Energy Efficiency and the Jevons Paradox

Printer-friendly versionPrinter-friendly version Share this

Will increasing efficiency really reduce energy consumption?

Big Ideas: 
  • Increases in energy efficiency have been shown to increase, rather than decrease, consumption

Increasing the energy efficiency of a process seems to be an ideal way to reduce energy consumption. But is it really?
In the 1980’s, two economists developed an idea, now known as the the Khazzoom-Brookes postulate, about the relationship between changing energy efficiency and the corresponding change in energy consumption. Contrary to what we would first guess, they said that increasing energy efficiency would actually increase energy consumption.

Their idea works like this: when the energy efficiency improves, it takes less energy than before to carry out the same task and thus the energy costs drop. Because of the money saved by lower energy bills, you would probably be tempted to use more energy.

This phenomenon was first noticed and analyzed by Willliam Jevons in the early to mid 1800’s – when the amount of coal used to produce a ton of iron was cut by over two thirds, there was, in Scotland, a ten-fold increase in total consumption between 1830 and 18631! The effect became known as the Jevons Paradox

As a more current example, we look at home gas bills. If the energy efficiency of a home heating system improves, it would take less energy to keep the room at a certain temperature. But since the gas bills are consequently lower, most people might be tempted to turn the temperature up2 or leave the heat on when the house is empty.

Lighting is another example. We moved from candles and oil lamps in to gas lamps in the 19th century, from incandescent bulbs to more efficient fluorescent bulbs in the late 20th century and now we are turning to Solid State lighting. Solid State lighting uses a fraction of the energy used by incandescent bulbs and somewhat less than compact fluorescent (CFL) bulbs3 . Solid state lamps use advanced versions of the LEDs (Light Emitting Diodes) as a source of illumination. LEDs can produce the same light intensity as incandescent bulbs while using only 10% of the power4.

A consequence of the savings that may come from solid state lighting is that, with relatively cheaper lighting options, many parts of the outdoors will be illuminated in the night to be as bright as day. Light pollution will also increase as a result of this. However, it can be argued that security and road safety trump energy conservation when it comes to lighting, and thus if lighting efficiency increases, the consumption of electricity from such public provisions as street lights will not drastically increase. Other parts of houses or buildings that weren’t very illuminated because of energy costs will now be lit up.

A recent paper predicts that, with an increased lighting-efficiency from solid state lighting, light consumption by the average person is predicted to increase from 20 to 200 megalumen hours in the next 20 years! (a megalumen-hour is the amount of light produced by burning a candle for an hour) . Even with the high-efficiency solid state lights, the amount of electricity needed to generate that power would more than double5

Another more classic example is how, despite increases in engine energy efficiency, the world’s total energy consumption continues to rise. The first steam engine, the atmospheric engine, built by Thomas Newcomen in 1712 had an efficiency of just 0.5%6. Currently, good diesel engines have an efficiency of up to 50%7 and modern jet engines are capable of converting 35% of their fuel into useful work8 (a number which has doubled in the last 50 years).! The diesel and jet engines are a drastic improvement to the steam engine, however world energy consumption is continually increasing. Part of this increase can be attributed to economic growth which in itself does increase the demand for energy, but, looking at other figures, energy consumption in the world’s 30 richest countries increased by 23% even though they exported their energy-intensive industries to poorer countries . This behaviour can be explained by the Khazzoom-Brookes postulate- the energy cost per service fell and thus energy consumption levels rose9.

Saving the planet with efficient lighting


Post new comment

Please note that these comments are moderated and reviewed before publishing.

The content of this field is kept private and will not be shown publicly.
By submitting this form, you accept the Mollom privacy policy.

a place of mind, The University of British Columbia

C21: Physics Teaching for the 21st Century
UBC Department of Physics & Astronomy
6224 Agricultural Road
Vancouver, BC V6T 1Z1
Tel 604.822.3675
Fax 604.822.5324

Emergency Procedures | Accessibility | Contact UBC | © Copyright The University of British Columbia