Friday, February 08, 2013

Energy Density is Inconsequential Comic

This is the comic I need to put up whenever someone makes an energy density argument to defend their favorite pet fuel. For whatever reason, one of the most common argument scientists or engineers in the field of energy make in favor or against any particular fuel is always about energy density. Ethanol's not as good as gasoline as it has lower energy density. Gasoline's not as good as diesel. Plants have a very low energy density so biofuels are dumb. Honestly, after net energy balance (something almost as useless) you hear this argument second most often. But that's only because as scientists its one of the only numbers they can grasp but its about as consequential to choosing a fuel as the color. If energy density really mattered, we'd only use uranium.

What really matters is an accounting of ALL the costs and ALL the benefits. Uranium may be a viable alternative fuel source but its costs and benefits have very little at all to do with the energy density. Just saying plants have a very low energy density doesn't mean it might not be cost effective. Sure, it takes 4.2 bushels of corn to make one gallon of ethanol based gasoline, but if it costs less (including all the externalities) of making energy that way compared to say getting an equivalent amount of power from building a solar power plant, shipping in materials, accounting for depreciation, building  a billion new electric cars, then ethanol is a better fuel source. The energy density is irrelevant.
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