Oregon Public Broadcasting is reporting on the efforts of a WSU researcher to turn poplar trees into transportation fuel:

[P]oplars [are] an on demand fuel source. Trees can be chopped down year round, chipped up and then fermented to create ethanol.

According to the researcher, an acre of poplar could supply about one thousand gallons of ethanol per year—which is about three times the per-acre yield of corn ethanol, with a lot less plowing and fertilizer consumption.  Cool!

Of course, inveterate skeptic that I am, I had to run the numbers…

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  • Let’s ignore, for a moment, any energy that’s used in harvesting, chipping, and fermenting the poplars. (In a proper analysis, we’d “net out” those energy inputs from the final ethanol output.) Instead, let’s just focus on the ethanol itself—and how many acres of poplars it would take to satisfy our demand for transportation fuels.

    Ethanol isn’t quite as “energy dense” as gasoline.  A thousand gallons of ethanol has about the same amount of energy as only 610 gallons of gas.

    Here in the Northwest (British Columbia, Washington, Oregon, and Idaho inclusive) we use about 6 billion gallons of gasoline per year.  So if the poplar research is close to being right, it would take about 9.2 million acres of poplar plantations to satisfy our gasoline appetite.

    That’s a lot of land—it’s area about 9 times the size of Washington’s Olympic National Park, or roughly the size of New Jersey and Connecticut combined.  Quite a poplar plantation, I’d say.

    Scaling up to meet the total gasoline demand of the US and Canada, you’d need a poplar plantation about the size of California plus Montana, with Mississippi thrown in for good measure, to satisfy the nations’ demand for gasoline.  And that doesn’t even cover diesel or airplane fuel.

    Needless to say, with numbers like these, it’d take a huge national effort, and a major disruption of forest ecosystems, for poplar-based ethanol to make a serious dent in our petroleum habit.

    I don’t mention all of this to throw cold water on alternative fuels.  I, for one, am guardedly optimistic about cellulosic ethanol, and am delighted that WSU is doing the research.  Still, it’s important to keep in mind the scale of our fuel consumption:  we use so much gasoline right now that biofuels just aren’t a silver bullet.  It’s going to take a lot more—everything from super-efficient vehicles, to compact neighborhoods that minimize travel, to incentives for filling empty seats—if we’re really going to create a transportation system that can last over the long haul.