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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.

1.4 World Energy Resources

With a view to meet the future demand of primary energy in 2050 and beyond, it is important to understand the available reserves of conventional energy resources including fossil fuels and uranium, and the limitations posed on them due to environmental considerations.

1.4.1 Conventional Oil

There is a considerable debate and disagreement on the estimates of "ultimate recoverable oil reserves." However, there seems to be a good agreement on the amount of "proven oil reserves" in the world. According to British Petroleum (2006), total identified or proven world oil reserves at the end of 2005 were 1200.7 billion barrels. This estimate is close to the reserves of 1266 billion barrels from other sources listed by IEA (IEA 2004). The differences among them lie in their accounting for the Canadian tar sands. Considering the present production rate of over 80 million barrels per day, these reserves will last for about 41 years if there is no increase in production. Of course, there may be additional reserves that may be discovered in the future. A recent analysis by the U.S. Energy Information Agency (2006) estimates the ultimately recoverable world oil reserves (including resources not yet discovered) at between 2.2 X1012 barrels (bbl) and 3.9 X1012 bbl with a mean estimate of the USGS at 3X1012 bbl.

Ever since petroleum geologist M. King Hubbert correctly predicted in l956 that U.S. oil production would reach a peak in l973 and then decline (Hubbert 1974), scientists and engineers have known that worldwide oil production would follow a similar trend. Today, the only question is when the world peak will occur. Bartlett (2002) has developed a predictive model based on a Gaussian curve similar in shape to the data used by Hubbert as shown in Figure 1.6. The predictive peak in world oil production depends on the assumed total amount of recoverable reserves.

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DIY Battery Repair

DIY Battery Repair

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