Is Shrub Willow a Viable Biomass Feedstock for the US?

Shrub willow — the short rotation crop that kept the world in wicker baskets for centuries — is gradually finding new life as a cold-resistant biomass, particularly in upstate New York where it’s augmenting traditional energy supplies of wood residues and heating oil.

Although willow biomass lab tests and field trials have been ongoing in the Northeastern and Great Lakes regions of the U.S. since the mid 1980s, it’s had mixed results here as an effective biomass replacement and is just now beginning to see commercial use for heat and electricity generation.

“Coupled with low grade natural forest residues, it’s a good complementary source of woody biomass,” said Tim Volk, a research forester at the State University of New York’s (SUNY) College of Environmental Science and Forestry (ESF) in Syracuse.  “It’s not the sole solution but a complementary woody feedstock.”

A cousin to the weeping willow, shrub willows grow 10 to 15 times faster than natural forest.

But it took nearly twenty years of research before, in 2004, the first commercial willow producer in New York state actually began planting cultivar hybrids from the SUNY breeding program.

“That was the shift in the paradigm,” said Larry Smart, a Cornell University horticulturalist and geneticist.

Smart notes that as part of a $1.2 million USDA multi-year willow development program, Celtic Energy Farm has planted some 1200 acres of willow in Cape Vincent, New York; the largest commercial plantation in the U.S.

Although willow grows across most of the U.S. and fares particular well in the Great Lakes regions, potential commercial willow sites range south to Maryland and Delaware; north to the upper reaches of New York state and west to Minnesota and Wisconsin.

By some estimates, New York state alone has an estimated one million acres of poorly drained marginal agricultural land on which the willow could thrive.

“We also have a number of rural counties that don’t have access to natural gas lines and are still reliant on fuel oil or wood,” said Smart.

It’s hoped that the willow will be used in these North country counties to generate electricity or replace costly heating oil.

Growing the cultivar is simply a matter of tilling existing acreage and machine-planting dormant stems, says Volk. 

After the first year in the ground, the willow is cut back to generate more sprouts, then grown for three more years before harvesting between October through April.  It sprouts again in the spring and is left to grow for three more years before again being harvested. 

“To put an acre of willow in the ground costs up to $1,000 an acre,” said Volk.  “But once you plant, you’ve got a crop that can grow 30 feet high and last 20 years.”

SUNY-ESF has spent more than two decades researching ways to genetically improve hybrids of Shrub willow, such as Salix miyabeana and Salix purpurea, in an ongoing effort to boost the willow’s productivity, cold- and pest-resistance.

At present, SUNY-ESF’s research is primarily aimed at lower production costs, which currently account for more than a third of the willow’s final “delivered cost.”

Researchers are actively working with agricultural equipment manufacturer Case New Holland on designing and improving cut and chip and harvesting systems that would allow more efficient cropping.

A double row planting density of some 6,000 individual plants per acre, in turn, can produce five dry tons of biomass per acre.  And unlike many agricultural crops, harvesting can be done with up to a foot of snow on the ground.

To harvest, a mechanized forager cuts off the stems and runs them through a chopper where they emerge as chips of an inch or less. 

Because the foragers and cutting heads can have a price tag of up to half million dollars, Volk says the most common business model would be to outsource harvesting to someone who has already made an investment in foraging equipment. 

Volk notes that the willow has a long commercial history in New England already.

From the late 1800s to the early 1900s in New England, a huge willow basket industry flourished, making hundreds of thousands of baskets per year.  But after World War II, basket-making became much less prominent and commercial production of willow languished.  The first field trials for willow as a biomass crop weren’t conducted in the U.S. until the mid-1980s.  

Smart says willow could have a bright future as a replacement for commercial wood-burning operations that currently rely on wood harvested from local forests and forest residues.

Although willow has a very low density, Smart notes that on a per weight basis, it has almost the same energy content as nearly every other hardwood species; including oak, ash and maple.

