The paper examines methods for calculating energy surpluses through anaerobic digestion and gives some examples of the practical application of these in crop-based systems. The surplus energy is the balance between that produced as a usable energy source and that used in crop production, conversion of the biomass into biogas, and conversion of biogas into a usable form: these are the direct energy inputs. The energy balance also takes into account the embedded energy used in the construction of machinery and buildings and for their repair and maintenance: the indirect energy inputs. The area of land available for fuel production is finite and therefore the energy yield is best considered on a per hectare basis. This allows comparison of energy conversion efficiency where the biomass yield for that area may vary depending on a range of inputs, e.g. rate of fertiliser application or irrigation requirements. It also allows direct comparison between different crop species or varieties within a single species. For an accurate energy balance analysis direct and indirect energy requirements have to be established for all the stages in the crop-based energy production cycle.
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Research Article| March 01 2009
Establishing an energy balance for crop-based digestion
Water Sci Technol (2009) 59 (6): 1053–1060.
A. Salter, C. J. Banks; Establishing an energy balance for crop-based digestion. Water Sci Technol 1 March 2009; 59 (6): 1053–1060. doi: https://doi.org/10.2166/wst.2009.048
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