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|This article is incomplete. (September 2011)|
Embodied Energy is the sum of all the energy required to produce any goods or services, considered as if that energy was incorporated or 'embodied' in the product itself. The concept can be useful in determining the effectiveness of energy-producing or energy-saving devices, or the "real" replacement cost of a building, and, because energy-inputs usually entail greenhouse gas emissions, in deciding whether a product contributes to or mitigates global warming. One fundamental question is: does the device produce more energy or save more energy than it took to make it?
Embodied energy is an accounting method which aims to find the sum total of the energy necessary for an entire product life-cycle. Determining what constitutes this life-cycle includes assessing the relevance and extent of energy into raw material extraction, transport, manufacture, assembly, installation, dis-assembly, deconstruction and/or decomposition as well as human and secondary resources. Different methodologies produce different understandings of the scale and scope of application and the type of energy embodied.
The history of constructing a system of accounts which records the energy flows through an environment can be traced back to the origins of accounting itself. As a distinct method, it is often associated with the Physiocrat's "substance" theory of value, and later the agricultural energetics of Sergei Podolinsky, a Ukrainian physician, and the ecological energetics of Vladmir Stanchinsky 
The main methods of embodied energy accounting as they are used today grew out of Wassily Leontief's input-output model and are called Input-Output Embodied Energy analysis. Leontief's input-output model was in turn an adaptation of the neo-classical theory of general equilibrium with application to "the empirical study of the quantitative interdependence between interrelated economic activities". According to Tennenbaum Leontief's Input-Output method was adapted to embodied energy analysis by Hannon to describe ecosystem energy flows. Hannon’s adaptation tabulated the total direct and indirect energy requirements (the energy intensity) for each output made by the system. The total amount of energies, direct and indirect, for the entire amount of production was called the embodied energy.
Embodied energy analysis is interested in what energy goes to supporting a consumer, and so all energy depreciation is assigned to the final demand of consumer. Different methodologies use different scales of data to calculate energy embodied in products and services of nature and human civilization. International consensus on the appropriateness of data scales and methodologies is pending. This difficulty can give a wide range in embodied energy values for any given material. In the absence of a comprehensive global embodied energy public dynamic database, embodied energy calculations may omit important data on, for example, the rural road/highway construction and maintenance needed to move a product, human marketing, advertising, catering services, non-human services and the like. Such omissions can be a source of significant methodological error in embodied energy estimations. Without an estimation and declaration of the embodied energy error, it is difficult to calibrate the sustainability index, and so the value of any given material, process or service to environmental and human economic processes.
The SBTool, UK Code for Sustainable Homes and USA LEED are methods in which the embodied energy of a product or material is rated, along with other factors, to assess a building's environmental impact. Embodied energy is a concept for which scientists have not yet agreed absolute universal values because there are many variables to take into account, but most agree that products can be compared to each other to see which has more and which has less embodied energy. Comparative lists (for an example, see the University of Bath Embodied Energy & Carbon Material Inventory) contain average absolute values, and explain the factors which have been taken into account when compiling the lists.
Typical embodied energy units used are MJ/kg (megajoules of energy needed to make a kilogram of product), tCO2 (tonnes of carbon dioxide created by the energy needed to make a kilogram of product). Converting MJ to tCO2 is not straightforward because different types of energy (oil, wind, solar, nuclear and so on) emit different amounts of carbon dioxide, so the actual amount of carbon dioxide emitted when a product is made will be dependent on the type of energy used in the manufacturing process. For example, the Australian Government gives a global average of 0.098 tCO2 = 1 GJ. This is the same as 1 MJ = 0.098 kgCO2 = 98 gCO2 or 1 kgCO2 = 10.204 MJ.
Selected data from the Inventory of Carbon and Energy ('ICE') prepared by the University of Bath (UK), and available at http://perigordvacance.typepad.com/files/inventoryofcarbonandenergy.pdf
|Material||Energy MJ per kg||Carbon kg CO2 per kg||Density kg /m3|
|Concrete block (Medium density)||0.67||0.073||1450|
|Cement mortar (1:3)||1.33||0.208|
|Steel (general, av. recycled content)||20.1||1.37||7800|
|Timber (general, excludes sequestration)||8.5||0.46||480–720|
|Glue laminated timber||12||0.87|
|Cellulose insulation (loose fill)||0.94–3.3||43|
|Glass fibre insulation (glass wool)||28||1.35||12|
|Expanded Polystyrene insulation||88.6||2.55||15–30|
|Polyurethane insulation (rigid foam)||101.5||3.48||30|
|Wool (recycled) insulation||20.9||25|
|Mineral fibre roofing tile||37||2.7||1850|
|Aluminium (general & incl 33% recycled)||155||8.24||2700|
|Vitrified clay pipe (DN 500)||7.9||0.52|
|Copper (average incl. 37% recycled)||42||2.6||8600|
|Lead (incl 61% recycled)||25.21||1.57||11340|
|Ceramic sanitary ware||29||1.51|
|Paint - Water-borne||59||2.12|
|Paint - Solvent-borne||97||3.13|
|Photovoltaic (PV) Cells Type||Energy MJ per m2||Carbon kg CO2 per m2|
|Thin film (average)||1305||67|
Embodied energy in telecommunications began in Mayaguez. Recently the embodied energy is going to used also in other sectors as ICT and telecommunication. The ICT energy consumption, in the USA and worldwide, has been estimated respectively at 9.4% and 5.3% of the total electricity produced. The Embodied Energy concept can help to evaluate the impact of devices and networks.