Gray energy is the amount of energy required to produce, transport to the place of consumption, and dispose of a product or material or to provide a service. Gray energy may also be referred to as "virtual energy", "frozen energy", or "hidden energy".
In general, the use of the term gray energy is accompanied by an indication of the methodology applied for evaluating the total amount of energy used during the entire lifetime of a product: extraction of raw materials, transportation, transformation, assembly, installation, destruction, and disposal. Some methodologies are based on the expression of gray energy in terms of the required oil consumption, while other calculate gray energy based on the amount of sunlight used in ecological processes.