Gray energy is the amount of energy required to produce, transport to the place of use, and dispose of a product or material or to secure a service. Gray energy can also be called "virtual energy," "frozen energy," or "hidden energy".
Generally, the term gray energy refers to a methodology for assessing the total amount of energy used throughout the product's life: raw material extraction, transportation, processing, assembly, installation, as well as demolition and disposal. Some methodologies aim to express gray energy in terms of the amount of oil consumption required; other methodologies evaluate gray energy in terms of the amount of sunlight that is used in ecological processes.