Reducing the energy intensity of economies, i.e., the quantity of energy used to create one unit of economic value, is key to meeting sustainable development goals. In the past, energy intensity has generally decreased or has shown inverted U-shape patterns when measured at the primary (extracted energy, e.g. crude oil) or the final (transformed energy, e.g. electricity) stages of energy conversion. On the other hand, when measured at the useful stage (used energy, e.g. light), energy intensity has shown to be roughly constant along very long periods. Thermodynamic constraints imply that this constancy is at odds with the very strong decoupling (decrease of energy intensity) at the final and primary stages envisaged bymost global energy scenarios . So, understanding the cause for the constancy of useful energy intensityis critical.
Focusing on energy intensity at the useful stage
In our recent study, published in the journal Energy, we analysed energy intensity at the useful stage for Portugal between 1960-2014. Previous research for this country pointed out a pattern of rough constancy for useful energy intensity, an emblematic result in the field of exergy economics. Whether this trend constitutes an intrinsic limit or is rather determined by a specific historical context needed investigation.
The Portuguese case
Portugal constitutes a very attractive case since many required economic and energy data are available from the 1960s,a period during which the Portuguese economy faced the conventional transitions of first industrialisation and then expansion of services. The Portuguese economy has faced several transitions by growing with especially high rates from the late 1950s until 1974, slowing down afterwards because of the first “oil shock” and the political and economic instability and accelerating again after 1986, by joining the European Economic Community (EEC). By the late 1990s, economic growth had slowed down drastically. Finally, the deep recession following the global financial crisis of 2008 was gradually overcome through an external assistance programme starting in 2011 which allowed a successful rebalancing of the trade balance.
Also, energy use changed profoundly between 1960 and 2014. Thanks to public investments in the 1950s and 1960s, electricity production increased more than fivefold, based on the exploitation of Portuguese hydropower potential. The expansion in the use of hydrocarbons took place later than in other European countries like Italy, Spain or Sweden and oil consumption surpassed firewood consumption only in 1965. The share of fossil fuels in the electricity production also started increasing later (from the mid-seventies) with the construction of several thermal power plants. In 2014, (imported) fossil fuels still constituted 73.3% of total primary energy supply.
Weak countervailing forces determine the constancy of useful energy
The novelty of our analysis lies in focusing on energy intensity changes at the useful stage for a long time range (1960-2014) while considering both productive and non-productive sectors of the economy. Indeed, we analyse the energy use in relation to the creation of economic value (energy intensity) not just considering economic sectors, e.g., the paper industry, but also including those energy flows which are not directly productive for the economy, e.g., residential energy use.
We find that the slight decrease of useful energy intensity during the period of highest industrialization (1960-1974) was the result of two opposing weak contributions. The increasing shares of energy intensive sectors (such as basic metal industries) due to industrialization contributed to increase energy intensity. On the other hand, a relatively slow increase of energy use in the residential sector compared to the fast economic growth taking place contributed to decrease the useful energy intensity. In general, considering the whole period, productive sectors contributed to a decrease in aggregate useful energy intensity only with the stagnation in industrialisation (1994-2014) while private transportation had an increasing effect on useful energy intensity throughout most of the period (1960-2004).
In conclusion, we find that a changing pattern of weak countervailing forces leads to the observed rough constancy of useful energy intensity and relative decoupling seems hard at the useful stage.
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The full article may be cited as:
Marco Vittorio Ecclesia, Tiago Domingos, 2026. Constancy of useful exergy intensity is explained by weak countervailing forces: an Index Decomposition Analysis. Energy, 342, 139616. https://doi.org/10.1016/j.energy.2025.139616