Extended exergy accounting applied to biodiesel production

When evaluating the production of renewable energies such as biofuels, it is necessary to include in the assessment the resource inputs, capital, labor investment and environmental remediation costs. Extended Exergy Accounting (EEA) is a system analysis method that calculates, on the basis of detailed mass and exergy balances, the total amount of primary exergy resources necessary to obtain a product or service. The conceptual novelty of EEA is represented by the fact that it also includes externalities (capital, labor and environmental impact) measured in homogeneous units (Joules).As an illustration of EEA, we assess and compare the production of 1 ton of biodiesel from used cooking oil (UCOME) and rapeseed crops (RME). The extended exergy “content” of UCOME and RME are 51.90 GJ and 77.05 GJ respectively. The production of UCOME uses 25.15 GJ less resources (materials and energy) and requires lower total investments and environmental remediation costs than that of RME. On the other hand, UCOME requires 35% more workhours. In summary, the extended exergy of UCOME is about 1.5 the extended exergy content of RME. Thus, we can conclude that biodiesel production from UCO is less resource use intensive than the production from RME.