Production costs and operative margins in electric energy generation from biogas : full-scale case studies in Italy

The purpose of this study was to observe the economic sustainability of three different biogas full scale plants, fed with different organic matrices: energy crops (EC), manure, agro-industrial (Plants B and C) and organic fraction of municipal solid waste (OFMSW) (Plant A). The plants were observed for one year and total annual biomass feeding, biomass composition and biomass cost (€Mg-1), initial investment cost and plant electric power production were registered. The unit costs of biogas and electric energy (€Sm-3biogas, €kWh-1EE) were differently distributed, depending on the type of feed and plant. Plant A showed high management/maintenance cost for OFMSW treatment (0.155€Sm-3biogas, 45% of total cost), Plant B suffered high cost for EC supply (0.130 €Sm-3biogas, 49% of total cost) and Plant C showed higher impact on the total costs because of the depreciation charge (0.146€Sm-3biogas, 41% of total costs). The breakeven point for the tariff of electric energy, calculated for the different cases, resulted in the range 120-170€MWh-1EE, depending on fed materials and plant scale. EC had great impact on biomass supply costs and should be reduced, in favor of organic waste and residues; plant scale still heavily influences the production costs. The EU States should drive incentives in dependence of these factors, to further develop this still promising sector.