Embodied energy does not referred to energy available or inherent in a material or product as a logical derivation of the words would suggest. A more accurate term for embodied energy is “Cumulative Energy Demand”, because it represents the sum of all the energy inputs into a product system, from all stages of the life cycle which are included in the study developing the embodied energy data. For building materials this is usually extraction of materials, processing, transport and manufacture, and sometimes including capital equipment and services supplied to the product system in question. For a full product system or service the use and disposal phase may be included in the value.

What constitutes energy?

This is a question that needs to be answered in developing and understanding embodied energy data. The most common approach [1] is to include all materials in a product system which are commonly used for energy supply, including oil and gas which are used to produce plastics and other hydrocarbon consumed by not burnt, in material production processes. This material is referred to as “feedstock energy”.

Feedstock energy is included because it represent a depletion of available energy reserves (oil & gas) even though, in some cases, a substantial proportion of this feedstock energy can be recovered at the end of life in energy recovery facilities, is they exist.

The argument gets more difficult looking a wood and crop products, which are not commonly used for energy production, although the search for renewable fuels is changing this situation [2].

Should renewable energy be counted?

It generally is counted, partly because just because a fuel is renewable, does not mean it has no impact in its extraction/generation, and partly because energy use is a one measure of system efficiency. Also improvements to a material or product utilizing large amounts of renewable energy may then liberate that fuel or material for other purposes.

Breakdown of embodied energy

Depending on the needs to the LCA study embodied energy may be broken down into a range of subcategories, based on the use in the product system and the source of the energy, such as:

Fuel by end use

• Electricity (delivered): Electricity as measure by end user
• Energy losses in electricity production: Loss in fuel conversion at power plant (typically 60-70% of primary fuel input) and transmission and distribution losses (typically 2-8%)
• Fuel extraction, processing and delivery: Energy consumption delivering fuel for use in power plants, transport equipment and industrial plant.(typically 2-10%)
• Process heat: fuel combusted in for it heat value but not for electricity generation
• Transport : fuel used in transport equipment
• Feedstock: fuel used in situation where they are not directly oxidized such as oil and gas in plastics, carbon in cokes and pitch and so on.
• Energy in capital: Energy use in capital equipment

Fuels by type

• Renewables (hydro, wind, solar, geothermal, tidal ect)
• Fossil Fuels (oil, gas, coal)
• Biomass (wood, agricultural waste, peat ect.)
• Nuclear (uranium)
• Other/Unknown: unidentified energy sources