Spring 2012

How It Works: Electric Drive Vehicles | Catalyst Spring 2012

How It Works

Electric-Drive Vehicles

We stand on the verge of an exciting transition in the auto industry. More than two dozen hybrids are available in showrooms today, and most major car companies are planning to offer even more advanced vehicles within the next few years, building on the recent introduction of the battery-electric Nissan Leaf and the gasoline-electric, plug-in hybrid Chevrolet Volt. As the market expands, electric-drive vehicles will play a critical role in cutting our nation’s oil dependence—and the environmental, security, and economic risks associated with it.

Trading Gasoline for Electricity

Electric-drive vehicles rely partially or completely on an electric motor to move down the road. Four types of electric-drive vehicles are currently on the market:

Hybrid electric vehicles (HEVs) comprise the majority of advanced vehicles on the market today. They rely on gasoline for fuel, but supplement the engine with an electric motor and battery. The battery pack can store excess energy produced by the engine under certain conditions, as well as energy that would otherwise be lost during braking (a process known as regenerative braking, which is featured in all electric-drive vehicles). This energy can then be used to power onboard electronics when the vehicle is stopped at a light or in traffic—eliminating the need for wasteful idling of the engine, allowing it to shut down or “idle off”—or to supplement the engine during acceleration. These features reduce fuel consumption by allowing the engine to be used more efficiently. 

Plug-in hybrid vehicles (PHEVs), like HEVS, include both a gasoline engine and electric motor, but have a larger battery that can be recharged via a household wall outlet or public charging station. When fully charged, PHEVs can travel about 15 to 50 miles using little or no gasoline, depending on the model and driving conditions. Once the battery is nearly depleted, PHEVs switch to gasoline and operate like a regular HEV.

Battery electric vehicles (BEVs) do away with the combustion engine completely, relying solely on a battery pack to power the electric motor. Like PHEVs, BEVs plug into an external electricity source. Today’s BEVs can travel at least 60 to 100 miles on a full charge, which is sufficient for the majority of Americans’ daily travel needs.

Fuel cell electric vehicles (FCEVs), like BEVs, eliminate the combustion engine, but the electric motor is powered by fuel cells that combine hydrogen, from an onboard tank, with oxygen from the air to produce electricity (and water—the only waste produced). Most of the 50 or so hydrogen refueling stations in the United States today are located in Southern California, which is the only region in the United States where an FCEV (the Honda Clarity) can currently be leased. No FCEV models are currently sold commercially, but the market holds promise: the Clarity can travel an estimated 240 miles before refueling, and most automakers expect to introduce models by 2015 that will have a range of about 400 miles.


Electric-drive vehicles incorporate a number of advanced technologies, like those highlighted below, to reduce fuel consumption and emissions. Plug-in hybrid electric vehicles (above left) supplement the battery pack with a small gasoline tank, while battery electric vehicles (above right) rely solely on battery power.

View larger image

Cut Down on Emissions – and Fuel Costs

In addition to saving consumers money on fuel, electric-drive technology has the potential to dramatically reduce global warming, smog-forming, and toxic pollution from cars and trucks. HEVs help by boosting fuel economy; PHEVs, BEVs, and FCEVs are not only very efficient, both in their operation and in how their fuel (electricity or hydrogen) is produced, but also replace petroleum fuels with cleaner alternatives, delivering their greatest potential reductions if the electricity or hydrogen used to power these vehicles comes from renewable energy sources (see the sidebar).

One hurdle some electric-drive vehicles must overcome in today’s market is cost. For example, BEVs and PHEVs cost more up front than their closest conventional counterparts, but federal tax breaks of up to $7,500, along with state incentive programs and lower fuel costs (on a per-mile basis, electricity can be about 50 to 75 percent less expensive than gasoline), can more than offset the initial investment.

The Future Needs a Push Start

Not All Electrons Are Created Equal

Electric vehicles are only as green as the power plants fueling them.

When charging a BEV or PHEV, it is important to consider the source of the electricity. For example, using renewable energy such as solar or wind power nearly eliminates smog-forming, heat-trapping, and toxic pollution associated with operating the vehicle, while using electricity produced exclusively from coal results in global warming emissions only slightly better than the average gasoline vehicle today. Electricity from natural gas falls somewhere in between, with a carbon footprint better than a good hybrid.

It can be difficult to determine the impact of operating a specific electric vehicle because the mix of electricity sources varies greatly across the United States.  To help consumers better understand these impacts, UCS has conducted an in-depth analysis of electric vehicle charging across of the United States, based on regional electricity generating resources. Look for the results soon on the UCS website and in our publications.

If a BEV or PHEV fits your budget, you should seriously consider purchasing one, especially if you live in an area of the country where much of the electricity is generated from natural gas or renewables. In addition to reducing fuel costs, global warming pollution, and oil use, you will show the auto industry there is a market for electric-drive vehicles. Early adoption is critical to help drive up production volumes and spur additional research that can lower costs and improve technologies. If you can’t purchase a BEV or PHEV, your next-best bet is a good HEV. There are many excellent models on the market, and the UCS Hybrid Scorecard can help you pick one.

Considering that our nation has relied on one basic engine technology and one fuel for more than a century, a full-scale shift to electric-drive vehicles will take time. However, the promise is simply too big and too important to ignore in a world facing the immense challenges of global warming and oil dependence. Policy makers must accept the reality that the typical two- to four-year political cycle is too short to deliver big results, and that we must invest in a portfolio of technologies if we are to succeed. Together, political action and consumer support can help move our transportation system—however belatedly—into the twenty-first century.

Amine Mahmassani is an analyst/engineer in the UCS Clean Vehicles Program.

To learn more about how electric-drive technologies can power a clean car revolution.