Temps de lecture :3 minutes
In the last year, the obvious substitution solution to fossil fuels has become biofuels, in France as well as elsewhere. However, before investing in specific industrial infrastructures, we should explore their durability. To do so, the strengths and weaknesses of the different techniques must be analyzed.
The results depend on the type of crop (sugar cane, corn, beets and wheat for ethanol, rapeseed, oil palm, and jatropha for biodiesel, Miscanthus and other perennial crops for second-generation biofuels, algae…), agricultural practices, crop location, as well as industrial transformation techniques. These techniques include fermentation and esterification for ethanol and biodiesel, gasification and methanogenesis for biogas, a natural gas substitute, and enzymatic hydrolysis and thermochemical treatment for second-generation biofuels.
Beyond standard investment criteria (cost and availability of production factors), more specific criteria are necessary to ensure the durability of this budding industry. These factors include the development of unexploited land, preservation of biodiversity (neutral biodiversity balance, particularly in terms of deforestation), net energy output (positive energy balance), net carbon storage (positive energy balance), and increase in organic matter in soil, which is an essential fertility factor (positive resource balance). No-regrets solutions are those that will make it possible to develop unexploited agricultural assets without polluting the environment and that will result in a positive global balance.
Furthermore, yields vary noticeably from one crop to another. Three crop groups stand out. The first, which encompasses wheat, corn, colza, sunflower, and soy, produces approximately 1 to 3 m3/ha (14 to 43 ft3/acre) of biofuel. The second, which includes beets, sugar cane, and oil palm, produces approximately 6 to 8 m3/ha (86 to 114 ft3/acre) of biofuel. The third group, which is made up of microalgae, produces over 50 m3/ha (715 ft3/acre). Thus, producing one liter of biofuel from microalgea requires 50 times less land than colza. In a world where space is limited, this number warrants attention—even more so since algae do not need any agricultural soil to grow since they can be cultivated in glass supports or plastic containers.
Why do yields differ depending on the crop? A portion of the energy received by the plants in the first two groups is devoted to the plant structure: the stems, roots, and leaves; the rest of the energy goes to the production of sugars or fat stored in the seeds. In contrast, microalgae use most of the energy they receive for oil production, without having to devote any to structure.
Also, contrary to popular belief, the majority of forest land is under-exploited: sustainable management would allow for more timber production. Furthermore, the analysis of industrial sectors that transform living organisms uncovers many considerable sources that could undergo methanogenesis or gasification.
Finally, algae cultivation that takes place in bioreactors on non-agricultural land offers exceptional substitution perspectives. These bioreactors come either in the form of solar panels or vertical plastic pouches, in which microalgae-filled water circulates in a closed circuit. More than a dozen companies, mainly in the US, are currently developing this process. The most famous of these is GreenFuel, which has the technology to capture industrial CO2 in order to increase algae biodiesel yield. Costs favor the use of algae: for non-subsidized cultivation in America, barrels of refined oil derived from rapeseed cost $110, from oil palm $100, and from algae $70.
More than ever, innovation is geared towards the exploitation of living organisms, from the most structured forms, for industrial raw materials, to the least structured, for the production of tomorrow’s fuel or other materials. Let’s support good industries according to their final product — with no regrets.
, 14 mai 2007