Transportation is another sector that has increased its relative share of primary energy. This sector has serious concerns as it is a significant source of CO2 emissions and other airborne pollutants, and it is almost totally based on oil as its energy source (Figure 1.5; Kreith, West, and Isler 2002). In 2002, the transportation sector accounted for 21% of all CO2 emissions worldwide. An important aspect of future changes in transportation depends on what happens to the available oil resources, production and prices. At present, 95% of all energy for transportation comes from oil.

As explained later in this chapter, irrespective of the actual amount of oil remaining in the ground, oil production will peak soon. Therefore, the need for careful planning for an orderly transition away from oil as the primary transportation fuel is urgent. An obvious replacement for oil would be biofuels such as ethanol, methanol, biodiesel, and biogases. Some believe that hydrogen is another alternative, because if it could be produced economically from RE sources or nuclear energy, it could provide a clean transportation alternative for the future. Some have claimed hydrogen to be a "wonder fuel" and have proposed a "hydrogen-based economy" to replace the present carbon-based economy (Veziroglu and Barbir 1992). However, others (Shinnar 2003; Kreith and West 2004; Mazza and Hammerschlag 2005) dispute this claim based on the lack of infrastructure, problems with storage and safety, and the lower efficiency of hydrogen vehicles as compared to plug-in hybrid or fully electric vehicles (West and Kreith 2006). Already hybrid-electric automobiles are becoming popular around the world as petroleum becomes more expensive.

The environmental benefits of renewable biofuels could be increased by using plug-in hybrid electric vehicles (PHEVs). These cars and trucks combine internal combustion engines with electric motors to

1971 1980 1990 2002

□ Share of transport in global oil demand

□ Share of oil in transport energy demand

FIGURE 1.5 Share of transport in global oil demand and share of oil in transport energy demand. (Data and forecast from IEA, World Energy Outlook, IEA, Paris, 2004. With permission.)

maximize fuel efficiency. PHEVs have more battery capacity that can be recharged by plugging it into a regular electric outlet. Then these vehicles can run on electricity alone for relatively short trips. The electric-only trip length is denoted by a number, e.g., PHEV 20 can run on battery charge for 20 miles. When the battery charge is used up, the engine begins to power the vehicle. The hybrid combination reduces gasoline consumption appreciably. Whereas the conventional vehicle fleet has a fuel economy of about 22 mpg, hybrids such as the Toyota Prius can attain about 50 mpg. PHEV 20s have been shown to attain as much as 100 mpg. Gasoline use can be decreased even further if the combustion engine runs on biofuel blends, such as E85, a mixture of 15% gasoline and 85% ethanol (Kreith 2006; West and Kreith 2006).

Plug-in hybrid electric technology is already available and could be realized immediately without further R&D. Furthermore, a large portion of the electric generation infrastructure, particularly in developed countries, is needed only at the time of peak demand (60% in the United States), and the rest is available at other times. Hence, if batteries of PHEVs were charged during off-peak hours, no new generation capacity would be required. Moreover, this approach would levelize the electric load and reduce the average cost of electricity, according to a study by the Electric Power Research Institute (EPRI) (Sanna 2005).

Given the potential of PHEVs, EPRI (EPRI 2004) conducted a large-scale analysis of the cost, battery requirements, economic competitiveness of plug-in vehicles today and in the future. As shown by West and Kreith, the net present value of lifecycle costs over 10 years for PHEVs with a 20-mile electric-only range (PHEV20) is less than that of a similar conventional vehicle (West and Kreith 2006). Furthermore, currently available nickel metal hydride (NiMH) batteries are already able to meet required cost and performance specifications. More advanced batteries, such as lithium-ion (Li-ion) batteries, may improve the economics of PHEVs even further in the future.

Guide to Alternative Fuels

Guide to Alternative Fuels

Your Alternative Fuel Solution for Saving Money, Reducing Oil Dependency, and Helping the Planet. Ethanol is an alternative to gasoline. The use of ethanol has been demonstrated to reduce greenhouse emissions slightly as compared to gasoline. Through this ebook, you are going to learn what you will need to know why choosing an alternative fuel may benefit you and your future.

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