Biogas production from crop residues on a farm-scale level in Sweden: scale, choice of substrate and utilisation rate most important parameters for financial feasibility.

Anaerobic digestion would enable the energy potential of agricultural crop residues such as ley crops and sugar beet tops to be harnessed in Sweden. In the present study, the financial prospects of single-stage fed-batch high-solids digestion on three different scales, 51, 67, and 201 kW, were calculated on the basis of experimental results and observations. In addition to scale, the effects of methane yield and fertiliser recovery (compared to green manuring) was investigated by testing different substrate mixtures. The biogas was disposed as heat, combined heat and power, or as vehicle fuel. Besides the positive effect of scale, the results indicate the importance of choosing substrates with a high methane yield and high nitrogen content, and the necessity of fully utilising both the capacity of the equipment installed and the energy carriers produced. Net unit costs of 5.3 and 8.1 ct/kWh were achieved (201 kW), heat and vehicle fuel, respectively.