The recent report ‘Bioenergy, chances and limits’, by the German Leopoldina National Academy of Sciences, is the newest in a growing list of critical reports on bioenergy. On a macro level, the report prefers solar and wind energy to biomass because of higher efficiency per unit of land use, and proposes to use biofuels only for special purposes, in particular biodiesel for heavy transport. The report makes a case for efficiently produced biogas, from a combination of bioethanol fermentation and biogas fermentation in decentralised reactors, using mainly agricultural waste as a feedstock.
The report lists many points of concern on the issue of biomass sustainability. The authors argue that the concept of CO2-neutrality of energy production from biomass falls short in important respects: this concept ‘fails to consider the intimate linkage between the carbon cycle and the nutrient cycles of nitrogen, phosphorus, sulphur and metals, as well as the water cycle, all of which are besides carbon constituents of biomass and are required for photosynthesis. Whenever biomass is produced, soil nutrients are consumed. Whenever biomass is repeatedly removed from an ecosystem or its production accelerated by human intervention, nutrients need to be added. Yet, fertilizer application induces release of nitrogen-based greenhouse gases (GHGs) with a much higher global warming potential than that of CO2.’ And, they add, this argument does not even take into account the effects of direct and indirect land use change.
Fodder rather than energy
The report makes a case against raw biomass transports around the globe, as in many cases, ‘biomass imports effectively export the environmental pressures of intensive agriculture and forestry.’ Using European biomass for fodder rather than for energy production, could therefore reduce biomass transports and reduce its environmental impact.
The report points out the enormous losses of biomass in the food chain. It calculates that in Germany, 87% of the calorific value of nationally produced biomass is lost in the chain. Large portions of biomass (cellulose and lignin) cannot be digested; much biomass is lost in meat production; and a large volume of food (30-50%) is never consumed but instead discarded or consumed by pests along the food supply chain.
The report concludes that sustainable use of biomass for energy purposes in Western Europe will be limited in volume, and that the EU 2020 target of 10 per cent renewable content in road fuel energy should be revisited.
Biochemicals: promising field of research, or reality?
These arguments would seem to lead to a plea for biorefinery, according to the concept of the value pyramid. However, these concepts do not appear in the report. In this line of thinking, biomass would be used first for the higher-value applications (food etc.), then for chemicals and materials; finally, side streams should be used for energy production. But apparently, to the authors the concept of chemicals production from biomass is still a fleeting goal: ‘the development of processes for production of platform chemicals is a promising field of research.’ And: ‘Although a new synthetic chemistry established on biological raw material is basically possible, it will require major efforts in research and development: common chemical production processes will need to be adapted or fundamentally changed.’ In view of the first commercial plants coming on stream now, this would seem to be the understatement of the year.
In a concluding chapter, the report makes a plea for hydrogen production from sunlight, in particular through the development of chemically synthesized catalysts (artificial photosynthesis). The efficiency of these processes could be much higher than that of natural photosynthesis, and the corresponding land use could be much lower.
For the Executive Summary and Recommendations, see: http://www.leopoldina.org/uploads/tx_leopublication/201207_Stellungnahme_Bioenergie_kurz_de_en_final.pdf