Embodied energy(Redirected from Virtual energy)
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 purpose for measuring this quantity is to compare the amount of energy produced or saved by the product in question to the amount of energy consumed in producing 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, disassembly, deconstruction and/or decomposition as well as human and secondary resources.
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.
In common materialsEdit
Selected data from the Inventory of Carbon and Energy ('ICE') prepared by the University of Bath (UK) 
|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|
According to Volkswagen, the embodied energy contents of a Golf A3 with a petrol engine amounts to 18 000 kWh (i.e. 12% of 545 GJ as shown in the report). A Golf A4 (equipped with a turbocharged direct injection) will show an embodied energy amounting to 22 000 kWh (i.e. 15% of 545 GJ as shown in the report). According to the French energy and environment agency ADEME  a motor car has an embodied energy contents of 20 800 kWh whereas an electric vehicle shows an embodied energy contents amounting to 34 700 kWh.
As regards energy itself, the factor energy returned on energy invested (EROEI) of fuel can be estimated at 8, which means that to some amount of useful energy provided by fuel should be added 1/7 of that amount in embodied energy of the fuel. In other words, the fuel consumption should be augmented by 14% due to the fuel EROEI.
We have to work here with figures, which prove still more difficult to obtain. In the case of road construction, the embodied energy would amount to 1/18 of the fuel consumption (i.e. 6%).
Overall embodied energy of a carEdit
The environmental calculator of the French environment and energy agency shows the usual fuel consumption of different means of transportation. If an embodied energy of 20 000 kWh is assumed, when taking a distance of 200 000 km into account, 10 kWh or one liter of gasoline per 100 km has to be added to the consumption. Moreover, the EROEI and the road construction represent approximately 20% of the fuel consumption. For a consumption of 6,4 l/100 km, it means that the corresponding embodied energy is equal to 1.3 l/100 km, so that the overall embodied energy amounts to 2.3 l/100 km.
Other figures availableEdit
Treloar, et al. have estimated the embodied energy in an average automobile in Australia as 0.27 terajoules (i.e. 75 000 kWh) as one component in an overall analysis of the energy involved in road transportation.
Although most of the focus for improving energy efficiency in buildings has been on their operational emissions, it is estimated that about 30% of all energy consumed throughout the lifetime of a building can be in its embodied energy (this percentage varies based on factors such as age of building, climate, and materials). In the past, this percentage was much lower, but as much focus has been placed on reducing operational emissions (such as efficiency improvements in heating and cooling systems), the embodied energy contribution has come much more into play. Examples of embodied energy include: the energy used to extract raw resources, process materials, assemble product components, transport between each step, construction, maintenance and repair, deconstruction and disposal. As such, it is important to employ a whole-life carbon accounting framework in analyzing the carbon emissions in buildings.
In the energy fieldEdit
EROEI provides a basis for evaluating the embodied energy due to energy.
Thanks to EROEI definition, it is possible to evaluate the efficiency according to
Under these circumstances, final energy has to be multiplied by in order to get primary energy.
Given an EROEI amounting to eight e.g., a seventh of the final energy has to be added to the final energy for obtaining primary energy.
Not only that, for really obtaining overall embodied energy, embodied energy due to the construction and maintenance of power plants should be taken into account, too. Here, figures are badly needed.
In France, by convention, EROEI related to electricity is equal to 2.58/1.58, i.e. 1.633
corresponding to an efficiency of 0.3875 or 38.8%. Moreover, if the grid efficiency is evaluated at 92.5%, overall electricity efficiency in France amounts to 35.8%.
In Germany, on the contrary, because of the swift development of the renewable energies, the ratio between primary energy and final energy in electricity amounts to only 1.8, leading to an EROEI of 1.8/0.8 = 2.25 corresponding to an efficiency of 55.5%.
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