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Making the Camparison
Because the Prius and the H-car are so similar, we can ignore many complications like regenerative breaking city driving patterns and only compare their essential differences.
Because H comes from natural gas and gasoline comes from oil, and because homes can heat with either natural gas or oil, which is used up makes little difference. If we use our natural gas to run H-cars, this will drive up the price of natural gas and oil will be substituted for home heating.
Starting with a Btu of oil/natural gas, the two cars differ up until this energy has been converted to electricity. We will compare this difference.
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Fuel Cell Efficiency
The fuel cell thermodynamic efficiency is given by the ratio of the Gibbs function change to the Enthalpy change in the overall cell reaction. The Gibbs function change measures the electrical work and the enthalpy change is a measure of the heating value of the fuel.
Efficiency = (dG/dH)
For the hydrogen -oxygen reaction: dH = - 68,317 cal/g mole of H2, and dG = - 56,690 cal/g mole of H2 . The efficiency of the Ideal Fuel Cell is therefore:
Efficiency = (56,690/68,317) = 83%
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Toyota 2003 Prius2 (83k PDF)
Well-to-Tank efficiency for gasoline = 88% according to Toyota Doc #70, p. 19.
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Steps in the H-Car's Conversion of NG to Electricity
1. Reform natural gas to H2.
2. Compress the H2 and fill the car's tank.
3. Generate electricity with the fuel cell.
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Steps in the Prius's Conversion of Oil to Electricity
1. Refine the Oil to Gasoline and fill the tank.
2. Generate electricity with the engine and a generator.
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http://zfacts.com/p/66.html | 01/18/12 07:22 GMT
Modified: Mon, 17 Apr 2006 05:43:55 GMT
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