National energy statistics are collected at the point of supply, which makes them good at describing what was bought and poor at describing what was achieved. Useful exergy accounting closes that gap by tracing each carrier through to the end-use category it serves and valuing the output by its work potential. This open access study in Energies applies the method to Mexico across 1971 to 2009, a period covering oil-led industrialisation, debt crisis, trade liberalisation and rapid urban growth.
What the series exposes
Two features recur in every national useful exergy study and are visible here. First, aggregate efficiency is low and improves slowly: most of the primary exergy entering an economy is destroyed in conversion and end use, and the headline number moves by a few points per decade at best. Second, the improvement is not evenly distributed. It concentrates in electricity generation and in mechanical drive, where competition and equipment turnover force efficiency, and stalls in low-temperature heat, where combustion is used to produce warmth that needs almost none of the fuel's work potential.
The structural story matters as much as the efficiency story. As an economy shifts from heat-intensive heavy industry towards services and electrified end uses, its useful exergy per unit of primary supply rises without any single device improving. Disentangling that composition effect from genuine technical gains is precisely what the accounting framework is for, and it is why the period boundaries in this study — spanning a substantial structural change in the Mexican economy — make it a useful case.
Reading it for policy
For a middle-income economy the practical implication is that efficiency policy targeted at conversion equipment will exhaust itself, while the largest untapped stock of destroyed exergy sits in heat supplied at the wrong grade. That is a case for electrification and heat pumping rather than for better boilers.
The exergy view
An energy transition described in primary energy terms is a story about substituting one fuel for another. Described in useful exergy, it becomes a story about how much work an economy extracts from what it consumes — and on that measure most economies, Mexico included, still discard the large majority of what they buy. The series shows that the discarded fraction is not randomly distributed: it is concentrated in a small number of end uses where high-grade fuel is burned to supply low-grade heat. Those are the same end uses that dominate every national exergy study ever published, and they remain the largest available efficiency resource anywhere in the system.
