Environmental Engineering Reference
In-Depth Information
it. This perversity is known as the “rebound effect”: demand rebounds
to nullify the efficiency improvement. The degree of rebound is usually
expressed as a percentage of the estimated savings from an efficiency
improvement. In other words, a rebound of twenty percent still leaves
eighty percent of the expected savings as a net reduction in demand.
The rebound effect has been recognized ever since the nineteenth-cen-
tury invention of the coal-fired steam engine. In the topic he published in
1865 called
The Coal Question
, William Stanley Jevons observed that coal
consumption had soared since the introduction of James Watt's coal-fired
steam engine, because this made coal a more cost-effective power source.
Jevons argued that any further efficiency improvements in the use of coal
would increase the consumption of coal.
This reasoning has sometimes been termed the “Jevons Paradox”, and
used to claim that all energy efficiency moves are therefore futile. Energy
economists used the term “backfire” to describe this counter-productive
effect, which also occurred after the introduction of the electric motor
in the twentieth century. Energy efficiency improvements can certainly
stimulate demand so much that overall energy use actually increases -
in other words the rebound is more than one hundred percent of the
expected energy savings.
However, this ignores the fact that increased welfare and income can
come from efficiency improvements, and also that the energy appetites
of individuals (though not necessarily companies) are ultimately limited
by their personal needs. Some rebound of demand is probably inevitable
with any genuine improvement in energy efficiency. A 2007 study by the
UK Energy Research Council (UKERC) estimated the rebound effect in
household energy and personal transport to be less than thirty percent
and nearer ten percent.
With these rebound and backfire concepts in mind, one should always
exercise a certain caution in estimating the actual energy savings from
energy efficiency technology. Looking forward, the backfire effect is
unlikely to occur again - not for lack of revolutionary advances, but
because so many extra charges (such as the costs of carbon permits and
of renewable energy subsidies) are being loaded on to energy bills that
energy is not likely to get any cheaper.
But for a fascinating view of past rebound and backfire effects, take
a look at the table overleaf, cited in the UKERC study. The amount of
lighting that the average individual was using increased much faster than
their income. This was because of the precipitous fall in the price of light-
ing services, which was in turn the result of the huge increase in lighting
