Challenges for Switchgrass-to-Energy Systems.

In the next quarter century, global demand for energy is expected to increase more than 25%, while some analysts have predicted that petroleum output will soon peak.  The reality of increasing demand in the face of diminishing fossil supplies – coupled with the environmental and national security impacts of reliance on petroleum – has spurred renewed interest in renewable energy sources. Herbaceous energy crops such as switchgrass offer great potential as feedstocks for the future biorefinery.  However, several questions and challenges all along the supply chain must be addressed if bioenergy cropping systems are to become reality.  Although switchgrass has a reputation for being difficult to establish, this may be the least of the production system issues.  Improved varieties and management systems for establishment are being tested and high levels of establishment success are reported for large-scale planting efforts in the southeast where weed control was not an issue.  Greater challenges are likely to be found in the harvest, storage, and transport of these materials.  A general recommendation is to harvest switchgrass after senescence, and this may be best in terms of plant physiology.  However, biorefineries will be year-round operations, and narrow harvest windows will both increase the logistic demands and the storage requirements.  Of course opening this window comes with tradeoffs in terms of long term stand productivity, nutrient input requirements, and feedstock quality issues, the latter being biorefinery-process dependent.  Harvest systems, irrespective of harvest timing, have yet to be optimized for handling and delivering herbaceous biomass.  For humid regions with smaller acreages, bundling biomass in round bales offers utility with existing infrastructure and the bales are well suited to ambient storage, but there is no system currently available with which round bales can be handled rapidly.  Large square bales allow for greater harvest tonnage per hour, but they are limited by field traffic-ability and greater storage costs.  Field chopping has merit from the standpoint of completing some size reduction in the field, but chopping systems require greater labor to remove the chopped material and will need further refinement to increase feedstock density for hauling.  These and other issues must be addressed to better realize the potential of bioenergy systems, and they do not stand in isolation.  Beyond the field lies what is perhaps the first hurdle for developing feedstock production systems: Uncertainty.  While current US policy calls for increased production of renewable fuels over time, lack of existing markets and questions about their future has kept many on the sidelines wondering if this is only a field of dreams or if when built “they will come”?  Social issues may also influence farmer decisions regarding market entry, in turn affecting the function and profitability of a future biorefining industry.