Historically focused on energy production and its decarbonation, public debate has integrated the question of sobriety. The war in Ukraine pointing to our dependence on Russian fossil fuels obviously contributes to this evolution. But what are we talking about exactly? And how to implement it?
The starting observation is simple: energy is not directly useful to us. It becomes it when we combine it with a machine providing an energy service: a boiler to heat our accommodation, a car to go on vacation, a lamp to enlighten us, a smartphone to connect to social networks, etc.
Two strategies are then available to reduce energy consumption: reduce the use of service, or invest in machines consuming less energy for the same level of service. Concretely, reduce our trips or buy a car that consumes less fuel, lower the interior temperature of our apartment or isolate it. Conceptually, reduce our uses or invest in energy efficiency.
The energy impact of the reduction in uses obviously depends on the type of action and the vigor with which it is implemented. Reduce the temperature of its housing by a degree reduces energy consumption by 7 %. And therefore the double if we go from 20 degrees – the average in French housing – to 18 degrees. Limit its speed to 110 km/h on a highway would reduce the amount of fuel consumed on the journey by 20 %. A carpooling can do much better.
rebound effect
Investing in energy efficiency has a more complex effect on energy consumption. A more efficient machine will indeed see its energy cost of reduced use. It will then be used more often. The purchase of a car consuming less gasoline per kilometer will allow its user to make more trips, the energy renovation of a housing will encourage its occupants to increase the interior temperature in winter.
Part of the energy benefit of the investment will thus be dissipated in an increase in use. This is the rebound effect. Will he cancel the energy benefit? Expressed otherwise, will energy consumption exceed that observed before investment? A positive answer to these questions would remove any relevance to the strategy of energy efficiency.
Economic research has advanced a lot about the measurement of the rebound effect. The results are available for different sectors (renovation of buildings, car traffic, industry), and they are unambiguous: the rebound does exist, but it does not cancel the energy benefits of the investment (see , for example, the synthesis of these results carried out by Gillingham, Rapson and Wagner in 2016 ).
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