Direct biogas methanation via renewable-based Power-to-Gas: Techno-economic assessment based on real industrial data

This paper presents a design and techno-economic assessment of different Power-to-Gas configurations based on direct biogas methanation and renewable electricity. The proposed concept integrates the anaerobic digestion of organic waste with the methanation of carbon dioxide using green hydrogen. Yearly data of an anaerobic digestion process operating at the industrial scale were considered. The methanation unit was designed through two cooled fixed-bed reactors in series; the first had 14 parallel tubes that were 2.5 m long, and the second one had 18 tubes (each one 1.5 m long). A global carbon dioxide conversion above 98 % occurs in the unit, ensuring an outlet composition suitable for injection into the natural gas distribution grid. Different options for energy storage were thus considered; hydrogen storage in pressurized tanks (‘Buffer’), electrochemical storage in batteries (‘Battery’), and a hybrid combination of the two systems (‘Hybrid’). A ≈40 MW photovoltaic park provided the required energy input. The configuration with hydrogen storage tanks was established as the most promising option based on current trends, medium-term, and target projections scenarios of capital costs. These three cost scenarios led to a synthetic natural gas (SNG) production cost range of 2.3–4.2, 1.6–2.9, and 1.1–2.0 euros per cubic meter, respectively. This configuration requires a ≈35 MW electrolysis unit and about 100 tons of hydrogen storage capacity. Considering the current methane price, results indicate that current capital costs of photovoltaics, electrolysis, and H2 storage still represent an obstacle to overcome, before achieving the profitability of the concept.