The “90-Billion Gallon Biofuel Deployment Study" used a new tool developed by Sandia—the Biofuels Deployment Model (BDM)—to determine that 90 billion gallons of ethanol can be produced per year in the US: 15 billion gallons per year from corn ethanol, with the balance from cellulosic ethanol.

Ninety billion gallons of ethanol (the energy equivalent of approximately 60 billion gallons of gasoline—about one-third of projected consumption by 2030) per year by 2030 was chosen as the book-end target to understand the requirements of an aggressive biofuels deployment schedule. Since previous studies have addressed the biomass supply potential, but not the supply chain rollout needed to achieve large biofuels production targets, the focus of this study was to develop a comprehensive systems understanding of the evolution of the complete biofuels supply chain and key interdependencies over time.

The study also evaluated a scenario with 15 billion gallons of corn-derived ethanol and 21 billion gallons of cellulosic ethanol by 2022, an amount that meets the Energy Independence and Security Act advanced biofuels mandate. In this scenario, cellulosic ethanol continues to ramp up to 45 billion gallons per year by 2030, for a total ethanol production of 60 billion gallons per year.

Producing 45 billion gallons per year cellulosic ethanol by 2030 requires 480 million tons of biomass, of which 215 million tons comes from dedicated energy crops. Allowing for storage, loss, and immature perennial crops, these energy crops utilize 48 million acres of planted cropland from what is now idle or pasture. The simulations assume technological progress in the conversion technologies, which results in average biomass conversion yields of over 95 gallons of ethanol per dry ton of biomass by 2030.

Conversion technologies are linked to feedstocks. Source: Sandia. Click to enlarge.

The study examined four sources of biofuels: agricultural residue, such as corn stover and wheat straw; forest residue; dedicated energy crops, including switchgrass; and short rotation woody crops, such as willow and poplar trees. Sandia’s analysis included land use, water availability, energy used to produce cellulosic biomass, transportation of feedstocks and other potential leverage points for the development and use of cellulosic biofuels. In conducting its research, Sandia utilized models that examined current and future technologies for development of ethanol.

In the study, conversion technologies are linked with specific feedstocks. For each new plant constructed, the BDM selected a feedstock/conversion pair resulting in the lowest cost of ethanol.

Sensitivity analyses were conducted to determine key parameters affecting production volumes, cost, and greenhouse gas savings. The effectiveness and costs of selected policy options to mitigate potential barriers were also examined. The study used state-level granularity in its assessments, rather than a national model.

Overview of the BDM. Source: Sandia. Click to enlarge.

The BDM is a ‘Seed to Station’ system dynamics model. The researchers chose system dynamics as the primary modeling approach because it is well suited to dynamic, non-linear problems involving time-varying inputs and feedback: two central features of the biofuels industry.

Although the 90 Billion Gallon Study focused only on starch-based and cellulosic ethanol, the BDM can be used with other types of advanced biofuel processes and molecules as well.

Among the findings of the study are:

• Achieving RFS2 (36 billion gallons by 2022) can be achieved by successful deployment of cellulosic biofuels (in addition to the baseline 15B gallons of corn ethanol), without displacing current crops grown.

• Transportation and distribution challenges, while substantial, are not insurmountable.

• Cellulosic biofuels can compete with oil at $90/bbl without subsidy assuming: average conversion yield of 91 gallons per dry ton of biomass; average conversion plant capital expenditure of $3.60 per installed gallon of nameplate capacity; and average farmgate feedstock cost of $40 per dry ton. Sensitivity analyses varying these assumptions individually gave potential cost-competitiveness with oil priced at $70/bbl to $120/bbl.

• At $50/bbl oil price, a $50/ton GHG tax keeps subsidies required for cellulosic ethanol below $8B per year; a price of $100/ton keeps it under $2B per year.

• Feedstocks for 45B gallons of cellulosic ethanol can be grown in states requiring little or no irrigation.

• 60B gal of biofuels would require only 5% of total 2030 water consumption; food and feed production requires 75%.

• Large-scale cellulosic biofuel production can be achieved at/below current water consumption levels of petroleum fuels from on-shore oil production and refining.

• 60B gallons of ethanol provides annual greenhouse gas (GHG) savings of 260 million tons of CO₂e per year, excluding GHG emissions from land use change.

• The energy in cellulosic ethanol is about 3.8 times the energy content of fossil fuels used for the entire supply chain (production and distribution; numbers based, in part, on assumptions in GREET). This is about 4 times the net energy ratio for gasoline (0.8).

• Continued support of R&D and initial commercialization is critical because sustained technological progress and commercial validation is a prerequisite to affordably producing the large volumes of ethanol considered in this study.

• Policy incentives such as a federal cap and trade program, carbon taxes, excise tax credits and loan guarantees for cellulosic biofuels are important to mitigate the risk of oil market volatility.

Future enhancements to Sandia’s BDM are planned, contingent on additional partnerships. Such improvements to the current software tool, says Sandia business development associate Carrie Burchard, would provide an even more comprehensive systems understanding of the biofuels industry.

Sandia enjoys a longstanding relationship with all the major US automakers and has worked previously with GM on a variety of automotive research activities. Sandia also plays a major role in the Joint BioEnergy Institute (JBEI) and several other transportation energy and biofuels projects.

Resources

• 90-Billion Gallon Biofuel Deployment Study Executive Summary