Why Electric Cars Are Cleaner

This resurgence is a testament to recent advances in electric car technology. While pure electric cars will continue to face challenges — such as expensive batteries, a limited driving range compared with conventional cars (although the 70 to 100 miles per charge offered by most electric cars is sufficient for many drivers), somewhat lengthy charging times, and a limited number of public recharging stations — they bring numerous benefits to the table.

Because electric cars consume no gasoline at all, they are a great option for drivers concerned with energy security and our nation’s oil dependence. They offer the convenience of being able to “refuel” a vehicle at home, and they’re more efficient and less expensive to operate compared with gas-only cars (see “How Much Does It Cost to Power an Electric Car?” near the end of this article). They also reduce noise pollution in most driving circumstances. Finally, of course, they’re perhaps best known for being zero-emission vehicles, and their lack of tailpipe emissions is a great step toward an improved environment.

Hold it right there, say some critics. Aren’t electric cars simply moving emissions from the vehicle’s tailpipe to a power plant smokestack? (This is the “long tailpipe” critique.) Aren’t there still greenhouse gas emissions and other pollutants associated with creating the electricity these vehicles use? And if that’s the case, are electric cars really all they’re cracked up to be?

“These are valid questions deserving of a thorough assessment,” says Bill Moore, editor in chief of EV World, a transportation technology and news website. While lamenting misinformation that perpetuates in the blogosphere and elsewhere, Moore values criticism that encourages progress. “We don’t want [electric cars] to become a burden on society, so we need to hear those criticisms, we need to weigh them, and we need to move forward to improve the technology,” he says.

Electric car emissions depend on multiple factors — particularly how your electricity is generated, which, for most, depends on where you live. Smog-forming pollution at the power plant from the use of an electric car can have higher emissions rates than typical gas-only or hybrid cars (such as the Toyota Prius), a fact owed largely to the effectiveness of catalytic converters in today’s gas cars. It’s important to note, though, that from a health standpoint, one major advantage of “moving” pollution from the tailpipe to the power plant is that it gets pollutants farther away from pedestrians and other drivers, lowering the pollutants’ adverse health impacts on the concentrated population.

However, some pollutants, such as those related to climate change, affect the environment regardless of where they are released. In terms of climate change emissions, electric cars are generally much cleaner than conventional gas vehicles. In areas of the country that have the cleanest power generation (more wind, solar and hydropower), electric cars emit far less greenhouse gases, not only compared with conventional vehicles, but also compared with efficient hybrid-electric vehicles. In areas of the country with the dirtiest power generation (coal), an efficient hybrid may be your best environmental bet, though if you’re gentle on the pedal, an electric car may yield comparable results. On a national average basis, an efficient electric car emits about half the amount of carbon dioxide as a conventional car, and roughly the same amount as an efficient hybrid. To fully understand these comparisons, we first need to understand the how, what and where of vehicle emissions.

For more information, see our map of electric car CO2 emissions by region and our chart comparing electric cars with hybrids and conventional vehicles. 

Vehicle Emissions, Explained

The vast majority of cars and trucks on today’s roads operate on internal combustion engines, which convert energy stored in a liquid fuel (usually gasoline) into mechanical motion by rapidly igniting an air-fuel mixture in the engine’s cylinders. This combustion process emits engine exhaust that contains a number of pollutants, including (but not limited to) carbon monoxide, hydrocarbons, nitrogen oxides and particulate matter. But automotive engineers have found ways to reduce these pollutants, both by adding emissions-control devices (such as catalytic converters) to the exhaust plumbing, and by precisely rendering the cylinders’ combustion process though computer control. The upshot is that, especially over the past decade, conventional vehicles have gotten much cleaner in terms of smog-forming pollution.

The bad news is that another pollutant created by combusting fuel — carbon dioxide, or CO2 — cannot be minimized through the use of emissions-control devices. Simply put, the more fuel your vehicle burns, the more CO2 it emits. This is particularly troublesome because CO2 is the primary human-caused greenhouse gas, contributing heavily to global warming. While a comparison of conventional vehicles and electric cars could be conducted for each of the major pollutants, the critical environmental issue today is the impact our vehicles have on global warming, which is why our calculations focus on CO2 emissions.

A vehicle’s emissions can be categorized into three types: in-use, upstream and vehicle-manufacturing emissions. In-use emissions — those produced when someone is actually driving the vehicle — constitute the majority of a typical car’s lifetime emissions. Upstream emissions are those that result from producing and transporting the fuel a car uses to its point of use (in the case of gasoline, that means extracting crude oil, refining it and transporting it to gas stations). The third category is manufacturing-related emissions, which, according to the latest research, only account for about 10 to 20 percent of a vehicle’s lifetime greenhouse gas output. (Given the modest impact of manufacturing emissions, calculations made in this article include only in-use and upstream emissions.)

