Probabilistic techno-economic assessment of large-scale anaerobic digestion plants for biomethane production: de-risking biomethane futures

• Probabilistic techno-economic analysis of 10, 20 and 40 GWh biomethane plants. • 40 GWh plant achieves highest return (22%) and lowest cost (0.091 €/kWh). • Economies of scale reduce grid and upgrading costs at larger plant sizes. • Biomethane price dominates profitability, while feedstock cost drives energy cost. • Uncertainty analysis shows larger plants increase positive NPV probability (77–85%). This study investigates the economic feasibility and profitability of large-scale biomethane production through anaerobic digestion (AD) at plant capacities of 10, 20, and 40 GWh, using grass silage and cattle slurry as feedstocks. A robust deterministic and probabilistic modelling approach was employed to evaluate essential financial indicators, including Levelized Cost of Biomethane (LCOB), Net Present Value (NPV), Internal Rate of Return (IRR), and Payback Period (PBP). Sensitivity analysis observed at changes in the costs of grass silage (±30%) and biomethane (±50%). A Monte Carlo simulation with 10,000 iterations assessed at uncertainty by figuring out mean values, the chance of a positive NPV, and Conditional Value at Risk (CVaR). The results show that there is a good link between scale and financial performance. The cost of capital expenditures (CAPEX) ranged from €2.9 million for 10 GWh to €7.9 million for 40 GWh. As the scale of the plant grew, the cost of modifications and grid connections went down. The 40 GWh AD plant exhibited the strongest performance, achieving an NPV of approximately €22.2 million, an IRR of 30%, an LCOB of 0.079 €/kWh (≈ €0.79/Nm 3 ), and a payback period of 3.2 years, whereas the 10 GWh plant delivered a lower IRR of 16% and a longer payback period of 6.7 years. A probabilistic investigation confirmed that larger investments are more resilient, with the probability of a positive NPV rising from 81% to 92%.