The most efficient use of biomass: bioelectricity or ethanol

Concerns about stable crude oil prices and the climate change effects of greenhouse gases (GHG) are influencing investments to develop a viable and more cost effective alternative energy source within the U.S. transportation sector. Campbell et al. claim that bioenergy is a near-term renewable solution to powering the vehicles of the future without affecting food prices or GHG emissions. Currently, the two leading alternative transportation technologies are cellulosic ethanol and electric vehicles, either pure electric or hybrid. Industrial biomass, which is derived from trees and plants including switchgrass and corn, either can be converted into ethanol to power an internal combustion engine or converted into electricity through composition or gasification via turbines and generators for battery-powered electric vehicles. Although there is uncertainty about which option will be technologically and economically possible first, the authors show that biomass converted directly into electricity is more land-efficient than biomass converted into ethanol. Blake Kos
Campbell, J., Lobell, D., Field, C., 2009. Greater transportation energy and GHG offsets from bioelectricity than ethanol. Science 324, 1055–1057.

     Campbell, Lobell and Field assess the performance of bioelectricity and ethanol with respect to transportation kilometers and GHG offsets achieved per unit area of cropland. They suggest biomass converted into electricity to power battery-powered vehicles offers much higher efficiency with respect to transportation kilometers and GHG offsets than does biomass converted into ethanol.
     Around the world and the U. S., there is a surging interest in developing alternative renewable energy sources for the transportation sector. In order to meet the many transportation and climate change goals, bioenergy has been regarded as a potential and feasible near-term solution. Given the limited area of land dedicated to growing biofuel crops, bioenergy efficiency should be maximized. Campbell et al. show that one can travel farther on biomass grown on a hectare of land when it is converted to electricity than when it is converted into ethanol. Also, the net transportation output, which subtracts the fuel-cycle costs (energy needed to grow the biomass and convert into electricity or ethanol) and the vehicle-cycle costs (energy needed to manufacture, maintain and dispose of vehicle) per hectare, is 56% greater for the bioelectricity option than for the ethanol option. (The vehicle-cycle costs are larger for the battery-powered vehicles than the internal combustion vehicles because of the cost of the batteries). In addition, several ethanol cases indicate a negative net transportation distances because the distance that could be traveled with the net fuel-cycle is greater than the distance that could be traveled with ethanol usage (1057).  Coupling carbon capture and sequestration technologies with bioelectricity production could result in carbon negative values that removes CO2 from the atmosphere. 

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