Harvesting heat
Vermont willow crops promise cheap biomass fuel
Vermont’s Middlebury College used to heat its buildings with oil, then switched to wood chips. Now it has planted a sustainable and relatively cheap fuel source —willow shrubs—that could help cut demand on the state’s forests.
With a nine-acre patch of the fast-growing willows, the college is conducting a biomass energy experiment that seeks to answer the question: What if wood chip-burning heat systems lead to the deforestation of Vermont?
Willows, which grow faster than other trees and branch out when pruned, may be the answer—and may be a resource for other cold-weather states, too. So Jack Byrne, director of sustainability for the college, and business services director Tom Corbin have turned into farmers of sorts, planting tightly packed rows of willows in a field west of Middlebury’s campus.
The question of biomass fuel supply has taken on new urgency for the college since last winter, when the exclusive liberal arts school opened a new boiler system that heats about 100 campus buildings, running turbines that meet about a fifth of the college’s electrical demand.
The system, in a glass-fronted building in the middle of campus, runs on a “gasifier,” heating wood chips and extracting carbon monoxide and other gases that are then burned in the boiler.
“We use our buildings to teach as much as we can,” Byrne said. “We wanted students to be aware that when they turn up a thermostat, there’s a connection to a tree getting cut down.”
The college now buys 20,000 tons of wood chips a year, mainly from loggers operating within 75 miles. That will provide about half the heat used by the campus— the rest comes from heating oil—and reduce Middlebury’s $1.5 million annual oil bill by about $700,000, Byrne said.
Byrne said the willow-growing experiment is aimed at a potential problem.
The concern is that if other colleges, institutions, businesses and homeowners follow Middlebury’s lead and begin relying on forests for fuel, Vermont’s wooded hillsides—already a source of lumber and firewood—could end up being depleted.
“We wanted to anticipate the possibility that our success might encourage increased use of the forests for other biomass systems, and we also wanted to take advantage of another natural resource that we have in abundance in Vermont, and that’s open land for use in agriculture,” Byrne said.
Joining in the experiment are scientists from the State University of New York’s College of Environmental Science and Forestry in Syracuse. Tim Volk, a SUNY research scientist whose school had been working with willow for about 20 years, sees a trend developing in willow fuel being used along with traditional wood harvest.
“It’s something that’s going to start happening fairly quickly in the next few years,” he said. “People can start up a small-scale heating system with biomass, using a mixture of willows and low-value wood harvested from natural forests.”
These aren’t shaggy weeping willows with narrow green leaves like those that grow in wet soil, nor pussy willows with cottony white flower clusters, or catkins. Rather, these tall, skinny saplings can reach 16 feet at harvest.
“We have trials and they’re working well from southern Virginia to Minnesota and Wisconsin and as far west as Alberta, Canada,” Volk said. The chosen varieties must have a certain amount of cold for proper growth, he added.
One challenge for willow is that while it grows faster than other trees, it’s slower to mature than traditional farm crops— and getting farmers to plant a crop with a three-year harvest cycle is a hard sell.
But it has some advantages: It can be harvested in winter, when the ground is frozen, so it can be grown on more ecologically sensitive land—near rivers, for example.
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