Transportation uses vast amounts of energy and has a major environmental impact. As a result, rigorous assessments of the sustainability of various modes of moving people and goods are critically important. Multiple studies have found that electric cars are more efficient, and therefore responsible for less greenhouse gas and other emissions than cars powered solely by internal combustion engines.
An EU study based on expected performance in 2020 found that an electric car using electricity generated solely by an oil-fired power station would use only two-thirds of the energy of a petrol car travelling the same distance. Although an electric car powered in this way is still ultimately burning the same fuel as the petrol car it replaces, it is burning much less of it.
And although greenhouse gas emissions are similarly harmful wherever they occur, some other emissions which are harmful to human health are less dangerous when they happen at a power plant outside the city than at the roadside near schools and houses.
There are Many Different Types of Electric Vehicle
The distinction between petrol and electric is not binary; a car’s green credentials vary according to whether and how it uses electricity, and how that electricity is generated, with important trade-offs for efficiency and range. A hybrid stores energy from braking and from its combustion engine at higher speeds to charge a battery. It uses the battery to power its drive chain at lower speeds, usually in towns. It is more efficient than an ordinary car even though it uses no grid electricity.
Today, most hybrid cars utilize the same technology, using an electric motor/gas engine. By doing so, the energy from gasoline could be used to power a battery, capacitor or directly power the engine, while the electric motor is used to drive the wheel. Alternatively, in “parallel” and “power split” hybrid vehicles, an engine and an electric motor share the work of driving the wheel.
Diesel vs Hybrid
Modern diesels can be as desirable to consumers as gasoline automobiles, but how does their environmental performance measure up?
To answer this question, we must examine the entire life-cycle of the vehicle, including extracting raw materials, manufacturing and assembling automobile components, producing and combusting fuel, and maintaining and disposing of vehicles. Several differences between diesels and hybrids are undeniable: diesel engines are inherently more efficient than gasoline engines, diesel fuel contains approximately 10 percent more energy per volume than gasoline, and diesels produce significantly more air pollution. A closer look at the models offered today highlights these differences.
Materials Use and Waste Production
Nearly all vehicle energy consumption (more than 85 percent) and pollutant emissions occur during vehicle usage, which includes the vehicle emissions themselves as well as the impacts associated with the fuel cycle: the extraction, refining, transport, and use of diesel and gasoline. The large environmental impact during vehicle use means that materials use for manufacturing is not a primary concern, though it is worth some consideration.
The vehicle lifecycle includes the production of about 6,700 kilograms (14,740 pounds) of hazardous waste per vehicle; half of that is produced during materials extraction and vehicle manufacture and half during fuel refining. Hybrid-car batteries are an additional source of hazardous waste, but the impacts are difficult to quantify. The potential longer lifetime of diesel vehicles also reduces materials use, though this may be offset by the extended usage of older vehicles with worse-than-average air emissions. Overall, there is no clear preference for either vehicle based on materials use.
Energy Use and Greenhouse Gases
The U.S. transportation sector produces 26 percent of the nation’s greenhouse gas (GHG) emissions and consumes 27 percent of the energy, making fuel economy particularly important in this analysis. It is clear that the gasoline hybrids have a significant advantage.
The U.S. transportation sector produces significant amounts of air pollution, including 40 percent of volatile organic compounds, 77 percent of carbon monoxide, and 49 percent of nitrogen oxide emissions. Vehicle use produces five key regulated air pollutants: nitrogen oxides (NOx), carbon monoxide (CO), sulfur dioxide (SO2), volatile organic compounds (VOCs), and particulate matter (PM). NOx and hydrocarbons combine to form ground-level ozone, which damages the lungs and increases the vulnerability of plant life to disease.
Carbon monoxide causes cardiovascular damage, and sulfur dioxide leads to acid rain. Particulate matter can contribute to lung cancer and respiratory problems at any ambient concentration; the World Health Organization estimates that it leads to 100,000 deaths per year in Europe. Approximately 10 percent by weight of the VOCs emitted are known or suspected to cause cancer; these include benzene, 1,3-butadiene, acetaldehyde, and formaldehyde.
The Accord produces twice the carbon monoxide and VOCs as the other cars, while the diesel automobiles have approximately six times more NOx and eight times more particulate matter than the Prius and Civic. Notably, the diesel vehicles do not currently meet some state air standards. The hybrids lead the diesel vehicles by far in terms of air emissions. The conclusions may vary with driving conditions though.
Since hybrid cars burn regular gasoline, they emit the same greenhouse gases as conventional cars. But since hybrid cars are much more fuel efficient than conventional vehicles, the U.S. Energy Information Administration sets the average mileage for a hybrid at 38.7 miles per gallon (16.5 kilometers/liter) compared with 26.7 (11.4 kilometers/liter) for a gas-only vehicle — they require far less gas to cover the same distance.
If every gallon of gasoline contains 20 pounds (9 kilograms) of carbon dioxide, then a hybrid car will emit 51.6 pounds (23.1 kilograms) of carbon dioxide every 100 miles (161 kilometers), while a conventional car will emit 74.9 pounds (34 kilograms). If you multiply those numbers over the lifetime of a vehicle, hybrids more than make up for their heavier production footprint.
The Argonne National Laboratory ran a side-by-side comparison of hybrid and conventional vehicles over their entire life cycle, which includes vehicle production, vehicle operation and the energy required to produce fuel for both cars. But there is an interesting side note to the hybrid vs. conventional debate. Hybrid carmakers like Toyota are set to release a new breed of plug-in hybrids.
Equipped with a bigger battery pack, these hybrids can be plugged into the wall like an electric car, giving an extra 10 to 20 miles (16 to 32 kilometers) of zero-emissions driving before the gas engine kicks in. Toyota expects to sell 20,000 to 30,000 units of its 2011 Plug-in Prius and more in the coming years. The trouble with plug-in hybrids (and electric cars, too) is that electricity isn’t always cleaner than gasoline. There is tremendous scope of innovations ahead in this sector. The world is hoping for the best.