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Reaping Willows

Waseca, Minn. – Skinny sticks with sporadic tufts of brown and gold leaves, five-foot willow shrubs stretch skyward, soaking up the last rays of the evening sun. In a few years, these shrubs could power lights needed when the sun goes down.

Willows grown on this four-acre plantation at the University of Minnesota Southern Research and Outreach Center in Waseca will be evaluated as a potential biomass energy source. Rus Miller expects this will be the first of many such plantations throughout southern Minnesota.

Miller is vice president of operations for NGP Power Corporation of Irving, Texas. The company intends to develop niche energy projects across the United States, including renewable and cogeneration projects. NGP Power owns a biomass-powered plant in New York, a landfill gas project in Texas and geothermal fields in California. Plans are underway to build a biomass-powered plant in the Waseca area using willow as one of the key feedstocks.

NGP Power is negotiating a contract, under a state mandate, to provide 35 megawatts of green power to Xcel Energy. The Texas company has prepared an environmental assessment worksheet and is optimistic that the Minnesota Pollution Control Agency will grant a plant permit by this summer.

A Swedish model

Miller is now signing up farmers to plant enough willows to feed the plant. “My objective is to have 1,500 acres planted next spring,” Miller says. “By the spring of 2005, we will need 7,500 acres and eventually 25,000 acres once the plant is up and running.” Miller says he wants the acreage to be within a 50-mile radius of Waseca but may have to go further.

NGP Power has identified the Waseca area as a potential plant site because of its proximity to high-voltage power lines and potential feedstock supplies, Miller says. The plant would not only burn biomass from willows but could also consume arbor trimmings, waste wood and crop residue such as corn stalks. The 35-megawatt plant would require 350,000 tons of biomass a year.

A willow-powered plant is currently operating in Sweden, Miller says. The Scandinavian country has 40,000 acres of willows in commercial production, which could be a model for Minnesota.

AURI’s Alan Doering, technical services specialist, and Lisa Gjersvik, project development director, met with Miller more than a year ago, providing information on available biomass sources, as well as connecting Miller to groups working in the renewable energy area. The U of M research center in Waseca already had a hybrid poplar plantation and now hosts the willow stand.

Why willow?

Extensive research on shrub willows is being conducted by the State University of New York College of Environmental Science and Forestry (SUNY-EFS) in Syracuse. The university has been studying willows for more than 20 years, currently has 500 acres in production and is evaluating thousands of clones and more than 200 crosses. SUNY-EFS researcher Tim Volk says willows are intriguing as a potential biomass-energy source.

“The willow has a large natural growing range, has high biomass production potential and provides heat value similar to other woods,” Volk says. “Willow has the same amount of energy per ton as oak, maple and other hard woods, but grows many times faster.”

Willow cuttings are planted in the spring and allowed to grow through the season. In the winter the trees are cut or coppiced at ground level. The shrub then resumes growing with multiple stems in a bush-like form. After three years, the shrub reaches a height of about 18 feet. The biomass can then be harvested using modified forage harvest equipment, similar to that used for corn silage. The willow can survive through six to eight of these three-year harvest cycles before new plantations have to be started. Volk says current willow strains yield about 15 dry tons of biomass per acre, per harvest.

Marginally friendly

Willow plantations have drawn interest from conservation groups, as the bush can provide erosion control, nutrient management and wildlife habitat on marginal land. Miller says he is not looking for farmers to commit prime production land for planting the shrubs. He is looking for marginal-yielding fields, pastures and buffers where he hopes producers will consider planting the woody crop.

That preference is based partly on economics. Miller says NGP Power cannot afford to pay producers enough for their biomass fiber to provide a positive return on high-value cropland.

Since willows shrubs are not actual trees, they may qualify for plantings on Conservation Reservation Program land, which would allow producers to receive payments for set-aside acres as well as for biomass provided to the power plant.

“The concept looks promising,” Doering says. “But each producer needs to look at the economics to determine whether it’s a fit for their particular operation or not.”