Grey energy

This article introduces and sensitizes the reader to the problem of grey or hidden energy in the objects and processes used every day by private individuals, industry and services. Users are sensitive to the energy they consume to operate an object, such as their car or electric heater, but much less so to the energy that went into making it, maintaining it (although they often pay for this maintenance) and disposing of it once it has become unusable or useless. This grey energy is also associated with various environmental impacts such as the emission of CO ₂ and pollutants, the creation of waste or the depletion of natural resources.

Defining energy consumption for the use of an object or good is no easy task. This quantity of energy, referred to as energy of use, is that which is accounted for and paid for directly or indirectly by the user. Defining the amount of grey energy associated with an object, good or service is even more difficult. Consumers often have no idea of the value of this hidden energy. And yet, the amount of energy required to manufacture an object can sometimes be considerable compared to the energy it can supply or consume during use. For example, it takes around fifty times more energy to make an alkaline battery than the amount of electricity it supplies when in use.

Primary energy corresponds to energy before transformation. This is the case, for example, with crude oil, coal or water from a dam. Secondary energy is obtained after transformation: petrol or diesel from oil, charcoal from wood, electricity from natural gas, etc. Final energy is that used by the consumer, such as electricity or heating oil. Finally, useful energy is that which is actually used for the required purpose. Between final energy, which the consumer pays for, and primary energy, which is used to produce it, significant losses occur. If we take the case of French electricity, for example, it took on average around 1.5 kWh of primary energy to produce 1 kWh of electricity consumed by the user.