Constancy of useful exergy intensity is explained by weak countervailing forces: an Index Decomposition Analysis

Most decomposition studies on energy intensity have considered energy at the primary or final stages. Here, we focus on the useful stage measured with the exergy metric. Previous research on aggregate useful exergy intensity, the ratio of the total useful exergy to economic output, has shown a pattern of rough constancy for Portugal, 1960–2014. Here, we use decomposition analysis to understand this finding, by focusing on both productive (e.g., industry) and non-productive (e.g., private transportation) sectors, the latter considering the ratio of the energy used by a non-productive activity to the total economic output. We find that the slight decrease of useful exergy intensity during the period of highest industrialization (1960–1974) was the result of two opposing weak contributions: the reduction in the intensity factor of the residential sector and the increase in the structural factor of industry. Afterwards (1974–1994), the increasing effect of structural change in industry was offset (especially between 1984 and 1994) by intra-sectoral intensity decline of most industries. Both effects were mainly driven by the non-metallic minerals and basic metals industries. In general, productive sectors contributed to a decrease in aggregate useful exergy intensity only when the structural factor of industry stopped increasing thanks to the stagnation in industrialization (1994–2014). Private transportation had an increasing effect on useful exergy intensity throughout most of the period (1960–2004). In summary, we find that a changing pattern of weak countervailing forces leads to the observed rough constancy of useful exergy intensity; relative decoupling seems hard at the useful stage.