Screening boreal energy crops and crop residues for methane biofuel production

The purpose of the study was to screen potential boreal energy crops and crop residues for their suitability in methane production and to investigate the effect of harvest time on the methane production potential of different crops. The specific methane yields of crops, determined in 100–200 d methane potential assays, varied from 0.17 to 0.49 m3 CH4 kg−1 VSadded (volatile solids added) and from 25 to 260 m3 CH4 tww−1 (tonnes of wet weight). Jerusalem artichoke, timothy-clover grass and reed canary grass gave the highest potential methane yields of 2900–5400 m3 CH4 ha−1, corresponding to a gross energy yield of 28–53 MWh ha−1 and ca. 40,000–60,000 km ha−1 in passenger car transport. The effect of harvest time on specific methane yields per VS of crops varied a lot, whereas the specific methane yields per tww increased with most crops as the crops matured.