woody biomass. Alfalfa was assumed to be harvested once during the first year and three times during the second year at a cost of $55 per acre per harvest. In addition to harvest costs, suppliers of short-rotation woody crops (SRWC) incur a stumpage fee (SF) with an assumed mean value of $20 per ton. Energy costs affect the cost of harvest through the price of diesel. The relationship between diesel and oil prices was derived using data from 1988-2008. Harvest costs increase by approximately $2.70 per ton at the high oil price and decreases by around $2.00 per ton at the low oil price.
Transportation Costs (DVC, DFC, and D)
Previous research on transportation of biomass has provided two distinct types of cost estimates: (1) total transportation cost and (2) breakdown of variable and fixed transportation costs. Research estimates for total corn stover transportation costs range between $3 per ton and $32 per ton (Aden et al., 2002; Perlack and Turhollow, 2002; Atchison and Hettenhaus, 2003; English et al., 2006; Hess et al., 2007; Perlack, 2007; Brechbill and Tyner, 2008a; Mapemba et al., 2008; Vadas et al., 2008). Total switchgrass and Miscanthus transportation costs have been estimated between $14 and $36 per ton (Tiffany et al., 2006; Kumar and Sokhansanj, 2007; Mapemba et al., 2007; Brechbill and Tyner, 2008a; Duffy, 2008; Khanna et al., 2008; Mapemba et al., 2008; Perrin et al., 2008; Vadas et al., 2008), adjusted to 2007 costs.5 Woody biomass transportation costs are expected to range between $11 and $30 per dry ton (Summit Ridge Investments, 2007; Sohngen et al., 2010). Based on the second method, distance variable cost (DVC) estimates range between $0.09 and $0.60 per ton per mile (Kaylen et al., 2000; Kumar et al., 2003; USFS, 2003; Kumar et al., 2005; USFS, 2005; Searcy et al., 2007; Brechbill and Tyner, 2008a,b; Petrolia, 2008; Huang et al., 2009; Jenkins et al., 2009; Sohngen et al., 2010), while distance fixed cost (DFC) estimates range between $4.80 and $9.80 per ton (Kumar et al., 2003, 2005; Searcy et al., 2007; Petrolia, 2008; Huang et al., 2009), depending on feedstock type. The BioBreak model utilized the latter method of separating fixed and variable transportation costs.
The DFC for corn stover, switchgrass, Miscanthus, wheat straw, and second-year alfalfa was assumed to range from $5 to $12 per ton with a mean value of $8.50 per ton. Besides loading and unloading costs, woody biomass requires an on-site chipping fee. Therefore, the DFC for woody biomass was assumed to have a mean value of $10 per ton. The DVC was assumed to follow a skewed distribution to account for future technological progress in transportation of biomass with a mean (likeliest) value of $0.38 ($0.41) per ton per mile for stover, switchgrass, Miscanthus, wheat straw, and second-year alfalfa and $0.53 ($0.56) per ton per mile for woody biomass. Energy costs affect the DVC through the price of diesel. The 1988-2008 relationship between diesel and oil prices was used to adjust DVC to each oil price scenario. The DVC increases by approximately $0.07 per ton per mile at the high oil price ($191 per barrel) and decreases by approximately $0.05 per ton per mile at the low oil price ($52 per barrel).
One-way transportation distance (D) has been evaluated up to around 140 miles for woody biomass (USFS, 2003, 2005; Miller and Bender, 2008; Spelter and Toth, 2009) and between 5 and 75 miles (Perlack and Turhollow, 2002, 2003; Atchison and Hettenhaus, 2003; English et al., 2006; Tiffany et al., 2006; Mapemba et al., 2007, 2008; BRDI, 2008; Brechbill and Tyner, 2008a,b; Khanna, 2008; Taheripour and Tyner, 2008; Vadas et al., 2008) for all other feedstocks. In the model, the average hauling distance was calculated using the formulation by French (1960) for a circular supply area with a square road grid provided in Equation (3)
5 Transportation costs were updated using USDA-NASS agricultural fuel prices from 1999-2007 (USDA-NASS, 2007a,b).