Hartmut Michel

Biofuels - sense or nonsense


Abstract

With this year’s report of the Intergovernmental Panel on Climate Change (IPCC) it becomes generally accepted that the global warming which we undoubtedly observe, is the result of an increased concentration of greenhouse gases like carbon dioxide and methane in the atmosphere. Within this scenario it is evident that we have to reduce the emissions of carbon dioxide in order to stop or to decrease global warming. It will be necessary to switch from energy mainly based on fossil energy to renewable energy. One big hope is the use of biofuels like bioethanol, biodiesel, sundiesel, biogas and so on. The biofuels directive of the European Union requests that 5.75 % of all fossil traffic fuel (based on energy contents) has to be replaced by biofuels by the year 2010. Biofuels are of course products derived from photosynthesis of plants. It will be shown that the overall efficiency of photosynthesis is very low: less than one percent of the energy of the sunlight is stored in the form of biomass, and there is not much hope for a substantial improvement. Biogas and biodiesel per area unit and year contain about 0.4 % of the energy of the sunlight which the area unit has received in the same time. In addition at least 50 % of the energy which is contained in biogas or biodiesel had to be invested from conventional (fossil) energy sources to produce the biogas or biodiesel. Therefore production and usage of biogas or biodiesel is also not carbon dioxide neutral.

In order to produce Germany’s electricity consumption from biofuels one would have to use the entire area of Germany for growing energy plants, even if one does not consider the energy input required to produce the biofuels. By comparison, usage of photovoltaic cells is more efficient by a factor of 50 to 100 with respect to energy conversion, and correspondingly less land is required. Growing energy plants therefore is a very inefficient way of using the land. The import of biofuels made of palm oil or soy beans from tropical countries will enhance the deforestation and lead to a loss of the tropical rain forest.


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