In the 2007 February 20 issue of Current Biology, Stanford University Professor, Chris Somerville, outlines the prospects and problems in the recent trend toward increasing reliance on liquid biofuels. Some of his findings are summarized below:

(1) Corn and cane ethanol: the production technology is reported to be mature. Studies have shown that cane ethanol has an energy output ratio of 8 (energy units produced for every energy unit consumed for its production). Life cycle studies on corn ethanol have also shown that it produces only 25% more energy than is consumed (considered not high). As such, corn ethanol is seen only as a “transition technology” while more cost effective and energy efficient technologies (like cellulose ethanol) are in development. Corn ethanol is not seen as a long term strategy for sustainably meeting energy needs.

(2) Biodiesel: the common raw materials for biodiesel production are annual oilseeds, soybean, palm, and canola. Although studies have shown that biodiesel has a better net energy output ratio than corn ethanol, it is not seen as a “significant component of fuel in the US or elsewhere in the developed world”. Some issues involved are: small oil yield per acre (relative to amount of biomass), and competition with its use as a component in the human diet. However, in developing countries, several tropical plants have been found to be potential raw materials for biodiesel production: oil palm, Babbasu palm, Jatropha.

(3) Cellulose ethanol: the common raw materials are cellulose from plant biomass. The biological route of production involves biochemical or microbiological breakdown of cellulose to component sugars, followed by fermentation to ethanol. Presently, there are still no large scale plants for commercial cellulose ethanol production. Many process components in the technology are reportedly not yet ready for commercial production. Despite the present bottlenecks, cellulose is still expected to become a significant component in transportation fuels in the future..