Trade-offs in land allocation for bioenergy production

Biomass as a renewable energy source is scarce and its exploitationmust be accurately planned in order to maximize the energy produced, the GHGemissions avoided, and the sustainability of other ecological services. By-productsand residues are one of the best sources of biomass since they are readilyavailable at no or at a very low cost. Moreover, in some cases, the use of residueshas positive co-benefits. This is the case of manure: typically its disposalconstitutes a cost to the farm, whilst its energy use facilitates the disposal,produces energy and decreases GHG emissions. However, the conversionefficiency of manures alone is very low and, therefore, they are often used incombination with energy crops. These provide an important contribution tocombustion processes as well. Our aim is thus to assess how much land should beallocated to the production of energy crops destined either to combustion oranaerobic digestion (AD) by formulating and solving a mathematical model that alsodetermines the number, capacity, location and collection basin of each type ofplants. The objective is to maximize the net energy produced accounting for energyneeded to grow and transport biomass and to dispose of the digestate that resultsfrom AD conversion. This closely corresponds to the reduction of local CO2emissions. A case study for a farming area is presented. Results show that acareful analysis is needed to determine relevant trade-offs since they stronglydepend on local conditions.