Obstacles to Commercial Development of Cellulosic Ethanol
August 21, 2016
Technological immaturity and high cost are two key barriers to cellulosic ethanol at present. Making this fuel competitive in the marketplace will require more experience and significantly reduced production costs, including capital costs. If the costs of cellulosic ethanol production come down as the technology matures, this fuel will still face some, although not all, of the obstacles that corn-based ethanol currently faces.
Flex-fuel vehicle deployment
Recent research indicates that current passenger vehicles may be capable of running on fuel blends containing up to 20 percent ethanol by volume (E20). Higher-level blends (up to E85) can be used by flex-fuel vehicles. Flex-fuel modifications are relatively inexpensive when made during vehicle production (estimated to be $50 - $100 per vehicle), but retrofitting existing vehicles could be costly. As of 2008, an estimated 7.3 million light-duty E85 vehicles, or roughly 3 percent of the roughly 250 million passenger vehicles currently registered in the United States, were flex-fuel vehicles. Higher-level blends also require dedicated pumps to dispense the fuel. Currently most of the 1,600 stations with E85 dispensing capability are concentrated in the Midwest, where most ethanol production occurs.
Infrastructure requirements
Ethanol cannot be shipped in existing crude oil or petroleum fuel pipelines, because ethanol can absorb water and other impurities that accumulate in these pipes, affecting fuel quality, and because ethanol’s corrosiveness can shorten pipeline lifetime. Instead, ethanol is currently transported via rail (60 percent of domestic ethanol shipped), truck (30 percent), and barge (10 percent). Currently in the United States, cellulosic feedstocks can be most easily grown in the Midwest and Southeast, but much of the demand for transportation fuels is along the coasts. Thus, large volumes of ethanol may need to be shipped long distances to reach areas of high demand in the future. Without substantial infrastructure investment, increased ethanol shipping could result in significant bottlenecks on both rail and highway networks. These problems could be reduced by encouraging the use of high-level ethanol blends (i.e., E85) regionally instead of low-level blends (E10) on a national basis. Distributing and using ethanol close to where it is produced – i.e., in the Midwest and Southeast – would also minimize the GHG emissions associated with transporting ethanol.
Food versus fuel
Unlike corn ethanol (or ethanol produced from sugarcane), cellulosic ethanol does not necessarily compete with food markets for feedstock directly. However, the production of cellulosic crops is constrained by land availability, which is a limited resource. To decrease competition with other agricultural crops, cellulosic feedstocks could be grown on degraded or marginal farmland unsuitable for production of food crops. However, doing so can decrease yields or increase input energy and fertilizer requirements, which could result in higher feedstock prices and increased GHG emissions.
Land use change
The production of fuels from biomass feedstocks has direct and indirect impacts on land use. For example, clearing grasslands or forests to plant biofuel crops are direct land use changes that result in releases of carbon stored in soils and vegetation. Indirect land use change refers to the land use changes that result from the impacts on land and biomass prices due to increased demand for biomass for biofuel production and the interactions with ongoing demand for food, feed, and fiber products. Accounting for indirect land use changes is particularly challenging and relies upon a number of estimates and assumptions. Recent studies have shown that the GHG impacts of indirect land use changes could significantly affect the overall life-cycle GHG emissions of biofuels. Both direct and indirect land-use change remain important areas of concern and a topic of continued scientific research.
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