Production, transportation and milling costs of sweet sorghum as a feedstock for centralized bioethanol production in the upper Midwest Albert S. Bennett * , Robert P. Anex Department of Agricultural and Biosystems Engineering, Room 3202 NSRIC Building, Iowa State University, Ames, IA 50011, USA article info Article history: Received 6 December 2007 Received in revised form 5 September 2008 Accepted 5 September 2008 Available online 23 October 2008 Keywords: Sweet sorghum Ethanol Harvest cost Fermentable carbohydrate Ensiled storage abstract Sweet sorghum has been identified as a possible ethanol feedstock because of its biomass yield and high concentration of readily fermentable sugars. It has found limited use, however, because of poor post-har- vest storage characteristics and short harvest window in cooler climates. Previous research (Bennett, A.S., Anex, R.P., 2008. Farm-gate production costs of sweet sorghum as a bioethanol feedstock. Transactions of the ASABE 51(2), 603–613) indicates that fermentable carbohydrates (FC) can be produced at less expense from sweet sorghum than from corn grain. Previous research, however, did not include costs associated with off-farm transportation, storage, or capital costs associated with milling and energy recovery equipment that are required to provide FC suitable for biological conversion. This study includes these additional costs and reevaluates sweet sorghum as a biocommodity feedstock. A total of eight harvest-transport-processing options are modeled, including 4-row self-propelled and 2-row tractor-pulled forage harvesters, two different modes of in-field transport, fresh processing, on- farm ensilage and at-plant ensilage. Monte Carlo simulation and sensitivity analysis are used to account for system variability and compare scenarios. Transportation costs are found to be significant ranging from $33 to $71 Mg 1 FC, with highest costs associated with at-plant ensilage scenarios. Economies of scale benefit larger milling equipment and boi- ler systems reducing FC costs by more than 50% when increasing annual plant capacity from 37.9 to 379 million liters. Ensiled storage of high moisture sweet sorghum in bunkers can lead to significant losses of FC (>20%) and result in systems with net FC costs well above those of corn-derived FC. Despite relatively high transport costs, seasonal, fresh processed sweet sorghum is found to produce FC at costs competitive with corn grain derived FC. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Since the 1970’s there has been considerable interest in devel- oping biorenewable alternatives to petroleum-based commodity chemicals such as transportation fuels. The most prominent exam- ple is ethanol, which has emerged as a potentially important alter- native transportation fuel. Considerable effort has gone into investigating the potential of different agricultural crops as feed- stock for bio-production of fuels and chemicals (Turhollow, 1994). Low-cost, plentiful supply and ease of conversion have made carbohydrates from corn and sugarcane the most likely feedstocks for biocommodities like ethanol. Cellulosic materials are generally thought to be the preferred feedstock for large-scale bio-produc- tion in the long-term, due to their larger ultimate supply and lower price compared to other carbohydrate sources (Perlack et al., 2005). Starch-rich materials, such as grains, have the advantage of established feedstock and processing infrastructure, and a more homogenous and reactive form of carbohydrate than that found in cellulosic materials. An advantage of both starch and sugar-rich materials over cellulosic materials is that they can be processed to sugar streams of sufficient purity to accommodate production of high-value products such as food, pharmaceuticals and fiber- grade polymers. Plant materials high in soluble sugars yield the most readily converted form of carbohydrate, requiring lower in- puts of chemicals and energy for processing, and the technology for the extraction of sugars is fully mature and highly efficient, reducing processing costs. Sugar is the preferred carbohydrate feedstock for many high-value products and is also used to pro- duce around half of the world’s largest biocommodity, ethanol (Murray, 2005). One of the most adaptable and highly productive sugar-rich plants is sorghum. Both sweet and grain varieties of sorghum are of interest as agricultural energy crops due to high-yields, drought tolerance, relatively low input requirements and ability to produce high-yields under a wide range of environmental conditions (Buxton et al., 1999; Grassi et al., 2004; Hunter, 1994; Hunter and Anderson, 1997; Miller and McBee, 1993). These qualities 0960-8524/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2008.09.023 * Corresponding author. Tel.: +1 515 294 4330; fax: +1 515 294 4250. E-mail address: asbnntt@iastate.edu (A.S. Bennett). Bioresource Technology 100 (2009) 1595–1607 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech