Testing willow as biomass

In 2008, Middlebury College finished construction on a $12 million biomass plant located near the center of campus. The project cut the College’s consumption of heating oil in half—by roughly 1 million gallons per year. The biomass plant is an integral part of Middlebury’s plan to become carbon neutral by 2016.

One of the major issues in building a biomass plant is maintaining a reasonably local, reliable, economical, and sustainable source of fuel for the boiler. Middlebury’s new boiler is designed to gasify any type of wood fuel source, but even with this versatility, finding roughly 20,000 tons of wood chips each year is no easy task. And with several other biomass projects planned around Vermont, pricing and supply issues could arise in the future if the college continues to rely solely on outside sources for wood chips.

The uncertainty over wood chip supply, among other issues, has led Middlebury into an agreement with the State University of New York College of Environmental Science and Forestry (SUNY-ESF) to develop a willow test plot on college land. The SUNY-ESF scientists, who have extensive experience studying and promoting willow as a source of biomass fuel, wanted a study plot in Vermont that would let them test willow varieties and cultivation methods in a different setting. In return, they are giving Middlebury technical advice and practical help with implementing the project.

The test plantings at Middlebury are divided between two fields just west of the campus on Route 125. The project is jointly managed by College Forester Steve Weber and SUNY EFS researchers under the direction of Dr. Timothy Volk. The Middlebury planted willows consist of five varieties and were field planted by machine to represent a mass planting. Several other varieties were hand planted in a grid to allow for more controlled study. Researchers are doing soil and water tests in the hand-planted plots and are applying measured amounts of compost, cow manure and fertilizers to test the results against a control plot. All of this research will help Middlebury decide on the varieties of willow to be planted in the future.

Depending on the success of the willow tests, Middlebury will decide whether to begin a long-term project, do additional testing, or abandon willow biomass as an option.


Willow FAQ

1. What is biomass energy?

Biomass energy is any form of energy—most often heat, electricity, or fuel—that is derived from plant matter sources. In contrast to fossil fuels, biomass energy comes from living or recently dead material. Fossil fuel energy—e.g. oil, gas, coal—on the other hand, comes from “fossilized” ancient biomass that has been altered by geologic processes. Biomass energy can be produced through simple processes such as the burning of wood in a fireplace or more complex ones like the gasifying boiler in Middlebury’s new biomass plant.

2. How is it sustainable?

Let’s take a hypothetical forest such as the one up at Bread Loaf as an example to demonstrate how biomass energy can be sustainable. The forest’s trees naturally take part in the earth’s carbon cycle through growth, death, and decomposition. During the growth stage, the trees absorb CO2 and convert it into carbohydrates through photosynthesis. The conversion process takes CO2 out of the atmosphere and stores it in the tree for the duration of its life. When it dies and then decomposes, the CO2 will be released back into atmosphere.

Biomass energy simply substitutes combustion for decomposition, inserting itself into the natural cycle. As long as the net amount of biomass in the form of trees remains constant, the biomass energy will be sustainable. This part is critical, because biomass energy becomes unsustainable if the trees are being cut down at a faster rate than they can regrow, causing an imbalance between the absorption and release of CO2.

So, if deforestation occurs as a result of higher wood demands, biomass energy quickly becomes very unsustainable. For that reason it is important for Middlebury and other biomass energy producers to carefully monitor their sources of wood and ensure that demand is not outstripping natural rates of forest growth.

3. Why willow?

Willow is a fast-growing, perennial, minimally intrusive, and efficient source for wood chips. A willow planting can reach optimal height within three years, be safely and easily harvested, and immediately begin regrowing without new tilling and planting. Ensuring sustainability is easier with willow as well because the fast regrowth can keep pace with the rate of harvesting. With a project that encompasses the entire life-cycle of the biomass source, Middlebury would be able to have greater oversight over the entire process.

Additionally, using highly-impacted farm sites would likely mean less environmental degradation than if one relied on a more pristine forest source for biomass. Finally, in the longer term willow biomass has the potential to spur local economic growth. The College could contract with local farmers to allot small portions of their fields to willow cultivation. Middlebury would then guarantee purchase of the third-year willows, giving farmers a stable secondary source of income.

4. When might this project become a reality?

At this point the project is in its testing phase. Willows were harvested and a 4 day test burn was conducted in January 2011. The College is planning a longer test burn with a larger quantity of willow chips sometime in 2012. Based on the results of the longer test burn, a decision will be made on whether or not to scale up the willow growing project.