Alternative options for biogas-to-energy: A comparison of electricity and biomethane generation based on the real operation of a production site

The production of biogas for energy generation through the anaerobic digestion is seen as an effective way to exploit local renewable resources as a substitute of fossil fuels. The two main applications that are currently adopted are the electricity production through biogas internal combustion engines, potentially combined with heat recovery, and the biogas upgrading to biomethane, to be supplied to the natural gas infrastructure. This research work contributes to the discussion by analyzing the performance of a real biogas plant in Italy, based on the anaerobic digestion of the organic fraction of municipal solid waste, that has shifted from power generation to biomethane generation. The performance of the two configurations is compared by means of the expected CO2 emissions savings against the current average electricity in Italy and natural gas carbon intensities, including upstream emissions. The results show that, based on the assumptions of our analysis for the current context of Italy, 1 MWh of biogas from organic fraction of municipal solid waste can lead to 152 kgCO2,eq savings if upgraded to biomethane and injected into the grid, but only to 120 kgCO2,eq when used in engines running in full-electric mode. If the engines are also producing useful heat, emission savings increase, reaching a trade-off with biomethane if 31% of the annual heat production can be recovered. However, considering the expected 2030 electricity mix in Italy, biomethane production would still be the best solution to maximize emission savings. Performance data from real plants are an important resource to develop reliable and effective energy system models, that can support policy makers in defining local energy plans and decarbonization strategies.