The ferment ability of energy plants will tested by a) determination of the maximum biogas yield in batch tests and b) determination of the technical realisable biogas yield in continuous fermentation tests. The characterisation of the substrates is realised with the so called “Hohenheim fermentation test” and in batch fermenters; the substrates vary in species, intensity of production and time of harvest. The selected variants will be tested in a continuous fermentation test unit, different practical conditions will also be simulated.