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Lecturer: André González Cabrera Honório Serrenho (PhD student and researcher)
IN+, Center for Innovation, Technology and Policy Research, and Department of Mechanical Engineering, Instituto Superior Técnico, Technical University of Lisbon
Abstract
Useful work is distinct from conventional primary and/or final energy analysis, because useful work is much closer to productive energy uses within an economy, providing better insights on the relation between economic growth and energy use.
A useful work accounting methodology is applied to Portugal from 1856 to 2009, considering five different useful work categories: heat, mechanical drive, light, other electric uses and muscle work and final–‘to–‘useful efficiencies for all energy uses, in contrast to previous useful work assessments. From historic energy records, final exergy was estimated, as well as its allocations to useful work categories and final–‘to–‘useful efficiencies for the entire Portuguese economy. The overall efficiency starts rising in the 1920’s with an increase in high temperature heat uses. The most significant increase in efficiency occurs from 1950 to 1980 as a consequence of electrification. From 1980 onwards the efficiency tends to stabilize due to an increase of the share of mechanical drive uses from oil products.
In spite of GDP and useful work having grown nearly by a factor of 30 from 1856 to 2009, we show that useful work economic intensity (useful work / GDP) varied by no more than 20% above and below its 154-year average, in contrast to the final energy and exergy intensities that decreased by a factor of 4 in the same timespan. This result reinforces the argument for a close relationship between economic growth and useful work and suggests that a reduction in the intensity of the use of energy resources can only be achieved by increasing energy efficiencies.
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