Energy analysis of rape methyl ester (RME) production from winter oilseed rape

Abstract

Energy ratios were calculated for production of the rapeseed-oil-based diesel substitute rape methyl ester (RME) from winter oilseed rape. The energy ratio of a biofuel can be defined as the ratio of the non-renewable energy used in its production to the energy value of the fuel and any utilised by-products, i.e. energy input:energy output. For each energy input and output, a range of energy values was calculated to account for different soil and weather conditions and variation in yield. In addition, the range of energy inputs calculated accounted for variation in published estimates of the amount of energy required for various processes. The range of inputs and outputs included values calculated for worst-case (i.e. lowest seed yield, highest pesticide applications, etc.) and best-case scenarios, and two intermediate values, which represented inputs and outputs expected under typical conditions in Scotland. From this data, energy ratios were calculated for rape methyl ester production under best-case, worst-case and intermediate scenarios, with and without the inclusion of by-products. The results indicated that RME production is sustainable under all but the worst conditions. Utilisation of rapemeal greatly improved the energy ratio, but there remained a net loss in energy under the worst-case scenario. Glycerol utilisation had relatively little effect on the energy ratio, while the use of straw resulted in a net energy gain from the production of RME under all scenarios.