Remarkably, burning 1 gallon of gasoline pushes more than 19 pounds of CO2 out of your vehicle’s tailpipe. One gallon of gasoline weighs only about 6 pounds, but the combustion process pulls in oxygen atoms from the surrounding air when creating carbon dioxide. But that’s not all. In addition to those 19 pounds of CO2, nearly another 5 pounds of CO2 are produced “upstream” during the creation and transportation of that gallon of gas from the wellhead to the refinery to the corner station, all before being put in the car’s tank. All told, our cars are responsible for emitting nearly 25 pounds of CO2 for every gallon of gas they burn.

Unlike vehicles with internal combustion engines, electric cars have zero in-use emissions. They do, however, have upstream emissions: those resulting from producing the vehicle’s fuel — in this case, the vehicle’s electricity.

Comparing Electrons

When it comes to electricity, the resource used to generate it plays a major role in determining how environmentally friendly its electrons are. The cleanest type of electricity is that generated from renewable energy sources, such as solar, wind and hydropower. Such sources create electricity without producing greenhouse gases or smog-forming pollutants at a power plant. Electric cars powered by electricity created from renewable sources are, for all intents and purposes, true zero-emission vehicles.

Electricity generated by natural gas plants falls in the middle of the pack. It’s cleaner than coal power, but not nearly as climate-friendly as power generated from renewable sources.

The worst electricity, from both a global warming and a smog-forming emissions standpoint, comes from coal-fired power plants. They emit the highest levels of carbon dioxide and, depending on the quality of the emissions-control devices on the plants, can emit high levels of smog-forming and toxic emissions as well, including particulate matter (soot).

Nuclear plants, while not a threat from a global warming or smog-forming pollution standpoint, pose the dangerous threats of nuclear disasters and nuclear proliferation. Safe, long-term storage of nuclear waste is also a serious concern. Because of these issues, nuclear energy isn’t considered by many (including myself) to be an eco-friendly option at this time.

Today, coal-fired power plants generate the majority of electricity in the United States (48 percent), followed by natural gas (22 percent), nuclear (19 percent) and renewables (9 percent). The efficiency of the power plant also affects the eco-friendliness of the electricity it generates. Some plants, such as combined heat and power facilities, make better use of waste energy, which reduces the amount of fuel necessary (and thus pollution emitted) to produce a given amount of energy. The cleanliness of power plant emissions is also tied to what pollution-control technology the plant utilizes. Plants can use scrubbers, for example, to control sulfur emissions. Short of still-unvalidated carbon capture and storage processes, however, there is no method for controlling CO2 emissions from power plants.

Different U.S. regions utilize vastly different electricity sources. The Northeast, Northwest and Pacific Coast generate electricity using large amounts of renewable hydroelectric power, while the Midwest uses a significant amount of coal. (See a map of regional energy sources.)

What does all of this mean for the typical electricity consumer? In short, it means the cleanliness of your electricity determines how eco-friendly it would be to operate an electric car. For example, if you live in California, which has some of the cleanest electricity in the nation, an electric car driven 12,000 miles (a typical year’s worth of driving) would emit about 1.6 tons of CO2. By contrast, a hybrid such as the Toyota Prius would emit about 2.9 tons, and a 25-mpg gas car would emit about 5.9 tons per year. If you live in the Midwest, where coal is king, your electric car’s annual emissions would be about 4.1 tons of CO2 — more than that of an efficient hybrid, but still far less than that from a gas-only vehicle. (See a chart comparing CO2 emissions.)

So, how do the numbers shake out for the rest of the country? The U.S. Department of Energy tracks power plant emissions in more than a dozen different regions and subregions across the nation. This regional emissions information is a good starting point for estimating the environmental impact of electric cars in different regions of the country. Making subsequent calculations to account for regional transmission and distribution losses, vehicle charging equipment losses, and estimated impacts of energy extraction, transportation and processing, it’s possible to estimate average electric car emissions around the country. See our regional emissions map to find out how much CO2 an electric car would emit in your area.

Another factor to consider is that, while power plants have multiple-decade lifetimes, emissions from the grid are not static. In time, electric cars have the potential to get even cleaner if concerted efforts are made to clean up our energy portfolio with cleaner fossil fuels (natural gas) and, far better yet, even more renewable energy. Each year, the U.S. Department of Energy projects how grid emissions are likely to change in the future. It predicts an electric car driven in California in 2035 will have 39 percent less annual CO2 emissions than an electric car driven today, and an electric car driven in the East Central region (the region labeled “8,259” on the map will have 9 percent less annual CO2 emissions. While constructive on a general level, this information should be viewed cautiously because of the many assumptions that go into such predictions.

