Various considerations throughout the full process chain have to be accommodated and the details of how this is achieved are governed by accounting rules or methodologies. There are a number of different methodologies which are proposed and these have different approaches to two essential aspects of the LCA of biofuels. One aspect concerns “co-product allocation” which determines how GHG emissions are divided between the different outputs that can arise during the production of certain biofuels.
The second aspect addresses “reference land use” which is a means for incorporating the GHG emissions effects of alternative uses of the land for growing biomass feedstocks. At the moment, there are at least three possible methodologies for assessing the total GHG emissions associated with biofuels production. These consist of the Renewable Fuels Agency (RFA) Technical Guidance (RFA, 2008), the British Standards Institution (BSI) PAS 2050 (BSI, 2008), and the European Commission (EC) Draft Renewable Energy Directive (EC, 2008). The differences between these accounting methodologies, with regard to co-product allocation and reference land use, are summarised in Table 2.
Differences between accounting methodologies can cause significant differences in estimates of the total GHG emissions associated with biofuels. Relevant and subsequent results have been derived from the Biomass Environmental Assessment Tool (BEAT) which has been produced for the Department for Environment, Food and Rural Affairs (DEFRA) and the Environment Agency in the United Kingdom (DEFRA, 2008).