A paper from a scientific advisory board to the German ministry of agriculture examines bio-energy policy in Germany, and recommends certain forms of bio-gas as the most efficient ways to reduce greenhouse gases. According to the paper, the forms of bio-energy that have received the most attention from policy makers in Germany have been liquid biofuels. However, these are relatively costly at between €150 and €300 per tonne of CO2-equivalent avoided for corn-based ethanol.

The study recommends that if Germany wants to use bio-mass to achieve its climate objectives, then it should concentrate on those forms of bio-energy that reduce greenhouse gases at a cost of under €50 per tonne of CO2-equivalent. That can be achieved today with biogas made from liquid manure, with combined heat and production (CHP) based on forest residues, and, to a limited extent straw, in existing central power stations.

Criticisms that current subsidies for bio-energy are inefficient does not lead to the conclusion that bio-energy has no future, says the paper's author, Dr. Yelto Zimmer. With an appropriate correction in Germany's climate-change policies, many times more CO2-equivalent could be avoided with the same subsidy budget, without devoting any more land to grow the biomass.

The paper, Nutzung von Biomasse zur Energiegewinnung: Empfehlungen an die Politik, is available in German on-line at: 
http://www.greenpeace.de/fileadmin/gpd/user_upload/themen/klima/Gutachten_Biosprit.pdf