Farm-Gate Production Costs of Sweet Sorghum as a Bioethanol Feedstock

Abstract

Sweet sorghum has been identified as a possible ethanol feedstock because of its high biomass yield, sugar content, and potential for grain co-production. Extracted fermentable carbohydrates (FC) can be easily fermented to ethanol. Residuals contain sufficient energy to power ethanol processing facilities. Sweet sorghum, however, has found limited use because of poor post-harvest storage characteristics and short harvest window in cooler climates. To help determine the practicality of sweet sorghum as an ethanol feedstock in the Midwest, production costs are estimated for different harvest scenarios including self-propelled (SP) and tractor-pulled juice, forage, and hypothetical whole-plant-grain (WPG) harvesters. Production cost estimates are generated using preharvest and harvest cost models in combinations representing current best practice and promising near-term solutions. Estimated net costs included income from co-products: residuals for fuel, ensilage, and grain. The most financially attractive scenario is the SP forage harvester. Depending on harvest conditions, and assuming combustion of co-produced residuals valued at $6 GJ-1, the expected net farm-gate FC costs are predicted to be $6.9 to $24 Mg-1. These values are considerably less than comparable net farm-gate FC costs for corn grain production. When sweet sorghum feedstocks are located in close proximity to processing facilities, lower FC costs will be sufficient to offset increased transportation costs associated with moving wet biomass. Further study, however, is required to evaluate the associated capital and logistical requirements for integrating seasonal sweet sorghum, or sorghum wet-stored via ensilage, into existing and future bioethanol processing facilities.