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Originally Posted by NeilBlanchard
Are they accounting for the greater energy content of the diesel fuel?
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Yes ... but it changes the results to the opposite of the original poster's title ... in all 3 posted links the Hybrids are more energy efficient ... see bellow:
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Originally Posted by Piwoslaw
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In this referenced paper it states:
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On a volumetric basis, the 24-month average fuel economy for the hybrid buses is 3.35 miles per gallon (mpg)—4.3% lower than that of the diesel buses. This difference is likely due to the lower efficiency of a throttled, spark-ignited engine as well as the lower energy content of a gallon of gasoline versus a gallon of diesel. On an equivalent energy per volume basis, the hybrids had an 8.5% mpg increase.
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It goes on to compare based on fuel costs ...
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During the evaluation period, gasoline at LBT cost an average of $2.49 per gallon and diesel cost an average of $2.29 per gallon. This lower fuel economy, combined with a higher fuel cost for gasoline, resulted in fuel costs per mile being $.74 per mile for the hybrids as compared to $.65 per mile for the diesels.
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The Diesel fuel was cheaper per gallon by enough of a margin to keep it cheaper to fuel per mile.
But it goes on to also look at the maintenance costs of the two:
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The hybrids cost $.31 per mile to maintain while the diesels cost $.54 per mile.
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The hybrids had brake system maintenance costs that were about 90% less than that of the diesel buses with no relines to date on the hybrids.
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The diesel fuel per mile saving are not large enough to compensate for the higher costs to maintain them... although the diesels were older buses ... The hybrids were newer ... a better comparison would have been between two groups of hybrid and diesels that were equally old / used.
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Originally Posted by Piwoslaw
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In this has the same findings and states:
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NREL looked at the performance of the buses and found that the gas hybrids got 4.3 percent lower fuel efficiency than the conventional diesel buses in the fleet. When the lower energy content of gasoline is factored in, though, the gas hybrid came out 8.5 percent better.
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Quote:
Originally Posted by Piwoslaw
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Also seems to have the same findings:
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found that on a volumetric basis, the average fuel economy for the gasoline hybrid buses is 3.35 mpg—4.3% lower than that of the conventionally-powered diesel buses
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On an equivalent energy per volume basis, the hybrids had an 8.5% mpg increase.
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