Three exergy accounting approaches are used to evaluate exergy efficiency: the Energy Resources Exergy Accounting (EREA), the Natural Resources' Exergy Accounting (NREA) and the Extended Exergy Accounting (EEA). To test the consistency of the results provided by these methodologies, we apply them to evaluate the Portuguese agricultural, forestry and fisheries (AFF) sector, from 2000 to 2012. EREA shows an increase of 30% in the efficiency of the Portuguese AFF sector, while NREA and EEA methodologies increases of 27% and 43%, respectively. Although the results are consistent for the AFF sector, the same does not happen in the fisheries subsector, whose exergetic efficiency increases 14% with the EREA but decreases 42% with the NREA approach. The ratio of output to useful exergy reveals that a better thermodynamic efficiency is not translated into a higher energy service efficiency because fishing vessels have to travel more to get the same fish. Thus, results provided by the EREA and NREA approaches are complementary and both are needed to provide a realistic picture of exergy efficiency. On the other hand, results obtained by the EEA approach are dominated by capital and environmental impacts, revealing the disproportionality between material and immaterial inputs in this methodology.

Extended exergy accounting (EEA) is a methodology which estimates the extended exergy cost (EEC) of a product or a service or the extended exergy efficiency (EEE) of a country or economic sector taking into account materials, energy, labour, capital, and environmental impact. The use of EEA results for policy or planning purposes has been hampered by: (1) the lack of data to quantify the EEC of most of the inputs, making it almost impossible to quantify the EEC of a product or service and (2) the lack of a conceptual framework to quantify in a consistent way the exergy of labour and capital. In this paper, we make a review of past studies to identify, synthesize, and discuss the different EEA methods. We identified 3 different EEA methods, that we further compare using the Portuguese Agriculture, Forestry, and Fishery (AFF) sector from 2000 to 2012. The equivalent exergies of labour and capital estimated for the AFF sector vary widely among the three EEA methodologies. We propose and test a new EEA methodology to estimate EEE which accounts for these fluxes in a more restricted scope but more consistently and that includes the Environmental Benefit (EB) that represents the capability of the forestry to capture carbon dioxide. Results show that the EEE of the Portuguese AFF sector has increased by 32% from 2000 to 2012.