Researchers study switchgrass bale storage

By Susanne Retka Schill
Web exclusive posted Sept. 11, 2008 at 11:33 a.m. CST

Uncovered big square bales will probably not work for biomass storage, even though it may be the most economical option. In their ongoing research of utilizing biomass for bioenergy, researchers at the University of Tennessee compared several systems of baling and storing switchgrass bales. Harvest and storage logistics will be key factors in switchgrass production systems, the researchers explained in a preliminary report on the study's results. The UT research team includes Burton English, James Larson, Daniel Mooney and Don Tyler.

The researchers compared the cost and quality of storing switchgrass in round bales measuring 5-feet by 4-feet and large rectangular bales measuring 4-feet by 8-feet. They compared setting the bales on pallets, gravel and well-drained ground, as well as compared uncovered and tarp-covered bales. The study began when the switchgrass was harvested in January and will continue for more than a year with samples being taken every 100 days for five sampling periods.

While having the highest investment cost, the large rectangular baler also had the highest capacity, harvesting 12 tons per hour compared to the round baler at a 5-ton per hour capacity. However, when left uncovered, the large rectangular bales became waterlogged even at the first sampling, while the round bales had 5 to 10 inches of weathering along the bale's outer edge. Covered round bales in the study showed little signs of weathering, while the covered rectangular bales had significant decomposition along the bottom edges and exposed sides of most bales.

The goal of the study is to provide Tennessee farmers with optimal switchgrass storage solutions, calculating the tradeoffs in higher cost storage systems versus losses in quality. They plant to develop guidelines to visually estimate the quality of stored biomass. The study also includes correlating ethanol content of bales with weathering, moisture content and storage method.