What 100 years of electricity efficiency and emissions can teach us about the energy transition

What is it about?

This study reconstructs the long-term evolution of electricity efficiency and carbon intensity in Portugal between 1900 and 2014. The research examines how electricity is produced and used across sectors and introduces a new indicator—the carbon intensity of useful electricity (ACIEU)—which measures CO₂ emissions per unit of useful energy services delivered by electricity. By combining historical electricity statistics with data on technology, energy sources, and end-uses (industry, transport, residential and commercial sectors), the paper identifies the key factors shaping changes in electricity efficiency and emissions over more than a century.

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Photo by Dmitrii E. on Unsplash

Photo by Dmitrii E. on Unsplash

Why is it important?

Electricity is expected to play a central role in the decarbonisation of modern economies, through electrification of transport, digitalisation, and the expansion of renewable power. Understanding how efficiency and carbon intensity evolved in the past helps identify the structural drivers of energy transitions and the conditions under which electricity systems become cleaner and more efficient. The study also shows that analysing electricity only at the production stage can be misleading: changes in how electricity is used across sectors can significantly affect the efficiency and carbon intensity of the services electricity provides.