Modelling of energy and carbon budgets of wood fuel coppice systems

The development and application of a standard methodology for evaluating th e energy and carbon budgets of biofuel production systems is described, wit h emphasis on wood fuel production from short rotation coppice. Five major tasks were involved: definition of the system boundary; estimation of energ y benefits; estimation of carbon sequestration; estimation of energy costs; estimation of carbon emissions. Calculation of overall energy and carbon b udgets required a set of 'standard' assumptions about practices and resulta nt energy inputs to be made, These standard assumptions accounted for all a ctivities involved in production and delivery of biofuel within the immedia te vicinity of the farm (3.2km). The energy ratio, that is the ratio of ene rgy produced to energy consumed by the biofuel producing system, was estima ted to be much greater than 1, typically around 30. This energy ratio prove d to be very sensitive to assumptions about crop management and wood proces sing, as well as associated energy inputs, varying from 20 to 64 when model input assumptions were varied between extremes. The carbon emissions coeff icient exhibited similar sensitivity to input assumptions, The gross non-re newable energy requirement, that is the total consumption of non-renewable energy associated with the direct consumption of I MJ of energy in the form of wood fuel, was estimated to be 0.035 MJ MJ(-1). The carbon emissions co efficient, that is the carbon emitted in producing I MJ of energy in the fo rm of wood from short rotation coppice, was estimated to be 0.0013 kgC MJ(- 1). Further research is needed to validate input assumptions and to estimat e budgets for complete, practical, energy generation systems. Crown Copyrig ht (C) 2001 Published by Elsevier Science Ltd. All rights reserved.