The current energy crisis, driven by geopolitical instability, has led to increased natural gas prices and consequently attracted the attention towards biogas as an alternative energy carrier with the same properties. Sweden and the European Union are actively promoting the transition from natural gas to biogas through various incentives. Biogas is a biobased fuel produced via anaerobic digestion of diverse organic substrates.
The raw biogas contains a significant fraction of carbon dioxide (~40% vol), which must be separated to obtain biomethane with a methane content of at least 97% vol, suitable for vehicle fuel or other high-purity applications. Rather than releasing the separated carbon dioxide into the atmosphere, it can be utilized in a power-to-gas system, where renewable hydrogen—produced via electrolysis—is reacted with CO₂ to generate e-methane through a process called methanation. Integrating a methanation system into an existing biogas production facility could offer several advantages, including improved utilization of organic feedstocks and waste streams, as well as increased methane yield.
This study aimed to evaluate various methanation technologies currently available on the market, assessing their energy efficiency, renewable methane production potential, and economic feasibility for integration into existing Swedish biogas plants. The project was structured into four phases: (i) knowledge synthesis, (ii) case definition for further analysis, (iii) techno-economic assessment of the selected cases, and (iv) evaluation of the feasibility of implementing methanation technologies within the Swedish biogas sector. The results highlight that the possibility of utilizing by-product and waste heat from the methanation system in the existing biogas plants is a critical factor for economic viability.
The findings suggest that wastewater treatment plants present particularly advantageous sites for methanation implementation. This is due to the potential utilization of oxygen generated in the electrolyzer for aerated water treatment basins, thereby reducing the plant’s electricity consumption. Additionally, excess heat from electrolyzers and catalytic methanation can be more effectively utilized in wastewater treatment facilities, which are often located near urban areas. In contrast, co-digestion plants do not benefit from oxygen utilization, and while some excess heat from electrolyzers can be used for hygienization and digester heating, a significant amount of heat remains unutilized.
The techno-economic assessment further indicates that the integration of a hydrogen storage and dynamic operation of the electrolyzer can improve economic performance by avoiding peak electricity prices. However, the optimal configuration of electrolyzer size and hydrogen storage depends on multiple factors, including electricity zone (bidding area), plant scale, choice of methanation and electrolyzer technology, and the extent of possible heat integration. The estimated levelized production cost of renewable methane (CBG) for the evaluated cases ranged from 23.6–26.1 SEK/kg CH₄ for 20 GWh biogas plants and 16.0–18.8 SEK/kg CH₄ for 120 GWh biogas plants. The renewable methane produced via methanation is classified as e-methane, which falls under the category of “renewable fuels of non-biological origin (RFNBOs)”.
Under the revised Renewable Energy Directive (RED III), a minimum of 1% RFNBO is required within the transport sector, putting e-methane in direct competition with other electrofuels such as e-methanol and e-ammonia. Consequently, the production cost of e-methane should not only be assessed in relation to biomethane but also in comparison to alternative RFNBOs to evaluate its market competitiveness. The study found that integration of methanation at biogas plants has the potential to increase production of renewable methane by approximately 62% without requiring additional biomass input.
Based on assumptions regarding average Swedish biomethane and electricity prices, the minimum biogas plant capacity required for economically viable methanation implementation is estimated to be ca 40 GWh per year. If methanation were to be implemented at all existing and planned biogas plants with a capacity of 40 GWh or greater, the national annual renewable methane production could increase by approximately 2 200 GWh. This can be compared to the total amount of biogas that is produced in Sweden today, 2 300 GWh. Furthermore, the increased renewable methane output, as a result of implementing methanation at biogas plants, would enhance the economic feasibility of LBG production by enabling economies of scale in liquefaction. Under the assumptions used in this study, an additional 500 GWh of annual LBG production could be achieved.
Malmö: IVL Svenska Miljöinstitutet, 2025.