The anaerobic digestion process is not modelled in detail, as this lies out of the scope of this study. According to the expected product composition from biogas plants similar to the case study, the average biogas composition was set to 40 % CO2 and 60 % CH4 . Biogas is cleaned to remove impurities such as H2S, volatile organic compounds and light tars. These steps are operated at low temperature and accounted for in the economic calculations. The estimated cost of biogas is set at 0.06 €/kWh. This cost is not the actual production cost, but rather a minimum cost to make the power-to-X process more convenient than combined heat and power production for the plant operator . Biogas is then upgraded in a membrane plant, to produce an injection-ready biomethane. The cost of the upgrading is estimated in 3000 €/Nmbiogas 3 /h installed and the operative expenditures are accounted as 0.15 €/NmCH4 3 /h. The methane losses in the upgrading are projected as 1 % of the feed . The produced biomethane is sold at 0.12 €/kWh . The produced CO2 is delivered to the PtX section or, when in excess, compressed to the liquefaction point and stored in a cryogenic tank, whose capacity is determined to contain the maximum reject CO2 during the year.