1. Uncertainties in energy consumption estimates

To illustrate the complexity of energy assessments, we'll start by looking at calculations of the energy consumption involved in the use of an object or good, highlighting the associated uncertainties. The same type of uncertainty exists when assessing grey energy, and it is important to be aware of this in order to put the value of the results obtained into perspective.

So, when we evaluate the energy consumed by a given object, a car or a refrigerator, for example, we generally consider the average value measured on a sample of consumers or estimated on the basis of models. Only very rarely is the dispersion around this average value given. Yet this dispersion is also an important piece of data.