Abstract
Decisions involving strain selection, biomass to biofuel technology, and the location of cultivation facilities can strongly influence the economic viability of an algae-based biofuel enterprise. We summarize our past results in a new analysis to explore the relative economic impact of these design choices. Our growth model is used to predict average biomass production for two saline strains (Nannocloropsis salina, Arthrospira sp.), one fresh to brackish strain (Chlorella sp., DOE strain 1412), and one freshwater strain (order Sphaeropleales). Biomass to biofuel conversion is compared between lipid extraction (LE) and hydrothermal liquefaction (HTL) technologies. National-scale models of water, CO2 (as flue gas), land acquisition, site leveling, construction of connecting roads, and transport of HTL oil to existing refineries are used in conjunction with estimates of fuel value (from HTL) to prioritize and select from 88,692 unit farms (UF, 405 ha in pond area), a number sufficient to produce 136E+9 L yr-1 of renewable diesel (36 billion gallons yr-1). Strain selection and choice of conversion technology have large economic impacts, with differences between combinations of strains and biomass to biofuel technologies being up to $10 million dollars yr-1 UF-1. Results based on the most productive strain, HTL-based fuel conversion, and resource costs show that the economic potential between geographic locations within the selection can differ by up to $4 million yr-1 UF-1, with 1.8 BGY of production possible from the most cost-effective sites. The local spatial variability in site rank is extreme, with very high and low sites within 10s of km of each other. Colocation with flue gas sources has a strong influence on rank, but the most costly resource component varies from site to site. The highest rank UFs are located predominantly in Florida and Texas, but most states south of 37°N latitude contain promising locations.
Highlights
PNNL’s biomass assessment tool (BAT) (Wigmosta et al, 2011) provides a national-scale, integrated modeling environment to study the complex interactions between algal biology, biomass to biofuel technology, and resource availability and costs
We explore the range of values and costs for each of these factors and how these can inform decisions on strain selection, choice of biofuel to biomass technology, and determining the best unit farm (UF) locations for cultivation sites, those with both a climate supporting high algae growth rates and low cost access to resources
We introduced one new resource cost component, where hydrothermal liquefaction (HTL) oils were sent to an existing refinery through road, rail, and/or ship, with costs estimated from Geographic Information System (GIS)-based cost distance models
Summary
PNNL’s biomass assessment tool (BAT) (Wigmosta et al, 2011) provides a national-scale, integrated modeling environment to study the complex interactions between algal biology, biomass to biofuel technology, and resource availability and costs. BAT enables detailed and rigorous incorporation of spatiotemporal information into site selection exercises (Venteris et al, 2014a) and in estimates of national biofuel production potential (Wigmosta et al, 2011; Venteris et al, 2013, 2014b,c), with a current focus on open-pond cultivation (Jorquera et al, 2010). An issue not fully explored in the previous contributions, is the relative import of economic and technical challenges between these three aspects of production. Evaluating these requires estimates of production values relative to costs at potential unit farm (UF) sites across the coterminous United States (CONUS).
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