Embodied energy is the sum of all the energy required to produce any goods or services, considered as if that energy were incorporated or 'embodied' in the product itself. The concept can help determine 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 that aims to find the sum total of the energy necessary for an entire product lifecycle. Determining what constitutes this lifecycle includes assessing the relevance and extent of energy in raw material extraction, transport, manufacture, assembly, installation, disassembly, deconstruction and/or decomposition, as well as human and secondary resources.
History The history of constructing a system of accounts that records the energy flows through an environment can be traced back to the origins of accounting. 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 Russian physician, and the ecological energetics of Vladmir Stanchinsky.
The main methods of embodied energy accounting that 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.
Methodologies 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 the 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, 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 economic processes.
Standards The SBTool, UK Code for Sustainable Homes was, and USA LEED still is, a method 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 InventoryG.P.Hammond and C.I.Jones (2006) Embodied energy and carbon footprint database, Department of Mechanical Engineering, University of Bath, United Kingdom) 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), t (tonnes of carbon dioxide created by the energy needed to make a kilogram of product). Converting MJ to t 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 GovernmentCSIRO on embodied energy: Australia's foremost scientific institution gives a global average of 0.098 t = 1 GJ. This is the same as 1 MJ = 0.098 kg = 98 g or 1 kg = 10.204 MJ.
Related methodologies In the 2000s, drought conditions in Australia generated interest in the application of embodied energy analysis methods to water. This has led to the use of the concept of embodied water.
Data Many databases exist to quantify the embodied energy of goods and services, including materials and products. These are based on various data sources, with geographic and temporal relevance variations and system boundary completeness. One such database is the Environmental Performance in Construction (EPiC) Database developed at The University of Melbourne, which includes embodied energy data for over 250 mainly construction materials. This database also includes values for embodied water and greenhouse gas emissions. The main reason for the differences in embodied energy data between databases is the source of data and methodology used in their compilation. Bottom-up 'process' data is typically sourced from product manufacturers and suppliers. While this data is generally more reliable and specific to particular products, the methodology used to collect process data typically results in much of the embodied energy of a product being excluded, mainly due to the time, costs and complexity of data collection. Based on national statistics, top-down environmentally-extended input-output (EEIO) data can be used to fill these data gaps. While EEIO analysis of products can be useful on its own for initial scoping of embodied energy, it is generally much less reliable than process data and rarely relevant for a specific product or material. Hence, hybrid methods for quantifying embodied energy have been developed, using available process data and filling any data gaps with EEIO data. Databases that rely on this hybrid approach, such as The University of Melbourne's EPiC Database, provide a more comprehensive assessment of the embodied energy of products and materials.
In common materials Selected data from the Inventory of Carbon and Energy ('ICE') prepared by the University of Bath (UK)
Material Energy MJ/kg Carbon kg /kg Material density kg/m3 Aggregate 0.083 0.0048 2240 Concrete (1:1.5:3) 1.11 0.159 2400 Bricks (common) 3 0.24 1700 Concrete block (Medium density) 0.67 0.073 1450 Aerated block 3.5 0.3 750 Limestone block 0.85 2180 Marble 2 0.116 2500 Cement mortar (1:3) 1.33 0.208 Steel (general, av. recycled content) 20.1 1.37 7800 Stainless steel 56.7 6.15 7850 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 Cork insulation 26 160 Glass fibre insulation (glass wool) 28 1.35 12 Flax insulation 39.5 1.7 30 Rockwool (slab) 16.8 1.05 24 Expanded Polystyrene insulation 88.6 2.55 15–30 Polyurethane insulation (rigid foam) 101.5 3.48 30 Wool (recycled) insulation 20.9 25 Straw bale 0.91 100–110 Mineral fibre roofing tile 37 2.7 1850 Slate 0.1–1.0 0.006–0.058 1600 Clay tile 6.5 0.45 1900 Aluminium (general & incl 33% recycled) 155 8.24 2700 Bitumen (general) 51 0.38–0.43 Medium-density fibreboard 11 0.72 680–760 Plywood 15 1.07 540–700 Plasterboard 6.75 0.38 800 Gypsum plaster 1.8 0.12 1120 Glass 15 0.85 2500 PVC (general) 77.2 2.41 1380 Vinyl flooring 65.64 2.92 1200 Terrazzo tiles 1.4 0.12 1750 Ceramic tiles 12 0.74 2000 Wool carpet 106 5.53 Wallpaper 36.4 1.93 Vitrified clay pipe (DN 500) 7.9 0.52 Iron (general) 25 1.91 7870 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 Energy kWh per m2 Carbon kg per m2 Monocrystalline (average) 4750 1319.5 242 Polycrystalline (average) 4070 1130.5 208 Thin film (average) 1305 362.5 67
In transportation Theoretically, embodied energy is the energy used to extract materials from mines, manufacture vehicles, assemble, transport, maintain, transform them to transport energy, and ultimately recycle these vehicles. Besides, the energy needed to build and sustain transport networks, whether road or rail, should also be considered. The process to be implemented is so complex that no one dares to put forward a figure.
According to the Institut du développement durable et des relations internationales, in the field of transportation, "it is striking to note that we consume more embodied energy in our transportation expenditures than direct energy", and "we consume less energy to move around in our personal vehicles than we consume the energy we need to produce, sell and transport the cars, trains or buses we use".
Jean-Marc Jancovici advocates a carbon footprint analysis of any transportation infrastructure project, before its construction.
In automobiles
Manufacturing 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(de) Volkswagen environmental report 2001/2002 see page 27). 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 (fr) Life cycle assessment website www.ademe.fr see page 9 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.
An electric car has a higher embodied energy than a combustion engine one, owing to the battery and electronics. According to Science & Vie, the embodied energy of batteries is so high that rechargeable hybrid cars constitute the most appropriate solution,(fr) Science & Vie # 1213 October 2018. see pages 48 till 51. with their batteries smaller than those of an all-electric car.
Fuel 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 14.3% due to the fuel EROEI.
According to some authors, to produce 6 liters of petrol requires 42 kWh of embodied energy (which corresponds to approximately 4.2 liters of diesel in terms of energy content).(de) Final energy analysis: gasoline vs. electromobility website springerprofessional.de
Road construction 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%). energy-and-road-construction website www.pavementinteractive.org
Other figures available 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.
In buildings