How can we improve the energy balance of ethanol production from wheat?

The gross energy in ethanol using wheat as a feedstock in Ireland is 66 GJ/ha/a. The net energy production is 25 GJ/ha/a. A model is proposed, whereby the ethanol production process is combined with combustion of straw, and digestion of stillage, resulting in two transport fuels; ethanol and biomethane. In the proposed system stillage is not dried, reducing the thermal demand by 35%. A quarter of the straw associated with the wheat grain is sufficient, when combusted, to satisfy the reduced thermal demands. Stillage is digested wet; the biogas is scrubbed, compressed and utilised as a transport fuel. The net energy now is 72 GJ/ha/a. The production cost of biomethane is two thirds that of ethanol.