- Biofuels can achieve gigaton scale by 2020 for an investment of $383 billion, and enhance energy security by displacing foreign oil imports.
- Corn ethanol cannot deliver 1 gigaton of CO2e reductions because of massive land-use requirements; next-generation biofuels (e.g., cellulosic ethanol) can scale to 1 gigaton.
- Biofuels are widely seen as a low-cost and rapidly deployable alternative for the transportation sector.
- Increased reliance on waste streams for fuel generation and use of regionally appropriate feedstocks for biofuels can address land-use concerns.
Biofuels blended with gasoline are one of the few alternatives that has not required significant new infrastructure or change on the part of consumers or auto manufacturers. As a result, biofuels are today the most widely deployed substitute for conventional fossil fuels in transportation. The scale-up of biofuels as a primary fuel in the transportation sector, not just a blending agent, would entail additional infrastructure investment but remains an attractive alternative.
The term biofuels encompasses two types of liquid fuels produced from biomass materials: ethanol, which is an alcohol produced when yeast ferments sugar from plant material such as corn or sugar cane, and biodiesel, which is made from plant oils, such as soy or canola (rapeseed), or animal fats. Ethanol production is significantly higher than biodiesel production globally; the main types of ethanol in production are corn ethanol and sugarcane ethanol. In the U.S., biofuels can currently be blended up to 10% (ethanol) and 20% (biodiesel) in every gallon of fuel, and an increasing number of vehicles can use blends of up to 85% ethanol. Biodiesel is an alternative for diesel vehicles. Although biodiesel is a promising low-carbon alternative for some transportation uses, it is a much smaller fraction of world production than ethanol and less commonly used in the light-duty vehicle (LDV) sector. In this chapter, we focus on the potential to scale up ethanol production to achieve the target of a 1-gigaton reduction of carbon dioxide equivalent (CO2e) emissions in 2020 through displacement of gasoline in the LDV sector.
Ethanol can be produced from a number of feedstocks; in addition to corn and sugarcane, other feedstocks include switchgrass, woody biomass, agricultural residue, wood residue, and municipal solid waste (MSW). Ethanol derived from plant fiber cellulose (e.g., plant stalks, trees, MSW) is known as cellulosic ethanol, as distinct from ethanol derived from starch (e.g., corn). The actual carbon dioxide equivalent (CO2e) savings from each of these feedstocks varies and depends, among other things, on land-use and agricultural practices and yields associated with a particular biomass material, use of fossil fuels in refining and transporting the biofuel, and the ability to "coproduce" electricity during refining.
Biofuels can achieve gigaton scale globally by 2020. The actual volume of biofuel production required to meet the gigaton target depends on the feedstock choice and the underlying technology used for production. For cellulosic ethanol, upwards of 150 billion gallons (550 billion liters) is needed for the various feedstocks, which include sugarcane, switchgrass, agricultural residues, and woody poplar. The 150-billion-gallon level is used as a reference for gigaton scale throughout this chapter.
Because ethanol has a lower energy density than gasoline, 150 billion gallons of ethanol replaces approximately 100 billion gallons of gasoline, or roughly 5% of the world's projected liquid fuel demand in 2020. Factoring in the CO2e savings from coproduction of electricity at biorefineries significantly lowers the volume of biofuel needed to achieve the gigaton target. For instance, use of switchgrass with an electricity coproduct requires only 76 billion gallons to reach gigaton scale.
The diversity of available feedstocks for biofuel production suggests that regionally tailored solutions can play a significant role in the short term. In the longer term, a number of technologies are evolving, such as algae-based biofuels, that promise to unlock even greater emissions reductions and more broadly adopted low-carbon-fuel solutions.
Challenges associated with biofuels include controversy over land-use and food-production impacts of growing biofuel energy crops and the varying feasibility of different feedstocks (e.g., corn ethanol is likely not feasible to meet the gigaton goal because of the large land area that would be required for growing). The land and water demands, and other challenges, associated with biofuels — and any alternative technology — need to be made integral, not peripheral, to the assessment of the transportation energy. The Low-Carbon Fuel Standard and Renewable Fuels Standards are two of a small set of implementation efforts in this vital area.
Other challenges include: the need to convert vehicles and gas stations to be compatible with biofuels; the need to build infrastructure including biorefineries, distribution facilities, and transportation networks for both the raw materials and the refined fuel; and the performance of biofuels whose use decreases gas mileage because they are less energy-dense than gasoline.
Biofuels are one of the least capital-intensive gigaton options; the estimated cost of scaling up biofuels to meet the gigaton target is $383 billion dollars, although costs rapidly escalate if vehicles need to be converted after-market for ethanol compatibility. The cost of converting new vehicles, when manufactured, is a fraction of the cost of after-market conversions. Ensuring ethanol compatibility in new vehicles would significantly decrease future investment costs for this pathway. Achieving gigaton scale with biofuels would create an estimated 200,000 new direct jobs in the industry.