“But if your market disappears in a few years, which happened with co-fired coal plants here in New York state,” said Volk, “landowners don’t want to take the risk.”

When growing an energy crop that’s in the ground for up to 20 years, Volk adds growers want some market assurance. 

Because willow has a very predictable yield and harvest cycle, its price can be locked in over the longterm.  Smart says that’s not true for forest harvesting operations. 

With 1,200 acres of willow now in the ground, Volk says their work has clearly moved out of the research realm and into the commercial development phase.

Thus, ReEnergy Holdings’ biomass-to-energy facilities in the state’s North country is operating a willow co-firing plant at its 60-MW Black River facility near Fort Drum and its 22-MW Lyonsdale facility in Lewis County.

“In harvesting years, we expect that shrub willow will comprise as much as 5 percent of our fuel supply,” said ReEnergy spokesperson Sarah Boggess.  

This Fall, says Boggess, the Black River plant is using forest residue as its primary fuel, with shrub willow in the mix; while Lyonsdale will use a mixture of forest residue with 6 to 12 percent shrub willow. 

But willow isn’t always a good biomass fit.

Despite a 2011 trial run with willow feedstock for its new $12 million biomass plant, Middlebury College in Vermont is now abandoning the shrub.

The college planted willow stands just west of campus before choosing a ChipTec system to co-generate electricity and heat, says Thomas Corbin, Middlebury’s director of business services.

Corbin says that the ten acres of willow harvested for use in the Middlebury system weren’t a good match — they were overloaded with moisture, had a high bark to wood ratio, and were too dusty and small to be efficiently converted. 

“We attempted to use them alone and mixed with hardwood chips,” said Corbin.  “Neither worked; so we have given up on willow for our system.”

A bit further north in eastern Canada, initially, there was a sense of possibility that the willow could fill a much-needed biomass gap while providing economically-depressed northern Quebec with an alternative to traditional forestry. 

With continual warming temperatures due to climate change, its Canadian proponents at first thought it might also be able to take advantage of abandoned, deforested government lands in Quebec’s Abitibi County which stretches to the subarctic.

Michel Labrecque, a research botanist at Montreal Botanical Garden, says from 2006 to 2011 several dozen acres of willow were successfully cultivated there.  But Labrecque says both changes in Canadian national energy policy and local hydro-power put a squelch on the willow’s inroads into Canada’s renewable energy strategy.

In the last three years, Labrecque says the price of natural gas has declined and Canadian Prime Minister Stephen Harper’s Conservative government is more supportive of fossil fuel extraction initiatives, such as oil sands or fracking, than green energy.

“I don’t see any change in this for the next five years,” said Labrecque.  “But I’m still convinced the willow is a longterm biomass solution for Canada.” 

In contrast, Europe has some 40,000 acres in shrub willow plantations, mostly in Sweden.

Swedish willow research started in the late 1960s as a hedge against predicted shortages of raw materials for the country’s paper and pulp industry.  As a result, Sweden has seen its willow plantations expand from a few acres in the 1970s to some 34,000 acres today; most of which is used for public heat and power generation.

What’s the willow’s ultimate feedback potential? 

Until now, says Smart, willow has been heavily reliant on government subsidies.  But he says a willow-growing operation’s high start-up costs can be overcome if there’s a market willing to amortize longterm costs. 

“We’re going to reach a tipping point,” said Smart, “when either the price of fossil fuels becomes excessive, or through a carbon tax, we truly start paying for their environmental damage.”  

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Bruce Dorminey is an award-winning science journalist who is a former Hong Kong bureau chief for Aviation Week & Space Technology magazine and a former Paris-based technology correspondent for the Financial Times newspaper. However, he has written about everything from potato blight to dark energy. Most recently, he has been covering climate change and the environment and is an active member of the Society of Environmental Journalists (SEJ). A frequent contributor to Astronomy magazine, he is the author of the book "Distant Wanderers: The Search for Planets Beyond the Solar System." Dorminey writes an over-the-horizon tech column for Follow me on Facebook , Twitter and Google + .

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