Home - Growing Alternative – Winter 2010
Maine has upward of 200,000 acres in which to produce perennial energy crops without displacing current food production, Plant says. If crop waste, such as straw from grain rotations, is included, the number of acres for energy crops doubles.
From a microeconomic perspective, grain production in Aroostook County is a drop in the bucket, Plant says. Most of Maine’s small grains now are going for livestock feed.
“In Aroostook County the question is not food versus fuel, but whether this could mean the difference between a farmer staying in business (and not),” he says.
To determine which perennial grasses will grow best in Maine, Plant began looking at species studied by the U.S. Department of Energy and Oak Ridge National Laboratory in the 1980s and 1990s. Those grasses include the superstar of bioenergy crops — switchgrass — that produces dense pellets shown to have a 14:1 energy balance. In other words, for every unit of energy it takes to produce the pellets, 14 units of energy are gained, through burning. By comparison, the 2008 energy balance for the corn-ethanol industry is 2.3:1, according to the U.S. Department of Agriculture.
There’s also reed canarygrass, a native Maine species known for its ability to grow high yields in cool seasons.
Studies in the north central United States and Europe have shown that reed canarygrass can yield 4 tons to 8 tons per acre, depending on fertilization regimes. If replicated in Maine, Plant says, commercial production cost estimates are $115 to $130 per ton of pellets — $5.50 to $6.25 per million British thermal unit (Btu). Wood pellets average $9.50 per million Btu.
When home heating oil is $2.70 a gallon, Mainers pay $19.50 per million Btu.
Compared with other biofuel crops, perennial grasses conserve soil resources, sequester carbon and nitrogen in their root systems, and can serve as valuable wildlife habitat. The perennial grasses have moderate to high productivity, stand longevity, low nitrogen requirements, and resistance to pests and diseases. They also are well adapted to marginal farmland and can be successfully established in northern climes.
And unlike forage crops harvested a couple times a year, energy grasses are cut annually at the peak of maturity. The baled grass has a moisture content of up to 15 percent, compared to upward of 50 percent moisture content of wood, which mandates extensive drying before pelletizing.
A large round bale of grass can produce up to 1,400 pounds of pellets, says Plant. It would take an average of 2 to 3 acres of grass made into pellets to annually heat a typical northern home.
The grasses, like wood, contain natural lignins that act as gluing agents. For the additional binding needed to improve the energy density of grass pellets, UMaine researchers are exploring the use of patented technology that incorporates recycled, nonchlorinated plastics.
Some of these plastics are even found on farms, including greenhouse film and hay bale wire.
The recovered plastics, such as polyethylene and polypropylene, certified by the U.S. Environmental Protection Agency to be used as fuel, are highly refined hydrocarbons with low levels of inorganics and high Btu values. Recent work has shown that bioplastics, such as polylactic acid, which are difficult to process in conventional recycling operations, can also be used in pellets.
Grass pellets may burn faster than wood, Plant says, but with the plastics as binder, they are more energy-dense.
However, when burned, grass pellets tend to be higher in ash content than wood — up to 5 percent versus 1 percent. Grass also has a higher natural chlorine content, making the pellets more corrosive than those made of wood.
In Europe and elsewhere, research is focusing on new technology for ash management in boilers and stoves, as well as higher-grade metals that better resist corrosion.
“A lot of people think there is one silver bullet to solve everything,” says Plant. “I think we’ll have to be diverse to eliminate fossil fuel use. I relate it to an investment. You don’t put all your money into one account or stock. It will have to be all cards on the table.”