OHLROGGE, J., ALLEN, D., BERGUSON, B., DELLAPENNA, D., SHACHAR-HILL, Y. & STYMNE, S. (2009) Driving on Biomass. Science 22 May 2009 324: 1019-1020.

The development of the internal combustion engine (ICE) vehicle dramatically influenced American society during the 20th century by providing affordable, reliable transportation. However, the ICE vehicle is an inherently inefficient converter of chemical energy to mechanical power; less than 20% of the energy in gasoline is transformed into mechanical work, and the remainder is lost as heat. With seemingly unlimited supplies of low-cost petroleum in the last century, the poor efficiency of the ICE was initially less important than the power, convenience, and reliability it provided. However, two major factors make it likely that electric vehicles, rather than the ICE, will be the power source of choice for passenger vehicles in the 21st century. First, heightened world petroleum demand coupled with more expensive oil recovery will continue to increase gasoline costs. Second, concerns over the environmental impact of CO₂ production are leading toward carbon taxes, cap-and-trade limits, and other strategies that will impact the ICE.

In response to escalating monetary and political costs of imported petroleum and the existence of surplus U.S. agricultural capacity in the 20th century, the U.S. government instituted policies to support the conversion of the chemical energy stored in plantderived starch to ethanol. This conversion now consumes almost 30% of U.S. corn production. Starch is a simple polymer of glucose that is easily converted to ethanol with existing technology, yet almost one-third of the chemical energy of starch is lost in producing ethanol (1). Concerns about fuel competing with food, fertilizer runoff, and potent greenhouse gases such as NO₂ released from microbial conversion of fertilizer in agricultural fields have brought into question the sustainability of corn-based ethanol production (2). Therefore, a major effort has begun to develop alternative feedstocks for ethanol (or other liquid fuels) by using crop residues, forest by-products, perennial grasses, and other forms of plant biomass that are collectively termed “lignocellulosics.” The 2005 “billion-ton vision” (3) proposed by the U.S. Departments of Energy (DOE) and Agriculture (USDA) has set a goal of replacing 30% of U.S. petroleum consumption with lignocellulosic-derived liquid fuels—a goal that would require the production of ~60 billion gallons of ethanol annually by 2030. Several billion dollars have been invested for research and development toward this goal, and tax advantages and other subsidies for ethanol and biodiesel production have been estimated at $9 billion for 2008 and could increase to over $30 billion annually under current legislation (4).

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