A Bright Future for Electric Cars

Electric cars are clearly cleaner than most other vehicles on the road today, but how large of a role can they play in cutting down our transportation sector’s greenhouse gas emissions? That depends in part on how many are sold. Unfortunately, predicting the size of the future electric car market is difficult at best. “If you did a Google search on this, you’d see a million hits with a million different answers,” says Mark Perry, director of product planning for Nissan North America and a key player behind the Nissan Leaf.

Citing internal market research, a government committed to advanced vehicle technologies, and greater public awareness of the ills of oil dependence, Perry is optimistic, predicting electric cars could account for 10 percent of new vehicles sold by 2020. Analysts at the other end of the spectrum suggest numbers as low as 0.5 percent in that time frame. Forecasting aside, one thing’s for certain: Building a successful electric car market will require technological advances, thoughtful infrastructure development, and supportive federal, state and municipal policies.

“There are a bunch of things colliding here,” Moore says, and it’s “very, very hard” to know how the market will unfold. But he’s confident that electric vehicle technology will succeed in time. If that happens, he’s correct that it’s important to answer difficult questions about the technology sooner rather than later. With that in mind, we revisit our initial question: Do electric cars truly deserve their environmentally friendly reputation, even if accounting for power plant emissions? On a national average basis, the answer today is a firm yes. Today’s electric cars are indeed responsible for some pollution, but nevertheless are a cleaner option than most other cars currently on the market. And if we increase our use of renewable energy, the future for electric cars will only get brighter.

How Much Does It Cost to Power an Electric Car?

Care to cut down on your annual fuel costs? You may want to consider going electric. About 3 cents per mile driven is all it costs to “fuel” a typical electric car today, assuming an electricity rate of 10 cents per kilowatt-hour (kWh). By contrast, at a pump price of $2.75 per gallon, a 25-mpg conventional car costs more than three times that amount. Why? A big reason is the inherent efficiency of electric motors.

According to the Department of Energy and the Environmental Protection Agency, about 75 percent of the chemical energy stored in an electric car’s battery can be translated to mechanical energy that rotates the wheels of the vehicle. By contrast, only about 20 percent of the energy stored in a conventional vehicle’s tank of gas actually moves the vehicle down the road. The rest is simply lost — primarily to heat created during the combustion process, but also to other factors, such as friction and air-pumping losses in the engine.

The efficiency advantage of electric motors means excellent on-road “fuel” economy. Today’s electric cars are rated at about 3 miles per kWh of electricity consumed. On a gasoline-equivalent basis, that’s roughly 100 mpg, and a number of drivers report even better results when driving with efficiency in mind. All told, while expensive batteries add to the upfront cost of an electric vehicle, lower fuel and maintenance expenses allow electric car drivers to recoup much of those costs over the life of the vehicle.

Determining Electric Car Efficiency

Multiple factors affect the ultimate efficiency of an electric car, including how you drive, where you drive and even the ambient temperature where you live.

The Environmental Protection Agency measures electric car “fuel economy” by accounting not only for energy used to move the vehicle down the road, but also for the energy needed to use the vehicle’s charging equipment (and the efficiency of that equipment). Based on this, the Nissan Leaf’s overall energy consumption rate is 340 Wh/mi. By comparison, the Chevy Volt (assuming it ran exclusively in “EV mode”) would consume 360 Wh/mi — slightly more energy per mile traveled than the Leaf.

The Leaf’s energy consumption rate serves as a representative value in this article for electric cars because at this time it best represents the mainstream electric car market. That said, the disclaimer “your mileage may vary” still applies to all vehicles. In fact, evidence indicates it applies even more so with electric-drive technology. Recent test drives of the Leaf report a sizable range of energy consumption rates, including some that are notably better (i.e., lower) than 340 Wh/mi.

So, what does all of this mean? If electric car drivers experience efficiencies on-par with that of the Leaf, then under a national average electricity grid mix, the representative electric car will be roughly as carbon-friendly as a 50-mpg hybrid (see chart). However, if an electric car is driven efficiently and consumes less energy than 340 Wh/mi, it would perform commensurately better. If driven aggressively and inefficiently, it would perform slightly worse. Either way, every scenario for electric cars would improve if more renewable energy were used in the grid.

In order to compare vehicle types in this article, aggregate data and a reasonable but specific set of assumptions were used. While attempts were made to ensure accuracy of the findings, alternate assumptions could change the results in either direction. Assuming different vehicle efficiencies, for example, would yield different results. Similarly, assuming electric cars are charged at a specific time of day or night when a given fuel is more likely to be used in power generation could also change the results. On an average basis, however, the numbers in our regional electric car emissions map and our chart comparing electric cars in different regions with a hybrid and a conventional vehicle reasonably represent electric car emissions.

Contributing editor James Kliesch is an expert in advanced and clean vehicle technologies, with more than a dozen years of experience in the field. He is a senior engineer at the nonprofit Union of Concerned Scientists.