According to a report published August 20 by the Bangor Daily News (Bangor, Me., USA) It’s not just cars and trucks that could be powered by the Maine woods. For the past few years, the university has been exploring the potential for wood to power jets. The Department of Defense’s recent investment could advance that research to develop wood into jet fuel.

Aviation is a promising market for wood-based biofuel because jets need the relatively light, compact energy of liquid fuel. Electric batteries can power cars but are too heavy for use in jets. Other renewables such as the solar panels that powered Solar Impulse 2 in a fuel-free flight across the globe between March 2015 and July 2016 likely won’t find commercial applications for some time.

"One day we might get electric cars that won’t need much gasoline, but planes are always going to need jet fuel," Hemant Pendse, director of the Forest Bioproducts Research Institute, said in a 2010 interview with Bangor Metro magazine. "And that’s a huge, huge market, and right now it only comes from petroleum."

Federal energy law calls for cellulosic ethanol, such as that derived from wood, to play a vital role in the nation’s energy future. Ethanol in the U.S. is almost exclusively made from corn, which accounts for about 95 percent of production, and sugarcane, which accounts for about 5 percent. The U.S. produced roughly 13.3 billion gallons of ethanol in 2013, of which only 810,000 gallons came from cellulosic sources.

Cellulosic ethanol, though, has advantages over its corn-based competitor. Unlike ethanol made from corn, cellulosic fuel is made from largely inedible material, so there isn’t a competition between food and fuel. (An estimated 38 percent of the 2013 U.S. corn crop was used to produce ethanol.) Corn also requires more labor and other resources, such as fertilizer, pesticides and fuel, to raise it for eventual use as fuel.

In addition, when measured from forest to fuel tank, the greenhouse gas emissions from ethanol made from cellulose are significantly less than emissions (in this case, from field to fuel tank) from ethanol made from corn.

And wood already is poised to power jet fleets across the country before the decade is out. Red Rock Biofuels, a Colorado-based energy company, plans to begin construction of a biorefinery this year in Lakeview, Oregon. It is expected to annually turn 140,000 dry tons of wood — mostly tree tops and limbs — sourced from within a 50-mile radius of the plant into 12 million gallons of jet fuel.

The company will sell 3 million gallons a year between 2017 and 2024 to FedEx to fuel its jet fleet. Southwest Airlines also will purchase 3 million gallons of jet fuel a year from the biorefinery.

Low gas prices, high uncertainty

With an annual appetite of about 5 billion gallons of fuel, the Department of Defense is the largest energy consumer in the country. The purchasing power of the military could jump-start demand for alternative fuels, such as Maine-made cellulosic biofuel, and military support could eventually make the fuels more cost-competitive.

The U.S. Navy, for instance, aims to source 50 percent of its energy from alternative fuels — including nuclear power, renewables and biofuels — by 2020. Currently, the Navy gets about 17 percent of its energy from alternative fuels, according to the U.S. Energy Information Administration. But this includes no biofuel.

The support from the federal government "helps us commercialize and learn how to make biofuels cheaper," UMaine economist Jonathan Rubin said.

Maine, with an abundant supply of wood, could support at least one modest-sized biorefinery to produce cellulosic biofuel and jet fuel, according to Rubin.

Rubin, along with fellow UMaine economist Sharon Klein and economics graduate students Binod Neupane and Stephanie Whalley, published a study in a recent issue of the Journal of the Transportation Research Board that estimated that 3.9 million dry tons of wood are available for biofuel production.

Not all of that wood, however, would realistically be available to a biorefinery. Hauling costs for wood are high, so a biorefinery would need to source its feedstock from within a smaller geographic area. A biorefinery based at the former Old Town mill, for example, could sustainably harvest from within a 50-mile radius between 650,000 and 735,000 dry tons of wood for biofuel production.

"Costs are significant for transportation of biomass," Rubin said. "You really have to look at how much is biologically available on a sustainable harvest basis in, say, a 100-mile radius."

A fundamental challenge cellulosic biofuel has to overcome in the short term before it can leap into commercialization is a prolonged slump in the price of oil. Crude oil prices have fallen from nearly $100 a barrel in 2014 to $41.16 this year, and prices are forecast to remain low into 2017, according to the Energy Information Administration. It’s a fact of life with which even the proposed biorefinery in Oregon has to grapple.

Unless the price of oil rises closer to $100 a barrel, low oil prices will be a barrier to cellulosic biofuels’ inclusion in the Department of Defense’s energy portfolio. Despite its stated goal of reducing its consumption of petroleum-based fuel, the Department of Defense between 2007 and 2014 purchased just 2 million gallons of alternative fuels for about $58.6 million, according to a 2015 Government Accountability Office report. Over the same period, it bought 32 billion gallons of petroleum-based fuels for about $107 billion.

What alternative fuels the Department of Defense has purchased have been used only for demonstration purposes. Federal law requires the department to consider whether the cost of alternative fuels is competitive with conventional fuels, slowing their adoption by the military.

"It’s a challenging world to produce a biofuel with gasoline at just over $2 a gallon," Rubin said.