Biological methanation (biomethanation) of syngas obtained from biomass gasification offers the opportunity to employ a low-pressure, low-temperature process to produce storable bio-derived substitute natural gas (bSNG), although its economic viability is limited by high energy and biomass costs. Research on syngas biomethanation techno-economic performance is limited and novel biomass-to-biomethane process configurations are required in order to assess opportunities for the enhancement of its efficiency and economic feasibility. In this study, we carried out the techno-economic modeling of two processes comprising integrated biomass gasification, electrolysis, and syngas biomethanation with combined heat and power recovery in order to assess and compare their fuel yields, energy efficiency, carbon efficiency, and bSNG minimum selling price (MSP). The first process operates standalone biomethanation (SAB) of syngas and can produce approximately 38,000 Nm³of bSNG per day, with a total plant efficiency of 50.6%. The second process (integrated biomethane-biomethanol, IBB) exploits the unconverted carbon stream from the biomethanation process to recover energy and synthesize methanol via direct catalytic CO₂hydrogenation. In addition to the same bSNG output, the IBB process can produce 10 t/day of biomethanol, at a 99% purity. The IBB process shows little global energy efficiency gains in comparison with SAB (51.7%) due to the large increase in electrolytic hydrogen demand, but it shows a substantial improvement in biomass-to-fuel carbon efficiency (33 vs. 26%). The SAB and IBB processes generate a bSNG MSP of 2.38 €/Nm³and 3.68 €/Nm³, respectively. Hydrogenation of unconverted carbon in biomass-to-biomethane processes comes with high additional capital and operating costs due to the large-scale electrolysis plants required. Consequently, in both processes, the market price gap of the bSNG produced is 0.13 €/kWh_bSNG(SAB) and 0.25 €/kWh_bSNG(IBB) even under the most optimistic cost scenarios considered, and it is primarily influenced by the cost of surplus electricity utilized in electrolysis, while the selling price of biomethanol exerts a very limited influence on process economics. Intensive subsidization would be required in order to sustain the decentralized production of bSNG through both processes. Despite their limited economic competitiveness, both processes have a size comparable with existing renewable gas production plants in terms of bSNG production capacity and the IBB process is of a size adequate for the supply of biomethanol to a decentralized biorenewable supply chain.

International energy institutions project large shares of bioenergy as part of the decarbonization mix and small-scale generators in mountain regions can be interesting options in this space. In this study we assessed the techno-economics of small-scale (225 kW_el) biomass gasification-combined heat and power based on updated costs, under present and future energy market conditions. We found that, at 7,500 operating hours/year and a 70 €/t biomass cost, a 388 €/MWh levelized cost of energy is obtained, which is uncompetitive compared to alternative options like photovoltaic-storage or biogas. A loss in yearly operating hours and a reduction in unit capital cost have large impacts on unit cost, while heat valorization and remuneration, biomass cost and plant size represent secondary factors. An econometric forecast of consumer electricity prices in Italy to 2040 showed a subsidy requirement of 237 €/MWh and a total lifetime subsidy of 142 M€ with a carbon tax on conventional electricity growing by 11 €/t/y over twenty years, which represents a suboptimal generation infrastructure investment compared to the photovoltaic-storage or biogas alternatives. The results illustrate fundamental aspects of current bioenergy economics and deliver useful evidence for renewable energy planning in European mountain regions and beyond.