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Plugging in to emission reductionsHybrid cars are taking off, promising substantial emission reductions over their conventional equivalents. Plug-in hybrids represent the next step, says David SandalowTo reduce oil dependence, nothing would do more good, more quickly than making cars that connect to the electric grid. The US has a vast infrastructure for generating electric power. Yet that infrastructure is essentially useless in cutting oil dependence, because modern cars can’t connect to it. Oil provides more than 96% of the energy for our cars and trucks. It provides less than 3% of the energy for electric generation. Solving the problem of oil dependence requires vehicles that run on other fuels. In the past few years, the popularity of hybrid engines has skyrocketed. These hybrid engines combine a traditional internal combustion engine with an electric motor, improving fuel efficiency. More than a million cars with hybrid engines – such as the Toyota Prius and Ford Escape Hybrid – are now on the road.
Yet these hybrid engines still take only one fuel – petroleum.The battery in the electric motor is recharged with energy captured from the braking system or other parts of the engine as the car moves. The next big step in automotive technology is the plug-in hybrid electric vehicle (PHEV). Like conventional hybrids, PHEVs combine an internal combustion engine and electric motor. But, as the name suggests, there’s an important additional feature. The battery in a plug-in hybrid can be recharged from the electric grid. It can – quite literally – be plugged into a wall socket. With plug-in hybrids, electricity from the grid becomes an alternative fuel. The idea is simple, but the consequences are far-reaching: With plug-in hybrids, many drivers would need no petroleum for their daily commute. Cars could be recharged at night and many drivers could travel back-and-forth to work or around town using the car’s electric motor. Driving costs would drop dramatically. At national average electricity prices, PHEVs would cost the equivalent of roughly 75 cents per gallon to drive when operating on their electric motors. (A plug-in hybrid car uses roughly the same amount of electricity as a space heater in the home.) As with many electric cars, torque and acceleration would be excellent. Historically, electric drive trains have been limited by battery cost, weight and size. But innovation is proceeding quickly in this area. Lithium ion batteries – the kind widely used in computer laptops – have particular promise, since lithium is the lightest metal and third lightest element. More than $1 billion is being spent on research and development of these batteries each year. General Motors has announced plans to sell plug-in hybrids in the next few years. Companies such as A123 Systems will soon be offering conversion kits, to allow current hybrid owners to convert their cars to plug-ins. One common question is, what impact will plug-ins have on global warming? The answer is that plug-in hybrids represent an important step forward in the fight against climate change. Plug-in hybrids reduce emissions of heattrapping gases, even if the power to recharge batteries comes from a coal-fired power plant. The reason is that a traditional internal combustion engine is astonishingly inefficient. With hundreds of moving parts constantly creating friction, an internal combustion engine wastes much of its energy in the form of excess heat. (That’s the main reason for cars’ cooling systems.) The thermal efficiency of an internal combustion engine – its ability to convert fuel to useful work – is much lower than the thermal efficiency of even an old-fashioned pulverised coal plant. Consider this calculation: Burning a gallon of gasoline releases roughly 20 pounds of carbon dioxide into the atmosphere. A gallon of gasoline moves the average US vehicle roughly 21 miles. That means the average vehicle releases just under one pound of carbon dioxide for each mile traveled. Generating a kilowatt-hour of energy at the average US coal plant releases roughly 2.1 pounds of carbon dioxide into the atmosphere. A kilowatt-hour moves a first generation PHEV roughly three miles. That means a first-generation PHEV recharged with energy from a coal plant will release roughly 0.7 pounds of carbon dioxide per mile when driving on its electric motor. In other words, from the global warming standpoint, driving a PHEV charged with energy from a coal plant is better than driving an average vehicle filled with oil. Driving a PHEV charged with energy from a standard wall socket – which draws only part of its power from coal – is less carbon-intensive still. Roughly half of the electricity in the US comes from coal. Other electric power sources emit far fewer heat-trapping gases than coal plants. Recent studies have found that, with today’s grid and driving patterns, plug-in hybrids would reduce total emissions of heat-trapping gases from vehicles in the US by 27–37%. Furthermore, it is possible to drive a plugin hybrid without producing any heat-trapping gases at all. If a plug-in is recharged from a wind turbine or solar panel, for example, the miles driven on that charge have essentially no impact on global warming. In some regions of the country, wind resources are especially good at night, when many drivers will be recharging cars. PHEVs are therefore an especially good way to capture wind energy. Oil dependence is a national security issue, heats the planet and strains family budgets when world oil prices rise. Plug-in hybrids can help solve these problems. David Sandalow is a senior fellow at the Brookings Institution. This article is adapted from his new book <em>Freedom from Oil</em> (McGraw-Hill 2007). E-mail: dsandalow@brookings.edu The opinions expressed in the above article are not necessarily the opinions of the EMA, its members or member companies
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