Digging Deeper:
The Road Map for Savings with Hybrid Cars

The Question
Our family is in the process of purchasing a new car, and we are considering a hybrid model. We keep vehicles for a long time (our current cars are six and 10 years old), and we are curious about the maintenance costs and reliability of hybrid cars, especially battery replacement. Will the larger investment of purchasing a hybrid vehicle pay off in the long run?

The Explanation
There are many kinds of hybrid vehicles, and some are more common than you might think. For example, busses in several major cities and most locomotive trains run on diesel and electricity. It is simply the combination of multiple types of energy that defines a vehicle as a “hybrid.”

The most popular hybrid car models on the American market are gasoline-electric hybrids, which combine a small version of the internal combustion engine found in conventional cars with an electric motor powered by a battery pack. These technologies substantially increase energy efficiency.  A conventional car can convert only 20 percent of the thermal energy produced by the combustion of gas into work, while hybrid cars convert roughly 70 percent.

In a gas-powered car, gasoline flows from a fuel tank to an internal combustion engine, providing the energy necessary for the engine to turn the car’s transmission, which then turns the wheels. A hybrid car has a smaller fuel tank and engine, typically with a few additional mechanical tweaks that increase efficiency and reduce emissions. These small engines use lighter parts, less fuel, and fewer energy-consuming cylinders, thus requiring less energy to propel the car.

Hybrids also have a sophisticated electric motor that can function as either an engine or a generator. When it acts like an engine, electricity flows into it from the battery pack, providing energy for the motor to turn the transmission and so turn the wheels. When the driver presses on the brakes and slows down, the electric motor acts like a generator, capturing the excess kinetic energy and storing it in the battery pack for future use.

Hybrid Cars Possible with Current Technology

From www.greencarcongress.com

There are several different kinds of hybrid cars currently on the market. “Micro” hybrids engage their electric motors only for non-driving functions, like activating the internal combustion engine. In “mild” hybrids, around 10 percent of the driving power comes from the electric motor. In “parallel” hybrids, both the electric motor and the conventional engine can turn the transmission at the same time; in “series” hybrids, the electric motor can accept power from either the engine or the battery pack to turn the transmission and move the car.

And in the Toyota Prius, the model with arguably the most sophisticated internal mechanics, parallel and series systems are combined. Toyota’s specially-engineered powertrain allows the Prius to reach about 15 miles per hour before the gas-powered engine is activated, which means that it can run completely on electric power during city driving or stop-and-go traffic.

Life-Cycle Analysis
The entire automotive life-cycle begins with the extraction of raw materials, continuing through the processing of these materials, car manufacture, vehicle operation, and ending with disposal.  Over the life-cycle, hybrid cars require less energy and contribute less to greenhouse gas emissions than conventional automobiles.

Stages in the Life-Cycle of an Automobile include Manufacturing,
Operation and Disposal/Material Re-Use

From Lesterlave et al., 2000
Raw Materials
Conventional and hybrid vehicles contain nearly the same raw materials. In 2004, a study of the British automobile industry estimated that four million of the 7.23 million tons of automobile products sold each year were derived from primary products. That’s a lot of mineral and metal extraction.

Ores Used during the Lifetime of a Conventional Automobile

Figure from MacLean & Lave 1998

Hybrid cars typically use lighter, and in some cases more sophisticated, machinery and body parts, and contain multiple advanced battery cells. Most conventional cars use lead acid batteries, but hybrids use nickel metal hydride batteries, which generally cause less overall environmental impact. In addition, most hybrid car manufacturers buy back used batteries (at a nominal cost) to ensure that the precious metals, plastic, wiring, plates, and steel casing are recycled. In the case of the alkaline found in Honda hybrid car batteries, the buyback allows the material to be neutralized properly before disposal. 

Making It

Above -- Energy consumed (total = 1.2 million MJ) and toxic releases (total = 66.3 kJ) over the lifetime of a conventional car (from MacLean & Lave 1998).

The manufacture of some hybrid car models may require more energy than that of conventional cars, but the evidence for this is contentious at best. Current research estimates that the energy consumed during a car’s manufacture is roughly 10 percent of the energy used over its entire lifetime. Manufacturing has been estimated to account for from 10 to 50 percent of a car’s overall emissions.

Using It
Operation: British automobiles are estimated to use energy equivalent to 41 million tons of oil, with the vast majority of this energy consumed during the vehicle operation stage. The environmental impacts from driving any car, such as greenhouse gas emissions, are less significant than the impacts of its manufacture, such as the extraction of raw materials for mechanical components. Between the two vehicle types, hybrid cars clearly use less gasoline and produce fewer emissions, and so are more energy efficient overall.

Maintenance: Some of the hybrid car’s special features may translate into lower lifetime maintenance costs. Because the electric motor does up to 80 percent of the work during the braking process -- it captures the excess kinetic energy and stores it in the battery pack -- brakes, brake pads, and other braking-related machinery tend to last longer in hybrid cars. Heat warping causes many common maintenance problems in conventional cars, such as belt and rotor wear. Since hybrids let a much smaller amount of energy escape as heat, they are likely to avoid these problems.

Hybrid battery packs are much more expensive than batteries found in gas-powered models, but they are designed to last for the vehicle’s entire lifetime, and always come with extended warranties. If these or any of the more advanced hybrid technology components need attention, owners will have to go to dealership specialists for repairs. When all of these maintenance concerns are added up, however, industry experts believe that hybrids are likely to require equivalent, or even lower, overall maintenance costs.

The Cost
Hybrid cars hold their value well over time: the Kelly Blue Book estimates that a 2005 Toyota Prius sold new for $22,500 is today worth roughly the same value. Equivalent conventional models lose at least 10 percent of their value each year, resulting in a much lower resale value.

All gasoline-electric hybrid vehicles cut tailpipe emissions, reducing the carbon monoxide, carbon dioxide, nitrogen oxides, and hydrocarbons a car releases into the atmosphere. Lowering the human contribution to greenhouse gases helps combat global warming, and diminishes smog. Other benefits often apply as well: in some states, hybrid car owners may drive in high occupancy vehicle (hov) or carpool lanes and have access to special hybrid car parking spaces or discount parking passes.

Conventional gas and electricity costs must also be considered. The machines used to extract the raw metals used in cars themselves run on gas or petrodiesel, the electricity used to power the manufacturing plant came from somewhere, and hybrid cars still require a not insubstantial amount of gasoline.

A consumer choosing a hybrid car for its great mileage and low emissions must consider that hybrids are still very close to conventional cars in terms of primary material requirements, energy used in manufacture, and emissions produced during manufacture. Though they may incur local benefits like reduced smog, these other energy uses and pollutants are only truly felt in the country where the car is manufactured, or at disposal sites.

The Rules
There are no special laws that apply to the purchase and operation of hybrid vehicles, but consumers will want to keep track of the tax rebates and other incentives offered by federal and state governments.

For More Information
A more detailed description of how a hybrid car’s moving parts work can be found here: http://consumerguideauto.howstuffworks.com/the-consumer-guide-to-hybrid-vehicles-cga.htm

The U.S. Department of Energy's 2007 Fuel Economy Guide provides information on hybrid vehicles, alternative fuel vehicles, energy efficiency, and the importance of fuel economy. www.fueleconomy.gov.

Consumer Reports has a very user-friendly site devoted to hybrid car performance.

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