll call them EVs) are in their adolescent phase, at least compared to hybrids. Electric cars run on electric motors that are powered by batteries. When the battery is drained, it can be juiced up on a public charging station or through a special adapter that runs off household current. Although EV batteries have improved considerably, they're still a weak link in the economics of owning an EV. Cost of replacement and the impact of disposal can get some people wringing their hands with anxiety. And in the early days of electric cars, critics pointed out that drivers had to be especially careful not to stray too far from a charging point. Battery range has increased and the power infrastructure has improved, but the need to charge up after each commute can still be an inconvenience.

A key theme in EVs is sustainability. For example, carmakers are looking for alternatives to the traditional electric high-powered permanent magnet-based motors that rely on rare-earth metals. They're also looking for more efficient ways to power up the cars -- even though they run clean, the electricity they use might come from dirty sources (like coal plants or fossil fuels).

Early attempts to integrate solar panels directly into cars didn't work, but a company in New Jersey has unveiled an EV charging station that uses solar energy to power up the cars' batteries. These SunStations are a lot more versatile than the existing EV infrastructure, since they don't necessarily have to tap into the power grid.

There are proposals being floated around that might make EVs even more efficient, as well as increasing cost effectiveness for their owners. A team of researchers from the University of Delaware suggests that EVs could primarily power up during off-peak times, when power is less expensive. Then, if a car is parked and plugged into its charger when there's an unexpected spike in power demand, the cars could be tapped to feed its stored energy back into the grid, and the utility company will send a rebate check or electricity credits to the owner.

On the EPA's list of top efficiency achievers, the bottom two are rated at a combined city/highway 50 miles per gallon (21.3 kilometers per liter) (both members of the Toyota Prius lineup, one edges out the other based on slightly higher city mileage). The most efficient vehicle on the list (and therefore, the most efficient vehicle available) is the electric Mitsubishi i-MiEV, which achieves the equivalent of a combined 112 miles per gallon (47.6 kilometers per liter).

Don't assume auto manufacturers are making these investments out of the goodness of their hearts. By law, they are held to emissions standards, which are usually enforced by averages. For example, BMW can offset the inefficient mileage of its performance cars by producing upscale hybrids and electrics that will appeal to BMW's target audience. Materials such as carbon fiber and other strong yet lightweight composites improve efficiency and help justify a premium price, both of which boost the brand's street cred.

Another luxury example, the Tesla Roadster (which is basically an electric drivetrain stuffed into a Lotus Elise body) would be a powerful small car by most standards, and is extra impressive for an EV. Its electric motor produces 288-horsepower and transmits 88-percent of the battery's power to the wheels [source: The Economist]. (The average car achieves about 30- to 40-percent drivetrain efficiency.) An electric sports car like this might be a mid-life-crisis car for the wealthy, but it still shows what's possible.