Question:

In the "Perspectives" section of issue 14 (pp. 16 to 18), you refer to biofuels. It would be interesting to see a ranking of these fuels based on land usage. With regard to energy, economy and society in general, fuel from sugar cane is infinitely more efficient than its counterpart from beets. For most French people, the bioethanol produced at home is speculatory and in fact only serves to protect agriculture by subsidizing the [bioethanol] program under the pretext that it contributes to national energy independence.

Answer:

You’re right; biofuels should be considered secondary fuels, since the land areas available for their production are too small to contribute to primary energy production in a significant way. Biofuels may be classified into two categories: oil (or Diester) from rapeseeds and sunflowers, and alcohol (bioethanol). The alcohol category may be further divided into several different types: plants with a high sugar content (beets, Jerusalem artichokes, sugar cane, corn), plants with a high starch content (potatoes, grains),and woody plants (wood, straw), all of which are fermented to produce biofuel. The first two types are also referred to as agrofuel. In Brazil, several million vehicles run on ethanol extracted from sugar cane, which is indeed preferable to fuel from beets, whose energy efficiency is four times lower.