Accounting for co-products in energy use, greenhouse gas emission savings and land use of biodiesel production from vegetable oils

Accounting for co-products of vegetable oil production is essential in reviewing the sustainability of biodiesel production, especially since oil crops produce valuable protein-rich co-products in different quantities and qualities. Two accounting methods, allocation on the basis of energy content and system expansion, are compared. Significant differences in results exist between the methods where system expansion is to be preferred because it can take actual use of co-products into account. Results are very sensitive to the choices made in system expansion. Differences can be large, especially between a system expansion where primarily the use of co-products of the oil crops is taken into account and an expansion that also includes direct oil exchange of the vegetable oil used for biodiesel for the marginal oil in the market.