Establishing an energy balance for crop-based digestion

摘要

The paper examines methods for calculating energy surpluses through anaerobic digestion andngives some examples of the practical application of these in crop-based systems. The surplusnenergy is the balance between that produced as a usable energy source and that used in cropnproduction, conversion of the biomass into biogas, and conversion of biogas into a usable form:nthese are the direct energy inputs. The energy balance also takes into account the embeddednenergy used in the construction of machinery and buildings and for their repair and maintenance:nthe indirect energy inputs. The area of land available for fuel production is finite and therefore thenenergy yield is best considered on a per hectare basis. This allows comparison of energynconversion efficiency where the biomass yield for that area may vary depending on a range ofninputs, e.g. rate of fertiliser application or irrigation requirements. It also allows direct comparisonnbetween different crop species or varieties within a single species. For an accurate energynbalance analysis direct and indirect energy requirements have to be established for all the stagesnin the crop-based energy production cycle.