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Find the green car that is just right
Looking to reduce your carbon footprint? Your car is an obvious place to start. While standard, gas-fueled cars dominate the roads, there are a few current alternatives and some promising future technologies.
Hybrid cars have proven a popular green alternative. These cars have a battery pack that gets charged from excess engine energy and braking, and an electric powertrain alongside a traditional gas engine. When the car needs extra power, the electric powertrain draws on the batteries to help turn the wheels. Hybrid cars generally get better mileage, produce lower amounts of the regulated emissions than their gasoline counterparts, and are especially economical in traffic.
There are two main varieties of hybrids on the roads today, full hybrids and mild hybrids. A third type, plug-in hybrids, have generated interest, but are not in mass production.
Full hybridsToyota Prius. Full hybrids use one to three electric motors that drive the car under full electric power. Typically, full hybrids run under electric power at low speeds, up to 25 mph. The electric motors also contribute power when the car accelerates, assisting the gas engine. A particular virtue of full hybrids in urban areas is that the engine shuts down when the car is stopped or creeping slowly in traffic, reducing all emissions to zero. The engine comes back on when the battery reserves run low or the driver requires more speed or acceleration. There is a wide array of full hybrid cars available today, from sedans to SUVs. Because of the extra equipment, especially the batteries, hybrids tend to cost more than their gas-only equivalents. On the plus side, many states let hybrids use car pool lanes no matter how many occupants are in the car. Here are two examples of full hybrids:
Plug-in hybridsTinkerers have found that recharging a full hybrid's batteries by plugging it in can yield 100 mpg. To convert a full hybrid into a plug-in, the car has to be modified, usually by changing the batteries from nickel metal hydride, used in current production full hybrids, to lithium ion, a battery type that better handles deep discharging. The power control software might also be modified to let the car run at higher speeds under electric power and, of course, a plug needs to be added. Plug-in hybrids offer all the benefits of a full hybrid, and they can keep the gas engine off for longer periods, ultimately releasing fewer greenhouse gases and other pollutants.
Of course, the electricity from the grid used to recharge the batteries might come from power plants that produce greenhouse gases. However, advocates point out that, if the car is recharged overnight, there is surplus electricity available because of low demand. Also, power plants, because they are a large, single source, can be made more efficient and less polluting than thousands of cars on the road.
As there are currently no production plug-in hybrids, the only option is to buy a previously converted hybrid, or buy a hybrid and pay for the conversion. CalCars has a page on plug-in hybrids that lists some of the companies doing conversions and the costs, which range from $6,000 to $24,000. Major automakers, including Toyota and GM, have expressed interest in developing plug-in hybrids, but no prototypes have yet been shown.
For more information on plug-in hybrids, watch CNET's Green Mile: Plug in your hybrid.
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Senior editor Wayne Cunningham covers the automotive beat for CNET. He covers cars, portable navigation units, and car entertainment systems.