The October 2007 issue of National Geographic includes an informative article on biofuels. A couple points come to mind. If you compare the fossil fuel energy used to make the fuel with the energy that is released by burning it, corn ethanol is not a very efficient way to go: for each unit of energy required to create the ethanol, you get 1.3 units of energy by burning it. Contrast that with ethanol derived from sugar cane: for each input unit you get 8 output units of energy. (Sugarcane ethanol is widely used in Brazil. For us, the cost would be higher since it would have to be shipped to North America). (Bourne, 2007)
Corn ethanol: 1:1.3
Sugarcane ethanol: 1:8
Biodiesel: 1:2.5 (make from soy or canola)
Cellulose-derived ethanol: 1: (anywhere from 2 to 36)
Another factor to consider is greenhouse gas emissions that result during production and use of various fuels. The article compares several alternative fuels to gasoline:
Corn ethanol: 22% less
Sugarcane ethanol: 56% less
Biodiesel: 68% less
Cellulose-derived ethanol: 91% less (however, this is still in experimental stages)
The downside of biofuels is that they consume either food crops (corn, soy, etc.) or take up the land that could otherwise be used to grow food crops. So, there's a fuel-food nexus that must be carefully managed.
Some researchers are evaluating using the stalks of food crops as a fuel source. The issue here is how to avoid degrading the soil, since the stalks are typically tilled back into the ground providing nutrition for the soil and future crops. How much of the plant material can be removed without harming soil fertility? (Wilhelm, 2004)
Another possible fuel source that is being researched? Algae. If somebody can figure out how to harvest this energy source it has several potential advantages. "Algae not only reduce a plant's global warming gases, but also devour other pollutants. . . . Best of all, algae in the right conditions can double in mass within hours. While each acre of corn produces around 300 gallons of ethanol a year and an acre of soybeans around 60 gallons of diodiesel, each acre of algae theoretically can churn out more than 5,000 gallons of biofuel each year." (Bourne, 2007, p57)
The potential of algae is also exciting from a water reuse point of view. It will grow in wastewater and in the process will also partially clean the water. (Hoffman, J P, 1998)
Biofuels: Boon or Boondoggle? National Geographic. Bourne, Jr., J K. October, 2007. pp38-59.
Wastewater treatment with suspended and nonsuspended algae. Journal of Phycology [J. Phycol.]. Hoffmann, J P. Vol. 34, no. 5, pp. 757-763. Oct 1998.
Crop and Soil Productivity Response to Corn Residue Removal, A Literature Review. Published in Agron. W. W. Wilhelm, W W, Johnson, J M F, Hatfield, J L, Voorhees, W B and Lindene, D R. J. 96:1-17 (2004).