Economic performances of anaerobic digestion plants: effect of maize silage energy density at increasing transport distances

In Italy, more than 1150 agricultural anaerobic digestion (AD) plants are currently running. Their concentration in specific areas resulted in an increase in the biomass price and transport distances. For the AD plants located on farms with small area, often the feedstock are purchased on the market. However, when transport distances increase, it can be less expensive to buy biomasses with high energy density. With this regard, maize experimental tests were carried out to evaluate the methane production by harvesting the whole plant, the plant cut at 0.75 m and only the ear. The aim of this paper is to evaluate the economic performances of biogas plants fed with different maize silages by considering increasing extra-farm transport distances. Two different scenarios were considered with regard to the subsidy framework and to the maize biomass yield. The results show that, for short distances (<3 km), the economic performances are similar for AD plants fed with the whole plant silage and with that from the plant cut at 0.75 m; however, they are substantially better than those of the plant fed with ear silage. Beyond 14 km ear silage becomes more interesting than the whole plant; up to 32 km the plant fed with silage from the high cut is the most profitable whereas, beyond this transport distance, the ear silage is the best solution. The achieved results are interesting for stakeholders and policymakers involved in the biogas agro-energy processes, because they can be useful to reduce the cost of feedstock supply.